Eaton Corporation

Robert W Spink

James C Vander Meer

Dennis H Braun

A three-phase motor control system (FIG. 1) having a current control regulator (CCR) that includes adjustable current ramp time or adjustable current level during starting and acceleration and incorporates a load voltage-current displacement regulator (VCFB) that automatically becomes effective when the motor approaches synchronous speed, thereby to reduce the power input to the motor to what is needed to run the load, thus saving energy. Additionally, a second quadrant detector (SQD) senses overhauling load conditions and operates a gate (NG) to lock out the load voltage-current displacement feedback signal thereby allowing the reference signal to place the motor across the line until the motor operation returns to the motoring quadrant. The system further includes means (24 in FIG. 2h) affording integral control and means (30 in FIG. 2h) affording proportional control of either the current control or the load voltage-current displacement control signal, with the gain of the proportional control being individually adjustable. The integral control is provided with high gain means (FET in FIG. 2h) that is rendered effective by a switch (TR in FIG. 2h) during current control and alternative low gain means (P4 in FIG. 2h) that is substituted during load voltage-current displacement control, the gain of the latter being individually adjustable.

Load voltage-current displacement regulator motor control system

The control system has application to polyphase AC wound rotor motor which employ opposed parallel connected phase controlled thyristors together with series connected fixed resistors in each leg of a delta connected secondary impedance network. The line-to-line secondary terminals of the motor provide a source of polyphase variable frequency and variable amplitude AC reference signals. The variable frequency, variable voltage reference signals are converted into complementary pairs of square wave synchronization voltages. These same reference voltages are also concurrently integrated during their respective positive and negative half cycles to provide complementary pairs of constant peak amplitude, variable frequency voltages which are combined with associated ones of the aforementioned synchronization voltages to provide synchronization locks. These synchronization locks will not allow the synchronization voltages to recognize multiple sinusoidal zero crossings which appear on the original AC reference voltages due to space harmonics generated by the motor or spurous electrical noise until a time dependent on the fundamental frequency, well beyond the desired control recognized zero crossing of the fundamental waveforms. The generated synchronization voltages are additionally used for speed detection, integrator reset and gate pulse lockout. The variable frequency, variable voltage reference signals are also integrated and compared with a DC command signal to provide a ramp and pedestal type 180.degree. gate current firing period for their associated pairs of the thyristors. The aforementioned control of the secondary thyristors is shown and described with a polyphase AC wound rotor motor as used in an industrial hoist system which additionally employs an auxiliary eddy current retarding brake. Establishment of proper directional power connection to the motor primary terminals is afforded through operation of a multiposition master controller. The master controller in certain positions in both hoist and lower direction effects shunting of the controlled thyristor and series resistors to permit the motor to run in an open loop mode. The master controller in accordance with its positioning concurrently effects changes in a speed reference voltage which is used in conjunction with the gate current firing control for the secondary thyristors. Operation of the controller also coordinates the energization of the eddy current brake in certain lower speed positions, and during plugging modes to insure smooth transition when going from lowering to hoisting modes.

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Wauwatosa, WI, United States of America

Robert W Spink