The design of an H∞ voltage regulator for a predictive current controlled three phase PWM power converter

In this project, an H∞ controller is proposed as a DC voltage regulator for the predictive current controlled pulse with modulated (PWM) three-phase power converter to compensate the uncertainty caused by the predictive current controller. The H∞ theory has its unique approach to the uncertainty issue, its design method allows both the stability robustness and performance robustness to be considered at the design stage. The design of the H∞ voltage regulator is based on the worst case scenario where the converter is subject to a load disturbance and its operation mode is changed from the rectifying to the regeneration, consequently, parameters and structure of the original plant transfer function derived, vary significantly. The proposed H∞ (DC) voltage regulator is to overcome the uncertainty problem and to work with the predictive current controller to achieve robust control of the entire system. The combined control scheme is simulated using MatLab/SIMULINK environment. The simulation results show that the closed-loop system is capable of achieving performance robustness and stability robustness for the worst case scenario. The output DC link voltage is stable and nearly sinusoidal, while the line currents are delivered with a unity power factor. A computer controlled three-phase PWM converter of lOkVA is developed and tested in the open-loop condition, and the performance of the power converter is examined. An INTEL industrial PC-486 single chip computer is used as a digital controller. For a given modulation index and output frequency, switching intervals are calculated using the space vector PWM algorithm, and are down loaded to a PWM generator board which synthesizes gating pulse to six switching devices (IGBT). There is a on-board synchronizing unit which synchronizes the fundamental frequency of the gating pulses with the mains. A computer program is developed in Borland C++ to perform the modulation process. The experimental results show that the developed converter system is ready to be used as a test bed for conducting experimental research in the area of converter control and machine control. To summarize the work accomplished by the author for this project: 1. The introduction of the H∞ control theory into the application of converter control and theoretical design of the H∞ voltage regulator; 2. The simulation of the entire closed-loop controlled power converter with the combination of a predictive current control and a H∞ voltage regulator; 3. The development of a computer controlled three-phase PWM power converter as a test bed.