JPH07236294A - Inverter apparatus - Google Patents

Abstract

PURPOSE:To perform the sensorless detection of the rotational speed of an induction motor utilizing the higher harmonic component of the groove of a rotor in excellent accuracy. CONSTITUTION:An inverter main circuit 4 undergoes switching operation through a driving circuit 10 based on the PWM signal from a comparator 27. An induction motor 5 is driven by the output of the circuit 4. The carrier frequency of the PWM signal (the output frequency of a rectangular-wave generator 28) is set at the value higher than the frequency of the higher harmonic wave of the rotor groove of the induction motor 5. A slip-frequency detecting means 17 has an adder 19, which removes the fundamental frequency component and the tertially higher harmonic component from the input voltage of each phase of the induction motor 5, and a filter 20, which attenuates the tertially higher harmonic component of the higher harmonic waves of the rotor grooves and the carrier frequency component, and extracts only the slip frequency component through these parts. The signal, which is extracted in this way, is converted into the frequency component signal FSLIP with an F/V converter 21, and the converted signal is provided for the speed feedback control of the induction motor 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for driving an induction motor at a variable speed, and more particularly to an inverter device for detecting the rotation speed of the induction motor by utilizing rotor groove harmonics.

[0002]

2. Description of the Related Art FIG. 3 shows a circuit configuration example of a conventional inverter device (current source inverter). In FIG. 3, the converter circuit 1 includes an inverter main circuit 4 through a smoothing reactor 3 that rectifies a DC output obtained by rectifying the output of a commercial three-phase AC power supply 2 while controlling the phase by a switching element such as a thyristor, GTO, or IGBT. To give to. The inverter main circuit 4 basically has a configuration in which a semiconductor switching element such as an IGBT is connected in a three-phase bridge and a flywheel diode is connected in an antiparallel state with each switching element. The AC power is switched and converted into AC power, and the converted output drives the three-phase squirrel-cage induction motor 5.

The speed command setting device 6 for commanding the speed of the induction motor 5 is composed of, for example, a variable resistor, and generates a DC voltage signal corresponding to the speed of the induction motor 5.
This voltage signal is converted in the ramp function generating circuit 7 into a speed reference signal SREF consisting of a voltage signal that linearly increases or decreases according to a predetermined change time constant. The ramp function generating circuit 7 is provided to prevent a situation in which an overcurrent flows through the induction motor 5 due to a sudden change in the command speed.

The speed feedback circuit 8 receives a difference signal between the speed reference signal SREF and a speed feedback signal SFB, which will be described later, and outputs a frequency reference signal FREF corrected for the slip frequency of the induction motor 5 to the speed of the induction motor 5. Is output as a command signal. The signal generation circuit 9 generates the switching control signal SSC based on the frequency reference signal FREF, and the drive circuit 10 uses the signal obtained by amplifying the switching control signal SSC as the switching element in the inverter main circuit 4. Is switched, and an AC voltage is generated from the inverter main circuit 4. In addition, between the drive circuit 10 and the inverter main circuit 4,
It is electrically insulated by using a photo coupler.

The frequency reference signal FREF from the speed feedback circuit 8 is also inputted to the V / f ratio control circuit 11, and this V / f ratio control circuit 11 is
It outputs a voltage reference signal VREF having a predetermined ratio relationship with the input frequency reference signal FREF.

The voltage feedback circuit 12 receives the difference signal between the voltage reference signal VREF and the voltage detection signal VFB from the voltage detection circuit 13 which detects the output voltage of the inverter main circuit 4, and the voltage reference signal VREF An error signal is calculated according to the difference between the voltage command value indicated by the signal VREF and the actual output voltage value of the inverter main circuit 4 indicated by the voltage detection signal VFB, and the error signal is calculated as a current reference signal for the converter circuit 1. It is given to the current control circuit 14 as IREF.

The current detection circuit 15 converts the input current to the converter circuit 1 by a current transformer 15 or the like.
It is detected by R and 15T, and a current detection signal IFB corresponding to the detected value is given to the current control circuit 14.

The current control circuit 14 generates the phase control signal SFC by the calculation based on the difference between the current reference signal IREF and the current detection signal IFB input as described above. The phase control of the thyristor in the converter circuit 1 is performed by a signal obtained by amplifying the phase control signal SFC, and the converter circuit 1 outputs a direct current having a value corresponding to the current reference signal IREF. The drive circuit 16 and the converter circuit 1 are also electrically insulated by using a photo coupler or the like.

On the other hand, the slip frequency detecting means 17 is for detecting the slip frequency of the induction motor 5 by utilizing the rotor groove harmonics of the induction motor 5, and has the following structure. . The phase voltage detector 18 for detecting the input voltage of each phase of the induction motor 5 is provided in a state of being electrically insulated from the induction motor 5, and the detection voltage by this is added by the adder 19, Fundamental frequency component and 3
The second harmonic component is removed. In this case, the output of the phase voltage detector 18 includes, in addition to the slip frequency component contained in the required rotor groove harmonic, a component three times the fundamental frequency contained in the rotor groove harmonic component and the inverter. Main circuit 4
Since the carrier frequency component related to the switching operation of 1 is included, by outputting the output from the adder 19 through the filter circuit 20, only the slip frequency component corresponding to the rotation speed of the induction motor 5 is extracted.

The signal thus taken out is converted by the F / V converter 21 into a slip frequency component signal FSLIP having a voltage level corresponding to the frequency thereof. A difference signal from the frequency reference signal FREF from the speed feedback circuit 8 is given to the speed feedback circuit 8 as the speed feedback signal SFB.

The principle by which the slip frequency can be detected from the rotor groove harmonics will be described below. That is, in a general squirrel-cage induction motor, since the rotor core has a groove for accommodating the secondary conductor (squirrel-cage conductor), the magnetic flux in the air gap viewed from the stator side depends on the number of grooves. Receive modulation. The groove harmonic generated due to this corresponds to the component with the lowest order among the harmonic components included in the stator magnetomotive force, and the influence appears in the phase voltage.
When the induction motor 5 is driven by the current source inverter as shown in FIG. 3, the stator phase voltage includes the power supply voltage and the third harmonic voltage caused by the magnetic flux saturation and the above-described rotor groove high frequency component. Will be done.

Assuming that the stator input frequency of the induction motor 5 is f, the rotor frequency when converted to a 2-pole machine is fr, and the number of rotor grooves per pole pair is Nr, the rotor groove frequency component fh. Is given by the following equation (1).

## EQU1 ## fh = Nr × fr ± f (1) Here, in the configuration of FIG. 3, the adder 19 sums the input voltages of the respective phases of the induction motor 5 to obtain the fundamental frequency component and the third harmonic. Since the wave component is removed, Nr is required to be an integer value other than a multiple of 3 for the number of rotor grooves per one pole pair. Therefore, Nr is expressed by the following equation (2). Be done.

[Equation 2] Further, when the slip frequency is fs, the rotor frequency fr when converted to a two-pole machine is expressed by the following equation (3).

## EQU3 ## fr = f-fs (3) Substituting the equations (2) and (3) into the equation (1),

[Equation 4] And the groove harmonic component causes 3 of the fundamental wave.
The second harmonic component and the slip frequency component will be detected.

[0013]

As described above, according to the circuit configuration as shown in FIG. 3, only the slip frequency component is extracted by utilizing the rotor groove harmonics of the induction motor 5 and obtained based on this. The slip frequency component signal FSLIP is applied to the electric motor 5
Although it can be used for closed-loop speed control by a current source inverter as a signal indicating the rotation speed, the current source inverter device is inferior in current responsiveness. In order to deal with such a situation, the speed control utilizing the slip frequency component as described above may be applied to the current control type voltage source inverter.

However, when current control is performed in a voltage source inverter, the inverter main circuit is generally set to P
Since the WM control is performed, there is a situation in which many harmonic components corresponding to the carrier frequency component included in the PWM signal appear in the phase voltage of the induction motor.
Therefore, the S / N of the detection signal indicating the rotor groove harmonic component
As a result, the ratio deteriorates, and the detection signal itself indicating the rotor groove harmonic component is a relatively low level signal, resulting in a decrease in the accuracy of rotation speed detection of the induction motor. there were.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an inverter device capable of accurately performing sensorless detection of an induction motor rotation speed using a rotor groove harmonic component. Especially.

[0016]

In order to achieve the above object, the present invention provides an inverter main circuit for driving an induction motor by a variable voltage / variable frequency AC output obtained by switching a DC output based on a PWM signal. In an inverter device equipped with a slip frequency detecting means for extracting a slip frequency component contained in a rotor groove harmonic of the induction motor as a rotation speed signal based on a power supply terminal voltage of the induction motor, the carrier frequency of the PWM signal is set to Attenuating means for setting the value higher than the frequency of the rotor groove harmonics of the induction motor and attenuating the signal in the carrier frequency band is provided in the slip frequency detecting means (claim 2).

In this case, input voltage detecting means provided for detecting the power supply terminal voltage of the induction motor in the slip frequency detecting means and output voltage detecting means provided for feedback control of the output voltage of the inverter main circuit. It can also be used as a means (claim 2).

Further, the detection output of the slip frequency detecting means may be used for the rotational speed feedback control of the induction motor (claim 3).

Further, frequency transition means for changing the carrier frequency of the PWM signal according to the passage of time can be provided (claim 4).
It is also possible to adopt a configuration in which the carrier frequency of the PWM signal is changed using a random number.

[0020]

In the inverter device according to the first aspect, the induction motor is driven at a variable speed by the AC output of the variable voltage and the variable frequency from the inverter main circuit which performs the switching operation based on the PWM signal. In this case, the rotor groove harmonics indicated by the power supply terminal voltage of the induction motor include the carrier frequency component of the PWM signal in addition to the slip frequency component of the induction motor, which corresponds to the carrier frequency component. The signal in the frequency band will be attenuated by the attenuating means in the slip frequency detecting means. As a result, the S / N ratio of the detection signal indicating the slip frequency component is improved, and the detection accuracy of the slip frequency component and thus the sensorless detection accuracy of the rotation speed of the induction motor are improved.

In the inverter device according to the second aspect of the present invention, the input voltage detecting means required in the slip frequency detecting means and the output voltage detecting means provided for feedback controlling the output voltage of the inverter main circuit are used in common. The circuit configuration can be simplified.

In the inverter device according to the third aspect of the present invention, the output detected by the slip frequency detecting means is supplied to the rotational speed feedback control of the induction motor, so that the rotational speed control can be accurately performed by the sensorless system.

In the inverter device according to the fourth aspect, the carrier frequency of the PWM signal that determines the switching operation state of the inverter device is changed with the passage of time by the frequency transition means, so that it is included in the power supply terminal voltage of the induction motor. The ratio of the rotor groove harmonic components is increased. As a result, the level of the detection signal indicating the rotor groove harmonic component is increased, and the detection accuracy can be further improved.

In the inverter device of the fifth aspect, since the change of the carrier frequency as described above according to the passage of time is performed by using the random number, random distortion is generated in the PWM signal, and the rotor is rotated. The level of the detection signal indicating the groove harmonic component is further improved.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.
Will be described with reference to. However, in this embodiment,
Since the same components as those of the conventional configuration shown in FIG. 3 exist, the detailed description is omitted by assigning the same reference numerals to those components. That is, the inverter device according to the present embodiment is configured as a current control type voltage source inverter, and accordingly, the full-wave rectification circuit 22 and the smoothing capacitor 23 using diodes are
It is provided as an AC-DC converter instead of the converter circuit 1 and the smoothing reactor 3 in FIG.

The sine wave reference generating circuit 24 is adapted to receive the frequency reference signal FREF from the speed feedback circuit 8 and the current reference signal IREF from the voltage feedback circuit. The frequency and current reference indicated by the frequency reference signal FREF. A sine wave signal having an amplitude proportional to the signal IREF is created and given to the error calculator 25. The current detection circuit 26 detects the output current of the inverter main circuit 4 by the current detectors 26U and 26W including current transformers, and supplies the detection signal to the error calculator 25.

The error calculator 25 is a sine wave reference generation circuit 2
The sinusoidal voltage command signal VC is generated by comparison calculation of the sine wave signal from 4 and the actual current waveform from the current detection circuit 26 (current waveform supplied to the induction motor 5). The command signal VC is given to the comparator 27 as a control voltage signal.

This comparator 27 has the voltage command signal VC
And the triangular wave signal output as the carrier signal from the triangular wave generator 28 are compared to determine the sine wave P
By creating a WM signal and applying the PWM signal to the drive circuit 10, the switching element in the inverter main circuit 4 is switched by the pulse width modulation method.

In this case, in the triangular wave generator 28, the frequency of the output triangular wave signal, that is, the carrier frequency is set to a value higher than the frequency of the rotor groove harmonics of the induction motor 5. Accordingly, as the filter circuit 20 '(corresponding to the attenuating means in the present invention) in the slip frequency detecting means 17, a low-pass filter having a function of attenuating the carrier frequency band (a band pass filter that passes only the slip frequency band, etc.) But yes) is used.

A random number generator 29 (corresponding to the frequency transition means in the present invention) provided in association with the triangular wave generator 28 applies a random harmonic voltage such as white noise to the comparator 27. Therefore, the carrier frequency is changed with the passage of time based on a random number, whereby random distortion is generated in the PWM signal to increase the proportion of rotor groove harmonic components. .

Therefore, according to the above-described embodiment, the frequency of the carrier frequency component included in the power supply terminal voltage of the induction motor 5 given to the slip frequency detecting means 17 becomes higher than the rotor groove frequency. Therefore, the carrier frequency component and the third harmonic component of the rotor groove harmonic can be easily removed by the filter 20 '. Therefore, the detection signal (F / V converter 2) indicating the slip frequency component is
The S / N ratio of the slip frequency component signal FSLIP from 1 is improved, and the detection accuracy thereof, and thus the sensorless detection accuracy of the rotation speed of the induction motor, is improved, and the rotation of the induction motor 5 by the sensorless method is improved. The reliability of speed feedback control can be improved. Moreover, since it is configured as a current control type voltage type inverter, it is possible to improve the current responsiveness.

Further, since the carrier frequency by the triangular wave generating circuit 27 is changed with the passage of time, the ratio of the rotor groove harmonic component contained in the power supply terminal voltage of the induction motor 5 is increased and the rotor groove harmonic is increased. The level of the detection signal indicating the component increases, and moreover, since the change of the carrier frequency according to the passage of time as described above is performed using random numbers, random distortion is generated in the PWM signal. As a result, the level of the detection signal indicating the rotor groove harmonic component is further improved, and the detection accuracy can be further increased. Incidentally, FIG. 2 shows an example of the output characteristic of the slip frequency detecting means 17 with respect to the slip frequency.

In the above embodiment, since the harmonic component only appears near the carrier frequency, there is no possibility that the output torque of the induction motor 5 will be adversely affected. Further, in the circuit configuration shown in FIG. 1, the voltage detection circuit 13 corresponds to the output voltage detection means in the present invention, and the phase voltage detector 18 in the slip frequency detection means 17 detects the input voltage in the present invention. Although it corresponds to the means, it is also possible to have a configuration in which these are also used by one voltage detecting means, and when such a configuration is adopted, simplification of the circuit configuration can be realized.

Further, the voltage detection function of the voltage detection circuit 13 in the above embodiment is controlled by the voltage command value (the voltage reference signal VREF from the V / f ratio control circuit 11) in the speed feed back control system or the comparator 27. The PWM signal may be obtained by using a signal that has passed through a filter.
In particular, in this case, if a circuit for compensating for the switching delay time of the switching element in the inverter main circuit 4, so-called dead time, is provided, the detection accuracy will be improved.

Besides, the present invention is not limited to the above-mentioned embodiments, but the following modifications or expansions are possible. The present invention can be applied not only to the voltage type inverter device having the rotation speed feedback control function but also to the vector control type inverter, and the slip frequency detected by the slip frequency detecting means 17 is simply the induction motor 5.
It may be used only for displaying the actual speed of. The switching element that constitutes the inverter main circuit 4 is an IGBT.
Not limited to T, a power transistor (or a giant transistor), a power FET, a GTO, or the like may be used.
Although the PWM signal is formed by comparing the triangular wave signal and the sine wave control voltage signal, the PWM signal may be formed by combining the function data stored in advance in the ROM or the like.

[0036]

As is apparent from the above description, according to the invention described in claim 1, the slip frequency component contained in the rotor groove harmonics of the induction motor driven by the inverter main circuit is used as the rotation speed signal. In an inverter device having a slip frequency detecting means for extracting, the PWM signal carrier frequency used for the switching operation of the inverter main circuit is set to a value higher than the frequency of rotor groove harmonics of the induction motor, and the slip Since the attenuating means for attenuating the signal in the frequency band of the carrier frequency band is provided in the frequency detecting means, it is possible to accurately perform sensorless detection of the induction motor rotation speed using the rotor groove harmonic component. It has a beneficial effect.

According to the second aspect of the present invention, the slip frequency detecting means is provided with an input voltage detecting means provided to detect the power supply terminal voltage of the induction motor, and the output voltage of the inverter main circuit is feedback controlled. The output voltage detecting means provided for this purpose is also used, so that the circuit structure can be simplified.

According to the third aspect of the present invention, the detection output of the slip frequency detecting means is used for the rotational speed feedback control of the induction motor, so that the rotational speed control can be performed accurately by the sensorless system. Become.

According to the invention of claim 4, the PWM is
Since the carrier frequency of the signal is changed according to the passage of time, the level of the detection signal indicating the rotor groove harmonic component is increased, and the detection accuracy can be further improved.

According to the fifth aspect of the present invention, the carrier frequency of the PWM signal is changed by using a random number so that random distortion is generated in the PWM signal. It is possible to further improve the level of the detection signal indicating the wave component.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an example of output characteristics by a slip frequency detecting means.

FIG. 3 is a circuit configuration diagram showing a conventional example.

[Explanation of symbols]

In the drawing, 4 is an inverter main circuit, 5 is an induction motor, 10
Is a drive circuit, 13 is a voltage detection circuit (output voltage detection means), 17 is a slip frequency detection means, 18 is a phase voltage detector (input voltage detection means), 19 is an adder, and 20 'is a filter circuit (attenuation means). , 24 are sine wave reference generating circuits, 2
Reference numeral 7 is a comparator, 28 is a triangular wave generator, and 29 is a random number generator (frequency transition means).

Claims (5)

[Claims] 1. An inverter main circuit for driving an induction motor with an AC output of a variable voltage / variable frequency, which is a DC output switched based on a PWM signal, and a rotor of the induction motor based on a power supply terminal voltage of the induction motor. In an inverter device having a slip frequency detecting means for extracting a slip frequency component contained in a groove harmonic as a rotation speed signal, a carrier frequency of the PWM signal is set to a value higher than a frequency of a rotor groove harmonic of the induction motor. An inverter device, characterized in that an attenuating means for setting and attenuating a signal in the carrier frequency band is provided in the slip frequency detecting means. 2. An input voltage detecting means provided in the slip frequency detecting means for detecting a power supply terminal voltage of the induction motor, and an output voltage detecting means provided for feedback controlling the output voltage of the inverter main circuit. The inverter device according to claim 1, wherein the inverter device is also used. 3. The inverter device according to claim 1, wherein the detection output by the slip frequency detecting means is provided to the rotational speed feedback control of the induction motor. 4. The inverter device according to claim 1, further comprising frequency transition means for changing the carrier frequency of the PWM signal according to the passage of time. 5. The frequency transition means uses P using a random number.
The inverter device according to claim 4, wherein the inverter device is configured to change the carrier frequency of the WM signal.