An electrical three-phase generator and motor control circuit. The generator is made of three alike wave-generating units in cascade each generating a respective trapezoidal wave corresponding to a respective phase of the generator. Each unit comprises a small detector in series with a control circuit varying the amplitude of the wave proportionately to a control voltage representative of and corresponding to variations of voltage from voltage sources and applied to a motor and an integrating circuit consisting of an integrating amplifier and an integrating capacitor and a double limiter in parallel therewith. The control voltage is developed by a voltage divider across the motor control circuit.
An inverter utilizes class B amplifiers to amplify a compressed sine wave signal. Increased efficiency of the inverter may be achieved by utilizing supplemental paths in the amplifier, to carry the load current with less dissipation, for at least a portion of the signal cycle. In addition, a filtering arrangement, including a transformer having a three leg core, may be utilized to provide a sine wave voltage between the output lines and a neutral point, as well as from line to line.
A commutatorless DC motor drive arrangement, in which an inverter is utilized to feed a synchronous AC motor, is provided with an all electrical speed control that eliminates the need for a motor shaft position sensor. The rate at which firing pulses are applied to the inverter, and hence the speed at which the synchronous motor is driven by the inverter output, is made dependent upon the magnitude of the applied DC voltage. Upon start-up of the drive arrangement, the applied DC voltage is made to increase in a linear fashion in order to provide gradual buildup of the motor speed. In order to ensure natural commutation of the inverter, an automatic trial-and-error method is utilized to determine that the inverter is started in the desired leading power factor mode of operation.
A method and apparatus is disclosed for reducing the heat generated by three-phase motors operating under load in cooled chambers such as industrial walk-in refrigerators and freezers. Specific control elements are introduced into the three power conductors connected to a three-phase motor, the elements chosen so as to cause the motor to turn at a speed below a certain critical speed, above which the elements have no control over the motor power used or the motor speed. The results of inserting the control elements into the motor power conductors are (1) the motor turns at a reduced speed and (2) the heat generated by the motor is reduced. In addition, the control elements themselves are specifically chosen and are of such a nature that they generate virtually no heat in the process of reducing the power supplied to the motor.
A motor control circuit includes a pulse width modulation (PWM) signal generating circuit, a driving circuit and a waveform-shaping circuit connected between the PWM signal generating circuit and the driving circuit. The PWM signal generating circuit generates a square wave with a sequence of alternating on-time and off-time. The waveform-shaping circuit adjusts the rise-time and the fall-time of the square wave to be both within a range of 5% to 15% of the square wave period, and the driving circuit outputs a driving signal to a fan motor according to the adjusted square wave.
A motor control circuit includes a pulse width modulation (PWM) signal generating circuit, a driving circuit and a waveform-shaping circuit connected between the PWM signal generating circuit and the driving circuit. The PWM signal generating circuit generates a square wave with a sequence of alternating on-time and off-time. The waveform-shaping circuit adjusts the rise-time and the fall-time of the square wave to be both within a range of 5% to 15% of the square wave period, and the driving circuit outputs a driving signal to a fan motor according to the adjusted square wave.
