Chung-You Lin

High-Performance Stand-Alone Photovoltaic Generation System

This study develops a high-performance stand-alone photovoltaic (PV) generation system. To make the PV generation system more flexible and expandable, the backstage power circuit is composed of a high step-up converter and a pulsewidth-modulation (PWM) inverter. In the dc-dc power conversion, the high step-up converter is introduced to improve the conversion efficiency in conventional boost converters to allow the parallel operation of low-voltage PV arrays, and to decouple and simplify the control design of the PWM inverter. Moreover, an adaptive total sliding-mode control system is designed for the voltage control of the PWM inverter to maintain a sinusoidal output voltage with lower total harmonic distortion and less variation under various output loads. In addition, an active sun tracking scheme without any light sensors is investigated to make the PV modules face the sun directly for capturing the maximum irradiation and promoting system efficiency. Experimental results are given to verify the validity and reliability of the high step-up converter, the PWM inverter control, and the active sun tracker for the high-performance stand-alone PV generation system.

High-Efficiency Power Conversion System for Kilowatt-Level Stand-Alone Generation Unit With Low Input Voltage

This paper mainly focuses on the development of a high-efficiency power conversion system for kilowatt-level stand-alone generation units with a low output voltage, such as photovoltaic modules, fuel cells, and small-scale wind generators, and it aims at having the same output ac voltage, i.e., 110 Vrms/ 60 Hz as the utility power for the utilization of a stand-alone power supply. This high-efficiency power conversion system includes one high-efficiency high-step-up dc-dc converter and one soft-switching dc-ac current-source inverter. This dc-dc converter is capable of solving the voltage spike problem while the switch is turned off, and it can achieve the objectives of high efficiency and high voltage gain. Because the techniques of soft switching and voltage clamping are used in the dc-ac current-source inverter, the conversion efficiency could greatly be improved. The effectiveness of the designed circuits is verified by experimentation, and the maximum efficiency of the entire high-efficiency power conversion system is over 91% based on the experimental measurements.

High Step-Up Bidirectional Isolated Converter With Two Input Power Sources

The objective of this paper is to develop a high step-up isolated converter with two input power sources. The proposed converter has two input ports for simultaneously converting two different input power sources with low voltages to a stable output power with a high voltage. Moreover, the demand of bidirectional power flow, which is dependent on the power management for charging and discharging power storage mechanisms, can also be satisfied in the proposed converter. According to various situations, the operational states of the proposed converter can be divided into three states, including a stand-alone state, a united power supply state, and a charge and discharge state. The effectiveness of the designed circuit topology is verified by experimental results, and the goals of high-efficiency conversion, high step-up ratio, and bidirectional power flow can be achieved by the proposed converter operation.

Newly Designed ZVS Multi-Input Converter

A newly designed zero-voltage-switching (ZVS) multi-input converter is proposed in this paper. The converter can boost the different voltages of two power sources to a stable output voltage. An auxiliary circuit is employed for achieving turn-on ZVS of all switches in the proposed converter. According to various situations, the operational states of the proposed converter can be divided into two states, including a single-power-supply and a dual-power-supply state. In the dual-power-supply state, the input circuits connected in series together with the designed pulsewidth modulation can greatly reduce the conduction loss of the switches. In addition, the effectiveness of the designed circuit topology and the ZVS properties are verified by experimental results, and the goal of high-efficiency conversion can be obtained.

High-Efficiency DC–DC Converter With Two Input Power Sources

The aim of this study is to develop a high-efficiency converter with two input power sources for a distributed power generation mechanism. The proposed converter can boost the varied voltages of different power sources in the sense of hybrid power supply to a stable output dc voltage for the load demand. An auxiliary circuit in the proposed converter is employed for achieving turn-ON zero-voltage switching (ZVS) of all switches. According to various situations, the operational states of the proposed converter can be divided into two states including a single power supply and a dual power supply. In the dual power-supply state, the input circuits connected in series together with the designed pulsewidth modulation can greatly reduce the conduction loss of the switches. In addition, the effectiveness of the designed circuit topology and the ZVS properties are verified by experimental results, and the goal of high-efficiency conversion can be obtained.

High-efficiency single-stage bidirectional converter with multi-input power sources

A multiple-input, single-stage bidirectional converter is proposed. It takes a three-winding coupled inductor as the main component of energy transmission, and utilises only two switches to accomplish the multi-input mechanism. Depending on the switching conditions, the circuit can be operated at discharge, charge and alone states. The winding voltage in the high-voltage side of the coupled inductor is manipulated to further increase the corresponding voltage gain, a strategy that is superior to one in the conventional coupled-inductor. This topology is useful for low-power applications. In addition, all switches and diodes have favourable voltage-clamping effects so that the voltage spikes caused by the leakage-inductor energy can be alleviated effectively, and reverse-recovery currents within diodes can be reduced, because the leakage inductor has limited capability to handle quick current changes. There is also a low-voltage-type charge circuit with no increase in additional circuit elements. This helps -to avoid power losses that arise from multistage conversions in traditional auxiliary power systems. This strategy also utilises the synchronous rectification technique to further decrease conduction losses. Numerical simulations and experimental results via examples of a proton exchange membrane fuel cell power source and a traditional battery module are given to demonstrate the effectiveness of the proposed power conversion strategy.

High step-up DC-DC converter for fuel cell generation system

Due to the electrochemical reaction, fuel cell has the power quality of low voltage as well as high current. However, the fuel cell stack with high output voltage is difficult to fabricate and its volume is overlarge. Besides, the output voltage of the fuel cell is varied easily with respect to the variation of loads. In order to satisfy the requirement of high-voltage demand, a high-efficiency DC-DC converter with superior voltage gain is one of the essential mechanisms in fuel cell applications. In this study, a newly-designed DC-DC converter utilized in the proton exchange membrane fuel cell (PEMFC) system is constructed on the basis of voltage-clamped and soft-switching techniques for alleviating the switching and conduction losses to further increase the conversion efficiency. The effectiveness of the proposed converter used for the PEMFC system is verified by experimental results.

Maximum-Power-Extraction Algorithm for Grid-Connected PMSG Wind Generation System

This study proposed a maximum-power-extraction algorithm (MPEA) including a maximum-power error driven (MPED) mechanism and a maximum-power differential speed (MPDS) control for a grid-connected wind generation system with a permanent-magnet synchronous generator (PMSG). The MPED mechanism works as the maximum-power-point-tracking (MPPT) method in the photovoltaic system gradually increasing to its maximum value by regulating the direction of grid-connected current command according to the power variation trend. Moreover, the MPDS control produces an additional step of current command based on the instantaneous difference of generator speeds so that it can prevent the wind turbine from stalling at the suddenly dropping wind speed and achieve the object of maximum power extraction instantly as a stiff wind flowing through the wind turbine. In addition, the output is connected to a utility grid for providing energy flexibility via a unipolar full-bridge inverter controlled by a digital-signal-processor. The grid-connected experimentations of the proposed MPEA scheme without any mechanical sensors for a wind-power emulation system via a PMSG driven by an induction motor are given to examine its feasibility in practice

Implementation of Novel Maximum-Power- Extraction Algorithm for PMSG Wind Generation System without Mechanical Sensors

This study focuses on the implementation of a novel maximum-power-extraction algorithm (MPEA) including a maximum-power error driven (MPED) mechanism and a maximum-power differential speed (MPDS) control for a wind generation system with a permanent-magnet synchronous generator (PMSG). In the proposed MPEA scheme, the MPED mechanism operating like a traditional hill-climbing method drives the output power gradually increasing to its maximum value by regulating the direction of voltage command according to the power variation trend. Moreover, the MPDS control produces an additional step of voltage command based on the instantaneous difference of generator speeds so that it can prevent the wind turbine from stalling at the suddenly dropping wind speed and achieve the object of maximum power extraction instantly as a stiff wind flowing through the wind turbine. In addition, the effectiveness of the proposed MPEA scheme without mechanical sensors for the wind generation system is indirectly verified by the experimental results of a wind-power emulation system with a PMSG driven by an induction motor

Novel Power Control Scheme for Stand-Alone Photovoltaic Generation System

This study mainly develops a novel power control scheme for a stand-alone photovoltaic (PV) generation system. In order to make the PV generation system more flexibility and expandability, the later power circuit is composed of a high step-up converter and a pulse-width-modulation (PWM) inverter. In the DC-DC power conversion, the high step-up converter is introduced to improve the conversion efficiency in conventional boost converters and to allow the parallel operation of low-voltage PV modules. Moreover, an adaptive total sliding-mode control (ATSMC) system is designed for the voltage control of the PWM inverter to maintain a sinusoidal output voltage with lower total harmonic distortion (THD) and less variation under various output loads. Experimental results are given to verify the validity and reliability of the high step-up converter and the PWM inverter control for a stand-alone PV generation system