Analysis and design of closed-loop control of power electronic converter systems

Abstract

In this thesis, analysis of two closed loop control systems for power electronic switching converters is presented. In particular, the closed loop behavior and performance optimization of the following two systems is examined in detail: (a)An active filter system to cancel neutral current harmonic (IOOA) in a threephase four-wire electric distribution system. (b)Input power factor correction and harmonic reduction stage of a commercially available electronic ballast (12OV, 64W) for fluorescent lighting system. In the active harmonic cancellation system, the transfer function of each block in the system control loop is derived. This includes the characteristics of a notch filter, controller, PWM gain stage, and a full-bridge inverter stage. The frequency response analysis of the closed loop based on the model developed for each block is presented. Extensive experimental results are presented to verify the transfer function of each block in the feedback loop. Bode plots of the closed loop system obtained from the individual transfer functions is compared with the experimentally measured data. Good agreements between calculated and measured phase margin are noted. A possible instability zone around 6OHz frequency is identified. Methods to improve system stability are discussed. Increasing the stop-bandwidth of the notch filter is shown to improve the stability of the system. Several experimental results on a 12OV, I OOA active filter unit are presented. In the electronic ballast used for fluorescent lighting, analysis of the input power factor correction stage with the voltage loop is presented. The frequency response analysis performed and compared with the experimented results. Methods to improve the system closed loop behavior and its performance are proposed and discussed in detail.