JPH0759160B2 - AC motor controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an AC motor for efficiently driving an AC motor by connecting a capacitive load in parallel to the output side of a current control type inverter. The present invention relates to a control device.

(Prior Art) There are various types of conventional AC motor control devices.

For example, a sine wave output current type GTO inverter uses an inverter circuit that uses a self-extinguishing type semiconductor device (gate turn-off thyristor or GTO) to PWM control the output current waveform,
This is a method of controlling to a sine wave. (The 59th National Conference of the Institute of Electrical Engineers of Japan, No. 582, "Induction motor characteristics when driving a sine wave output current type GTO inverter") However, the above method results in forced commutation of the inverter circuit in all operating areas, resulting in self-extinguishing type. Snubber circuit loss to absorb the switching surge voltage of the semiconductor element increases,
There is a problem that the inverter operating efficiency is reduced.

As a conventional system, there is a current source inverter shown in FIG. In the figure, the input AC terminals 11, 12 a rectifier, 13 a DC reactor, 14 denotes an inverter, 15 is an induction motor load, 16 capacitive load, 14 ₂ is a thyristor. In this circuit, the AC power supplied from the input AC terminal 11 is forward converted into DC power by the rectifier 12, smoothed by the DC reactor 13, and the DC power is converted back to AC power again by the inverter 14. The inversely converted AC power is supplied to the induction motor 15 and the capacitive load 16.

The current vectors of the induction motor 15 and the capacitive load 16 in this case are shown in FIG. The load current IM of the induction motor 15 is the power factor angle θ.
_{With 1} , the active current component I _P and the delayed reactive current component IL can be separated. On the other hand, the current IC of the capacitive load 16 is a leading reactive current component. Therefore, if the IC is larger than IL, the inverter 14 supplies the current I ₁ having the lead power factor angle θ ₂ and thus the operation by natural commutation is possible. In other words, if ₂ is 10 ° to 20 ° power factor angle θ proceeds at a commercial frequency basis, even if a switching element of each arm of the inverter 14 in thyristor 14 _2, since the thyristor 14 ₂ between the reverse pressure period is sufficient Load commutation (natural commutation) is possible.

While the thyristor 14 ₂ was loaded commutated, if it is possible to speed control the induction motor 15 and variable speed operation, as compared with the case of forced commutation, the operating efficiency of the inverter circuit has the characteristic that greatly improved. Further, since the circuit configuration of the inverter 14 becomes simple, it is easy to increase the voltage of the inverter circuit. The same applies when the induction motor 15 is a synchronous motor.

(Problems to be Solved by the Invention) However, the circuit system shown in FIG. 4 has the following problems. In FIG. 5, the current IC of the capacitive load 16 is determined by the following equation.

Current IC ∞ (inverter output frequency) ₂ This is because when the induction motor 15 is controlled at a variable speed by the inverter 14, it is common to control the ratio between the inverter output frequency and the output voltage to be constant. As a result, when the operating frequency of the inverter 14 decreases, the current IC of the capacitive load 16 decreases significantly, but since the reactive current component IL of the delay of the induction motor 15 is almost constant regardless of the operating frequency, the inverter output If the frequency changes widely, the output current I ₁ of the inverter 14 cannot maintain the predetermined advance power factor angle θ ₂ , and the inverter 14 has a problem that load commutation becomes impossible.

When the capacitance of the capacitive load 16 is increased so that the advanced power factor can be maintained even at a low output frequency, there is a problem that the output capacitance of the inverter 14 increases at a high output frequency. For example, the output frequency is 100 when estimated with a constant torque load.
In order to operate in the range of 50% to 50%, the output KVA of the inverter 14 needs to be 300 to 400% of the input KVA of the induction motor 15, and the circuit system shown in FIG. 4 is economically and practically large. There was a problem.

Therefore, the applicant of the present application has proposed a method in which each arm of the inverter is composed of a self-arc-extinguishing type semiconductor element and spontaneously commutates at a frequency higher than a predetermined frequency (Japanese Patent Application No. 60-223455 (Japanese Patent Application Laid-Open No. 62-85693)),
And a system in which each of the arms is composed of a series circuit of a self-proof semiconductor device and a thyristor and is controlled in the same manner as described above (Japanese Patent Application No.
60-223456 (Japanese Patent Laid-Open No. 62-85691).

The present invention is a further development of the above method, which can improve the operation efficiency of the inverter, prevent the expansion of the operation range and the increase of the output KVA capacity, and provide an AC current that efficiently gives a gate to the self-extinguishing type semiconductor device. It is intended to provide a control device for a machine.

[Structure of Invention]

(Means for Solving Problems) The present invention relates to a rectifier that converts AC into DC, a DC reactor that smoothes the output of the rectifier, and an inverter that converts the smoothed DC into AC and drives an AC motor. In an AC motor control device including a circuit, an arm that constitutes the inverter is configured by a series circuit of a self-extinguishing semiconductor element and a thyristor, and a capacitive load is connected to an output of the inverter circuit, and the inverter circuit. Of the thyristor, the first gate signal for turning on the self-arc-extinguishing semiconductor element and the second gate signal for turning off the other self-extinguishing semiconductor element when the load power factor is delayed power factor. A third gate signal for conduction is output to forcibly commutate the self-extinguishing type semiconductor device to operate as a self-excited inverter, and when the load power factor is advanced, the self-extinguishing process is performed. A first gate signal for turning on the arc-shaped semiconductor element and a third gate signal for turning on the thyristor are output, and a second gate signal for turning off the other self-extinguishing semiconductor elements is not output. Gate control means for operating as a separately excited inverter by natural commutation of the thyristor is provided.

(Operation) In the above configuration, the load power factor becomes a lag power factor in a region where the output frequency of the inverter is low, and the gate control means brings the self-arc-extinguishing semiconductor element into a conduction state with the first gate signal. A second gate signal for turning off the other self-arc-extinguishing semiconductor element and a third gate signal for turning on the thyristor are output to forcibly commutate the self-extinguishing semiconductor element and self-excited. Operate as an inverter. Further, in a region where the output frequency of the inverter is high, the load power factor advances and becomes a power factor, and the gate control means causes the first gate signal for conducting the self-arc-extinguishing semiconductor element and the third gate for conducting the thyristor. A second device for outputting a signal to turn off the other self-extinguishing semiconductor element
The gate signal is not output and the thyristor is operated as a separately excited inverter by natural commutation so that the self-extinguishing semiconductor element does not interrupt the current.

(Example) An example of the present invention is shown in FIG. In the figure, those having the same reference numerals as in FIG. 4 are circuit elements having the same function. Further, 17 is a speed reference, 18 is a control circuit, 14 ₁ is a self-arc-extinguishing semiconductor element, 14 ₂ is a thyristor, 14 ₃ is a gate circuit for turning on / off the self-arc-extinguishing semiconductor element 14 ₁ , and 144 is a thyristor.
This is an on-gate circuit that turns on 14 ₂ .

In FIG. 1, the AC power supplied from the input AC terminal 11 is forward-converted into DC power by the rectifier 12, and the DC reactor 13
After being smoothed by, the power is inversely converted by the inverter 14 and AC power is supplied to the capacitive load 16 and the induction motor 15. At this time, the rotation speed of the induction motor 15 is controlled via the control circuit 18 according to the set value of the speed reference 17, and the rotation speed and the input voltage are generally controlled in a proportional relationship.

If the speed reference 17 is set in the low output frequency range, the inverter
14 is carried out in forced commutation due to the self-extinguishing type semiconductor elements 14 _1. That is, as shown in FIG. 2A, the self-arc-extinguishing type semiconductor device 14 ₁ is turned on by an on-gate pulse 21 output from the gate circuit 14 ₃ and turned off (forced commutation) by an off-gate pulse 22. As shown in FIG. 2 (b), the thyristor 14
₂ is turned ON gate pulse 23 outputted from the gate circuit 14 _4. At this time, the commutation surge voltage due to the forced commutation of the self-arc-extinguishing semiconductor element 14 ₁ is initially borne by the self-arc-extinguishing semiconductor element 14 ₁ and then the thyristor 14 ₂ recovers insulation (turns off). It comes to share the voltage. In the low output frequency region, the output voltage of the inverter 14 is low, and the commutation surge voltage is also suppressed by the capacitive load 16, so that it can be suppressed within the rated value of the self-arc-extinguishing type semiconductor device 14 ₁ .

In the medium output frequency range in which the set value of the speed reference 17 is intermediate, the phase of the output current I ₁ of the inverter 14 is near the power factor angle of 0 (output power factor 1), so the thyristor does not completely commutate. Forced commutation of the self-extinguishing type semiconductor device 14 ₁ is performed in the same manner as at the low output frequency.

With this forced commutation in the output power factor near 1, the output voltage instantaneous value immediately after the self-turn-off semiconductor element 14 ₁ has flowed forced rolling is small, even the commutation surge voltage is applied, within the rated value Can be suppressed to.

When the set value of the speed reference 17 is in the high output frequency region, the lead reactive current component IC of the capacitive load 16 becomes sufficiently large, and the current phase of the output current I ₁ of the inverter 14 becomes the lead phase. Accordingly, the thyristor 14 ₂ previously to divert the load commutation mode,
Without interrupting the self-turn-off semiconductor element 14 ₁ in the current. That is, the self-extinguishing type semiconductor elements 14 _1, as shown in FIG. 2 (c), but is turned on by the on-gate pulse 21 do not give off a gate pulse 22. In addition, the thyristor 14 ₂ is the second
As shown in FIG. 7D, the gate is turned on by the on-gate pulse 23 and is turned off by the load commutation (natural commutation) because of the leading power factor. Since the commutation is performed in the load commutation mode as described above, generation of surge voltage and commutation loss due to commutation can be significantly suppressed. Also,
Since the off-gate pulse 22 is not applied to the self-arc-extinguishing type semiconductor device in the high output frequency region, the off-gate circuit loss is eliminated. Further self-extinguishing type semiconductor elements 14 ₁ because they do not cut off the current, thereby improving the reliability.

In the control device for an induction motor of the present invention which operates as described above, the capacitance of the capacitive load 16 can be reduced as compared with the conventional device, and as a result, the self-extinguishing type semiconductor device 14 that constitutes the inverter 14 can be used. The snubber circuit capacity of ₁ can also be downsized and the operating efficiency can be improved. Since the current is small in the low and medium output frequency regions (in particular, the tendency is remarkable in the square load characteristic), the capacitance of the self-arc-extinguishing semiconductor element can be determined according to the current in the low and medium output frequency regions. It is possible and can be miniaturized. Further, since the off-gate pulse is not applied to the self-arc-extinguishing type semiconductor device in the region where the current of high output frequency is large, the capacity of the off-gate circuit becomes small.

It is not particularly limited to the characteristics and form self-turn-off type semiconductor device 14 ₁ in the present invention. FIG. 3 shows 1 of the inverter 14
The circuit structure for the arm is shown, but _two thyristors 142,
The self-turn-off type semiconductor device 14 ₁ are connected one in series constitutes one arm minute. In this case, the self-extinguishing type semiconductor device 14 ₂
When the reverse voltage rated value of 1 is small, the diode 14 ₅ is provided in anti-parallel so that the reverse voltage applied to this arm can be entirely shared by the thyristor 14 ₂ . Since the self-arc-extinguishing type semiconductor device 14 ₁ generally has a small reverse voltage withstanding capability, it is necessary to connect a diode in series to have a reverse voltage withstanding capability.However, by connecting a thyristor 14 ₂ in series, the diode There is also a feature that can omit o. Note there is no particular limitation to the number of series configuration and a thyristor 14 ₂ and a self-extinguishing semiconductor element 14 ₁ in each arm of the inverter 14 in the present invention.

The self-extinguishing type power conversion element 14 ₁ generally has a large turn-on loss at the start of conduction, but as a means for reducing this turn-on loss, the thyristor 14 ₂ has a time longer than that of the self-extinguishing type semiconductor element 14 _1. It is possible to reduce the turn-on loss by starting the conduction after a delay.

In the present invention, the output current waveform of the inverter 14 is not particularly limited to a sine wave, and for example, it can be operated as a sine wave current by pulse width control in the low output frequency region and as a 120 ° square wave current in the medium and high output frequency regions. You can also

In addition, various modified circuits can be configured without changing the gist of the present invention.

〔The invention's effect〕

According to the control device for an AC electric motor of the present invention, the following effects can be obtained.

(1) In the low and medium output frequency range, the current is small (especially, the tendency is remarkable in the square load characteristic).
The capacity of the self-arc-extinguishing type semiconductor element can be determined according to the current in the low and medium output frequency regions, and the size can be reduced.

(2) Since the off-gate pulse is not applied to the self-extinguishing type semiconductor device in the high output frequency region, the loss of the off-gate circuit is eliminated and the efficiency is improved.

(3) The reliability of the self-extinguishing semiconductor element is improved because the self-extinguishing semiconductor element does not block the current in the high output frequency region.

(4) The current is large in the high output frequency region, but the off-gate pulse is not applied to the self-arc-extinguishing type semiconductor device in this region, so that the capacity of the off-gate circuit can be reduced and the size can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the control device for an AC electric motor of the present invention, FIG. 2 is a gate pulse waveform diagram for explaining the operation of the present invention, and FIG. 3 is an arm configuration of an inverter 14 in the present invention. FIG. 4 is a main circuit configuration diagram of a conventional AC motor control device, and FIG. 5 is a vector diagram showing the phase relationship of various currents. 11 ...... input AC terminal, 12 ...... rectifier, 13 ...... DC reactor, 14 ...... inverter, 15 ...... induction motor, 16 ...... capacitive load, 17 ...... speed reference, 18 ...... control circuit, 14 ₁ ...... self-turn-off power converter, 14 ₂ ...... natural commutation power converter element, 14 ₃ ...... gate circuit of the self-turn-off power converter, 14 _3a ...... on-gate circuit, 14 _3b ...... off-gate circuit , 14 ₄ …… Natural commutation type power conversion element gate circuit, 14 ₅ …… Diode.

Claims (1)

[Claims] 1. A control device for an AC electric motor comprising a rectifier for converting AC into DC, a DC reactor for smoothing the output of the rectifier, and an inverter circuit for converting the smoothed DC into AC and driving the AC motor. In, the arm constituting the inverter is configured by a series circuit of a self-arc-extinguishing type semiconductor element and a thyristor, a capacitive load is connected to the output of the inverter circuit, and the load power factor of the inverter circuit is a delay power factor. At this time, a first gate signal for turning on the self-turn-off semiconductor element, a second gate signal for turning off the other self-turn-off type semiconductor element, and a third gate signal for turning on the thyristor are output. Then, forcibly commutating the self-extinguishing type semiconductor element to operate as a self-excited inverter,
When the load power factor is the advanced power factor, a first gate signal for turning on the self-arc-extinguishing semiconductor device and a third gate signal for turning on the thyristor are output to output the other self-turn-off semiconductor device. A control device for an AC electric motor, comprising gate control means for operating as a separately excited inverter by natural commutation of the thyristor so as not to output a second gate signal which is non-conductive.