JPH08126400A - Vector controller for induction motor - Google Patents

Abstract

PURPOSE: To obtain a vector controller for operating an induction motor stably without causing any failure under a steep deceleration state within a constant output range. CONSTITUTION: ACR sections 10, 11 for controlling the primary current to a target value in vector control has variable gains. The ACR gain is switched, at a correction coefficient generating section 15 and an ACR gain control section 16, to a high gain under high speed region and to a constant gain under low speed region depending on the detection speed of an induction motor IM. Consequently, when the induction motor IM is decelerating steeply within a constant output range, the response is quickened in a high speed region and hunting is prevented in a low speed region to prevent run-out of vector control thus realizing a good control. Furthermore, a predetermined limit is imposed by the output of a drive/regeneration discriminator 18 to the primary voltage V1 generated from a PWM signal generating section 4 at the time of regeneration. This constitution prevents overcurrent being generated under step-out state thus preventing failure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction motor vector control device for controlling the number of revolutions of an induction motor by vector control by an inverter.

[0002]

2. Description of the Related Art A vector control device for an induction motor based on a vector control theory for controlling a secondary magnetic flux and a secondary current orthogonal to the secondary magnetic flux in a non-interfering manner has been widely applied (JP-A-3-135388). See the prior art). In the vector control described in this publication, in the case of a three-phase induction motor, currents and magnetic fluxes are treated as vectors of orthogonal biaxial dq coordinate systems that rotate at the same speed as the rotating magnetic field generated by the power supply, and the calculation result is three-phase. This is a method of controlling by converting the current command value of each phase of the power supply.

It should be noted that this calculation result includes both the voltage fluctuations due to the changes in the primary resistance and the secondary resistance. Therefore, if the secondary resistance change is compensated by obtaining the component that does not include the voltage variation due to the primary resistance change, it is possible to perform the compensation that is not affected by the primary resistance change. Therefore, the rotation coordinate γ-δ axis with the reference axis γ placed on the vector of the primary current is taken, and the primary voltage fluctuation Δv ₁ δ of this δ axis is calculated to obtain Δv ₁
There is also proposed a vector control device that employs a method of expressing δ by an expression that does not include the primary resistance and preventing the influence of the primary resistance change.

[0004]

However, in the vector control device for the induction motor according to the above-mentioned conventional technique, the speed of the induction motor is controlled by the inverter using the vector control theory, and the induction motor absorbs the energy of the load. However, if the speed is rapidly decreasing in the constant output range, due to changes in the secondary time constant, speed detection error, etc.,
An error occurs in the inverter output voltage calculation. Particularly, in the above-mentioned load state, there is a problem that control becomes difficult.

The reason is as follows.

(1) The inverter tries to raise the voltage in order to suppress the regenerative current when the speed drops rapidly, but due to the above error, the control deviates from the vector control.
The ratio of the exciting current to the current increases, and as a result, the voltage of the induction motor rises, making it impossible to control the regenerative current.

(2) In the above state, the control of the inverter is operated in consideration of the magnetizing effect, but the value becomes improper due to the error of the secondary time constant. Therefore, the regenerative current cannot be controlled for the same reason as (1).

In normal vector control, ACR (auto current regulation) control is used to detect the primary current and control it to a target value. This ACR control has a constant gain in any state. .
In the above problems, it is effective to increase the gain in ACR control, but the leakage inductance may change depending on the frequency and so on.
ACR control hunting (overcompensation, etc.) will occur.

The present invention has been made to solve the above problems, and an object thereof is to provide a vector control device for an induction motor capable of stably operating without a failure in a rapid deceleration state in a constant output range. To provide.

[0010]

In order to achieve the above object, in the vector controller for an induction motor according to the present invention, the primary current of the induction motor is controlled by a rotating coordinate system which rotates in synchronization with the power source angular frequency of the induction motor. In a vector controller for controlling the speed of an induction motor by calculating respective target values of the excitation current and the torque current, the detected value of the primary current is compared with the target value and controlled to the target value. It is characterized in that the gain of the control means is variable, and means for changing or changing the gain of the control means to be higher as the detection speed of the induction motor is higher is provided.

In the vector control device for the induction motor described above, it is preferable to provide limit means for limiting the primary current when the induction motor is regenerated, which is suitable for preventing overcurrent in the event of loss of synchronization in vector control. is there.

[0012]

In the vector controller for the induction motor of the present invention,
When the induction motor is absorbing the energy of the load and rapidly lowering the speed in the constant output range, the gain of the control means for controlling the primary current to the target value is changed or switched to an appropriate value according to the detected speed. As a result, the gain is increased in the high speed range to speed up the response, and the gain is decreased in the low speed range to prevent hunting (overcompensation, etc.), thereby preventing deviation of the vector control and realizing good control.

Further, by giving a fixed limit to the primary current at the time of regeneration, the overcurrent that occurs in the out-of-synchronization state of the vector control is prevented, and the accident caused by the overcurrent is prevented.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, 1 is a dq axis-γδ axis coordinate conversion unit (hereinafter referred to as a first coordinate conversion unit), 2 is a γδ axis non-interference control unit, 3 is a polar coordinate conversion unit, and 4 is PWM (pulse width control).
A signal generator, 5 is a base signal generator, 6 is an inverter using a power transistor, HCT is a current sensor, IM
Is a three-phase induction motor, pp is a rotation speed detection sensor, 7 is a current detection unit, 8 is a speed detection unit, and 9 is a 3φ (3 phase) -γδ axis coordinate conversion unit (hereinafter referred to as a second coordinate conversion unit). 10 is the γ-axis ACR (auto current regulation)
Section, 11 is a δ-axis ACR section, 12 is a constant output excitation control section, 1
3 is a field primary advance circuit, and 14 is an integrator. The above configuration is almost the same as the conventional configuration.

First, the basic operation of the above configuration will be described.

For the first coordinate conversion unit 1, the excitation current component command value I ₁ d * and the torque component current command value I ₁ q of the primary current vector in the dq axis coordinate system with the secondary magnetic flux as the reference axis. *
When is input, the first coordinate conversion unit 1 performs coordinate conversion of the command value of the primary current into a γ-δ axis coordinate system with the primary current as a reference axis and outputs I ₁ , sin φ, cos φ. Note that I ₁
d * is given the rotation speed detected by the rotation speed detection sensor pp and the speed detection unit 8 via the constant output excitation control unit 12 and the field primary advance circuit 13.

When the output from the first coordinate conversion unit 1 is received, γ
The −δ axis non-interference control unit 2 calculates and outputs ideal primary voltages V ₁ γ * and V ₁ δ * for flowing the primary current. On the other hand, the three-phase current flowing in the induction motor IM detected by the current sensor HCT and the current detection unit 7 is converted into each axis component i ₁ γ, i ₁ δ of the γ-δ axis coordinate system by the second coordinate conversion unit 9. Target values i ₁ γ * (= I ₁ ) and i ₁ δ * are converted, respectively.
(= 0) and the deviation is compared with the γ-axis ACR unit 10,
It is input to each of the δ-axis ACR units 11.

The γ-axis ACR unit 10 and the δ-axis ACR unit 11 are
Based on the input deviations, primary voltage fluctuations ΔV ₁ γ and ΔV ₁ δ are obtained at the outputs. Obtained ΔV ₁ γ, ΔV ₁
δ is added to the target values V ₁ γ * and V ₁ δ *, respectively, to obtain V
₁ γ and V ₁ δ are input to the polar coordinate conversion unit 3.

The coordinate transformation unit 3 outputs the magnitude V ₁ of the vector of the primary voltage and the phase angle φ with the γ axis from the outputs of V ₁ γ and V ₁ δ. This phase angle φ is added to θ described later, and the added value and V ₁ are input to the PWM signal generation unit 4 and converted into primary voltage command values corresponding to the three phases U, V, and W phases. As a result, the base signal of the inverter 6 is generated by the base signal generator 5, the inverter 6 is controlled, and the speed of the induction motor IM is controlled.

In the above, θ is the sum of φ obtained by the γ-δ axis non-interference control unit 2 and the signal obtained by integrating the angular velocity detected by the velocity detection unit 8 by the integrator 14. .

In contrast to the above configuration, in this embodiment, each AC
A variable gain amplifier is used as an amplifier forming the R units 10 and 11, and an ACR gain correction coefficient generating unit 15 and an ACR gain control unit 16 are added to switch the ACR gain according to the detected speed state. That is, the ACR gain correction coefficient generation unit 15 outputs a correction coefficient for the detected speed (angular speed) of the speed detection unit 8 using, for example, the correction coefficient function shown in the graph of FIG. 2, and the ACR gain control unit according to this correction coefficient. 1
6 is AC linearly or in multiple thresholds stepwise
Change or switch R gain. In the example of FIG. 2, the ACR gain is kept constant in the low speed range so that overcompensation does not occur, and in the high speed range, the ACR gain is changed to a higher value or switched at a higher speed to speed up the response, thereby preventing deviation of vector control. To do. Thus, in order to always have an appropriate gain according to the change in the leakage inductance depending on the frequency, the ACR gain is switched depending on the detection speed state, so that good control is performed.

In the vector control as described above, if the vector control state is out of synchronization for some reason, an overcurrent is generated in the regenerative state. In order to suppress this, it is preferable to provide means for limiting the primary current during regeneration. In the present embodiment, the limit circuit at the time of regeneration is the PW from the polar coordinate conversion unit 3 as the limit means.
The signal line of V ₁ output to the M signal generation unit 4 is provided.
Then, the drive / regeneration discriminator 18 discriminating the regeneration time from the torque current command value I ₁ q * etc. limits the V ₁ only at the regeneration time by the regeneration time discrimination output. When driving other than that,
It is output as it is without any limit.

As a result, in the case of the problem described in the problem to be solved by the present invention, as a result, the excitation voltage is limited by limiting the inverter voltage to a value that does not cause overcompensation, and the overcurrent is reduced. Suppress the occurrence of.

[0025]

As is clear from the above description, according to the vector control device for an induction motor of the present invention, even in the rapid deceleration state in the constant output range, an appropriate ACR gain is set to accelerate the response, Out-of-synchronization in vector control can be prevented, and hunting can be prevented as an appropriate ACR gain corresponding to low speed, and stable vector control can be realized.

Further, when the primary voltage is limited to a constant value during regeneration, it is possible to prevent an overcurrent from being generated when synchronization is lost during vector control for some reason, and an accident due to an overcurrent occurs. Can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a correction coefficient function when changing or switching the ACR gain in the above embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... dg axis-γδ axis coordinate conversion unit (first coordinate conversion unit) 2 ... γδ axis non-interference control unit 3 ... polar coordinate conversion unit 4 ... PWM signal generation unit 6 ... inverter 7 ... current detection unit 8 ... speed detection unit 9 ... 3-phase-γ-delta axis coordinate conversion section (second coordinate conversion section) 10 ... γ-axis ACR section 11 ... δ-axis ACR section 15 ... ACR gain correction coefficient generation section 16 ... ACR gain control section 17 ... Regenerative limit circuit 18 ... Drive / regeneration discriminator IM ... Induction motor

Claims (2)

[Claims] 1. A speed of an induction motor is calculated by dividing a primary current of the induction motor into an excitation current and a torque current by a rotating coordinate system that rotates in synchronization with a power source angular frequency of the induction motor and calculating respective target values thereof. In a vector control device for controlling, the gain of control means for comparing the detected value of the primary current with the target value and controlling to the target value is made variable, and the gain of the control means increases as the detection speed of the induction motor increases. A vector control device for an induction motor, characterized in that means for changing or switching to a high value is provided. 2. The vector controller for an induction motor according to claim 1, further comprising limit means for limiting a primary current during regeneration of the induction motor.