METHOD FOR OPTIMISING THE POWER INPUT OF A PLURALITY OF HYSTERESIS MOTORS CONNECTED IN PARALLEL

摘要

A method for optimizing the power input to a plurality of parallel connected hysteresis motors wherein a three phase alternating voltage source jointly supplies the motors with an adjustable operating voltage. The method includes measuring, during the operation of each motor, the phase angle difference between motor voltage and motor current and determining the power factor therefrom for each motor. The effective current value of each motor is measured during operation and is combined with the power factor to obtain the active current for each motor. An active current limit value at which each motor transitions from synchronous to asynchronous operation is measured once and stored for each motor prior to commencement of continuous synchronous operation. After the motors reach synchronous speed at rated voltage, the control voltage is adjusted to reduce the supply voltage to an optimum working point just above the voltage level at which a first one of the parallel connected motors begins to transition from synchronous to asynchronous operation. The active current of each motor is then compared with its associated limit value to determine whether it is operating synchronously or asynchronously. The control voltage of the voltage source is thereafter regulated for increasing the supply voltage to the rated voltage value when it is determined that one of the motors is operating asynchronously and for decreasing the supply voltage to the optimum working point when the motors are all determined to be operating synchronously.