Dc bus voltage regulation by controlling the frequency in a variable

Abstract

The invention is a direct current bus voltage regulator for an alternating current inverter, where draws direct current from a DC bus, and the inverter supplies alternating current having a controlled frequency to an AC motor. The alternating current frequency controlled by a signal received through a precedence determining circuit that determines which signal will control the AC current frequency. This circuit receives signals from a ramp generator, an AC current limiting circuit and a DC bus voltage sensing circuit. The precedence determining circuit passes the signal with the highest priority on to a voltage control oscillator which in turn controls the AC current frequency delivered to the AC motor, thereby controlling the motor speed. The ramp generator signal indicates an operator input motor control command and has the lowest priority of the three signals. The AC current limiting circuit has second priority and indicates that current flow between the inverter and the AC motor is greater than a predetermined current value. The DC bus voltage signal, which has the highest priority, indicates the presence of a DC bus voltage greater than a predetermined value of DC bus voltage. During the deceleration of an AC motor electric power is generated. This generated power is fed back into the DC bus causing it to overshoot the predetermined DC bus voltage value. By permitting the DC bus voltage signal to have first priority in controlling the motor speed during deceleration, overshoot of the DC bus voltage can be eliminated thereby reducing the chance of damage to electrical components of the motor control device.