According to studies on active damping and the stability margin, grid impedance variation does not make active damping ineffective; instead, it attenuates the stability margin. The harmonic resonance mechanism of grid-tied inverters has been revealed by researching the influence of stability margin reduction on harmonic current amplification coefficients around the cut-off and phase crossover frequencies. With the stability margin decreasing, amplification to harmonics around relevant frequencies is strengthened. The harmonic resonance around the cut-off frequency is triggered as the stability margin decreases to zero. An online phase margin (PM) compensation strategy is proposed in this study to improve system robustness to grid impedance variation. The strategy is implemented by the lead network to enhance the phase and the proportional component to regulate the cut-off frequency according to the grid impedance measured online. Hence, the system can be maintained with a sufficient PM to mitigate the harmonic resonance caused by grid impedance. Simulation and experimental results validate the theoretical analysis presented in this study. Comparisons show that the proposed strategy is superior to the zero compensation strategy in suppressing the harmonic resonance.

This study considers the design of a solar photovoltaic (PV)-based stand-alone system using a battery for energy storage. Its main feature is a new boost inverter, derived by integrating a dc–dc buck–boost converter and a full bridge dc–ac inverter, which can perform simultaneous voltage boosting and dc–ac conversion. Inclusion of this inverter has led to the development of a three stage stand-alone scheme which can operate with low voltage level(s) for the PV and the battery. The logical evolution and operating principles of this inverter are presented, followed by an overview of the entire stand-alone scheme and its control structure. The complete scheme is validated both by detailed simulation studies and exhaustive experimental studies on a laboratory prototype.

In this study, a zero voltage transition (ZVT)–zero current transition (ZCT) pulse-width modulated (PWM) multiphase synchronous buck converter (SBC), with an active auxiliary circuit is proposed, that reduces the stresses and enhances the efficiency abating the switching and conduction losses of the converter. The important design feature of ZVT–ZCT PWM multiphase SBC converters is the placement of resonant components that pacifies the switching and conduction losses. Due to the ZVT–ZCT, the resonant components with low values are used that results in the increase of switching frequency. High current multiphase buck converters found applications in the advanced data control, solid state lasers, communication equipment, Pentium processors etc. The ZVT–ZCT operation of the proposed converter is presented through theoretical analysis. A simple design method for the auxiliary circuit is discussed. The characteristics of the proposed converter are verified with the simulation in the PSIM co-simulated with MATLAB/SIMULINK environment and validated with experimental results.

Converter parallel techniques can increase the power rating, but there is a circulating current problem. Therefore, this study focuses on the circulating current problem in parallel full-scale wind power converter systems. The general definition of circulating currents is first introduced. The concept of circulating current percentage is then defined to quantitatively analyse the relatively serious situation of circulating currents for parallel converter systems. Then, the generation mechanisms of circulating currents are analysed based on the mathematical model of circulating currents. Actually, circulating currents can be regarded as a kind of disturbance to the load currents of a parallel system. Thereby, a novel control strategy, based on circulating current feed-forward compensation for parallel converter systems, is proposed and a feed-forward controller is designed. Finally, simulations based on MATLAB/Simulink and hardware-in-loop experiments based on RT-LAB are carried out. Both simulation and experimental results validate the proposed circulating current control method.

Three-dimensional space-vector modulation (3D SVM) has more popularity among the other modulation techniques of the four-leg inverter due to higher DC-link voltage utilisation. Sequencing schemes of the switching vectors in the 3D SVM are divided into Class I and II categories. Each of these classes itself has four kinds: (a) rising-edge aligned, (b) falling-edge aligned, (c) symmetrically aligned and (d) alternative sequence. In this study, implementation of the conventional 3D SVM technique in abc-coordinate for four-leg voltage source inverters is simplified, while it can be so easily adopted in all kinds of sequencing schemes. Unlike conventional techniques, the proposed technique needs no switching vector determination and duty ratio calculation as well as reduces the computational burden. In this technique, turn-on interval of the upper switches, in every switching period, is calculated without need of a look-up table and complex equations. Applying the dead time by software is very straightforward in the proposed technique. In addition, by simplification of the proposed modulation technique, it can be applied to the three-leg inverters. Simulation results in PSCAD/EMTDC environment confirm the validity and effectiveness of the proposed technique. Experimental results are also provided to confirm the validity of the new approach.

This study presents an active third-harmonic injection indirect matrix converter (3HI2MC) topology with dual three-phase outputs. The presented 3HI2MC has the advantages of sinusoidal input and output currents, bi-directional power flow, and can provide two sets of three-phase outputs, whose frequencies and amplitudes can be regulated independently. Compared with the conventional indirect matrix converter (IMC), the input reactive power control range is extended significantly, and the converter can even work as a static compensator. Moreover, a maximal voltage transfer ratio of 0.866 is achievable under all operation conditions. Furthermore, operations of the rectifier and inverters are independent. Thus, for a 3HI2MC system containing multiple voltage-source-type inverters (VSIs), modulation and control task can be implemented flexibly by a separate controller for each VSI, while it is difficult for the conventional IMCs to achieve such a goal. All of the features above make 3HI2MC competitive for the applications that require multiple three-phase outputs such as multiple drives. After describing the topology structure, operating principles and control algorithm in detail, simulation and experimental results are presented to demonstrate the validity and effectiveness of the proposed topology.

This study proposes a new control method for Z-source inverter (ZSI) – called the one-dimension ZSI (ODZSI) – based on the single-phase modulator technique. The notable feature of the proposed control compared with the space-vector modulation strategy is its reduced computational processing time, which is attractive for digital implementation. Compared with the maximum boost control (MBC), which uses carrier-based pulse width modulation control methods, the proposed algorithm enhances the output voltage and current quality. In this study, the results of MBC are compared with those obtained with a single-phase modulator for three-phase ZSI showing its advantage for improving the line output current and voltage total harmonic distortion. The obtained simulation and hardware results ensure the feasibility and validate the performance of the ODZSI modulation method applied to each phase. The proposed method is easier for digital implementation with less computation, and will be beneficial for further industrial applications of ZSIs. The simulation results are carried out using MATLAB/Simulink, and the hardware performance are provided and discussed.

This study describes the design and development of a 20 kV rated damped oscillating voltage (DOV) generator that can detect the partial discharge (PD) condition in 6/10 kV power cables. A complete system using a novel high-voltage switch consisting of a series of connected insulated gate bipolar transistors (IGBTs) is designed and tested. The switch consists of ten identical IGBT switch units, a multiple output isolated power supply system and a trigger unit. Physically, it is a 60 cm diameter fan-shaped printed circuit board. To coordinate the various tested objects and to comply with the IEC 60060-3 standards, an air-core inductor is calculated to precisely fit the most general application conditions using the magnetic vector potentials method. A laboratory prototype is assembled and tested. Waveforms illustrating the performance of the IGBT switch and the output of the DOV are presented. Finally, an application-oriented test demonstrates that the scheme can successfully complete the PD test and PD location test for a cable sample.

To understand the functioning of the gallium arsenide (GaAs) pin diode and to allow predictive simulations it is essential to have knowledge of the underlying physics. The GaAs pin diode is described with the help of experimental and simulation results. The static characteristics of 15 A – 600 V GaAs pin diodes were measured at ambient and elevated temperature. A quasi-one-dimensional simulation model was designed and compared with experimentally measured results. The surge current behaviour was investigated for GaAs pin diodes at two different temperatures. A thermal simulation was performed to give an overview over temperature distribution inside the GaAs pin diode. Several important physical device models and various parametric data were incorporated for theoretical investigation of these diodes. Good agreement between experimental and simulated results of GaAs pin diodes was found at all temperatures.

Multilevel inverter (MLI) is receiving remarkable recognition due to its reduced voltage stress across the power switches and low total harmonic distortion in output voltage. However, MLI incorporates large number of semiconductor switches and hence increases its complexity. In this study, new structures of symmetrical and asymmetrical MLI are proposed. The proposed structures offer reduced number of controlled switches, power diodes, capacitors and DC sources as compared with classical and recently proposed topologies in the line. Reduction of switch count, driver circuit and DC voltage sources reduces the size, cost, complexity and enhances overall performance. Moreover significant reduction in voltage stress across the switches can be achieved. A comparative analysis of proposed topologies with the classical topology and recently published topologies has been made in terms of controlled switches, power diodes, driver circuit requirement, DC voltage sources and blocking voltage. Multi-carrier pulse width modulation strategy is adopted for generating the switching pulses. The detailed simulation study of the proposed topology has been carried out using MATLAB/Simulink and feasibility of topology has been validated experimentally.

This study presents the analysis and results of a technique that allows the conventional series resonant DC/DC converter to work as a step-up and step-down converter. The controller can choose between several novel step-up modes and the traditional step-down mode. These modes are analysed by presenting their DC characteristics. The choice of mode is governed by the converter's main controller. The converter reduces the operation frequency range and maximises efficiency by selecting the appropriate mode for the particular load and voltage conversion ratio case. Experimental results in a 6 kW prototype validate the analysis and the proposed controller. Finally, the presented converter is compared with a step-up fixed mode converter in order to appreciate the advantages.

This study presents a new zero-voltage-switching (ZVS) buck converter. The proposed converter utilises a coupled inductor to implement the output filter inductor as well as the auxiliary inductor which is commonly employed to realise ZVS for switches. Additional magnetic core for the auxiliary inductor in traditional ZVS converters is eliminated and hence reduced cost is achieved. Moreover, thanks to the series connection between the input and output, the switch voltage stress in the steady state is reduced and thus the ZVS operation can be easier achieved. Then the leakage inductor current circulating in the auxiliary switch is decreased, contributing to reduced conduction losses. In particular, low-voltage rating devices with low on-state resistance can be adopted to further improve efficiency in applications with non-zero output voltage all the time, such as the battery charger. Furthermore, the reverse-recovery problem of the diode is significantly alleviated by the leakage inductor of coupled inductor. In the study, operation principle and steady-state analysis of the proposed converter are presented in detail. Meanwhile, design considerations are given to obtain circuit parameters. Finally, simulations and experiments on a 200 W prototype circuit validate the advantages and effectiveness of the proposed converter.

To reduce the active power filter (APF) system switching loss, the usual method is to apply different soft-switching techniques. However, this would increase the system initial cost. In this study, a switching loss and switching noise reduction control strategy for APF under reactive power and current harmonics compensation is proposed, which can be applied to the existing APF systems in worldwide, thus causing economic benefits. The minimum dc-link operating voltage of APF is computed through both fundamental and harmonic frequencies analysis. Then an adaptive dc-link voltage controller for the APF is proposed, such that the compensating range of the APF is adaptively varied according to the variation of the loading. Thus, the switching loss and switching noise of the APF can be lowered. Moreover, the design criteria of the proportional and integral gains of the adaptive dc voltage controller are presented and discussed. Finally, simulation and experimental results of a 110 V, 5 kVA APF experimental prototype are given to prove the validity of the proposed control strategy for the APF in current quality compensation, and at the same time reducing switching loss and switching noise during operation.

The constant power control strategy of matrix converter (MC), which is commonly adopted in practice to suppress input disturbances, could result in system instability and oscillations of source currents and input voltages. To stabilise the system, a novel control method is proposed in this study, which is based on filtering the input voltages in stationary frame with digital high-pass filters of zero gain at the fundamental frequency. The filtered signals are injected to input currents so as to increase the input admittances for stability improvement. Since the filtered signals do not contain any fundamental frequency components, the proposed method would not affect the normal operation of MC. No matter the operation mode of MC is motoring or generating, the proposed method is always effective to improve system stability by adjusting the proportional coefficient and time constant of the digital filters. The feasibility and validity of the proposed method is verified by experimental results.

A new full-bridge converter is presented to have the advantages of low conduction loss and wide zero-voltage switching (ZVS) range. The proposed converter includes two dc–dc converters connected in parallel to reduce the current stresses of power components. Each dc–dc converter integrates a phase-shift pulse-width modulation full-bridge circuit and an un-regulated half-bridge circuit sharing the lagging-leg switches in order to reduce the switch counts. The un-regulated half-bridge circuit is adopted to extend the ZVS range of the lagging-leg switches to improve the drawback of the narrow ZVS range in conventional full-bridge converter. Two dc–dc converters share the lagging-leg switches so that the switch counts in the proposed converter are less than the switches in conventional parallel full-bridge converters. The resonant capacitors are used on the primary side of full-bridge converters to reduce the primary current to zero at the freewheeling state. The secondary windings of full-bridge and half-bridge converters are connected in series to generate two positive voltage levels at the secondary rectified voltage. Therefore, the output inductor voltage at the freewheeling state is decreased and the output inductor size is reduced. Finally, the effectiveness of the proposed converter is verified by the experiments.

Multi-functional grid-connected inverters (MFGCIs) not only interface renewable energy sources into the utility, but also provide ancillary power quality enhancement service. Therefore, extra installment of power quality conditioners can be partially avoided in a micro-grid including MFGCIs. Because the capacity of an MFGCI employed for power quality compensation is limited, how to balance the multiple functions and optimally utilise the limited capacity becomes a challenging for MFGCI application, and this is studied in details in this paper. First, to set up a benchmark for balancing the multiple functions of the MFGCI, a comprehensive power quality evaluation (CPQE) index is presented based on the catastrophe decision theory to quantify the power quality of a micro-grid. Then, for the strategic utilisation of the limited capacity, a multi-objective optimal compensation model is proposed in which the objectives are to optimise the CPQE index and minimise the occupied capacity of an MFGCI for power quality compensation. Finally, the solutions of the model are derived on the basis of Pareto approach. As a result, the MFGCI can flexibly customise the power quality of the micro-grid according to its available capacity margin and the users’ requirement. Finally, the experimental results performed on a 10 kVA MFGCI prototype have confirmed the validity of the proposed model.

During the past few decades, a constant global effort to increase clean energy production by driving down the overall production and conversion costs has paved way for many efficiency-enhancing technologies in the field of power electronics. Marine propulsion systems incorporating power inverter systems have become the ‘new frontier’ for various marine utility applications. Hence, an inverter system with high efficiency and faultless performance has become a necessity. A novel tank-less, non-resonant soft-switched inverter that operates at high switching frequency is presented in this study. High-frequency inverter operation offers advantages in terms of power quality, output voltage distortions, and dynamic current control. The proposed inverter topology is able to achieve zero current/voltage switching throughout the load operating range without the use of any bulky resonant tank circuit. Key results of the inverter operating at 5 kHz and with a load power of 1 kW are documented. The experimental results confirm the effectiveness of the design.

This study described a novel digital regulation scheme for multimode primary-side controlled flyback converter. This approach ensured good energy continuity at the modes transition points of the converter. Compared with the normal control methods, the proposed digital regulation scheme could achieve smooth modes transition and suppress the large output voltage ripple when the converter works at the boundaries of different working modes. A prototype of a multimode primary-side controlled flyback converter had been made to verify the proposed digital regulation scheme.

The droop control method is one of the simplest methods for load sharing control of multiple converters. Although the current sharing precision can be adjusted to be well through the droop parameter, the voltage regulation precision is hard to be maintained well due to the voltage droop. In addition, the stability and dynamic response is usually degraded since the small-signal model of multiple converter system is usually changed significantly. To cope with these two limitations, this study presents an improved droop control method with automatic master to correct the voltage regulation. A robust control scheme is also provided to maintain a good stability and dynamic response as the design of the normal condition. The proposed method is confirmed with some simulation and experimental results.

In this study, the structure of Y-source converter is improved in order to achieve continuous current at the input side of the Y-source converter. Continuous input current reduces the size and stress of utilised elements. In addition to shoot-through duty cycle, the proposed converter uses coupled transformer to produce the required voltage gain. The obtained gain can be tuned by varying the turns ratio of the coupled transformer. Shared core is used for all windings. Hence, the cost of transformer is almost fixed in comparison with the related structures, but voltage gain is much higher than similar structures. The operating principles and steady-state analyses are presented to express the operational concept. Also, experimental results are given to verify the validity of the proposed converter.

A simple and robust digital peak current mode controller is proposed in this study. The controller replicates an analogue peak current mode control in the discrete domain. The inner current loop has negligible delay, which results in a high controller bandwidth. The controller structure allows the compensation slope to be updated in each switching cycle; therefore, the controller can maintain a high bandwidth over a wide range of operating points. The modelling principles of an analogue peak current mode controller are used to model the proposed controller. For experimental verification, the controller is implemented in a field programmable gate array to control a 100 W buck converter. The measured loop gain of the system correlates very well with the modelling results. The achieved controller crossover frequency is ∼1/10 of the switching frequency which is close to the crossover frequency of analogue peak current mode controllers.

This study presents the system analysis and circuit implementation of a new hybrid DC/DC converter. The proposed circuit includes a dual three-level converter and an un-regulated half-bridge converter. The un-regulated half-bridge converter, shared the lagging-leg switches of three-level converter, is adopted to extend the zero voltage switching (ZVS) range of lagging-leg switches. The dual three-level circuit based on phase-shifted pulse-width modulation is adopted to regulate the output voltage and reduce the current stress of passive components on the output side. To overcome the high circulating current losses in conventional three-level converter, a resonant capacitor is used on the primary side to reduce the circulating current to zero in the freewheeling interval. The secondary windings of three-level converter and half-bridge converter are connected in series so that the rectified voltage on the secondary side is positive instead of zero voltage in the conventional three-level converter. Therefore, the output current ripple can be reduced. The main advantages of the proposed converter are low circulating current losses, low voltage stress of switches, wide ZVS range and less output current ripple. Finally, experiments based on a 1920 W prototype are provided to validate the theoretical analysis and the effectiveness of the proposed converter.

A novel sectional linear driving method for light-emitting diode (LED) driver is studied. Considering several issues to be concerned in LED lighting applications, a complete introduction and analysis of the technique is proposed in this study. As the performance of the sectional linear LED driver can be affected by the LED distribution in each LED sub-string, a behavioural model is established to guide the design. Simulation results are obtained by utilising the behavioural model to optimise the output power and efficiency. The LED driver is fabricated with a 1 µm 5 V/20 V/500 V BCD technology, and a 15-W T-8 LED tube light prototype is established on the basis of the driver IC. A series of experiments are conducted to verify the theoretical analysis and the accuracy of the proposed model. The experimental data agrees with the simulation results, above 0.9 power factor (PF) and 90% efficiency are achieved with few peripheral components based on the design guidance made by the proposed model. Both the driving technique and the behavioural model are believed to be useful in the high efficiency, high PF, and cost-effective ac LED lighting applications.

This study presents a high-voltage gain zero-current switching (ZCS) push–pull resonant converter for small energy sources. The converter provides a high voltage from a 12 V _DC battery via isolated transformer and full-bridge rectifier. The main switches of the push–pull and full-bridge diode rectifier operate under ZCS condition. The advantage of this technique is the use of leakage inductance for ZCS operation of the power switch and in designing the secondary side of a resonant tank. A prototype high-voltage gain push–pull resonant converter was built and operated at 110 kHz fixed switching frequency, 350 V _DC output voltage, and 200 W output power to analyse the effect of parasitic junction capacitance of the full-bridge rectifier, which significantly affects the operating point of the resonant tank and the voltage. This study introduces the implementation and design using the data of a single diode to calculate the parameters. The simulation and experimental results verified the proposed and designed circuits. Both results agreed with the theoretical analysis.

Since shunt active power filters (SAPFs) are designed to inject harmonic current, its bandwidth should be much wider compared to regular inverters. LCL filters are commonly employed in regular inverters. However, it cannot completely meet the requirements of SAPF due to its filtering performance and the impact on system stability. This study proposes a novel double resonant LCL (DR-LCL) filter for SAPFs. Derived from the conventional LCL filters, one RC damping circuit and two LC resonant circuits are employed in the proposed filter. Meanwhile, a resistor is connected in parallel with the grid-side inductor. The mutual impact among different components of the filter is discussed, and the stability of SAPF with DR-LCL filter is studied. This DR-LCL filter can not only inherit the advantages of LCL filters, but also eliminate the tradeoff between bandwidth and switching ripple in SAPFs. Finally, the design principle of the proposed output filter is presented and the parameters of the filter are applied to a 66 kW three-phase three-wire SAPF prototype. Simulation and experimental results verify the feasibility of DR-LCL filter.