JP2675451B2 - Current limiting method in vector control of magnetic flux direct control of induction motor. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to current limiting in vector control of an induction motor.

[0002]

2. Description of the Related Art FIG. 3 shows a block diagram of prior art vector control relating to the present invention, by which vector control will be described. The detailed theoretical development is based on "Torque control method based on secondary magnetic flux control of induction motor and its characteristics" in Proc. To do.

Three-phase induction motor (hereinafter abbreviated as IM) 3
Is a DC voltage obtained by rectifying an AC input voltage V _in with a rectifier 1 composed of a diode and a smoothing capacitor C _O , and 6
The currents flowing through IM are connected by the inverter unit 2 composed of individual transistors and detected by the current detector 5 as the motor current I _m to operate the IM.

Now, the magnetic flux generated inside the IM in this state is calculated as the electric motor internal magnetic flux Φ by the arithmetic unit 6 from the electric motor current I _m and the electric motor constant given from the electric motor constant memory 7. The calculation formula is omitted), and the magnetic flux command value Φ ^* to be generated inside IM is calculated from the torque command value τ ^* set externally by the calculator 8 and the motor constant and the rotation speed of IM (calculation formula). Will be omitted). IM
The rotation speed of the pulse generator (hereinafter PG
The output pulse of 4) is detected by the counter 10 as ω _m by counting it as the number of pulses for each fixed time.

[0005] The difference between the flux command value [Phi ^* and the motor magnetic flux inside [Phi, and by a motor current I _m and the motor constants, calculated by the magnetic flux vector [Delta] [lambda] ^* the calculator 9 to be provided to the IM, a magnetic flux vector [Delta] [lambda] ^* Vector control of IM is performed by deciding and switching the switching of each transistor of the inverter unit 2 to generate, and matching the electric motor internal magnetic flux Φ generated inside IM with the magnetic flux command value Φ ^* . Here, as the control, the magnetic flux inside the IM is directly controlled, and there is a reason why it is called the magnetic flux direct control type vector control.

[0006]

As described above, in the magnetic flux direct control type vector control, the magnetic flux is directly controlled, and the electric motor current I _m , which is seen in other vector control, is not controlled. Therefore, the electric motor is controlled. It has a drawback that the limit value cannot be set for the value of the current I _m .

Generally, as seen in other vector control, the one having a current control loop has a control loop so that the motor current matches the current command value.
Although it is possible to limit the current by setting a limit value on the current command value itself, this was not possible with the magnetic flux direct control type as in this method. The present invention is intended to solve such a drawback.

[0008]

According to the present invention, there is provided a current limiting method in the magnetic flux direct control type vector control of an induction motor, wherein a torque command value used for the magnetic flux command value calculation is K _G × (a torque command set from outside). Value is used to determine this K _G , the preset limiting current value of the electric motor is constantly compared with the actual flowing electric motor current, and the limiting current value I _L ≦ When (motor current I _m ) is set to 0 as a minimum value, K _G is gradually decreased, and when (limit current value I _L )> (motor current I _m ) is set to 1.0 as maximum and K _G is gradually increased. It is possible to limit the current flowing through the electric motor.

That is, the torque command value τ set from the outside used for calculating the above-mentioned magnetic flux command value Φ ^*
* To use a ^** value obtained by multiplying the K _G consisting coefficient τ as an operational torque command value. The relational expression is the following expression (1). τ ^** = K _G × τ ^* (0 ≦ K _G ≦ 1.0) (1) Here, K _G is determined by the motor current I _m and the limiting current value I _L to be limited, FIG. 2 is a flow chart of the K _G determination algorithm. By using such means, it becomes possible to limit the current in the magnetic flux direct control type vector control.

[0010]

As shown in FIG. 2, the motor current I _m is compared with the limiting current value I _L, and when I _L ≤I _m , K _G is gradually decreased, and the minimum value is set to 0. When I _L > I _m , K _G is gradually increased, and K _G is determined so that the maximum value is 1.0, and the magnetic flux is calculated using the calculated torque command value τ ^**. By calculating the command value Φ ^* , the current I _m flowing through IM can be controlled to be equal to or less than the limiting current value I _L.

The reason will be described below. Motor current I
_m can be expressed by the following equation (2) by using the reluctance current (no-load current) I _O and the torque current I _{T. ^{I m = √ {I O 2}} + I T 2} ...... (2) where, for a normal vector control, which is controlled to keep the magnetic flux constant, the torque current I _T is the torque command value tau ^* It is proportional. Accordingly, will be able to adjust the motor current I _m by adjusting the torque command value tau ^*, it is possible to limit the motor current I _m.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the block diagram of FIG. 1 showing an embodiment of the present invention. Of the reference numerals in FIG. 1, the same reference numerals as those of the conventional method shown in FIG. 3 are the same constituent elements, and the overall operation is basically the same, so the description thereof will be omitted. Only the K _G calculator 11 which is a different part will be described.

The input of the K _G calculator 11 is the torque command value τ ^{*, the} limiting current value I _L and the motor current I _m , and the calculated torque command value τ ^** which is the output of the K _G calculator 11 is a coefficient in the algorithm shown in FIG. to determine the K _G are calculated by the equation (1).
Using the output τ ^** of the K _G calculator 11, the calculator 8 calculates and determines the magnetic flux command value Φ ^* . As a result, the magnitude of the torque current I _T is controlled as shown in the equation (2), and the value of the motor current I _m can be controlled to be equal to or less than the limiting current value I _L.

[0014]

As described above, according to the present invention, it is possible to realize the current limitation which cannot be realized by the conventional magnetic flux direct control type vector control. Moreover, since the vector control is generally controlled by the central processing unit or the like, the current limiting method of the present invention requires only software addition and no hardware modification is required. There is no increase in reliability or decrease in reliability.

[Brief description of the drawings]

FIG. 1 is a block diagram of current limiting magnetic flux direct control type vector control according to the present invention.

FIG. 2 is a flow chart showing an algorithm of a coefficient calculator for performing current limitation according to the present invention.

FIG. 3 is a block diagram of conventional magnetic flux direct control type vector control without current limitation.

[Explanation of symbols]

1 rectifier 2 inverter unit 3 a three-phase induction motor 4 pulse generator 5 a current detector 6, 8, 9 computing unit 7 motor constant storage unit 10 counter 11 K _G calculator

Claims (1)

(57) [Claims] 1. A vector control of an induction motor driven by a voltage-type inverter device composed of six transistors, wherein a magnetic flux generated inside the motor is calculated from a motor constant and a motor current, and further the motor constant is calculated. The magnetic flux command value to be generated inside the motor is calculated from the torque command value and the motor rotation speed set from the outside, and the switching of the transistor is directly determined from the magnetic flux command value, the generated magnetic flux, the motor constant and the motor current. In the magnetic flux direct control type vector control of the switching method, the torque command value used for the magnetic flux command value calculation is obtained by K _G × (the torque command value set from the outside), and this K _G is used. When deciding, always compare the preset current limit value of the motor and the current of the motor that is actually flowing, When (limit current) ≤ (motor current), 0 is set to the minimum value and K _G is gradually decreased, and when (limit current)> (motor current), 1.0 is maximized and K _G is gradually increased to increase the motor. A method for limiting current in magnetic flux direct control type vector control of an induction motor, which is capable of limiting the current flowing in the coil.