JPS6111550B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a starting device for a synchronous motor that does not require the use of a large-capacity circuit breaker and can be provided at low cost.

As a conventional starting device for this type of synchronous motor,
Fig. 1 shows what is generally known. In this figure, 1 is a synchronous motor, 2 is an AC power supply, 3 is a converter that converts the AC power supply 2 into DC, and 4 is a converter that converts the AC power supply 2 into DC.
5 is a first switching device connected between the inverter 4 and the synchronous motor 1; 6 is a step-up transformer; and 7 is the inverter 4 and the transformer. 8 is a third switching device connected between the transformer 6 and the synchronous motor 1, and 9 is an excitation device for the synchronous motor 1.

Next, the operation will be explained. The transformer 6 is provided for the purpose of being able to select the voltage of the inverter 4 lower than the voltage of the synchronous motor 1, but it has sufficient transformer action against the low frequency voltage of the synchronous motor 1 at low speed. is not obtained. Therefore, when starting the synchronous motor 1, the first switching device 5 is closed, the second and third switching devices 7 and 8 are opened, and the synchronous motor 1 is excited by the excitation device 9. Then, the output of the inverter 4 is supplied to the synchronous motor 1 via the first switching device 5. When the output frequency of the inverter 4 is gradually increased from a low frequency, the speed of the synchronous motor 1 increases in proportion to the frequency. When the frequency increases to a frequency sufficient for the transformer 6 to act as a transformer, the first switchgear 5 is opened, the second and third switchgears 7 and 8 are closed, and the output of the inverter 4 is transferred to the transformer. Synchronous motor 1 through 6
supply. In this way, the output frequency of the inverter 4 is further increased, and the rotational speed of the synchronous motor 1 is increased to the synchronous speed.

On the other hand, when stopping the synchronous motor 1, so-called regenerative braking can be performed in which the rotational energy of the synchronous motor 1 is returned to the AC power supply 2 via the starting device. That is, the inverter 4 is a converter,
Using converter 3 as an inverter, the second,
Close the third switching device 7, 8, and close the first switching device 5.
are kept open and excited by the excitation device 9 of the synchronous motor 1, and the rotational energy of the synchronous motor 1 is returned to the AC power supply 2 via these starter devices. When the speed of the synchronous motor 1 decreases to a frequency at which the transformer 6 cannot function as a transformer, the second and third switching devices 7 and 8 are opened, the first switching device 5 is closed, and the synchronous motor is further switched on. 1 slows down and stops.

Since the starting device of the conventional synchronous motor 1 is configured in this way, the first, second, and third switching devices 5, 7, and 8 are required to open and close very low frequency currents, so A reliable disconnection function for frequency currents is required, which necessitates the use of a large-capacity disconnector, which has the disadvantage of being expensive.

This invention was made with the aim of eliminating the above-mentioned drawbacks, and it is possible to gate the inverter and simultaneously cut off the excitation of the synchronous motor when switching circuits at low frequencies. Accordingly, the present invention aims to provide an inexpensive starting device for a synchronous motor by eliminating the need for low-frequency cut-off functions of the first, second, and third switching devices. This invention will be explained below.

FIG. 2 shows an embodiment of the present invention, and reference numerals 1 to 9 indicate the same components as those of the conventional example shown in FIG. 10 is a gate disconnection circuit of the inverter 4, and 11 is an excitation disconnection circuit that makes the output current of the excitation device 9 zero.

In FIG. 2, while the synchronous motor 1 is being started, the frequency gradually increases and when the first switching device 5 is opened and the second and third switching devices 7 and 8 are closed,
First, the inverter 4 is
The output current of the inverter 4 is made zero by gating it and then the output current of the inverter 4 is made zero, and then the excitation device of the synchronous motor 1 is made zero by the excitation and disconnection circuit 11. In this state, the circuit between the inverter 4 and the synchronous motor 1 is voltage-free, so the first, second, and third switching devices no longer require a disconnection function when they are opened or closed. After opening the first switching device 5 and closing the second and third switching devices 7 and 8, the excitation current is supplied to the synchronous motor 1 again, and the gate cutting of the inverter 4 is stopped and the inverter 4 If the output of synchronous motor 1 is supplied to synchronous motor 1, synchronous motor 1
can continue booting.

On the other hand, when stopping the synchronous motor 1, the second and third switching devices 7 and 8 are opened in the low speed range, and the first
When closing the opening/closing device 5, as in the case of starting,
If the inverter 4 is gated, the excitation current of the synchronous motor 1 is then reduced to zero, and the switchgear is opened and closed in this state, the first, second, and third switchgears 5, 7, and 8 are No cutting function is required.

As explained above, the present invention provides a gate/disconnection circuit for gating/disconnecting the inverter and an excitation/disconnection circuit for discontinuing the excitation device, and switches the starting circuit during starting or stopping of the synchronous motor. Since the output of the inverter and the excitation current of the synchronous motor are set to zero, the first, second, and third switching devices for switching the starting circuit no longer require a disconnection function, and therefore a disconnector is required. Since it is also possible to use the synchronous motor, it is possible to provide an economical starting device for a synchronous motor.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional starting device for a synchronous motor, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the figure, 1 is a synchronous motor, 2 is an AC power supply, 3 is a converter, 4 is an inverter, 5 is a first switchgear, 6 is a transformer, 7 is a second switchgear, and 8 is a third switchgear.
9 is an excitation device, 10 is a gate and disconnection device, and 11 is an excitation and disconnection device. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An inverter composed of a synchronous motor, a transformer, a converter that converts alternating current to direct current, and a thyristor that converts the direct current output of this converter to alternating current, a first switchgear connected between this inverter and the synchronous motor, a second switchgear connected between the transformer and the inverter; a third switchgear connected between the transformer and the synchronous motor;
The synchronous motor starting device selectively selects the first switchgear or the second and third switchgears to switch a circuit connection between the inverter and the synchronous motor, wherein the synchronous motor gates a thyristor of the inverter. A gate opening/closing circuit is provided, and an exciting opening/disconnecting circuit is provided to temporarily reduce the excitation current of the synchronous motor to zero, and the gate opening/closing device is connected from the first switching device to the second or third switching device at the time of startup, or When the circuit is switched from the second and third switchgear to the first switchgear at the time of stoppage, the inverter gate is cut off due to the gate breakage and disconnection, and then the synchronous motor is A starting device for a synchronous motor, characterized in that the circuit is switched by cutting off excitation.