METHOD FOR CONTROLLING SPEED OF THREE-PHASE MOTOR Russian patent published in 2000 - IPC

FIELD: adjustable high-speed drives of compressors, gas and air blowers, and power units. SUBSTANCE: frequency of supply voltage across motor terminals is varied by applying control voltage pulses to thyristor bridges connected to two three-phase voltage systems shifted in phase through 30 electrical degrees. They are first applied to bridges connected to first voltage system, then, in time space t_sp1= T₁/12, where T₁ is supply voltage cycle, to bridges connected to second voltage system, whereupon this cycle is repeated. During each time space t_sp1 control voltage pulses are fed simultaneously to three thyristors of rectifier anode group of one bridge connected to one phase winding of motor and to three thyristors of rectifier cathode group of other bridge connected to other phase winding of motor; then, after time space t_sp2= T₁n/12, where n is integer number from 1 to 20, pulses are not applied any more to one of rectifier groups of bridge connected to one of motor phase windings while similar group of rectifiers of other bridge connected to other phase winding is still supplied with these pulses; then mentioned cycle is repeated. EFFECT: enlarged speed control range. 2 dwg