a speed regulator and control system for controlling a motor from a polyphase ac source includes a data processor and a regulator and rectifier control interfacing the data processor with a controllable rectifier driving the motor is disclosed . the regulator and rectifier control , under control of the data processor , selectively transfers system parameters to the data processor , receives a calculated value proportional to firing angle from the data processor and supplies firing pulses to the rectifier to selectively connect each phase of the ac source to the motor as calculated by the data processor .