JP2922716B2 - DC braking method of inverter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC braking method for an inverter device for driving an induction motor using semiconductor switching elements.

[0002]

2. Description of the Related Art Conventionally, in this type of inverter control device, a DC braking system using only a semiconductor switching element of an inverter has been performed.

[0003]

However, in the case of the DC braking system using only the semiconductor switching element of the inverter as described above, a sufficient braking force cannot be obtained when the inertia of the load is large due to the limitation of the allowable maximum current of the switching element. Therefore, there was a problem that it was not possible to stop immediately in an emergency stop or the like.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a three-phase voltage type inverter device that drives an induction motor using a semiconductor switching element and that can provide a large braking force. To provide a DC braking method.

[0005]

In order to achieve the above object, the present invention relates to a three-phase voltage type inverter device which has an opening / closing means and drives an induction motor using a semiconductor switching element. The switching means is disposed between any one of the above and the positive or negative DC bus, and the switching means is turned on during DC braking, and the other two-phase semiconductor switching element to which the switching means is not connected. Are turned on / off so that the current flowing through each semiconductor switching element does not exceed the maximum allowable current of each semiconductor switching element, and each semiconductor does not exceed the maximum allowable current of each semiconductor switching element. The duty ratio of the switching element is adjusted, then the two-phase semiconductor switching element is turned off, and after the current is reduced to zero or sufficiently, It is characterized in that so as to turn off the serial switching means.

[0006]

According to the present invention having the above-described structure, the opening / closing means includes a second switch for controlling the semiconductor switching element.
The currents flowing in the phases combine and flow. For this reason, the current flowing into the opening / closing means is twice as large as the current flowing through the semiconductor switching element, and the braking force of the induction motor is increased nearly four times, so that a large braking force can be obtained. Also, the switching means is energized only when the contacts are completely closed, and is opened after the DC braking operation is stopped and the current is reduced to zero. .

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. In this embodiment, a case of a three-phase inverter using the most common transistor as a main switching element will be described.

FIG. 1 shows a circuit diagram of an embodiment of the present invention. In the figure, 1 is a positive DC bus P, 2 is a negative DC bus N, 3 is a main circuit capacitor, and the main circuit capacitor 3 is disposed between the DC buses PN and holds a voltage between the DC buses PN. Have the function of doing. 4 is a U-phase positive side main switching element, 5 is a U-phase negative side main switching element, 6 is a V-phase positive side main switching element, 7 is a V-phase negative side main switching element, 8 is a W-phase positive side main switching element, 9 is a W-phase negative side main switching element, and 10 is an induction motor. 4 and 5, 6
7, 8 and 9 operate complementarily, and when one is on, the other is off, and the terminal potential of the induction motor 10 is either the positive DC bus P1 or the negative DC bus N2. Become. 11 is an electromagnetic relay, 12 is a control circuit, 13 is a base signal to each main switching element, 14 is a U-phase current detection signal, 15 is a V-phase current detection signal, and 16 is an electromagnetic relay on signal.

In a normal inverter operation, the control circuit 12 does not output the electromagnetic relay on signal 16, the electromagnetic relay 11 is turned off, and the PWM is performed by using the main switching elements 4 to 9.
Under the control, the induction motor 10 is driven by giving an arbitrary voltage and frequency.

Next, when it becomes necessary to stop the rotation rapidly while the induction motor 10 is rotating, the control circuit 12
Turns off all the base signals 13 of the main switching elements 4 to 9 once, makes the current of the induction motor 10 zero, and outputs an electromagnetic relay on signal 16 to turn on the electromagnetic relay 11.

Thereafter, the control circuit turns on / off the main switching element 4 and monitors the U-phase current detection signal 14 so that the U-phase current does not exceed the maximum allowable current of the switching element 4. When 14 increases, the duty ratio of the main switching element 4 is reduced, the duty ratio of the freewheel diode inserted in anti-parallel to the main switching element 5 is increased, and the U-phase current is reduced. When the U-phase current detection signal 14 becomes small, the main switching element 4
To increase the U-phase current.

Also, the V phase is exactly the same as the U phase,
The V-phase current detection signal 15 is monitored so that the V-phase current does not exceed the maximum allowable current of the switching element 6, and the conduction rate of the switching element 6 is adjusted. As a result, since the U-phase current and the V-phase current merge and flow through the electromagnetic relay 11, the braking force generated from the induction motor 10 is proportional to the square of the current, so that only the semiconductor switching element is energized. 4 times of

After that, a predetermined time elapses, and the induction motor
At the time when 10 stops, all the main switching elements 4 to 9 are turned off, the current of the induction motor 10 is reduced to zero or the current that can be cut off by the electromagnetic relay 11, and then the electromagnetic relay on signal 16 is turned off to turn off the electromagnetic relay 11. This can prevent a contact arc when the electromagnetic relay 11 is opened. In addition, U-phase current and V
As a detector for detecting a phase current, a detector prepared for overcurrent protection can be used, so that it is not necessary to newly add a detector.

As described above, in the present embodiment, the method of the present invention is described to be performed immediately when it is necessary to stop the rotation rapidly. However, the voltage and the frequency are gradually reduced by the PWM control using the semiconductor switching element. It is a matter of course that the system may be switched to the system of the present invention after performing a deceleration operation to a certain extent. In addition, when a deceleration operation in which the voltage and frequency are gradually reduced is performed, the voltage of the main circuit capacitor rises because energy is regenerated from the induction motor, but when the voltage of the main circuit capacitor reaches the allowable value, By switching to the method of the present invention, the voltage of the main circuit capacitor can be rapidly reduced, and overvoltage can be prevented.

In the above embodiment, the overcurrent is prevented by detecting the current. However, even if the conduction ratio is fixed, only a current substantially determined by the motor constant flows. By setting the rate, it is possible to carry out without performing current control.

[0016]

As described above, according to the present invention, the current flowing into the switching means is twice the current flowing through the semiconductor switching element, and the braking force of the induction motor is about 4 times.
The braking force is increased by a factor of two. In addition, the switching means is energized only when the contacts are completely closed, and is opened after the DC braking operation is stopped and the current is reduced to zero, so that the breaking current capacity may be low. Not only that, PW using semiconductor switching elements
In the case of performing a deceleration operation in which the voltage and frequency are gradually reduced by the M control, when the voltage of the main circuit capacitor reaches the allowable value, switching to the method of the present invention can prevent overvoltage of the main circuit capacitor. Such an excellent effect is achieved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive side DC bus P2 ... Negative side DC bus N3 ... Main circuit capacitor 4-9 ... U-W phase positive and negative side main switching element 10 ... Induction motor 11 ... Electromagnetic relay 12 ... Control circuit 13 ... Each Base signal to main switching element 14 ... U-phase current detection signal 15 ... V-phase current detection signal 16 ... Electromagnetic relay on signal

Claims (1)

(57) [Claims] 1. A three-phase voltage type inverter device having an opening / closing means and driving an induction motor using a semiconductor switching element, between one of output three-phase terminals and a positive or negative DC bus. The switching means is disposed, the switching means is turned on in a DC braking manner, and the other two-phase semiconductor switching elements not connected to the switching means are turned on / off. The conduction ratio of each semiconductor switching element is adjusted so as not to exceed the allowable maximum current of each semiconductor switching element, and then the two-phase semiconductor switching elements are turned off, and after the current is reduced to zero or sufficiently reduced. ,
A DC braking method for an inverter device, wherein the opening / closing means is turned off.