JPH0937582A - Variable-speed control equipment for induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent discontinuity in applied frequencies at the time of switching from slip frequency compensation control to torque limit control, and torque calculation errors that may be produced depending on operating conditions of an induction motor. SOLUTION: A torque limit adjuster 17 that outputs torque limit signals is fed with a calculated torque value τ# through a second time-lag of first order filter 22. A slip compensation adjuster 18 that outputs slip frequency compensation signals is fed with the calculated torque value τ# through a third time-lag of first order filter 23. The filter 22 has its time constant changed by a time constant switching circuit 25 according to whether a motor is in uniform speed operation, accelerated operation or decelerated operation. A dead zone 23 has its time constant changed by a time constant switching circuit 26 according to whether the motor is in low speed, medium speed or high speed operation. A dead zone width calculator 61 is built in the slip compensation adjuster 18, which is supplied with dead zone data corresponding to the operation speed and load factor of the motor and made to change its values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable speed control device for an induction motor which controls the speed of an induction motor driven by an inverter which controls the voltage and frequency at a constant ratio.

[0002]

2. Description of the Related Art FIG. 9 is a circuit diagram showing a conventional example of a control device that drives an induction motor at a variable speed by an inverter that controls the ratio of voltage and frequency to a constant value. An inverter control method for controlling the ratio of voltage to frequency (hereinafter abbreviated as V / f) to be constant is widely known. Also such V
In order to improve the performance of the / f constant control inverter, a method of performing torque limitation control and slip frequency compensation control is also known, and the torque limitation control and slip frequency compensation control are adopted in the conventional example circuit of FIG. ing.

In the conventional circuit of FIG. 9, the acceleration / deceleration calculator 2 inputs the frequency first command value f ^* set by the frequency setter 1 and outputs the frequency second command value f ^** . The frequency second command value f ^** becomes the frequency fourth command value f4 ^* via the adder 3A and the adder 3B. This frequency fourth command value f ^{4 *}
The V / f computing unit 4 for inputting the signal outputs a voltage signal corresponding to the input value, and the control computing circuit 5 outputs this voltage signal as d
Convert to voltage command values V _1d and V _{1q on the} −q coordinate system. Further, the voltage command value calculation circuit 6 calculates the voltage command value V ^* and the voltage phase command value δ ^* from these V _1d and V _1q according to the following formulas 1 and 2.

[0004]

[Equation 1]

[0005]

[Equation 2]

The voltage command value V obtained by these calculations
The voltage command values V _U ^* , V _V ^* , and V _W ^* for each phase are calculated using Equation 3 of the oyster using ^* and the voltage phase command value δ ^*, and PWM as an inverter that performs constant V / f control Each phase voltage command value obtained by Equation 3 is given to the inverter 7.

[0007]

[Formula 3] V _U ^* = V ^* · cos (θ + δ ^* ) V _V ^* = V ^* · cos (θ + δ ^* + 120 ⁰ ) V _W ^* = V ^* · cos (θ + δ ^* −120 ⁰ ) of the PWM inverter 7 The U-phase output current I _U and the V-phase output current I _V are detected by the current detector 8, and the three-phase / two-phase converter 12 is detected.
Through the vector rotator 13 and I of the dq coordinate system.
Converted to _1d and I _1q . These I _1d and I _1q and the above V _1d and V _1q are input, and the torque calculation circuit 15 calculates the torque calculation value τ ^# . The calculated torque value τ ^# is given to the torque limit adjuster 17 composed of a PI calculator and the slip compensation adjuster 18 also composed of a PI calculator via the first-order lag filter 16. Torque limit adjuster 17
Gives a torque limiting signal, which is its output signal, to the adder 3A. The adder 3A operates the second frequency command value f ^** described above with this torque limit signal to generate the third frequency command value f.
Output ^{3 *} . Since the slip frequency compensation signal further outputs the slip compensation adjuster 18 is supplied to the adder 3B, obtain frequency fourth command value f ^{4 *} by the adder 3B operates the frequency third command value f ^{3 *} . This frequency fourth command value f
^{4 *} is input to the V / f calculator 4 as described above. Thus, torque limit control and slip frequency compensation control are performed.

FIG. 10 is a circuit diagram showing the details of the torque limit control and slip frequency compensation control in the conventional circuit of FIG. 9, in which the torque calculation value τ ^# from the torque calculation circuit 15 is the first-order lag filter 16. Through torque limit adjuster 1
7 and slip compensation adjuster 18. The torque limit adjuster 17 outputs a torque limit signal and the slip compensation adjuster 18 outputs a slip frequency compensation signal. The torque limit signal from the torque limit adjuster 17 is the torque limiting detector 1
Also given to 9. When the torque limit signal reaches a predetermined value, the torque limit detector 19 sends a switching signal to a signal switcher incorporated in the slip compensation adjuster 18, so that the slip compensation adjuster 18 receives the input signal as the calculated torque value. Switch from τ ^# to zero signal. Thus, the slip frequency compensation control is switched to the torque limit control.

[0009]

In the slip frequency compensation control in the conventional circuit described above with reference to FIG. 9, assuming that the set frequency is f ^* , the slip compensation frequency is ω _Sl , and the applied primary frequency is ω ₁ , these are as follows: There is a relationship shown in Equation 4.

[0010]

Equation 4] As already mentioned in the detailed circuit diagram of ω ₁ = f ^* + ω _Sl 10, the input of the slip compensation adjuster 18 by switching to the torque limit control is zero. That is, since the slip compensation frequency ω _Sl in Equation 4 becomes zero, the applied primary frequency ω ₁ is reduced by this amount and the torque limit control is performed.

FIG. 11 is a graph showing the state change when the slip frequency compensation control is switched to the torque limit control in the conventional circuit of FIG. 9, in which the vertical axis represents the torque of the induction motor 9 and the horizontal axis. The rotation speed of the induction motor 9 is shown. That is, when the torque increases during operation by the slip frequency compensation control at the rotation speed corresponding to the applied primary frequency ω ₁ and reaches point A (torque limit value τ _{L at} this time), the torque limit control is performed as described above. Since the switching is performed and the slip compensation frequency ω _Sl becomes zero, the operating state shifts from point A to point B. At this time, there arises a problem that a large discontinuity occurs in the frequency.

Further, when the induction motor 9 is operating at a low speed, an error occurs in the torque calculation value due to voltage distortion caused by the effect of the on-delay time for preventing the upper and lower arms of the PWM inverter 7 from being short-circuited, and pulsation occurs. Cause.
Since the slip frequency is compensated based on the calculated torque value,
If the calculated torque value pulsates, the compensation amount also pulsates. For example, when the slip frequency compensation amount is 1.5 Hz, the applied primary frequency ω ₁ also changes by ± 0.5 Hz when the compensation amount changes ± 0.5 Hz due to the pulsation of the torque calculation value described above. Therefore, when the set frequency is low such as 1.0 Hz, as shown in Equation 5 below, compared to the set frequency,
The amount of compensation becomes large.

[0013]

[Equation 5] 2.5 Hz (ω ₁ ) = 1.0 Hz (f ^* ) + 1.5 Hz (ω _Sl ) When this compensation amount changes ± 0.5 Hz, the applied primary frequency ω ₁
Fluctuates between 2 Hz and 3 Hz, so that the sensitivity of the fluctuation given to the control system becomes very high, causing an inconvenience that causes an unstable phenomenon such as uneven rotation of the induction motor 9. (However, the error of the torque calculation value is small because the output voltage becomes large at medium speed and high speed.) Therefore, the object of the present invention is to apply the applied frequency when switching from the slip frequency compensation control to the torque limit control. Is to suppress the torque calculation error that occurs due to the discontinuity of the torque and the operating condition of the induction motor.

[0014]

In order to achieve the above-mentioned object, a variable speed control device for an induction motor according to the present invention is an induction motor driven by an inverter for controlling a constant ratio of output AC voltage to frequency. A torque calculation circuit for calculating the torque, a slip frequency controller that inputs the calculated torque value and outputs a slip frequency compensation control signal until the induction motor reaches a torque limit value, and the calculated torque value is input. And a torque limit adjuster for outputting a torque limit control signal, and a frequency command value is obtained by operating a frequency set value set separately by the frequency compensation control signal or the torque limit control signal to determine the output frequency of the inverter. In the variable speed control device for an induction motor, which drives the induction motor at a desired rotation speed by controlling to match the frequency command value, Motivation an output signal of the slip frequency regulator at the time of switching to the torque limit control from the slip frequency compensation control reaches the torque limit value, shall be maintained after that time.

Alternatively, the output side of the torque calculation circuit is provided with a first variable time constant low pass filter capable of changing a time constant in accordance with the operating condition of the induction motor, and the induction motor reaches a torque limit value and slips. At the time of switching from the frequency compensation control to the torque limit control, the time constant of the first variable time constant low pass filter is set to a large value.

Alternatively, on the input side of the torque limit controller for inputting the calculated torque value and the input side of the slip frequency controller, a second variable time constant capable of individually changing the time constant corresponding to the operating condition of the induction motor. A low pass filter and a third variable time constant low pass filter are provided, and when the induction motor reaches a torque limit value and switches from slip frequency compensation control to torque limit control, the time constant of the second variable time constant low pass filter is increased. Shall be set to a value.

Alternatively, the slip frequency adjuster is provided with a dead zone calculation circuit for calculating a dead zone width corresponding to the operating condition of the induction motor. Alternatively, the first,
The second or third variable time constant low-pass filter changes the magnitude of its time constant in accordance with the operating conditions of the induction motor.

[0018]

According to the present invention, when the slip frequency compensation control is switched to the torque limit control, the torque calculation value for slip frequency compensation is not set to zero but the slip frequency compensation amount at that time is maintained. Alternatively, although the slip frequency compensation control is stopped, a low pass filter for inputting the torque calculation value is provided and the slip frequency compensation control is performed using the output value,
When the slip frequency compensation control is stopped, the time constant of the low-pass filter is made sufficiently long to prevent a sudden change in the slip frequency compensation amount at the time of stop.

When the induction motor operates at a low speed, the pulsation of the torque calculation value increases and the error of the torque calculation value increases, but at the medium speed and high speed, both the pulsation and the error decrease. Further, if the load factor of the induction motor is high, the output voltage of the PWM inverter will also be high, and the aforementioned pulsation and error will be reduced. Therefore, the performance is improved by changing the time constant of the low-pass filter, which has been constant in the past, in accordance with the operating conditions of the induction motor, that is, the load factor that can be determined by the applied primary frequency and the calculated torque value.

The higher the applied primary frequency is, the smaller the distortion of the output voltage due to the on-delay is. Therefore, the pulsation and the error generated in the torque calculation value are also reduced. Therefore, the dead band width of the slip frequency compensation control is reduced. Further, since the output voltage command value becomes large when the load factor is high, the torque calculation error becomes small, so the dead band width of the slip frequency compensation control is made small.

[0021]

1 is a circuit diagram showing a first embodiment of the present invention. In the first embodiment circuit, a torque calculation circuit 15 is used.
Is provided with a first first-order lag filter 21 as a first variable time constant low-pass filter, and a time constant switching circuit 24
The circuit configuration is such that the time constant of the first first-order lag filter 21 can be changed, which is different from the conventional circuit described in FIG. 9, but other than that, the conventional circuit described in FIG. 9 is used. Is the same as in. Therefore, the description of the same part is omitted.

In the first embodiment circuit, when the slip frequency compensation control is switched to the torque limit control, the time constant of the first first-order lag filter 21 is switched to a sufficiently long value via the time constant switching circuit 24. FIG. 2 is a partial circuit diagram showing a second embodiment of the present invention. In the first embodiment circuit described above, the torque calculation value τ ^# calculated by the torque calculation circuit 15 is given to the torque limit adjuster 17 and the slip compensation adjuster 18 via the first first-order lag filter 21. In the circuit of the second embodiment, the calculated torque value τ ^# to the torque limit adjuster 17 is given through the second first-order lag filter 22 as the second variable time constant low pass filter, but the torque to the slip compensation adjuster 18 is increased. The calculated value τ ^# is the third first-order lag filter 23 as the third variable time constant low-pass filter.
Given through. Here, the second first-order lag filter 22
Is attached to the time constant switching circuit 25, and the third first-order lag filter 23 is attached to the time constant switching circuit 26.
The time constant of each first-order lag filter 22 and 23 can be switched independently.

FIG. 3 is a flow chart showing the functional operation of the slip frequency compensation control. In this flowchart, the start sequence processing of slip frequency compensation control is performed by the processing 31, 32, and 33. Process 41 is an operation delay timer at the time of starting the slip frequency compensation, and when the slip frequency compensation control is not prohibited (decision 32), if the delay timer times up (decision 34), the calculated torque value τ ^# is used by process 43. The slip frequency compensation control is performed and the data is sent to the first-order lag filter (process 44). When the slip frequency compensation control is prohibited (decision 32), the torque calculation value τ ^{# is set} to zero (process 42) and the data is transmitted. Is sent to the first-order lag filter (process 44). As will be described later, dead band width calculation (process 45) and dead band calculation (process 4)
6) is performed in the slip compensation adjuster 18.

If the torque limit control is being performed (decision 35), the slip compensation adjuster 18 is bypassed in the present invention. FIG. 4 is a time chart showing the operation of the flow chart described above with reference to FIG. 3. FIG. 4 shows a change in the torque applied to the induction motor 9, FIG. 4 shows a change in the frequency first command value f ^* , and FIG. The change of the output signal of the limit adjuster 17, the change of the output signal of the slip compensation adjuster 18, the change of the input signal (frequency fourth command value f ^{4 *} ) to the V / f calculator 4 is shown in FIG. Each represents.

In the time chart of FIG. 4, the frequency first command value f ^* set by the frequency setter 1 is constant (see FIG.
See). The torque of the induction motor 9 increases in accordance with the frequency first command value f ^* and reaches the torque limit level τ _L at time t ₁ (see FIG. 4). Slip compensation controller 18
Output is also increased becomes zero at time point t ₁ from t ₀ start time point to the time point t ₁ (see FIG. 4). Since the torque limit control is performed from the time point t ₁ , the torque limit adjuster 17 starts its output (see FIG. 4). If the time constant of the first-order lag filter in the process 44 is significantly lengthened, the judgment 35 can be omitted.

Conventionally, the output of the slip compensation controller 18 is t ₁
Since it becomes zero at the time point, the frequency fourth command value f ^{4 *} input to the V / f calculator ⁴ is E → F → H → as shown in FIG.
The change was J. That is, when the slip frequency compensation control is switched to the torque limit control at time t ₁ , the frequency
There was a problem that the command value f ^{4 *} fell sharply. On the other hand, in the present invention, the output of the slip compensation adjuster 18 at the time of switching to the torque limit control is held at the same value by increasing the time constant of the third first-order lag filter 23, for example, so that V / f calculator frequency input to 4 fourth command value f ^{4 *,} as shown in FIG. 4, the frequency fourth command value f ^{4 *}
Changes from E → F → G to avoid a sudden drop in the frequency fourth command value f ^{4 *} .

FIG. 5 is a flow chart showing a third embodiment of the present invention, which shows the operation of the dead band width arithmetic circuit incorporated in the slip compensation controller 18. An appropriate dead zone is selected according to the magnitude of the frequency first command value f ^* that is the set frequency of the induction motor 9 and whether or not the load torque is the rated value. That is, depending on whether the set frequency is high speed, medium speed, or low speed, a dead zone suitable for each is selected. In either case, when the load factor is high, the pulsation and error of the torque calculation value become small. Therefore, the dead zone is not set. The dead zones are classified according to the set frequency instead of the applied frequency in order to suppress the fluctuation of the dead zone due to the slip frequency compensation.

FIG. 6 is a partial circuit diagram showing the fourth embodiment of the present invention, and shows the configuration of a circuit for calculating the dead band width. This dead band width calculation circuit is built in the slip compensation adjuster 18 as described above, and the selector 63 corresponds to the set frequency and the dead band data 64 at the time of high speed, the dead band data 65 at the time of medium speed, and the dead band at the time of low speed. Any one of the data 66 is selected. Further, the switching unit 62 operates depending on whether or not the calculated torque value τ ^# input to the dead band width calculator 61 via the third primary delay filter 23 reaches the rated value. The dead band data is input to the dead band width calculator 61. If the load factor is less than 100%, the dead band data at each speed obtained via the selector 63 is input to the dead band width calculator 61.

FIG. 7 is a partial circuit diagram showing a fifth embodiment of the present invention and shows a circuit for changing the time constant of the second variable time constant low pass filter. In this FIG.
The second first-order lag filter 22 as the second variable time constant low-pass filter inputs the torque calculation value τ ^# from the torque calculation circuit 15 and outputs the torque limit torque calculation value to the torque limit adjuster 17. In the time constant switching circuit 25,
A signal during acceleration operation, a signal during constant speed operation, and an applied frequency that indicate the operation status of the induction motor 9 are given, and in response to this, a time constant during acceleration operation, a time constant during constant speed operation, or during low speed operation. Any one of the time constants is selected, and the time constant of the second first-order lag filter 22 is set to the selected value.

Since there is a large pulsation and error in the calculated torque value during low speed operation, a sufficiently long time constant (for example, 0.5 seconds) is used to average this. The time constant during constant speed operation is set to a value longer than during acceleration operation. FIG. 8 is a partial circuit diagram showing a sixth embodiment of the present invention.
Variable time constant Shows a circuit that changes the time constant of the low-pass filter. In FIG. 8, the third first-order lag filter 23 as the third variable time constant low-pass filter inputs the torque calculation value τ ^# from the torque calculation circuit 15 to the slip compensation controller 18 and calculates the slip frequency compensation torque calculation value. Is output. The applied frequency of the induction motor 9 is given to the time constant switching circuit 26, and one of the time constant during high-speed operation, the time constant during medium-speed operation, or the time constant during low-speed operation is supplied corresponding to this frequency value. Any one is selected, and the time constant of the third first-order lag filter 23 is set to the selected value. At this time, the time constant during low speed operation is set long, and the time constant is shortened as the speed increases.

[0031]

When the induction motor is driven by the conventional V / f constant control inverter, when the slip frequency compensation control is switched to the torque limit control, there is a disadvantage that the applied frequency becomes discontinuous. According to this, it is possible to avoid the occurrence of discontinuity in the applied frequency due to the change of the time constant of the filter or the setting of an appropriate dead zone according to the operating condition of the induction motor. As a result, it is possible to obtain the effect that the stability during operation of the electric motor can be favorably maintained. In particular, stability can be improved at low speed operation.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a partial circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a flowchart showing a functional operation of slip frequency compensation control.

FIG. 4 is a time chart showing the operation of the flowchart described above in FIG.

FIG. 5 is a flowchart showing a third embodiment of the present invention.

FIG. 6 is a partial circuit diagram showing a fourth embodiment of the present invention.

FIG. 7 is a partial circuit diagram showing a fifth embodiment of the present invention.

FIG. 8 is a partial circuit diagram showing a sixth embodiment of the present invention.

FIG. 9 is a circuit diagram showing a conventional example of a control device that drives an induction motor at a variable speed with an inverter that controls a constant ratio of voltage and frequency.

FIG. 10 is a circuit diagram showing details of the torque limit control and slip frequency compensation control in the conventional circuit of FIG.

11 is a graph showing a state change when switching from slip frequency compensation control to torque limit control in the conventional circuit of FIG.

[Explanation of symbols]

1 Frequency setter 2 Acceleration / deceleration calculator 4 V / f calculator 5 Control calculation circuit 6 Voltage command value calculation circuit 7 PWM inverter 9 Induction motor 12 Three-phase / two-phase converter 13 Vector rotator 15 Torque calculation circuit 16 First-order lag Filter 17 Torque limit adjuster 18 Slip compensation adjuster 19 Torque limiting detector 21 First first-order lag filter as first variable time constant low-pass filter 22 Second first-order lag filter as second variable time constant low-pass filter 23 Third Third-order lag filter as variable time constant low pass filter 24-26 Time constant switching circuit 31-35 Judgment 41-48 Processing 51-53 Judgment 55-58 Processing 61 Dead band calculator 62 Switcher 63 Selector 64 High speed dead band data 65 Dead band data at medium speed 66 Dead band data at low speed 67 Load factor 100% Dead zone data 68 Inverter δ ^* Voltage phase command value f ^* Frequency 1st command value f ^** Frequency 2nd command value f ^{3 *} Frequency 3rd command value f ^{4 *} Frequency 4th command value τ ^# Torque calculation value V ^* Voltage command value

Claims (5)

[Claims] 1. A torque calculation circuit for calculating a torque of an induction motor driven by an inverter for controlling a ratio of an output AC voltage and a frequency to a constant value, and a torque calculation circuit for inputting the torque calculation value to limit the torque of the induction motor. A slip frequency adjuster that outputs a slip frequency compensation control signal until the value is reached, and a torque limit adjuster that inputs the torque calculation value and outputs a torque limit control signal are provided. By operating the frequency compensation control signal or the torque limit control signal to obtain a frequency command value, and by controlling the output frequency of the inverter to match the frequency command value,
In a variable speed control device for an induction motor that operates the induction motor at a desired rotation speed, the slip frequency adjuster outputs when the induction motor reaches a torque limit value and switches from slip frequency compensation control to torque limit control. A variable speed control device for an induction motor, which maintains the signal amount even after that time. 2. A torque calculation circuit for calculating the torque of an induction motor driven by an inverter for controlling the ratio of the output AC voltage to the frequency to be constant, and the induction motor limiting the torque by inputting the calculated torque value. A slip frequency adjuster that outputs a slip frequency compensation control signal until the value is reached, and a torque limit adjuster that inputs the torque calculation value and outputs a torque limit control signal are provided. By operating the frequency compensation control signal or the torque limit control signal to obtain a frequency command value, and by controlling the output frequency of the inverter to match the frequency command value,
In a variable speed control device for an induction motor that drives the induction motor at a desired rotation speed, a first variable time constant low pass device that can change a time constant corresponding to operating conditions of the induction motor at an output side of the torque calculation circuit. An induction motor comprising a filter, wherein the time constant of the first variable time constant low-pass filter is set to a large value when the induction motor reaches a torque limit value and switches from slip frequency compensation control to torque limit control. Variable speed controller for electric motor. 3. A torque calculation circuit for calculating a torque of an induction motor driven by an inverter for controlling a ratio of an output AC voltage and a frequency to be constant, and a torque calculation circuit for inputting the torque calculation value to limit the torque of the induction motor. A slip frequency adjuster that outputs a slip frequency compensation control signal until the value is reached, and a torque limit adjuster that inputs the torque calculation value and outputs a torque limit control signal are provided. By operating the frequency compensation control signal or the torque limit control signal to obtain a frequency command value, and by controlling the output frequency of the inverter to match the frequency command value,
In an induction motor variable speed control device for operating the induction motor at a desired rotation speed, the input side of the torque limit adjuster and the slip frequency adjuster for inputting the torque calculation value, respectively, to the operating conditions of the induction motor. A second variable time constant low-pass filter and a third variable time constant low-pass filter, each of which can change the time constant correspondingly, are provided, and the induction motor reaches a torque limit value and switches from slip frequency compensation control to torque limit control. Then, the variable speed control device for the induction motor, wherein the time constant of the second variable time constant low-pass filter is set to a large value. 4. The variable speed control device for an induction motor according to claim 1, wherein the slip frequency controller calculates a dead band width corresponding to an operating condition of the induction motor. A variable speed control device for an induction motor, comprising a dead zone arithmetic circuit. 5. The variable speed control device for an induction motor according to claim 2, wherein the first, second, or third variable time constant low-pass filter is an operating condition of the induction motor. A variable speed control device for an induction motor, wherein the magnitude of the time constant is changed in accordance with the above.