This paper presents a new three-level reduced switch-count three-phase F-type rectifier and its control without current sensing. Unlike the existing three-level three-phase rectifier topologies, which use twelve switching devices, the proposed topology uses only nine switches. This, in turn, reduces costs and enhances reliability. Moreover, the voltage stress on the switching devices is more evenly distributed across the components, leading to the use of lower voltage-rated devices. The control of the proposed rectifier is achieved by a control strategy that eliminates the need for current sensing which reduces control implementation costs. The functionality of the proposed topology and its control method is verified using MATLAB/Simulink simulations under different operating conditions, including steady-state operation, step changes in resistive load, and variations in the reference DC-link voltage. The simulation results verify that the DC-link voltage is effectively controlled, and the total harmonic distortion (THD) of the grid currents remains within the limits defined by international standards.

This paper proposes a multi-objective model predictive control (MPC) for a grid-connected ten-switch three-phase three-level inverter. The main objective of the proposed MPC method is to control the grid current. In addition, the voltage balancing of the DC capacitors in the ten-switch three-level inverter is essential to generate voltage levels properly. Therefore, two objectives need to be achieved simultaneously. The multi-objective cost function feature of the MPC method is used to achieve these objectives. The simulation studies are performed using MATLAB/Simulink environments to investigate the effectiveness of the proposed MPC method. The results show that the proposed control method exhibits accurate performance under steady-state conditions and fast dynamic responses under transient conditions. Moreover, the grid current spectrums show that the total harmonic distortion is 2.21% in normal operation, and it is under the desired limits, even with a 50% parameter mismatch in filter inductance.

This paper presents an adaptive rate reaching law based sliding mode control method for a three-phase F-type converter. Unlike the existing reaching laws in which the gain is always constant, the proposed reaching law employs an adaptive gain that is continuously updated with the grid current errors. This means that the gain can reach to its smallest value when the grid current errors are zero. It is shown that the minimum gain reduces the reaching time. As a consequence of using adaptive gain, the dynamic response of system is improved considerably (i.e: the reaching time is reduced). Moreover, it is shown that the three-phase F-type converter can be operated as bidirectional battery charger as well as shunt active power filter (SAPF) for compensating the nonlinear loads connected at the point of common coupling. The proposed control and correct operation of system are validated by MATLAB/Simulink simulations under various operating conditions which include battery charging mode, battery discharging mode, and simultaneous operation as SAPF and battery charging/discharging.

This paper presents a model predictive control (MPC) for a grid-connected voltage source inverter (VSI) with current limitation. The control algorithm is performed in the dq frame to obtain the amplitude of the inverter currents. First, a state observer with a reduced model of the converter is used to estimate the inverter current and perform active damping. Then, an MPC algorithm is used to regulate the currents to a desired reference but with the advantage that these currents can be limited to a maximum value by introducing a constraint in the cost function instead of clipping the current of the inverter above a maximum current. This controller has been tested experimentally under a current reference step change and without a physical damping resistor.

This paper presents a hysteresis current control for single-phase single-stage buck-boost grid-connected inverters. The inverter topology employs four switches that are operated with the grid frequency and two bidirectional switches that are operated with high switching frequency. Hence, unlike the existing single-stage inverter topologies, the switching losses are minimized. Moreover, this inverter configuration has the capability to operate both in buck and boost modes and utilizes only a single inductor. The proposed hysteresis current control eliminates the need for designing a dedicated modulation technique for this inverter topology. An active damping technique is utilized to cope with the resonance damping problem without employing additional sensor. The reference current needed in the hysteresis controller is produced using a proportional-resonant (PR) controller whose input is the grid current error. The use of PR controller guarantees zero steady-state error in the grid current. The validity and superiority of the proposed control method are confirmed by MATLAB/Simulink simulations under various operating conditions which include buck mode, boost mode, transition from boost mode to buck mode, reference current change and virtual resistor variation. The simulation results show that the proposed control method is able to transfer the desired current into grid successfully under all operating conditions.

This paper proposes a hysteresis current control (HCC) method for a single-inductor buck-boost non-isolated onboard charger for electric vehicles. The charger is capable of working both in the boost and buck modes. The proposed HCC relies on the buck-boost inductor current and its reference which is generated using a proportional-resonant (PR) controller using grid current error. The reference current generated by PR controller is modified to suppress the oscillations in the inductor currents. An active damping by using a virtual resistor connected in series to filter inductor is used which does not require an additional sensor. A proportional-integral (PI) controller is used to generate the amplitude of grid current reference, which is utilized in constant current (CC) and constant voltage (CV) modes. The effectiveness of the proposed control strategy as well as the control method, is investigated by simulation studies by considering two different battery voltage levels (48V and 350V). The results show that the proposed method is able to charge the battery in CV and CC modes. Moreover, the grid current is maintained in unity power factor at a reasonably low total harmonic distortion (THD) which is smaller than the limits recognized by international standards.

48th Conference of the Industrial Electronics Society-IECON-Annual -- OCT 17-20, 2022 -- Brussels, BELGIUM

48th Conference of the Industrial Electronics Society-IECON-Annual -- OCT 17-20, 2022 -- Brussels, BELGIUM

This paper presents a passivity-based control approach for four-switch buck-boost (FSBB) DC-DC converters. The state variables are selected as the inductor current and the capacitor voltage errors. The passivity based control is formulated that targets to drive the inductor current and capacitor voltage to their reference values. The reference of the inductor current is produced by a proportional-integral controller that operates on the capacitor voltage error. Two control input equations are defined for buck and boost operations due to the fact that FSBB converter contains separate switches for buck and boost stages. As a consequence of controlling each stage by the dedicated control input, the passivity based control method eliminates the need for using a mode detection algorithm. The validity and superiority of the proposed approach has been studied by Matlab/Simulink simulations under load step, reference voltage step and operation mode variations for buck and boost modes. The results reveal that the proposed control approach can regulate the output voltage under all cases.

This paper proposes a super twisting sliding mode control for a bidirectional dual active bridge (DAB) converter. First of all, the mathematical model of the DAB converter developed around the Fourier expansion of the switching functions is defined and then a super twisting sliding function is proposed to regulate the output voltage while utilizing a sliding mode observer to estimate the load disturbance to get a feedforward term to the control input. On the contrary of the classical sliding mode control methods, the proposed sliding function is capable of alleviating the chattering while attaining zero steady state error and finite time convergence by estimating the load current and feedforwarding to the control loop. Since the control input is smooth, it can be directly injected to the PWM block for generating switching signals that cause fixed switching frequency. The effectiveness of the proposed method is verified in the MATLAB/ simulation software. The results confirm the disturbance rejection, fast response, and chattering alleviation of the proposed strategy thanks to the inherent characteristics of the super twisting method.

In this study, a current control strategy is proposed for nine-level packed-E-cell (PEC) rectifier without using current sensor. The proposed control strategy is based on mathematical model of rectifier. A modulation signal is obtained from the differential equation of the system. The modulation signal requires the inductor current reference whose amplitude is obtained by using a proportional-integral (PI) regulator. The input signal to the PI regulator is the dc load voltage error. Hence, while the grid current control is achieved by the proposed control, the regulation of load voltage is achieved by PI. The performance of the proposed control strategy is tested under load variations, reference load voltage change, and grid voltage variation. Moreover, the robustness of the proposed control method under inductance variations is also investigated. Computer simulations are conducted to show the steady-state and dynamic performances of the proposed control method.

In order to mitigate the periodic disturbances in voltage-source converter (VSC)-based applications, different techniques have been comprehensively investigated to mitigate these periodic disturbances, either using additional disturbance-mitigation controller or by means of modifying the modulation stage. As well as providing an in-depth analysis of various periodic disturbances in VSC-based applications, this article presents an overview of the controller-based periodic disturbance mitigation techniques. And these techniques, different in concept, can be categorized into two types, i.e., the internal-model-based methods and the feedforward-based methods. The controller prototypes and their variants are comprehensively introduced with motivations and distinct features. The characteristics of different strategies and the corresponding implementation methods are compared and summarized. And the practical issues such as computational burden and frequency adaptability are simultaneously included as well to present a comprehensive illustration. In addition, the characteristics of different strategies are compared and summarized with the aim of providing a clear illustration.

In this paper, a sliding mode control (SMC) strategy is proposed for a three-phase two-leg grid-connected T-type quasi-Z-source inverter with LCL filter. The large dc input voltage requirement of three-phase two-leg inverter has been resolved by employing a quasi-Z-source network. The proposed SMC can achieve the control of both dc- and ac-side variables. Furthermore, the proposed SMC does not require additional active damping to remove the resonance existing due the LCL filter. The chattering is eliminated by smoothing the sliding surface functions through boundary layers. The validity of the proposed SMC strategy is investigated by computer simulations. It is shown that the dc capacitor voltages are regulated and grid currents track their references.

This paper presents a weighting factor free Lyapunov-function-based model predictive control (MPC) for single-phase T-type rectifiers. The stability of the rectifier can be guaranteed if the derivative of Lyapunov function is negative. Motivated from this fact, the design of cost function (Lyapunov function) is based on stability of the rectifier. Since the coefficient used in the formulation of the Lyapunov function does not have any effect on the performance, the cost function becomes weighting factor free. The weighting factor free based MPC brings simplicity in the practical implementation. The performance of the proposed control technique has been investigated under normal and distorted grid voltage conditions during steady-state and transients caused by the load change. In all cases, the output and capacitor voltages are regulated at desired voltage levels, grid current tracks its reference and achieves unity power factor operation.

This article presents an indirect sliding mode control (SMC) for single-ended primary-inductor converters (SEPIC). Unlike the conventional SMC methods, the proposed SMC method employs a sliding surface function based on the input current error only. The use of such sliding surface function not only simplifies the implementation but also reduces the cost of implementation. It is shown that the output voltage control can be achieved indirectly. The input current reference is generated by a proportional-integral (PI) regulator. The existence condition and the region of the closed-loop system are determined for all possibilities of the PI gains. The performance of the proposed SMC method is investigated on a laboratory prototype converter, operated in buck and boost modes, in terms of the voltage regulation ability under abrupt changes in the input voltage and load resistance. Simulation and experimental results are presented and discussed.

The special section presents the recent advances on sliding mode control and its applications in modern industrial systems. With the increased utilization of modern equipment in wide industry applications such as renewable energy systems, distributed generation, smart grid, transportation, robot manipulators, power systems and automotive, emphasis on better performance in terms of the robustness, optimization, reliability and implementation simplicity has become an important requirement. Sliding mode control is recognized as one of the popular and powerful tools in achieving these requirements in industrial systems. The robustness feature eliminates the burden of the necessity of system parameters required for accurate modelling in most applications. In spite of these attractive advantages, the sliding mode control method suffers from chattering existing due to unmodelled dynamics and switching time delays. The effort of the researchers and industry has led to a rapid development of different sliding mode control methods in terms of sliding surface design, sliding surface coefficient selection, sliding-mode observers, chattering reduction methods, and modulation techniques. Especially, the observer and disturbance estimation techniques are widely studied and substantial new observation and estimation techniques have been proposed in the literature. Hence, the objective of this special section is to share the new ideas of researchers and industry on sliding mode control and its applications in modern industrial systems. The summaries of thirteen papers accepted for publication are given below.

In this paper, a sliding mode control strategy is proposed for single-phase grid-connected three-level neutral-point-clamped quasi-z-source inverters with constant switching frequency. While dc-side variables are controlled by using simple boost control, ac-side variables are controlled via SMC method. The sliding surface function is passed through a boundary layer so as to eliminate chattering and achieve a continuous modulating signal. The switching signals are then obtained by using traditional sinusoidal pulse width modulation which leads to constant switching frequency. The proposed SMC strategy offers many advantages such as fast dynamic response, zero grid current error, simple implementation, robustness to parameter variations and constant switching frequency. In addition, it does not need an active damping method for damping the oscillations arising due the LCL filter resonance. The effectiveness of the proposed strategy is verified by computer simulations under steady-state and transient conditions.

In this work, a three-phase two-leg T-type active power filter topology is investigated when a three-level hysteresis band current modulation technique is applied. The three-phase two-leg T-type configuration which utilizes eight switching devices together split DC link capacitor banks is able to improve the reliability of the system as well as effectively reduces the power losses. The compensation of the current harmonics at each phase are achieved successfully with the control of phase-a and phase-b. Using this technique, the phase-c is directly connected to the midpoint of the split capacitors, which eliminates the necessity of additional control on the phase-c. The performance of the proposed topology and control method is demonstrated through the simulation results.

This paper presents a sliding mode control (SMC) strategy for three-phase three-level T-type rectifiers with capacitor voltage imbalance compensation capability. The proposed SMC strategy which is formulated in the natural frame is based on generating a modulating signal from the difference of line currents and their references. The amplitude of line current references is generated by regulating the output voltage using a proportional-integral (PI) regulator. In order to satisfy the unity power factor requirement, the generated amplitude is multiplied by the corresponding unity sinusoidal waveforms for each phase. For the sake of eliminating the imbalance in the capacitor voltages, a compensation term involving the capacitor voltage feedback through a suitable gain is added into the line current reference obtained for each leg. The performance of the proposed control strategy is investigated by simulation study during steady-state, transients caused by load change, and unbalanced grid. It is shown that the dc output voltage is regulated at desired level and line currents track their references in all cases.

This paper introduces a proportional-integral (PI) and sliding mode based control strategy for three-phase grid-tied three-level T-type quasi-Z-source inverter with LCL filter. The proposed control strategy has two parts. While the PI controller regulates the dc capacitor voltages and inductor currents in the quasi-Z-source network, the sliding mode control (SMC) achieves the grid current control. The proposed SMC removes the filter capacitor voltage requirement of phase c leading to simplicity in the implementation. In addition, for the sake of eliminating chattering, the sliding surface functions are passed through a boundary layer (smoothing) which removes the discontinuity and leads to fixed switching frequency operation. The validity of the presented control strategy is investigated by computer simulations during steady-state and transients caused by the reference change. It is shown that the dc capacitor voltage regulation is achieved and grid currents track their references.

In this paper, a sliding mode control (SMC) strategy is proposed for three-phase three-level T-type shunt active power filters (SAPF). The proposed control strategy has the ability to balance the capacitor voltages with respect to the neutral-point. The proposed SMC strategy is formulated in the natural frame which eliminates abc/dq transformation and two PI controllers compared to the design in the dq frame. In natural frame, only one PI controller is needed to generate the amplitude of grid current reference. The output of the PI controller is multiplied by the unity sinusoidal waveforms, obtained from the grid voltages, so as to obtain the grid current references. The filter current references are obtained by subtracting the measured load currents from grid current references. The performance of the proposed control method is investigated by simulation study during steady-state and transients caused by load change. It is shown that the grid currents are almost sinusoidal with small THD, grid currents and dc-link voltage track their references and capacitor voltages are balanced with respect to the neutral-point.

The twelve papers in this special section present relevant research works concerning identification and observation informatics for energy generation, conversion, and applications. It has always been known that high-performance operation of machines and power converters requires fast dynamic response and accurate regulation of controlled variables. As well as proper design of specific control schemes, accurate acquisition, and knowledge of system information based on parameter identification and state observation is an effective measure to obtain enhanced performances regarding disturbance rejection, sensorless operation, parameter adaption, etc. With the increased emphasis on higher efficiency, effectiveness, reliability, and flexibility in energy generation, conversion, and applications, the level of interest and pace of developments in area of identification and observation have further accelerated and witnessed great breakthrough.

In this study, sliding-mode and proportional-resonant based control strategy is proposed for three-phase two-leg T-type grid-connected inverter with LCL filter. The sliding surface function is formed by using the inverter current and capacitor voltage errors. When the inverter current and capacitor voltage feedbacks are included into the control loop, the active damping requirement is automatically resolved. The PR controllers are employed in cascaded manner to generate the references for inverter current and capacitor voltage. The use of PR controllers ensures zero steady-state error in the inverter current, capacitor voltage and grid current. In addition, since the proposed three-phase inverter has only two legs, the total switch count is reduced resulting in cheaper and reliable topology. The proposed system is validated through computer simulations which show that proposed control algorithm can achieve the control of grid currents. The total harmonic distortion level of the grid currents is in the limits of international standards.

This paper presents a modified MIMO sliding mode control (SMC) approach with constant switching frequency for single-phase grid-connected LCL-filtered quasi-z-source inverters (qZSI). In this approach, the sliding manifold is formed so as to achieve a concurrent SMC of both dC and ac side variables simultaneously. Such control is possible by generating the modulation signal and shoot through duty ratio. The constant switching frequency operation is achieved by smoothing the sliding manifold using a boundary layer. Cascaded PR controllers are employed to produce the ac side inductor current and capacitor voltage references alleviating the steady-state error in the grid current and tackling the damping issue. Dc side inductor current reference is produced by using power balance law in the circuit. Simulation results show the effectiveness of the proposed control approach.

This paper presents a Lyapunov stability theory-based control technique for a single-phase quasi-impedance source neutral-point-clamped (qZS-NPC) inverter with LCL filter. The proposed control technique handles two control objectives, which are the grid current control and the dc-link voltage control. The dynamic and steady-state performances of the proposed control method have been demonstrated by simulations using Matlab/Simulink.

In this paper, a proportional-integral (PI) and proportional-resonant (PR) based control strategy is proposed for packed-U-cell (PUC) inverters. In the conventional PI-PI based control strategy, while the first PI regulates the DC capacitor voltage, the second PI regulates the AC load current. However, it is shown that the second PI cannot guarantee zero tracking error in the load current. The main reason of this comes from the fact that PI controllers are not able to achieve zero tracking error for the AC signals. Also, in an attempt to reduce the tracking error by tuning PI gains distorts the load current. In this study, a PI-PR based control strategy is obtained by replacing the second PI by a PR controller. The performances of both PI-PI and PI-PR control methods have been compared. It is shown that the load current to tracks its reference in all circumstances provided that the inverter current reference is generated accurately. Computer simulations are conducted to show the steady-state and dynamic performances of both control methods.

In this study, three-phase two-leg grid-connected neutral point clamped (NPC) inverter with LCL filter is proposed for distributed generation systems. Since the proposed inverter has only two legs, only two of the three-phase currents are controlled. Once the control of two currents is achieved, the control of third current is achieved automatically. The control objective is achieved by using sliding mode controller (SMC). Unlike the existing methods, the sliding surface function involves the inverter current and capacitor voltage errors. Hence, the reference signals of the inverter currents and capacitor voltages are essential in the SMC. In this study, these reference signals are generated by cascaded connected proportional resonant (PR) controllers without making use of filter parameters and derivative operations. The proposed control algorithm is validated with MATLAB/Simulink simulations. Simulation results show that the proposed three-level two-leg NPC inverter injects sinusoidal and balanced currents to the grid. In addition, the designed controller provides fast transient response.

This paper investigates nonlinear control methods for single-ended primary-inductor converters (SEPIC). The fast-switching and average models show the converter nonlinearity in terms of inductor currents, capacitor voltages, and the switching duty cycle. The control law intuitively should be nonlinear to drive and guarantee the system stability. Two different control laws based on the passivity and back-stepping technique are examined and designed to have asymptotically global stability in the system. Unlike the passivity method which regulates the duty cycle directly, the back-stepping method adjusts the switching duty by a driver integrator/low pass filter system. The simulation results have shown the benefits from the passivity control law over the back-stepping one. Moreover, an observer is introduced in order to reduce the number of voltage and current sensors for the control system. The nonlinear control law is thus a combination of the measured signal and the estimated ones. Simulation results are also presented to verify the effectiveness of the observer in the control system.

In this paper, the performances of various active damping methods for model-based-current-control (MBCC) of single-phase grid-tied LCL-filtered voltage source inverters (VSIs) are investigated. It is shown that the proposed MBCC approach enforces the inverter current to track its reference in all circumstances provided that the inverter current reference is generated accurately. In this study, a proportional-resonant (PR) controller is used to generate the inverter current reference. Also, it is shown that the dynamics of this tracking can be made faster by adding an additional virtual time constant into the control variable equation. In spite of these features, the closed-loop system is subject to the adverse effects of the LCL resonance. Therefore, the possibilities of adding various active damping methods into the closed-loop system are investigated. Computer simulations are conducted to show the performance of the proposed MBCC approach with various active damping methods.

DC-DC converters are commonly used in many fields such as renewable energy sources, electrical vehicles, power supplies, battery chargers and fuel cell applications. These converters are used for purposes such as voltage conditioning, regulation of their outputs, obtaining maximum power and providing isolation. In practice, various criteria such as cost, performance, efficiency and size are considered while converter topology is determined. Filter components (L-C) which are used in DC-DC converter determine the converter size. In this study, an interleaved quadratic boost converter is designed for fuel cell applications and different inductor designs are investigated for the proposed quadratic boost converter. Four different inductor models are designed and simulation studies of the interleaved quadratic boost converter with these inductor models are carried out. Effects of the designed inductors on converter output waveform quality, total weight and volume, and converter efficiency are investigated and obtained results are compared. It is seen from obtained results that, the coupled inductor improves performance and efficiency of the interleaved quadratic boost converter.

There has been increased attention in the industry to solve consumer related power quality problems using photovoltaic based grid-tie inverters. The main idea here is to integrate active power filter features on the control algorithm of conventional on-grid photo-voltaic (PV) inverters. However, such products have not yet matured broadly in the market and calls for more research. In this study, we show a simple and effective method to suppress grid current harmonics during pushing the harvested power from PVs to the grid. The proposed grid-tie inverter can also support reactive power requirement on the load side. Moreover, the performance of the proposed control strategy is compared with the conventional grid-tie PV inverter. The proposed system is modelled using MATLAB/Simulink and also tested in real-time environment. Results are then presented as a verification of the studied system.

A sliding-mode and proportional-resonant based control strategy for three-phase grid-connected LCL-filtered voltage source inverter (VSI) is proposed. The generation of three-phase capacitor voltage references is essential in the proposed control strategy. Although the reference capacitor voltage for a specific phase can be generated by adding the measured grid voltage for that phase with the voltage drop on the grid-side inductor caused by the reference grid current, the computation of the voltage drop on the inductor requires a derivative operation which is not preferred in a control algorithm. Therefore, a proportional-resonant (PR) controller is employed to generate the three-phase reference capacitor voltages. The consequence of using PR controller is that the need for using the derivative operation is eliminated. The PR controller offers another advantage regarding the ability to track ac quantities with zero steady-state error. In addition, the equation for the optimum sliding coefficient is derived analytically. Computer simulation results are presented and reported to validate the proposed control approach.

In this paper, a modified Lyapunov-function based control strategy for three-phase grid-connected LCL-filtered voltage source inverter is presented. The grid-connected system is modeled in the synchronously rotating frame. Lyapunov-function based control is derived from the Lyapunov's direct method which guarantees the global stability of the closed-loop system. Although the conventional Lyapunov-function based control strategy offers global stability, it is not able to damp the inherent oscillations that occur on the grid current. Therefore, a modified Lyapunov-function based control strategy is proposed by adding the capacitor voltage feedback into the control loop. In the proposed control strategy, the measurement of inverter currents, capacitor voltages and grid currents are essential. The generation of reference functions in the d- and q-components can be achieved by using the reference d-component grid current. Computer simulation results are presented and reported to validate the proposed control approach.

This paper presents an optimized sliding mode control (SMC) strategy to maximize existence region for single-phase dynamic voltage restorers. It is shown analytically that there exists an optimum sliding coefficient which enlarges the existence region of the sliding mode to its maximum. Also, it is pointed out that the optimum sliding coefficient improves the dynamic response. In addition, a double-band hysteresis control which ensures the switching of a transistor in the voltage source inverter during a half-cycle while it remains either on or off in the other half cycle is used to mitigate the switching frequency. The theoretical considerations and analytical results are verified through computer simulations and experimental results. Simulation and experimental results show that the proposed SMC strategy not only compensates the undesired voltage disturbances and maintains the load voltage at desired level with low total harmonic distortion, but also exhibits fast dynamic response and operates at reasonably low switching frequency.

In this study, a new method is proposed for the suppression of voltage amplitude fluctuations on the load terminals. Moreover, the voltage harmonics on the load terminals are effectively reduced below the defined limits in the IEEE-519 standard. In the studied topology, a twelve-switch three-phase voltage source converter is used for effective control on the zero-sequence components due to the unbalanced voltages or single phase voltage sags. In order to obtain a fast dynamic response, sliding mode control strategy is used to control the system. The existence condition of the sliding mode is presented. The performance of the closed-loop system is verified with cases of voltage sag and utility voltage harmonics. The overall system is explained in detail and verified by using MATLAB/Simulink.

In this study, a novel multi-level type bidirectional half-bridge inverter for wireless power transfer applications is presented. The proposed converter provides high power application by splitting the voltage in each switch. The converter topology is explored to reveal the maximum efficiency points with a variable phase-shift function between the dual active level (DAL) switches. The analysis of the converter is provided in terms of variable load and coupling co-efficient factor at a constant switching frequency. A 1 kW contactless system is designed with an output of 100 V by testing the different load conditions at an 8 inch gap between coils. Experimental results are clearly indicate that the demonstrated system, which has an average efficiency improvement of 3% with an optimized phase shift between switches, offers higher efficiency in comparison to conventional multi-level topologies.

A double-band hysteresis current-control (DBHCC) strategy for single-phase UPS inverters with the use of proportional resonant (PR) controller is introduced. The PR controller eliminates the steady-state error in the output voltage. The output of PR controller serves as reference inductor current which is compared with the measured inductor current. The current error is then fed to the DBHCC block whose outputs are the control signals of the inverter switching devices. The use of double band hysteresis function is very effective in reducing the switching frequency of the inverter switching devices. It is shown that the output voltage can track its reference with zero steady-state error regardless of the hysteresis width. The performance of the proposed control method has been tested by simulations and experiments under resistive and diode bridge rectifier loads. The results demonstrate that the proposed method not only maintains the advantages of DBHCC method such as fast dynamic response, reduced switching frequency and simplicity in implementation, but also achieves zero steady-state error in the output voltage regardless of the hysteresis width.

A double-band hysteresis current-control (DBHCC) approach for three-phase four-switch shunt active power filters is introduced. The four-switch topology employs four switching devices and two capacitors connected in series. The phase C is connected to the midpoint of these capacitors. This topology with the DBHCC strategy has the advantages of reduced cost and switching frequency and increased reliability. It is shown that the imbalance existing in the capacitor voltages can be successfully eliminated. Also, the DBHCC strategy eliminates the unwanted load current harmonics and achieves sinusoidal supply currents having no phase difference with the supply voltages. The effectiveness of the DBHCC strategy has been simulated under a nonlinear load which draws non-sinusoidal currents from mains supply.