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The increasingly extensive use of non-linear loads, mostly including static power converters, in large industry, commercial, and domestic applications, as well as the spread of renewable energy sources in distribution-generated units, make the use of the most efficient power quality improvement systems a current concern. The use of active power filters proved to be the most advanced solution with the best compensation performance for harmonics, reactive power, and load unbalance. Thus, issues related to improving the power quality through active power filters are very topical and addressed by many researchers. This paper presents a topical review on the shunt active power filters in three-phase, three-wire systems. The power circuit and configurations of shunt active filtering systems are considered, including the multilevel topologies and use of advanced power semiconductor devices with lower switching losses and higher switching frequencies. Several compensation strategies, reference current generation methods, current control techniques, and DC-voltage control are pointed out and discussed. The direct power control method is also discussed. New advanced control methods that have better performance than conventional ones and gained attention in the recent literature are highlighted. The current state of renewable energy sources integration with shunt active power filters is analyzed. Concerns regarding the optimum placement and sizing of the active power filters in a given power network to reduce the investment costs are also presented. Trends and future developments are discussed at the end of this paper. For a rigorous substantiation, more than 250 publications on this topic, most of them very recent, constitute the basis of bibliographic references and can assist readers who are interested to explore the subject in greater detail. [ABSTRACT FROM AUTHOR]

There are many possible LED lighting applications where separate regulation of the LED current (luminous flux) of individual LED strings would be desirable—specialized variable correlated color temperature lights for ambient lighting, decorative lighting, surgical lights, horticultural lights, etc. Separate regulation of the current or light flux of individual LED strings is associated with a known problem: the necessity of using a controllable LED driver for each string, which increases the total component count, overall system complexity and costs. One of the possible solutions—a current source mode single-inductor multiple-output LED driver—was discussed in previous different papers. However, the practical implementation of this solution was not discussed in detail. This article aims to correct this omission. [ABSTRACT FROM AUTHOR]

Modular multilevel converters with non-sinusoidal ac voltage output can reduce cost and volume in medium-voltage-connected electric vehicle battery charging applications. The use of full-bridge submodules in such converters enables single-stage ac/ac voltage conversion, allowing a medium-voltage grid to be directly connected to a medium-frequency isolation transformer. The application of a square wave voltage at the medium-frequency transformer's single-phase port enhances the converter's efficiency and power density in comparison to a sinusoidal voltage. This paper presents the analysis and modelling of a modular multilevel converter, comparing its operation with sinusoidal and square wave output voltages. A single control scheme for both output voltage waveforms is proposed for the three-phase and single-phase ac currents, circulating currents, and the energy stored in the submodule capacitors. The control strategy of the three-phase and single-phase port currents is verified through simulation and experiments using a scaled-down prototype, thereby validating its suitability for high-power bidirectional battery chargers. [ABSTRACT FROM AUTHOR]

Three LED drivers which can be used for illumination, but whose main task is the transmission of information (data) via the light of the LEDs, are explored in this paper. The converter circuits need no capacitors for the energy transformation and avoid an inrush current. The lack of necessity of electrolytic capacitors reduces cost and space. Dimming the illumination is also easy to achieve. The control concept of the converters and the generation of pulsing of the LEDs for transmitting the information (data) are explained. The converters can also be expanded to more stages to drive more LEDs with different types of information. All three converters are explained in detail; all presented circuits are built up and simulated with LTSpice. Several data transmission concepts are applied and demonstrated through simulations. [ABSTRACT FROM AUTHOR]

Power sharing among multiterminal high voltage direct current terminals (MT-HVDC) is mainly developed based on a priority or sequential manners, which uses to prevent the problem of overloading due to a predefined controller coefficient. Furthermore, fixed power sharing control also suffers from an inability to identify power availability at a rectification station. There is a need for a controller that ensures an efficient power sharing among the MT-HVDC terminals, prevents the possibility of overloading, and utilizes the available power sharing. A new adaptive wireless control for active power sharing among multiterminal (MT-HVDC) systems, including power availability and power management policy, is proposed in this paper. The proposed control strategy solves these issues and, this proposed controller strategy is a generic method that can be applied for unlimited number of converter stations. The rational of this proposed controller is to increase the system reliability by avoiding the necessity of fast communication links. The test system in this paper consists of four converter stations based on three phase-two AC voltage levels. The proposed control strategy for a multiterminal HVDC system is conducted in the power systems computer aided design/electromagnetic transient design and control (PSCAD/EMTDC) simulation environment. The simulation results significantly show the flexibility and usefulness of the proposed power sharing control provided by the new adaptive wireless method. [ABSTRACT FROM AUTHOR]

It is simple to implement conventional current control with a proportional integral (PI) controller. However, system stability and dynamic performance are not perfect, particularly when operating under unfavorable conditions. In this paper, an improved control method is proposed by introducing a compensation unit. The compensation unit can effectively compensate the system's phase around the crossover frequency, greatly enhancing the system's phase margin and stability. It is also capable of handling weak-grid conditions. In this paper, the concept of the proposed compensation unit is explained first. Then, the corresponding mathematical model for the current control loop is built, and system bode diagrams for the conventional and proposed methods are compared. Furthermore, the effect of the parameters for the compensation unit is investigated, and an optimization method is proposed to determine optimal parameters. In addition, to handle weak-grid conditions, the proposed scheme is expanded by including the compensation unit in the grid's feed-forward loop. Finally, an experimental platform is constructed, and the experimental results are presented to validate the proposed method. [ABSTRACT FROM AUTHOR]

As the inverter-based generation replaces the conventional synchronous generators, it may also need to fill in the missing ancillary service support. One of these ancillary services is dynamic reactive power provision and voltage control. This paper analyzes optimal strategy of reactive and active fault-current support of the inverter-based generation leading to fast voltage recovery of the system. For the purpose of the analysis, new ramping active current controller able to emulate different behavior of active current injection is proposed. By optimizing its parameters for different case studies of the system, the conclusions about optimal behavior of the inverter based generation with respect to system parameters and operating conditions are drawn. It is observed that the optimal combination of active and reactive fault-current is the most sensitive to the dynamic load component penetration levels in the system. With the increasing penetration levels, the significance of active fault-current injection increases. The results show that with higher penetration levels of dynamic load component in the heavy load areas, the ramping down of the inverter-based generation active fault-current results in slower voltage recovery of the system. Following this conclusion, a recommendation on update of current European grid codes is proposed. [ABSTRACT FROM AUTHOR]

This paper deals with the current control strategy of a permanent magnet linear generator (PMLG) for a direct‐drive wave energy converter (DDWEC). As the mover is in a linear reciprocating motion, the reference of the controller of the generator is dynamic fluctuations with the mover movement under maximum power point tracking (MPPT) conditions. Therefore, the dynamic requirements of the controller become higher. To increase dynamic control performance, an improved model predictive current control (IMPCC) strategy is proposed here. Through a three‐step cascaded optimization algorithm, the target voltage vector is optimized from the three dimensions of the sector of the voltage vector, the angle of the voltage vector and the length of the voltage vector. The target voltage vector is output to the three‐phase rectifier by using SVPWM to complete the entire control process. Simulation and experimental results show that the proposed control strategy effectively reduces the current ripple and the vibration of PMLG and improves the stability of DDWEC. [ABSTRACT FROM AUTHOR]

This paper presents the first approach to a current control problem for the direct matrix converter (DMC), which makes use of the deep reinforcement learning algorithm. The main objective of this paper is to solve the real-time capability issues of traditional control schemes (e.g., finite-set model predictive control) while maintaining feasible control performance. Firstly, a deep Q-network (DQN) algorithm is utilized to train an agent, which learns the optimal control policy through interaction with the DMC system without any plant-specific knowledge. Next, the trained agent is used to make computationally efficient online control decisions since the optimization process has been carried out in the training phase in advance. The novelty of this paper lies in presenting the first proof of concept by means of controlling the load phase currents of the DMC via the DQN algorithm to deal with the excessive computational burden. Finally, simulation and experimental results are given to demonstrate the effectiveness and feasibility of the proposed methodology for DMCs. [ABSTRACT FROM AUTHOR]

To improve the torque accuracy for open-end winding permanent magnet synchronous motor (OEW-PMSM) with common dc bus, it is necessary to eliminate the zero-sequence torque (ZST) caused by zero-sequence current (ZSC) and the third back electromotive force. But the third flux linkage mismatch can enlarge ZSC which causes torque ripple. To deal with the above problem, firstly, a q-axis current injection method combined with deadbeat predictive current control (DPCC) is adopted to inject an extra current into the reference q-axis current. The extra torque generated by this injected current can compensate for ZST. Secondly, to ensure the accuracy of the q-axis injected current, a parameter identification method based on recursive least square (RLS) algorithm with forgetting factor is presented to identify the third flux linkage accurately. The identification value can reduce ZSC and torque ripple under different working conditions. And the accurate q-axis injected current can be obtained to counteract ZST and output accurate torque. Finally, three methods are comparatively analyzed in this paper, namely the traditional DPCC method, the DPCC method with q-axis current injection and the proposed DPCC method based on RLS with forgetting factor. The simulation and experimental results verify the effectiveness of the proposed DPCC method. [ABSTRACT FROM AUTHOR]

This paper presents a simple pulse width modulation algorithm for control of an ultracapacitor based energy storage system used for source and load support applications. As opposed to dual loop control philosophy that is widely used for backup applications, this paper presents a simple single loop current control that is only useful for controlling the ultracapacitor based DC/DC converters used in source and load support applications. The proposed PWM blocking method necessitates the DC/DC converter to operate in five states and takes into consideration the essential operational limits associated with the ultracapacitors. The performance of the proposed algorithm is verified experimentally using a 24 V laboratory prototype setup. Further, the shortcomings of dual loop control when applied to source and load support applications are demonstrated. [ABSTRACT FROM AUTHOR]

Although Switched Reluctnace Motors have many advantages, vibration is known as their most severe drawback acting as an impediment limiting their widespread use in industrial and domestic applications. Through electromechanical relationships, it is shown that the first-order time derivative of applied phase voltage and second-order time derivative of radial force directly affect the amplitude of generated vibration, especially at the beginning of demagnetization instance. Therefore, a set of criteria is stated in this paper meeting which ensures having low vibration intensity. In this paper, three types of demagnetization voltages are proposed which comprehensively meet the stated criteria. These voltages share the same characteristics contributing to the vibration reduction in Switched Reluctance Motor. Two vital parameters of Synchronous Counter and Coefficient are included in the proposed demagnetization voltages which must be meticulously chosen in order to be effective. Noticeable contribution of the proposed methods to the vibration alleviation is validated through simulation and experimental tests conducted under different working conditions. [ABSTRACT FROM AUTHOR]

During the brushless DC (BLDC) motor working process, the system encounters inevitable uncertainties. These ambiguities stem from potential fluctuations, random occurrences, measurement inaccuracies, varying operational conditions, environmental shifts such as temperature alterations, among other factors. Uncertainties, an inherent aspect of any real control system, can be broadly classified into two categories: sensor signal uncertainties and discrepancies between the mathematical and actual models due to parameter perturbations. To mitigate the impact of sensor noise and parameter perturbations on the BLDC motor, a robust control strategy utilizing infinite norm mixed sensitivity based on PI control strategy (PI-H∞-MIX) is proposed in this paper. Firstly, the closed-loop control structure and transfer function model of the BLDC motor control system current loop are analyzed based on the current loop circuit topology, and then, the model parameters perturbation is analyzed, and the multiplicative uncertainty bound is given. In addition, the appropriate weighting function is selected to ensure the robustness of the system. In this case, the controller design problem is transformed into the H∞ standard control problem, and then, the system augmentation matrix is established, and the controller is solved by Matlab/Simulink. Finally, the performances of the traditional PI control strategy and the PI-H∞-MIX are compared and analyzed. The results show that (1) the proposed PI-H∞-MIX strategy can improve the control system robustness under the parameter perturbation condition effectively, and (2) the proposed PI-H∞-MIX strategy can suppress the noise signal of the sensor. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of the dynamic properties of a photovoltaic generator (PVG) on the stability of a grid-connected current-source inverter (CSI)-based photovoltaic system and presents a simple yet effective active compensator to ensure system stability. A detailed equivalent model of the PVG that considers the dynamic resistance, diffusion capacitance, series inductance, and dc cable resistance and inductance is used, and the effects of these parameters are assessed. It has been found that when the PVG operates in the constant-current region (CCR), the phase margin becomes negative in the control-to-input dynamics, which alters the stability of the dc-link current control. The change in the system dynamics when the operating point of the PVG shifts from the constant-voltage region (CVR) to CCR is verified through a detailed small-signal state-space model of the complete system. Furthermore, an active compensator is proposed to ensure stable dc-link current control operation at all operating points of the PVG. The influence of different control parameters on the integrated system dynamics is examined to determine the range of the control parameters required for stable operation. The performance of the proposed system under utility-grid fault, grid voltage parameter variation, weak grid, and changes in insolation level is also evaluated. Detailed nonlinear time-domain simulation results, using a typical utility-scale CSI-based PV system, validate the analytical results and the effectiveness of the proposed active stabilization under different operating conditions. [ABSTRACT FROM AUTHOR]

The paper deals with the optimal control of the electrical drive systems with linear dependent on speed load torque. The minimum of the Joule losses in the transient period is imposed. Different types of motors are considered. The approach refers to the current control. Two types of problems depending on the final conditions are considered. The optimization is done in the sense of minimization of the losses in the transient period. Taking into account the great values of the current in the transient period, the dominant losses are the copper ones and consequently, only these losses are considered. One considers that the flux is constant and therefore, only one control current (torque producing current component in the case of the vector control) is used. The basic results for the optimal control of an electrical drive system in the above mentioned conditions are presented [ABSTRACT FROM AUTHOR]

In this paper, consideration from the viewpoint of the dq-axis current vector locus is reported on the clues for improving the output of wound-field motor utilizing space harmonic for field excitation. It is experimentally verified by visualizing the vector locus on the dq coordinates. First, voltage equation will be explained, and then the offline parameter estimation will be discussed. Then, visualization of the voltage-limit ellipse and vector locus will reveal clues for performance improvement. [ABSTRACT FROM AUTHOR]

The paper addresses an improved inner current reference calculation to be employed in the control of modular multilevel converters operating during either balanced or unbalanced conditions. The suggested reference calculation is derived based on the AC and DC additive and differential voltage components applied to the upper and lower arms of the converter. In addition, the impacts caused not only by the AC network’s impedances but also by the MMC’s arm impedances are also considered during the derivation of the AC additive current reference expressions. Another issue discussed in this article regards that singular voltage conditions, where the positive-sequence component is equal to the negative one, may occur not only in the AC network but also internally (within the converter’s applied voltages). Several different inner current reference calculation methods are compared and their applicability during the former fault conditions is analyzed. The paper presents a detailed formulation of the inner current reference calculation and applies it to different unbalanced AC grid faults where it is shown that the presented approach can be potentially used to maintain the internal energy of the converter balanced during normal and fault conditions. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Engineering Technology is the property of Editorial Department of Electric Power Engineering Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Single-loop current sensorless control allows for abolishing of the instantaneous current measurement in the control system using only a single control loop with voltage feedback to stabilise the DC-bus voltage. This approach eliminates current sensors in the control circuit, benefiting from saving space on the printed circuit board and minimising power dissipation in the current measurement circuitry. This paper focuses on the single-loop current sensorless control applied to bidirectional three-phase four-wire three-level NPC MLC by simulation analysis and demonstrates the performance of the proposed current control algorithm in the rectifier and inverter modes and the step response with power direction change and grid-voltage change. In capacitor voltage balancing, an additional controller is applied, which is capable of compensating for the voltage asymmetry caused by adding a 2.5 kOhm resistor in parallel to one of the DC-bus capacitors. Our results demonstrate good performance of the proposed control method both in the inverter and rectifier modes, showing stable current shape in the low power and full power modes with acceptable harmonics content, meeting the requirements of the IEC 61000-3-2 standard for Class A devices. The analysis showed that the proposed control approach is suitable for industrial application. [ABSTRACT FROM AUTHOR]

Copyright of e & i Elektrotechnik und Informationstechnik is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, it is identified that unstable weak grid connection of voltage source inverters (VSIs) is dominantly caused by the current control. In particular, it is found the proportional gain $ k_p$ of conventional PI controller cannot balance the grid voltage impact and damping capability especially when a very weak grid with short circuit ratio (SCR) $ < $ 1.3 is connected. This issue is solved in this paper by simply restructuring the PI controller as an IP controller for current control. This IP controller will not change the tuning method of current control and make this VSI indeed connect to a very weak grid with rated power injection. [ABSTRACT FROM AUTHOR]

This paper proposes an improved SOC balancing strategy for the modular energy storage system (ESS) based on low bandwidth communication (LBC) technology, aiming at solving the drawbacks of the conventional balancing strategy based on droop control. The proposed control scheme can improve the SOC balancing efficiency and remove the current deviation by using the SOC slope-adjusting and current-shifting approaches simultaneously. The average value of SOC can be derived through the LBC line, and the droop coefficient based on SOC can be controlled in the local control layer. Thus, the SOC of each sub-module can converge to the average SOC value in system dynamic process, and the balancing speed under the condition of low SOC difference between sub-modules can be improved. Furthermore, the current regulation performance in steady and transient states can be enhanced by using the proposed method. At last the effectiveness of the proposed strategy is verified by experimental results. [ABSTRACT FROM AUTHOR]

An improved two-stage model predictive current control (MPCC) for three-phase three-level converters in the paper, which can simultaneously achieve common-mode voltage (CMV) reduction, effective dc-link capacitor voltage control, and decreased computational burden, is proposed. Compared to the other current control strategies, it has the capability of handling multiple control objectives and possesses a simple structure. Furthermore, it greatly reduces the CMV since the peak CMVs of all the candidate voltage vectors are constrained to be less than one sixth of the dc-link voltage. In addition, an optimal two-stage voltage vector selection mechanism is employed in the proposed method. It helps to significantly reduce the computational complexity. Simulation and experimental results are provided to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In the search for efficient non-permanent magnet variable-speed wind generator solutions, this paper proposes a maximum power point tracking (MPPT) current-control method for a wound rotor synchronous wind generator. The focus is on direct-drive, medium-speed wind generators. In the proposed method, the currents of the wound rotor synchronous generator (WRSG) are optimally adjusted according to the generator speed to ensure maximum power generation from the wind turbine without needing information on wind speed. The design, modeling, and simulation of the MPPT current controllers are done in Matlab/Simulink with the WRSG in the synchronous reference frame. The controller is put to the test using different wind speed profiles between cut-in and rated speeds. The simulation results indicate that the proposed current control method is simple, effective, and robust, suggesting its practical implementation. To validate the simulation results, experimental work on a 4.2 kW WRSG prototype system is presented to demonstrate the stability and robustness of the MPPT current control method in operating the turbine at or near the maximum power point. [ABSTRACT FROM AUTHOR]

This paper deals with the implementation and performance analysis of discrete-time sliding mode (DTSM) current control applied to a seven-level cascade H-bridge converter to track three-phase reference currents for a reactive load. The converter output voltages are synthesized using a modulation scheme based on phase-shifted carrier modulation. Simulation and experimental tests have been added to demonstrate the performance of the proposed controller. At the same time, the effectiveness of the DTSM is verified under transient and steady-state conditions, respectively, by measuring the total harmonic distortion and the mean square error. [ABSTRACT FROM AUTHOR]

In this paper, constant-frequency peak-current control is analyzed focusing on the operation above the subharmonic threshold limit. The analysis is performed by mixing analytical and numerical approaches. Two levels of normalization are introduced: on the converter level and on the switching cell level, resulting in unified analysis regardless of the converter type. A function that maps the inductor current value at the beginning of a switching period to its value at the end of the switching period is derived. The analysis is performed by iterating this mapping, leading to information of the inductor current periodicity and the switching cell averaged output current. It is shown that before reaching chaotic state a converter passes through a sequence of bifurcations involving discontinuous conduction modes characterized by higher order periodicity. Boundaries of the region where the higher order discontinuous conduction modes occur are derived. Obtained dependence of the switching cell output current average on the operating parameters is used to derive a small signal model. The model parameters expose huge variations in the areas of deep subharmonic operation. The results are experimentally verified. [ABSTRACT FROM AUTHOR]

This paper analytically derives oscillatory stability criteria of a grid-connected PMSG based on the block diagram model. The derivation reveals the general mechanism about how the condition of grid connection, loading and converter control parameters setting of the PMSG jointly affect the oscillatory stability of the PMSG. It logically explains why the condition of weak grid connection and heavy loading may cause destabilization. In addition, computationally simple and modal-computation free indices are proposed to identify the instability risk caused by the “improper parameters setting” of the control system of grid side converter (GSC) and the phase locked loop (PLL). Following analytical conclusions are obtained: (1) When the PLL is of high-frequency bandwidth, high-frequency oscillations are mainly caused by the PLL or the open-loop modal resonance between the PLL and current control of the GSC. In addition, the low-frequency oscillations may also occur as caused by the power control of the GSC. (2) When the PLL is of low-frequency bandwidth, low-frequency oscillations may be caused jointly by the power control of GSC and the PLL. An example grid-connected wind farm with eighteen similar PMSGs is presented to demonstrate and evaluate the stability criteria derived and analytical conclusions obtained in the paper. [ABSTRACT FROM AUTHOR]

In this paper, a novel hysteresis-based current control approach is presented. The basis of the developed control approach is the theory of switched systems, in particular, the system class of switched systems with multiple equilibria. The proposed approach guarantees the convergence of the state trajectory into a region around a reference trajectory by selective switching between the individual subsystems. Here, the reference trajectory is allowed to be time varying, but lies within the state space spanned by the subsystem equilibria. Since already published approaches only show convergence to a common equilibrium of all subsystems, the extension to the mentioned state space is a significant novelty. Moreover, the approach is not limited to the number of state variables, nor to the number of subsystems. Thus, the applicability to a large number of systems is given. In the course of the paper, the theoretical basics of the approach are first explained by referring to a trivial example system. Then, it is shown how the theory can be applied to a practical application of a voltage source converter that is connected to a permanent-magnet synchronous motor. After deriving the limits of the presented control strategy, a simulation study confirms the applicability on the converter system. The paper closes with a detailed discussion about the given results. [ABSTRACT FROM AUTHOR]

The paper presents a design of repetitive control (RC) in the current control system of a three-phase grid-tied converter. The goal of the control system is to provide sinusoidal input filter currents under the conditions of distorted and asymmetrical grid voltage. A novel design of the RC is presented, in which the repetitive part is not excited by sharp and non-periodic changes of the reference signal, but it enables high-quality performance under periodic disturbance conditions. In the proposed system. RC cooperates with a discrete state feedback controller. An innovative approach to tuning is proposed in which parameters of the repetitive, as well as the state feedback controller, are selected as a result of the optimization process with the use of a particle swarm algorithm. The proposed control system is verified experimentally on a laboratory test bench. The achieved results confirm the high-quality system performance. [ABSTRACT FROM AUTHOR]

This paper develops an inner stator current controller based on an enhanced reaching-law-based discrete-time terminal sliding mode. The problem of tracking stator currents with high accuracy while ensuring the robustness of a six-phase induction motor in the presence of uncertain electrical parameters and unmeasurable states is tackled. The unknown dynamics are approximated by using a time delay estimation method. Then, an enhanced power-reaching law is used to make each stage of the convergence faster. A stability analysis and the system controller's finite-time convergence are demonstrated in detail. Practical work was conducted on an asymmetrical six-phase induction machine to illustrate the developed discrete approach's robustness and effectiveness. [ABSTRACT FROM AUTHOR]

Due to the full-wave AC–DC power conversion, second-order frequency oscillations of current and voltage are created in single-phase PV-grid-connected inverters. These oscillations propagate toward the input and adversely affect the PV power utilization ratio. Large power decoupling capacitors are the preliminary solution for coping with voltage ripples across PVs, and they decrease the lifetime of the overall system. This paper proposes the average current mode control (ACMC) of the input inductor in a DC–DC boost converter in a double-stage PV power conversion system. Through extensive explanations of the modeling and control of a DC–DC boost converter, it is shown that the ACMC reduces the propagation of the second-order frequency components (SOFCs) toward the input PV array. Two controllers—a proportional–integral controller and an integral single-lead controller—are considered to adjust the average value of the PV output current in a single-loop control structure. This control approach is simple to implement and exhibits high impedance to current oscillatory components, which, in turn, reduces the size of the required capacitance. [ABSTRACT FROM AUTHOR]

In recent times, multilevel inverters (MLIs) are gaining popularity for grid integration of distributed power generation sources. In this paper, a proportional‐resonant (PR) controller based on current control logic is proposed for a single‐phase eleven‐level inverter topology, enabling the integration of distributed power generation sources into the grid. The presented topology utilizes eight two‐quadrant switches and three dc sources to produce an eleven‐level output voltage. The level‐shifted pulse width modulation (LS‐PWM) scheme is used for providing switching signals to the inverter under grid‐connected operation. Simulation and real‐time results are presented for the eleven‐level inverter to validate the presented current control logic under the grid‐connected mode of operation. The hardware‐in‐loop emulator (Typhoon HIL‐402) is used for taking real‐time results of the presented grid‐connected topology. The total harmonic distortion (THD) of the eleven‐level inverter voltage and grid current is 12.10% and 0.46%, respectively. The efficiency of the inverter while supplying 2 kW active power to the grid is 98.4%. [ABSTRACT FROM AUTHOR]

A soft starter is commonly utilized in various industrial induction motor systems to reduce the inrush current during motor startup. The conventional voltage ramp-up method, used in the typical soft starter, gradually increases the voltage over the startup period. However, this method can result in a significant voltage increase as the induction motor approaches its rated speed, resulting in a rapid torque increase compared to the beginning part of the startup phase. This sudden torque increase can potentially cause physical damage to the induction motor system due to a transient current overshoot, which in turn can result in resonance. Additionally, the changes in the parameters of the induction motors can lead to the variations in torque during startup, especially because of the air gap permeance. Therefore, a firing angle control method for the soft starter that maintains a constant torque, facilitating a gradual increase in speed, is desirable. This paper proposes a novel firing angle control method, to achieve a constant torque and a gradual speed increase, using only current feedback. This paper is the first time that a change in air gap permeance is considered and compensated for in controlling the firing angle of the soft starter. The air gap permeance variation is modeled as an effective inertia in the transient response of the induction motor. Experimental results demonstrate that the proposed method effectively reduces rapid torque increases and speed variations compared to the conventional voltage ramp-up method, through its application to a 30kW industrial induction motor system.

Due to the relatively low operational reliability of the MMC valve, it is necessary to establish corresponding test methods to examine the tolerance of the valve to electrical and thermal stresses under engineering requirements through operational tests, to verify its operational reliability. To meet the operational testing requirements for higher voltage and larger current converter valves, an appropriate test topology is required. The paper first analyzes the voltage and current stress characteristics of capacitor components and MMC converter valves in ±800 kV/8 GW Flexible DC transmission system, providing a theoretical basis for the stress of operational testing valve, requiring that to be equivalent to actual operating conditions. Addressing the operational testing demands for high voltage and large current converter valves in the ±800 kV/8 GW flexible DC transmission MMC, a test topology is proposed. This topology can meet the operating conditions of higher voltage and larger current and simultaneously conduct tests on valve segments and modules, significantly improving operational testing efficiency and reducing testing costs. Additionally, a control method applicable to this test topology is proposed, enabling flexible adjustment of DC and AC in the test circuit, thereby enhancing the equivalency of operational tests. In this paper, the proposed topology and control method have enhanced testing efficiency, reduced testing costs, improved testing equivalence, and enhanced the precision of current and capacitor voltage control. Finally, simulations and experiments are constructed to validate the feasibility and effectiveness of the proposed operational test topology and its control method through simulations and experiments.

In the grid-connected systems, LCL filters are widely used for eliminating the generated switching current ripples due to better attenuation in comparison with L or LC filter. However, it is known that stability of digital controlled LCL filter can present a challenge due to induced delay. This paper presents conditions of system stability in dependence of filter characteristics such as resonant frequency, inductors and capacitor parameter variations. Stability analysis and system performance are observed and compared. Derived results are tested and confirmed on Hardware-in-the-loop HIL402 device. Obtained results are discussed and suggestions are provided in terms of the practical implementation of the control system. [ABSTRACT FROM AUTHOR]

The digital implementation of all the control loops of a versatile buck-boost (VBB) dc–dc converter used in a stand-alone photovoltaic application is proposed in this paper to improve existing digital-analog sliding-mode-based implementations. All three control loops: maximum power point tracking (MPPT), fast input voltage regulation, and inner high-bandwidth current control, have been programmed in the same digital signal controller (DSC). A Model Predictive Control (MPC) based algorithm has satisfactorily solved the challenge of implementing the nominal 100 kHz switching frequency current loop. The MPC cost function is distributed throughout the algorithm to achieve three specific goals: the tracking of the reference current (G1), a quasi-constant steady-state switching frequency (G2), and the assurance that the duration of an interval is larger than the time required to calculate it (G3). The third goal requires the current control to toggle between peak- and valley-modes depending on the operating point. The correct fulfillment of these control objectives on the proposed MPC-based algorithm has been validated through simulations and experimental tests performed on a purpose built-prototype. [ABSTRACT FROM AUTHOR]

In this paper, a fault-tolerant control of a symmetrical six-phase induction generator based on a variable structure strategy is experimentally tested and compared with a classical proportional-integral controller. For this, we use a linear feedback sliding mode controller with switched feedback gains in such a way to control the inner current loops of this machine. One main drawback of the classical three-phase induction generator is that it is no longer possible to generate electrical power if only one phase is lost on the stator side. To overcome this issue, we will use a squirrel cage six-phase induction machine that can still operate when at least three phases remain on the stator side. This article proposes to use a variable structure control in order to cope with unbalanced currents and also maintain the generation of power when a loss of the stator's phases occurs. The proposed controller shows its robustness and good regulation performance in healthy and faulty modes. The simulation and experimental tests were carried out with a 24 kW induction machine that represents 1/100 of the electrical power of a real wind turbine. [ABSTRACT FROM AUTHOR]

Controlling voltage, frequency, and current in an islanded microgrid is a challenging problem because the distributed generation sources, stochastic and intermittent in nature, are not connected to the main electricity network to provide stable and clean energy. Therefore, the design of a robust controller to control the output parameters of the islanded microgrid and suppress load variations and disturbances is essential. In this paper, a hysteresis controller is proposed and designed to control the output voltage of an islanded AC microgrid and an improved sliding mode controller (SMC) based on adaptive control principle is designed to control the current of the microgrid. The current controller consists of two parts: An adaptation part, which aims to eliminate disturbances and system uncertainties, and a second part, which aims to deal with the tracking problem of the system under parameter-varying topologies. The adaptation strategy has the advantage of solving the gain tuning problem and chattering reduction. It also requires limited information about disturbance and uncertainties of the system. To validate the proposed control methodology and show its effectiveness, a case study of a simulated islanded microgrid is presented. The results show that the proposed controllers can effectively control the current and voltage underload changes and increase the stability and resilience of the microgrid. The results also reveal that the performance of the proposed controller in terms of total harmonic distortion (THD) and dynamic response overcome the performance of conventional controller by a 4× reduction in THD and 40–200× reduction in settling time. [ABSTRACT FROM AUTHOR]

The power – voltage (P-V) characteristics of photovoltaic (PV) systems exhibit multiple power peaks under partially shaded conditions. Several global maximum power point tracking (GMPPT) algorithms in the literature recognize the irradiance change, only after the convergence of operating point to global peak, or use additional hardware to call GMPPT subroutine at definite time intervals to detect any insolation change, and thus track the global peak. However, during fast changing partial shading conditions, these methods are less effective, as they do not detect any irradiance change during the tracking phase of any shading pattern. This paper proposes a novel modified current control approach that uses current as a parameter to detect the insolation change during the tracking phase and track the global peak under fast changing partial shading conditions without any additional hardware. The proposed technique improves the tracking efficiency by as much as 39%, thus proving to be effective under fast-changing partial shading conditions. The superior tracking performance of the proposed algorithm over the existing techniques in terms of its tracking efficiency, dynamic tracking capability, tracking speed, and convergence to the global peak is demonstrated with extensive simulations using MATLAB/Simulink and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents the analysis, design, and simulation of a power system composed of a grid-tied single-phase five-level inverter with an LCL filter. First, the analysis of the proposed system has been carried out in the decoupled Direct-Quadrature frame, where the Phase-Lock-Loop technique has been used for synchronizing the LCL-filter-connected-grid with the five-level inverter. Next, the design of the LCL filter has been discussed. In this paper, we focused on the active power control based on grid current adjustment using a proportional-integral regulator and a high-frequency modulation technique for the switching of a five-level inverter, where the Sinusoidal-Pulse-Width-Modulation technique is selected. All circuit design and control schemes are discussed step by step to provide the effectiveness of the system analysis. The theoretical analysis is verified through simulation results in MATLAB/Simulink environments. An important finding when using the five-level inverter in a grid-connect system is improving the system output voltage; the total standing voltage and the total harmonic distortion are decreased compared to a conventional H-bridge inverter. The results indicate that the total harmonic distortion of grid-current is less than 0.2%, which is according to the international standards. [ABSTRACT FROM AUTHOR]

The present paper aims to introduce an effective control system which enhances the dynamics of a doubly fed induction generator (DFIG) operating at fixed and variable speeds. To visualize the effectiveness of the formulated control algorithm, the performance of the DFIG is evaluated using other control techniques as well. Each control algorithm is primarily described by showing its operation principles and how it is adapted to manage the DFIG's operation. The main used control strategies are stator voltage-oriented control (SVOC), model predictive current control (MPCC), model predictive direct torque control (MPDTC), and the formulated predictive voltage control (PVC) algorithm. A detailed comparison is performed between the controllers' performances, through which the advantages and shortcomings of each method are outlined, and finally, the most effective technique is identified amongst them. The obtained results reveal that the proposed PVC approach possesses multiple advantages such as a faster dynamic response and simpler control structure when compared with SVOC and a faster dynamic response, reduced ripples, and reduced computational burdens when compared with the MPCC and MPDTC approaches. In addition, the robustness of the proposed PVC scheme is confirmed by performing extensive performance evaluation tests considering the parameters' variation. [ABSTRACT FROM AUTHOR]

Dead-beat predictive current control (DPCC) has great potential in the field of motor control due to its fast response. However, it suffers from low robustness due to its sensitivity to parameter variations. In this paper, a DPCC of permanent magnet synchronous motors (PMSM) combined with parameter adaptation is proposed to enhance the robustness of the dead-beat control under parameter misalignment. Firstly, the basic principles of dead-beat current control are introduced. Then, the influence of parameter errors on the control loop of dead-beat current control under imprecise motor parameters is analyzed. To address the issue of imprecise motor parameters, a predictive current control method combined with a parameter-adaptive algorithm is proposed. The motor parameters are identified online, and the parameters of the predictive current controller are modified in real-time to achieve parameter correction. Finally, comparative simulations and performance evaluations are conducted to validate the effectiveness of the proposed method. The results show that the robustness of the current control system is significantly improved, resulting in better control performance when applying the method proposed in this paper.

Directional, phase-selection, and distance elements of a relay are prone to misoperation in the presence of inverter-based resources (IBRs). To address these problems, modifications of relay elements as well as new control schemes for IBRs have been proposed in the literature. These methods focus mainly on addressing the misoperation of only one of the above relay elements. The available solutions that are based on a new control system focus only on the negative-sequence current loop. Thus, they work only for unbalanced faults. This paper proposes a comprehensive dual current control scheme for IBRs during all types of faults such that all of these relay elements operate correctly. The proposed method controls the IBR to operate as a voltage source behind a virtual impedance in the positive-sequence circuit, and a single impedance in the negative-sequence circuit, thereby emulating the phase angles of a synchronous generator's (SG's) fault current. The proposed method also maximizes the active, and reactive current generation of the IBR during faults, and emulates the incremental sequence current magnitudes of an SG. The proposed method does not require altering the relay elements. Moreover, correct operation of the relay elements is achieved regardless of the fault type, resistance, and location. The effectiveness of the proposed method is verified through not only simulation studies, but also hardware-in-the-loop testing of commercial relays. [ABSTRACT FROM AUTHOR]

A major reason for compromised audio quality with a coil-type loudspeaker is its complex impedance profile, which disturbs the intended algebraic linearity or linear phase behavior between the amplifier input and speaker driving force. Though switch-mode amplifiers are increasingly preferred in such audio systems owing to their superior energy efficiency, their inherent non-linearity and finite internal impedance further degrade audio reproduction. This paper investigates the effect of stated impedance on the loudspeaker driving current, hence on the loudspeaker driving force, and proposes a Hybrid controller-amplifier to enhance the proportionality between the audio reference and driving force without compromising on loudspeaker damping. The Hybrid amplifier combines a sliding mode controlled amplifier (SMCA) and a linear controller, designed after exhaustive modeling of the input–output behavior of the SMCA and best-fit approximation of the loudspeaker impedance. An 8 W, 500 Hz to 20 kHz prototype of the proposed amplifier is fabricated on the basis of the presented design. Time and frequency-domain results obtained with the experimental hardware are presented to validate the performance improvement. • Enhancing linearity between the audio input and the loudspeaker driving current • Accurate modelling of integrated amplifier-loudspeaker system • Proposing a Hybrid control strategy to improve the audio quality • Development of 8 W laboratory prototype and experimental validation [ABSTRACT FROM AUTHOR]

It is simple to implement conventional current control with a proportional integral (PI) controller. However, system stability and dynamic performance are not perfect, particularly when operating under unfavorable conditions. In this paper, an improved control method is proposed by introducing a compensation unit. The compensation unit can effectively compensate the system’s phase around the crossover frequency, greatly enhancing the system’s phase margin and stability. It is also capable of handling weak-grid conditions. In this paper, the concept of the proposed compensation unit is explained first. Then, the corresponding mathematical model for the current control loop is built, and system bode diagrams for the conventional and proposed methods are compared. Furthermore, the effect of the parameters for the compensation unit is investigated, and an optimization method is proposed to determine optimal parameters. In addition, to handle weak-grid conditions, the proposed scheme is expanded by including the compensation unit in the grid’s feed-forward loop. Finally, an experimental platform is constructed, and the experimental results are presented to validate the proposed method.

The electrodynamic tether (EDT) system is used as one of the end-of-life disposal technologies to deorbit defunct satellites with the benefit of Earth's magnetic field and plasma environment. However, due to the flexibility of the conductive tether, the orbit-attitude coupling effects as well as the influence of Multiphysics fields, this system suffers from time-consuming computations using complicated mathematical model in long-term simulations. Therefore, this paper proposes a high-fidelity high-efficiency dynamics model for the EDT system, in which the tether libration and transverse motions are described by the articulated model, and the system equations are formulated using recursive dynamics algorithm. Computational cost of the recursive method is compared with a nonrecursive method, and the result shows that with the number of tether elements larger than 15, the recursive method would show better computational efficiency. Since the conductive tether tends to be kilometers long in application, this new model would definitely contribute to the numerical efficiency. In addition, simulations are conducted with 2 and 16 tether elements solutions. By comparing the obtained results, it is found that the two cases show large differences over time. For a long tether, it is reasonable to use a larger number of elements in the dynamics analysis. Besides, in order to suppress the libration motion and avoid unstable states in the EDT system, a current control strategy is proposed and verified by a deorbit simulation in low Earth orbit. • A high-fidelity high-efficiency model is proposed for the electrodynamic tether system. • The recursive method shows better efficiency with the number of elements larger than 15. • Different tether elements would result in large differences in simulation. • A current control strategy is proposed to stabilize the libration motion. [ABSTRACT FROM AUTHOR]

This article proposes a novel flux weakening scheme for five-phase PMSM with active harmonic currents injection. The conventional flux weakening control schemes applied in the five-phase PMSM do not consider the voltage limit drop in the fundamental subspace due to the harmonic current controller. Thus, the derivation between the reference current trajectory and actual current trajectory would cause the current distortion when applying deadbeat current controller (DBCC). This article analyses the precise voltage limit circles considering the voltage drop caused by the resistance and harmonic currents control at first. Then, a feed-forward flux weakening control algorithm is designed to optimize the current trajectory online. The gradient descent method is used to ensure the converge speed and stability of the optimized current trajectory. Thirdly, the peak value of phase currents would be clipped by the harmonic currents to prevent the inverter current limit, where a new non-linear harmonic current controller is designed to precisely control the harmonic currents. Finally, the DBCC and modified SVPWM technology are utilized to generate the duty cycle. The proposed improved flux weakening control strategy is successfully implemented in an interior five-phase PMSM, and the performance demonstrate the effectiveness of this strategy. [ABSTRACT FROM AUTHOR]

The penetration of distributed energy resources is drastically increasing in the distribution systems. Inverters are employed to efficiently process the harvested energy of these energy resources. These inverters are commonly operated in parallel with some loads to form a microgrid. The control of these inverters has become a vital component to operate their microgrid. The microgrid formed by the inverters and loads can be operated into two main modes, which are the grid-connected mode and the islanded mode. Any control (operational) scheme for the microgrid should be able to operate these inverters along with their microgrid in these two modes, and it should enable the whole microgrid to have a seamless transition from one mode to another. This paper articulates different control schemes that are employed to operate parallel/several inverters within microgrids or connected to distribution systems. There are serval classifications for these control schemes used for inverters in microgrids. The main focus of this review paper is dedicated to the centralized control (with/without inter-communications) schemes that are developed to operate several parallel inverters within the microgrid to control current, voltage, and power at different operating conditions.