A transformer-less dynamic voltage restorer (DVR) with bipolar voltage gain capability is proposed in this study. The DVR is formed by a three-leg ac/ac converter with its output capacitor in series with the transmission line. Since the energy used for voltage compensation is obtained from the grid, long-time voltage disturbances can be compensated without using bulky energy storage elements. As a result, the proposed DVR has the features of compact structure, light weight, and low cost. Moreover, it also has a high reliability as the commutation problem is avoided by adopting the proposed modulation strategy. A detailed analysis of the topology structure and operation principle is given, followed by the developed control method. Finally, simulations and experimental results are presented to verify the validity of the DVR.

A new 11-level inverter using a coupled inductor and a transformer is proposed. The proposed inverter increases maximum output voltage and decreases current stress on switches. A comprehensive comparison is conducted among the proposed inverter and some of the recent presented inverters in terms of number of components, maximum output voltage, and voltage and current stresses on the switches. Moreover, the design calculations of a single-phase inverter in addition to the transformer and coupled inductor design are given. In order to verify the performance of the proposed topologies, the experimental results are presented.

The performance of a sensorless predictive current controlled boost converter is usually susceptible to the accuracy of the employed converter and current estimator models. Since the accuracy of conventional current estimator would be degraded due to parasitic parameter variations, a charge balance current estimator (CBCE) is proposed to overcome this issue. Its estimation of peak inductor current is based on the charge balance principle of output capacitor and characteristics of inductor current ripple. Only one parasitic parameter – capacitor equivalent series resistance (ESR) is used in CBCE. Furthermore, the capacitor ESR is also estimated together with output load by a proposed equivalent load estimation scheme which can improve the current estimation accuracy. Besides, to achieve a high dynamic performance digital control, a discrete-time model considering current ripple is developed, in which the ripple is taken into account rather than treats inductor current as a constant in each switching cycle. It can achieve a higher accuracy than conventional averaged model, especially in the high-frequency region. Finally, its effectiveness is verified by simulation and experiment results.

A selective finite states model predictive control is proposed for a grid interfaced three-level neutral point clamped solar photovoltaic inverter. The proposed control approach eliminates the weighting factor selection for dc-link capacitor voltage balancing and reduces the computational burden for real-time implementation. The switching states required for the prediction and objective function optimisation are selected based on the position of reference voltage vector in the space vector plane, inverter current directions and the charge status of the dc-link capacitors. As a result, the selection of optimal switching state is fast, easy to implement and eliminates the selection of weighting factor for capacitor voltage balancing. The feasibility of the proposed control approach is verified through simulation and laboratory-scale experimentation. The results confirm that the proposed method attains the inherent dc-link capacitor voltage balance and also retains the dynamic and steady-state current tracking in comparison with the classical finite control-set model predictive control.

In this study, a new non-isolated high step-up dc–dc converter using one switch and low-voltage stress on semiconductors is presented for photovoltaic applications. The proposed converter consists of one switch in the input side (S), voltage multiplier units (D–C–L), one diode in the output side (D _o) and one capacitor (C _o). To achieve high-voltage gain and power level, the proposed converter can be extended to n stages of voltage multiplier units. Hence, the output voltage level will be reasonably increased and the nominal value of power devices will be decreased. Therefore, the voltage stress across the power switch is decreasing for different duty cycles at high power levels. As a result, the efficiency of the proposed converter can be increased by using one switch with lower resistance r _DS(on). To verify the carried mathematical analysis of the proposed converter and circuit implementation are validated through both the simulation and experimental results that accordance each other well. The experimental results of two prototypes (with n = 2, 3) in about 290 W operating at 33 kHz are provided.

In the two-stage photovoltaic (PV) micro-inverters, the bipolar hysteresis current control with soft switching for dc/ac inverter can achieve fast dynamic response, robust current regulation and high efficiency even with higher switching frequency. To further reduce the switching losses, unipolar hysteresis current control is desirable. However, it suffers from zero-crossing distortions and low frequency harmonics in the grid current. To solve those problems, this paper proposes a combined proportional resonant (PR) and hybrid hysteresis current control strategy. By investigating the reasons for zero-crossing distortions, hybrid hysteresis current control is applied to enable bipolar modulation around the zero-crossing zone and unipolar modulation in all other zones of the line period. At the same time, due to the wide hysteresis bands for soft switching, low output inductance and non-negligible sampling intervals from the digital controller, there will be many low frequency harmonics in the spectrum of output inductor current which deteriorates the quality of power absorbed by the grid. Therefore, the PR control may be used as well to mitigate the low frequency harmonics. The theoretical analysis of the proposed solutions are explained in this paper. Detailed simulation and experimental results are presented to verify the feasibility of the proposed control strategy.

Magnetic coupling resonant-wireless power transfer (MCR-WPT) has attracted considerable attention in recent decades. A relay-coil structure is utilised to extend the transfer distance between the transmitter side (Tx) and receiver side (Rx). This structure increases the complexity of analysing and optimising the operation of the system. The optimal compensatory capacitors of a three-coil wireless power transfer (WPT) system with a relay coil were investigated based on the transfer efficiency. The WPT system is modelled according to the circuit theory using the magnetic coupling between the Tx and the Rx. The condition to derive the optimal efficiency is deduced into a polynomial equation using only the compensatory reactance of the relay coil. These real solutions are theoretically compared to determine the global optimum. An experimental prototype is implemented, and the experimental results agree well with the calculations.

This study is focused on modulation strategies and soft-switching techniques of the isolated dual-active-bridge (DAB) converter for power-electronics applications, where wide input/output voltage and power ranges are required. The aim of this work is to study the different operation modes and to propose a modulation schema combining five operation modes. The objective of the proposed control strategy is to reduce the switching losses of semiconductors and to improve the overall converter efficiency. Thanks to the use of the single-active-bridge modulation, the zero-voltage-switching (ZVS) region of the DAB topology is extended, achieving high-efficiency levels in a wide operation range, even with output voltages close to zero. New analytical expressions are presented in this study to model accurately the behaviour of the DAB converter operation in this extended ZVS region. The influence of non-dissipative snubbers is also studied including experimental measurements with an insulated gate bipolar transistor-based 10 kW prototype for the validation of the theoretical study.

Photovoltaic (PV) source simulators are widely used to evaluate the performance of solar inverters and study their grid integration issues in the laboratory settings. Most of the commercial PV simulators are designed based on the programmable dc power supply platform. Owing to bulky output capacitors, the dynamic response and the bandwidth of these PV simulators are significantly limited, which, therefore, cannot meet the requirements to test advanced features of the solar inverters. In this study, a cost-effective high bandwidth PV simulator is proposed. A three-phase interleaved buck converter is utilised as the power stage and a novel sliding mode duty-cycle controller with auto current balancing algorithm is proposed to ensure the accurate and fast reference tracking along with phase current balancing. Both simulation and experimental studies are carried out to validate the feasibility and effectiveness of the proposed PV source simulator.

In this study, an improved control method of the grid-connected inverter is presented to enhance the harmonic suppression. The capacitor-current-feedback-based active damping is applied to the LCL-type grid-connected inverter, which is controlled in the virtual synchronous generator mode. A virtual-impedance design method based on modulation signal is proposed, which can not only enhance the stability of the inverter under the weak-grid situations, but also improve the quality of voltage and current. The transfer function and the impedance model of the system are established to analyse the performance of the methodology. Finally, the experiment results are presented to verify the correctness and effectiveness of the control method.

This study presents a time domain modelling method for sources of electromagnetic disturbance. For the identification of an equivalent model, the proposed method is based on the synchronised temporal measurements of the magnetic near field above a power electronic system. To determine the parameters of the model, the proposed methodology is combined with an optimisation method based on the genetic algorithms. Unlike the classical approaches developed in the frequency domain, the proposed method allows finding a valid equivalent model for all radiation frequencies of measured time signals. It also enables knowing the phase shift in time between the radiating sources. The proposed method is applied in order to find the equivalent radiating sources of an AC/DC flyback converter. The accuracy and precision of the proposed method are validated by the good agreement between the measured cartography of the magnetic near field and that calculated using the parameters of the developed model. Finally, the latter's parameters are used to predict the cartography of other components of the magnetic field, which will be compared with the measured cartography. The superposition of the results confirms that the identified equivalent sources can represent real sources in the studied structure.

This study presents a bi-directional single-inductor multi-input single-output battery system with state-of-charge (SOC) balancing controller. In the discharging operation mode of the battery system, the SOC balancing between multiple batteries is achieved by adaptively modulating the multipliers of the discharging rate of each battery cell, while maintaining the output voltage regulated at the desired value by modulating the average value of duty cycle of the power converter. The SOC balancing is achieved naturally during the operation of the system without extra energy dissipation or charge transfer between the batteries. In the charging operation mode, each battery can be charged independently by using the same bi-directional power stage. The convergence ability of the SOC balancing controller is discussed and results obtained from a proof of concept experimental prototype are presented and discussed in order to evaluate and validate the operation of the controller and system.

A new non-isolated high-voltage gain three-port converter for standalone photovoltaic systems is proposed. The magnetic element of this converter is only one coupled inductor. The primary winding of the coupled inductor is shared between battery charger circuit and main converter. Leakage inductance energy of the coupled inductor is either transferred to battery or is regenerated via the passive-clamp circuit. Using switched capacitor and voltage lift techniques, the voltage gain is significantly increased for both low-voltage ports. Single magnetic element, high-voltage gain with reasonable duty cycle, low-voltage stress on the switches, low winding turn ratio of coupled inductor and high efficiency are the merits of this converter. The operation principles and the steady-state analysis are described for the three modes of: single-input single-output, single-input dual-output and dual-input single-output. To verify the theoretical analysis, a laboratory prototype with 28 V input, 48 V battery voltage and 380 V output voltage is implemented and tested.

Features of the wide input voltage, high efficiency, and high power density are eagerly required in electric vehicle charging pile applications (EVCPA). To realise these features, this study devises a novel variable frequency and double phase-shift hybrid modulation method into the full-bridge three-level LLC resonant converter for EVCPA. Therein, this study deeply analyses the characteristics and conditions of soft switching in dual phase-shift operations, and wide voltage gain range realisations under technique of variable frequency. A 10 kW/400 V/25 A prototype with 95.5% efficiency is built for verification, whose experimental results show that the proposed converter can well achieve the aforementioned features to further drive its wide applications.

In this study, a method for suppression of common-mode current in the transformerless cascaded H-bridge (CHB) photovoltaic inverter is proposed. The proposed approach reduces the leakage current in the transformerless 5-level CHB inverters to a negligible value. By adding an ac switch to the structure of the CHB inverter, a new redundancy state for synthesising the zero voltage is obtained. Using this new redundancy state and available switching redundancies, the common-mode voltage is kept constant and the leakage current is reduced. The performance of the proposed approach is compared with the already existing approach for reduction of leakage current, in the MATLAB/Simulink environment. Experimental investigations are also provided to verify the theoretical and simulation results.