SE338610B - - Google Patents

Abstract

1,193,979. Control of A.C. motors. LICENTIA PATENT - VERWALTUNGS G.m.b.H. 1 Nov., 1967 [2 Nov., 1966], No. 49659/67. Heading H2J. [Also in Division G3] A squirrel cage induction motor 2 is supplied from a pulse inverter 1 having a control unit 3 for determining the frequency of commutation of the inverter, the motor frequency, and the motor voltage. A main control signal is applied to an integrator 4 connected to a voltage-frequency converter 5 for pre-setting the motor frequency. The outputs of a generator 8 and the integrator 4 are compared and the error signal is applied to a trigger 9 providing feedback to the generator so that it oscillates. Thus, when the main control signal is increased, for example, the commutation and motor frequencies are increased, together with the motor voltage. The flux of the motor is detected by choke coils connected to the motor supply-lines, the reactive currents representing the magnetization current of the motor and hence its flux. The reactive currents are rectified and applied to a Hall converter whose output is amplified by a proportional-integral amplifier shunted by an R-C network, Fig. 2 (not shown). The output of this amplifier modifies the operation of the inverter so that the output voltage is increased when the flux of the motor is insufficient, for example. The output current of the inverter is detected by current transformers 16a, 16b, 16c, associated with rectifier 17 and trigger 18. The triggers 9, 18, are connected to AND-gate 19 for voltage control of the inverter which is switched-off when the current becomes excessive.