JPS6122558B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a control system for a synchronous motor that can operate stably without commutation failure in a control method for a synchronous motor driven by a forced commutation type current source inverter having a commutation circuit. Regarding.

FIG. 1 shows a conventional synchronous motor control device using a current source inverter. In the figure, 1 is a three-phase AC power supply, 2 is a forward converter that converts the AC of the three-phase AC power supply 11 into DC, 3 is a DC reactor that smoothes the output current of the forward converter 2, and 4 is smoothed by the DC reactor 3. 5 is a synchronous motor energized by the inverter 4; 7 is an armature winding and a field winding 6 of the synchronous motor;
14 is a phase control circuit that controls the phase of the gate pulse of the thyristor of the forward converter 2; 13 is a phase control circuit that controls the phase of the forward converter 2; 12 is a synchronous motor 5 is a current control circuit that controls the input current; 15 is a current detector that converts the current detected by the current transformer 8 to DC; 17 is a position detection signal from the position detector 7 that determines the commutation timing of the inverter 4; 18 is a speed detection circuit that detects the speed of the synchronous motor 5; 11 is a speed control circuit that controls the speed of the synchronous motor 5; 16;
β detects the polarity of the output signal of the speed control circuit 11 and outputs the transition/phase ripple signal of the control advance angle β.
The switching circuit 10 is a speed setting device.

When driving the synchronous motor 5 with a current source inverter device having such a configuration, commutation is forcibly carried out using a commutation capacitor, so the predetermined control advance angle β cannot be controlled like a natural commutation type non-commutator motor. Although it has the advantage that it does not need to be installed, can operate at a power factor of 1, and has minimal torque pulsation, it has the following problems. In other words, when an attempt is made to reduce the speed reference signal that is the output of the speed setter 10 to decelerate the synchronous motor 5, the speed feedback signal that is the output of the speed detection circuit 18 becomes larger than the speed reference signal, and the polarity of the output signal of the speed control circuit 11 changes. is reversed. The β switching circuit 16 detects this and increases the control advance angle β to 90° or more at once to bring it into the regeneration region.At the same time, in order to suppress the rush of current, the phase of the forward converter 2 is controlled to make the current once zero. After that, regenerative current is applied to perform regenerative operation. However, when the load on the synchronous motor 5 is light, the commutating capacitor voltage is low, and when decelerating by lowering the speed reference signal, the phase of the forward converter 2 is first changed to make the current zero, so the commutating capacitor voltage is low. The voltage further decreases, and in this state, the phase shift is removed and a regenerative current flows, causing the inverter 4 to fail in commutation and stop operating.

An object of the present invention is to provide a control device for a synchronous motor that can drive a synchronous motor using a forced commutation type current source inverter device and continue stable operation without commutation failure at the start of deceleration, and that eliminates the above-mentioned drawbacks. Our goal is to provide the following.

The present invention will be explained below with reference to the drawings.

An embodiment of the present invention is shown in FIG. 2 corresponding to FIG. 1, and will be described with reference to this. Items with the same reference numerals have the same functions. In FIG. 2, 20 is an absolute value conversion circuit that outputs a current reference signal of negative polarity regardless of whether the polarity of the output signal of the speed control circuit 11 is positive or negative, and 21 is an output signal that changes in a stepwise manner from the β switching circuit. The first-order delay circuit 9, which changes the speed with a predetermined time constant, is a pulse generator for detecting the speed of the synchronous motor 5. The output frequency of the inverter 4 is determined by the terminal voltage of the synchronous motor 5 and the output signal of the speed detection circuit 18. 24 is a three-phase AC signal that is the output of the three-phase AC synthesizer circuit 23 and a β phase control signal that is the output of the first-order lag circuit. A β phase control circuit 25 controls the phase of the inverter 4, and a β logic circuit 25 determines the commutation timing of the thyristor of the inverter 4 based on the output of the β phase control circuit.

In a synchronous motor control device using a current source inverter having such a configuration, when the synchronous motor 5 is decelerated by lowering the speed reference signal that is the output of the speed reference circuit 10, the speed feedback signal of the output of the speed detection circuit 18 is It becomes larger than the speed reference signal, and the polarity of the output signal of the speed control circuit 11 changes. The β switching circuit 16 detects a change in the polarity of the output signal of the speed control circuit 11 and outputs a signal that changes in a stepwise manner. However, the first-order delay circuit 21 converts the signal into a signal that changes over a predetermined time. Ru. Since the output signal of this first-order lag circuit 21 is a β phase control signal, if the β phase control signal changes over time, the phase of the output current of the inverter 4 is changed by the β phase control circuit 24 from β=0° to β= The angle changes over the predetermined time up to 150°. In other words, the power running state changes to the regenerative state over a predetermined period of time, and the phase of the forward converter 2, that is, the polarity of the output DC voltage of the forward converter 2, changes to follow the inverter, and the current becomes zero. It flows continuously. Therefore, the commutation capacitor voltage of the inverter 4 does not decrease, and the deceleration can be stably performed without commutation failure.

As explained above, according to the present invention, the synchronous motor is driven using a forced commutation type current source inverter, so unlike the natural commutation type, there is no need to provide a control lead angle β, and the power factor is 1. I can drive with
Torque pulsation is also minimized, and when further deceleration is performed, stable operation can be continued without commutation failure at the start of deceleration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional synchronous motor control device, and FIG. 2 is a block diagram of an embodiment of a synchronous motor control device according to the present invention. 1...Three-phase AC power supply, 2...Forward converter, 3...
DC reactor, 4... Inverter, 5... Synchronous motor, 11... Speed control circuit, 12... Current control circuit, 14... Phase control circuit, 17... Position detector, 16... β switching circuit, 21 ...first-order delay circuit, 24 ....beta. phase control circuit, 25 ....beta. logic circuit, 23 .... three-phase AC synthesis circuit.

Claims (1)

[Claims] 1. A forward converter that converts alternating current into direct current, a direct current reactor that smoothes the direct current output of the forward converter, a self-excited inverter that converts the smoothed direct current back into alternating current of a predetermined frequency, and the self-excited inverter. A control device comprising a synchronous motor to which an AC output of β to detect the polarity of the phase AC signal and the output signal of the speed control circuit
A β phase control circuit is provided to control the phase of the self-excited inverter using the output signal of the first-order lag circuit which changes the step signal of the output of the switching circuit over a predetermined period of time and outputs the resultant signal. A control device for a synchronous motor that changes over a predetermined period of time.