Analysis and Design of a UPS with Near-Optimum Dynamic

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Uninterruptible power supply (UPS) is usually installed to solve the power line disturbances that damage computers and electronic equipments. However,ac-to-dc converters used in the UPS may cause the harmonic and power factorp roblems in the power distribution system. The purpose of this dissertation is to discuss and further investigate the power factor and harmonic problems of the UPS. A complete research for the analysis and design of a high performance UPS with near optimum dynamic regulation power factor correction converter is presented. Making the dc-side capacitor of the rectifier as small as possible, it can improve the input power factor of a single phase on-line UPS due to thec haracteristics of single phase rectifiers and the output voltage of the UPS synchronizes with the input line voltage. This will cause a rapid dc voltage fluctuation and the conventional sinusoidal pulsewidth modulation is not suitable to use. The current waveshaping techniques are widely used to improve the input power factor of the single phase or three phase ac-to-dc converters. However, the voltage dynamic regulation is limited because the bandwidth of the voltage control loop can not be too wide to distort the current command in the current control loop. Based on the power balance of the input and output of the ac-to-dc converter and the instantaneous reactive power theory, two new control strategies for three-phase PWM ac-to-dc converters with near-optimum dynamic regulation are presented in this dissertation. That is the output dc voltage of converters is nearly not affected by the variations of the line voltages and loads. In this dissertation, a complete study on the static characteristics of the harmonic injected pulsewidth modulation (HIPWM) for three phase inverters is presented and a new control configuration combining an instantaneous voltage feedback and an averaged voltage feedback under the HIPWM scheme is proposed to improve the static and dynamic characteristics