Jiann-Fuh Chen

Novel maximum-power-point-tracking controller for photovoltaic energy conversion system

A novel maximum-power-point-tracking (MPPT) controller for a photovoltaic (PV) energy conversion system is presented. Using the slope of power versus voltage of a PV array, the proposed MPPT controller allows the conversion system to track the maximum power point very rapidly. As opposed to conventional two-stage designs, a single-stage configuration is implemented, resulting in size and weight reduction and increased efficiency. The proposed system acts as a solar generator on sunny days, in addition to working as an active power line conditioner on rainy days. Finally, computer simulations and experimental results demonstrate the superior performance of the proposed technique.

Transformerless DC–DC Converters With High Step-Up Voltage Gain

Conventional dc-dc boost converters are unable to provide high step-up voltage gains due to the effect of power switches, rectifier diodes, and the equivalent series resistance of inductors and capacitors. This paper proposes transformerless dc-dc converters to achieve high step-up voltage gain without an extremely high duty ratio. In the proposed converters, two inductors with the same level of inductance are charged in parallel during the switch-on period and are discharged in series during the switch-off period. The structures of the proposed converters are very simple. Only one power stage is used. Moreover, the steady-state analyses of voltage gains and boundary operating conditions are discussed in detail. Finally, a prototype circuit is implemented in the laboratory to verify the performance.

Combination voltage-controlled and current-controlled PWM inverters for UPS parallel operation

In this paper, a scheme of combination of voltage-controlled and current-controlled PWM inverters for parallel operation of a single-phase uninterruptible power supply (UPS) is proposed. The voltage-controlled PWM inverter (VCPI) unit as a master is developed to keep a constant sinusoidal wave output voltage. The current-controlled PWM inverter (CCPI) units are operated as slave controlled to track the distributive current. The power distribution center (PDC) performs the function of distributing the output current of each active unit. In this proposed scheme of parallel operation, each of the units can be designed as nearly independent, and the CCPI units do not need a PLL circuit for synchronization. As a result, the parallel operation of UPS is easy to implement and to expand system capacity. For the purpose of illustration, the system, including three single-phase units which operate in parallel, is analyzed and experimental results are given. >

InGaN-GaN multiquantum-well blue and green light-emitting diodes

InGaN-GaN multiquantum-well (MQW) blue and green light-emitting diodes (LEDs) were prepared by organometallic vapor phase epitaxy, and the properties of these LEDs were evaluated by photoluminescence (PL), double crystal X-ray diffraction, and electroluminescence (EL) measurements. It was found that there were only small shifts observed in PL and EL peak positions of the blue MQW LEDs when the number of quantum well (QW) increased. However, significant shifts in PL and EL peak positions were observed in green MQW LEDs when the number of QW increased. It was also found that there was a large blue shift in EL peak position under high current injection in blue MQW LEDs. However, the blue shift in green MQW LEDs was negligibly small when the injection current was large. These observations could all be attributed to the rapid relaxation in green MQW LEDs since the In composition ratio in the InGaN well was high for the green MQW LEDs. The forward voltage V/sub f/ of green MQW LEDs was also found to be larger than that of blue MQW LEDs due to the same reason.

Novel High Step-Up DC–DC Converter for Fuel Cell Energy Conversion System

A novel high step-up dc-dc converter for fuel cell energy conversion is presented in this paper. The proposed converter utilizes a multiwinding coupled inductor and a voltage doubler to achieve high step-up voltage gain. The voltage on the active switch is clamped, and the energy stored in the leakage inductor is recycled. Therefore, the voltage stress on the active switch is reduced, and the conversion efficiency is improved. Finally, a 750-W laboratory prototype converter supplied by a proton exchange membrane fuel cell power source and an output voltage of 400 V is implemented. The experimental results verify the performances, including high voltage gain, high conversion efficiency, and the effective suppression of the voltage stress on power devices. The proposed high step-up converter can feasibly be used for low-input-voltage fuel cell power conversion applications.

A Cascaded High Step-Up DC–DC Converter With Single Switch for Microsource Applications

This paper proposes a new high step-up dc-dc converter designed especially for regulating the dc interface between various microsources and a dc-ac inverter to electricity grid. The figuration of the proposed converter is a quadratic boost converter with the coupled inductor in the second boost converter. The converter achieves high step-up voltage gain with appropriate duty ratio and low voltage stress on the power switch. Additionally, the energy stored in the leakage inductor of the coupled inductor can be recycled to the output capacitor. The operating principles and steady-state analyses of continuous-conduction mode and boundary-conduction mode are discussed in detail. To verify the performance of the proposed converter, a 280-W prototype sample is implemented with an input voltage range of 20-40 V and an output voltage of up to 400 V. The upmost efficiency of 93.3% is reached with high-line input; on the other hand, the full-load efficiency remains at 89.3% during low-line input.

Novel High Step-Up DC–DC Converter With Coupled-Inductor and Voltage-Doubler Circuits

In this paper, a novel high step-up dc-dc converter with coupled-inductor and voltage-doubler circuits is proposed. The converter achieves high step-up voltage gain with appropriate duty ratio and low voltage stress on the power switches. Also, the energy stored in the leakage inductor of the coupled inductor can be recycled to the output. The operating principles and the steady-state analyses of the proposed converter are discussed in detail. Finally, a prototype circuit of the proposed converter is implemented in the laboratory to verify the performance of the proposed converter.

Novel High Step-Up DC–DC Converter With Coupled-Inductor and Switched-Capacitor Techniques

A novel high step-up dc-dc converter with coupled-inductor and switched-capacitor techniques is proposed in this paper. The capacitors are charged in parallel and are discharged in series by the coupled inductor, stacking on the output capacitor. Thus, the proposed converter can achieve high step-up voltage gain with appropriate duty ratio. Besides, the voltage spike on the main switch can be clamped. Therefore, low on-state resistance RDS(ON) of the main switch can be adopted to reduce the conduction loss. The efficiency can be improved. The operating principle and steady-state analyses are discussed in detail. Finally, a prototype circuit with 24-V input voltage, 400-V output voltage, and 200-W output power is implemented in the laboratory. Experiment results confirm the analysis and advantages of the proposed converter.

Influence of Si-doping on the characteristics of InGaN-GaN multiple quantum-well blue light emitting diodes

A detailed study on the effects of Si-doping in the GaN barrier layers of InGaN-GaN multiquantum well (MQW) light-emitting diodes (LEDs) has been performed. Compared with unintentionally doped samples, X-ray diffraction results indicate that Si-doping in barrier layers can improve the crystal and interfacial qualities of the InGaN-GaN MQW LEDs. It was also found that the forward voltage is 3.5 and 4.52 V, the 20-mA luminous intensity is 36.1 and 25.1 mcd for LEDs with a Si-doped barrier and an unintentionally doped barrier, respectively. These results suggests that one can significantly improve the performance of InGaN-GaN MQW LEDs by introducing Si doping in the GaN barrier layers.

A Novel High Step-Up DC–DC Converter for a Microgrid System

A novel high step-up dc-dc converter for a distributed generation system is proposed in this paper. The concept is composed of two capacitors, two diodes, and one coupled inductor. Two capacitors are charged in parallel, and are discharged in series by the coupled inductor. Thus, high step-up voltage gain can be achieved with an appropriate duty ratio. The voltage stresses on the main switch and output diode are reduced by a passive clamp circuit. Therefore, low resistance R for the main switch can be adopted to reduce conduction loss. In addition, the reverse-recovery problem of the diode is alleviated, and thus, the efficiency can be further improved. The operating principle and steady-state analyses of the voltage gain are also discussed in detail. Finally, a 24-V input voltage, 400-V output voltage, and 400-W output power prototype circuit of the proposed converter are implemented in the laboratory to verify the performance.