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Abstract An equal‐weighted cost function‐based weighting factor tuning method for model predictive control (MPC) in power converters is presented here. In conventional MPC methods developed for power converters, the use of weighting factors is a necessity to determine the importance of sub‐terms in multi‐objective cost functions. The proposed method is based on equalizing the importance of cost terms by using normalized values rather than the actual values. As a consequence of normalized values, all sub‐terms are transformed into a similar range independent from their actual values. Hence, the weights of cost terms are equalized, leading to the elimination of weighting factor tuning necessity. The proposed equal‐weighted cost function not only offers simplicity in the MPC design but also guarantees the desired controller performance with the dynamically weighted sub‐terms. The proposed control method is validated on a grid‐connected single‐phase three‐level T‐type inverter. Experimental results are carried out to demonstrate the effectiveness of the proposed method under steady‐state and dynamic conditions. Moreover, the comparative results with the conventional MPC are presented. The results reveal that the proposed approach exhibits excellent performance against the variations in the operating point of the inverter.

Abstract In applications where DC current is superimposed, such as inductors for non‐isolated DC‐DC converters, powder core can be considered as an attractive solution owing to its superior features such as: high saturation flux density, high Curie temperature, and soft‐saturation property. However, in powder cores, a drop of inductance appears prominently due to DC superimposition characteristics. This feature is not a desirable characteristic because it leads to an increase in the inductor ripple current under heavy load, which complicates the thermal design of power semiconductors and capacitors. This paper verifies the improvement of DC superimposition characteristics of powder cores by applying coupled inductors. First, the effect of coupled inductors on the improvement of DC superimposition characteristics is experimentally verified. Second, a measurement method for the DC superimposition characteristics of coupled inductor is proposed. Then, a magnetic circuit model is built using the measurement results. Finally, a coupled analysis of magnetic and electric circuits is performed, and it is confirmed that lower magnetic field operation can be realized by coupled inductors even under heavy load conditions. It has been proven that coupled inductors are effective in improving the DC superposition characteristics of the powder cores.

Abstract In droop‐controlled DC microgrids, parasitic resistances of long conductive lines introduce additional terms for the power calculation and impact the power sharing accuracy. This paper proposed a comprehensive local control design for enhancing power sharing accuracy and restoring DC bus voltage while increasing stability performance in DC microgrids. A passive controller is used in the primary control to ensure the sufficient bandwidth of controller in case of frequent operation modes alteration and voltage deviation in the DC microgrid. A concept of Virtual Negative Line Resistance (VNLR) is used in the secondary control layer to compensate the real line resistance such that line resistance no longer degrades power sharing accuracy. The common DC bus voltage needs to be monitored in the proposed secondary controller. Simultaneously, the common DC bus voltage can be restored as the designed value. The monitored DC bus voltage signal is filtered by a designed low‐pass filter such that mid‐high frequency dynamics can be decoupled between secondary controls and primary controls. Then the entire local control scheme relaxes three Degrees of Freedom (DoF) which can be used for upper layer controls. Finally, the proposed control method has been experimentally validated in a 50 V DC microgrid laboratory testing system.

Abstract This study suggests a dynamic current cut‐off frequency‐based pole‐zero cancellation speed controller for permanent magnet synchronous motors (PMSMs). The proposed self‐tuning algorithm automatically increases the current cut‐off frequency during only the transient periods and restores it as approaching the steady‐state operation. The outer loop control injects the active damping effect, resulting in a closed‐loop order reduction by pole‐zero cancellation from the particularly structured feedback gain. These two benefits contribute to the following advantages: (a) lowering the steady‐state current cut‐off frequency to improve the relative stability margin and (b) securing the capability of assigning the desired cut‐off frequency to both the inner and outer loops in the first‐order low‐pass filter form. A 500‐W PMSM experimental prototype platform confirms the effectiveness of the proposed controller.

Abstract This paper focuses on design of a control system for full bridge DC‐DC converter based on Lyapunov stability theorem which guarantees system stability. To achieve this goal, a full bridge DC‐DC converter is used as a Li‐ion battery charger and sinusoidal ripple current (SRC) is implemented as the charging algorithm. In initial step, state space equation of the system including DC‐DC converter and battery are obtained. After that, switching function is extracted by applying Lyapunov stability theorem to state space equation. Also in order to achieve unity power factor and allowable current Total Harmonic Distortion (THD) range based on standards, an Active Front End (AFE) PWM Rectifier is used. To evaluate the effectiveness of the proposed controller scheme, a laboratory prototype is implemented. Experimental result shows appropriate performance of proposed controller in tracking of reference values in comparison with fixed PI controller. In addition, results of AFE rectifier performance is evaluated by showing the unity power factor and low THD value.

Abstract Non‐isolated inverters have the disadvantage of large leakage current, which will damage the equipment and personal safety. In order to solve this problem, this paper proposes two H10 three‐phase inverter topologies named forward‐clamped and reverse‐clamped H10 inverters. Each of the topologies is composed of two DC bus switches, a clamping circuit and a traditional three‐phase inverter, but the clamping method of these two topologies is different. A general control strategy combining carrier modulation and logic operation for these two topologies are proposed. The control strategy allows the common‐mode voltage of these two topologies to vary between one third and two thirds of the DC bus voltage, but the frequency of the common‐mode voltage of the reverse‐clamped inverter is three times that of the forward‐clamped inverter. The loop impedance of the reverse‐clamped inverter increases significantly at high frequency, so the leakage current suppression capability is better. Simulation and experiment platforms of the inverter systems are built. The obtained results verify the correctness of the theoretical analysis.

Abstract When traditional finite‐set predictive power control is applied to Vienna rectifier, the input current will produce a large number of third harmonics under unbalanced power network, which will seriously affect the normal operation of Vienna rectifier. This paper proposes a compound control strategy for three‐phase Vienna rectifier based on grid imbalance. And the new finite control set‐model predictive direct power control (N‐FCS‐MPDPC) is used in the inner current loop. By introducing a redefined reactive power, this method can effectively control the second harmonic of instantaneous active power and the second harmonic of instantaneous reactive power at the same time, and realizes the normal operation of Vienna rectifier under the condition of unbalanced power grid. Linear auto disturbance rejection control (LADRC) is adopted in the outer voltage loop, which overcomes the problem of voltage overshoot and slow dynamic response in PI control. Furthermore, in order to solve the difficulty of grid‐side voltage acquisition when the grid is unbalanced, a virtual flux based no‐grid voltage sensor is introduced to measure the grid voltage. Simulation, along with experimental results, is presented to show that the proposed control strategy has good robustness and fast tracking performance under the condition of power grid imbalance.

Abstract It is known that constant power load (CPL) may cause a negative impedance, which seriously affects the stability of power system. In this paper, a new control algorithm for DC–DC buck converter feeding unknown CPL is proposed. First, under the assumption of known extracted power load, the standard passivity–based control (PBC) is presented to reshape the system energy and compensate for the negative impedance and a proportion‐integration (PI) action around passive output is added to improve disturbance rejection performance, which forms the PBC plus PI (PBC+PI). Then, a parameter estimation algorithm is developed, based on immersion and invariance (I&I) technique, in order to online estimate the extracted power load. In the next step, the online estimation scheme is adopted to construct an adaptive strategy. Finally, the stability analysis of the cascaded system containing a closed‐loop control system and observer error dynamics is conducted. Simulation and experimental results are demonstrated to validate the performance of the proposed controller.

Abstract In the non‐effectively grounding distribution system, residual current under single‐line‐to‐ground (SLG) fault threatens the safety of human being and power supply equipment. Active arc suppression device has been proved to be effective for SLG fault arc suppression when the line impedance is ignored. However, in practice, line impedance varies with the fault location and the load current flowing through the impedance brings about additional voltage drop, which increases the fault current and is not dealt with by the conventional methods. To achieve accurate SLG fault arc suppression with the existence of line impedance, the neutral‐to‐ground voltage reference for full ground‐fault current compensation is firstly derived and a detection method is then proposed. The pre‐fault and post‐fault line currents are used to eliminate the influence of load current on the line impedance voltage drop. A dual‐loop voltage and current controller is then designed. The prototype of active arc suppression device was developed. The results of simulation and prototype experiment validate the effectiveness of the proposed method.

Abstract This paper presents a novel voltage self‐balancing converter (VBC) applied to DC solid‐state transformer (DCSST), analyzes the operating principle of the proposed VBC, and proves the voltage balance performance. Based on this converter, a novel DCSST topology is proposed, which can be used in medium and low voltage DC distribution application, microgrid and medium and low voltage energy storage system. Compared with the previous work, under the same voltage level, it can effectively reduce the number of transformers and switches, reduce the voltage level of switches, and realize the soft switching of the VBC switches, so as to improve the system efficiency and power density, and then improve the system reliability. Meanwhile, the fault handling ability and fault tolerance ability of DCSST are improved, which makes DCSST more reliable when multiple isolated bi‐directional DC/DC Converters (IBDC) are connected in series. In addition, with this topology, the input voltage self‐balancing control strategy of the IBDC is not needed because of the voltage self‐balancing characteristic of VBC, which simplifies the control complexity and greatly improves the control accuracy of the control system. Experimental results agree well with the accuracy and correctness of the proposed topology.

Abstract A series of DC power supply converters can be described as linear affine systems with finite inputs and constrained switching frequency. In this study, a practical‐stability‐oriented general control framework with duty‐cycle‐like characteristics is deduced for such converters. First, a concept called End Point Equivalence Modulation (EPEM) is introduced to release constraints. Following this, a Control Lyapunov Function (CLF) is employed to design the switching law and the relationship between the boundary of the convergence zone and the switching frequency is derived. In addition, an optimized switching strategy is presented to halve the switching frequency without degrading the control performance, which is also helpful for reducing switching loss. Finally, a single‐phase inverter and buck converter are considered as case studies and analysis show that Sinusoidal Pulse Width Modulation (SPWM) and volt‐second balance guarantee their practical stability, respectively, which can be theoretically derived and proved under EPEM. All the proposed methods and controllers are validated both by simulations on MATLAB/Simulink and experiments in a rapid control prototype platform based on a FPGA module.

Abstract An inverter‐based microgrid is a small‐scale power network governed by a distributed control system. In this system, the nodes are the digital controllers of the power inverters, normally located at separate points within the microgrid. A relevant issue is that these controllers operate at different frequencies due to inherent clock deviations in the local hardware oscillators. This paper evaluates the effects of these clock deviations on the performance of microgrids equipped with inverters that emulate the operation of synchronous machines. A systematic procedure is presented to derive steady‐state expressions of the inverter active power and microgrid frequency as a function of clock drift rates. This procedure is applied to swing and governor equations of the virtual synchronous generators, revealing the mechanism that allows clock drifts to be absorbed, making their presence negligible. In addition, it allows recognising the controllers that should never be implemented in a distributed control system, since they cause an unsatisfactory behaviour that can even lead to a blackout in the microgrid. Therefore, the relevance of this study is the identification of the control schemes that are most sensitive to clock drifts, which makes it easier to choose the most suitable control implementation for a particular application. Furthermore, technical guidelines are reported to help researchers on developing control solutions more robust to clock drifts. In this study, the theoretical results are validated by experimental tests in a laboratory microgrid.

Abstract This paper proposes an equivalent temperature estimation‐based finite control set model predictive control (ETE‐FCS‐MPC) method to balance the thermal stress among transistors in three level neutral point clamp (3L‐NPC) traction inverters, which can be used to prolong the whole service life and improve the reliability of the traction inverter. Compared with other methods, the proposed ETE‐FCS‐MPC method requires lesser calculation without additional sensor. Firstly, an energy loss‐based equivalent temperature estimation method is proposed to avoid the complexity of junction temperature prediction. Secondly, an energy variance‐based thermal stress balance control objective is introduced. Then, a normalized evaluation function is established to select the optimal switching state. Finally, the effectiveness of this method is verified on hardware‐in‐the‐loop tests.

Abstract Three‐level inverter systems based on the conventional Finite Control Set‐Model Predictive Control (FCS‐MPC) principle are characterized by large current ripples, difficult‐to‐design weighting factors and variable switching frequencies. In order to solve these problems, in this study a two‐stage model predictive control is proposed that consists of two objective functions: the current prediction and neutral point potential prediction objective functions. The first objective function was based on the mathematical model of a three‐level T‐type, and the second was based on the zero‐sequence injection principle and intended to modify the modulated signals. Then, a multi‐carrier modulation method was adopted to attain the switching signal for the inverter system. In addition, this paper analyses the sensitivity of the inductance and load resistance parameters for the predictive model. Finally, the performance of the proposed strategy is evaluated based on the time‐domain simulation and experiment study.

Abstract To ensure the safety and effectiveness of charging a battery, constant current and constant voltage (CC‐CV) charging is widely used in inductive power transfer (IPT) systems. A double‐channel T‐circuit (DT) is proposed to obtain CC output or CV output by selecting different work modes with a simple feedback control for various power demands. With the merit of the proposed circuit, fewer components are employed compared to previous work with zero phase angle (ZPA) of inverter in the whole charging process. Besides, an IPT system using DT cascaded with LCC‐S (DTLS) is proposed to improve design freedom of the charge current and charge voltage with the constraints of the magnetic coupler (MC) parameters for CC‐CV charging. Finally, a prototype with 60 V/2 A output was built to verify the theoretical analysis. The experimental results show that the fluctuation of the charging current is less than 2% in CC mode, and that of charging voltage in CV mode is within 4% with the maximum efficiency up to 93.36% during the whole charging process.

Abstract For the dual three‐phase permanent magnet synchronous motor(dual‐PMSM), the deadtime can introduce fifth and seventh current harmonics, and they are only constrained by the small stator leakage impedance, which means even if there are only small fifth and seventh voltage harmonics, the resulting fifth and seventh current harmonics will be very large. The harmonic current will make an increment of the system loss, thus lead to an reduce of the efficiency of the speed control system. This paper proposes a harmonic current suppression strategy for dual‐PMSM based on least mean square (LMS) adaptive notch filter. This strategy suppresses the fifth and seventh harmonic currents by introducing four LMS adaptive notch filters in the subspace. The proposed algorithm has good dynamic performance and is insensitive to motor parameters that are offset within a certain range. The effectiveness of proposed method is verified by a set of comparative simulations and experiments.

Abstract In this article, a single‐stage bridgeless LLC resonant converter with a constant frequency control method is proposed for a high‐brightness light‐emitting diode (LED) driver. LED strings require drivers with high power density and high efficiency. This article presents a novel LED driver circuit topology based on switch integration and the switching controlled capacitor (SCC) technique. By combining the merits of a totem‐pole bridgeless boost PFC unit and a high frequency SCC‐LLC half‐bridge resonant converter, the proposed topology can achieve high efficiency. Due to the SCC‐LLC circuit topology structure, constant frequency control of the LLC resonant converter is achieved by the regulation of the equivalent resonant capacitance. The proposed novel LED driver topology can automatically achieve soft‐switching characteristics and a high power factor. The operating principle of different operation modes and the characteristics of the proposed LED driver are analysed in detail. Finally, to demonstrate the feature of the proposed topology, a 100 W/70 V laboratory prototype is built. The satisfactory experimental results correspond with the theoretical analysis and parameter design.

Abstract For the LCL‐type grid‐connected inverter, when the capacitor voltage feedforward is applied, the delay in the digital control system could change the phase characteristics of capacitor voltage feedback and affect the stability of the system. To solve the problem, a delay compensation method based on lead compensator is proposed in this paper, which can reduce the impacts of control delay on the capacitor voltage full feedforward control system. In this study, a lead compensator is introduced into the feedforward channel to compensate the phase lag, and the compensation function is designed to compensate for the phase margin but not change the system amplitude gain. The proposed strategy can keep the phase margin of the system above 25° when the grid impedance changes from 0 to 2.6 mH (0.1 p.u.), which enhances the robustness of the grid‐connected inverter under weak condition. The grid current distortion caused by grid background harmonics is greatly reduced and is kept within 4%. Moreover, the proposed strategy has fast dynamics while ensuring the system stability. Finally, the simulation and experimental results are presented to verify the effectiveness and robustness of the proposed control strategy.

Abstract Capability to deliver maximum power of a converter is essential for increasing power density that is limiting in many applications. Therefore, control algorithm should guarantee operation within converter thermal limits. This requirement can be formalized by a hard constraint in the cost function of model predictive control (MPC). However, the temperatures of the converter elements are not constant in the steady state, which complicates evaluation of the cost on long prediction horizon. Therefore, the evaluation is simplified utilizing the analysis of steady state behaviour of the model and derived current derating laws calculated in off‐line manner. The derating law is used as the terminal set in MPC which allows using one‐step‐ahead evaluation for efficient real‐time implementation. The steady state analysis also provides coefficients for power loss balancing. The proposed approach is applied to control of dual converter, which has high redundancy of switching elements and, thus, wide space for optimization. It is shown in simulation that the proposed approach has better performance than previously published algorithms, at lower computational cost. Experimental evaluation of the algorithm performed on a converter prototype of rated power of 10 kW shows that the proposed controller is able to safely operate the converter near the thermal limit.

Abstract Wireless power transfer (WPT) has been widely used in recent years due to its convenient access to power and security in some specific cases. However, the inherent non‐linearity of the WPT system can result in unexpected stability problems. In this paper, the stability issue of voltage‐mode controlled inductor‐capacitor‐capacitor and series (LCC/S) compensated WPT system is studied for the first time. The discrete‐time model is first introduced to establish the voltage‐mode proportional (P) controlled and proportional integral (PI) controlled LCC/S compensated WPT system. Meanwhile, a modelling method of PI controller without introducing new state variables is proposed in this paper. Then, with the bifurcation diagram and eigenvalues of the Jacobian matrix, the stability of the LCC/S compensated WPT system is analysed with respect to the proportional coefficient and integral coefficient of the controller. Furthermore, by studying the eigenvalues of the Jacobian matrix, the stability boundary can be obtained. In addition, how the load and mutual inductance affect the stability boundary is investigated compressively, the law of influence provided by the operating condition upon the stability can be concluded. Finally, simulation and experimental measurements are provided to verify the accuracy of the discrete‐time model and the effectiveness of the theoretical stability analysis.

Abstract Permanent magnet machines have been used in the high‐speed drive applications due to their high‐efficiency, high‐power‐density, and wide‐speed range characteristics. However, control of such high‐speed permanent magnet machines machine is always challenging and proper flux‐weakening controller design is essential to achieve high performance of these machines. In this paper, an improved feedforward flux‐weakening control scheme for interior permanent magnet synchronous machine (IPMSM) drives are proposed. The proposed method identifies optimal d‐axis and q‐axis currents under different operation regions using maximum‐torque‐per‐ampere curve, voltage limit, and current limit curves with a fast Newton–Raphson algorithm. To ensure the optimal performance of the control mechanism, effects of inductance variations due to the magnetic saturation are considered and an innovative high‐frequency staircase voltage injection method is used to identify the q‐axis inductance. The experimental results show that compared with other existing flux‐weakening methods, the proposed technique can improve the DC‐link voltage utilisation without the need to tune any controller gains and can fully utilise maximum available torque with desirable transient performance.

Abstract As one of the most widely adopted topologies in power electronics, the H‐bridge circuit has been used for numerous kinds of power converters. With the emphasis on reliability and lifetime management of power converters, it could be helpful to decrease or rebalance the thermal stress of semiconductors to prolong the entire converter's lifetime. However, current switching frequency or power routing‐based methods will more or less deteriorate the performance of converters. Therefore, an active thermal control method for the H‐bridge rectifier is presented here, which has limited influence on the converter. This method puts four bridgeless modulation types into operation by the redundant switching states of the H‐bridge. The power losses were reduced by alternately changing a couple of bridgeless modes. Finally, the effectiveness of this active thermal control method has been analyzed of loss and temperature comparisons and validated with simulation and experimental results.

Abstract Here, a novel control strategy based on sliding mode control for the single‐stage boost inverter is presented. The goal is to achieve a system with robustness against inherent delays and variations in parameters, fast response, and high‐quality AC voltage. Therefore, according to the idea of current‐mode control, a new type of dynamic sliding mode control (DSMC) is proposed to improve the response performance on various input and parameter operation conditions. In comparison with the conventional controllers, the proposed DSMC utilized only a single loop while presenting attractive features such as robustness against parametric uncertainties and input delay by definition new sliding surfaces. Furthermore, the proposed system has a fast and chattering‐free response, provides an appropriate steady‐state error, good total harmonic distortion (THD), while its implementation is very simple. In a fair comparison with conventional sliding mode control, simulations and laboratory experiments verified satisfactory performance and effectiveness of the DSMC method.

Abstract Single‐stage switched boost inverter (SBI) with buck‐boost capability finds wide applications in renewable energy systems (RES). This paper aims at a comprehensive topological review of various single stage SBI circuits. The boosting techniques of SBI include switched inductor, switched capacitor, and transformer assisted switches. Each SBI derived structure has its own merits and demerits depending on the applications. The performance evaluation of SBIs, based on various perspectives like boost factor, voltage stress across active devices, passive elements count, DC link voltage, switching losses, voltage gain, and efficiency, are also discussed. A suitable modulation strategy is used to obtain the desired boosted and inverted ac output voltage in one stage SBI. Different modulation strategies adopted for SBIs are also included at the end of the topological review. This topological review's contribution enlightens the researchers in selecting appropriate SBI with effective modulation strategies suitable for renewable energy applications. Besides, the benefits and shortcomings of these converters are discussed in detail.

Abstract In this paper, a novel active current co‐efficient extraction (ACCE)‐based control method is presented for a three‐phase grid‐interfaced voltage source inverter (VSI). Since the VSI performance largely depends on the reference current generation method, it is of significance to identify the active current co‐efficient of the load current contaminated with harmonics, as it is a key governing factor that decides the shape of the compensating current. The proposed ACCE structure functions with minimal mathematical operators like product, sum, and integrators and thereby identifies the fundamental current with computational effectiveness. Besides, in comparison to existing prevalent state‐of‐the‐art methods, the proposed ACCE structure is devoid of any low‐pass filter and zero‐crossing detector, and hence serves the following two distinctive purposes: (i) Ensures minimum steady‐state oscillations and (ii) exhibits improved dynamic performance under disturbances in the grid and load. The proposed structure effectively confronts the various power quality challenges while injecting the active power into the utility grid. Further, the incremental‐conductance‐based maximum power point tracking algorithm is equipped to extract the maximum possible power from the photovoltaic array. Finally, the effectiveness of the proposed ACCE structure has been investigated through MATLAB/Simulink software studies followed by dSPACE‐1104‐based experimental setup.

Abstract This paper presents a sparse quaternion‐valued minimization (SQVM) based control technique of a two‐stage grid supportive photovoltaic (PV) power system with power conditioning capabilities. The grid side converter (GSC) is controlled by utilizing an SQVM control technique. The proposed algorithm enables the GSC to mitigate the load harmonics current and provides reactive power compensation at the point of common coupling (PCC). The proposed control is tuned to mitigate the DC offset error, harmonics current and to improve the frequency response of the proposed system. A DC link pre‐predictive is incorporated to improve the dynamic response by reducing the burden on the outer Proportional‐Integral (PI) voltage controller loop. Further, it is used to extract the fundamental component of load currents for generating the reference currents. An adjustable DC link voltage loop is incorporated in the proposed control technique to adapt the PCC voltage variation, which helps in minimizing the losses of the PV system. For real‐time execution of the adjustable DC link voltage concept, the DC link voltage is adapted with a variation in the PCC voltage. The operation and control of the system topology are validated experimentally under various scenarios.

Abstract This paper presents an improved Multi‐level Inverter topology utilizing the concept of boosting‐capacitor and two DC sources with reduced switches count for generating 17‐level output. The topology employs 10 unidirectional switches including one bidirectional switch. Comparison with other recent topologies shows that the proposed topology employs a reduced number of devices and better performance. The topology combines the modularity of H‐Bridge with the boosting capacity of the switched capacitor topology. Special care is taken while designing the switching strategy for voltage balancing of the capacitors. The authors also have generalized the topology to produce ‘n’ level output. Relevant expressions are also formed and reported. Experimental validation, as well as simulation, is performed, and results are verified. Nearest level control is used as the modulation technique.

Abstract The aim of this paper is to present a new topology of single‐phase transformerless inverters, which can be tied to the local grid as a low‐scaled ac module system. The proposed topology offers a common ground between the neutral point of the ac grid and the negative terminal of the dc supply, and can properly alleviate the concern of variable common mode voltage and leakage current problems. This promising feature is acquired by the aim of both the switched‐capacitor and charge pumped circuit cells. In order to inject a tightly controlled ac current to the grid, an adaptive hysteresis current controller scheme is also presented, which can guarantee almost fixed switching frequency operation of the involved power switches. A complete theoretical analysis, comparative study, and the relevant experimental results are also given to confirm the superior performance of the proposed topology.

Abstract Modular multilevel converters (MMC)s are promising candidates for large‐scale grid‐connected photovoltaic (PV) systems. Due to their modular structure, MMCs provide a direct connection of the PV arrays to the converter submodules. They also offer scalability, independent maximum power point tracking, and enhanced power quality with internal power flow capabilities. However, the intermittent nature of PV arrays introduces a power unbalance inside the converter, which affects its operation. This paper addresses the issue and proposes an energy balancing strategy for the grid‐connected MMC‐based PV system. It uses the internally generated leg currents to control the power flow inside the converter and inject a three‐phase balanced current to the grid with low total harmonic distortion. Compared to the existing strategies, the proposed strategy can overcome any condition of the power unbalance with minimal submodule voltage fluctuations. A 162‐kW, 9‐kV PV grid‐connected system is modelled and simulated in MATLAB Simulink environment. The corresponding results are presented to demonstrate the effectiveness of the proposed control strategy for grid‐connected PV systems.

Abstract Multilevel converters have seen rising demands in the past decades, due to their increased power ratings, enhanced power quality, low switching losses and reduced electromagnetic interference. Prominent among them are the three‐level (3L) neutral point clamped and the flying capacitor inverter topologies along with their derivatives. Nevertheless, the main drawback of these topologies is the requirement of a front‐end boost DC–DC converter to compensate the high dc‐link voltage demand, which is usually twice the grid peak voltage. This multi‐stage power conversion further pulls down the overall system efficiency. A single‐stage dc–ac power converter with boost capability offer an interesting alternative compared to the two stage approach. Considering this aspect, a novel three‐level three‐phase boost type inverter is introduced in this paper for general‐purpose applications (prominently grid‐connected renewable energy). The proposed inverter would reduce the DC‐link voltage requirement to half using the same or even less number of active and passive components, compared to the conventional three‐level neutral point clamped and flying capacitor family. The principle of operation and theoretical analysis are discussed in detail. The design methodology along with simulation and experimental waveforms for a 5 kVA inverter are presented to prove the concept of the proposed inverter topology for practical applications.

Abstract This paper presents a single‐switch zero‐voltage switching (ZVS) power‐factor correction converter based on the class‐E2 converter at 1 MHz switching frequency. A design method for ensuring the ZVS for the entire line‐voltage period is proposed. By visualising the ZVS region in the parameter space, circuit parameters can be easily obtained to achieve the ZVS for the entire line‐voltage period. Additionally, a closed‐loop controller is applied for achieving a high power factor, low total harmonic distortion of the input current and output voltage regulation. The experimental circuit achieved the ZVS in the entire line‐voltage period against load variations. As a result, the implemented converter achieved the same level of power‐conversion efficiency as the 100‐kHz power‐factor correction converters and a high power factor with low total harmonic distortion, which denoted the effectiveness of the proposed design method.

Abstract This paper studies the interaction between the damping characteristics and the initial‐stage short‐circuit current of modular multilevel converter based high voltage direct current (MMC‐HVDC) transmission system. First, the MMCs' input–output characteristics are obtained through the operator approach, and the influences of both linear part and nonlinear part are analysed. Second, an input–output characteristics based short‐circuit current calculation method is proposed. Third, an eigenvalue‐based comprehensive index is proposed to evaluate the damping characteristics of the MMC‐HVDC transmission system. Finally, the interaction between the damping characteristics and the initial‐stage DC short‐circuit current is analysed under different system parameters and DC system structures. The analysis results show that there is a negative correlation between the system damping characteristics and the average rising rate of the short‐circuit current. The proposed index G can effectively evaluate the short‐circuit current of MMC‐HVDC and can provide guidance for the planning of DC system structure, the selection of operation mode and system parameters.

Abstract The six‐phase motor control system has low torque ripple, low harmonic content, and high reliability; therefore, it is suitable for electric vehicles, aerospace and other applications requiring high power output and reliability. This study presents a superior sensorless control system for a six‐phase permanent magnet synchronous motor (PMSM). The mathematical model of PMSM in stationary coordinate system is presented; its sliding mode observer (SMO) of back electromotive force (BEMF) acquires the motor speed and position information. As torque ripple and harmonic components affect the BEMF estimated value through the traditional SMO, the function of the frequency‐variable tracker of the stator current (FVTSC) is used instead of the traditional switching function. By improving the SMO method, the BEMF is estimated independently, and its precision is maintained under startup or variable‐speed states. To improve performance of the system, the auto disturbance rejection controller (ADRC) is used to suppress load disturbance and speed overshoot. To reduce model parameters, an ADRC with sliding mode algorithm is proposed, simplifying the structure and simultaneously solving the parameter tuning problem. Finally, comparing the ADRC with FVTSC SMO and the traditional PI controller shows that the new ADRC effectively improves the dynamic and static performance of the PMSM.

Abstract Due to its several advantages (especially low volume and weight), power electronic transformer has gained notable attraction in railway applications. The main focus of this work is devoted to development a fully filed programmable gate array (FPGA)‐based control platform for power electronic transformer in the aforementioned application. Due to the parallel processing of FPGAs that results in a faster control algorithm execution, reliable operation (which is of major importance in traction applications) is guaranteed. For this purpose, an input series output parallel power electronic transformer structure is built, and various considerations for reliable and stable operation of the power electronic transformer in traction applications, such as safe start‐up and bidirectional power flow, along with the required control and pulse generation schemes, have been designed and implemented in a Xilinx FPGA control platform. Moreover, a modified control algorithm is proposed for controlling the power electronic transformer in a simple and more reliable manner. This control scheme is developed based on the output voltage of the DC–DC–LLC resonant converter, and can effectively control the sum of rectifier DC‐link voltages and track the input sine reference current, with a lower number of required sensors. Finally, the effectiveness of the proposal has been tested from various aspects by experimental tests.

Abstract For three‐level inverters, hysteresis current control (HCC) has been widely used in applications such as active power filters due to its fast‐dynamic response, and it does not need to control each frequency separately with multiple controllers, which makes it simpler. However, the large fluctuation range of switching frequency is a serious disadvantage of hysteresis current control. Especially, the switching frequency decreases significantly during grid voltage zero‐crossing. This frequency fluctuation will cause low‐frequency harmonics. The purpose of this paper is to propose a sampling compensation scheme, which can solve the problem of switching frequency fluctuation near the zero‐crossing of grid voltage. Based on the variable hysteresis band strategy, the virtual sampling and switching time prediction algorithm is designed, which does not need to increase the sampling frequency or add additional controller. Therefore, nearly fixed switching frequency can be achieved while maintaining the control performance. Both simulation and experimental tests have verified the efficacy of the proposed scheme.

Abstract The design of a cascade controller is demonstrated for a buck–boost converter that is combined with two control loops consisting of inner and outer controllers. The outer loop is implemented by a fractional‐order proportional‐integrated‐derivative (FO‐PID) controller that works as a voltage controller and generates a reference current for the inner control loop. To provide faster dynamic performance for inner loop, a self‐tuning regulator adaptive controller, which tries to regulates the current with the help of a novel improved exponential regressive least square identification in an online technique, is designed. Moreover, in the outer loop, to tune the gains of the FO‐PID controller, a novel algorithm of antlion optimizer algorithm is used that offers many benefits in comparison with other algorithms. The system provided by the boost mode is a non‐minimum phase system, which creates challenges for designing a stable controller. In addition, a single loop controller is proposed based on a PID controller tuned by a particle swarm optimization algorithm to be compared with the cascade controller. Cascade loop can present significant benefits to the controller such as better disturbance rejection. Finally, the strength of the presented cascade control scheme is verified in different performing situations by real‐time experiments.

Abstract Solid‐state transformers (SSTs) have flexible capabilities to improve the power quality issues. These improvements impose disturbances into the SST converters that require proper control algorithms. In this paper, the problems of the unequal active power flow in different phases of the SST due to the grid voltage unbalance conditions and the negative sequence current injection are discussed, and an effective method is proposed to equally sharing the active powers between the SST clusters by creating an optimum zero sequence current. Based on the power dependencies, an analytical vector for the zero‐sequence current is proposed, which can equally share the power among the SST clusters and balance the HVDC‐link voltages. Also, the proposed control strategy by using PIR controllers can achieve the zero‐sequence current based on a direct current control method. The provided equal power‐sharing among the clusters is kept in the considerable unbalanced voltage of the grid and prevents the SST outage during faults. The simulation and experimental results confirm the proposed control method to equalise the power‐sharing among the SST clusters and voltage equalisation of the HVDC‐links while the SST tries to improve the grid voltage unbalance and in the fault conditions of the grid.

Abstract Voltage sags and momentary interruptions of power are the most severe voltage disturbances. Here, a tansformerless active voltage quality regulator with the novel three‐leg circuit is proposed to mitigate long duration and deep voltage sags. The shunt rectifier and series inverter of this novel three‐leg circuit are all full‐bridge structures, so it has lower DC bus voltage and smaller filter parameters than the conventional half‐bridge topologies. The totem‐pole bridgeless boost circuit is formed among the three bridge arms and the DC bus voltage will be charged to exceed the peak value of the supply voltage. It can compensate for deep voltage sags (that may be more than 50% of the nominal voltage). Compared to the conventional transformerless series‐connected topology, the proposed topology has the merits of higher efficiency, smaller volume and lower cost. The validity and feasibility of the proposed topology are verified by theoretical analysis, simulation and experiment.

Abstract The beat phenomenon can be a critical issue in railway traction applications. This paper proposes a dual‐frequency compensation (DFC) method for the beat‐less algorithm to shift the spectrum of the beat voltages to a higher‐frequency region. Two variables for frequency compensation are derived by mathematical calculations based on the single‐frequency compensation (SFC) method. The applicability and superiority of the DFC method are analyzed. It is proposed that the DFC method can be a transition between the modulation index compensation (MIC) method and the SFC method, so the beat phenomenon can be greatly suppressed in the full speed range. The implementation of the DFC method is proposed to guide how to generate the two variables. The experimental verification is carried out on the StarSim hardware‐in‐loop platform, and the results demonstrate that the DFC method is more effective compared with the SFC method for beat phenomenon suppression. It also shows the modulation index with the DFC method is higher than that with the MIC method.

Abstract This paper presents a novel coupled converter with high‐voltage insulation protection in magnetic isolated way by taking the case of heater/ignitor/keeper supply for powering discharge cathode in the space ion electric propulsion (EP) thruster. The topology, working principle and igniting timing, as well as the adaptive closed‐loop control and heating‐igniting interlock control are also illustrated. For the proposed converter, the coupled topology and control strategy only adopt three straddling magnetic components to realize all functions. Meanwhile, the number of electronic components suspending over the high‐voltage side of beam supply is small enough. Additionally, the test on the coupled converter prototype shows that, the maximum efficiency is 88.6%, close to the traditional tightly coupled supply; the proposed converter could realize the function of heating/igniting/keeping for the discharge cathode under the magnetic isolated way and corresponding control strategy; and there is no “spark phenomenon” for the converter during low‐pressure discharge test. Hence, the magnetic isolated way to obtain the physical separation between high‐voltage and low‐voltage side in the converter is useful to achieve the high‐voltage insulation protection.

Abstract A hybrid switched inductor with flexible high voltage gain boost converter for 400 V DC microgrid application is presented in the paper. The three operating modes of the converter are controlled using three switches by two‐duty ratios. The proposed converter provides flexibility in the selection of the duty cycle to achieve desired output voltage. Moreover, with two duty ratio, high gain with a wide duty range is accomplished in the proposed converter while an individual switch does not need to operate at a very large duty ratio. The power circuit analysis, operating principles, steady‐state voltage gain analysis during continuous conduction mode (CCM) and discontinuous continuous mode (DCM), boundary condition, efficiency analysis, comparison, and circuit parameter design of the proposed are presented. A closed‐loop controller design and small‐signal modeling are discussed. The dynamic behavior of the proposed converter is validated with a change in duty ratio, input voltage, and load power. A laboratory prototype converter is designed and developed to verify the model, and feasibility of different operation modes. The prototype is tested for a power range of 100 W–500 W for different duty cycles.

Abstract Electrical vehicle (EV) technology has gained popularity due to its higher efficiency, less maintenance, and lower dependence on fossil fuels. However, a longer charging time is a significant barrier to its complete adaptation. Solid state transformer (SST) based extreme fast charging schemes have emerged as an appealing idea with an ability to provide a refuelling capability analogous to that of gasoline vehicles. Therefore, this paper reviews the EV charger requirements, specifications, and design criteria for high power applications. At first, the key barriers of using a traditional low frequency transformer (LFT) are discussed, and potential solutions are suggested by replacing the conventional LFT with high frequency SST at extreme fast‐charging (XFC) stations. Then, various SST‐based converter topologies and their control for EV fast‐charging stations are described. The reviewed control strategies are compared while considering several factors such as harmonics, voltage drop under varying loading conditions, dc offset load unbalances, overloads, and protection against system disturbances. Furthermore, the realization of SST for EV charging is comprehensively discussed, which facilitates understanding the current challenges, based on which potential solutions are also suggested.

Abstract This paper proposes a common‐mode voltage injection‐based pulse width modulation strategy to optimize the AC current ripple of parallel interleaved converters. In general, modulation methods entail a trade‐off between switching times and voltage error. Given the redundancy in the available vector sequences, we sequentially minimize the switching times and the voltage error. Specifically, we propose eight candidate vector sequences with minimized switching times for each 60° sector. Then, we quantitate the current ripple introduced by the eight vector sequences, and according to the calculations, we split each 60° sector into eight subsectors, each employs the respectively optimal vector sequence with the minimized current ripple. For implementation, the candidate vector sequences are further unified by a common‐mode voltage injection scheme. The injection depends on the momentary subsector in which the reference lies. Despite the complex geometry of the subsectors, we propose a simple decision procedure that can be easily implemented in mainstream microcontrollers. Compared to the conventional methods, the proposed common‐mode voltage injection‐based pulse width modulation has a smaller AC current ripple at the same switching loss. The experimental results verify the theoretical analysis and the effectiveness of the proposed common‐mode voltage injection‐based pulse width modulation strategy.

Abstract The proposed technology deals with the reduction in torque ripple of five‐phase induction motor. The machine is controlled by direct torque control technique and fed by three‐level five‐phase inverter (TL‐FPI). In the fraternity of multiphase induction motor, five phase is the most researched drive, considering complexity of control mechanism and advantages which multiphase machine has offered. The selection of TL‐FPI is based on availability of more voltage vectors (243) than two‐level five‐phase inverter (32). The 41 voltage vectors are employed out of 243 based on simplicity and advantages of multiphase machine. The selected vectors are operated through modified seven‐level torque comparator. An increase in levels of the comparator restrains the ripple in a predefined boundary. Here, modification in the predefined boundary of the comparator is suggested which allows the utilization of optimal voltage vectors. According to modification, zero voltage vectors are replaced with small active vectors when actual torque is lower than its reference value. To substantiate the claim various results of simulation and experimentation are given.

Abstract A control approach for three‐phase four‐leg LC‐filtered voltage source inverters (VSIs) is proposed for an uninterruptible power supply (UPS) application. A filter inductor in the fourth (neutral) leg of the VSI is considered to enhance the output voltage quality when feeding different types of loads in such a system. The proposed approach is based on the modelling of UPS VSI system in the dq0 synchronous frame. First, the switching functions of the inverter under study are extracted from the achieved system model. Afterward, the control approach is developed by introducing a virtual time constant, which simultaneously affects the system's damping ratio, and a virtual undamped natural frequency in the switching functions. It offers flexibility for improving the system dynamic and steady‐state responses as desired. While the final time constant decreases the transient response time and overshoot, the resulting undamped natural frequency leads to alleviation of steady‐state error in the output voltage. The performance of the proposed control approach is evaluated via SIMULINK‐based and real‐time simulation results.

Abstract This paper presents an adaptive power sharing control method of parallel‐connected hybrid inverters in microgrid. Normally the AC microgrid is composed of hybrid inverters, other power generation equipment and some loads in parallel. Droop control or virtual synchronous generator is usually adopted to control parallel inverters, so the output power ratio between each inverter is fixed by droop parameters. The input of hybrid inverter is PV panel and battery, so the power output ability of each hybrid inverter is different because of the different PV panel capacity, illumination condition, battery capacity and battery state of charge. Hence, the output power of some hybrid inverters is short or redundant sometimes, which makes microgrid unstable or causes power generation restraints. It is necessary to recognize the actual power capacity of each inverter and control the output power reasonably. This paper analyzes the characteristics of parallel‐connected hybrid inverters with droop control in microgrid. An adaptive power sharing method is developed to identify the unbalanced between the each inverter on DC bus. By adjusting the droop parameters, the output power of each inverter is regulated where the controlled parameters are defined in system transfer function with an optimal target. Experimental tests are executed following the numerical simulation. The results show that the output power of each inverter can be adjusted adaptively according to the practical needs. The excessive power from one inverter can be absorbed by the others. Therefore, the stability and the power capability in the system are both ensured by adopting the proposed methods. The outcomes of the study provide a reference to the development of the adaptive inverter in microgrid.

Abstract Bidirectional DC‐DC converters are widely used in electric vehicle charger, where excellent steady‐state and dynamic performances are crucial. However, those two performances are easily affected by external disturbances and parameter uncertainties. To solve this problem, this paper proposes a disturbance observer‐based second‐order sliding mode control (SOSMC) for the buck/boost converter. With the super‐twisting algorithm (STA) second‐order sliding mode control method, satisfactory steady‐state and dynamic performance is achieved. In addition, to further improve the dynamic performance and reduce the control burden, a high‐order sliding mode disturbance observer (HOSMDO) is employed to estimate the lumped disturbances. Thus, the mismatched disturbances caused by input voltage fluctuation, load variation, output voltage regulation, power flow change, and model uncertainties can be effectively suppressed. Moreover, the state variable containing inductor current is also observed, which removes one current sensor, reducing system cost. The design methods of the second‐order sliding mode control and the high‐order sliding mode disturbance observer are presented as well as the stability analysed through the Lyapunov theory. Simulation and experimental results verify the effectiveness of the proposed control strategy.

Abstract Here, a general state‐space average model of the half‐wave zero‐voltage switching quasi‐resonant Cuk converter (HW‐ZVS‐QRCC) is derived and validated. The development of an extended Lyapunov‐function‐based robust passivity‐based control strategy for HW‐ZVS‐QRCC is carried out using the derived model. The first feature of the proposed controller is that that the resulted closed‐loop HW‐ZVS‐QRCC is globally asymptotically stabilized even if the physical constraint on the magnitude of the control signal is taken into account. Also, to deal with the uncertainties in the conventional passivity‐based control (PBC) design, an integral function of the output voltage error is incorporated in PBC structure such that zero‐voltage regulation error is assured. Lastly, it shows which variables are most suitable for feedback purposes over a wide range of controller gains. Simulation and experimental results are also provided to validate the theoretical conclusions.

Abstract A 17‐level hybrid multilevel inverter (HMLI) using modified grey wolf optimisation (MGWO) is proposed here. The proposed HMLI requires only a single dc source and a lesser number of circuit elements to obtain a multilevel voltage level. The proposed HMLI can also enhance the input voltage and has reverse current carrying capability. The selective harmonic elimination pulse width modulation technique is implemented through MGWO for determining the optimal switching angles of the proposed HMLI to eliminate lower order harmonics. The MGWO algorithm gives improved results as compared to other existing optimisation algorithms in terms of fitness value, convergence speed and harmonic profile of the output voltage. The proposed HMLI is also compared with some of the other existing HMLIs in terms of the number of circuit elements, peak inverse voltage and total blocking voltage to exhibit its advantages. Finally, a 550 W prototype is fabricated in the laboratory to evaluate the effectiveness of the proposed HMLI.

Abstract It is generally known that, with conventional PI control, the stability and dynamic response performances of a power converter cannot be optimized simultaneously. To overcome this limitation, an uncertainty and disturbance estimator assisted sensorless load current feedforward control for dc‐bus voltage regulation is presented to achieve fast dynamic response to load variations while stability is guaranteed by tuning PI controller. The proposed control scheme is verified on a cascaded converters system comprising a front end dc‐dc DAB converter followed by a single‐phase inverter as an illustrative case. Load‐current feedforward is used to enhance the transient response of the front end DAB converter while an uncertainty and disturbance estimator is used to compensate for any non‐idealities arising from model uncertainties and error in load current estimation. To validate the proposed control scheme, experimental results obtained from a 250‐W cascaded converter system are presented and compared rigorously to the performance of conventional PI control.