JPS631398A - Controller for ac motor - Google Patents

Abstract

PURPOSE:To reduce the output capacity of an inverter circuit by composing the arms of the inverter circuit of a series circuit of a self-extinguishing type power converter and a natural commutation type power converter to improve the output power factor of the inverter. CONSTITUTION:A voltage phase detector 19 for detecting the output voltage phase of an inverter circuit 14 is provided, and controlled while deciding which kind of commutation is to be conducted, forced commutation by means of a self-extinguishing type power converter 141 or natural one by means of a natural commutation type power converter 142. Here, a range for forced commutation by means of the converter 141 is increased to a range of high output frequency, such as the intermediate high speed output frequency range of the inverter 14. As a result, the necessity of increasing the capacity of a capacitive load 16 is reduced, and the inverter circuit 14 is reduced in its output capacity even in a high output frequency range.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to a control m+ device for an AC motor, and in particular, when the AC motor is operated at variable speed, the input voltage (primary voltage ) and an input current (primary current) to control the commutation and current of a power conversion element in an inverter circuit.

(Prior Art) In recent years, as a control device for driving an AC motor at variable speed, one using a self-extinguishing power conversion element as the power conversion element of an inverter circuit has been proposed. FIG. 5 shows an example of the circuit configuration of this type of AC electric control device.

In FIG. 5, 11 is an input terminal of an AC Ti source, 12 is a rectifier that converts AC into DC, 13 is a DC reactor that smoothes the output from this rectifier 12, and 14 is a DC that is smoothed by this DC reactor 13. Convert it to alternating current. An inverter circuit that drives the AC power train 1ff15 such as an induction 'RDR' which is a load, 16 a capacitive load such as a capacitor connected to the output terminal of this inverter circuit 14, and 17 a speed standard setting device for setting a speed standard. , 18 is a control circuit, 141 is a self-extinguishing power conversion element such as a gate turn-off thyristor that constitutes the inverter circuit 14, 1
Reference numeral 42 designates natural commutation type power conversion elements such as thyristors, which are provided in series with this self-extinguishing type power conversion element 141 and constitute the inverter circuit 14.

The operation of such an AC-powered emergency control device can be summarized as follows. That is, AC power supplied from the input terminal 11 of the AC power source is converted into DC power by a rectifier 12, smoothed by a DC reactor 13, and further converted back to AC power by an inverter circuit 14. This AC power is supplied to the AC power D^15 and the tolerant load 16.

When the AC power i71115 is driven at variable speed in this way, the output current I1 of the inverter circuit 14, the input current (primary current) IM of the AC ri frame 15, and the input current 1c of the displacement load 16 are The relationship is shown in a vector diagram as shown in Fig. 6. In FIG. 6, the input current of the convex load 16 is ■. The relationship is as shown in the following equation.

Ioct- (output frequency of the inverter circuit 14) 2 Therefore, in the operating region where the output frequency of the inverter circuit 14 is low, the output current I of the inverter circuit 14 has a delayed phase, and the self-extinguishing power conversion that constitutes the inverter circuit 14 Forced commutation is performed with element 14. On the other hand, in an operating range where the output frequency of the inverter circuit 14 is high, the output current 11 of the inverter circuit 14 has an advanced phase, and natural commutation can be performed in the natural commutation type power conversion converter 142 that constitutes the inverter circuit 14. .

However, the above-mentioned AC motor control I1l device has the following problems. In other words, as described above, the input current of the tolerant load 16 is ■.

changes in proportion to the square of the output frequency of the inverter circuit 14. Therefore, in the intermediate range of the output frequency of the inverter circuit 14, when a large load is applied to the AC motor 15. Since the output current I1 of the inverter circuit 14 has a delayed phase as is clear from the vector relationship shown in FIG. We need to increase the world. In other words, the input current (primary current) IM of the AC motor 15 is
It is necessary to reduce the frequency as the output frequency of the inverter circuit 14 decreases, making it impossible to operate the AC jammer t115 in a wide variable frequency range.

On the other hand, in an operating range where the output frequency of the inverter circuit 14 is high, in order to cause the natural commutation type power conversion element 142 to naturally commutate, it is necessary to advance the phase at the vector opening in FIG. 6 by about 30 degrees based on the commercial frequency. When the output frequency of the inverter circuit 14 increases, the leading phase angle θ2 increases accordingly, and as a result, the output power factor of the inverter circuit 14 decreases. The output capacity of the inverter circuit 14 is greatly increased compared to the input capacity of the AC power supply ii11fil5.

(Problems to be Solved by the Invention) As described above, in the conventional AC motor control device, not only is it not possible to perform AC motor-like operation in a wide variable frequency range, but the output power of the inverter circuit is There was a problem in that the rate decreased and the output capacity ω increased significantly.

Therefore, the present invention aims to improve the output power factor of the inverter circuit and reduce its output capacity, as well as to provide a compact, economically advantageous, and reliable inverter circuit that can perform separate AC operation in a wide variable frequency range. The purpose is to provide a control device for a high AC power TLL machine.

[Configuration of the Invention (Means for Solving the Problems)] In order to achieve the above object, the present invention includes a rectifier that converts alternating current into direct current, a direct current reactor that smoothes the output from this rectifier, and a direct current reactor that smooths the output from this rectifier. In the control equipment for an AC electric motor, which is composed of an inverter circuit that converts DC smoothed by a reactor into AC and drives an AC electric converter, the arm that constitutes the inverter circuit is connected to a self-arc-extinguishing power conversion element. and a naturally commutated power conversion converter, and a first control means for controlling the inverter circuit by forced commutation by connecting a capacitive load to the output terminal of the inverter circuit; a second control means for controlling the inverter circuit by natural commutation; a voltage phase detection means for detecting the output voltage phase of the inverter circuit; The output voltage phase detected by the voltage phase detection means is compared with a predetermined phase angle value. Further, the present invention is characterized in that the determination means for determining whether to perform the forced commutation or the natural commutation based on the comparison result is biased.

<<Function>> Since the above-mentioned control device for AC electric power is provided with voltage phase detection means for detecting the output voltage phase of the inverter circuit, the timing at which the output current I1 of the inverter circuit reaches the advance phase θ2 described above is determined. When the self-arc-extinguishing power conversion element is forced to commutate, if the line voltage of the input voltage (primary voltage) of the AC motor is the effective value EM, then the self-arc-extinguishing power converter element has F] - EMs. A reverse voltage of *nθ2 is applied. Therefore, this reverse voltage .rl E Msi
While the voltage phase detection means detects the output voltage phase of the inverter circuit, the self-extinguishing power conversion element performs forced commutation until nθ2 becomes a value lower than the rated voltage of the self-extinguishing power conversion element. By controlling the inverter circuit in this manner, the inverter circuit can be operated with high reliability through forced commutation. As a result, there is no need to increase the capacity of the capacitive load, and even if the AC motor is operated at variable speeds over a wide range, it is possible to prevent the output capacity of the inverter circuit from increasing.

(Embodiment) The present invention provides a voltage phase detection means for detecting the output voltage phase of an inverter circuit, and controls the timing of extinguishing a self-extinguishing power conversion element of the inverter circuit based on a detection signal from now on. By doing so, even if the self-extinguishing power conversion elements constituting the inverter circuit have a lower voltage rating than the naturally commutated power converter, self-extinguishing can be achieved even in the operating range where the output frequency range of the inverter circuit is relatively high. This allows for forced commutation using a shaped power conversion element.

Hereinafter, an embodiment of the present invention based on the above-mentioned concept will be described with reference to the drawings.

Figure 1 shows an AC power supply according to the present invention! This shows an example of a different control device circuit; the same parts as those in FIG. That is, in FIG. 1, in addition to FIG. 5, a voltage phase detector 19 for detecting the output voltage phase of the inverter circuit 14 is provided, and the voltage phase detection signal from this is introduced into the control circuit 18, and this voltage phase saving is performed. The column is configured to perform forced commutation or natural commutation based on the output signal.

When the AC power U machine configured as described above is used for charging, the AC power supplied from the input terminal 11 of the AC power source is converted to DC power by the rectifier 12, and this is converted to DC power by the DC reactor 13.
The inverter circuit 14 converts the AC power into variable voltage/variable frequency AC power based on the speed standard set value from the speed standard setter 17. From this, this AC power is used to power the AC motor 15 and the electric load. 16 respectively.

Further, the output voltage phase of the inverter circuit 14 is detected by the voltage phase detector 19, and the voltage phase/phase detection signal from this is introduced into the control circuit 18. Based on this voltage phase detection signal, the control circuit 18 causes forced inversion. υ1611 of current or natural commutation takes place.

Next, we will discuss the details of the control in detail.

In FIG. 2, (a) shows the output voltage phase of the inverter circuit 14, and eu, ev, and ew show the voltage waveforms of each phase, respectively. Similarly, (b) shows the conduction phase of the power conversion elements (141 and 142) of each arm of the three-way bridge circuit that constitutes the inverter circuit 14.
Each arm is electrically connected by 120°. Furthermore, the same (
c) shows the voltage waveform applied to the power conversion element Up. That is, in FIG. 2, when the power conversion element Up conducts at a phase that is advanced by a phase angle θ2 with respect to the phase voltage eu, the input voltage of the AC electric power converter 15 (
If the effective value of the line voltage (primary voltage) is EM, then. 1! A reverse voltage of F E M S i nθ2 is applied to the force transducing element Up. Therefore, as shown in FIG. 3, which shows part of the configuration of the voltage phase detector 19 and the control circuit 18, this reverse voltage f
Control is performed by determining whether lEMs+nθ2 is within a predetermined value and determining whether forced commutation is performed by the self-extinguishing power conversion element 141 or natural commutation is performed by the natural commutation type power conversion element 142. will be carried out. That is, in FIG. 3, the voltage phase detector 19 detects the above-mentioned 02, and the phase angle discriminator 181 detects the predetermined phase angle value θ2 1aX.
The magnitude relationship between the two is determined. Further, the voltage detection circuit 182 in the control circuit 18 detects the magnitude of the output voltage of the inverter circuit 14, and the detected voltage is determined to be a predetermined voltage effective 1 in the voltage determination 183! It is compared with E M t.

As a result of the above comparison, if the detected phase from one voltage phase detector is smaller than the predetermined phase angle θ2 10aX and the detected voltage from the voltage detection circuit 182 is smaller than the predetermined voltage effective value EMI, then , signal combiner (AND
>184 selects forced commutation control. In cases other than the above, natural commutation control is selected by the signal combiner (OR) 18s.

As described above, in this embodiment, the voltage phase detector 19 for detecting the output voltage phase of the inverter circuit 14 is provided, and self-extinguishing power conversion is performed in the region where forced commutation is performed in the self-extinguishing power conversion element 14l. Motoko 14! Since the control is performed while determining whether or not the voltage applied to It is possible to expand the output frequency range to a high output frequency range.

In this way, the output frequency range for forced commutation of the self-extinguishing power conversion element 14l is expanded, and as a result, the need to increase the capacitance of the capacitive load 16 is reduced, and the inverter circuit 14 has a higher output frequency. Even in this region, the output capacitance does not decrease. That is, the following effects can be obtained.

(a) The AC motor 15 can be operated in a wide variable frequency range without increasing the phase advance capacity m of the capacitive load 16 connected to the output side of the inverter circuit 14.

(b) As a result of being able to reduce the phase advance capacity surface of the capacitive load 16, the operating efficiency of the inverter circuit 14 in the highest frequency operating region is improved, and the output capacity a of the inverter circuit 14 can be reduced.

(C) In the vicinity where forced commutation and natural commutation of the inverter circuit 14 are switched. Since the voltage applied to the forcedly commutated self-extinguishing power conversion element 141 is also monitored and controlled, the reliability of the commutation system can be improved.

It should be noted that the present invention is not limited to the embodiments described above, but can also be implemented in the following manner.

(a) For example, as shown in FIG. 4, which shows an example of the circuit configuration for one arm of the inverter circuit 14, the self-extinguishing power conversion element 1
41 and a plurality of natural commutation type power conversion elements 142 are connected in series, and the diode 143 is connected because the reverse breakdown voltage of the self-extinguishing type power conversion element 141 is almost zero, as described above (" 2 E M S i nθ2 cannot be selected within the reverse voltage rating of the self-extinguishing power conversion element 141, but even in such a case, fl
Evs; nθ2 should be within a predetermined value. Alternatively, by determining whether the advance time of the phase angle θ2 should be within a predetermined time in relation to the current overlap IIl1, the self-extinguishing power conversion element 14! It is clear that the area in which forced commutation of can be performed can be expanded. That is, in the present invention,
This does not limit only the magnitude of the reverse voltage in the region where forced commutation is performed.

(b) In the present invention, the means for determining whether forced commutation or natural commutation is to be performed using the detection signal from the voltage phase detector 19 is performed over the entire output frequency range of the inverter circuit 14. However, the above-mentioned discrimination means may be applied only to a part of the medium to high speed output frequency region of the inverter circuit 14.

In addition, the present invention can be modified and implemented in various ways without changing the gist thereof.

[Effects of the Invention] As explained above, according to the present invention, the output power factor of the inverter circuit is improved and the output capacity thereof is reduced, and
Exchange Net! Therefore, it is possible to provide a compact, economically advantageous, and extremely reliable AC motor control device that can perform the operation described in Section 3 over a wide variable frequency range.

[Brief explanation of drawings]

Fig. 1 is a circuit configuration diagram showing an embodiment of an AC electric illumination device according to the present invention, Fig. 2 is a waveform diagram for explaining the operation of the embodiment, and Fig. 3 is a voltage diagram in the embodiment. A waveform diagram for explaining the functions of the phase detector and the control circuit, FIG. 4 is a circuit configuration diagram showing another embodiment of the present invention,
FIG. 5 is a circuit configuration diagram showing a conventional AC electric motor control device, and FIG. 6 shows the output current It of the inverter circuit when the AC motor in FIG. 5 is driven at variable speed. AC electric power input current (
primary current)! 、． +, is a vector diagram showing the relationship between input current IC of capacitive load; 11... Input terminal of AC power supply, 12... Rectifier, 1
3... DC reactor, 14... Inverter circuit,
15... AC electric machine a, 16... Benign load, 17.
...Speed standard setter, 18...Control circuit, 19...
Voltage phase detector, 141... Self-extinguishing power conversion element, 142... Natural commutation type power conversion element, 143...
Diode, 181... Phase angle discriminator, 182...
Voltage detection circuit, 183... Voltage discriminator, 184, 18
5... Signal coupler, I1... Output current of inverter circuit, IM... Input current of AC motor (primary current),
Ic...Input current of capacitive load.

Claims (1)

[Claims] An AC motor consists of a rectifier that converts AC to DC, a DC reactor that smoothes the output from the rectifier, and an inverter circuit that converts the DC smoothed by the DC reactor into AC to drive the AC motor. In the control device, an arm constituting the inverter circuit is configured with a series circuit of a self-extinguishing power conversion element and a naturally commutated power conversion element, and a capacitive load is connected to the output terminal of the inverter circuit. and a first control means for controlling the inverter circuit by forced commutation, a second control means for controlling the inverter circuit by natural commutation, and a voltage phase detection means for detecting the output voltage phase of the inverter circuit. and in at least a part of the operating range of the inverter circuit,
a determining means for comparing the output voltage phase detected by the voltage phase detecting means with a predetermined phase angle value, and determining whether to perform the forced commutation or the natural commutation based on the comparison result; A control device for an AC motor, comprising: