Gate control of thyristor converters for reversibly driving a D.C. electric motor

A gate control for reversibly driving a D.C. electric motor comprising:

• a first thyristor converter for operating as a rectifier for energizing the motor to drive it forward;
• a second thyristor converter for remaining still during the time the motor runs in the forward direction;
• means for energizing the motor from the first thyristor converter and then from the second thyristor converter;
• means for connecting an A.C. voltage supply to the converters;
• means for generating gating pulses synchronized with the frequencies of the A.C. voltage supply for the converters;
• first and second gating circuits for selectively applying the gating pulses from the gating pulse generating means to gate electrodes of the converters;
• means for comparing a voltage signal corresponding to the rotational speed signal of the motor with a speed reference voltage signal and for feeding a speed deviation voltage signal to the pulse generating means to phase shift the gating pulses to enable adjustment of the output voltage from the converter operating as a rectifier to adjust the motor speed to coincide substantially with the reference speed indicated by the speed reference voltage signal;
• operational amplifier means having an integrating function for effecting current control of the converters in response to the deviation current signal by comparing the converter current with the deviation derived from the speed deviation feeding means to render the converter current substantially equal to the amplitude of the speed deviation;
• and
• means for dinconnecting the operational amplifier means from the speed deviation feeding means and for alternately applying an electrical voltage signal responsive to the motor speed and a modified feedback signal from the output terminal of the operational amplifier to an input terminal of the operational amplifier during the time the converters are switched from one state to another to prepare for reverse rotation of the motor so that the phase adjustment of the gating pulses emanating from the gate control follows the electrical signal voltage responsive to the motor speed during the time the thyristor converters are switched from one state to another.