JPS598155B2 - Control circuit of inverter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved control circuit for an inverter device that serves as a power source for driving an AC motor, and is particularly characterized by control when stopping a driven AC motor.

Conventionally, as an example of this type of inverter device, as shown in FIG. Ta.

In the figure, 1 is a DC power supply, 2 and 3 are DC reactors, 10 to 15 are second control elements forming the main part of the inverter circuit section C, 16 is an ACIJ actor, and 1? is a capacitor, and these AC reactor 16 and capacitor 11 are for smoothing the output current.

24 to 25 are first control elements constituting the current control chopper circuit section B; 4 to 9 and 20 to 21 are diodes; 22 is a diode stack; these diodes 4 to 9, 20 to 21 and the diode stuff 22 are , second control elements 10 to 15 and first control element 24
The second control element 10 can be used to bypass reactive power when .about.25 switches or to prevent overvoltage caused by switching.
-15, are provided to protect the first control elements 24-25.

18 is an AC motor serving as a load, and 36 is this AC motor 1.
8 is a switch, 19 is a tachometer generator attached to the rotating shaft of the AC motor 18, and 23 is a DC-CT that detects the DC current supplied to the inverter circuit section C.

30 is a start/stop circuit that controls starting and stopping of the inverter device; 33 is a base signal cutoff circuit that operates according to a command from the start/stop circuit 30; this base signal cutoff circuit 33 controls all control elements 10-15, 24- This is a circuit for generating a signal to cut off or turn off the base signal of No. 25.

29 is a frequency command circuit, and 31 is a speed detection circuit that detects the rotation speed of the AC motor 18 via the tachometer generator 19. The output of this speed detection circuit 31 and the output of the frequency command circuit 29 are compared, and the The difference is input to the PWM circuit 2T and the current finger ◆ circuit 28.

35 is the second control element 1 constituting the inverter circuit section C
This distribution control circuit has a function of generating on-off signals of 0 to 15. This distribution control circuit 35 includes a PWM circuit 27.
The output of the base cutoff signal circuit 33 and the output of the base cutoff signal circuit 33 are input.

32 is a DC-C current supplied to the inverter circuit section C.
A current detection circuit detects via T23, 26 is the first control element 2 constituting the current control chopper circuit section B.
This chopper signal circuit 26 has the function of generating 4 to 25 on-off signals. Output is input.

34 is a base signal amplification circuit that directly controls on/off of the first control elements 24 to 25 and the second control elements 10 to 15; this base signal amplification circuit 34 is connected to the distribution control circuit 3;
5 and the chopper signal circuit 26, and base signals B7-B8 (FIG. 2) for controlling the first control elements 24-25 and the second control elements 10-1.
It outputs base signals B1 to B6 (FIG. 3) that control 5.

AC power having current waveforms as shown by U, V, and W in FIG. 4 is supplied from the inverter device configured as described above to the AC motor 18, which is a load, and the AC motor 18 is driven.

Furthermore, when stopping the AC motor 18 driven by this inverter device, set the command ◆ value of the frequency command circuit 29 to 0, decelerate and stop the AC motor 18 by three-phase DC excitation, and then use the base signal The base signal cutoff circuit is output from the cutoff circuit 33, and the first control elements 24 to 24 of the main circuit are outputted from the cutoff circuit 33.
25 base signals B7-B8 and second control elements 10-
15 base signals B1 to B6 are turned off at the same time, the AC motor 18 is placed in a non-energized state, and then the switch 36 is controlled to be opened.

However, when the conventional inverter device is controlled as described above, the three-phase DC excitation current flowing through the AC motor 18 after the command value of the frequency command circuit 29 is set to 0 is
If the current flowing in the U phase is I, the current flowing in the phase is αI
, the current flowing in the W phase is (1-α)I.

Note that α=0≦α≦1 here. In this state, the base signal cutoff signal causes the first control elements 24 to 2 to
5 and the second control element 10-15 are turned off simultaneously, the current flows through the diode stack 22 for a certain period of time.

At this time, when the voltage of the DC power source 1 is E, reverse voltages of 1%E, %E, and %E are applied to the three windings of the AC motor 18, respectively. That is, although the voltages applied to the V-phase and W-phase windings are equal, the current values generally differ as shown in FIG. 5, so the current in the phase with the smaller current attenuates faster. (α
%, the V-phase and U-phase currents are equal, so in this case, this phenomenon does not occur. ) That is, since the AC motor 18 will be shifted from three-phase DC excitation to two-phase DC excitation, at this time, the direction of magnetic flux will change in electrical angle by a maximum of 6' in the forward or reverse direction.

As a result, the AC motor 18, which has once stopped due to braking by DC excitation, will again rotate slightly in the forward or reverse direction, resulting in a drawback that the accuracy of the fixed position stop control of the AC motor 18 will deteriorate. .

The present invention aims to eliminate the above-mentioned drawbacks and smoothly control the stopping of an AC motor driven by an inverter device.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 6 shows the circuit configuration of the main part of this embodiment, where 37 is a time limit circuit added to the circuit of the conventional example shown in FIG. 1, and the other circuits are the conventional circuit shown in FIG. 1. It has the same circuit configuration as the inverter device. In this example,
When stopping the AC motor 18, the command value of the frequency command circuit 29 is set to O, and the AC motor 18 is decelerated to a stop by three-phase DC excitation, and then the base signal cutoff signal is output from the base signal cutoff circuit 33 as a chopper signal. input to the circuit 26,
The first control elements 24 to 25 constituting the current control circuit section B are turned off, and the time limit circuit 37 is operated at the same time. After a certain period of time, the base signal cutoff signal is input to the distribution control circuit 35, and the inverter is switched off. The circuit configuration is such that the second control elements 10 to 15 forming the circuit section C are turned off.

Therefore, when the inverter circuit section C is operated with the current control chopper circuit section B turned off by turning off the first control elements 24 to 25, the main circuit current is changed from the DC power supply section A. The diode 21 and DC reactor 2 in the current control chopper circuit part B are connected from one terminal (for example, the lower terminal in FIG. 1) of the DC power supply 1 in the middle.
, further passes through the diode 4 and second control element 10 in the inverter circuit section C, further passes through the AC reactor 16, switch 36, AC motor 18 switch 36 and AC reactor 16, and then further passes through the inverter circuit section C. It returns to the other terminal of the DC power supply 1 through, for example, the diode 9 and second control element 15 therein, and further through the DC reactor 3 and diode 20 in the current control chopper circuit section B. Moreover, this current rapidly attenuates from the time when the first control elements 24 to 25 in the current control cutter circuit section B are simultaneously turned off. On the other hand, the second control elements 10 and 1 in the inverter circuit section C
5 remains on under the same conditions even after the first control elements 24 to 25 are turned off, so the three-phase AC current flowing through the AC motor 18 will attenuate at a constant rate.
No change in magnetic flux occurs until the current becomes zero. As a result, the three-phase DC excitation currents of the AC motor 18 are simultaneously attenuated as shown in FIG. 7, the direction of the magnetic flux of the AC motor 18 does not change, and the AC motor 18 can be stopped smoothly.

Although one embodiment of the present invention has been described above, the inverter device having the circuit configuration shown in this embodiment is not limited to the inverter device having a power supply control function and a frequency control function.
It goes without saying that this invention can be applied to all inverter devices for driving AC motors.The present invention is applicable to all inverter devices for driving AC motors. Since the alternating current motor is stopped at the same time, the effect of being able to stop the alternating current motor very smoothly is extremely large.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram of an example of a conventional inverter device, and Fig. 2 is a circuit diagram of an example of a conventional inverter device.
3 shows the output signal of the base signal amplification circuit applied to the control element of the inverter circuit, FIG. 4 shows the output signal of the base signal amplification circuit applied to the second control element constituting the inverter circuit, and FIG. Figure 5 shows the current flowing to the AC motor when the current is cut off, Figure 6 is a circuit diagram of the main part of an embodiment of this invention, and Figure 7 shows the waveform of the AC motor when the current is cut off in this embodiment. This is the current flowing through the

Claims (1)

[Claims] 1 A first control element that has the function of controlling the amount and frequency of AC power supplied to the AC motor and controls the amount of DC current supplied, and controls the on/off of this first control element. a chopper signal circuit that converts the DC power controlled by the first control element into the AC power, and a distribution control circuit that controls on/off of the second control element. In the inverter device, when stopping the inverter device, a signal to cut off the first control element is given to the chopper signal circuit, and then a signal to cut off the second control element is given to the distribution control circuit. 1. A control circuit for an inverter device, characterized in that a time limit circuit is provided to obtain a delay time until