JP2003339199A - Speed sensorless vector control inverter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a speed sensor less vector control inverter having control characteristics improved such that stall does not occur even if the load torque increases during low speed operation due to the polarity in the regenerating direction. <P>SOLUTION: A speed reference is increased by adding a low speed reference correction signal fc at the time of regeneration load torque proportional to the amount of regeneration load torque to the speed reference fr according to a speed function. Since the output frequency reference for does not reach a lower limit even if the regeneration load torque increases when an induction motor 5 is operating at a low speed, mismatch between a speed fm estimated from a corrected output frequency reference fo and a slip frequency fs and the actual speed of the induction motor is eliminated. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed sensorless vector control inverter device, and more particularly to a speed sensorless vector control inverter device having improved control characteristics during regenerative load of an induction motor in a low speed region.

[0002]

2. Description of the Related Art Recently, a technique of vector-controlling an induction motor without using a speed sensor has been put into practical use. For example, Japanese Laid-Open Patent Publication No. 11-69896 discloses a conventional so-called speed sensorless vector control inverter device, and its configuration and operation are as follows.

An inverter device converts a direct current power supply into an alternating current output having an arbitrary frequency and voltage to drive an induction motor at a variable speed. For the control of the inverter device, vector control without using a speed sensor is adopted as follows.

That is, the two phase currents flowing in the induction motor are detected and converted into D and Q axes, and the D axis current and Q axis are detected.
Get the axis current. On the other hand, the speed control circuit compares the speed reference with the estimated speed and controls so that the difference becomes zero to obtain the torque reference. From this torque reference and the amount of magnetic flux of the induction motor, the current reference for the D and Q axes is obtained. This current reference is compared with each of the currents of the D and Q axes to obtain the voltage reference of each of the D and Q axes, and the coordinates of the voltage reference are converted back to the three-phase voltage reference, which is PWM-modulated. Obtaining the gate pulse of the inverter device. Further, the output frequency reference applied to the induction motor is obtained from the Q axis voltage reference, and the slip frequency calculated from the torque reference and the magnetic flux amount of the induction motor is subtracted from the value to obtain the estimated speed.

In the sensorless vector control inverter device having the above-described structure, the control can be separated into the D axis and the Q axis, that is, the exciting axis and the torque axis, and these can be controlled independently, and therefore, the control equivalent to that of the DC motor is possible. It is known that the characteristics can be obtained.

However, satisfactory characteristics have not always been obtained at low speeds. This is because the lower the speed of the induction motor estimated by the calculation is, the larger the error from the actual speed becomes. The cause of the error is the constant error of the induction motor, its frequency characteristic, or the difference between the output voltage command and the actual output voltage.

In order to solve this problem, in the low speed range, a limit is set so that the above-mentioned output frequency reference does not fall below a predetermined value, so that the starting torque of the induction motor can be maintained even if there is some calculation error. It is possible to improve so that it can be obtained.

[0008]

As described above, consider a case where the speed sensorless vector control inverter device having improved starting characteristics is applied to, for example, control of a traveling induction motor of a container crane. When the container crane receives a tailwind during low-speed operation and the load torque increases in polarity in the regenerative direction, the output frequency reference is limited by the lower limiter, so the estimated speed determined by the corrected output frequency reference and slip frequency is actually Therefore, the voltage phase of the induction motor and the phase of the output voltage of the inverter do not match, resulting in a problem that torque cannot be sufficiently generated and the motor stalls.

This is because the estimated speed of the induction motor during the regenerative operation is obtained by adding the slip frequency increased due to the large regenerative torque to the reference of the corrected output frequency when the lower limiter is applied, so that the actual induction This is because it is estimated to be considerably higher than the motor speed. When the engine stalls, the induction motor may be accelerated by the regenerative load torque, which may lead to runaway.

According to the present invention, even when the load torque increases in the regenerative direction during low-speed operation, the estimated speed is adjusted to the actual speed of the induction motor to improve the control characteristics so as not to stall. An object is to provide a control inverter device.

[0011]

In order to achieve the above object, a speed sensorless vector control inverter device of the present invention comprises a converter for converting a commercial power source into a direct current, and an output of this converter into an alternating current power having an arbitrary frequency and voltage. An inverter for conversion is compared with an estimated speed of the induction motor obtained by calculation and a speed reference to obtain a torque reference, and a D and Q axis current reference based on the torque reference and the magnetic flux amount of the induction motor. Compute and compare the D and Q axis current references with the output currents of the inverters that have undergone D and Q coordinate conversion,
A D- and Q-axis voltage reference is obtained, and a three-phase voltage reference is obtained based on the D- and Q-axis voltage reference and the output frequency reference of the inverter, and the output is used for PWM control of the inverter. And a frequency calculation unit configured to calculate the output frequency reference from the Q-axis voltage reference and the impedance of the induction motor. The frequency calculation unit has a lower limit to the output frequency reference,
A means for obtaining a corrected output frequency reference is provided, and the speed controller calculates a slip frequency from the Q-axis current reference and the magnetic flux amount of the induction motor, and the induction motor is calculated from the slip frequency and the corrected output frequency reference. Means for obtaining an estimated speed and means for adding a speed reference correction signal proportional to the torque reference with a function of speed to the speed reference when the vehicle is operating at low speed and the regenerative load torque is equal to or greater than a predetermined value And

In order to achieve the above object, a speed sensorless vector control inverter device of the present invention comprises a converter for converting a commercial power supply into direct current, an inverter for converting this output into alternating current power of an arbitrary frequency and voltage, and an arithmetic operation. The estimated speed of the induction motor and the speed reference obtained in step 1 are compared to obtain a torque reference, and the D and Q axis current references are calculated from the torque reference and the magnetic flux amount of the induction motor. The Q-axis current reference and the D- and Q-coordinate-converted output currents of the inverters are respectively compared to obtain a D- and Q-axis voltage reference, and the D- and Q-axis voltage reference and the output frequency reference of the inverter are compared. A three-phase voltage reference is obtained on the basis of the output, and the output is obtained from the current control section that PWM-controls the inverter by this output, the Q-axis voltage reference, and the impedance of the induction motor. A frequency calculation unit adapted to calculate a wave number reference, wherein the frequency calculation unit is provided with a means for obtaining a corrected output frequency reference by attaching a lower limit to the output frequency reference, and the speed control unit is provided with: A means for calculating a slip frequency from the Q-axis current reference and the magnetic flux amount of the induction motor, and obtaining an estimated speed of the induction motor from the slip frequency and the corrected output frequency reference, and a low speed operation and a regenerative load torque having a predetermined value. In the above case, means for bypassing the means for obtaining the corrected output frequency reference is provided.

According to the present invention, even when the induction motor has a large regenerative torque even during low speed operation in which the lower limit of the frequency reference is applied, the frequency reference is corrected or the lower limit of the lower limiter is set. Since the bypass operation is performed, it is possible to provide the speed sensorless vector control inverter device in which the estimated speed does not become inconsistent with the actual speed of the induction motor and the control characteristic is improved so as not to stall.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <First Embodiment> A first embodiment of a speed sensorless vector control inverter device according to the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a block diagram of a speed sensorless vector control inverter device of the present invention.

The AC voltage of the commercial power supply is converted into a DC voltage by the converter 1. The inverter 2 receives the DC voltage and converts it into an AC voltage of arbitrary frequency and voltage,
The induction motor 3 is driven at a variable speed. The above is the main circuit configuration of the speed sensorless vector control device according to the present invention.

First, a schematic configuration of the control circuit of the present invention will be described. The control circuit includes a speed controller 4, a current controller 5, and a frequency calculator 8. The speed control unit 4 generates current references Idr and Iqr for the D-axis and the Q-axis based on the speed reference fr and the estimated speed fm of the induction motor 3 calculated.

The current controller 5 compares these signals with the D-axis current Id and the Q-axis current Iq converted from the current detector 6 into the D-axis and the Q-axis, respectively, and outputs the voltage reference Vr. PW
The M converter 7 PWM-modulates this signal and outputs the gate pulse Gp of the inverter 2 to control the inverter 2.

On the other hand, the frequency calculator 8 calculates the output frequency reference fo of the inverter 2 from the Q-axis voltage reference Vqr generated by the current controller 5.

Next, the detailed structure of the speed controller 4 will be described.

The speed reference correction signal fc is added to the speed reference fr by the adder 48, and the resulting corrected speed reference fc is obtained.
The r is compared with the estimated speed fm which is the output of the estimated speed calculator 44. The estimated speed fm is obtained by subtracting the slip frequency fs from the output frequency reference fo obtained from the frequency calculator 5.

The speed control calculator 41 calculates the torque so that the speed deviation obtained as the difference between the corrected speed reference fcr and the estimated speed fm is zero, and the torque reference Tr is obtained.
This torque reference Tr is divided by the magnetic flux amount 43A of the induction motor using the divider 42A to obtain the Q-axis current reference Iqr.
Ask for. Further, the magnetic flux amount 43A of the induction motor is converted into the D-axis current reference Idr by the magnetic flux saturation function 43B. On the other hand, the slip frequency fs is obtained by dividing the Q-axis current reference Iqr by the magnetic flux amount 43A of the induction motor using the divider 42B. The speed reference correction signal fc is determined as follows.

First, the estimated speed fm is converted into an absolute value by the absolute value converter 45. The low speed function generator 46 receives this signal and outputs a function according to the absolute value of the speed. FIG. 2 shows an example of output characteristics of the low-speed function generator 46. In this example, the low speed function generator 46 is set to output a convex shape between the speeds of 1% and 15%.

The torque multiplier 47 at the time of regenerative load torque inputs the output of the low-speed function generator 46 and the torque reference Tr, and multiplies the output of the low-speed function generator 46 at the time of the regenerative load torque by the torque reference Tr to regenerate at low speed. The speed reference correction signal fc is output when the load torque is applied. The adder 48 adds the value of the speed reference fr and the value of the speed reference correction signal fc, and the corrected speed reference fcr obtained as a result is input to the speed control calculator 41.

The detailed structure of the current controller 5 is as follows.

An arbitrary two phases of the induction motor 3, for example, a U-phase current and a W-phase current are detected by the current detector 6 and input to the current coordinate converter 51. The current coordinate converter 51 converts the U-phase current and the W-phase current into the Q-axis currents Iq and D based on the phase signal φ obtained by integrating the output frequency reference fo with the integrator 55.
Convert to shaft current Id.

The Q-axis current control calculator 52 compares the Q-axis current reference Iqr which is the output of the speed control unit 4 with the Q-axis current Iq, and sets the Q-axis voltage for making the difference between them zero. Generate the reference Vqr. In addition, the D-axis current control calculator 53
Compares the D-axis current reference Idr, which is the output of the speed control unit 4, with the D-axis current Id, and generates the D-axis voltage reference Vdr for making the difference between the two zero.

The voltage coordinate converter 54 converts the Q-axis voltage reference Vqr and the D-axis voltage reference Vdr into a three-phase voltage reference Vr based on the phase signal φ from the integrator 55. This 3
The phase voltage reference Vr is given to the PWM controller 7, where the gate pulse Gp given to the switching element of each arm of the inverter 2 is generated.

The detailed structure of the frequency calculator 8 is as follows.

The Q-axis induced voltage calculator 81 calculates the Q-axis induced voltage Eq from the Q-axis voltage reference Vqr generated by the Q-axis current control calculator 52 of the current controller 5 and the impedance 82 of the induction motor, Output to the frequency converter 83. The Q-axis induced voltage Eq, which is the output of the Q-axis induced voltage calculator 81, is converted by the frequency converter 83 into the output frequency reference for. The output frequency reference for is the frequency reference lower limit limiter 8 provided to secure torque at startup.
4, the output frequency reference for is converted into a corrected output frequency reference fo having a lower limit value, and is input to the estimated speed calculator 44 in the speed control unit 4 described above.

The estimated speed fm from the estimated speed calculator 44 input to the speed control calculator 41 is regenerated by the estimated speed calculator 44 by subtracting the slip frequency fs from the corrected output frequency reference fo during power running. At this time, the slip frequency fs is added to the corrected output frequency reference fo.

In the speed sensorless vector control inverter device configured as described above, when the induction motor 3 is operated at a low speed and the regenerative load torque amount increases, the absolute value converter 45 and the low speed function generator. 46, a speed reference correction signal fc at a low speed and at the time of regenerative load torque proportional to the regenerative load torque amount is added to the speed reference fr via a speed multiplier 46 and a torque multiplier 47 at the time of regenerative load torque, Increase speed reference.

As a result, even when the induction motor 3 is operated at a low speed and the regenerative load torque becomes large, the output frequency reference for falls from the lower limit set by the frequency reference lower limiter 84. Disappeared
The estimated speed fm obtained by the estimated speed calculator 44 from the corrected output frequency reference fo and the slip frequency fs does not become inconsistent with the actual speed of the induction motor 3. Therefore,
Since the phase difference between the voltage phase of the induction motor 3 and the output voltage of the inverter 2 can be prevented and a sufficient torque can be generated, there is no stall.

In addition, at low speed, even if the speed reference is increased by adding the speed reference correction signal fc at a low speed and at the time of regenerative load torque proportional to the regenerative load torque reference to the speed reference fr and increasing the speed reference, Since the speed reference fr settles to a predetermined value when the torque amount decreases, the increase of the speed reference fr is only temporary and does not pose a problem.

<Second Embodiment> FIG. 3 shows a second embodiment of the present invention.
FIG. 3 is a block diagram showing an example of a speed sensorless vector control inverter device according to the embodiment of FIG. With respect to each part of the second embodiment, the same parts as those of the speed sensorless vector control inverter device according to the first embodiment of FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.
The second embodiment differs from the first embodiment in that the low-speed function generator 46, the regenerative load torque-time torque multiplier 47, and the adder 48 of the speed controller 4 are different from the configuration of FIG. Instead of this, a low speed and regenerative load torque detector 49 is used.

The estimated speed fm is input to the absolute value converter 45 and converted into an absolute value of the estimated speed. The low speed and regenerative load torque detector 49 detects the absolute value of the estimated speed output from the absolute value converter 45 and the torque reference Tr from the speed control calculator 41.
Is input, and the signal Bp for low speed and regenerative load torque is output.

The frequency reference lower limit limiter 84 is configured to be bypassed by the low speed and regenerative load torque signal Bp.

In the speed sensorless vector control inverter device constructed as described above, when the induction motor 3 is operated at a low speed, if the load torque is in the regenerative direction and exceeds a predetermined value, a low speed and regenerative load torque is generated. Detector 49
Outputs a low-speed and regenerative load torque signal Bp, shorts the input and output of the frequency reference lower limit limiter 84, and bypasses the frequency reference lower limit limiter 84. That is, the corrected output frequency reference fo becomes the output frequency reference for itself. As a result, when the induction motor 3 is operated at a low speed, the output frequency reference fo does not fall on the lower limit provided by the frequency reference lower limiter 84 even when the load torque increases with the polarity in the regenerative direction. Thus, the estimated speed fm obtained from the output frequency reference fo and the slip frequency fs does not become inconsistent with the actual speed of the induction motor 3. Therefore, a phase shift between the voltage phase of the induction motor 3 and the output voltage of the inverter 2 can be prevented, and sufficient torque can be generated, so that stall does not occur.

[0038]

According to the present invention, when the induction motor is operated at a low speed, the control characteristic is improved so that the induction motor does not stall even when the load torque becomes large due to the polarity in the regenerative direction. It is possible to provide the speed sensorless vector control inverter device.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a speed sensorless vector control inverter device according to the present invention.

2 is an input / output diagram showing an example of the operation of a low-speed function generator in the speed sensorless vector control inverter device of FIG.

FIG. 3 is a block diagram showing a second embodiment of a speed sensorless vector control inverter device according to the present invention.

[Explanation of symbols]

1 converter 2 inverter 3 induction motor 4 Speed control section 5 Current control section 6 Current detector 7 PWM controller 8 Frequency calculator 41 Speed control calculator 42A, 42B divider 43A Induction motor magnetic flux 43B Flux saturation function 44 Estimated speed calculator 45 Absolute value converter 46 Low-speed function generator Torque multiplier for 47 regenerative load torque 48 adder 49 Low speed and regenerative load torque detector 51 Current coordinate converter 52 Q-axis current control calculator 53 D-axis current control calculator 54 Voltage coordinate converter 55 integrator 81 Induction motor impedance 82 Q-axis induced voltage calculator 83 Frequency converter 84 Frequency reference lower limiter

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Claims (2)

[Claims] 1. A converter for converting a commercial power source into direct current, an inverter for converting this output into alternating current power of an arbitrary frequency and voltage, an estimated speed of an induction motor obtained by calculation and a speed reference, and a torque reference. From the speed control unit adapted to obtain D, from the torque reference and the magnetic flux amount of the induction motor,
The Q-axis current reference is calculated, and the D and Q-axis current references are calculated.
The output currents of the inverters that have undergone the Q coordinate conversion are respectively compared to obtain D and Q axis voltage references, and a three-phase voltage reference is obtained based on the D and Q axis voltage references and the inverter output frequency references. The inverter outputs P
The current control unit is configured to perform WM control, and the frequency calculation unit is configured to calculate the output frequency reference from the Q-axis voltage reference and the impedance of the induction motor. The frequency calculation unit includes the output frequency reference. Is provided with a lower limit to obtain a corrected output frequency reference, and the speed control unit calculates a slip frequency from the Q-axis current reference and the magnetic flux amount of the induction motor, and the slip frequency and the corrected output frequency. Means for obtaining an estimated speed of the induction motor from the reference, and means for adding a speed reference correction signal proportional to the torque reference as a function of the speed to the speed reference when the operation speed is low and the regenerative load torque is a predetermined value or more. A vector control inverter device without a speed sensor, characterized in that: 2. A converter for converting a commercial power source into direct current, an inverter for converting this output into alternating current power of an arbitrary frequency and voltage, an estimated speed of an induction motor obtained by calculation and a speed reference, and a torque reference. From the speed control unit adapted to obtain D, from the torque reference and the magnetic flux amount of the induction motor,
The Q-axis current reference is calculated, and the D and Q-axis current references are calculated.
The output currents of the inverters that have undergone the Q coordinate conversion are respectively compared to obtain D and Q axis voltage references, and a three-phase voltage reference is obtained based on the D and Q axis voltage references and the inverter output frequency references. The inverter outputs P
The current control unit is configured to perform WM control, and the frequency calculation unit is configured to calculate the output frequency reference from the Q-axis voltage reference and the impedance of the induction motor. The frequency calculation unit includes the output frequency reference. Is provided with a lower limit to obtain a corrected output frequency reference, and the speed control unit calculates a slip frequency from the Q-axis current reference and the magnetic flux amount of the induction motor, and the slip frequency and the corrected output frequency. A speed sensorless device is provided which includes means for obtaining an estimated speed of the induction motor from the reference and means for bypassing the means for obtaining the corrected output frequency reference when the regenerative load torque is a predetermined value or more at low speed operation. Vector control inverter device.