Optimal-current control of convertor-fed DC motors. I. Special case for continuous current with negligible resistance

The paper describes a new method of firing control for a three-phase thyristor bridge supplying a DC motor in both motoring and regenerating modes. The method uses the firing points as the sampling instants and the `cusp current´ at these instances as the controlled variable. For continuous-current operation, the method enables the current to be changed from one steady-state level to another in two thyristor firings (6.6 ms). The paper provides the theoretical analysis on which the method is based and, assuming the resistance to be negligible, derives an algorithm for control implementation. The paper gives examples of current waveforms for transient changes in current obtained from computer simulations, an equivalent zero-resistance practical circuit and a DC motor. The results verify the theoretical predictions