JPS6335189A - Control method of induction motor - Google Patents

Abstract

PURPOSE:To decrease excitation current and load current and to miniaturize an induction motor by amount corresponding to this, by a method wherein terminal voltage is increased even at control region other than constant torque region. CONSTITUTION:A control element 5 compares a detected value VM of the present rotational speed of an induction motor 3 with a target speed value VFS given from a command circuit. Output frequency of a DC/AC converter 2 is varied so that both values are coincident, and a control element 6 constituted by a read only memory generates a control signal of the output voltage value corresponding to output voltage frequency, thereby controlling the output voltage of the DC/AC converter 2. In this case, a control signal varying corresponding to variation in terminal voltage V is previously set to the control element 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of controlling an induction motor suitable for use in rotating wheels of a vehicle.

[Conventional technology]

Conventionally, DC motors have been mainly used as motors for rotating the wheels of vehicles. However, as semiconductor device technology has improved in recent years, there has been a shift to a method that combines a DC/AC converter and an induction motor, and controls the torque and speed of the axle by controlling the voltage and frequency using the DC/AC converter. be.

Therefore, the speed V, voltage V, and current ■ shown in FIG.

As shown in the relationship characteristic diagram between magnetic flux φ and tensile force TE.

A constant torque region, a constant voltage region, and a characteristic region are established in the control range of the induction motor, and the ratio of voltage V and frequency is kept constant and increased until the terminal speed of the constant torque region is reached, and at higher speeds, A method of driving an induction motor by controlling the voltage V to a constant voltage has been proposed (Japanese Patent Laid-Open No. 53-96111).

[Problem that the invention seeks to solve]

However, according to the conventional control method described above, the amount of magnetic flux reaches its maximum at the #V end speed in the constant torque range, so magnetic design must be performed based on the amount of magnetic flux at this end speed, resulting in extreme If the size of the wheel is reduced, the magnetic flux density becomes larger than necessary, which increases both the excitation current and the load current, resulting in a decrease in the driving performance of the wheel.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for controlling an induction motor that can reduce the size of the induction motor without reducing the drive performance of wheels.

[Means for solving problems]

The present invention is designed to increase the terminal voltage even in a control range other than the constant torque range.

[Operation] The stall torque of an induction motor is inversely proportional to the square of the frequency. Further, the required torque in the constant power range is inversely proportional to the frequency.

Therefore, when the constant power range is wide, the ratio of the stall torque to the torque required for acceleration increases at the speed of transition from the constant torque range to the constant power range. Therefore, conventionally, the terminal voltage was increased to ensure the maximum amount of magnetic flux at this point, and the terminal voltage was kept constant once the transition to the constant power region occurred. It also resulted in However, while reducing the amount of magnetic flux by lowering the terminal voltage at the terminal speed in the constant torque range, the excitation current and load current can be reduced by compensating for the decelerated magnetic flux by increasing the terminal voltage in the constant power range. Therefore, the induction motor can be made smaller accordingly.

〔Example〕

Hereinafter, the present invention will be explained based on Examples.

FIG. 1 shows an example of a terminal voltage control pattern of an induction motor according to the present invention, with magnetic flux φ and load current I.

This is a diagram shown together with the tensile force TE, where the horizontal axis is the speed V, and the constant torque range is from V = O to V1, and V = v1 to v2.
The range up to is the constant power range, and the range from v=vz to ■8 is the characteristic range,
It is shown that in the constant torque region, the voltage (2) is increased to Ex with the change in speed (2), and furthermore, in the constant power region, it is increased to the rated power E2.

Figure 2 is a graph showing the qualitative relationship between the terminal voltage V, magnetic flux φ, load current, and exciting current Ioo of the induction motor when the torque is constant at a given frequency. , the magnetic flux φ decreases, and the excitation current Ioo decreases accordingly, but as for the load current, even if the excitation current Ioo decreases, if the terminal voltage is below a specific terminal voltage E1, the power is increased to compensate for the decrease in the terminal voltage. This shows that the effective current increases and again shows an increasing trend. Here, if the terminal voltage E1 when the load current ■ is minimum is controlled to the terminal voltage at the terminal speed v1 in the constant torque region.

The size can be reduced by the amount that the magnetic flux φ is reduced. However, at this time, the magnetic flux φ when shifting to the constant power region becomes insufficient. Therefore, even in the constant power range, the decrease in magnetic flux φ is compensated for by increasing the terminal voltage V to the rated voltage E2.
The required amount of magnetic flux can be secured. That is, in the constant torque region, the load current ■ is increased to the terminal voltage E1 where it is minimum, and the magnetic flux is controlled to be as small as possible, and the magnetic flux in the constant power region is
By increasing , it is possible to downsize the induction motor while maintaining the relationship between the speed V and the tensile force TE.

FIG. 3 is a graph showing changes in terminal voltage V and magnetic flux φ in comparison with the conventional method, where the broken line shows the change due to the method of the present invention and the solid line shows the change due to the conventional method. As is clear from the figure, according to the method according to the present invention, the magnetic flux φ
is significantly smaller in the constant torque range.

In FIG. 1, the terminal voltage V in the constant power range is increased linearly, but the rising curve may not be linear. Furthermore, the terminal voltage V may be increased even in the characteristic range. In addition, although the rated voltage E2 is set at speed ■2, it may be controlled so that the rated voltage E2 is reached at speeds other than v2, and if the required amount of magnetic flux is secured, the rated voltage E2 can be reached. It doesn't have to be raised.

Fig. 3 is a block diagram showing an embodiment of a control system to which the present invention is applied, in which the DC voltage of the DC power supply 1 is converted to a 3-phase AC voltage by the DC/AC conversion table @ 2, and the induction motor 3 is applied to The rotational speed of the induction motor 3 is determined by a speed detector 4
is detected and input to the control element 5. The control element 5 is
The detected value VM of the current rotational speed of the induction motor 3 is compared with the target speed value VFS given from a command circuit (not shown), and the output voltage frequency of the DC/AC converter 2 is adjusted so that the two match. At the same time, the output voltage of the DC/AC converter 2 is controlled by generating a control signal having an output voltage value corresponding to the current output voltage frequency from a control element 6 composed of a read-only memory or the like. At this time, voltage control as shown in FIG. 1 becomes possible by setting in advance a control signal that changes in accordance with the change pattern of the terminal voltage (2) shown in FIG. 1 in the control element 6.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to downsize the induction motor while maintaining wheel drive performance equivalent to that of the conventional motor.

[Brief explanation of drawings]

FIG. 1 is a graph showing an example of the terminal voltage control pattern of an induction motor according to the present invention, and FIG. 2 is a graph showing the relationship between the terminal voltage, magnetic flux, load current, and exciting current when the torque is constant. Fig. 3 is a graph showing changes in terminal voltage and magnetic flux in comparison with the conventional method, Fig. 4 is a block diagram showing an example of a control system to which the present invention is applied, and Fig. 5 is a graph showing the terminal voltage according to the conventional method. 3 is a graph showing a control pattern of FIG. ]-...DC power supply, 2...DC/AC converter, 3
...Induction motor, 4...Speed detector, 5,6...
control element.

Claims (1)

[Claims] 1. Control of an induction motor in which the induction motor is driven and controlled by a variable voltage variable frequency type DC/AC converter and has a constant torque region and a constant power region in its drive control range. A method for controlling an induction motor, the method comprising: increasing a terminal voltage of the induction motor even in a drive control range other than a constant torque range. 2. The method for controlling an induction motor according to claim 1, wherein the terminal voltage outside the constant torque range is increased as the frequency increases.