JPH0640751B2 - Induction motor drive - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an induction motor drive device, and more particularly to a frequency for separately controlling a primary current of an induction motor into a component contributing to magnetic flux generation and a component contributing to torque generation. The present invention relates to an induction motor drive device suitable for supplying an output power of a frequency converter to a induction motor via a transformer by using a converter and operating the induction motor at a variable speed.

[Technical background of the invention and its problems]

Due to recent technological advances, many types of drive systems have been put to practical use as variable speed drive systems for induction motors using frequency converters. Of these control methods,
Vector control is one of the applications whose applications are expanding as the ones that can achieve the same excellent control performance as DC motors. The induction motor has a drawback in that the exciting current and the torque-generating current exist only in a combined form of the primary current, and they cannot be controlled independently. The vector control is such that the primary current can be separated and controlled independently by various control means, and high control performance similar to that of the DC separately excited motor can be obtained.

First, a frequency converter system for performing vector control will be described.

FIG. 4 is a schematic configuration diagram of a conventional induction motor drive device by a frequency conversion device adopting vector control. Although there are various types of frequency conversion devices, the current source inverter is illustrated in the configuration of FIG. As shown in the figure, this induction motor drive device includes a rectifier 1 that rectifies an input AC power supply into a DC current, a DC reactor 2 that smoothes a DC current, an inverter 3 that converts the DC current into an AC of an arbitrary frequency, an induction motor. 4, a speed sensor 5 for detecting the rotation speed of the induction motor 4, a speed control circuit 6 for controlling the speed of the induction motor 4,
Magnetic flux detection circuit 7 for detecting magnetic flux of induction motor 4, magnetic flux control circuit 8 for controlling magnetic flux of induction motor 4, induction motor 4
Primary current reference calculation circuit 9 for calculating the primary current reference, current detector 10, current control circuit 11 for controlling the magnitude of DC current, and phase control circuit 1 for controlling the ignition phase of the rectifier 1.
2, a phase angle calculation circuit 13 for calculating the angle between the primary current and the magnetic flux of the induction motor 4, a slip calculation circuit 14 for calculating the slip of the induction motor 4, and the rotation of the induction motor 4 from the output signal of the speed sensor 5. The rotor position calculation circuit 15 calculates the child position, and the commutation control circuit 16 calculates the primary current phase of the induction motor 4 and determines the output current phase of the inverter 3.

In such a configuration, the AC power of the input AC power source is converted to DC power by the rectifier 1, smoothed by the DC reactor 2, inversely converted to AC power of any frequency by the inverter 3, and supplied to the induction motor 4. Exercise at variable speed.
The rotation speed of the induction motor 4 is detected by the speed sensor 5 and fed back as a speed feedback signal ω _r .

The speed feedback signal ω _r is compared with the speed reference ω _r ^*, and its deviation is given to the speed control path 6. as a result,
The speed of the induction motor 4 is closed loop controlled. The output signal of the speed control circuit 6 serves as a reference i ▲ ^* _1q ▼ of a current component (hereinafter, referred to as torque current) of the primary current I ₁ of the induction motor 4 that contributes to torque generation.

On the other hand, the magnetic flux Φ of the induction motor 4 is directly detected from the induction motor 4 by a sensor or the like, or indirectly calculated from the terminal voltage of the induction motor 4, or fed back by the magnetic flux detection circuit 7 through either method. . Magnetic flux Φ
Is compared with the magnetic flux reference Φ ^*, and the deviation is compared with the magnetic flux control circuit 8
Given to. As a result, the magnetic flux is closed loop controlled. The output signal of the magnetic flux control circuit 8 is the primary current I ₁ of the induction motor 4.
Of these, the current component (hereinafter, referred to as an exciting current) that contributes to the generation of magnetic flux becomes a reference ∇i ^* _1d∇ .

The reference I ₁ ^* of the primary current is calculated by the primary current reference calculation circuit 9 from the torque current reference ▲ i ^* _1q ▼ and the excitation current reference ▲ i ^* _1d ▼. The primary current I ₁ flowing in the induction motor 4 is detected by providing a current detector 10 on the input side of the rectifier 1 or the output side of the inverter 3, and the current control circuit 11 is set so that this becomes equal to the reference I ₁ ^* of the primary current. Controlled by. The output signal of the current control circuit 11 is input to the phase control circuit 12 as the phase reference PHC, and the rectifier 1 is phase-controlled by the phase signal α to control the magnitude of the current.

Also, torque current reference ▲ i ^* _1q ▼ and excitation current reference ▲ i ^* _1d
The angle θ between the primary current I ₁ and the magnetic flux Φ is calculated by the phase angle calculation circuit 13 from ▼. Furthermore, the slip angle θ _s is calculated from the torque current reference ▲ i ^* _1q ▼ and the magnetic flux Φ. On the other hand, the velocity feedback signal ω _r of the induction motor 4
The rotor position angle θ _r is calculated by time integration of the rotor position calculation circuit 15. Phase theta ₁ of the primary current I ₁ these angles theta, slip angle theta _s, rotor position angle theta
It can be obtained as the sum of _r .

The commutation of the inverter 3 is controlled by the commutation control circuit 16 based on the primary current phase signal θ _1, and the primary current flows in a predetermined phase.

Since the induction motor driving device with the frequency converter configured as described above can separately control the primary current of the induction motor 4 into the torque current and the exciting current, the same high control performance as that of the DC separately excited motor is obtained. The advantage is that On the other hand, in such an induction motor drive device, the primary frequency and the terminal voltage of the induction motor 4 are not directly controlled, but the primary frequency is indirectly controlled as the rate of change of the primary current phase signal θ _1. The terminal voltage is indirectly controlled to a value determined by the exciting current i _1d and the characteristic peculiar to the induction motor 4.
This point is a big difference compared with the conventional induction motor drive device using the frequency converter that directly controls the primary frequency and the terminal voltage of the motor.

Generally, when driving a high voltage induction motor using a frequency converter, a step-up transformer is inserted between the frequency converter and the induction motor. In this case, since the transformer is not magnetically saturated when starting the induction motor, the lower limit is limited so that the primary frequency does not become too low, or the ratio of the terminal voltage of the induction motor to the primary frequency (V / F ratio). It is done to limit it so that it does not become too large.

However, in the drive device for the induction motor shown in FIG. 4, the primary frequency and the motor terminal voltage are not directly controlled. Therefore, when the step-up transformer is used as it is, magnetic saturation should be prevented in advance. There was a drawback that you couldn't.

[Object of the Invention]

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, and by performing vector control, while maintaining high control performance, prevent saturation of the transformer between the frequency converter and the induction motor. Accordingly, it is an object of the present invention to provide an induction motor drive device capable of applying vector control to a high voltage induction motor.

[Outline of Invention]

In order to achieve the above object, the present invention provides a frequency converter that separately controls a primary current of an induction motor into a component that contributes to magnetic flux generation and a component that contributes to torque generation, and the output power of this frequency converter as a voltage. An induction motor drive device including a transformer for converting and supplying the same to the induction motor, and a correction unit for reducing a control amount of a component contributing to magnetic flux generation when the induction motor is started or at a low speed in order to prevent saturation of the transformer. Is provided.

Further, the present invention provides a frequency converter that separates and controls a primary current of an induction motor into a component that contributes to magnetic flux generation and a component that contributes to torque generation, and an output electric power of this frequency converter is converted into a voltage to be an induction motor. (EN) An induction motor drive device provided with a transformer to be supplied and means for correcting the slip frequency so as not to become smaller than a predetermined value at the time of starting or low speed of the induction motor in order to prevent saturation of the transformer. is there.

Example of Invention

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an induction motor drive device according to an embodiment of the present invention. The configuration of FIG. 4 is different from that of FIG. 4 in that the induction motor 4 is provided with an inverter 3 via a transformer 20.
And the magnetic flux reference correction circuit 17 is provided when the velocity feedback signal ω _r and the velocity reference ω _r ^* are input in order to weaken the magnetic flux reference Φ ^* in a certain velocity range.

The operation of this structure will be described below with reference to the velocity vs. magnetic flux characteristic diagram of FIG.

In general, the magnetic flux reference Φ ^* is generally constant (characteristic A) regardless of the speed ω _r or reduced (characteristic B) in the high speed region. It is widely used for field weakening or magnetic flux weakening control to reduce the magnetic flux reference Φ ^* in this high speed region. On the other hand, the magnetic flux reference correction circuit 17 reduces the magnetic flux reference signal Φ ^{* 1} (however, to a magnetic flux reference Φ ₂ ^* reduced from the normal magnetic flux reference Φ ₁ ^* at a speed equal to or lower than a predetermined speed ω _r1 . Φ ₂ ^* <Φ ₁ ^* ) is output. The saturation of the transformer 20 can be prevented by reducing the magnetic flux reference Φ ^* to Φ ₂ ^* when the induction motor 4 is started. The speed ω _r is not always the speed sensor 5
Is not necessary, and the speed reference ω _r ^* may be used.

As described above, by weakening the magnetic flux of the induction motor 4 only when the induction motor 4 in which saturation of the transformer 20 is a problem is started, it is possible to apply the vector control to the induction motor while preventing the saturation of the transformer 20. Become.

FIG. 3 is a schematic configuration diagram of an induction motor drive device according to another embodiment of the present invention. The difference between the configuration of FIG. 1 and the configuration of FIG. 1 is that a slip correction circuit 18 is installed in place of the magnetic flux reference correction circuit 17.

In such a structure, the following operation will be described.

Usually, the slip frequency f _s of the induction motor 4 is expressed by the following equation.

However, T ₂ is a secondary time constant of the induction motor 4.

By the way, the slip correction circuit 18 causes the transformer 20 to fail because the slip frequency becomes too small when the induction motor 4 is started.
Has a function to prevent the saturation. That is, the secondary time constant T ₂ of the induction motor 4 is corrected and reduced only at the time of starting,
Or preventing the slip frequency f _s may become excessively small at start-up by increasing modifies only at startup torque current reference ▲ i ^* _1q ▼, to prevent saturation of the transformer 20 as a result.

As described above, the saturation of the transformer 20 is prevented by operating the slip correction circuit 18 in order to prevent the slip frequency of the induction motor 4 from becoming excessively small only when the induction motor 4 in which the saturation of the transformer 20 is a problem. It becomes possible to prevent and effectively apply the vector control to the induction motor 4.

In each of the above embodiments, the case where the current source inverter is applied as the frequency converter is illustrated, but the embodiment of the present invention is not limited to this, and any frequency converter capable of vector control is applied. Of course it is possible.

〔The invention's effect〕

As described above, according to the present invention, while maintaining high control performance by vector control, a transformer is interposed between the frequency converter and the induction motor, and the operation can be continued without saturating the transformer. It is possible to obtain the induction motor drive device that is enabled.

[Brief description of drawings]

1 is a schematic configuration diagram of an induction motor drive device according to an embodiment of the present invention, FIG. 2 is a characteristic diagram for explaining the operation of the device of FIG. 1,
FIG. 3 is a schematic configuration diagram of an induction motor drive device according to another embodiment of the present invention, and FIG. 4 is a schematic configuration diagram of a conventional induction motor drive device. 1 ... Rectifier, 3 ... Inverter, 4 ... Induction motor,
5 ... Speed sensor, 10 ... Current detector, 17 ... Magnetic flux reference correction circuit, 18 ... Slip correction circuit, 20 ... Transformer.

Claims (2)

[Claims] 1. A frequency converter for separately controlling a primary current of an induction motor into a component that contributes to magnetic flux generation and a component that contributes to torque generation, and an output electric power of this frequency converter that is converted into a voltage to an induction motor. An induction motor drive device comprising: a transformer to be supplied; and a correction unit that reduces a control amount of a component that contributes to magnetic flux generation when the induction motor is started or at a low speed in order to prevent saturation of the transformer. 2. A frequency converter for separately controlling a primary current of an induction motor into a component that contributes to magnetic flux generation and a component that contributes to torque generation, and an output electric power of the frequency converter that is converted into a voltage to form an induction motor. An induction motor drive device comprising: a transformer to be supplied; and means for correcting the slip frequency so that the slip frequency does not become smaller than a predetermined value when the induction motor is started or at a low speed in order to prevent saturation of the transformer.