Search

A grid-connected power converter for a distributed power generation system is proposed in this paper. The functions of islanding detection and active power filter are incorporated into the control of the grid-connected power converter. The operation theory of the proposed islanding detection method is that a small perturbation is added into the amplitude of utility current only when the amplitude of the utility current is smaller than a setting value that approximates zero. The salient feature of the proposed islanding detection method is that the small perturbation for detecting islanding operation is added only when the real power between the grid-connected power converter and the load is balanced or when islanding operation occurs. Thus, the perturbation for islanding detection is less frequent than that in conventional active islanding detection methods. The computer simulation results show that the expected performance of the proposed grid-connected power converter can be achieved.

In this paper, a three-phase four-wire active load capable of energy regeneration is proposed. The proposed active load comprises a load characteristic power converter, an energy regeneration power converter and a DC capacitor. The load characteristic power converter and the energy regeneration power converter are connected in series, and the DC capacitor acting as the energy buffer is located at the common dc bus of both power converters. The load characteristic power converter can be used to simulate a resistive load, a resistive/inductive load, a resistive/capacitive load and a rectifier load. The energy consumed by the load characteristic power converter will be regenerated back to the utility through the energy regeneration power converter. Moreover, the energy regeneration power converter also serves as an active power filter (APF) to suppress the harmonic current and compensate for the reactive power of the tested equipment. Hence, the utility supplies only a small real power to overcome the power loss of the active load and tested equipment. A prototype is developed and tested to verify the performance of the proposed active load. Experimental results show that the proposed active load can efficiently perform the expected function.

This paper presents a method for diagnosing the degradation of the lead-acid battery unit. This method can diagnose the degradation of the lead-acid battery unit caused by internal short, opening of internal short or cell reversal. The salient feature of the proposed method is that the state-of-health (SOH) of the battery unit is estimated automatically at the end of each discharge cycle by measuring the battery voltage and current of a battery unit, so that no complicated measurement is required. To verify the proposed method, aging experiments for lead-acid battery are developed. Experimental results show that the proposed method can achieve expected performance.

A voltage-mode grid-connected solar inverter with high frequency isolated transformer is proposed in this paper. Besides, the functions of MPPT (maximum power point tracking) and the islanding detection are incorporated into the controller of this voltage-mode grid-connected solar inverter. The experimental results show that the performance of this isolated voltage-mode grid-connected photovoltaic generation system is as expected.

A novel maximum power point tracking (MPPT) method for the voltage-mode grid-connected inverter of photovoltaic generation system is proposed in this paper. The proposed MPPT method incorporated in the controller of the voltage-mode grid-connected DC/AC inverter is used to track the maximum power of solar cell array by monitoring the output voltage of the solar cell array. The main feature of the proposed method is that no current is sensed for MPPT. Therefore, it has the advantage of simplifying the control circuit in comparison with the conventional perturbation and observation methods where both current and voltage are sensed. A prototype based on the DSP controller is developed and tested to verify the performance of the proposed MPPT method. The experimental results show that the proposed method has the expected performance.

In this paper, a new control method is proposed for the DC/DC boost converter of the grid-connected renewable power generation system. The proposed control method can suppress the ripple voltage with double fundamental frequency of the utility superimposed on the output voltage of renewable energy source. Hence, the power efficiency of the renewable power generation system is increased. Only a voltage detector detecting the output voltage of DC/DC boost converter is used in the proposed control method, so that the control circuit is simplified evidently. Experimental results of the developed prototype show that the performance of the proposed method is as expected.

In this paper, a residual capacity estimation method based on the multilevel Peukert equations is proposed for the lead-acid battery. Multilevel Peukert equations and ampere hour accumulation are used in this paper to estimate residual capacity of the battery, and several Peukert equations are used for different range of discharge current to improve the accuracy of the conventional Peukert methods. The residual capacity of the battery is estimated during each discharge cycle by measuring the battery voltage and current. The salient features of the proposed method are that no complicated measurement is required in the proposed residual capacity estimation method. To verify the proposed residual capacity estimation method, experiments for lead-acid batteries are developed. The experimental results show that the proposed residual capacity estimation method provides the expected results.

In this paper, an intelligent aging estimation method based on Sample Entropy (SampEn) is proposed for the lead-acid batteries serially connected in a string. This method can prevent the potential battery failure and guarantee the battery availability. Since SampEn can quantify the regularity of a data sequence, it can serve as an indicator for the aging or degradation of the lead-acid battery. The salient feature of the proposed method is that aging of the individual battery is estimated automatically at the end of each discharge cycle by only measuring individual battery voltage in a string of batteries, so that no complicated measurement is required. To verify the proposed SampEn based aging estimation method, aging experiments for lead-acid batteries are developed. The experimental results show that the proposed intelligent aging estimation method provides the expected results.

A novel maximum power point tracking (MPPT) method for the photovoltaic system is proposed in this paper. The main feature of the proposed MPPT method is that only a current is required to be detected. Therefore, the proposed method has the advantage of simplifying the control circuit compared with the conventional perturbation and observation method where both current and voltage should be detected. A prototype based on the digital signal processor (DSP) controller is developed and tested to verify the performance of the proposed MPPT method. The experimental results show the proposed method has the expected performance.

A novel auxiliary diagnosis method for state-of-health (SOH) of a lead-acid battery unit is proposed in this paper. This method is based on the concept that the discharging curve for a health battery unit is smooth, however, the degradation of battery unit caused by the internal cell shorts, shorted cells open or the cell reversal will distort the discharging curve. Some experimental results are carried out to verify the proposed SOH diagnosis method. The experimental results show that the proposed method has the expected performance.

A novel active islanding detection method for a distributed power generation system is proposed in this paper. The distributed power generation system includes a dc power source and a grid-connected power converter. The grid-connected power converter acts as a virtual inductor as the frequency is slightly higher than the fundamental frequency of utility voltage. The distributed power generation system can only supply power to the load as the utility power interruption occurs. At this instant, the load voltage will be changed in amplitude or frequency due to the operation of virtual inductor. Hence, the proposed method can immediately detect the islanding operation.

A new current-mode voltage-source parallel processing UPS is proposed in this paper. It uses only one power stage, however, it has the performance of active power line conditioner (APLC) and back-up power. The operation of the proposed UPS can be divided into two modes, APLC and back-up power modes. Due to the use of current-mode control in both operation modes, its transient performance at the moment of the change of operation mode is very good, and the output voltage of back-up power mode will not be distorted under nonlinear load. A prototype is developed and tested to verify its performance. The test 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 neutral-current suppressor is proposed. The proposed neutral-current suppressor comprises a zero-sequence transformer, a single-phase power converter and a rectifier. The proposed zero-sequence transformer is implemented by only two single-phase transformers, which are connected to three-phase lines of the three-phase four-wire distribution power system to supply a zero-sequence current path. The single-phase power converter is connected between the zero-sequence transformer and neutral line. A rectifier with small power rating is connected to the DC bus of single-phase power converter for overcoming the power loss of single-phase power converter to sustain a constant DC voltage. The performance of neutral-current suppression for the zero-sequence transformer is advanced by controlling the single-phase power converter so as to make the neutral load current flow through the proposed neutral-current suppressor. Moreover, the proposed neutral-current suppressor can also avoid the neutral current caused by the unbalanced voltage of three-phase four-wire distribution power systems. Hence, the proposed neutral-current suppressor is an effective solution to the neutral-current problem of three-phase four-wire distribution power systems. Both computer simulation and experimental results verify that the proposed neutral-current suppressor can achieve 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 new AC/DC power conversion interface for the self-excited induction generator (SEIG) is proposed here. The proposed AC/DC conversion interface includes an excitation system and a diode rectifier connected in parallel. The variable frequency AC power generated by the SEIG is converted into DC power by the diode rectifier. The DC power of the diode rectifier can charge a battery set and supply DC loads or be further converted into fixed-frequency AC power by an inverter for AC loads. The DC voltage is expected to be regulated in the above applications. The excitation system supplies an exciting reactive current to maintain the amplitude of the SEIG output voltage to be a constant value. Moreover, it can also serve as an active power filter to suppress the harmonic current generated by the diode rectifier. The excitation system is composed of an AC power capacitor and a power converter connected in series. The AC power capacitor is adapted to provide a basic reactive power, and it can also reduce the voltage rating and the capacity of the power converter. The salient point of the proposed AC/DC power conversion interface is that the capacity of the power converter in the AC/DC power conversion interface can be minimised, and the power loss of the AC/DC power conversion interface can also be reduced. A prototype is developed and tested to verify the performance of the proposed AC/DC power conversion interface.

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.

An islanding detection method is proposed for a distributed power generation system that comprises a DC power source and a grid-connected power inverter connected in parallel to the utility. Besides serving to generate the fundamental real power, the grid-connected power inverter also acts as a virtual inductor when the frequency is slightly higher than the fundamental voltage frequency of the utility. The distributed power generation system is the only source supplying power to the load when the utility is interrupted; consequently, the amplitude or frequency of the load voltage changes because of the operation of the virtual inductor. Hence, the proposed method can immediately detect the islanding operation. A prototype was developed and tested to demonstrate the performance of the proposed islanding detection method. Experimental results show that the proposed method can detect islanding operations effectively.

The parallel operation of several low-capacity inverters is better than a singular high-capacity inverter owing to the advantages of better extensibility and reliability. A simplified control method for parallel-connected inverters is proposed, which can balance the current distribution among the parallel-connected inverters with no interconnected communication lines. To verify the performance of the proposed control method, a prototype consisting of two inverters has been developed. The experimental results verify that the performance of the proposed control method is as desired.

A new active power filter with harmonic suppression and adjustable reactive power compensation is proposed. The power converter of the proposed filter can generate a compensating voltage, including a harmonic voltage for compensating the load harmonic current and a fundamental voltage for adjusting the reactive power of the utility side, connected to the power feeder via an impedance. The waveform of the utility current after compensating by the proposed active power filter can be approximated as a sinusoidal waveform, and the input power factor is also improved. A 20 KVA prototype has been developed and tested to verify its performance. The test results indicate that the proposed active power filter has the desired performance.

In the paper, a novel uninterruptible power supply (UPS) is proposed with the performance of input current harmonic suppression, input power factor correction and output voltage regulation. This UPS comprises two power converters, a shunt power converter and a series power converter. The shunt power converter is connected to the utility via a link inductor, for providing a compensating voltage, to suppress the input current harmonic and improve the input power factor. The series power converter is connected serially to the load to provide a clean and regulated output voltage. A voltage-mode control algorithm with fast response and simple control circuit is proposed to control the shunt power converter. The series power converter is controlled by a current-mode control to ensure the quality of output voltage. A single-phase prototype is developed and tested to verify the performance of the proposed UPS. Experimental results show that the proposed UPS has expected performance.