Abstract: An apparatus for controlling the supply of power to a variable-speed induction motor converts an AC power source voltage to a motor supply voltage at a designated frequency, with the amplitude of the motor supply voltage being controlled in accordance with the motor load such that the degree of slip conforms to a predetermined optimum slip charactistic, whereby high efficiency and stability are maintained over a wide range of load values. The motor supply voltage amplitude is detected to provide an indication of the motor load, an optimum value of an operating parameter of the motor which varies in accordance with degree of slip is derived based on the designated frequency and the detected voltage amplitude, using a predetermined function corresponding to that frequency, and the motor supply voltage amplitude is controlled such as to reduce an amount of difference between the optimum value of the operating parameter and a detected value of that parameter.

Abstract: An AC-to-AC power inverter apparatus and a control method thereof are described in which the effects of AC ripple contained in an intermediate DC voltage produced in the apparatus are eliminated from the output AC voltage, thereby enabling the inverter apparatus to function without a large-capacitance smoothing capacitor. The amplitude of the DC voltage, including the AC ripple amplitude, is detected, the amplitude of a reference AC waveform is divided by the detected amplitude, and the value of the resultant ratio is applied to control the duty factor of a PWM signal, which controls a DC-to-AC inverter circuit. Changes in the DC voltage due to AC ripple are thereby prevented from affecting the output AC voltage obtained, which has an average value waveform corresponding to the reference waveform.

Abstract: An induction motor control apparatus, for converting an AC power supply voltage to a motor supply voltage for an induction motor, includes a feedback control loop for controlling the level of the motor supply voltage such that the induction motor operates close to a predetermined value of power factor, and also includes circuits for deriving a signal which varies in accordance with the motor admittance (or impedance), and for differentiating that signal to obtain a parameter variation signal which indicates an amount and direction of any sudden change in the motor load torque. The parameter variation signal is applied to the control loop such as to immediately increase or decrease the motor supply voltage, as required, when any sudden change in load occurs, thereby ensuring rapid control response together with stability of control.

Abstract: An energy-saving induction motor control apparatus maintains the operation of a motor at an optimum power factor irrespective of changes in motor load, by generating a power factor compensation value which is varied in accordance with the motor supply voltage. The motor supply voltage is controlled such as to reduce any difference between the optimum power factor value and a measured power factor value, thereby ensuring that stable operation with minimum energy consumption are achieved over a wide range of motor load values.

Abstract: An automatic power factor control apparatus for an inductive load such as an AC induction motor includes a circuit for producing a signal varying in accordance with the load power factor, which is applied to control the duty cycle with which switching elements are alternately set in the conducting and non-conducting states by high frequency switching operation. A level of voltage applied to the control winding of a saturable reactor connected in series with the load is controlled by the switching elements, and the saturable reactor thereby continuously controls the input voltage and load current of the inductive load in accordance with the power factor.