JPH072038B2 - Induction motor controller - Google Patents

Description

The present invention relates to an induction motor controller, and more particularly to an input voltage (primary voltage) of an AC motor when the induction motor is operated at a variable speed. The present invention relates to a control device for an induction motor that controls a relationship with an input frequency (primary frequency) to control commutation of a power conversion element of an inverter circuit.

(Prior Art) In recent years, as a control device for driving an AC electric motor, for example, an induction motor at a variable speed, a device in which a capacitive load for commutation is connected to the output side of an inverter circuit has been proposed. FIG. 4 shows an example of the circuit configuration of a control device for this type of induction motor.

In FIG. 4, 11 is an input terminal of an AC power supply, 12 is a rectifier that converts AC into DC, 13 is a DC reactor that smoothes the output from the rectifier 12, and 14 is DC that is smoothed by the DC reactor 13. And an inverter circuit for driving an AC motor that is a load, for example, an induction motor 15,
The capacitive load of the capacitor or the like connected to the output terminal of the inverter circuit 14, 17 speed reference setter for setting a speed reference, 18 control circuit, 14 ₁ gate turn-off constituting the inverter circuit 14 Self-extinguishing power conversion element such as thyristor, 14 ₂ is this self-extinguishing power conversion element 1
4 ₁ and arranged in series, and the natural commutation type power conversion device of the thyristor or the like constituting the inverter circuit 14 shown respectively.

The operation of the control device for the induction motor is summarized as follows. That is, the AC power supplied from the input terminal 11 of the AC power supply is converted into DC power by the rectifier 12, smoothed by the DC reactor 13, and further converted by the inverter circuit.
It is converted into AC power again at 14 and this AC power is supplied to the induction motor 15 and the capacitive load 16. In this way, the output current I _i of the inverter circuit 14 when the AC motor, for example, the induction motor 15 is driven at a variable speed,
AC motor, for example, input current and (primary current) I _M of the induction motor 15, and the relationship between the input current I _c of the capacitive load 16 as FIG. 5 when indicated by vector diagram. Note that I _P represents an effective component current of the input current I _M of the AC motor 15, and I _L represents a delay reactive component current of the input current I _M of the AC motor 15.
In FIG. 5, the input current I _c of the capacitive load 16 has the following relationship.

I _c ∝ (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 _i of the inverter circuit 14 becomes a lag phase, and the self-extinguishing power that forms the inverter circuit 14 is generated. the forced commutation in the conversion element 14 _1. On the other hand, in the operating region where the output frequency of the inverter circuit 14 is high, the output current I _i of the inverter circuit 14 is in the advance phase, and the natural commutation type power conversion element 14 ₂ forming the inverter circuit 14 can perform natural commutation. it can.

However, the control device for the AC motor as described above has the following problems. That is, the input current I _c of the capacitive load 16, as described above, since the changes in proportion to the square of the output frequency of the inverter circuit 14, in the middle region of the output frequency of the inverter circuit 14, a large load is an induction motor When added to 15, the output current I _{i of the} inverter circuit 14
Since the apparent delayed phase from the vector relation of FIG. 5, or to increase the voltage rating of the self-turn-off power converter element 14 _1, or it is necessary to increase the capacity of the capacitive load 16. That is, the input current (primary current) I _M of the induction motor 15, it is necessary to decrease with decreasing output frequency of the inverter circuit 14, it was unable to operate the induction motor 15 in a wide variable frequency range.

On the other hand, the output frequency is high operating range of the inverter circuit 14, in order to flow naturally rolling the natural commutation power converter element 14 ₂ proceeds in the vector diagram of FIG. 5 to about 30 ° position with a commercial frequency based phase It is necessary to make the angle θ ₂ and the inverter circuit
As the output frequency of 14 increases, the phase angle θ ₂
Is increased, and as a result, the output power factor of the inverter circuit 14 is decreased, and the output capacity of the inverter circuit 14 is greatly increased as compared with the input capacity of the induction motor 15. Note that such a problem is caused by the capacitive load on the output side of the inverter circuit 14.
For all of the induction motor control devices to which 16 is connected,
It occurs similarly.

(Problems to be Solved by the Invention) As described above, in the conventional induction motor control device, not only the operation of the induction motor cannot be performed in a wide variable frequency range, but also the output power factor of the inverter circuit increases. There is a problem in that the output capacity decreases and the output capacity greatly increases.

Therefore, in the present invention, the output power factor of the inverter circuit is improved to reduce its output capacity, and at the same time, the induction motor can be operated in a wide variable frequency range. It is an object of the present invention to provide a control device for an electric motor.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above-mentioned object, in the present invention, a rectifier that converts alternating current into direct current, a direct current reactor that smoothes the output from this rectifier, and this direct current A control device for an induction motor that is composed of an inverter circuit that drives a dielectric motor by converting direct current smoothed by a reactor into an alternating current motor, and that controls the ratio of the output voltage and the output frequency of the inverter circuit to a constant value. , In the case where a capacitive load for commutation is connected between the inverter circuit and the induction motor, in the region where the output frequency of the inverter circuit is equal to or higher than the frequency at which the phase of the output current of the inverter circuit becomes the predetermined lead phase angle. , Control the output voltage of the inverter circuit so that the ratio of the output voltage of the inverter circuit to the output frequency becomes smaller than the above-mentioned normal ratio. To have.

Here, in particular, the output voltage of the inverter circuit is controlled in proportion to the square root of the output frequency of the inverter circuit, or is controlled to be maintained at a substantially constant value with respect to the change of the output frequency of the inverter circuit. ing.

(Operation) Therefore, in the induction motor control device of the present invention, in the region where the output frequency of the inverter circuit is equal to or higher than the frequency at which the phase of the output current of the inverter circuit becomes a predetermined lead phase angle, Since the output voltage of the inverter circuit is controlled so that the ratio with the output frequency is not a constant value, that is, the ratio between the two is smaller than the normal ratio, for example, at an output frequency f ₁ or higher, By controlling the output voltage V of the inverter circuit to increase in proportion to the square root of the output frequency f, the input current I _c of the capacitive load is I _c ∝ (f / f ₁ ) 3 at the output frequency f ₁ or higher. / will be increased by 2 relationship, resulting in the input current I _c of the capacitive load decreases the output current I _i of the inverter circuit decreases than before, the output torque of the induction motor Even when the increase in the rotational speed of the square or a square, and improved output power factor of the inverter circuit, the output capacity of the inverter circuit is can be reduced.

(Example) As described above, the present invention is a ratio of the output voltage (primary voltage) V of the inverter circuit 14 to the output frequency (primary frequency) f.
Due to controlling V / f to a constant value, capacitive load 16
The input current I _c of the inverter circuit 14 increases with the relationship of I _c ∝ (output frequency of the inverter circuit 14) ^2. The ratio V / f of the output voltage V of the inverter circuit 14 to the output frequency f is In a region where the output frequency f of 14 is a predetermined value f ₁ or more, that is, in a region where the phase of the output current of the inverter circuit 14 is a predetermined lead phase angle or more, the ratio of both is smaller than the normal ratio, that is, The output voltage V of the inverter circuit 14 is controlled so that the output voltage V is weakly controlled.

An embodiment of the present invention based on the above concept will be described below with reference to the drawings.

Since the circuit configuration example of the induction motor control device according to the present invention is the same as that shown in FIG. 4, the description thereof will be omitted and the characteristic points will be described. That is, in the control device for the induction motor according to the present embodiment, as shown in FIG.
In a region where the output frequency f of the inverter circuit 14 is a predetermined value f ₁ or more, that is, in a region where the phase of the output current of the inverter circuit 14 is a predetermined lead phase angle or more, the output voltage V of the inverter circuit 14 is 14 output voltage V
The output voltage f is controlled in proportion to the square root of the output frequency f of the inverter circuit so that the ratio V / f of the output frequency f becomes smaller than the normal ratio.

Although it is difficult to quantitatively explain the action and effect by the control device of the induction motor, here, it is assumed that the input current (primary current) I _M of the induction motor 15 increases in proportion to the square of the primary frequency. The effects of this embodiment and the conventional method will be compared and described. That is, at the above-mentioned primary frequency f ₁ , the input current is I _M1 , I _c1 , the output current is I _i1 , and the phase angle θ _{1 in} FIG. 5 is 53.13 degrees (input power factor 60% of the induction motor 15). , Θ ₂ = 36.87 degrees (the output power factor of the inverter circuit 14 is 80%), while the output frequency f _{2 is}
Is set to twice the output frequency f _{1 and} the following calculation is performed. Under the above-mentioned assumption conditions, the following relationships are established.

I _L1 = I _M × sin (53.13 °) ＝ 0.8I _M1 …… (1) I _P1 ＝ I _M × cos (53.13 °) ＝ 0.61I _M1 …… (2) I _i1 ＝ I _Pi ÷ cos (36.87 °) ) = 0.6I _M1 /0.8=0.75I _M1 (3) I _c = I _L1 + I _i1 × sin (36.87 °) = 0.8I _M1 +0.75 × .6 I _M1 = 1.25I _M1 ...... (4) Previous At the output frequency f _{2 of} , the input power factor of the induction motor 15 is
Assuming 90% (θ ₁ = 25.84 degrees), the following is obtained in the conventional V / f constant control.

From f ₂ / f ₁ = 2, I _M2 = 4 I _M1 (5) I _P2 = I _M2 × 0.9 = 3.6 I _M1 (6) I _L2 = I _M2 × sin (25.84 °) = 0.44I _M2 = 1.76I _M1 …… (7) I _c2 ＝ 4I _c1 ＝ 5I _M1 …… (8) θ ₂ = cos ^-1 (I _P2 / I _i2 ) ≈42 ° (10) Therefore, the input power factor is 74.3%.

On the other hand, the V / f control according to this embodiment is as follows.

I _M2 ＝ 4I _M1 …… (11) I _P2 ＝ 3.6I _M1 …… (12) I _L2 = 1.76I _M1 …… (13) θ ₂ = cos ⁻¹ (I _P2 / I _i2 ) = 26.42 ° (16) Therefore, according to the V / f control according to the present embodiment, the action and effect are compared between the equations (9) and (15). Can be clarified by That is, as in the present embodiment, the inverter circuit
In a region where the output frequency f of 14 is a predetermined value f ₁ or more, that is, in a region where the phase of the output current of the inverter circuit 14 is a predetermined lead phase angle or more, the output voltage V of the inverter circuit 14 is set to the output of the inverter circuit 14. By controlling in proportion to the square root of the frequency f, it is apparent that the output capacity of the inverter circuit 14 can be reduced by 20% as compared with the conventional method.

As described above, in this embodiment, the following operational effects can be obtained.

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

(B) As a result of the fact that the phase advancing capacity of the capacitive load 16 can be reduced, the operating efficiency of the inverter circuit 14 in the highest frequency operation region is improved, and the output capacity of the inverter circuit 14 can be reduced.

As a result, a compact and economically reliable AC motor control device can be obtained.

It should be noted that the present invention is not limited to the above-described embodiments, but can be carried out as follows.

(A) In the above embodiment, the output voltage V of the inverter circuit 14
When the output voltage V of the inverter circuit 14 is controlled so that the ratio between the output frequency f and the output frequency f becomes smaller than the normal ratio, the output voltage V of the inverter circuit 14 is set to the inverter circuit 14
Although the case has been described where the output frequency f is controlled in proportion to the square root of the output frequency f, the output voltage V of the inverter circuit 14 is almost equal to the change of the output frequency f of the inverter circuit 14 as shown in FIG. may be controlled so as to maintain a constant value, the input current (primary current) I _M of the induction motor 15 in accordance with how changes with respect to the output frequency f by the load characteristics, the output of the inverter circuit 14 In the present invention, the relationship between the voltage V and the output frequency f can be selected and controlled at a predetermined output frequency f or higher.

(B) In the above embodiment, the case where the inverter circuit 14 is configured by using the self-extinguishing type power conversion element 14 ₁ and the natural commutation type power conversion element 14 ₂ has been described.
For the case where the inverter circuit 14 is constructed by using only natural commutation power conversion element 14 ₂ as shown in FIG well, in which it is possible to apply the present invention in the same manner as described above. That is, the present invention can be similarly applied to all of those in which a capacitive load is connected between the inverter circuit 14 and the induction motor 15.

In addition, the present invention can be variously modified and implemented within the scope of the invention.

As described above, according to the present invention, a rectifier that converts AC into DC, a DC reactor that smoothes the output from this rectifier, and a DC that is smoothed by this DC reactor are converted into AC. A control device for an induction motor that is configured to control the ratio of the output voltage and the output frequency of the inverter circuit to a constant value by using an inverter circuit that drives the induction motor. In the case where the diversion capacitive load is connected, in the region where the output frequency of the inverter circuit is equal to or higher than the frequency at which the phase of the output current of the inverter circuit becomes the predetermined lead phase angle, the output voltage of the inverter circuit and the output frequency Since the output voltage of the inverter circuit is controlled so that the ratio becomes smaller than the above-mentioned normal ratio, the output power factor of the inverter circuit It is possible to provide a small-sized, economically advantageous and extremely reliable control device for an induction motor, which can improve the output capacity and reduce the output capacity thereof and can operate the induction motor in a wide variable frequency range.

[Brief description of drawings]

FIG. 1 shows the relationship between the output voltage and the output frequency of an inverter circuit according to an embodiment of the present invention, and FIG. 2 shows the relationship between the output voltage and the output frequency of an inverter circuit according to another embodiment of the present invention. 3 is a circuit configuration diagram showing another embodiment of the induction motor control device according to the present invention, FIG. 4 is a circuit configuration diagram showing a conventional induction motor control device and an induction motor control device according to the present invention, and FIG. FIG. 4 is a vector diagram showing the relationship among the output current I _i of the inverter circuit, the input current (primary current) I _{M of} the induction motor, and the input current I _c of the capacitive load when the induction motor is driven at a variable speed in FIG. 4. 11 …… AC power supply input terminal, 12 …… rectifier, 13 …… DC reactor, 14 …… Inverter circuit, 15 …… Induction motor, 16 …… Capacitive load, 17 …… Speed reference setter, 18 ……
Control circuit, 14 ₁ ...... Self-extinguishing power conversion element, 14 ₂ ...... Natural commutation power conversion element, I _i …… Inverter circuit output current, I _M …… Induction motor input current (primary current) , I _c ……
Input current of capacitive load, V ... Output voltage of inverter circuit 14, f ... Output frequency of inverter circuit 14.

Claims (3)

[Claims] 1. A rectifier for converting AC into DC, a DC reactor for smoothing the output from the rectifier, and an inverter circuit for converting DC smoothed by the DC reactor into AC to drive an induction motor. In the controller of the induction motor, which controls the ratio of the output voltage and the output frequency of the inverter circuit to a constant value, a capacitive load for commutation is connected between the inverter circuit and the induction motor. In the region where the output frequency of the inverter circuit is equal to or higher than the frequency at which the phase of the output current of the inverter circuit becomes a predetermined lead phase angle, the ratio of the output voltage of the inverter circuit to the output frequency is higher than the normal ratio. A control device for an induction motor, wherein the output voltage of the inverter circuit is controlled so as to be smaller. 2. The control device for an induction motor according to claim 1, wherein the output voltage of the inverter circuit is controlled in proportion to the square root of the output frequency of the inverter circuit. . 3. An output voltage of the inverter circuit is controlled so as to be maintained at a substantially constant value with respect to a change in the output frequency of the inverter circuit, according to claim (1). Induction motor controller.