Comparison of FPGA based Digital Control Method for Low Carrier-Frequency PWM Inverter

In this paper, five kinds of real time digital feedback control method for the PWM inverter with FPGA (filed programmable gate array) based hardware controller are compared for a low carrier-frequency PWM inverter system. It was reported that the deadbeat control method with FPGA based hardware controller had the very good transient response for various loads, but these reports were mainly focused on a few KW class PWM inverter system, so the high carrier frequency were adopted. But in MW class PWM inverter system, the carrier frequency is limited up to 2 kHz range, because of the performance of the switching devices and the trade off against the efficiency of the inverter. In this condition, the controllability of the PWM inverter is not so much expected and still the conventional PI control method is widely used. Five different digital control methods (1. singlerate deadbeat control, 2. multirate deadbeat control, 3. multirate 2 degree of freedom deadbeat control, 4. quasi multirate deadbeat control, 5. quasi multirate 2 degree of freedom deadbeat control) are verified to clarify the possibility to improve the control characteristics in a low carrier-frequency PWM inverter system. Simulations were carried out in case of 20 kHz carrier and in case of 2 kHz carrier, for each control method, also the robustness to the filter parameter variations was investigated. As a result, the advantages of the proposed control methods were verified