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In order to cope with the current engineering demand for increasing the current‐carrying capacity of resin impregnated paper (RIP) bushing, an optimization scheme of RIP bushing was proposed in this paper. Simulation and experimental studies were carried out to verify the rationality of the scheme. An improved simulation method was proposed. To ensure as much accuracy as possible, the physical model of simulation considers the influence of heat conduction, thermal convection and thermal radiation process according to the actual operation environment. To boost the computational efficiency, the improved method simplified the relationship between temperature and heating power of the current‐carrying conductor as a fitting formula to avoid the iterative calculation between electromagnetic field simulation and temperature field simulation. The temperature rise test was carried out according to the engineering requirement and the standard international electro technical commission (IEC) 60137:2008. The simulation and experimental results show that the RIP bushing can carry a current with the heating power of its conductor equivalent to that generated by a 50‐Hz current of 6736 A while running in a converter station. It is a breakthrough of the current‐carrying capacity of high voltage bushing. Meanwhile, the regularity of temperature distribution of the RIP bushing was discussed. [ABSTRACT FROM AUTHOR]

The Buck converter is a commonly used voltage regulator (VR) structure that supplies power to the load devices and responds to load transients. In most of the applications, the VR is controlled by voltage or current mode control, and some nonlinear approaches are used to improve the transient response which brings more complexities to the closed loop design. To achieve a fast transient response without over-regulation under a load step transient, this paper proposes a digital single-cycle regulation (SCCR) controller, which comprised a fast path, a slow path, and a neutralization path. Unlike the conventional PID control, the neutralization path of the SCCR controller is used to offset the excessive energy change in the first cycle after a load step occurs, which makes the inductor current reach its new static condition in a shorter period of time. The mathematical model of the SCCR control is established in this paper and a scanning algorithm is proposed for the design of the compensator parameters. Experimental results are presented to verify the improvement of the transient response when compared to the conventional and nonlinear PID control, the recovery time is decreased by 64.3% and 43% for load step-up and step-down when compared with nonlinear PID control. [ABSTRACT FROM AUTHOR]

This paper proposes a new hybrid control strategy to solve the problem of bidirectional wide voltage range regulation in CLLC converters. On the (LLC) side (G2V direction), the SSSA control method is employed for voltage boost, combined with bus voltage and burst control to achieve wide voltage regulation. On the (C) side (V2G direction), the SSSA and full/half‐bridge mode switching control are used to achieve V2G direction wide voltage regulation. This hybrid control strategy also enables high conversion efficiency in both directions without the need for additional components to reduce the converter power density. This is particularly suitable for OBC applications with strict requirements for converter volume and weight. A detailed analysis with mathematical derivation, hybrid control strategy, and converter operation principles is introduced in this paper. The following subchapters supplement the converter voltage gain, soft switching implementation conditions, and design considerations. Finally, the feasibility of the proposed control strategy was verified through an experimental prototype with an input voltage ranging from 340 to 430 V to an output voltage ranging from 225 to 450 V and bidirectional rated power of 6.6/3.3 kW. This prototype achieved a maximum conversion efficiency of 97.7% in the G2V direction and 97.1% in the V2G direction. [ABSTRACT FROM AUTHOR]

This paper presents a charging architecture for the Reconfigurable Cascaded Multilevel converter, which was specifically designed for electric vehicle (EV) powertrain applications. The RCMC topology is capable of executing power conversion and actively managing battery systems concurrently. The active battery management is achieved using the Reconfigurable Battery Module, which regulates the serial connection of cells via a switch pattern. In this paper, the RCMC is directly interfaced with an AC three-phase power system, facilitating the dynamic control over battery cells charging. Its inherent design allows for the implementation of various charging algorithms, customizable to specific requirements, without necessitating additional intermediary power stages. Firstly, an overview of the RCMC topology is given, and an analysis to define the optimal filter inductance is carried out. Subsequently, after the AC system characteristics are explained, two charging algorithms are presented and described: one prioritizes State of Charge (SOC) balancing among battery cells, while the other focuses on minimizing power losses. Moreover, a time estimation computation for the RCMC is carried out considering a two-level AC charging station. The result is compared with the time required for a conventional battery pack. The results show a reduction of 10 s in charging time for a mere 20% increase in SOC. Finally, the experimental setup is presented and used to validate the efficacy of the proposed algorithms. [ABSTRACT FROM AUTHOR]

In searching for the optimal control strategy of sub-module capacitance voltage equalization of Modular Multilevel Converter (MMC), the most important issue is how to address the significant increase in computing time of the controller, switching frequency of the sub-module, device switching loss and MMC fault rate led by the increase in the number of sub-modules of the upper/lower bridge arm of the MMC. Therefore, this paper proposes a control strategy based on the retaining factor method + improved quick sort, namely, an improved quick sort algorithm is used to sort the sub-module capacitance voltages to reduce the amount of computation of the MMC controller; at the same time, a retaining factor is introduced to participate in the improved quick sort to significantly reduce the switching frequency of the sub-module. MMC of large ship grid-connected photovoltaic power system is taken as a research object in this paper, a 31-level MMC model is built in Matlab/Simulink. Simulation results verify that the improved quick sort has a good rapidity compared to the algorithms of bubble sort, quick sort, bidirectional bubble sort, and improved merge sort, that the retention factor method has a good frequency reduction effect, and that the proposed retention factor + improved quick sort can provide a good performance compared to improved quick sort and retention factor + improved merge sort under conditions of the normal operation and introducing disturbance. [ABSTRACT FROM AUTHOR]

Summary: Although LLC converters have widespread applications due to their advantages of high efficiency, high power density, and soft switching, in wide voltage gain range applications, a large switching frequency range is inevitably required, which may bring difficulties in converter design and efficiency improvement. In this paper, a dual LC parallel multi‐resonant converter (MRC) is introduced. The converter contains two parallel LC resonant branches in the resonant tank, which exhibit the notch filter characteristic on the gain curve. It enables the converter to provide wide voltage gain regulation, soft startup, and overcurrent protection over a limited frequency range. Compared to other five‐element MRCs, since the converter provides different current loops for the fundamental wave and the third harmonic to transmit active power, the circulating reactive energy and stress on the resonant components are reduced. Finally, a detailed design procedure for a 3.3 kW converter prototype with an output voltage range of 250–450 V is provided. [ABSTRACT FROM AUTHOR]

This paper presents the topology and machine learning-based intelligent control of high-power PV inverter for maximum power extraction and optimal energy utilization. Modular converters with reduced components economic and reliable for high power applications. The proposed integrated intelligent machine learning based control delivers power conversion control with maximum power extraction and supervisory control for optimal load demand control. The topology of the inverter, operating modes, power control and supervisory control aspects are presented. Simulation is carried out in MATLAB/SIMULINK to verify the feasibility of the proposed inverter and control algorithm. The experimental study is presented to validate the simulation results. The operational performance of the proposed topology is evaluated in terms of operational parameters such as regulation of output power, and load relay control and is compared to existing topologies. The economic performance is also evaluated in terms of power switch sizing and reliability in power delivery concerning switch or power sources failure. [ABSTRACT FROM AUTHOR]

The cascade converter system has been widely concerned along with the medium power operating conditions, and it is crucial to address the intricate interplay among individual modules to ensure stability of both the source and load subsystems. This paper analyzes the DC‐link voltage stability based on impedance matching and proposes a normalized sensitivity calculation method based on the control strategy, which prevents the complex products and matrix calculations of traditional methods. The three‐level boost (TLB) output impedance model is derived based on state‐space averaging for open‐loop and considering the double‐loop, and the full‐bridge LLC (FBLLC) input impedance model is derived based on the fundamental equivalent circuit. Then the effect of the double‐loop PI parameters on the output impedance of the TLB is analyzed in detail based on the normalized sensitivity and verified by the Bode plots. The experimental results of the 30 kW prototype indicate that the control parameters were varied by a factor of 10 compared to the theoretical control group. The most significant alteration was the modification of the kp_i, resulting in an 8.9% increase in the DC‐link voltage ripple, while the ki_v was modified, resulting in a 0.53% increase, indicating that the effects of the PI parameter are consistent with the normalized sensitivity results. [ABSTRACT FROM AUTHOR]

This paper presents two control design strategies for voltage regulation in a single inductor dual-output DC-DC buck converter system. Based on a nominal multiple input multiple output plant model and performance requirements, both a Linear Quadratic Regulator and a Decoupled PI control law are designed to control the power converter system under parametric uncertainties such as voltage source variation, constant power load variation, and load resistance variation. Therefore, the converter can cascade operation, which may cause the undesired effects of voltage oscillation and reduce the system's stability margin. The control performance was assessed under both the uncertainties of resistive loading and the power variation in a constant power load. A single inductor dual-output DC-DC buck converter board was developed for experimental tests. The experimental results show that the Linear Quadratic Regulator strategy, compared to the PI strategy, presented a robust performance in the presence of parametric uncertainties in the resistive load-bearing; however, it was sensitive to uncertainties due to the presence of constant power loads. [ABSTRACT FROM AUTHOR]

This paper presents a novel, state-of-the-art predictive control architecture that addresses the computational complexity and limitations of conventional predictive control methodologies while enhancing the performance efficacy of predictive control techniques applied to three-level voltage source converters (NPC inverters). This framework's main goal is to decrease the number of filtered voltage lifespan vectors in each sector, which will increase the overall efficiency of the control system and allow for common mode voltage reduction in three-level voltage source converters. Two particular tactics are described in order to accomplish this. First, a statistical approach is presented for the proactive detection of potential voltage vectors, with an emphasis on selecting and including the vectors that are most frequently used. This method lowers the computational load by limiting the search space needed to find the best voltage vectors. Then, using statistical analysis, a plan is presented to split the sectors into two separate parts, so greatly limiting the number of voltage vectors. The goal of this improved predictive control methodology is to reduce computing demands and mitigate common mode voltage. The suggested strategy's resilience is confirmed in a range of operational scenarios using simulations and empirical evaluation. The findings indicate a pronounced enhancement in computational efficiency and a notable diminution in common mode voltage, thereby underscoring the efficacy of the proposed methodology. This increases their ability to incorporate renewable energy sources into the electrical grid. [ABSTRACT FROM AUTHOR]

This paper proposes fractional delay filter-based repetitive controllers (FDF-RCs) for grid-tied converters. Finite impulse response filters and infinite impulse response filters are used to estimate the fractional-order delay filter in a conventional repetitive controller. To do this, both the Lagrange filter-based repetitive controller (LF-RC) and Thiran filter-based repetitive controller (TF-RC) are utilized as FDF-RCs to compensate a fractional delay. The operating principle, the ladder structure, and the performance analysis of FDF-RCs are addressed. The simulation and the experimental results on a single-phase grid-tied converter verify the harmonic suppression ability and reference-tracking performance of the proposed FDF-RC under the grid frequency variation. Moreover, the advantages of the TF-RC over the LF-RC are discussed by comparing and analyzing the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Summary: In this paper, a high voltage gain hybrid interleaved DC‐DC converter (HIC) with quadratic voltage gain is proposed that is suitable for renewable energy systems. The hybrid technique is used in this converter to increase the output voltage. The proposed DC‐DC converter utilizes the interleaved boost converter on the input side, and the input current is shared with a low ripple that lengthens the lifetime of the renewable power source. In addition, the proposed converter has low voltage stress across the components that can be adopted to reduce conduction losses and the cost of the elements. In addition, the proposed converter share ground between the input and output and has high efficiency. The operation modes of the proposed converter are analyzed, and its equations are calculated. Then, the elements of the proposed converter are designed in continuous conduction mode. A comprehensive comparison of the proposed converter with other recently presented existing converters is discussed to show the advantages and disadvantages of the proposed structure. Finally, to verify the performance of the proposed converter and the obtained relations, a 400 W prototype is built to demonstrate the effectiveness of the proposed converter. [ABSTRACT FROM AUTHOR]

This article proposed an off-board bidirectional battery charger for electric vehicles (EVs) that have been designed to perform various modes of operation of EVs like grid-to-vehicle (G2V) and vehicle-to-grid (V2G) while improving the grid power quality (PQ). During the charging process, the charger operates in the G2V mode. In this mode, power flows from the utility grid to the EV, ensuring a smooth and efficient transfer, which has the ability to maintain a sinusoidal grid current waveform and a unity power factor throughout the operation. This not only ensures efficient power transfer but also minimizes disruptions and distortions in the grid. On the other side of the operational spectrum lies the discharging phase, governed by the V2G mode. This mode allows the charger to deliver power from the EV's batteries back to the utility grid. This capability is a significant step toward establishing a two-way relationship between EVs and the grid, enabling EVs to act as energy reservoirs and support grid stability during peak demand or emergencies. This paper presents the proposed adaptive direct power control (ADPC) theory for the proposed electric vehicle charger (EVC), which consists of a grid-side converter and an EV side converter. The proposed control algorithm on both sides of the converters plays a significant role in various operating modes. The ADPC employs a control strategy referred to as the second-order generalized integrator to estimate the actual synchronizing voltage templates specifically designed for single-phase grid-side converters. Consequently, the appropriate current reference used by the charger is to ensure that the power factor remains unity throughout various operating modes. Similarly, for the EV side converter, the integration of the power delivery error further enhances steady-state responses with the proposed ADPC by generating actual phase shifted pulses for the DAB. The overall performance under similar conditions is studied with virtual direct power control to further check the robustness of the proposed ADPC. The adopted topology and control technique further implemented in the prototype of an off-board EVC to verify the various operating conditions to demonstrate its effectiveness and justified as per the IEEE 519-2022 standard. [ABSTRACT FROM AUTHOR]

This paper proposes a modeling and analysis method for a Caputo–Fabrizio (C-F) definition-based fractional-order Boost converter with fractional-order inductive loads. The proposed method analyzes the system characteristics of a fractional-order circuit with three state variables. Firstly, this paper constructs a large signal model of a fractional-order Boost converter by taking advantage of the state space averaging method, providing accurate analytical solutions for the quiescent operating point and the ripple parameters of the circuit with three state variables. Secondly, this paper constructs a small signal model of the C-F definition-based fractional-order Boost converter by small signal linearization, providing the transfer function of the fractional-order system with three state variables. Finally, this paper conducts circuit-oriented simulation experiments where the steady-state parameters and the transfer function of the circuit are obtained, and then the effect of the order of capacitor, induced inductor, and load inductor on the quiescent operating point and ripple parameters is analyzed. The experimental results show that the simulation results are consistent with those obtained by the proposed mathematical model and that the three fractional orders in the fractional model with three state variables have a significant impact on the DC component and steady-state characteristics of the fractional-order Boost converter. In conclusion, the proposed mathematical model can more comprehensively analyze the system characteristics of the C-F definition-based fractional-order Boost converter with fractional-order inductive loads, benefiting the circuit design of Boost converters. [ABSTRACT FROM AUTHOR]

This paper presents a three-port isolated hybrid converter (3PIHC) with extended phase-shift modulation (EPM) to reduce voltage and current stress in the converter for DC microgrid applications. A high-frequency transformer with three independent windings is employed for isolating three ports in the converter. A wide variation in voltage transformation ratio is one of the main concern in DC microgrid, which need to be addressed for effective power conversion and utilization of the energy generation systems. Traditional phase-shift modulation (TPM) in 3PIHC leads to high conduction and core losses in the converter under wide variation in voltage transformation ratio. This paper proposes an extended phase-shift modulation in 3PIHC for different sequence of voltage transformation ratios between port 1 and port 2 (m 12) and between port 1 and port 3 (m 13) , which is a cost-effective solution for reducing losses in the converter. The peak current at all ports and power equations in 3PIHC are deduced, and the computational method for obtaining the phase-shift values with minimum current stress is explained in detail. A comparative evaluation study proves that the proposed three-port converter with EPM outperforms to TPM in the aspects like low current stress, reduced semiconductor switching losses and transformer losses for wide variation in voltage transformation ratios. A hardware prototype of the proposed converter is built, and the results are evaluated and presented. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to better design the resonant tank parameters for LLC resonant converter. And, it is found that under heavy load, the voltage gain is affected by junction capacitors of the primary side switching and the parasitic parameters of the secondary side diodes converted to the primary side, which will cause the voltage gain decreased when the switching frequency decreased. Design/methodology/approach: This paper proposes an optimization parameters design method to solve this problem, which was based on impedance model considering the parasitic parameters of switching devices and diodes. Findings: The effectiveness of the proposed method is verified by impedance Bode plots and experimental results. Originality/value: From the perspective of impedance modeling, this paper finds the reasons for the insufficient voltage regulation capability of LLC resonant converters under heavy load and finds solutions through analysis. [ABSTRACT FROM AUTHOR]

Summary: The application of modular multilevel converters (MMC) in medium voltage static synchronous compensators (STATCOMs) has been investigated in recent years. A huge challenge for MMC‐STATCOM is to compute the gain of the controllers. Therefore, the contribution of this paper is the proposal of a control tuning methodology for MMC‐STATCOM. For this purpose, the control and tuning strategies are presented. Since MMC‐STATCOM can employ different modulation strategies, two distinct modulation strategies are considered: nearest‐level control, with variable switching frequency; and phase‐shifted carrier pulse‐width modulation, with fixed switching frequency. Moreover, the proposal was validated through simulation and an experimental platform. The results indicate that the power response follows the reference, besides supplying the internal losses of the converter. The 10% ripple tolerance of the submodule voltages is respected in steady state for both modulation strategies. Moreover, the 5% total demand distortion (TDD) limit recommended by the Institute of Electrical and Electronics Engineers (IEEE) standard is attended. These results demonstrate the effectiveness of the controls employed. [ABSTRACT FROM AUTHOR]

This study describes a laboratory model of a battery energy storage system (BESS) designed for testing algorithms aimed at reducing peak power consumption in railway traction substations. The system comprises a DC/DC converter and battery energy storage. This article details a laboratory model of a bidirectional buck-boost DC/DC converter, which is used to transfer energy between the battery energy storage and a DC line. It presents an analysis of DC/DC converter systems along with simulation studies. Furthermore, the results of laboratory tests on the DC/DC converter model are also provided. The control algorithm of the system in the traction substation is focused on reducing peak power, offering benefits such as lower charges for the railway operator due to the possibility of reducing contracted power requirements. From the perspective of the power grid, the reduction in power fluctuations and, consequently, voltage sags, is advantageous. This paper includes a description of a hardware simulator for verifying the system's control algorithms. The verification of the control algorithms was performed through experimental tests conducted on a laboratory model (a hardware simulator) of the system for dynamic load reduction in traction substations, on a power scale of 1:1000 (5.5 kW). The experimental tests on the laboratory model (hardware simulator) demonstrated the effectiveness of the algorithm in reducing the peak power drawn from the power source. [ABSTRACT FROM AUTHOR]

Wind power systems, which are currently being constructed for the electricity worldwide market, are mostly based on Doubly Fed Induction Generators (DFIGs). To control such systems, multilevel converters are increasingly preferred due to the well-known benefits they provide. This paper deals with the control of a standalone DFIG-based Wind Energy Conversion System (WECS) by using a three-level Neutral-Point-Clamped (NPC) converter. The frequency and magnitude of the stator output voltage of the DFIG are controlled and fixed at nominal values despite the variable rotor speed, ensuring a continuous AC supply for three-phase loads. This task is achieved by controlling the DFIG rotor currents via a PI controller combined with a new Simplified Direct Space Vector Modulation strategy (SDSVM), which is applied to the three-level NPC converter. This strategy is based on the use of a line-to-line three-level converter space vector diagram without using Park transformation and then simplifying it to that of a two-level converter. The performance of the proposed SDSVM technique in terms of controlling the three-level NPC-converter-based standalone WECS is demonstrated through simulation results. The whole WECS control and the SDSVM strategy are implemented on a dSPACE DS 1104 board that drives a DFIG-based wind system test bench. The obtained experimental results confirm the validity and performance in terms of control. [ABSTRACT FROM AUTHOR]

When the operating state of the power system changes, a modular multilevel converter power electronic transformer (MMC-PET) based on modular multilevel converters cannot perform efficient energy transfer and power conversion under conventional control strategies. To address the above problems, this paper proposes a passive, second-order super-helical sliding mode control strategy for MMC-PET by combining passive control and second-order super-helical sliding mode control with a stronger anti-interference capability. First, a Euler–Lagrange model based on positive and negative sequence separation is established according to the mathematical model of the MMC; second, the model of the system is passively analyzed, and a passive controller is designed according to its passivity, and the passive controller is further optimized by using the super-helical second-order sliding mode control, which improves the overall robustness and interference immunity; finally, the effectiveness and superiority of the super-twisting second-order sliding mode passive control strategy is demonstrated by verifying it through the construction of the MMC-PET simulation model and testing it under various non-ideal working conditions. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid control method with adaptive phase-shifting modulation (PSM) and pulse-frequency modulation (PFM) is proposed to optimize the steady-state performance of an LLC resonant converter in wide voltage-gain range application. For the primary-side switches under the hybrid control method, zero-voltage switching (ZVS) performance is maintained over wide voltage-gain range and the turn-off loss is reduced; therefore, the converter reconciles wide voltage-gain range and high efficiency. Mode characteristics under different phase-shifting-angle-θ and switching-frequency-fs combinations is analyzed, and then the soft-switching characteristic is revealed. By introducing time domain analysis, the turn-on current of the primary-side switches is calculated, and thus the ZVS boundary of different θ and fs combinations is inferred. In addition, to acquire the optimum steady-state operation of the converter, the turn-off current is calculated; by making the converter work near to the minimum turn-off current operating point, the turn-off loss can be reduced greatly. With the principles of achieving ZVS performance and minimizing turn-off current, the phase-shifting angle θ of PSM is designed to be adaptive to the reference output voltage, no additional circuits are needed, and the two control degrees (θ and fs) are simplified to one (fs). The simulation and experiment are developed to verify the feasibility and effectiveness of the hybrid control method; the results show that ZVS performance is maintained at wide voltage-gain range and the turn-off current of the hybrid control method is reduced to that of the single PFM, and thus the turn-off loss is reduced. The efficiency comparison validates the fact that the hybrid control method has less power loss than single PSM and single PFM. [ABSTRACT FROM AUTHOR]

In this paper, an improved AC-link voltage matching control (IVM) strategy is proposed for the multiport modular multilevel DC transformer (M3DCT), which comprises a single-phase modular multilevel converter (MMC) and a series of cascaded H-bridge units. The objective of the proposed IVM strategy is to address the AC-link voltage mismatch phenomenon. Distinct from existing control methods, such as various phase-shifting control methods and the conventional AC-link voltage matching control strategy, the proposed IVM strategy orchestrates the operation of the M3DCT in an innovative fashion. It allows the sum of inserted submodule (SM) numbers in the upper and lower arms to be flexible, no longer confined to a specific SM number per arm. Consequently, the AC-link voltage of the M3DCT is maintained proximate to the matched operating condition, regardless of the degree of mismatch in the DC side voltage of the M3DCT. This enables the enhancement of the M3DCT's overall operational performance, particularly under conditions of light loads within medium-voltage DC (MVDC) distribution systems. The correctness and effectiveness of the proposed control strategy and the corresponding analysis are substantiated through simulation results. [ABSTRACT FROM AUTHOR]

Summary: Traditional multiple‐output AC‐DC power supply with power factor correction (PFC) function usually employs a two‐stage cascaded topology that is composed of prestage PFC converter and N independent poststage DC‐DC converters to achieve PFC and voltage or current regulation of N outputs. Hence, the conventional two‐stage cascaded multiple‐output AC‐DC power supply needs N + 1 magnetic components as power inductors or transformers and N + 1 controllers, which increases the cost and size of the multioutput converters. The conventional multiple‐string AC‐DC LED driving circuits usually employ a two‐stage topology to realize PFC and independent current regulation of each LED string. To address the issue of complexity, high cost, and large size of the two‐stage multistring LED driving circuit, a single‐stage triple‐output Cuk PFC converter is proposed by cascading boost converter and single‐inductor triple‐output buck converter with sharing main power switch in this paper. The topology operation principle, control strategy, design consideration, and operation characteristics of the proposed circuit are investigated in detail. With the switch sharing and inductor multiplexing technologies at the same time, the proposed converter utilizes only single‐stage converter to achieve PFC function, independent regulation of triple‐channel output current, and flicker‐free with low twice line frequency LED current ripple. The proposed converter is verified by a 50‐W experimental prototype of LED driver for triple string LEDs. The proposed converter only uses two power inductors and a set of controller to achieve greater than 0.945 PF, up to 90.5% efficiency, low LED current ripple, and independent current regulation for triple LED strings with different forward voltage, which may significantly reduce the cost and size of the traditional AC‐DC multistring LED driving circuit. [ABSTRACT FROM AUTHOR]

Direct current transformer (DCT) is a key piece of equipment in direct current (DC) microgrids, and the mainstream topologies mainly include LLC resonant converter (LLC) and dual active bridge (DAB). In this paper, a novel bi-directional buck/boost + CLLLC cascade topology is proposed for the input-series-output-parallel cascade converter system of a DC microgrid. To solve the problem that frequency variation causes the converter to deviate from the optimal operating point, resulting in low efficiency, and the inability to achieve a soft switching function. The CLLLC converter operates near the resonant frequency point as a DCT, only providing electrical isolation and voltage matching, while the buck/boost converter controls the output voltage and the voltage and current sharing of each module. Compared to other cascaded converter systems, the cascaded converter proposed in this paper has high efficiency, simplifies the parameter design, and is suitable for wide input and wide output operating conditions. The system adopts a three-loop control strategy, establishes the small-signal modeling of the system, and its stability is verified by theoretical analysis and simulation. The simulation and experimental results verify the correctness of the proposed cascaded converter based on buck/boost + CLLLC and the effectiveness of the control strategy. [ABSTRACT FROM AUTHOR]

Nonlinear controllers are useful if the equations governing the system dynamics are nonlinear. The fuel cell (FC)-fed boost converter is a nonlinear system as the VI characteristics of the fuel cell and the output voltage to duty cycle transfer function of the boost converter are nonlinear. The choice of a nonlinear controller depends on the dynamic performance of the FC-fed boost converter for wide load variations. This paper compares the performance of the system using conventional sliding mode control (CSMC) and super twisting sliding mode control (STSMC) strategies for tight voltage regulation for the load disturbance and reference voltage tracking. Simulation and experimental results of the fuel cell-fed 600 W boost converter prove the supremacy of STSMC strategy over CSMC strategy in terms of overshoot, undershoot, settling time and chattering reduction. [ABSTRACT FROM AUTHOR]

Summary: Nonagonal modular multilevel converter (MMC) is a three‐port AC/AC converter promising as a soft open point (SOP) to connect different AC feeders or buses in distribution networks, owing to its flexible power control, transformerless structure, and low power component count and its capability of accommodating multiple AC ports of different frequencies. An SOP should be able to work under port reduction condition, which is often encountered when maintenance is required or the network structure is reconfigured. However, as a component reuse converter of circular structure, nonagonal MMC cannot turn off one or some of its branches to achieve this. To address this issue, a control scheme is proposed in this paper to enable nonagonal MMC to operate under port reduction condition by switching the nonagonal MMC to a hexagonal MMC, which is an AC/AC topology of a similar circular structure but has only two ports. Without inserting extra switches, the nine branches of nonagonal MMC is redistributed into six branches. By alternately operating the submodules, no submodules need to be shut down, reducing the submodule capacitor voltage fluctuation during port reduction operation. RTlab results verify the feasibility of the quasi‐hexagonal topology and the effectiveness of port reduction control. [ABSTRACT FROM AUTHOR]

The stability and dynamic performance of the system are impacted by the uncertainties present in the converter model and controller parameters. This paper introduces a robust non-fragile control approach that addresses the influence of these uncertainties. The approach involves developing a control law that achieves quadratic stabilization of the closed-loop system while also satisfying the H∞ norm constraint for disturbance attenuation. Based on this concept, a robust non-fragile PI controller is designed explicitly for voltage mode control of a dc–dc buck converter. The effectiveness of the proposed control technique is evaluated from two perspectives: (i) its ability to withstand significant perturbations in plant parameters and load disturbances and (ii) its resilience in the presence of variations in controller parameters. The effectiveness of the proposed control scheme is validated using simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper focuses on sliding mode controller (SMC)-based master–slave parallel operation of DC–DC converters using a modified sliding manifold to achieve a fast dynamic response and very low steady-state error. The converter performance is analyzed in a novel way starting from a simple case of paralleling of two converters and then concept is extended for parallel operation of multiple converters. An investigation of the choice of the sliding surface on the performance of parallel converter is carried out in detail, and a mathematical design guideline for sliding coefficients for the proposed manifold for the master converter is derived to achieve stable operation. The proposed manifold ensures an improved dynamic response with an excellent steady-state accuracy in stand-alone mode. However, when it is incorporated with master–slave control for parallel operation with finite tie wire impedance, there is a degradation in the steady-state accuracy. In order to improve the steady-state performance of the sliding mode controller, two new hybrid (SMC + PI) controllers are proposed and implemented for parallel connected DC–DC converters. Finally, the proposed SMC techniques are verified through simulation study and through a scaled down experimental (laboratory) prototype. [ABSTRACT FROM AUTHOR]

The main contribution of the paper concerns the use of an LCL trap filter with a PFC isolated Ćuk converter. Further, SiC MOSFET is used with a PFC isolated Ćuk converter designed for 50 W with 42 kHz in DCM. A small-signal model of the converter is cascaded with the filter model to investigate the effect of the filter on the whole system. Moreover, large-signal and small-signal models of the converter are compared to investigate the requirement of the small-signal analysis. In addition, an LTspice simulation using SiC MOSFET of the system is conducted and the results are compared by the applications for both LC and LCL trap filters with respect to different loading conditions. Further, the LCL trap filter is compared with the LC filter regarding the PF, THD, and efficiency. Controller design considering the filter is also presented. In addition, the converter is operated and compared using linear and nonlinear loads for each filter. Parametric variation in the filter components is investigated. As a result of the simulation and applications, the THD of the grid current is 4.83% and the PF is 0.998, meeting the standards, and the overall efficiency of the system is 85% with the LCL trap filter. It can be concluded that the presented filter provides better results than the LC filter. [ABSTRACT FROM AUTHOR]

In response to the challenges faced by traditional LLC resonant converters in simultaneously achieving a wide output voltage and high efficiency, this paper proposes a cascaded DC-DC converter. The front stage of the converter adopts a new LLC topology, and it is cascaded with a boost converter through a reutilization of the output-side inductor. The proposed DC-DC converter leverages the electrical isolation and wide output voltage range advantages of LLC and boost converters, enabling the overall system to achieve broad output voltage regulation and high-efficiency operation. The reutilization of the inductor design further enhances the integration density of the DC-DC converter. A minimum loss collaborative control strategy is introduced for the proposed DC-DC converter. When determining the output voltage and operating the circuit in step-up mode, the duty cycles of the switch in the proposed LLC converter and the switch in the boost converter are adjusted to minimize overall circuit losses while ensuring the rated output voltage. Ultimately, the correctness and practicality of the proposed DC-DC converter and its control strategy are validated through a simulation and an experiment. The overall efficiency of the DC-DC converter can reach up to 94% under optimal conditions. [ABSTRACT FROM AUTHOR]

A totem-pole bridgeless boost converter is one of the most promising topologies for the power factor correction (PFC) stage in high-power applications due to its high efficiency and small number of components. However, due to the totem-pole structure of the field-effect transistor (FET), very high switching loss occurs via the reverse recovery current of the body diode. To solve these problems, critical mode (CRM) control is a good solution to achieve the valley switching technique. With valley switching of CRM control, the switching loss decreases drastically with decreasing turn-on voltage. But, although the CRM control enables valley switching, it is hard to make an exact valley switching control with general zero-voltage detection circuits. In addition, when a frequency limitation scheme is applied to prevent a very high frequency, the switch can operate with hard switching at the boundary of the frequency limitation. Furthermore, the CRM boost PFC has a low PF and high total harmonic distortion (THD) under light-load conditions due to the large negative current resulting from resonance between the inductor and parasitic capacitance. It becomes worse at near-zero input voltage since the resonance current becomes larger near zero-input voltage. Therefore, in this paper, a totem-pole bridgeless boost PFC converter with high efficiency, high PF, and low THD is developed using TMS320F28377 by Texas Instruments. Based on the basic digital structure of the totem-pole bridgeless converter, the proposed controls help with exact valley switching, PF and THD improvement, and frequency limitation. The prototype converter is verified using 90–264 VAC input voltages and 450 V/3.3 kW output specifications. [ABSTRACT FROM AUTHOR]

In this paper, the combination of a high step-up boost converter with extended voltage multiplier cell and isolated SEPIC converter with a series output module is presented. Since these converters use the same current source in their inputs, they can share the common parts, so the structure of the proposed converter is simple. In this converter, the high frequency transformer used in the SEPIC converter and the inductor of the extended voltage multiplier cell are coupled, so the volume of the magnetic parts is reduced. In addition, an active-clamp circuit is used to solve the problem of leakage inductor and achieve to Zero Voltage Switching (ZVS) turn on/off for switches and ZCS for diodes. Compared to its high step-up counterpart, the proposed converter has the following: (1) distributed voltage stress on the diodes and voltage of the output capacitors are fair. (2) Higher voltage gain. (3) Voltage stresses on the diodes are lower and the reverse-recovery problem of the diodes is eliminated. (4) Minimum root mean square (RMS) leakage inductor current. The operational principle and characteristics of the proposed converter are presented, and in order to verify the proposed converter, a 200 W, 20–400 V prototype converter is implemented and experimental results are provided. [ABSTRACT FROM AUTHOR]

This paper aims to outline the process of dimensioning a controller tailored for a fourth-order step-down converter. In order to conduct a thorough small-signal analysis, it is imperative to find the state–space model in matrices form. Given its fourth-order nature, the control-to-output transfer function also aligns with this order, although its degree is ultimately reduced to a second-order using the tfest function. It is remarkable that the design of the type III error amplifier assumes a central position in the overall controller design process. The theoretical analysis was then subjected to rigorous validation via simulation, with particular attention paid to the step response in both input voltage and output resistance. This study developed from the desire to validate the efficacy of reducing the control-to-output transfer function degree using the tfest function, aiming to highlight a fourth-order converter to which controller design theory can be applied, related to that for a second-order converter. [ABSTRACT FROM AUTHOR]

For decentralized electrification in remote areas, small-sized wind energy systems (WESs) are considered sustainable and affordable solution when employing an efficient, small-sized component converter integrated with a less-sophisticated, cost-effective MPPT controller. Unfortunately, using a conventional buck DC/DC converter as a MPP tracker suffer from input current discontinuity. The latter results in high ripples in the tracked rectified wind power which reduces the captured power and affects system operation especially in standalone applications which are self-sufficient and independent of grid support. Furthermore, these ripples propagate to the machine side causing vibration and torque stress which impacts turbine performance and safety. To solve this issue, a large electrolytic capacitor is placed at the buck converter input to buffer these ripples, yet at the cost of larger size, losses and reduced reliability. Oppositely, the developed C1, D4 and D6 buck converters have the merit of continuous input current at small component-size. In this paper, dynamic modelling of these three converters is developed to select the one with the least input current ripples to replace the traditional buck converter in the considered WES system. Consequently, fluctuations in the tracked power are minimized and the large buffer capacitor is eliminated. This enhances system lifetime, reduces its cost and increases tracking efficiency. Moreover, mechanical power and torque fluctuations are minimized, thus maintaining machine protection. Furthermore, a sensorless MPPT algorithm, based on converter averaged state-space model, is proposed. Being dependent on variable-step P&O algorithm, the proposed approach features simple structure, ease of control and a compromise between tracking time and accuracy besides reduced cost due to the eliminated current sensor. Simulation results verified the effectiveness of the selected converter applying the proposed MPPT approach to efficiently track the wind power under wind variations with cost-effective realization. [ABSTRACT FROM AUTHOR]

The integration of renewable energy sources performs a crucial role in dealing with the issue of energy accessibility for people living in remote areas. It is expected to enhance the overall quality of life by utilizing photovoltaics and microinverters to support energy needs. The proposed microinverter-based two-stage topology design is to provide successful conversion of low DC power to the voltage level necessary for the inverter requirement as the first stage. Afterwards, the modified Cuk converter is intended to ably convert the input voltage DC power into a 220 Vac 50 Hz output during the second stage of operation. To prevent possible disruptions triggered by fluctuations in solar irradiation, this paper also presents a closed-loop system designed to maintain a consistent output of 220 Vac 50 Hz. The study successfully established the viability of the proposed design and control mechanism in ensuring a stable output voltage from a single photovoltaic (PV) panel. [ABSTRACT FROM AUTHOR]

Examining impacts of differential mode (DM) filter topologies covering pi, LC with damping, LC, LCL filter through isolated Ćuk single phase PFC converter is realized in this paper regarding to power factor, THD and efficiency. Application of PFC isolated Ćuk converter is conducted with 42 kHz switching frequency and 50 W power. Each filter is modeled, designed, and applied experimentally via isolated PFC Ćuk converter. Average model derivation based on state-space, for DCM operation of input side inductor of isolated PFC Ćuk converter that is not introduced in literature is the main contribution of the paper. Second main contribution is to analyze filter types by linear methods for the transfer functions cascading the converter and filter transfer functions, which is not presented for PFC converters. It is also presented that solely LCL filter which is not analyzed for PFC converters in detail in literature, does not give desired results. So, increasing the effectivity of LCL filter, new filter structure LCL with parallel C filter is proposed and modeled in this paper. Thanks to the applications, presented results of LCL with parallel C filter is better than others with 4.9% current THD and '1' power factor. Proposed LCL filter ensures 45% reduction of total inductor value, comparing to LC filter. Besides, LCL with C filter provides better control characteristics with maximum allowable gain for stability as 0.7585 higher than other topologies. Moreover, practical design methodology of filter types avoiding complex mathematical procedure is given in this paper. Applications with each filters provide THD requirements, obtained 4.9% as a best value, lower than IEC61000-3-2 standard. Maximum percentage improvement comparing to the IEC61000-3-2 is 27.5% for third harmonic. Furthermore, SiC and Si Mosfets are employed separately in the converter and compared by using each DM filters regarding to power factor, THD, efficiency through applications. As a result, better efficiency with SiC Mosfet as 83% and better THD with Si Mosfet as 4.9% are conducted. [ABSTRACT FROM AUTHOR]

Summary: This paper proposes a power factor correction (PFC) method in a single‐phase AC/DC converter using a predictive control algorithm (PCA) through a boost DC/DC converter. The minimum value of the DC‐link capacitor has been evaluated on the DC distribution side for stable operation of the converter. The proposed technique can be applied to the cascade connection of the converters, that is, the uncontrolled rectifier with boost converter and load. The value of the minimum capacitance is obtained as a function of the reference voltage of the DC‐link capacitor, the frequency of the supply, the input power, and the maximum DC‐link voltage. The proposed design is applied to control the boost converter for PFC applications using PCA at the minimum DC‐link capacitor value. The calculated value of DC‐link capacitance has been reduced to a greater extent as compared to the conventional calculation of DC‐link capacitance. The converter operation with the designed value of DC‐link capacitance has been verified through the MATLAB and Typhoon Simulink environment, and an experimental prototype model is used for the validation by using the FPGA based Typhoon HIL‐402 kit. [ABSTRACT FROM AUTHOR]

Summary: Multi‐input converters (MICs) play a significant role in the aspect of the integration of sources. The reliability of the converter can be enhanced by using a suitable fault tolerance converter design and control algorithm. A dual‐input single‐output (DISO) DC–DC converter with source fault tolerance is proposed in this paper. In the literature, there are many topologies in this area of work; however, most of them are based on time‐sharing control. In this control scheme, one input source is contributed to the load, and others are kept idle in a particular duty interval; hence, this control scheme leads to underutilization of the converter. The proposed converter is designed to circumvent these challenges and can produce boost, buck–boost, and buck operations. And also, it has a source fault feature for achieving the preserved output voltage under source V1 or V2 failure conditions. A 200‐W prototype is designed, and the feasibility of the proposed converter is validated through simulation and experimental results. [ABSTRACT FROM AUTHOR]

Summary: In order to improve power regulation capability and system reliability, an interconnected hybrid microgrid (MG) topology with back‐to‐back (BTB) converters is a promising solution, but it also brings new technical challenges to the control system. The paper proposes a two‐level power management and coordinated control strategy for hybrid MG with BTB converters to ensure the stable operation of the system. Firstly, the structure of hybrid MG is analyzed, and model of BTB converters, photovoltaic (PV) cell and battery are established. Secondly, multiple constraints and operation characteristics of DG, ESS, and BTB converters are considered, the detailed operation modes are analyzed, and system‐level power management strategy is developed under grid normal, single‐terminal grid fault, and island operation conditions. A local‐level coordinated control strategy of BTB converters, battery energy storage system (BESS), and PV units is presented to ensure stable operation of the system in multi operation modes. The control coordination between the BTB converters and the ESS can ensure the stability of the AC voltage and frequency in the fault area and achieve uninterrupted power supply for important loads. Meanwhile, voltage recovery and current sharing control are proposed based on the voltage and current information provided by the upper power management system to eliminate DC voltage deviation and realize accurate current allocation. The current sharing and voltage recovery control is embedded in the local devices and will not have any impact on the upper power management system. Finally, the effectiveness of proposed method is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

Hybrid Energy Storage Systems (HESSs) have gathered considerable interest due to their potential to achieve high energy and power density by integrating different storage technologies, such as batteries and capacitors, to name a few. Among the various topologies explored for HESSs, the multi-output multilevel converter stands out as a promising option, offering decoupled operation of the AC ports while maintaining an internal balance among the diverse storage units. In this paper, the operation and restrictions of a HESS based on a multi-output multilevel converter with a carrier-based modulation scheme are presented. The study provides compelling evidence of the correct operation of the proposed modulation scheme and highlights its advantages, including simplicity and stability. [ABSTRACT FROM AUTHOR]

In accordance with the requirements of unmanned robot driving power supply for power supply reliability, strong power output, and portability, this paper introduces a design scheme for unmanned robot driving power supply on the basis of a flyback converter, establishes the mathematical model of driving power supply (flyback converter), designs the transformer part of a flyback converter, and recommends a straightforward and efficient clamping circuit to enhance it. The controller of the flyback converter is designed in detail. Ultimately, the feasibility and effectiveness of the design method in the driving power supply of unmanned robots are demonstrated by simulation and experiments. [ABSTRACT FROM AUTHOR]

In a DC microgrid, the dual active bridge (DAB) converter is employed for voltage conversion and power transfer. DAB-based energy storage systems (ESSs) are known as constant power loads (CPLs). To improve the input current quality of DAB converter, an LC filter is cascaded to a DAB converter. Impedance interaction takes place between the impedance of the LC filter (Zout) and the impedance of the DAB converter (Zin). ESSs are affected by the impedance interactions of cascaded systems. This interaction leads to significant oscillation and instability, which in turn causes voltage fluctuation and power loss. To overcome instability, this paper proposes a modified fuzzy logic controller (FLC), an active voltage stabilizer (AVS), and feed-forward (FF) controller to reshape the impedance of the DAB converter. In the modified controller, the FLC handles precise voltage monitoring, the AVS handles the transient stability limit, and the FF controller removes the impedance interaction between Zin and Zout. The feed-forward coefficient is calculated through the Routh–Hurwitz criterion. The suggested controller assures system stability during load variation, a quick dynamic response, and precise voltage monitoring. In addition, it achieves reductions in the settling time, rise time, and overshoot. This leads to reliable microgrid operation when compared to the traditional PI (PI + AVS), and (PI + AVS + FF) controllers. The modified controller is verified by results obtained with an OPL-RT-based hardware-in-the-loop (HIL). [ABSTRACT FROM AUTHOR]

In this paper, an improved modular multilevel converter (MMC) topology has been proposed with fault-tolerant capability and reduced submodule capacitor voltage fluctuation (SMCVF) in a low frequency operating range. In the proposed converter, a novel middle SM, which has salient features, is inserted between the upper and lower arms. For regular operation, the middle SM is applied to mitigate the power fluctuations in both arms by providing distribution of high-frequency power components, which reduces the AC voltage fluctuation on the SM capacitor. When a fault occurs in any SM in the upper or lower arms, a new half-bridge SM can be configured from the middle SM to replace the faulty SM without any interruption, which means the converter is operated in the fault-tolerant mode. Therefore, the performance of the converter is maintained well, and the system reliability is enhanced. Simulation and experimental results have verified the effectiveness of the proposed topology and control strategy. [ABSTRACT FROM AUTHOR]

The stability of an MMC AC/DC hybrid system shows differences with changes in its operating state. However, the time domain analysis method cannot quantitatively evaluate the dynamic characteristics of the system. In this paper, a small-signal model of an MMC AC/DC hybrid system is established to analyze the system stability under continuous changes of the parameters. First, the dynamic characteristics of the small-signal model and the time-domain simulation model are compared to verify the accuracy of the small-signal model. Second, the dynamic stability of the MMC under four typical operating states is analyzed, and the influences of the AC system capacity and impedance angle on the stability domain of the system are evaluated. Then, the modal analysis method is used to solve the dominant mode and participation factor of the critically stable system. In addition, the oscillation characteristics of the system are solved. Finally, the variation trend of the system stability dominated by the controller parameters and DC capacity is obtained. The obtained results show that the controller parameters of the MMC do not contribute to the system oscillation characteristics. The selection of the AC/DC capacity leads to differences in system stability. Under PV control, the MMC AC/DC hybrid system presents stronger stability, and the system is easily affected by low-frequency oscillation. [ABSTRACT FROM AUTHOR]

To address the instability of the input voltage of photovoltaic (PV) in a stand-alone PV storage power generation system, a wide input range non-isolated three-port converter that can operate in a range that is greater than and less than the voltage of the storage port is proposed in this paper. The proposed converter can realize the energy flow and power balance between the PV, the battery, and the load. This converter is a combination of conventional Buck, Boost, and Buck–Boost converters with a four-switch bi-directional Buck–Boost converter (FSBB). The FSBB is used to connect the PV and battery ports, which can reduce the voltage constraint of the storage port on the PV port voltage, and broaden the selection of the voltage levels of the storage port to meet the application requirements of the PV port with a wide voltage input. In this paper, an experimental prototype is designed by combining the Boost converter and the FSBB converter. Finally, the correctness of the theoretical analysis and the feasibility of the energy management strategy of the converter are verified through experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a new single‐phase direct step‐up ac–ac converter by modifying the p‐type impedance source. It provides a high boost factor as well as high efficiency, while only six parts are required to design it, involving just two bidirectional power switches. A safe commutation method has been applied to power switches to make the converter snubber‐free and high efficient. Input and output harmonic filters are no longer required since input and output currents variate continuously with small ripple and low total harmonic distortion (THD). The proposed topology only modulates the output voltage amplitude, not the phase and frequency, so the output frequency is identical to the input frequency and constant. Thus, it can be utilized in step‐up conversion applications, like inductive power transmission from low ac voltage sources. Input and output have the same ground, which is a good protective feature. In this paper, the operating principle of the converter is demonstrated. Experimental results have been represented to evaluate the performance of the converter. For this purpose, an experimental prototype has been fabricated. Results are investigated and compared with other previous step‐up ac–ac converters. Results confirm the theory, operating principle, and performance of the converter. [ABSTRACT FROM AUTHOR]

The main challenges of the input current control in synchronous DC-DC buck converters are the nonlinear model of the system, changes of the operating point in a wide range, and the need to use an input LC filter for current smoothing, which may result in the instability of the closed-loop system. In this paper, a step-by-step approach is developed for the design and improvement of a PI-feedforward closed-loop controller. It is shown that a linear PI controller cannot stabilize the closed-loop system properly during wide changes in model parameters, e.g., an equivalent series resistance of the input filter. To cope with the stability issues, a fixed-frequency sliding mode controller (SMC) has been developed in this paper for the implementation of an electro-mechanical actuator (EMA) emulator. Moreover, a systematic approach is proposed for controller tuning and the selection of the SMC's gains. To achieve high power efficiency, high-frequency GaN switches are used for the practical implementation of the DC-DC converter. Despite large changes in the load current, the designed nonlinear controller can track the input current reference satisfactorily. Steady-state and dynamic responses of the proposed SMC are compared with conventional linear controllers. Considering the Lyapunov stability theorem, it is proved that the designed SMC can stabilize the closed-loop system in the entire utilizable domain. The proposed nonlinear SMC controller enjoys a very simple control law. Hence, despite having very high switching and sampling frequencies, it can be easily implemented. The experimental response of the designed synchronous DC-DC buck converter is evaluated experimentally by implementing the control strategy in a TMS320F28335PGFA DSP from Texas Instrument. Moreover, the comprehensive comparison of the proposed SMC controller and a PI-feedforward controller proved the superior performance of the developed closed-loop system, in terms of the transient time response, robustness, and stability of the EMA emulator. [ABSTRACT FROM AUTHOR]