Motor control system

A motor control system comprising:

• a motor with a primary winding connecting to an AC power source and a secondary winding;
• a first converter connecting at its AC side to the AC power source;
• a second converter connecting at its DC side to the DC side of said first converter and at its AC side to the secondary winding of said motor;
• phase modifying equipment connected to the AC power source and consuming a leading reactive power corresponding to a lagging reactive power consumed by the motor in the rated running in order to improve the power factor of said motor;
• a speed detector for detecting the speed of said motor;
• a speed command circuit for providing a speed command of said motor;
• a speed adjustor for producing a current command value corresponding to a signal representing the difference between the output signal from said speed detector and the speed command;
• a current detector for detecting current flowing through said first and second converters;
• a current adjustor for producing a first firing phase command signal corresponding to a signal representing the difference between the output signal from said current detector and the current command value;
• a first automatic pulse phase shifter for controlling a firing angle of said first converter by the first firing phase command signal;
• a second automatic pulse phase shifter for controlling a firing angle of said second converter;
• a reactive power detector for producing an electrical signal corresponding to the reactive power consumed by said motor, said first converter, and said second converter;
• a reactive power command circuit for providing an electrical signal representing a lagging reactive power command value corresponding to the lagging reactive power consumed by said motor, said first converter and said second converter in the rated running of said motor;
• a reactive power control unit for applying to said second automatic pulse phase shifter a second firing phase command signal corresponding to a signal representative of the difference between an electrical signal corresponding to said reactive power and the lagging reactive power command value;
• and
• phase detector means for detecting a reference phase synchronized with the induced voltage of said motor, said second automatic pulse phase shifter being connected to receive the outputs of said reactive power control unit and said phase detector means to control the firing phase of said second converter.