The present invention relates to a motor controller made up of a power supply circuit for rectifying an AC power source to output desired DC voltages while, at the same time, improving the power factor of the AC power source, and to a motor drive circuit for driving a motor.
A motor controller operating as a rectifying circuit for rectifying an AC power source to provide a DC power supply and for performing speed control of a motor by using, in combination, a power supply circuit, which is capable of suppressing harmonics occurring in the power source current, and a motor driving circuit is disclosed in Japanese Laid-open Patent No. Hei 6-105563.
The motor controller is formed of a power factor improving converter circuit employing a step-up chopper circuit, which simultaneously performs suppression of harmonics in the power source current and control of the DC voltage, and an inverter circuit for driving the motor. The motor controller, at the time of low load operation, controls the DC voltage to take on the lowest voltage value which will allow the power factor to be improved and performs speed control of the motor through PWM control by the inverter circuit and, at the time of high load operation, stops the PWM control performed by the inverter and performs speed control of the motor through DC voltage control by the converter circuit, i.e., PAM control.
In the above described motor controller, the configuration of the motor speed control circuit at the time of low load operation and that at the time of high load operation is different, and so different speed controlling operations are necessary according to the conditions of the load. Namely, at the time of low load operation, the duty ratio of the PWM signal for the inverter is calculated from the speed deviation and, at the time of high load operation, the DC voltage command for the converter is calculated from the speed deviation.
Further, switching between the control circuit at the time of low load operation and the control circuit at the time of high load operation is carried out in accordance with the DC voltage value of the duty ratio of the PWM signal for the inverter, the speed command value and the present speed.
Thus, in the above described motor controller, it is required to have two kinds of speed control circuits, one for low load operation and another for high load operation, and hence, the control circuit becomes complex.
Further, since the determination of the condition for switching of the control circuits between the low load operation and high load operation is based on a number of different signals, many detector circuits are required.
An object of the invention is to solve the above described problems inherent in the known motor controller and to provide a motor controller which is capable of executing motor speed control by the use of one simple speed control circuit, whether the load is high or low.
The present invention relates to a motor controller comprising a rectifier circuit for converting AC power to DC power and a smoothing circuit, a converter circuit constituted of a chopper circuit for controlling the DC voltage by utilizing a switching operation and the energy storing effect of an inductance, a motor drive device made up of an inverter circuit connected between the output of the converter circuit and a motor, a converter control circuit for controlling the switching operation of the chopper circuit, an inverter control circuit for controlling the switching operation of the inverter circuit for driving the motor, a speed detector circuit for detecting the position of the rotor of the motor for calculating the speed of the motor, a speed control circuit responsive to a calculated speed value and a speed command value for performing speed control of the motor through the inverter control circuit, and a DC voltage control circuit responsive to the output signal of the speed control circuit for controlling the DC voltage through the converter control circuit.
As a preferred embodiment, the DC voltage control circuit is adapted to output to the converter control circuit a signal causing the DC voltage to increase or decrease when the output of the speed control circuit reaches a predetermined value.
As a preferred embodiment, the DC voltage control circuit is adapted to control the DC voltage through the converter control circuit such that the output of the speed control circuit takes on a predetermined value.
As a preferred embodiment, a duty ratio signal or a speed deviation signal representing a deviation of the calculated speed value from the speed command value is provided as the output of the speed control circuit.
As a preferred embodiment, the motor controller further comprises a DC voltage pulsation correcting circuit for detecting pulsating components of the DC voltage for changing the input signal to the inverter control circuit in accordance with the pulsating components.
In the above described structure, the inverter control circuit drives the switching device of the inverter to drive the motor in accordance with a position signal received from the speed detector circuit and the duty ratio signal received from the speed control circuit. The speed detector circuit detects an induced voltage by the motor and calculates the position of the rotor from the induced voltage to output the detected position signal in a pulse form and, at the same time, calculates the speed from the calculated position signal to output the same as the detected speed value to the speed control circuit. The speed control circuit calculates the duty ratio signal of the PWM pulse for the inverter from an external speed command and the detected speed value so that the speed deviation becomes zero. The inverter circuit, motor, speed detector circuit, inverter control circuit, and the speed control circuit constitute a motor speed control circuit, and speed control of the motor is executed in accordance with the external speed command. The converter control circuit controls the switching device of the chopper circuit in accordance with the signal from the DC voltage control circuit. The DC voltage control circuit detects the DC voltage and the output signal of the speed control circuit, for example, the duty ratio signal, and controls the DC voltage such that the DC voltage rises by a predetermined amount when the duty ratio signal reaches a predetermined value, for example, the upper limit value of a range of the duty ratio signal, and such that the DC voltage falls by a predetermined value when the duty ratio signal reaches a lower limit value. The converter circuit, converter control circuit, and the DC voltage control circuit constitute a DC voltage control circuit of the converter and the DC voltage is controlled thereby.
By combining the motor speed control circuit with the converter DC voltage control circuit and allowing both the circuits to operate respectively, speed control of the motor can be achieved by the use of a simple structure irrespective of the load conditions.