Predictive Fast DSP-Based Current Controller for Thyristor Converters

The predictive current controller presented in this paper provides fast current control for thyristor converters without relying on the accurate load model. Unlike load-model-based predictive methods of current control, this method does not use load parameters in the calculations of the firing angle. Instead, thyristors are fired when the sum of the measured instantaneous load current and the load current rise, which is predicted from the voltage-time area on the dc-side inductor, is equal to the current reference. This way, accurate current control is achieved just by knowing the dc-side inductor parameters and by measuring line voltages, the load current, and the load voltage. The proposed predictive current controller exhibits a practically negligible steady-state error, the fastest possible transient response, and the fastest possible and smooth transitions between continuous- and discontinuous-current conduction modes, for both the rectification and inversion modes of operation of the converter. It shows great stability and robustness. The controller also compensates for sudden changes in both line and load voltages, as well as for voltage drops due to the commutation process. Based on the proposed algorithm, the computer simulation model and the laboratory prototype of the system were developed. Both the simulation and experimental results demonstrated an excellent dynamic performance of the proposed controller.