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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.

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.

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.

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.

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 ...

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 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.

A novel power electronic interface for the grid-connected fuel cell power generation system is proposed in this paper. This power electronic interface is composed of a DC–DC power converter and a DC–AC inverter. A voltage doubler based topology is adopted to configure the DC–DC power converter to perform high step-up gain for boosting the output voltage of the fuel cell to a higher voltage. Moreover, the input current ripple of the fuel cell is suppressed by controlling the DC–DC power converter. The DC–AC inverter is configured by a dual buck power converter and a full-bridge power converter to generate a five-level AC output voltage. The DC–AC inverter can perform the functions of DC–AC power conversion and active power filtration. A 1.2 kW hardware prototype is developed to verify the performance of the proposed power electronic interface for the grid-connected fuel cell power generation system. The experimental results show that the proposed power electronic interface for the grid-connected fuel cell power generation system has the expected performance.

In this paper, a five-level inverter is developed and applied for injecting the real power of the renewable power into the grid to reduce the switching power loss, harmonic distortion, and electromagnetic interference caused by the switching operation of power electronic devices. Two dc capacitors, a dual-buck converter, a full-bridge inverter, and a filter configure the five-level inverter. The input of the dual-buck converter is two dc capacitor voltage sources. The dual-buck converter converts two dc capacitor voltage sources to a dc output voltage with three levels and balances these two dc capacitor voltages. The output voltage of the dual-buck converter supplies to the full-bridge inverter. The power electronic switches of the full-bridge inverter are switched in low frequency synchronous with the utility voltage to convert the output voltage of the dual-buck converter to a five-level ac voltage. The output current of the five-level inverter is controlled to generate a sinusoidal current in phase with the utility voltage to inject into the grid. A hardware prototype is developed to verify the performance of the developed renewable power generation system. The experimental results show that the developed renewable power generation system reaches 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.

In this paper, a grid-connected battery charger is developed. The developed battery charger is composed of a power factor corrector and a buck converter. The power factor corrector control the input current to be sinusoidal and in phase with utility voltage to perform unity power factor. The buck power converter is step-down the output power of power factor corrector to charge the battery set in constant current or constant voltage. The power factor corrector contains a rectifier, a boost converter and a switched-capacitor circuit. The switching capacitors circuit is applied to be the output of the boost converter and the input of the buck converter. Controlling the switched-capacitor circuit, the output voltage of boost converter is divided into two levels according to the utility voltage such that step-up voltage gain can be reduced when the utility voltage is small. In addition, the switched-capacitor circuit can reduce the step-down voltage ratio of the buck converter. Accordingly, the efficiency of the grid-connected battery charger is advanced. A prototype is developed and tested to verify the performance of the proposed grid-connected battery charger.

A novel active power line conditioner (APLC) using power sources of fuel cell and battery set is proposed. The proposed APLC is composed of a current-fed full-bridge converter, a three-port three-leg power converter (TPTLPC), a fuel cell and a battery set. The TPTLPC manages the power conversion between the fuel cell, the battery set, the load and the utility. The power and control circuits of the proposed APLC are simplified because the TPTLPC integrates both DC-DC and DC-AC power conversions into a single power converter. The proposed APLC can perform the functions of active power filter and supplying back-up power. A prototype is developed to verify the performance of the proposed APLC. The experimental results show that the performance is as expected.

In this paper, a hybrid power filter is proposed to solve problems of line harmonic currents and neutral line currents of three-phase four-wire power distribution system. This hybrid power filter is configured by a there-phase tuned power filter and a three-phase power converter. The tuned power filter is configured by a capacitor and an inductor, and its tuned frequency is setting at the frequency of third-order harmonics. The three-phase power converter has a four legs bridge structure and is connected to the inductor of the tuned power filter in parallel. The three-phase power converter is applied to solve the problems of series/parallel resonance and improve poor filter performance. Furthermore, it also forces the fundamental current of the tuned power filter and the dominant harmonic current of the nonlinear load to flow through the inductor of the tuned power filter. In this way, the voltage rating of the three-phase power converter is reduced because it is serially connected to the power capacitor of the tuned power filter, and the current rating can be diminished because it is connected to the inductor of the tuned power filter in parallel. Hence, the power rating of the power converter applied in the proposed hybrid power filter is minimized. A DSP based prototype is developed and tested to verify the performance of the proposed three-phase four-wire hybrid power filter. Experimental results show that the proposed three-phase four-wire hybrid power filter achieves the expected performance.

This paper proposes a novel transformerless grid-connected power converter with negative grounding for a photovoltaic generation system. The negative terminal of the solar cell array can be directly connected to the ground in the proposed grid-connected power converter to avoid the transparent conducting oxide corrosion that occurs in some types of thin-film solar cell array. The proposed grid-connected power converter consists of a dc-dc power converter and a dc-ac inverter. The salient features of the proposed power converter are that some power electronic switches are simultaneously used in both the dc-dc power converter and dc-ac inverter, and only two power electronic switches operate at high switching frequency at the same time (one is in the dc-dc power converter and the other is in the dc-ac inverter). The leakage current of the photovoltaic generation system is reduced because the negative terminal of the solar cell array is connected directly to the ground. Finally, a prototype was developed to verify the performance of the proposed grid-connected power converter. The experimental results show that the performance of the proposed grid-connected power converter is as expected.

A DC power distribution interface for data centers is developed in this paper. This DC power distribution interface is composed of two power stages, a three-phase T-type multi-level AC-DC power converter and an isolated multi-level DC-DC power converter. The first power stage, three-phase T-type multi-level AC-DC power converter, is used to convert the utility AC voltage to a constant DC voltage and control the utility current to be sinusoidal and unity power factor. The isolated multi-level DC-DC power converter is the second power stage, and it converts the output DC voltage of the first power stage to the desired DC voltage of the DC power distribution system with galvanic isolation. This isolated multi-level DC-DC power converter consists of an isolated power converter with a three-winding transformer, a series/parallel switching circuit and an output L-C filter. Only three power electronics switches are used in the isolated multi-level DC-DC power converter to generate a two-level output DC voltage. Hence, the control circuit is simplified and the capacity of output L-C filter is reduced. Computer simulation is carried out to verify the developed DC power distribution interface. The simulation results show that the developed DC power distribution interface has the expected performance.

This paper proposes a health auxiliary diagnosis method for the lead-acid battery unit. The proposed method is based on Approximate Entropy (ApEn). Since ApEn can quantify the regularity of a data sequence and the discharging curve for a health lead-acid battery unit is smooth, the proposed method can detect the degradation of battery unit caused by the internal short, opening of internal shorted or cell undergoing reversal using the distorted discharging curve. Aging experiments for the lead-acid battery are developed to verify the proposed method. The experimental results verify that the proposed health auxiliary diagnosis method can diagnosis the degradation of battery unit caused by the internal short, opening of internal shorted or cell undergoing reversal.

In this paper, a health auxiliary diagnosis method based on Sample Entropy (SampEn) is proposed for the lead–acid battery unit. The concept of the proposed method is that the discharging curve for a health battery unit is smooth; however, the degradation of battery unit caused by the internal shorts, opening of internal short or cell undergoing reversal will distort the discharging curve. Since SampEn can quantify the regularity of a data sequence, it can serve as an indicator for the state-of-health (SOH) of the lead–acid battery. The salient feature of the proposed method is that SOH of the battery is estimated automatically at the end of each discharging cycle by measuring the battery voltage and current of a battery unit, so that no complicated measurement is required. To verify the proposed health auxiliary diagnosis method based on SampEn, aging experiments on lead–acid battery are developed. The experimental data shows that the proposed health auxiliary diagnosis method provides the expected results.

A novel maximum power point tracking (MPPT) method for the grid-connected wind power generation system is proposed in this article. The main feature of the proposed method is that the MPPT of the wind power generation system can be obtained via only adjusting the amplitude of the DC/AC inverter's output current and observing the output DC voltage of an AC/DC power converter connected with a permanent magnet synchronous wind generator (PMSWG). Thus, no practical calculation of generated power of the PMSWG is required. Experimental results of the developed prototype show that the performance of the proposed method is as expected.

A novel configuration for the power converter of a three-phase hybrid power filter is proposed in this paper. This power converter uses only a two-arm bridge structure and a DC capacitor. The hybrid power filter is configured by the proposed power converter serially connected with a passive power filter set. The salient feature of this hybrid power filter is that it permits one of the power lines of the utility connected directly to the negative terminal of the DC capacitor located in the DC side of the power converter through the passive power filter set. Consequently, the power converter uses less number of power electronic switches to reduce the manufacturing cost. A three-phase prototype is developed and tested to verify the performance of the hybrid power filter using the proposed power converter. The experimental results show that the hybrid power filter using the proposed power converter can reach the expected performance.

Active power filters (APFs) have been developed to solve the problems of harmonic suppression and reactive power compensation simultaneously, In this paper, a three-phase four-wire power filter comprising a three-phase three-wire APF and a Zig-Zag transformer is developed. A hardware prototype is implemented and tested to verify the performance of the proposed power filter under various ideal and non-ideal power conditions. Experimental results show that this three-phase four-wire power filter has the desired performance under limited zero sequence utility voltage.

A novel power converter for protecting three-phase AC power capacitors is proposed. The salient point of this power converter is that the power converter is configured by a two arms bridge structure without split capacitors. Two of the three-phase AC power capacitors are serially connected via filter inductor set to two AC terminals of power electronic switch set, and another of the three-phase AC power capacitors is connected via filter inductor set to the negative DC terminal of power electronic switch set through no power electronic switches. The power converter acts as virtual harmonic resistors to be inserted into the AC power capacitors. Hence, the power converter, acting as the virtual harmonic resistors, can damp the harmonic resonance and avoid the harmonic current injection of AC power capacitors. Hence, the proposed method can effectively protect the power capacitor from harmonic damage. The proposed power converter has the advantage that the number of power electronic switches is redu...

In this paper, a hybrid compensation system for harmonic suppression and power factor correction is developed and analyzed. This compensation system consists of a hybrid power filter and an AC power capacitor. A small capacity power converter and a passive power filter is serially connected to have the function of hybrid power filter, and then the hybrid power filter is connected in parallel to the AC power capacitor to form a hybrid compensation system. The major function of the hybrid power filter is the harmonic suppression, and the AC power capacitor performs the power factor correction. Furthermore, a method, inserting an inductor in series with the AC power capacitor, is proposed in this paper for avoiding high frequency resonance amplification between the hybrid power filter and the AC power capacitor. To demonstrate the performance of this hybrid compensation system, a three-phase prototype is developed and tested. The tested results show that the insertion of an inductor in series with the AC power capacitor can prevent high frequency resonance amplification between the hybrid power filter and the AC power capacitor.

A simplified method for protecting the power capacitor from over-voltage/over-current is proposed. The proposed method retrieves the voltage across the power capacitor to calculate the root mean square (RMS) values of the power capacitor voltage and the power capacitor current. The salient point of the proposed method is this method can protect the power capacitor from over-voltage/over-current caused by harmonic or power resonance only sensing the power capacitor voltage. The control circuit generates a trigger signal to actuate the electromagnetic switch to switch off the power capacitor from the power system or adjust the impedance characteristic of inductor/power capacitor for protecting the power capacitor from over-voltage/over-current if an abnormal voltage or current is detected. The proposed method has the advantages of simplified control circuit, easy installation and low implementation cost. A prototype is implemented to verify its performance. The test results show that the proposed method has the expected performance.

The parallel operation of several low-capacity harmonic filters is better than the singular operation of one high-capacity harmonic filter due to the advantages of extensibility and higher reliability. Furthermore, the use of a harmonic filter with the function of parallel operation is an important trend. In this paper, a control method for the parallel-connected hybrid power filters is proposed. This control method can automatically balance the current distribution among parallel-connected hybrid power filters. In order to verify the performance of the proposed control method, a prototype consisting of two hybrid power filters is developed. The experimental results show that the performance of the proposed control method is as desired.

In this paper, a novel active power filter is proposed and implemented by using a voltage-source power converter with a series connected inductor and capacitor set. The power converter is controlled to generate a compensating voltage that is converted into a compensating current via the series connected inductor and capacitor set. The compensating current flows into the power feeder in order to suppress the harmonic currents generated by nonlinear loads. The salient advantages of the proposed active power filter are lower voltage rating of dc capacitor and power switching devices, smaller filter inductor, smaller dimension, light weight, better filter performance and low electromagnetic interference (EMI). A three-phase 100 kVA active power filter is developed to demonstrate the performance of the proposed method. The results show that the proposed active power filter has the expected performance.