JPH04308491A - Current limiting method in direct flux control type vector control for induction motor - Google Patents

Abstract

PURPOSE:To realize limitation of motor current by employing a value, obtained by multiplying an externally set torque command value for operating a flux command value by a coefficient, as an operational torque command value. CONSTITUTION:An KG operating unit 11 receives a torque command value tau', a limit current value IL and a motor current Ia, and outputs an operational torque command value tau' operated by determining a coefficient KG through an algorithm. Output tau' from an KG operating unit 11 is fed to an operating unit 8 and employed in the determination of a flux command value phi'. Consequently, magnitude of torque current IT is controlled and the value of the motor current Ia can be controlled lower than the limit current value IL.

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 conventional vector control related to the present invention, and vector control will be explained using this diagram. Detailed theoretical development is based on ``Torque control method based on secondary magnetic flux control of induction motor and its characteristics'' in the Proceedings of the 1986 National Conference of the Institute of Electrical Engineers of Japan, Industrial Applications Division, pp. 361-364, so we will only give an overview here. do.

Three-phase induction motor (hereinafter abbreviated as IM) 3
The AC input voltage Vin is connected to the DC voltage rectified by the rectifier 1 consisting of a diode and the smoothing capacitor CO2, and the inverter section 2 consisting of six transistors, and the current flowing to IM is connected to the current detector 5. IM is operated by being detected as motor current Im.

Now, the magnetic flux generated inside the IM in this state is calculated as the motor internal magnetic flux Φ by the calculator 6 from the motor current Im and the motor constant given from the motor constant memory 7. (formula omitted) and I
The magnetic flux command value Φ* to be generated inside M is calculated by the calculator 8 from the torque command value τ* set from the outside, the motor constant, and the rotational speed of the IM (the calculation formula is omitted). Note that the rotational speed of the IM is detected as ωm by counting the output pulses of a pulse generator (hereinafter abbreviated as PG) 4 directly connected to the IM as the number of pulses every fixed time using a counter 10.

[0005] This magnetic flux command value Φ* and the motor internal magnetic flux Φ
, and the motor current Im and motor constant,
The magnetic flux vector Δλ* to be given to the IM is calculated by the calculator 9, the switching of each transistor of the inverter section 2 for generating the magnetic flux vector Δλ* is determined and switched, and the motor internal magnetic flux Φ generated inside the IM is
Vector control of the IM is performed by matching the magnetic flux command value Φ*. Here, since the control directly controls the magnetic flux inside the IM, there is a reason why it is called magnetic flux direct control type vector control.

[0006]

[Problems to be Solved by the Invention] As described above, magnetic flux direct control type vector control directly controls the magnetic flux and does not control the motor current Im as seen in other vector controls. This method has the disadvantage that it is not possible to set a limit value on the value of Im.

Generally, as seen in other vector controls, those with a current control loop are constructed so that the motor current matches the current command value, so a limit value is set for the current command value itself. This makes it possible to limit the current, but this was not possible with the magnetic flux direct control type as in this method. The present invention is intended to solve these drawbacks.

[0008]

[Means for Solving the Problems] A current limiting method in magnetic flux direct control type vector control of an induction motor according to the present invention is such that the torque command value used in the magnetic flux command value calculation is set to K.
G x (torque command value set externally) is used, and when determining this KG, always compare the preset limit current value of the motor with the actual motor current flowing. , (Limited current value IL)
When ≦(motor current Im), KG with 0 as the minimum value
It is possible to limit the current flowing through the motor by gradually decreasing KG and gradually increasing KG with a maximum value of 1.0 when (limited current value IL) > (motor current Im). Features.

That is, the torque command value τ* which is set from the outside and is used to calculate the magnetic flux command value Φ* mentioned above.
is multiplied by a coefficient KG, and the value τ** is used as the calculated torque command value. The relational expression is the following equation (1). τ**=KG ×τ* (0≦KG≦1.0
) ... (1) Here, KG is determined by the motor current Im and the limiting current value IL to which a limit is to be applied. The algorithm for determining KG is shown in a flowchart as shown in FIG. 2. By using such a means, it becomes possible to apply current limitation in magnetic flux direct control type vector control.

0010

[Operation] As shown in Fig. 2, the motor current Im is compared with the limit current value IL, and when IL≦Im, KG is gradually decreased, and the minimum value is set to 0. >Im, gradually increase KG and set the maximum value to 1.0 to determine KG, and use the calculated torque command value τ** to calculate the magnetic flux command value Φ*. For example, the current Im flowing through IM can be controlled to be below the limit current value IL.

The reason for this will be explained below. Motor current I
m is the force current (no-load current) IO and the torque current IT
This can be expressed as the following equation (2). Im =√{IO 2 +IT 2 }
...(2
) Here, in normal vector control, since the magnetic flux is controlled to be kept constant, the torque current IT is proportional to the torque command value τ*. Therefore, torque command value τ
By adjusting *, the motor current Im can be adjusted, and it becomes possible to limit the motor current Im.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained using the block diagram of FIG. 1 showing one embodiment of the present invention. Among the symbols in FIG. 1, the same symbols as those in the conventional system shown in FIG. KG is a different part
Only the arithmetic unit 11 will be explained.

[0013] The input of the KG calculator 11 is the torque command value τ
* and the limiting current value IL and the motor current Im,
The calculated torque command value τ**, which is the output thereof, is calculated by formula (1) by determining the coefficient KG using the algorithm shown in FIG. 2 described above. Using the output τ** of the KG calculator 11, the calculator 8 calculates and determines the magnetic flux command value Φ*. As a result, the magnitude of the torque current IT is controlled as shown in equation (2), and the value of the motor current Im can be controlled to be equal to or less than the limit current value IL.

[0014]

As described above, according to the present invention, it is possible to realize current limitation that could not be achieved with conventional magnetic flux direct control type vector control. Moreover, since vector control is generally controlled by a central processing unit or the like, the current limiting method of the present invention requires only the addition of software and does not require any modification of hardware, reducing the cost of the control device. No deterioration in reliability will occur.

[Brief explanation of drawings]

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

FIG. 2 is a flowchart showing an algorithm of a coefficient calculator for current limiting according to the present invention.

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

[Explanation of symbols]

1 Rectifier 2 Inverter section 3 Three-phase induction motor 4 Pulse generator 5 Current detector 6, 8, 9 Arithmetic unit 7 Motor constant memory 10 Counter 11 KG computing unit

Claims (1)

[Claims] Claim 1: In vector control of an induction motor driven by a voltage source inverter device composed of six transistors, the magnetic flux generated inside the motor is calculated from the motor constant and the motor current, and the magnetic flux generated inside the motor is calculated from the motor constant and the motor current. A magnetic flux command value to be generated inside the motor is calculated from a torque command value and motor rotation speed set from the outside, and switching of the transistor is directly determined from the magnetic flux command value, the generated magnetic flux, a motor constant, and a motor current. , in the magnetic flux direct control type vector control of the switching method, KG ×
(torque command value set externally), and when determining this KG, always compare the preset limit current value of the motor with the actually flowing motor current; When (limiting current) ≦ (motor current), gradually decrease KG with 0 as the minimum value, and (
A magnetic flux direct control type of induction motor, characterized in that it is possible to limit the current flowing through the motor by gradually increasing KG with a maximum value of 1.0 when (limited current) > (motor current). Current limiting method in vector control.