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This paper develops a cascaded AC-DC power conversion interface (CADPCI) to convert AC power to charge the battery set. The proposed CADPCI is composed of a cascaded converter (CC) and a dual-input buck converter (DIBC). The CC is formed by connecting a full-bridge converter (FBC) and a bridgeless rectifier (BLR) in series. The CADPCI generates an 11-level input voltage and performs unity power factor correction. The switching loss is reduced because only the FBC with a lower DC port voltage is switched at a high frequency. The DIBC uses a buck converter and a selection switch set to generate a two-level DC voltage on the DC port of the BLR. By controlling the DC input voltage of the buck converter, the injected power of the BLR can match the input power of the utility. Therefore, the FBC does not require to handle the real power, saving an isolated converter for regulating the DC port voltage of the FBC, thus simplifying the power circuit of the CC. The buck converter also acts as a DC active filter to filter out low-frequency ripples of the charging current. A prototype is constructed to verify the performance of the proposed CADPCI.

A bidirectional dc–dc wireless power transfer (WPT) based on LCC-C resonance compensation is proposed in this article. For the power flowing from the primary side to the secondary side (P2S), the voltage source is converted to a current source (V–C) on the primary side and the current source is converted to a voltage source (C–V) on the secondary side. For the power flowing from the secondary side to the primary side (S2P), the V–C conversion occurs on the secondary side and the C–V conversion occurs on the primary side. The proposed bidirectional dc–dc WPT using LCC-C resonance compensation exhibits several advantages: 1) it operates in bidirectional power flow; 2) it prevents burn out of the coil when there is an open circuit on the load side or the coils are misaligned; and 3) it outputs a constant current (CC) or a constant voltage (CV). A hardware prototype is designed using the specification SAE-J2954, the operating frequency is 85 kHz, the maximum output power is 3.7 kW and the vertical distance for the coil gap is 15 cm. The experimental results verify that the proposed bidirectional dc–dc WPT performs as expected.

A power converter for 60–400 Hz bilateral power conversion (BPC) is proposed in this article. This power converter is composed of three power switch arms, a set of filter inductors, a frequency decoupling circuit, a 60 Hz ac capacitor and a 400 Hz ac capacitor. The proposed BPC has the salient feature that it has the function of 60–400 Hz bilateral power conversion using only one power electronic converter. Hence, the proposed BPC can simplify the power circuit. Both simulation and experimental results verify the performance of the proposed BPC is as expected.

This paper proposes a photovoltaic power conversion topology (PVPCT). The proposed PVPCT is connected to the utility grid, a PV array and emergency loads. The proposed PVPCT comprises a boost DC-DC power converter (DDPC) and a three-port power converter (TPPC). The TPPC has three ports: a DC port, a grid port and an isolated grid port. The input for the boost DDPC is connected to a PV array and the output from the boost DDPC is connected to the DC port of the TPPC. The grid port connects to the utility grid, and the isolated grid connects to emergency loads. The isolated grid port continuously supplies an uninterruptible voltage with constant amplitude and constant frequency for emergency loads, without the need of battery regardless of whether the utility grid is nominal or interrupted in the condition of sunshine. Hence, the proposed PVPCT can continuously supply high-quality uninterruptible power to the emergency loads, such as charger of cell phone during the natural disasters. In addition, the power circuit is simplified and isolating transient is smooth due to the use of TPPC, and the initial cost and maintenance cost are reduced due to no use of battery. The proposed PVPCT has six operation modes for four conditions. A prototype is set-up for validating the performance of proposed PVPCT. The experimental results of the proposed PVPCT have the expected performance.

In this paper, a grid-connected power conversion topology is developed to convert a DC power from the renewable energy into a high-quality AC power. This grid-connected power conversion topology co...

This study proposes a seven-level power conversion system for a solar power generation system. This seven-level power conversion system consists of a DC–DC power converter and a cascade DC–AC inverter. The cascade DC–AC inverter comprises a full-bridge inverter and a T-type inverter. The T-type inverter generates a three-level quasi-square-wave voltage and the full-bridge inverter provides a three-level high-frequency pulse voltage. The amplitude of the three-level quasi-square-wave voltage is double that of the three-level high-frequency pulse voltage, so seven levels of AC voltage are synthesized. Only the full-bridge inverter with lower DC bus voltage uses high-frequency switching so switching losses are effectively reduced. The novelty of the proposed cascade DC–AC inverter is that the output power of T-type inverter is controlled by regulating the DC bus voltage, so no real power is supplied from the full-bridge inverter and an independent power source is not required to provide power to the full-bridge inverter. The negative terminal voltage for solar cell array keeps almost constant to reduce the leakage current of proposed seven-level power conversion system. A hardware prototype with a digital signal processor controller is developed to verify the performance of seven-level power conversion system for a solar power generation system.

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 a multi-level power converter for a battery energy storage system (BESS) with bidirectional power flow. The multi-level power converter includes a DC-DC power converter, a selec...

This paper proposes an asymmetric unidirectional isolated multi-level DC-DC power converter (AUIMLDDPC). A three-winding transformer (TWT) is used as the interface between a half-bridge inverter (HBI) and two full-bridge rectifiers (FBRs). The turn numbers for two secondary windings of TWT are not the same. Thus, it results in unequal DC output voltages of the two FBRs. A selection circuit is adopted to control the unequal DC output voltages of two FBRS to be connected in series or stand-alone, and thus, generates a non-zero two-level voltage to control the magnitude of the output DC voltage of the proposed AUIMLDDPC. An output L-C filter is applied to filter out the high frequency harmonic of the non-zero two-level voltage. The secondary windings with unequal turn numbers for TWT can reduce the voltage change of the non-zero two-level voltage. Therefore, it can reduce the L-C filter capacity. To validate the performance of the proposed AUIMLDDPC, a hardware prototype is developed. The experimental results are as expected. Keywords: Multi-level, DC-DC, Half-bridge inverter, Full-bridge rectifier

The interleaved boost power converter has the advantages of ripple cancellation and better efficiency. The major problem of the interleaved boost power converter is the current balancing am...

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.

A conventional DC-AC inverter can only output either a single-phase AC voltage or a set of three-phase AC voltages. A new three-port DC-AC inverter which can simultaneously output a single-phase AC voltage and a set of three-phase AC voltages is proposed in this paper. This three-port DC-AC inverter is based on the three-port T-type multi-level power converter which is composed of three T-type power electronic legs, a decoupling transformer set, a filter inductor set, a single-phase filter capacitor, and a three-phase filter capacitor set. The DC port of the proposed power converter is connected to a DC power source to act as the input port, and the single-phase AC port and the three-phase AC port serve as two output ports to supply power to the single-phase load and the three-phase load, respectively. The zero-sequence transformer is used to decouple the single-phase and three-phase AC components, which are generated by the three T-type power electronic legs. The operation principle of this three...

—This paper proposes a new three-port, T-type multi-level converter (TPTMC) that simultaneously outputs two sinusoidal AC voltages with different frequencies: 50 Hz and 60 Hz. The proposed TPTMC is composed of a DC voltage source, two T-type power electronic legs, a filter inductor set, a frequency separated transformer (FST), a 60 Hz filter capacitor, a 50-Hz filter capacitor, and a DSP controller. The most salient feature is that the proposed TPTMC outputs two sinusoidal AC voltages with different frequencies using only a power converter. A hardware prototype is developed to verify the performance of the proposed TPTMC. The experimental results are as expected.

This paper proposes a transformer-less multi-level solar power generation system. This solar power generation system is composed of a solar cell array, a boost power converter, an isolation switch ...

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.

A solar charger is proposed in this article. This solar charger, which is composed of a solar module and a three-port power converter, is used to charge a battery set with two batteries. Three ports of the three-port power converter are respectively connected to the solar module and two batteries. The three-port power converter integrates the power circuit for the interface for photovoltaic power generation and for voltage equalisation of the battery set. The operational mode for the three-port power converter varies depending on the voltage of the solar module. The current ripple and voltage stress of power semiconductor devices for the three-port power converter are less than those for a conventional boost power converter. A prototype is developed and tested to verify the performance of the proposed solar charger.

An isolated multilevel dc–dc power converter is proposed in this paper. The proposed isolated multilevel dc–dc power converter consists of an isolated power converter, a series/parallel switching circuit, and an output L–C filter. The isolated power converter is composed of a half-bridge inverter, a three-winding transformer, and two full-bridge rectifiers. The half-bridge inverter is switched in constant duty to generate two output dc voltages through two secondary windings of the three-winding transformer and two full-bridge rectifiers, respectively. The series/parallel switching circuit is used to control the two output dc voltages of the isolated power converter connected in series or in parallel, to control the output voltage of isolated multilevel dc–dc power converter. To verify the performance of the proposed isolated multilevel dc–dc power converter, a prototype is developed and tested. The experimental results show that the proposed isolated multilevel dc–dc power converter has the expected performance.

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.

This paper proposes a three-port single-phase three-wire (TPSPTW) power converter interface integrating an isolated current-fed full-bridge power converter (ICFPC), a three-port power converter (TPPC), a fuel cell and a battery set for micro grid (MG).The ICFPC is used to control the output power of fuel cell and to step-up its output voltage to the voltage of high-voltage DC port of the TPPC. The TPPC can manage the power conversion between the fuel cell, the battery set, the loads and the utility. This power converter interface charges the battery set, outputs AC power and acts as an active power filter (APF) in the grid-connection mode, supplies uninterruptible power to the loads when it operates in the stand-alone mode. The fuel cell outputs a programmed power regardless of whether the power converter interface operates in the grid-connection mode or in the stand-alone mode. The programmed power outputted from the fuel cell is the average power of load under the stand-alone mode. The battery set is used to respond to the varied power of loads under the stand-alone mode. A prototype is developed to verify the performance of power converter interface, and the experimental results are as expected.

This study proposes a single-phase to three-phase power conversion interface which converts the power from a single-phase utility to three-phase power for a three-phase load. The proposed single-phase to three-phase power conversion interface comprises a bridge-type switch set, a set of three-phase inductors, a transformer set and a set of three-phase capacitors. A current-mode control controls the switching of bridge-type switch set, to generate a set of nonzero-sequence (NZS) currents and a set of zero-sequence (ZS) currents. The transformer set is used to decouple the NZS currents and the ZS currents. The NZS currents are used to generate a high-quality three-phase voltage that supplies power to a three-phase load. The ZS currents flow to the single-phase utility so that the utility current is sinusoidal and in phase with the utility voltage. Accordingly, only a bridge-type switch set is used in the single-phase to three-phase power conversion interface to simply the power circuit. A prototype ...

A novel isolated four-level DC-DC battery charger with constant current/constant voltage (CC/CV) charging strategy is proposed in this paper. The proposed charger consists of a asymmetrical T-type DC-AC inverter, a high frequency transformer, a full-bridge diode rectifier and a digital signal processor based controller. A hardware prototype is developed and tested to verify the performance of the proposed isolated four-level DC-DC battery charger. The experimental results show that the performance is as expected.

In this paper, a buck-boost type battery charger is developed for charging battery set with a lower voltage. This battery charger is configured by a rectifier circuit, an integrated boost/buck power converter and a switched capacitors circuit. A boost power converter and a buck power converter sharing a common power electronic switch are integrated to form the integrated boost/buck power converter. By controlling the common power electronic switch, the battery charger performs a hybrid constant-current/constant-voltage charging method and gets a high input power factor. Accordingly, both the power circuit and the control circuit of the developed battery charger are simplified. The switched capacitors circuit is applied to be the output of the boost converter and the input of the buck converter. The switched capacitors circuit can change its voltage according to the utility voltage so as to reduce the step-up voltage gain of the boost converter when the utility voltage is small. Hence, the power efficiency of a buck-boost type battery charger can be improved. Moreover, the step-down voltage gain of the buck power converter is reduced to increase the controllable range of the duty ratio for the common power electronic switch. A prototype is developed and tested to verify the performance of the proposed battery charger.

The operation strategy for a lab-scale grid-connected photovoltaic generation system integrated with battery energy storage is proposed in this paper. The photovoltaic generation system is composed of a full-bridge inverter, a DC–DC boost converter, an isolated bidirectional DC–DC converter, a solar cell array and a battery set. Since the battery set acts as an energy buffer to adjust the power generation of the solar cell array, the negative impact on power quality caused by the intermittent and unstable output power from a solar cell array is alleviated, so the penetration rate of the grid-connected photovoltaic generation system is increased. A lab-scale prototype is developed to verify the performance of the system. The experimental results show that it achieves the expected performance.

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.

A seven-level active power conditioner (SLAPC) used to inject the real power of the clean power source into the grid is proposed in this study. This SLAPC is composed of a four-level DC–DC power converter and a full-bridge inverter. The four-level DC–DC power converter converts the output voltage of the clean power source into a four-level pulse voltage. The full-bridge inverter is switched at low frequency and synchronised with the utility voltage and the output voltage of SLAPC is a seven-level AC voltage. Accordingly, the switching power loss, harmonic distortion and electromagnetic interference caused by the switching operation of power electronic switches are reduced because of the four-level in the DC side and the seven-level in the AC side of the full-bridge inverter. In addition, the proposed SLAPC acts as an active power filter that filters out the harmonic current of the load, so the utility current of the proposed SLAPC is a sinusoidal current and in phase with the utility voltage. A hardware prototype is developed to verify the performance of the proposed SLAPC. The experimental results show that the performance of the proposed SLAPC is as expected.

In this paper, a new hybrid power conditioner is proposed for suppressing harmonic currents and neutral-line current in three-phase four-wire distribution power systems. The proposed hybrid power conditioner is composed of a neutral-line current attenuator and a hybrid power filter. The hybrid power filter, configured by a three-phase power converter and a three-phase tuned power filter, is utilized to filter the nonzero-sequence harmonic currents in the three-phase four-wire distribution power system. The three-phase power converter is connected to the inductors of the three-phase tuned power filter in parallel, and its power rating can thus be reduced effectively. The tuned frequency of the three-phase tuned power filter is set at the fifth harmonic frequency. The neutral-line current suppressor is connected between the power capacitors of the three-phase tuned power filter and the neutral line to suppress the neutral-line current in the three-phase four-wire distribution power system. With the major fundamental voltage of the utility dropping across the power capacitors of the three-phase tuned power filter, the power rating of the neutral-line current suppressor can thus be reduced. Hence, the proposed hybrid power conditioner can effectively reduce the power rating of passive and active elements. A hardware prototype is developed to verify the performance of the proposed hybrid power conditioner. Experimental results show that the proposed hybrid power conditioner achieves expected performance.

This paper proposes a new solar power generation system, which is composed of a dc/dc power converter and a new seven-level inverter. The dc/dc power converter integrates a dc-dc boost converter and a transformer to convert the output voltage of the solar cell array into two independent voltage sources with multiple relationships. This new seven-level inverter is configured using a capacitor selection circuit and a full-bridge power converter, connected in cascade. The capacitor selection circuit converts the two output voltage sources of dc-dc power converter into a three-level dc voltage, and the full-bridge power converter further converts this three-level dc voltage into a seven-level ac voltage. In this way, the proposed solar power generation system generates a sinusoidal output current that is in phase with the utility voltage and is fed into the utility. The salient features of the proposed seven-level inverter are that only six power electronic switches are used, and only one power electronic switch is switched at high frequency at any time. A prototype is developed and tested to verify the performance of this proposed solar power generation system.

Power conversion interface for small-capacity wind power generation system based on permanent-magnet synchronous generator (PMSG) is proposed in this paper. The proposed power conversion interface will convert the wind power generated from the three-phase PMSG to a high quality power to inject into the single-phase utility. This power conversion interface comprises of a power converter and a zero-sequence transformer set. The power converter is controlled to generate a set of positive-sequence currents to absorb a real power from the three-phase PMSG and a set of zero-sequence currents to pass through the zero-sequence transformer set to the single-phase utility. A feed-forward control is used to control the proposed power conversion interface so as to simplify the control circuit. A simplified maximum power point tracking method is also proposed and incorporated in the control circuit of the power conversion interface to extract the maximum power of the PMSG-based wind power generation system. Hence, the proposed power conversion interface has the advantages of simplifying both the power circuit and the control circuit. A prototype is developed to demonstrate the performance of the proposed power conversion interface. The experimental results show that the proposed power conversion interface can achieve the expected performance.

This paper proposes an islanding detection method for a hybrid photovoltaic generation system (HPGS). This HPGS is controlled using an improved voltage-mode control method in both the grid-connected and the stand-alone conditions to unify and simplify the control circuit. The inverter of this HPGS is multi-functional, so it can perform the functions of active power filter, charging/discharging a battery set, uninterruptible power supply, and injecting power into the grid of distribution power system. The proposed islanding detection method is incorporated into the controller of the inverter. The advantage of islanding detection method is the time required to add a disturbance for detecting the islanding operation is very short. A prototype is developed and tested to verify the performance of the proposed HPGS. The experimental results verify that the proposed islanding detection method can effectively detect the islanding operation, so this HPGS achieves the expected performance.

A single-phase three-wire grid-connected power converter (STGPC) with energy storage for positive grounding photovoltaic generation system (PGPGS) is proposed in this paper. The positive terminal of the solar cell array can be directly connected to the ground to avoid unexpected degradation of the special thin-film solar cell array. The proposed PGPGS consists of a solar cell array, two DC–DC power converters, a battery set, a switch set and a three-port power converter. The three-port power converter comprises a high-voltage DC port, a low-voltage DC port and an AC port. The solar cell array is connected to the high-voltage DC port through two DC–DC power converters whose positive terminal is directly connected to the ground. The battery set is connected to the low-voltage DC port, and the AC port is connected to the utility. No transformer is required in this PGPGS even when using the low-voltage battery set. A prototype is developed and tested to verify the performance of the PGPGS. The experimental results show that the proposed power converter has the expected performance.

In this article, a voltage equaliser is proposed for a battery string with four Li–Fe batteries. The proposed voltage equaliser is developed from a flyback converter, which comprises a transformer, a power electronic switch and a resonant clamped circuit. The transformer contains a primary winding and four secondary windings with the same number of turns connected to each battery. The resonant clamped circuit is for recycling the energy of leakage inductance of the transformer and for performing zero-voltage switching (ZVS) of the power electronic switch. When the power electronic switch is switched on, the energy is stored in the transformer; and when the power electronic switch is switched off, the energy stored in the transformer will automatically charge the battery whose voltage is the lowest. In this way, the voltage of individual batteries in the battery string is balanced. The salient features of the proposed voltage equaliser are that only one switch is used, the energy stored in the leakage indu...

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.