JPH10225158A - Controller for induction machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a brake resistor surely by estimating a temperature rise of the brake resistor from a regenerative power determined based on a value corresponding to the torque of an induction motor and a detected rotational speed thereof. SOLUTION: Based on a speed detection value N and a torque current command value iT* of an induction motor, a mode decision circuit 21 makes a decision that the motor is operating in a regenerative mode if N<0, iT*>0 or N>0 and iT*<0. Consequently, a switch 26 is turned to the regenerative power operating circuit 22 side and a regenerative power P is inputted to a heat model 23. A comparison circuit 24 compares the output from the heat model 23 with an alarm detection set value operated by an operating circuit 25. When the output from the heat model 23, i.e., a temperature rise, exceeds the alarm detection set value, an alarm signal is turned on to alarm that a brake resistor is overheated and a stop command is delivered to the controller for the induction motor. Consequently, the brake resistor can be protected accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an induction motor driven by a power conversion circuit.
The present invention relates to a control device having improved protection means for a braking resistor.

[0002]

2. Description of the Related Art FIG. 9 shows a prior art of this type of control device.
It is a block diagram showing the so-called induction motor vector
It is a control system. In the figure, 1 is an induction motor 15
Pulse encoder as rotation speed detector
Thermistor as a temperature detector of the machine 15, 3 is a speed command
Value N^*Adder for calculating the deviation between the speed and the speed detection value N
Torque command value τ required to make the deviation zero^*Output
Speed control circuit, 5 is the temperature detected value by thermistor 2.
The secondary resistance R of the motor 15 according to_Two’And the temperature_Two
The arithmetic circuit 6 outputs a torque command value τ^*The secondary
Magnetic flux command value φ_Two ^*Divided by the secondary magnet of the motor primary current
Torque current command value i which is a direction component perpendicular to the bundle_T ^*Ask for
, A secondary magnetic flux command value φ_Two ^*1 / M (M is electric
Multiplied by the mutual inductance of the motor 15)
Excitation current command value i which is a direction component parallel to the secondary magnetic flux of_M ^*
And 8 is a secondary resistor R_Two, Secondary magnetic flux command value
φ_Two ^*, Torque current command value i_T ^*Performs predetermined calculation based on
Sliding frequency ω_Sl9 is a speed detection value
Rotational angular frequency ω converted from N_TwoSlip frequency ω_SlWhen
Adder 10 integrates the output of adder 9 to add
Estimated position of next magnetic flux φ_TwoIs an integrator for obtaining the estimated position.
φ_TwoCommand value i of the secondary magnetic flux coordinate system using_T ^*,
Excitation current command value i_M ^*Is converted to the stator coordinates
Current command value i for each phase of the system_a ^*, I_b ^*, I_c ^*Coordinate transformation to convert to
, The primary motor 12 detected by the current detector 14
Current detection value i_a, I_b, I_cAnd each phase current command value i_a ^*, I_b
^*, I_c ^*And each phase voltage command value v_a ^*, V_b ^*, V_c
^*The current control circuit 13 outputs the voltage command value.
v_a ^*, V_b ^*, V_c ^*Generates an applied voltage to the motor 15 according to
This is a power conversion circuit composed of a generated inverter.

In the above-described configuration, when the torque command value τ ^* and the secondary magnetic flux command value φ ₂ ^* are input to the vector control unit, the arithmetic circuit 7 and the divider 6 respectively use equations 1 and 2
To calculate the exciting current command value i _M ^* and the torque current command value i _T ^* .

[0004]

## EQU1 ## i _M ^* = φ ₂ ^* / M

[0005]

[Equation 2] i _T ^* = τ ^* / φ ₂ ^*

Further, the coordinate converter 11 performs coordinate conversion according to equation (3).

[0007]

(Equation 3)

[0008] Further, the arithmetic circuit 8 calculates the slip frequency ω _Sl according to equation (4).

[0009]

Ω _Sl = (R ₂ × i _T ^* ) / φ ₂ ^*

FIG. 10 is a diagram for explaining a dynamic braking system of an induction motor using a braking resistor. The braking system, the rotational energy of the load 16 is converted into electric energy by utilizing the power generation action of the motor 15, consumed as thermal energy by the braking resistor R _B to this was connected to an external power conversion circuit (inverter) 13 It is a method to make it. Specifically, to turn on the transistor switch TR _B when the DC intermediate voltage of the power converter circuit 13 exceeds the set value, the thermal energy by the braking resistor R _B to discharge the electrical energy stored in capacitor C _S Consumption as.

[0011]

BRIEF Problem to be Solved] Conventionally, to protect the brake resistor R _B had performed fault detection by monitoring the temperature sensor or, or the surface temperature of the resistor itself with a thermal relay. However, this braking resistor R
_Since the current flowing in _B is pulse-shaped, the detection error is large in the thermal relay. Further, since the surface temperature of the resistor becomes extremely high, it is necessary to use a special temperature sensor, which causes an increase in cost.

Accordingly, an object of the present invention is to provide a control device for an induction motor that can reliably protect a braking resistor and can reduce the cost.

[0013]

In order to solve the above-mentioned problems, an invention according to claim 1 comprises an induction motor having a power conversion circuit for driving an induction motor and a braking resistor connected to the power conversion circuit. In a motor control device, a regenerative power calculation circuit for obtaining regenerative power based on a torque equivalent value of an induction motor and a rotational speed detection value, and a temperature rise value of a braking resistor is estimated and calculated from the regenerative power obtained by the calculation circuit. And a comparison circuit that outputs an alarm signal when the temperature rise value of the braking resistor estimated and calculated by the thermal model exceeds an alarm detection set value.

According to a second aspect of the present invention, there is provided an induction motor control device including a power conversion circuit for driving an induction motor, and a braking resistor connected to the power conversion circuit. A regenerative power calculation circuit for obtaining regenerative power based on the voltage detection value and the primary resistance, a thermal model for estimating and calculating the temperature rise value of the braking resistor from the regenerative power obtained by the arithmetic circuit, A comparison circuit that outputs an alarm signal when the temperature rise value of the braking resistor exceeds the alarm detection set value.

The third aspect of the present invention provides the first or second aspect.
In the control device for an induction motor described above, a new regenerative power obtained by subtracting a preset generated loss amount from a regenerative power obtained by a regenerative power calculation circuit is input to a thermal model.

According to a fourth aspect of the present invention, in the control device for an induction motor according to the first, second or third aspect, the temperature rise value of the braking resistor estimated and calculated by the thermal model is lower than the alarm detection set value. It is provided with a comparison circuit that outputs a forecast signal when the set value is exceeded.

The fifth aspect of the present invention provides the first, second, and third aspects.
Or a mode discriminating circuit for discriminating whether the temperature of the braking resistor is in a rising mode or a falling mode based on the regenerative power obtained by the regenerative power calculation circuit; Means for switching the thermal time constant of the thermal model in accordance with the determination result by the circuit.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a main part of a first embodiment corresponding to the first aspect of the present invention. In the figure, reference numeral 21 denotes a mode discriminating circuit to which a detected speed value N and a torque current command value i _T ^* of the induction motor are inputted, and 22 denotes a regenerative power calculation to which the detected speed value N and the torque current command value i _T ^* are similarly inputted. circuit, 26 is a switching control by the output signal of the mode determination circuit 21, the switching switch for switching the regenerative power P "0" and an output of the regenerative power calculating circuit 22, 23 braking resistor R _B shown in FIG. 10 Heat model,
25 is an arithmetic circuit for calculating and outputting the alarm detection set value,
24 is a comparator circuit for comparing the outputs of the thermal model 23 of the arithmetic circuit 25, an alarm signal to protect the braking resistor R _B from this comparison circuit 24 are outputted.

The thermal model 23 has a changeover switch 26
Is input regenerative power P or "0" through, and outputs a temperature rise value of the braking resistor R _B estimated operation under a predetermined resistance thermal time constant (set as a specification or actual value) It is.

Next, the operation of this embodiment will be described. The mode determining circuit 21 determines whether the motor is operating in the power running or the regenerative mode based on the speed detection value N of the induction motor and the torque current command value i _T ^* . Now
Consider the rotation of the motor in the counterclockwise direction to be forward rotation, and forward rotation is N>
0 and the reversal is N <0. Also, a torque current command value i _T ^* for rotating the electric motor in the forward direction is represented by i _T ^* > 0. Motor speed detection value N and torque current command value i _T ^*
If the positive / negative combination of is Equation 5 or Equation 6, the mode discriminating circuit 21 judges that the mode is the powering mode.

[0021]

N> 0, i _T ^* > 0

[0022]

N <0, i _T ^* <0

[0023]

N <0, i _T ^* > 0

[0024]

N> 0, i _T ^* <0

The calculation of the regenerative power P performed by the regenerative power calculation circuit 22 is divided into the following two formulas 9 and 10 according to the magnitude of the speed detection value N. That is, when the detected speed value N is equal to or higher than the base rotation speed of the electric motor, Expression 9 is used, and when the detected speed N is lower than the base rotation speed, Expression 10 is used. In Equations 9 and 10, k ₁ and k ₂ are coefficients.

[0026]

## EQU9 ## P = i _T ^* × k ₁

[0027]

P = i _T ^* × | N | × k ₂

If the mode discriminating circuit 21 determines that the regenerative mode is selected, the changeover switch 26 is switched to the regenerative power calculating circuit 2.
Switching to the second side, the regenerative power P is input to the thermal model 23. The output of the heat model 23 and the alarm detection set value by the arithmetic circuit 25 are compared by the comparison circuit 24, and the heat model 2
If the temperature rise value, which is the output of 3, exceeds the alarm detection set value, the alarm signal is turned on to warn that the braking resistor is overheated, and a stop command is sent to the control device of the induction motor. The alarm detection set value in the arithmetic circuit 25 is calculated by multiplying the output rating of the motor by the set braking frequency (% ED).

In this embodiment, when the motor is in the regenerative mode, the temperature rise value of the braking resistor is estimated and calculated based on the regenerative power, and when the value exceeds the alarm detection set value, an alarm signal is output. I have. Therefore, there is no need to use a thermal relay to protect the braking resistor as in the related art, or to monitor the surface temperature of the resistor itself with a sensor. Therefore, the braking resistor can be protected with higher accuracy than a thermal relay that generally has a large detection error, and there is no need to use a special and expensive temperature sensor. Note that the torque command value τ ^*
May be used.

Next, a second embodiment corresponding to the second aspect of the present invention will be described.
An embodiment will be described with reference to FIG. In FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals. This second embodiment differs from the first embodiment only in the method of calculating the regenerative power P. That is, the voltage detection value of the induction motor is calculated by the equation 11 using the M-phase and T-phase components V _Mist ,
V _Tist, and the detected current value is divided into M-phase and T-phase components I _Mist and I _{Tist according} to equation (12).

[0031]

[Equation 11]

[0032]

(Equation 12)

The regenerative power calculation circuit 22 obtains the T-phase component E _Tist of the induced voltage from the voltage detection value, the T-phase component of the current detection value, and the set value of the primary resistance R ₁ of the motor according to the following equation (13). 14 to calculate the regenerative power P and calculate the thermal model 23
To enter. In this embodiment, the same effect as in the first embodiment can be obtained.

[0034]

[ _Equation 13] E _Tist = V _Tist -R ₁ × I _Tist

[0035]

P = E _Tist × I _Tist

Next, a third embodiment of the present invention will be described.
An embodiment is shown in FIG. This embodiment, the output of the regenerative power calculating circuit 22 in the first embodiment, i.e. regenerative power P were input to an adder 27, a new regenerative power P a minus generation loss P ₁ of future control device itself 'Is input to the thermal model 23 via the changeover switch 26. FIG. 4 shows a fourth embodiment corresponding to the third aspect of the present invention.
This is an embodiment in which the same idea as described above is applied to the second embodiment.

[0037] In these embodiments, by subtracting the generated loss P ₁ of the control device itself from the regenerative power P that is calculated by the regenerative power calculating circuit 22 calculates the regenerative electric power consumed by the brake resistor to more closely be able to. In other words, the temperature rise value of the braking resistor estimated and calculated by the thermal model 23 becomes more accurate, and the reliability of the alarm signal output from the comparison circuit 24 improves.

FIG. 5 shows a fifth embodiment corresponding to the fourth aspect of the present invention. This embodiment includes an arithmetic circuit 28 that calculates a forecast set value of the temperature rise value of the braking resistor;
A comparison circuit 29 for comparing the output of the thermal model 23 with the forecast set value is added to the first embodiment. The comparison circuit 29 outputs a forecast signal when the output of the thermal model 23 exceeds the forecast set value. I do. FIG. 6 shows a sixth embodiment corresponding to the fourth aspect of the present invention.
8 and a comparison circuit 29 are added to the second embodiment. Note that the forecast setting value is obtained by multiplying the alarm detection setting value by the braking frequency (% ED), and is set to a value lower than the alarm detection setting value.

According to these embodiments, the forecast signal is output before the alarm signal is output, and the overheating state is forecast before the temperature of the braking resistor becomes high enough to stop the operation of the control device. can do. Then, the generation of the forecast signal is used as an opportunity to review the operation pattern including the regenerative mode, and the generation of the alarm signal is avoided by actually changing the operation pattern due to the limitation of the torque command value and the like. Can be performed.
Note that these embodiments are also applicable to the third embodiment and the fourth embodiment.

Next, FIG. 7 shows a seventh embodiment corresponding to the fifth aspect of the present invention. Thermal model of braking resistor 2
In No. 3, the thermal time constant may be different between when the temperature rises and when the temperature falls, due to the cooling method of the braking resistor and the like. In view of this point, in the present embodiment, two thermal time constants of the thermal model 23 are prepared according to both the mode when the temperature rises and when the temperature falls, and two thermal time constants are set according to the change in the regenerative power P. I changed it.

In the seventh embodiment shown in FIG. 7, a mode discriminating circuit 30 for judging whether a braking resistor is in a temperature increasing mode or a temperature decreasing mode based on a change in regenerative power P, and an output signal of the discriminating circuit 30 A changeover switch 31 for switching between two thermal time constants is added to the first embodiment. FIG. 8 shows an eighth embodiment corresponding to the fifth aspect of the present invention, in which the mode discriminating circuit 30 and the changeover switch 31 are added to the second embodiment.

According to these embodiments, the thermal time constant is finely switched depending on whether the temperature of the braking resistor is increasing or decreasing, and the thermal model 23 estimates the temperature rise value according to the thermal time constant. And performs the comparison with the alarm detection set value, thereby enabling a highly accurate alarm signal output operation and a protection operation of the braking resistor. In addition,
These embodiments are also applicable to the third to sixth embodiments.

[0043]

As described above, according to the first or second aspect of the present invention, it is necessary to use a thermal relay as in the prior art to protect the braking resistor or to monitor the surface temperature of the resistor itself with a sensor. Disappears. Therefore, the braking resistor can be protected with higher accuracy than a thermal relay that generally has a large detection error, and a special temperature sensor is not required, which can contribute to a reduction in manufacturing cost.

According to the third aspect of the present invention, the regenerative electric power causing the temperature rise of the braking resistor can be accurately obtained. Since the accurate thermal time constant is selected, the calculation for estimating the temperature rise value can be accurately performed in any case, and the output operation of the alarm signal and, consequently, the protection operation of the braking resistor can be further improved. It is possible.

According to the fourth aspect of the present invention, the forecast signal obtained by comparing the output of the thermal model with the forecast set value can be used as an opportunity to review the operation pattern of the induction motor. , The generation of an alarm signal can be avoided, and the control device can be continuously operated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of a first embodiment of the present invention.

FIG. 2 is a block diagram showing a main part of a second embodiment of the present invention.

FIG. 3 is a block diagram showing a main part of a third embodiment of the present invention.

FIG. 4 is a block diagram showing a main part of a fourth embodiment of the present invention.

FIG. 5 is a block diagram showing a main part of a fifth embodiment of the present invention.

FIG. 6 is a block diagram showing a main part of a sixth embodiment of the present invention.

FIG. 7 is a block diagram showing a main part of a seventh embodiment of the present invention.

FIG. 8 is a block diagram showing a main part of an eighth embodiment of the present invention.

FIG. 9 is a block diagram of a vector control system of the induction motor.

FIG. 10 is an explanatory diagram of a dynamic braking system in a conventional technique.

[Explanation of symbols]

13 power conversion circuit 15 induction motor 21, 30 the mode determination circuit 22 Regenerative power computing circuit 23 thermal model 24, 29 comparator circuit of the braking resistor 25 and 28 arithmetic circuits 26 and 31 changeover switch 27 adders R _B braking resistor

Continued on the front page (72) Inventor Masataka Oji 1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (72) Inventor Yuji Tetsuya 1-1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-ku, Kanagawa Prefecture Fuji Electric Co., Ltd.

Claims (5)

[Claims] A power conversion circuit for driving an induction motor;
A control device for an induction motor having a braking resistor connected to the power conversion circuit, a regenerative power calculation circuit for obtaining regenerative power based on a torque equivalent value of the induction motor and a detected rotation speed; A thermal model for estimating and calculating the temperature rise value of the braking resistor from the regenerative power obtained by the above, and outputting an alarm signal when the temperature rise value of the braking resistor estimated and calculated by this thermal model exceeds the alarm detection set value A control device for an induction motor, comprising: a comparison circuit; 2. A power conversion circuit for driving an induction motor,
A control device for an induction motor including a braking resistor connected to the power conversion circuit, a regenerative power calculation circuit for obtaining a regenerative power based on a current detection value, a voltage detection value, and a primary resistance of the induction motor; A thermal model that estimates and calculates the temperature rise value of the braking resistor from the regenerative power obtained by the circuit, and outputs an alarm signal when the temperature rise value of the braking resistor estimated and calculated by this thermal model exceeds the alarm detection set value A control device for an induction motor, comprising: a comparison circuit; 3. The control device for an induction motor according to claim 1, wherein a new regenerative power obtained by subtracting a preset generated loss amount from the regenerative power obtained by the regenerative power calculation circuit is input to the thermal model. A control device for an induction motor, comprising: 4. The control device for an induction motor according to claim 1, wherein the temperature rise value of the braking resistor estimated and calculated by the thermal model exceeds a forecast setting value lower than the alarm detection setting value. A control device for an induction motor, further comprising a comparison circuit for outputting a forecast signal. 5. The control device for an induction motor according to claim 1, wherein the temperature of the braking resistor is in a rising mode or a falling mode based on the regenerative power obtained by the regenerative power calculation circuit. A control device for an induction motor, comprising: a mode discriminating circuit for discriminating whether or not, and a means for switching a thermal time constant of a thermal model according to a discrimination result by the mode discriminating circuit.