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This study proposes a power conversion interface for a DC grid and a single-phase utility. The proposed power conversion interface is configured using an interleaved AC–DC power converter and a DC hybrid power filter. The interleaved AC–DC power converter controls the real power between the DC grid and the single-phase utility in both directions. The interleaved AC–DC power converter can effectively reduce the high-frequency harmonic currents at both the AC side and DC side. A new current-sharing control method is used to equalise the currents in the interleaved power-electronic arms using only one current sensor in the interleaved AC–DC power converter. The DC hybrid power filter is connected between the DC bus of the interleaved AC–DC power converter and the DC grid. The DC hybrid power filter is controlled to be operated as a virtual low-frequency AC resistor connected to the DC grid in series and the low-frequency harmonic for the DC input current of the interleaved AC–DC power converter is suppressed. Accordingly, the problems of harmonic currents for a power conversion interface used between the DC grid and the single-phase utility are attenuated. A hardware prototype is developed to verify the performance of the proposed power conversion interface.

This study proposes an interleaved multi-level power converter (IMPC) for a battery energy storage system. The proposed IMPC is composed of two power-electronic legs. The first power-electronic leg is an interleaved multi-level leg that contains eight power-electronic switches. Four power-electronic switches constitute a two-phase interleaved switch set and these are switched in a high-frequency interleaved pulse-width modulation. The other four power-electronic switches constitute a level-selection switch set that determines the dc bus voltage for the two-phase interleaved switch set according to the magnitude of the utility voltage. The second power-electronic leg is the low-frequency switching leg, which is composed of two power-electronic switches. Since the proposed IMPC integrates the performances of the multi-level power converter and interleaved power converter, the effective switching frequency is twice the practical switching frequency and the output voltage has five voltage levels. The ripple of the output current is significantly attenuated and the power capacity of the output filter is reduced. The proposed IMPC can also be used to adjust the real and the reactive power flows, in order to control the charging/discharging of battery sets and to compensate for the reactive power. A hardware prototype is developed to verify the performance of the proposed IMPC.

This study proposes a novel seven-level cascade inverter (SLCI) with asymmetrical DC voltages. The proposed SLCI consists of two full-bridge inverters, a DC–DC converter (DDC) and a DC power source. The DC power source is parallel connected to the high-voltage full-bridge inverter (HVFB). The DDC is used to create a DC voltage with half of the DC power source and connect to the low-voltage full-bridge inverter (LVFB). The HVFB is switching at low frequency, and the LVFB is switching at high frequency. The salient points of the proposed SLCI are that only one DC power source is required and no transformer is used. Therefore, the power circuit for the proposed SLCI is simplified. A hardware prototype is established in order to verify the functions of the proposed SLCI. The tested results show that the functions of the proposed SLCI are as expected.

This paper presents an isolated battery charger which is configured by a seven-level AC-DC power converter and an isolated DC-DC power converter. The seven-level AC-DC power converter is composed of a diode rectifier and a three-port DC-DC power converter. The three-port DC-DC power converter generates a four-level voltage at the DC bus of the diode rectifier by controlling its power electronic switches. Accordingly, the voltage at the AC input terminals of the diode rectifier is an AC voltage with seven levels, and the input current is sinusoidal and in phase with the utility voltage to perform unity power factor. The inductance of the filter inductor and the capacity of the EMI filter can be reduced due to the seven-level AC voltage at the input AC terminals of the seven-level AC-DC power converter. The isolated DC-DC power converter is a two-level forward power converter to regulate the voltages of the three-port DC-DC power converter and generate an isolated output power to charge the battery set. A prototype is developed and tested to verify the performance of the isolated battery charger. The experimental results show the isolated battery charger performs as expected.

This study proposes a single-phase multi-level AC–DC power conversion interface that is composed of a power factor correction stage and a buck power conversion stage. The power factor correction stage is configured using two power factor correctors (PFCs) connected in cascade. Only the power electronic switch in one of the PFCs is switched in high-frequency pulse-width modulation to generate a five-level voltage at the input AC terminals of the power factor correction stage. The input current of the power factor correction stage is controlled to be sinusoidal and in phase with the utility voltage. Accordingly, the voltage stress and switching loss are improved because the change in voltage in each switching operation is reduced. The filter inductance and the electromagnetic interference are also reduced. The buck power conversion stage integrates a buck power converter and a forward power converter that combines the output voltages of the two PFCs in a stable DC voltage that supplies the load. The controllers for the buck power converter and the forward power converter are integrated to simplify the controller for the buck power conversion stage. A hardware prototype is developed to verify the performance of the proposed single-phase AC–DC power conversion interface.

A small-capacity grid-connected solar power generation system, configured by a dual-output DC–DC power converter and a seven-level inverter, is proposed in this study. Voltage doubler based topology is used to configure the dual-output DC–DC power converter to convert the output voltage of a solar cell array into two dependent voltage sources with multiple relationships. The grid-connected seven-level inverter is configured by a dual-buck power converter and a full-bridge power converter. The dual-buck power converter is switched at high-frequency pulse-width modulation to generate a four-level DC voltage. The full-bridge power converter is switched synchronous with the utility voltage, to convert the four-level DC voltage into a seven-level AC voltage. The proposed solar power generation system generates a sinusoidal output current in phase with the utility voltage. The novelty of this proposed seven-level inverter is that two asymmetric DC voltage sources are used to increase the voltage levels and only two of the six power electronic switches in the seven-level inverter are switched at high frequency. A prototype is developed and tested to verify the performance of the proposed solar power generation system. The experimental results show that the proposed solar power generation system has the expected performance.

In this study, a five-level inverter-based grid-connected power conversion interface is proposed. The output current of grid-connected power conversion interface is controlled to be sinusoidal and in phase with the utility voltage so as to perform the unity power factor. The grid-connected power conversion interface is configured by a DC–DC boost converter and a proposed five-level inverter. The DC–DC boost converter is employed to boost a lower DC voltage source. The presented five-level inverter is composed of a series/parallel capacitor set and a full-bridge converter. The presented five-level inverter contains only five power electronic switches, thus simplifying the circuit configuration. In addition, only one power electronic switch is switched in high frequency and only three semiconductor devices are conducting in series at the same time in the presented five-level inverter. Thus, the power loss will be reduced and the power efficiency will be improved. Moreover, the control for balancing the voltages of DC capacitors of the presented five-level inverter is simplified because the DC capacitors are discharged in series and in parallel alternately. A prototype is developed and tested to verify the performance of the proposed grid-connected power conversion interface. The experimental results show that the proposed grid-connected power conversion interface achieves the expected performance.

This study proposes a novel transformerless single-phase three-wire line-interactive uninterruptible power supply (UPS). This UPS comprises a three-leg power converter with series-connected DC capacitors, a decoupling circuit, a filter inductor set, a filter capacitor set, a battery set, a switch set and a digital signal processor. The first and the second power electronic legs are controlled to generate a set of mixed currents, containing DC and AC components, to perform the functions of charging/discharging battery set, active power filter (APF) and an inverter. The third power electronic leg is controlled to generate an AC current to serve as an APF and an inverter. The series-connected DC capacitors act as the energy buffer and establish the DC bus voltage for the power converter. The power flow of the power converter is bidirectional. When the utility is in the normal condition, the power converter will charge the battery set and serve as an APF. When the utility fails, the power converter will generate a sinusoidal voltage to supply the uninterrupted power to the critical loads. A prototype is developed and tested to verify the performance of the proposed UPS. The experimental results show that the proposed UPS has the expected performance.

This study proposes a novel transformer-less three-port grid-connected power converter for a distribution power generation system with dual renewable energy sources. The proposed three-port power converter is configured by a three-leg bridge converter, a common-mode circuit and a filter inductor set. The proposed three-port power converter has a high-voltage DC port, a low-voltage DC port and an AC port. The high-voltage and low-voltage DC ports are connected to the dual renewable energy sources, a solar cell array as well as a fuel cell, and the AC port is connected to the utility. The proposed three-port power converter uses the concept of the differential-mode and the common-mode paths of electromagnetic interference filter. Consequently, the three-port power converter is controlled to generate a set of differential-mode currents and a set of common-mode currents. As a result, the differential-mode currents and common-mode currents pass through the differential-mode current path and the common-mode current path to perform the power conversion between the dual renewable energy sources and the utility. A prototype is developed and tested to verify the performance of the proposed three-port power converter. The experimental results show that the proposed three-port power converter achieves the expected performance.

In this study, a three-leg power converter battery charger for the lithium-iron phosphate battery is proposed. The proposed power converter is configured by a three-leg power converter. The operating principle of the proposed three-leg power converter is based on the concept of the common mode and differential mode used in the analysis of the conducted electromagnetic interference. In the proposed battery charger, no transformer is required for matching the voltage levels between the utility with a higher AC voltage and the battery set with a lower DC voltage. Moreover, the unity input power factor can be obtained. A prototype is developed and tested to verify the performance of the proposed battery charger. The experimental results show the performance of the proposed power converter is as expected.

A novel power converter topology for three-phase four-wire hybrid power filter is proposed. It is configured by a three-arm bridge structure without split capacitors. The salient feature of the three-phase four-wire hybrid power filter using the proposed power converter is that it permits the neutral line of the utility directly connecting to the negative or positive terminal of the DC capacitor located in the DC side of the power converter. Consequently, the power converter uses less number of power electronic switches to reduce the manufacturing cost. A three-phase four-wire hybrid power filter prototype is developed and tested to demonstrate the performance of the three-phase four-wire hybrid power filter using the proposed power converter. Experimental results show that the proposed three-phase four-wire hybrid power filter using the proposed power converter has the expected performance.