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The fast development of renewable energies leads to an increase in the power electronics penetration in transmission systems. This is particularly true if one considers a 100% renewable energies power system, where wind and solar photovoltaic energies, which make most of the renewable energies connections today, are connected to the grid through power electronics converters. Because power electronics-based generators and synchronous machines-based generators have very different dynamic behaviours, some approximations usually used to run transient simulations of transmission systems might not be optimal for future grids. The systematic use of the phasor approximation applied to the power lines, implemented in most of the Transient Simulation Programs, is indeed not relevant any more. To avoid the use of Electromagnetic Transient simulations, that are resource-demanding and time-consuming, this paper presents a novel Model Order Reduction technique for large grids with a high penetration of power electronic devices. Compared to the classical phasor approximation, this event-based state residualization approximation allows accurate transient simulations and at the same time an optimal reduction of the number of the system’s state variables depending on the observed variables, the considered events and the tolerated approximation error. [ABSTRACT FROM AUTHOR]

A phase-locked loop (PLL) is commonly used in grid-connected power converter for synchronization. A single input single output (SISO) linear model of PLL with the phase angle of the point of common coupling (PCC) voltage as input and the estimated phase angle as the output is generally used in the PLL analysis and design. However, an undesirable coupling between the magnitude and phase of the input voltage is present when a filtering stage is incorporated before the control loop, which a SISO model cannot capture, and could result in a significant disturbance in the PLL estimated phase during grid faults. This paper proposes a generalized multi-input multi-output (MIMO) linear model that captures the complete PLL dynamics during symmetrical faults for a PLL equipped with any prefilter. Furthermore, a compensation method that decouples the magnitude dynamics of the input voltage from the phase dynamics is proposed in this paper. The proposed compensation improves the PLL's phase tracking performance by ensuring that the prefiltered PLL acts only on the PCC voltage phase changes. A vital application of the proposed compensation method for PLL is during a grid fault case, wherein the converters are expected to contribute to the fault current, which requires an accurate measurement of the PCC voltage phase. The compensation method's effectiveness is demonstrated using power hardware in the loop simulation of a hardware voltage source converter interfaced to a distribution system simulated in real-time. [ABSTRACT FROM AUTHOR]

A power buffer is a power electronics converter with a large capacitor that shields a weak DC grid from abrupt load changes. Distributed control solutions have been shown to be superior to the decentralized ones; however, the effects of the communication network topology on the control performance of these buffers have not yet been studied. This article offers a data-driven optimal solution to reduce the interactions between different control loops of power buffers while minimizing a closed-loop performance function. Reinforcement learning methods deal with the optimal control of nonlinear systems, and a Tabu Search method addresses the resulting combinatorial problem. The proposed solutions are validated for a DC microgrid in a controller/hardware-in-the-loop environment. [ABSTRACT FROM AUTHOR]

A dc–dc converter used for fuel cell vehicles should be characterized by a wide voltage-gain range and low input current ripple. In order to meet the above requirements, a new nonisolated dc–dc converter consisting of an active switched-inductor cell, a zero current ripple cell, and a switched-capacitor (SC) cell was proposed in this article. The proposed converter integrates with the advantages of a wide voltage-gain range, zero input current ripple, low voltage stresses across power semiconductors, and common ground structure. Thanks to the use of a zero current ripple cell, not only the input current ripple is reduced but also the energy transfer path of the SC cell is changed, thereby reducing the instantaneous peak current of the SC structure. The operating principles, the characteristics analysis, and the parameter design of the proposed converter are given. In addition, to show the merits of the proposed converter, a comparison study is demonstrated. Finally, a prototype of 400 V, 1000 W/50 kHz is developed to validate the effectiveness of the proposed converter. [ABSTRACT FROM AUTHOR]

This article presents a novel low-cost, single-switch, high-step-upresonant dc–dc converter with high reliability. The proposed converter topology comprises a low count of components and a simple structure and achieves the low ripple input current characteristic. The inductors in the resonant network participate in the resonant process rather than creating voltage spikes across the switch and likely reverse recovery problems. The circuit operates in the soft-switching condition (ZVS–ZCS conditions in the turn-off and turn-on transitions), leading to a significant reduction of the switching losses. Moreover, employing film capacitors instead of electrolytic capacitors reduces the size of the circuit and improves reliability. The operational principle and comprehensive steady-state analysis in the continuous conduction mode are discussed in detail, alongside the design considerations of the proposed converter. The validity of the theoretical equations is investigated via experiments, achieving maximum efficiency of 97.69% for a converter designed at the input of 24.5 V, the negative output of 200 V, and the maximum powerof 200 W. [ABSTRACT FROM AUTHOR]

The traditional active neutral-point-clamped (APC) dc–ac converter maintains great common-mode voltage with high-frequency (CMV-HF) reduction capability, so it has limited voltage gain. This article presents a new five-level APC (FL-APC) dc–ac converter capable of voltage step-up in a single-stage inversion. In the suggested design, a common ground not only reduces the CMV-HF but also improves dc-link voltage usage. While comparing with traditional two-stage FL-APC dc–ac converter, the proposed design has lower voltage stresses and greater uniformity. While improving overall efficiency, the suggested clamped dc–ac converter saves three power switches and a capacitor. Modeling and actual tests have proven the suggested APC inverter’s overall operation, efficacy, and achievability. The proposed circuit is finally tested with fault clearance capability. [ABSTRACT FROM AUTHOR]

Parallel dc–dc converters are commonplace in applications such as computing power supplies, point of load systems, and dc microgrids. The presence of multiple converters in such systems allows for switch interleaving and ripple cancellation. One class of existing ripple reduction methods depends on central controllers that require communication among the converters. These approaches compromise system scalability and reliability. When it comes to decentralized methods, the state-of-the-art is limited to uniform conditions and cannot handle mismatches in physical parameters and operating points among converters. In this article, we address these shortcomings with fully decentralized controller that robustly drives the pulsewidth modulation carriers of a collection of heterogeneous converters to the phase-shifts that give minimized ripple. More precisely, the proposed controller eliminates the dominant fundamental switching harmonic from the output current and voltage using only local voltage feedback. After outlining a comprehensive analytical model, we experimentally validate our approach on a system of five parallel-connected buck converters under a variety of parametric and operational mismatches. Measurements show ripple reduction of more than $4\times$ in the output voltage and the fundamental switching frequency harmonic is attenuated by more than 30 dB compared to conventional symmetric interleaving. [ABSTRACT FROM AUTHOR]

Power electronics converters operating at elevated temperature usually have degraded performance, such as reduced efficiency, lower noise immunity, and decreased system reliability, compared to those operating at room temperature. Nevertheless, harsh-environment applications, such as deep earth drilling, automotive, avionics, and space exploration, have been utilizing converters in high-temperature environments and are continuously pushing the temperature limits higher and higher with the advances in device technologies and converter design methodologies. This article starts with a literature study to identify the temperature dependence and the temperature limits of individual components. Then, published works about high-temperature converters are examined. Their selection of components is compared. Experimental results are analyzed to reflect on the efficacy of different component selections. Finally, since the latest published high-temperature converter was developed more than five years ago, a 1-kV input, 520-V output, 1-kW, $150$ °C-ambient-temperature-rated dc–dc converter is designed with state-of-the-art devices. Based on the literature review, and the test of the $150$ °C prototype, the main challenges of designing high-temperature power electronics converters are identified and concluded to be time-consuming, difficult, and expensive characterization of components, lack of accurate and computationally efficient models of converters, and optimizing component selection within short development time. [ABSTRACT FROM AUTHOR]

The presence of unbalanced loads in power systems creates voltage imbalances that perturb the operation of sensitive loads, such as induction motors, power electronics converters, and adjustable speed drives. This article presents a novel control scheme that achieves accurate voltage balance at any node of an islanded ac microgrid with seamless integration with the existing hierarchical control of the microgrid. A master–slave architecture is adopted for the unbalance compensation due to its low network traffic requirements and its modular conception. The unbalance compensation follows a collaborative principle where current injections are computed as a function of the current rating of each inverter, thus avoiding the overcurrent stress of the unbalance compensation by a single inverter. This article presents the stability analysis and the design guidelines for the control parameters. The performance of the control proposal has been successfully tested in a laboratory microgrid. Selected experimental results are presented. [ABSTRACT FROM AUTHOR]

Due to the increasing performance and decreasing price of microcontrollers in recent years, applying a high sampling frequency has become more feasible in modern control that is known as multisampling technology. The first motivation to use multisampling is emulating the analog control, thereby reducing the control delay and improving the stability of power electronics controllers. On the other hand, more information can be acquired from the multisampled current/voltage, which helps to save the cost and improve the reliability. In this article, a review of the multisampling application in power electronics converters is provided. Starting from the control delay analysis in single/double-sampling control, the modeling, implementation, and related control strategies are given when using multisampling pulsewidth modulation. Then, based on the multisampled data, the applications in condition monitoring and parameter estimation are discussed. Finally, perspectives on challenges and future trends are discussed. [ABSTRACT FROM AUTHOR]

In the design process of power electronics converters, the power semiconductors thermal modeling is one of the most critical tasks. An accurate estimation of the junction temperature allows the validation of the converter design and also the calibration of the thermal models during prototyping. Therefore, this article presents a straightforward method to estimate the junction temperature directly on the target converter using a plug-in measurement system. The estimation is based on the IGBT on-state voltage measurement under high current with a dedicated sensing circuitry externally connected to the converter under test. This solution is specifically designed to fulfill the needs during the prototyping process and design validation since allows a fast and reliable monitoring in all working conditions of interest and the sensing circuitry does not affect the normal operation of the converter under test (CUT). The acquisition circuitry and the calibration procedure are described and tested on a 68-kVA IGBT industrial three-phase inverter. The experimental results obtained on the target inverter prove that the proposed design validation based on the implemented estimation of the junction temperature provides better results than the conventional design methods based on thermal models implemented in simulators. [ABSTRACT FROM AUTHOR]

Power electronics converters are equipped with current controls that protect the converter from over-currents. This protection introduces non-differentiable equations into the power flow problem. The conventional Newton's method is not suitable in that conditions. This letter proposes a fixed-point iteration to overcome this difficulty. The technique is derivative-free, and hence, it can naturally include the saturation given by the converters’ current protection. Exact conditions for convergence and uniqueness of the solution are demonstrated using Banach's fixed point theorem. Numerical experiments in Matlab complement the analysis. [ABSTRACT FROM AUTHOR]

Condition-monitoring systems are used to determine the best timing for predictive maintenance of power electronics converters. These monitoring systems can significantly reduce the converter repair time and increase system availability. In this article, an investigation has been conducted on the possibility of using the dissipation factor as a lifetime indicator of electrolytic capacitors. A criterion is also proposed based on the dissipation factor to detect electrolytic capacitors’ end of useful life. A method has been presented for measuring the dc-link capacitor dissipation factor in a back-to-back converter. Using this technique, it is possible to estimate the switching component of the capacitor current by measuring the output currents of the converter without a need to measure the capacitor current directly. The proposed method is simulated, and the impact of various factors, such as switching frequency, capacitor series inductor, and the network filter on the accuracy of the dissipation factor measurement, is discussed. Experimental results are also provided to validate the acceptable accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

Different from the typical topology derivation of power electronics converters (PECs) depending on manual effort, this article aims to explore a programmable method based on graph theory for multiport dc–dc converters with reduced switches. By mathematically modeling converters with graph theory and transforming their working criteria into the corresponding graph constraints, the topology derivation can be automatically and conveniently solved with the aid of computer program. In this article, first, the principle of the proposed graph theory-based programmable method is introduced in detail. Then, it is employed to derive multiport dc–dc converters with reduced switches, and a diversity of new topologies are simultaneously excavated, among which a favorable one is selected to be theoretically introduced and experimentally verified. The proposed method remains relatively simple with the increasing number of ports, as the graph constraints of working criteria are almost the same for different number of ports. More importantly, because PECs can be essentially regarded as graphs with different components and their connecting relationships, the proposed method is applicable for many various converters. [ABSTRACT FROM AUTHOR]

This article presents a robust passivity-based control (PBC) strategy to mitigate the instability effect of the dc–dc boost power converter supplying a constant power load and a constant voltage load in dc microgrid systems. The control robustness of the PBC against both line and load variation is significantly improved by adding the nonlinear disturbance observer (NDO). Using the disturbance estimation technique, this observer works in parallel with the PBC strategy to compensate the disturbances of the system through a feed-forward compensation channel. Based on the dissipation property, the PBC strategy ensures the system stability, whereas the NDO guarantees global trajectory tracking to the reference voltage during disturbances. This control strategy not only ensures large-signal stability of the system, but also provides a fastest recovery performance during disturbances of the system as compared with other PBC strategies. The hardware-in-loop and real-hardware experimental results are provided to verify the control robustness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Electric machine emulation (EME) is becoming a popular solution in advanced testing and validation of power-electronics-based machine drive systems. In terms of a typical EME, the stator current references are first calculated in response to the sampled terminal voltage, and then, are electrically generated by power electronics converters. In this type of structure, closed-loop current control and low-pass sampling for the voltage are inevitably introduced, resulting in distortion in frequency-domain behaviors of EME. Consequently, the steady-state performance under a high fundamental frequency, and the dynamic performance under load transients, may deviate from those of the target machine system. In this article, the bandwidth limitations of the typical EME are identified and analyzed in detail, and a novel structure that realizes full-bandwidth mission profile emulation is proposed. Theoretical analyses are given to prove that the frequency-domain characteristics of the proposed structure would be identical to the actual machine systems, which allows for the extended operating range of mission profile emulation. Simulation and experimental results are provided to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Soft switching is one of the effective techniques to improve the efficiency and power density of power electronics converters. This article presents a comprehensive review of the soft-switching topologies used in single-phase photovoltaic (PV) inverters for residential applications. The topologies of single-phase PV inverters are investigated and divided into two types of power conversion stages: the PV interface stage for boosting PV voltage and the grid interface stage for feeding ac power to the grid. The soft-switching topologies for each type of power conversion stage are reviewed and compared, respectively, including the soft-switching mechanisms, efficiency, device ratings, and design challenges. Discussions and recommendations of soft-switching topologies for each stage are also provided. This article is an attempt to provide a helpful reference for engineers working on high-performance single-phase PV inverters. [ABSTRACT FROM AUTHOR]

Synchronous rectification (SR) is an effective method to reduce the secondary side conduction loss of CLLC bidirectional resonant converter and improve its efficiency, but the SR driving signal in CLLC converter is hard to determine. Existing SR signal generating methods can be divided into three categories: theoretical calculation, voltage detection, and current detection. Compared with the other two methods, the current detection method has wider applicability and is insensitive to parasitic parameters, but usually requires lossy, bulky and costly current sensors, increasing the cost and size of the converter. This article proposed a SR scheme based on resonant inductor voltage. The polarity of the resonant current is obtained indirectly through the inductor voltage, thereby avoiding the use of current sensors. To handle the false pulses problem caused by parasitic oscillation, a corresponding SR control strategy is proposed. The SR driving signal is then adjusted according to the delay and transient requirements. Experimental results on a 380V/270V 3kW CLLC converter prototype were presented to verify the effectiveness of the proposed SR method. [ABSTRACT FROM AUTHOR]

Free positioning wireless charging for consumer electronics allows the devices to be charged at arbitrary positions and angles to improve user experience. However, a user-initiated sudden movement of the device during charging can cause hazards due to the abrupt variation of the coupling coefficient. To solve this issue, the coupling coefficient variation at different positions should be mitigated, which is also good for the design and high-efficiency operation of power electronics converters. This article proposes a design methodology to employ antiparallel windings to smooth the coupling coefficient variation over different positions by reducing the coupling coefficient at central positions and enhancing it at boundary positions. Two optimization methods are proposed: turn-by-turn optimization and winding-by-winding optimization. A design flow is offered. The hexagonal coil is compared with the square coil and proved to achieve better performance than the latter. An experimental prototype is implemented to validate the effectiveness of the proposed design methodology. [ABSTRACT FROM AUTHOR]

Power decoupling is always a strong desire for single-phase voltage source inverter (VSI) due to the inherent double-line (2ω) frequency ripple caused by the instantaneous power unbalance between dc- and ac-side. The existing solutions either apply a large capacitor or employ a small power converter to compensate it, which inevitably increases the system cost and control complexity. To overcome these drawbacks, this article performs the transient modeling analysis and it reveals that 2ω frequency power component in the converter achieves minimum value when the inductor current ripple is minimized. A novel capacitors’ voltage ripple complementary control algorithm based on three-level boost fed single-phase VSI is proposed. By mitigating the 2ω power component from the inductor and redistributing the stored energy between two intermediate series-connected capacitors, the oscillating power is absorbed with notably eliminated input current ripple and significantly reduced dc-link voltage ripple. Thus, the good power quality of both dc- and ac-side is guaranteed. Furthermore, the total capacitance requirement is minimized under the given dc-link ripple tolerance without any more electric stress increment and lifetime reduction. Simulation and experiment results verify the theoretical analysis and proposed control method. It is promising in applications, where both input current ripple is strictly limited and ac output voltage quality is highly required with small dc-link capacitance. [ABSTRACT FROM AUTHOR]

Under weak grid condition, negative influence is brought in on system stability because the grid impedance and the grid-connected converter control system are coupled to each other. The key factor affecting the stability of the system is the perturbation of the voltage fluctuation at the point of common coupling (PCC) to the phase-locked loop (PLL) and the dc-link voltage loop. In this article, the impedance model of a three-phase grid-connected converter, including the current loop, PLL, and dc-link voltage loop in the dq frame, is adopted, because it includes coupling information of the converter and reflects the transferring relationship among grid-connected system variables. Based on the transferring relationship, this article analyzes the perturbation paths of PCC voltage and proposes the corresponding compensation methods, i.e., the PLL and dc-link voltage loop compensation terms, which are inserted into the q and d axes of the current loop controller, respectively. The impedance analysis results show that the proposed method can effectively improve the system stability. In addition, the experimental results verify the correctness of the theoretical analysis and the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A double-input bidirectional dc–dc converter, with an innovative architecture, exploiting the use of only three switches, is taken into account in this article. The modulation strategy proposed in the technical literature for controlling such a converter leads to a very low efficiency at low-load because the converter is only able to operate in continuous conduction mode when currents are low. A new modulation strategy, for exploiting discontinuous conduction mode, is here proposed. The efficiency increase is evaluated with a MATLAB/Simulink Plecs simulation model. The control algorithm and the simulation model are validated with experimental results carried out on a converter prototype. [ABSTRACT FROM AUTHOR]

A new nonisolated bidirectional dc–dc converter with noninverting output and buck–boost operation is proposed and described in this article. The passive components arrangement in the proposed magnetically coupled buck–boost bidirectional dc–dc (MCB3) converter makes it possible to use triple-phase shift (TPS) modulation, originally intended for the classical dual active bridge (DAB) converter. TPS allows the MCB3 converter to achieve soft switching and conduction losses minimization for any load and voltage requirement. In this article, the mathematical analysis of the proposed converter operation is shown for the step-up operation, which is the worst-case design. The multiple operation possibilities that allow the use of the three TPS control variables are identified, classified, and used to find the operating points that minimize the power losses for any voltage and power range. Besides, the theoretical study demonstrates that MCB3 converter operation is equivalent to that in the classical DAB converter; thus, the DAB converter know-how can be employed in the proposed converter, but for nonisolated applications. MCB3 converter feasibility is validated by comparing the simulation-level results to the experimental measurements for a 460-W-scaled prototype. [ABSTRACT FROM AUTHOR]