Yung-Chun Wu

Soft-Switching Bidirectional Isolated Full-Bridge Converter With Active and Passive Snubbers

A bidirectional isolated full-bridge dc-dc converter with a conversion ratio around nine times, soft start-up, and soft-switching features for battery charging/discharging is proposed in this paper. The converter is equipped with an active flyback and two passive capacitor-diode snubbers, which can reduce voltage and current spikes and reduce voltage and current stresses, while it can achieve near zero-voltage-switching and zero-current-switching soft-switching features. In this paper, the operational principle of the proposed converter is first described, and its analysis and design are then presented. A 1.5-kW prototype with a low-side voltage of 48 V and a high-side voltage of 360 V has been implemented, from which measured results have verified the discussed features.

Design considerations for single-stage electronic ballast with dimming feature

Design considerations for single-stage electronic ballast with a dimming feature are presented in this paper. When the lamps are dimmed out to a lower light level, the density of electrons will drop significantly, which would result in visible striation. Moreover, power imbalance exists between the power factor correction semistage and the ballast semistage, which usually results in a high DC-link voltage and might damage the switching devices. Strategies for suppressing the high DC-link voltage and eliminating the effect of striations occurring in a fluorescent lamp are therefore proposed. In addition, an improvement on the jump phenomenon of lamp luminous output when it is controlled by varying the switching frequency is also proposed. Hardware measurements have been presented to verify the theoretical discussions.

A current-sharing control strategy for paralleled multi-inverter systems using microprocessor-based robust control

A current-sharing control strategy for paralleled multi-inverter systems using microprocessor-based robust control is presented in this paper. With an averaged current-sharing control (ACSC) strategy, the inverters are in parallel connection and each inverter has a voltage robust controller to achieve system stability and robustness, and a current robust controller to track the averaged inductor current of the inverters to achieve an equal current distribution. Simulation results and hardware measurements of a single-inverter system and a two-inverter system, and simulation results of a three-inverter system with linear and nonlinear loads have demonstrated the feasibility of the proposed control scheme in equal current distribution and fast regulation.

CWDC strategy for paralleled multi-inverter systems achieving a weighted output current distribution

A current-weighting-distribution-control (CWDC) strategy for paralleled multi-inverter systems is presented in this paper. With a CWDC strategy, the inverters in the systems can have different power ratings and they can be connected in parallel to achieve a weighted output current distribution by only adding weighted distribution circuits to each inverter. In such systems, each inverter has an outer-loop voltage controller to govern system stability, an inner-loop current controller to improve the system response and a weighted current distribution controller to achieve a weighted output current distribution. Simulation results and hardware measurements from a two-inverter system, and simulation results from a three-inverter system have demonstrated the feasibility of the proposed strategy in weighted current distribution and fast regulation.

A compensation strategy for parallel inverters to achieve precise weighting current distribution

This paper proposes a compensation strategy for parallel inverters to achieve weighting current distribution. In addition to the conventional current weighting distribution control (CWDC), the reference current of each inverter is fed back as a compensation signal to improve weighting current distribution. With the proposed compensation strategy, the output current of each inverter module can precisely track weighting current command. Experimental and simulated results from a three-inverter system with equal or different power ratings and with different kinds of loads have demonstrated the feasibility of the proposed strategy.

A voltage-error-sharing scheme for parallel-inverter systems to improve weighting current distribution and dynamic response

This paper proposes a voltage- and current-error-sharing scheme for parallel-inverter systems to improve weighting current distribution and dynamic response. The proposed scheme is based on the conventional current weighting distribution control (CWDC) and weighting the output voltage error signal according to the power ratings of the inverters to distribute current signals to each inverter module. Weighting current controllers are also designed according to the power ratings of the inverters. With the proposed scheme, a new duty-ratio control signal for the next switching cycle can be updated more precisely; thus, current distribution among inverters with different power ratings will be more precise and transient time under a step-load change can be shortened. Simulated and experimental results from a three-inverter system with identical or different power ratings and with linear or nonlinear loads have demonstrated the aforementioned performance

A single-stage electronic ballast with emergency lighting features

This paper presents a single-stage electronic ballast with emergency lighting features. The ballast can function as a regular ballast, emergency ballast, battery charger or discharger and power failure detector, achieving regular and emergency lighting features. The single-stage converter used in the ballast is an integration of a bidirectional flyback converter and two half-bridge series-resonant parallel-loaded inverters. Derivation and operating principle of the proposed converter is first presented and an application to regular and emergency lighting is then developed. With the proposed converter and a single-chip microcontroller (EM78P458), a low cost, multifeature electronic ballast can be readily implemented and installed. Simulation results and hardware measurements have verified its feasibility and the desired features.