In this study, a single-stage half-bridge flyback converter using a synchronous rectifier (SR) is proposed to achieve unity power factor and higher efficiency. The proposed power factor correction can achieve almost a unity power factor and low input ripple current. The asymmetrical pulse-width modulation (APWM) half-bridge flyback converter operates under zero-voltage switching to reduce switching losses. The conduction loss of the system can be reduced by replacing the diode rectifier with an SR using a low on-resistance metal oxide semiconductor field effect transistor and the SR switch operates under zero-current switching. Detailed analysis is presented on the proposed converter. Experimental results for a 24 V/200 W converter at a constant switching frequency of 100 kHz were obtained to prove the analysis.

In the past years, the development of topologies with step-up capacities has been important to satisfy the new requirement of renewable source energy. This study presents a quadratic boost converter based on the reduced redundant power processing (R ² P ²) principle, well as the controller design methodology using current-programmed control to satisfy the specifications of output voltage regulation. Non-linear and linear models are developed; the latter exhibits fourth-order characteristic dynamics with complex right-half plane zeros. In the proposed control scheme, the current of the switch is used for feedback purposes. When the current loop is implemented, the fourth-order dynamics are changed to a dominant first order, which simplifies the controller design of outer loop. For this loop, a conventional controller is designed. At the end, experimental results are given for a 23 W quadratic boost converter, where open-loop and closed-loop responses are compared.

Operation of distributed generators in microgrids has been widely discussed, but would not be fully autonomous if distributed energy storages are not considered. Storages are important since they provide energy buffering to load changes, energy levelling to source variations and ride-through enhancement to the microgrids. Recognising their importance, this study presents a scheme for sharing power among multiple distributed storages in coordination with the distributed sources and loads. The scheme prompts the storages to autonomously sense for local operating conditions, requesting for maximum charging energy only when excess generation capacity is available. As generation capacity drops or demand increases, energy drawn by the storages decreases spontaneously to avoid over-stressing the sources. When full generation capacity is near, the storages will automatically release their stored energy to help with meeting the extra load demand. The described process takes place autonomously with energy eventually shared among the storages in proportion to their ratings. To test the concepts discussed, experiments have been performed with favourable results obtained for performance verification.

This study presents the hybrid direct torque control (HDTC) method for medium voltage-range induction motor (IM) drive. The control method comprising the torque control by rotor-reference frame quadrature-axis current instead-of conventional DTC and speed control similar as in space-vector-modulation (SVM)-DTC is proposed. Hence the scheme is referred as HDTC. A carrier-based space-vector-modulation controlled five-level diode-clamped multilevel inverter with proposed control scheme is providing promising-step towards performance enhancement of IM drive in respect of torque ripple contents and steady-state performance over wide speed-range. The effectiveness of the proposed control scheme is confirmed by comparison with DTC in matlab-simulink. A prototype is fabricated for three-phase, 3-HP IM. A 32-bit fixed-point DSP-based control algorithm is developed for DTC and the proposed control scheme. Experimental results show qualitative improvement in performance in terms of reduction in torque ripple by 30%, fast dynamic response even at low speed and improvement in steady state characteristics.

For a Vienna type rectifier, unbalanced grids introduce twice the fundamental frequency ripples in dc-link voltage and input active/reactive power. To eliminate the input power ripple, the common current reference generation strategy, such as dual-frame hybrid vector control, can be adopted to maintain constant input power and eliminate ripples in dc-link voltage under light unbalanced grids. However, this control method does not work when under severe unbalanced grids. The theoretical operation area of the constant power control method under unbalanced grids is analysed in this study, furthermore, a compromised control method, which injects a small amount of input power ripple and makes a compromise between the working area and the output voltage ripples, is proposed. The control method can work when the grids have severe unbalance. The experimental operating area of constant power control is presented. The performance comparison and waveforms of three control strategies under different unbalanced grids are given.

In this study, a novel individual voltage balancing control scheme for multilevel cascade active-front-end rectifier is proposed to allow a different voltage setting capability among different dc outputs in series. First, the proportional resonant controller and admittance compensation controller are introduced for the active inner-current control loop of cascade active-front-end rectifier to achieve better steady-state and dynamic performance. Second, an assumption based on conservation of energy is proposed to decouple a series connected ac–dc system into several individual subsystems to facilitate the individual dc-bus controller design. Both simulation and experimental results based on the cascade two-unit cascade dual-buck/boost-type active-front-end rectifier proved the effectiveness of the proposed individual balancing control scheme, which also verified the proposed assumption.

In this study, a comprehensive review of existing technological solutions for wireless power transfer used in electric vehicle battery chargers is given. The concept of each solution is thoroughly reviewed and the feasibility is evaluated considering the present limitations in power electronics technology, cost and consumer acceptance. In addition, the challenges and advantages of each technology are discussed. Finally, a thorough comparison is made and a proposed mixed conductive/wireless charging system solution is suggested to solve the inherent existing problems.

In this study, a zero voltage switching (ZVS) isolated bidirectional DC/DC converter is proposed for high step-up and high step-down conversion systems. In the low voltage side, an interleaved Buck and Boost converter is employed to reduce the current ripple and improve the power level. In the high voltage side, a modified three-level structure is adopted to bring each power switch sustain half of the high bus voltage, which makes the low voltage rated MOSFETs available for the performance improvement. Two coupled inductors are interleaved in the low voltage side and in series in the high voltage side, which can not only serve as the filter inductors for the current ripple cancellation, but also as the transformer for isolation, which is named as winding-cross-coupled inductors. As a result, the magnetic size can be reduced to enhance the power density. ZVS operation is ensured from light load to full load conditions by the advanced pulse width modulation plus phase shift control strategy. The voltage regulation and transferred power are decoupled for easy design and implementation. Finally, a 1.5 kW 48 V/800 V prototype is built to verify the effectiveness of the proposed converter.

It is well known that when a wireless power transfer system bifurcates, the maximum power transfer capability reduces significantly. This research proposes a dynamic zero voltage switching (ZVS) controller to track the middle ZVS operation curve so as to maintain the peak power potential the system can deliver. A prototype wireless power transfer system has been developed, and it has found that the system can deliver 10 W power required to drive an implantable heart pump with a reduced input voltage, increased coil separation and improved end-to-end power efficiency.

A new zero-voltage switching (ZVS) DC converter with less power switches is presented in this study. The proposed converter includes three subcircuits connected in parallel with the same switches to share load current. Thus, the proposed converter has less switch counts compared with the conventional parallel ZVS DC/DC converter and the output filter inductances and the transformer windings are reduced. Three-level diode clamped converter is used to reduce the voltage stress of switches at V _in/2. The input two capacitor voltages are automatically balanced by adding two flying capacitors in three-level DC/DC converter. The current doubler rectifiers are used at the output side to reduce the output current ripple. The output capacitances of metal oxide semiconductor field effect transistors (MOSFETs) and resonant inductances are resonant at the transition interval. Thus, MOSFETs can be turned on under ZVS. Finally, experiments are provided to verify the effectiveness of the proposed converter.

Application of multilevel inverters for higher voltage goals in industries has become more popular. In this study, new structures for symmetric, asymmetric and hybrid multilevel inverter are recommended. The proposed hybrid structure is used in high-voltage levels. The proposed structures can generate a great number of output voltage levels with minimum number of power electronic components such as insulated gate bipolar transistors (IGBTs) and gate drivers. For proposed asymmetric and hybrid inverter, new methods for determination of dc voltage sources values are presented. Comparison of the results of various multilevel inverters is presented to reflect the merits of the recommended structures. The operations of the proposed multilevel inverter structures are verified with the experimental and simulation results of an asymmetric 15-level prototype and a 19-level hybrid inverter. Fundamental frequency-switching method is applied to the new topologies to trigger the power switches for controlling the voltage levels generated on the output. Verification of the analytical results is performed using MATLAB/SIMULINK software.

In this study, a single-stage power-factor-corrected flyback converter is used as the main power stage, which is controlled by a critical mode control integrated circuit and is used to drive light-emitting diode (LED) strings. Since the output voltage of this converter possesses a double line frequency ripple, one energy-recycling circuit without any control is added to render the instantaneous output power close to the instantaneous input power, so as to reduce the energy stored/released in the output capacitor and hence to reduce the output voltage ripple of the double line frequency. Accordingly, the effect of the low-frequency voltage ripple on the colour, luminance, life and stability of the LED can be reduced. For the dimming circuit to be considered, the gate voltage detecting circuit is employed herein so as to achieve efficiency improvement in LED dimming. Based on the dimming command and the variation in gate voltage, the voltage reference command for the flyback converter is dynamically adjusted so as to make the voltage across the metal oxide semiconductor field effect transistor reduced as the LED string is dimmed up/down and hence to increase the efficiency of the overall system.

In this study, a direct torque and flux control is described for a six-phase asymmetrical speed and voltage sensorless induction machine (IM) drive, based on non-linear backstepping control approach. First, the decoupled torque and flux controllers are developed based on Lyapunov theory, using the machine two axis equations in the stationary reference frame. In this control scheme, the actual stator voltages are determined from dc-link voltage using the switching pattern of the space vector pulse-width modulation inverter. Then, for a given motor load torque and rotor speed, a so-called fast search method is used to maximise the motor efficiency. According to this method, the rotor reference flux is decreased in the small steps, until the average of real input power to the motor reaches to a minimum value. In addition, a model reference adaptive system-based observer is employed for online estimating of the rotor speed. Finally, the feasibility of the proposed control scheme is verified by simulation and experimental results.

A new DC/DC pulse-width modulation (PWM) converter with the functions of zero voltage switching (ZVS) for power switches and zero current switching (ZCS) for rectifier diodes is presented for high-input voltage and high-load current applications. Three-level PWM circuit with two clamped diodes and one flying capacitor is adopted to achieve ZVS turn-on for all power switches, to balance two input capacitor voltages and to limit the voltage rating of each switch at one-half of input voltage. Two three-level PWM circuits with the same power switches are used to share the load current for medium power applications. Series–parallel resonant converter or LLC (L _r, L _m and C _r) converter is adopted to achieve ZCS turn-off for rectifier diodes. Thus, the switching losses of power switches are reduced and the reverse recovery losses of rectifier diodes are eliminated. In order to high load current application, four centre-tapped rectifiers are connected in parallel to reduce the current rating of rectifier diodes and transformer windings. Experiments are provided to verify the effectiveness of the proposed converter.

This study presents some specific problems concerning the DC–AC commutation of the power converters used in frequency controlled electromagnetic actuators. Starting from the initial conditions imposed for a low-cost simple inverter used for driving an electromagnetic vibrator, two commutation possibilities are analysed (unmodulated voltages and simple modulated voltages). The harmonic analysis performed in this study, permitted the analytic determination of the load current distortion coefficient against the control angle in the case of simple modulated voltage. The energetic performances (the real power and the power factor) of the system were evaluated through the power factor, determined analytically as a function of the operating frequency and the control angle α. The influence of the control angle on the current distortion factor has been highlighted experimentally using a programmable source, which allowed the synthesis of different waveforms at different frequencies. The novelty of this study consists in the analysis of the influence of the control variable angle α on energy parameters of electromagnetic vibrators, which allows a lower distortion factor and an appropriate power factor, both at a lower cost and lower commutation losses compared with pulse width modulation converters. Section 1 presents the technologies using commutation techniques analysed in Sections 2 and 3; Section 4 represents an analysis of the energetic performances, whereas in Section 5 experimental results for a vibro-compaction equipment are presented.

This study deals with the safety operation of AC resistance spot welding (RSW) system. The input of the RSW system is the firing angle of the silicon-controlled rectifier (SCR) during each control cycle. Wrongly choosing a firing angle may induce disastrous consequence. The range of firing angle depends on the system's power factor angle; the relation between the firing angle, power factor angle and conduction angle is highly non-linear. After comparing three methods, a simple mathematical model is proposed in this study to facilitate the online calculation of the power factor angle and selection of the proper firing angle, so that the safety operation of RSW system can be guaranteed. In this condition, the RSW machine can work at the machine's the most capacity, the calculated value of power factor angle should be the lowest limit for actual selected firing angle of SCR. Finally, experimental results confirmed the effectiveness of the proposed mathematical model.

This study presents an interleaved pulse-width modulation (PWM) converter to achieve the functions of zero-voltage switching (ZVS) for all power switches and zero-current switching (ZCS) for rectifier diodes at the secondary side. A three-level hybrid DC converter is adopted to reduce the voltage stress of power switched at one-half of the DC bus voltage and automatically balance the two input capacitor voltages. Therefore MOSFETs with 600 V voltage stress can be used at the second stage DC/DC converter after the three-phase power factor correction circuit. The fixed frequency PWM is used in three-level PWM resonant converter to regulate output voltage. Since the selected switching frequency is less than the series resonant frequency, MOSFETs can be turned on at ZVS and rectifier diodes can be turned off at ZCS. Thus, the switching losses of power switches are reduced and the reverse recovery losses of rectifier diodes are eliminated. Interleaved PWM scheme is adopted to share load current and further cancel current ripple at output capacitor side. Thus, output capacitance can be reduced. Finally, experiments are provided to verify the effectiveness of the proposed converter.

The cascaded multilevel converters are the most favorable topologies of multilevel converters. However, they have the main disadvantage of using multiple independent dc voltage sources. This study proposes new cascaded multilevel converter topologies in which the number of independent dc voltage sources is reduced. In the proposed topologies, for a specific number of voltage levels, the number of dc voltage sources is halved. Beside the number of dc voltage sources, in one of the proposed topologies the number of switches is also reduced in comparison with that of the conventional cascaded multilevel converter. A new modified pulse-width modulation method is presented to control the proposed topologies. Also, a method for compensating non-ideality of the dc voltage sources is presented. Simulation results using PSCAD software as well as experimental results from a laboratory-scale prototype are presented to verify the proposed multilevel converters.

This study presents a new boost converter based on Sheppard–Taylor topology for low-power applications. The proposed converter is capable of regulating output voltage under wide range of input voltage or load variations. Compared with the Sheppard–Taylor converter, the converter can be implemented with fewer components. The main switches of converter are turned on with zero-current-switching, and the rectifier diodes are turned off with zero-voltage-switching. A small-signal average model for the proposed converter is derived and transfer functions for the system output voltages are derived. The guidelines for the system design are provided. Finally, experimental results are given to confirm the system performance.

A novel high-voltage-boosting converter is presented herein, which combines the traditional buck–boost converter, the charge pump capacitor and the coupling inductor. By doing so, the proposed converter possesses a high-voltage conversion ratio, which can be obtained based on not only the duty cycle, but also the turn ratio so as to increase design feasibility. Above all, the used switch is driven without isolation and hence the gate driving circuit is relatively simple, thereby upgrading the industrial application capability of this converter. In this study, the basic operating principles and the associated mathematical deductions are firstly described in detail, and finally some experimental results are provided to demonstrate the effectiveness of the proposed high-voltage-boosting converter.

For low voltage motor drive applications, in order to enhance the utilisation rate of dc bus voltage and extend the operating boundary of induction motors, the modulation index is often extended from the linear modulation region to the over-modulation region. The relationship between two-level space-vector pulse-width modulation (SVPWM) and carrier-based pulse-width modulation (CBPWM) in the linear modulation region has been widely investigated and it was shown that the conventional SVPWM is a special type of CBPWM algorithm with zero sequence components injection. On the basis of that, this study focuses on investigating their relationship in the over-modulation region. Firstly, the superposition principle is adopted to analyse the features of SVPWM algorithm in the over-modulation region. Second, the modulating functions of CBPWM equivalent to SVPWM in the over-modulation modes I and II are derived, respectively, which are on the basis of the CBPWM regular sampling rule. Theoretical analysis shows that SVPWM is a special type of CBPWM algorithm not only in the linear modulation region but also in the over-modulation region, which provides a bidirectional bridge for the transformation between SVPWM and CBPWM in the full modulation region. Finally, the validity and effectiveness of the theoretical analysis are verified by simulation and experimental results.

This study presents voltage magnitude and frequency control of a three-phase voltage source inverter for distributed generations to achieve a seamless transfer between grid-tied mode and intentional islanding mode. When the grid is normal, the inverter works in grid-tied mode. On the contrary, when the grid fault occurs, the breaker connecting the inverter to the grid must be turned off and the inverter just supplies the power for local loads. By varying the frequency and the magnitude of the inverter output voltage, an output power control, with which the output active and reactive power can be precisely controlled, is presented. To improve the transient response, a virtual inductor with high-pass filter in synchronous d–q frame is proposed. The effectiveness of the virtual inductor is explained by the frequency response of the inverter. Finally, experimental results are given to verify the effectiveness of the scheme.

Multilevel converters are growing fast, whereas industry needs particular tools to evaluate efficiency and performance of such converters. This study focuses on the analysis and practice of power losses in a three-level neutral-point clamped (NPC) inverter. First, a precise mathematical model for three-level inverters is introduced to be used for simulating power losses of the switches, providing AC voltage and current of each phase, voltage and current of the switches as well as both the conduction and switching losses. Further, an NPC inverter was developed to validate the analytical work by comparing experimental results with those of simulations. Additionally, the thermal modelling of semiconductors is obtained using datasheet parameters. Then, the temperature rise is further modelled using the power losses along with the thermal model in the form of RC ladder. Finally, the lifetime of semiconductors is predicted using the heating curves in line with the power-cycling concept. The measured power losses and temperatures in comparison with the presented model suggest this kind of research as an applicable replacement for expensive measuring devices.

This study presents new direct regular-sampled pulse width modulation (DRSPWM) for grid connected three-phase current source inverters. The theoretical basis of the presented modulation strategy is described in detail and includes dwell time calculations and switching sequence selection. The modulation strategy is simple and suited for digital implementation, and has the flexibility and degree of freedoms of space vector modulation. This is because some switch sequences ensure a minimum number of switching transitions per fundamental cycle, unlike other methods presented in the literature. It is therefore applicable for high-power medium-voltage applications. The validity of the presented DRSPWM is confirmed using simulation and experimentation of a current source inverter, in open and closed-loop operations.

A comparative study of linear current-mode controllers (using input and output inductor currents) for regulation of a high-order boost dc–dc converter is presented. The high-order boost converter gives a much higher output voltage as compared with that obtained from the conventional boost dc–dc converter. It is demonstrated that the current-mode controller using the output inductor current is the most appropriate for the high-order boost converter. Experimental results showing the effectiveness of the proposed controller in the presence of load disturbances are also presented.