JPH11243700A - Current controller in ac motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control an AC motor at high performance in a wide range, from low speed region to high speed region. SOLUTION: Adders 61 to 63 are provided at a pre-stage of a power converter 40 for switching an Ac current control system with a DC current control system. A U-phase voltage command from a current controller 31 and a U-phase voltage command from a two-phase three-phase converter 55 are added by the adder 61, and a U-phase voltage command Vu* as the sum, is fed to a power converter 40. A V-phase voltage command from a current controller 32 and a V-phase voltage command from the two-phase and three-phase converter 55 are added by the adder 62, and a V-phase voltage command Vv* as the sum, is fed to the power converter 40. A W-phase voltage command from a current controller 33 and a W-phase voltage command from the two- phase and three-phase converter 55 are added by the adder 63 and a W-phase voltage command Vw* as the sum is fed the power converter 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current controller for an AC motor, and more particularly to a current controller for an AC motor capable of controlling an AC motor with high performance over a wide speed range from a low speed region to a high speed region. .

[0002]

2. Description of the Related Art As is well known, AC motors are classified into induction motors and synchronous motors. The current control device according to the present invention is applicable to both of these motors.

Conventionally, this type of AC motor (AC motor)
As the current control device, the following two systems are employed. One of the methods is to apply current feedback to three-phase alternating current, and is called an AC current control system (see FIG. 3). On the other hand, another method is a method of performing current feedback in a two-phase rotating coordinate system using a coordinate converter, and is called a DC current control system (see FIG. 4).

First, an AC current control system will be described with reference to FIG. A torque current command value It ^* and an excitation current command value Im ^* are supplied from a control circuit such as a microcomputer (not shown). Further, the control circuit calculates the current command value Ic and the phase angle φ from the torque current command value It ^* and the excitation current command value Im ^* according to the following equations (1) and (2).

[0005]

(Equation 1)

[0006]

(Equation 2) Next, the control circuit calculates 12 according to Equations 3 to 5 below.
Three-phase AC current commands Iu ^* , Iv ^* ,
Calculate Iw ^* . It should be noted that Iu ^* , Iv ^* , and Iw ^* are called a U-phase current command value, a V-phase current command value, and a W-phase current command value, respectively.

[0007]

(Equation 3)

[0008]

(Equation 4)

[0009]

(Equation 5) Here, θ is a magnetic pole position obtained from a position detector (not shown) directly connected to an AC motor (AC motor) M or the like.

U-phase current command value Iu ^* , V-phase current command value I
v ^* and the W-phase current command value Iw ^* are the first
To the third to third subtractors 11, 12 and 13. On the other hand, U-phase current detection value I flowing through AC motor M
u, V-phase current detection value Iv, and W-phase current detection value Iw
Are the first to third current detectors 21 and 22, respectively.
And 23 are detected by the first to third subtractors 11 to 11
13 is supplied. First to third current detectors 21 and 2
3 are called a U-phase current detector, a V-phase current detector, and a W-phase current detector, respectively.

The first subtractor 11 has a U-phase current command value Iu.
^The U-phase current detection value Iu is subtracted from ^*, the difference between them is calculated, and the U-phase current error is calculated. Similarly, the second subtractor 12 subtracts the V-phase current detection value Iv from the V-phase current command value Iv ^* , calculates a difference therebetween, and calculates a V-phase current error. The third subtractor 13 outputs the W-phase current command value I
The W-phase current detection value Iw is subtracted from w ^*, and a difference between them is calculated to calculate a W-phase current error. Therefore, the first to third subtractors 11 to 13 are called a U-phase subtractor, a V-phase subtractor, and a W-phase subtractor, respectively.

The U-phase current error, the V-phase current error, and the W-phase current error are respectively calculated by the first to third current controllers 3.
1, 32, and 33. Each of the first to third current controllers 31 to 33 includes a PI (proportional / integral) controller or the like. The first current controller 31 generates a U-phase voltage command value Vu ^* based on the U-phase current error. Similarly, the second current controller 32 generates a V-phase voltage command value Vv ^* based on the V-phase current error. Third current controller 3
3 generates a W-phase voltage command value Vw ^* based on the W-phase current error. Therefore, the first to third current controllers 31
33 are respectively referred to as a U-phase current controller, a V-phase current controller, and a W-phase current controller.

U-phase voltage command value Vu ^* , V-phase voltage command value V
v ^* and W-phase voltage command value Vw ^* are
Supplied to The power converter 40 performs pulse width modulation (PW
M) It is composed of an amplifier and the like. U-phase voltage command value V
u ^* , V-phase voltage command value Vv ^* , and W-phase voltage command value V
In response to w ^* , power converter 40 applies U-phase power, V-phase power, and W-phase power to AC motor M.

Next, a DC current control system will be described with reference to FIG. First to third current detectors 21 to 23
U-phase current detection value Iu, V-phase current detection value Iv,
The W-phase current detection value Iw is supplied to the three-phase / two-phase converter 50, where the torque current component It and the excitation current component Im are calculated according to the following equations (6) and (7).

[0015]

(Equation 6)

[0016]

(Equation 7) Here, θ is a magnetic pole position obtained from a position detector (not shown) directly connected to an AC motor (AC motor) M or the like.

The torque current component It and the exciting current component I
m is the fourth and fifth subtractors 14 and 1 respectively
5 is supplied. The fourth and fifth subtractors 14 and 15 are supplied with a torque current command value It ^* and an excitation current command value Im ^* from a control circuit such as a microcomputer (not shown). The fourth subtractor 14 subtracts the torque current component It from the torque current command value It ^* , takes the difference therebetween, and calculates a torque current error. Similarly, the fifth subtractor 15 subtracts the exciting current component Im from the exciting current command value Im ^* , takes the difference between them, and calculates the exciting current error. Therefore, the fourth and fifth subtractors 14 and 15 are called a torque subtractor and an excitation subtractor, respectively.

The torque current error and the excitation current error are supplied to fourth and fifth current controllers 34 and 35, respectively. Fourth and fifth current controllers 34 and 3
Each of 5 is constituted by a PI (proportional / integral) controller or the like. The fourth current controller 34 generates a torque voltage command value Vt ^* based on the torque current error. Similarly, the fifth current controller 35 generates the excitation voltage command value Vm ^* based on the excitation current error. Therefore, the fourth and fifth current controllers 34 and 35 are called a torque current controller and an exciting current controller, respectively.

The torque voltage command value Vt ^* and the excitation voltage command value Vm ^* are supplied to a two-phase / three-phase converter 55, where the U-phase voltage command value is calculated according to the following equations (8), (9) and (10). Vu ^* , V-phase voltage command value Vv ^* , and W-phase voltage command value Vw ^* are calculated.

[0020]

(Equation 8)

[0021]

(Equation 9)

[0022]

(Equation 10) The U-phase voltage command value Vu ^* , the V-phase voltage command value Vv ^* , and the W-phase voltage command value Vw ^* are supplied to the power converter 40,
Here, the power is converted into U-phase power, V-phase power, and W-phase power and applied to AC motor M.

[0023]

However, the aforementioned AC current control system (FIG. 3) and DC current control system (FIG. 4) each have the following disadvantages.

First, the disadvantages of the AC current control system will be described. The AC current control system shows relatively good characteristics in a low-speed region (for example, 15 rpm) of the AC motor M. However, since the feedback control of the AC amount is performed, in the AC current control system, the phase error increases in a high-speed region (for example, 1500 rpm) of the AC motor M. Therefore, in the AC current control system, there is a problem that torque linearity is impaired in a high-speed region.

On the other hand, since the DC current control system performs the feedback of the DC amount, in the high-speed region, there is no problem such as the AC current control system. However, in the low speed region, the DC current control system uses PWM.
There is a problem in that current distortion increases due to the influence of the dead time included in the conversion, and torque ripple is induced. still,
In the high-speed region, the output voltage increases in the DC current control system, so that the influence of the dead time becomes small and such a problem does not occur.

Accordingly, an object of the present invention is to provide an AC motor current control device capable of controlling an AC motor with high performance over a wide speed range from a low speed region to a high speed region.

Another object of the present invention is to provide a current control device for an AC motor capable of reducing torque ripple in a low-speed region and securing torque linearity (high-precision torque control) in a high-speed region. It is in.

Still another object of the present invention is to provide a current control device for an AC motor capable of achieving a uniform current control frequency response in all speed ranges.

[0029]

SUMMARY OF THE INVENTION A current control device for an AC motor according to the present invention includes an AC current control system for applying current feedback to a three-phase AC and a two-phase rotating coordinate system using a coordinate converter. A DC current control system that performs current feedback, and adopts an AC current control system in the low-speed region of the AC motor, and switches their gains so as to employ a DC current control system in the high-speed region of the AC motor. Coupling means.

[0030]

The present invention adopts an AC current control system at a low speed (in a low-speed region) and a DC current control system at a high speed (in a high-speed region) to achieve high-performance current control in all speed regions.

[0031]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a configuration of a current control device for an AC motor according to an embodiment of the present invention. As shown in FIG.
The current control device for an AC motor according to the present embodiment is shown in FIG.
And a DC current control system shown in FIG. Further, in order to switch these control systems, first to third adders 61, 62, and 6
3 is provided before the power converter 40.

More specifically, the first adder 61 is provided with a U-phase voltage command value output from the first current controller 31 and a 2-phase 3
The U-phase voltage command value output from phase converter 55 is added, and the added U-phase voltage command value Vu ^* is supplied to power converter 40. Similarly, the second adder 62 adds the V-phase voltage command value output from the second current controller 32 and the V-phase voltage command value output from the two-phase three-phase converter 55, The added V-phase voltage command value Vv ^* is supplied to the power converter 40. The third adder 63 adds the W-phase voltage command value output from the third current controller 33 and the W-phase voltage command value output from the two-phase / three-phase converter 55 and adds the added phase. The voltage command value Vw ^* is supplied to the power converter 40. Anyway, the combination of the first to third adders 61 to 63 employs an AC current control system in the low-speed region of the AC motor M and a DC current control system in the high-speed region of the AC motor M. In addition, as described later, it works as a means for coupling while switching those gains.

The AC coordinate converter 70 calculates the U-phase current command value Iu ^* , the V-phase current command value Iv ^* , and the W-phase current command value Iw from the torque current command value It ^* and the exciting current command value Im ^{*. *} Is required. That is, the AC coordinate converter 70 is means for executing the above-described calculations of Equations 1 to 5.

In this embodiment, an AC current control system is employed in the low-speed region of the AC motor M, and a DC current control system is employed in the high-speed region of the AC motor M.
The gain distribution of the current controller is expressed by the following equations (11) and (12).
Set according to.

[0036]

[Equation 11]

[0037]

(Equation 12) Here, K is a variable related to the motor rotation speed and changes as shown in FIG.

In FIG. 2, the horizontal axis is the number of rotations (rotational speed).
ω, the vertical axis is the gain K. In FIG. 2, a broken line indicates the gain Gac (s) of the AC current control system, and a solid line indicates the gain Gdc (s) of the DC current control system. FIG.
As is clear from FIG.
(S) is 1 in the low-speed area, but gradually decreases as the speed increases in the middle-speed area between the low-speed area and the high-speed area, and is 0 in the high-speed area. On the contrary,
The gain Gdc (s) of the DC current control system is 1 in the high speed region, but gradually decreases as the speed decreases in the middle speed region between the high speed region and the low speed region, and is 0 in the low speed region.

With this operation, the characteristics of the AC current control system can be obtained at low speeds, and the characteristics of the DC current control system can be obtained at high speeds.

In this embodiment, in order to further improve the performance of current control, three compensations (dead time feed forward compensation, motor winding resistance loss compensation, and induced voltage compensation) as shown in FIG. At least one of
It is desirable to put one.

More specifically, in order to realize dead time feed forward compensation, a dead time compensator 80 is provided.
And fourth to sixth adders 64, 65 and 66 are added. The dead time compensator 80 includes first to third dead time compensating elements 81, 82, and 83, which are called a U-phase dead time compensating element, a V-phase dead time compensating element, and a W-phase dead time compensating element, respectively. . U-phase dead time compensation element 81 generates a U-phase dead time compensation signal based on U-phase current command value Iu ^* . Similarly, V-phase dead time compensating element 82
A V-phase dead time compensation signal is generated based on the phase current command value Iv ^* . W-phase dead time compensation element 83 generates a W-phase dead time compensation signal based on W-phase current command value Iw ^* . The fourth to sixth adders 64-66 are inserted between the two-phase to three-phase converter 55 and the first to third adders 61-63. The fourth adder 64 adds the U-phase voltage command value output from the two-phase / three-phase converter 55 and the U-phase dead time compensation signal to generate a dead-time compensated U-phase voltage command value in the first phase. It is supplied to the adder 61. Similarly, the fifth adder 65 adds the V-phase voltage command value output from the two-phase / three-phase converter 55 and the V-phase dead time compensation signal to generate a V-phase voltage command value with dead time compensation. The signal is supplied to the second adder 62. The sixth adder 66 adds the W-phase voltage command value output from the two-phase / three-phase converter 55 and the W-phase dead time compensation signal to obtain a dead-time compensated W-phase voltage command value in the third phase. It is supplied to the adder 63.

To realize the motor winding resistance loss compensation, the resistance loss compensator 90 and the seventh and eighth adders 6 are used.
7 and 68 are added. Resistance loss compensator 90
Is composed of first and second resistance loss compensating elements 91 and 92, which are called a resistance loss compensating element for torque and a resistance loss compensating element for excitation, respectively. The torque resistance loss compensation element 91 generates a torque resistance loss compensation signal based on the torque current command value It ^* . The excitation resistance loss compensation element 92 generates an excitation resistance loss compensation signal based on the excitation current command value Im ^* . Seventh and eighth adders 6
7 and 68 are inserted between the torque current controller 34 and the exciting current controller 35 and the two-phase to three-phase converter 55. The seventh adder 67 adds the torque voltage command value output from the torque current controller 34 and the torque resistance loss compensation signal, and converts the torque voltage command value Vt ^* that has been subjected to the torque resistance loss compensation into two-phase three. It is supplied to the phase converter 55. Similarly,
The eighth adder 68 adds the excitation voltage command value output from the excitation current controller 35 and the excitation resistance loss compensation signal to obtain an excitation voltage command value Vm ^* that has been subjected to excitation resistance loss compensation by two.
It is supplied to the three-phase converter 55.

In order to realize induced voltage compensation, an induced voltage compensator 100 and a ninth adder 69 are added. Rotation speed (rotation speed) ω is supplied to induced voltage compensator 100 from a speed detector (not shown) attached to AC motor M. The induced voltage compensator 100 generates an induced voltage compensation signal based on the rotation speed ω. The ninth adder 69 is inserted between the torque resistance loss compensating element 91 and the seventh adder 67. Ninth adder 69
Adds the torque resistance loss compensation signal output from the torque resistance loss compensation element 91 and the induced voltage compensation signal, and supplies the torque resistance loss / induced voltage compensation signal to the seventh adder 67.

By incorporating the above-described compensation, the response of the current control can be designed to be constant irrespective of the constant speed or the high speed.

Although the present invention has been described with reference to preferred embodiments, the present invention is not limited thereto, and various modifications and changes can be made without departing from the spirit of the present invention.

[0046]

As described above, the present invention employs an AC current control system at a low speed (in a low speed region) and a DC current control system at a high speed (in a high speed region). In this case, it is possible to achieve higher performance of current control.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a current control device for an AC motor according to an embodiment of the present invention.

FIG. 2 is a gain characteristic diagram showing a change in gain of a current controller used in the current control device shown in FIG.

FIG. 3 is a block diagram showing a configuration of a first conventional AC motor current control device (AC current control system).

FIG. 4 is a block diagram showing a configuration of a second conventional AC motor current control device (DC current control system).

[Explanation of symbols]

 M AC motor (AC motor) 11-14 Subtractor 21-23 Current detector 31-35 Current controller 40 Power converter 50 Three-phase two-phase converter 55 Two-phase three-phase converter 61-69 Adder 70 AC coordinates Converter 80 Dead time compensator 90 Resistance loss compensator 100 Induced voltage compensator

Claims (4)

[Claims] 1. An AC motor, comprising: an AC current control system for performing current feedback on a three-phase AC; and a DC current control system for performing current feedback in a two-phase rotary coordinate system using a coordinate converter. An alternating current motor having means for adopting the alternating current control system in a low-speed region and switching the gains thereof so as to employ the direct current control system in a high-speed region of the ac motor. Current control device. 2. The current control device for an AC motor according to claim 1, further comprising dead time feed forward compensation means. 3. The current control device for an AC motor according to claim 1, further comprising a motor winding resistance loss compensating means. 4. The current control device for an AC motor according to claim 1, further comprising an induced voltage compensating means.