JP4006630B2 - Control method of induction motor driven by inverter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling an induction motor driven by an inverter, and more particularly, to a more accurate derivation method of the polarity of a load during which the induction motor is operating, that is, a driving load or a braking load.
[0002]
[Prior art]
In recent years, as a control method for variable speed control of an induction motor driven by an inverter, so-called control using a current vector has become mainstream.
[0003]
As a conventional control method of an induction motor driven by this type of inverter, the phase of the detected value derived in the vector control calculation with respect to the detected value of the output current of the inverter is Depending on whether the phase of the output voltage command value is in phase or opposite phase, for example, when the detected value is in phase with the output voltage command value, it is “+ polarity”, and when it is in reverse phase, it is “−polarity”. Thus, variable speed control of the induction motor has been performed.
[0004]
[Problems to be solved by the invention]
When variable speed controlled by a method using the current vector of the induction motor that will be driven by the inverter, it is performed to the slip compensation of the induction motor. At this time, depending on the polarity of the load that the induction motor is operating, that is, whether it is a driving load or a braking load, the calculation of either adding or subtracting the slip frequency to the primary frequency command value commanded to the motor is performed. Done. Further, in order to prevent a stalled state of the induction motor driven by the inverter, depending on whether the load of the induction motor is a drive load or a brake load, that is, when the load is a drive load, the primary frequency of the motor is decreased, and when the load is a brake load Increasing the primary frequency is performed. Conventionally, the polarity of the load, that is, whether it is a driving load or a braking load, the phase of the detected value derived during the vector control calculation with respect to the detected value of the output current of the inverter is the output voltage command to the inverter. It was determined based on whether the value was in phase or in phase.
[0005]
However, the loss due to the resistance component of the primary winding of the induction motor driven by the inverter exists in the same polarity as the driving load regardless of whether the load of the motor is a driving load or a braking load. The method of deriving the polarity of the load causes an error, and in the slip compensation, the slip may increase depending on the braking load, and the stall state at the braking load may not be prevented. There was a risk of disturbing.
[0006]
An object of the present invention is to provide a method for controlling an induction motor driven by an inverter that solves the above-described problems.
[0007]
[Means for Solving the Problems]
The first invention is a control method for induction motor driven by the inverter, the induction motor the induction motor from the magnitude relationship between the active power values fed from the inverter no-load loss value at no-load operation Derives the polarity of the load during operation, and performs variable speed control of the induction motor based on the derived polarity of the load.
[0008]
According to a second aspect of the present invention, in the method for controlling an induction motor driven by the inverter according to the first aspect of the invention, the no-load loss value is corrected based on a no-load loss characteristic with respect to a primary frequency obtained from the inverter. And
[0009]
According to a third aspect of the present invention, there is provided a method for controlling an induction motor driven by an inverter according to the second aspect of the present invention, wherein the inverter is configured to have an AC voltage having a constant voltage to frequency ratio for a plurality of predetermined different frequencies. Is output, and the induction motor is operated with no load with these AC voltages, and the no-load loss value characteristic corresponding to the frequency at this time is obtained.
[0010]
According to a fourth aspect of the invention, there is provided a method for controlling an induction motor driven by an inverter according to the first or second aspect of the invention, wherein the no-load loss value uses an active power value measured by the induction motor during no-load operation. Features.
[0011]
According to a fifth aspect of the present invention, there is provided a method for controlling an induction motor driven by an inverter according to the first aspect of the invention, wherein the no-load loss value is determined by the output current of the inverter and the stator winding of the motor when the induction motor is in no-load operation. The power value calculated from the resistance value of the wire is used.
[0012]
According to a sixth aspect of the present invention, in the method for controlling an induction motor driven by the inverter according to the first to fifth aspects of the present invention, the active power value corresponds to an output voltage command value, an output current to the inverter, and the output voltage command value. The active power value derived from the polarity of the phase of the output current is used.
[0013]
7th invention is the control method of the induction motor driven by the inverter of the said 1st-5th invention, The said active power value is the phase of the said output current with respect to the output voltage and output current of the said inverter, and the said output voltage The active power value derived from the polarity is used.
[0014]
According to the present invention, the induction motor driven by the inverter is determined from the no-load loss value during no-load operation and the active power value fed from the inverter as to the polarity of the load during operation of the induction motor, that is, the driving load. It is possible to improve the control performance by deriving whether the load is a braking load and performing variable speed control of the induction motor based on the derived more accurate load polarity.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Prior to the description of the embodiment of the present invention, the no-load loss during the no-load operation of the induction motor driven by the inverter will be described.
[0016]
First, the general formula indicating the loss (P) of the induction motor is expressed by the following formula 1.
[0017]
[Expression 1]
P = P _Cu (I ² ) + P _ih (ω ₁ ) + P _ie (ω ₁ ² ) + P _M (ω ₁ )
Here, P _{Cu is} equivalent to the copper loss and is proportional to the square of the current (I). P _ih : Hysteresis loss of iron loss, which is proportional to the primary frequency (ω ₁ ). P _ie : It corresponds to eddy current loss of iron loss, and is proportional to the square of the primary frequency (ω ₁ ). P _M : Mechanical loss, which is proportional to the rotational speed and substantially proportional to the primary frequency (ω ₁ ). Therefore, in the following description, it is assumed to be proportional to the primary frequency (ω ₁ ).
[0018]
Each loss on the right side of Equation 1 is different for each induction motor, and each has a magnitude relationship. Therefore, it is necessary to know the loss (P) in order to derive the polarity of the load that the induction motor is operating.
[0019]
Further, the no-load loss (P ₀ ) of the induction motor driven by the inverter is calculated by the following equation 1 based on the output voltage, output current, and output frequency information of the inverter when the induction motor is operated with no load. Corresponding measurement is possible.
[0020]
FIG. 1 is a circuit configuration diagram of an induction motor drive device according to a first embodiment of the present invention. Reference numeral 1 denotes an induction motor , and 2 denotes a drive device of the induction motor 1.
[0021]
This driving device 2 is composed of a semiconductor power conversion circuit, performs PWM calculation on a voltage command from a vector control circuit 23 described later, and turns on / off each switching element forming the semiconductor power conversion circuit based on the calculation result. an inverter 21 for generating the desired output voltage, the output current from the inverter 21, i.e., a current detector 22 for detecting the primary current of the induction motor 1, the torque current component of the induction motor 1 detected value of the current detector 22 And the excitation current component are converted into coordinates by a known technique, and the induction motor 1 is enabled by known vector control based on the component-converted component current and the primary frequency command value to the induction motor 1 commanded from the outside. A vector control circuit 23 for generating the above-described voltage command for shift control, and multiplication of the voltage command and the detected value of the current detector 22 And its power factor, a power calculator 24 for determining the instantaneous active power value induction motor 1 from the polarity of the torque current component is supplied from the inverter 21 during operation (with polarity), the induction motor 1, for example, A storage circuit 25 that stores a measured value of no-load power measured during no-load operation at approximately the rated rotational speed, that is, the no-load loss (P ₀ ), and a magnitude relationship between the instantaneous active power value and the measured no-load power value And a comparator 26 for judging the above.
[0022]
Here, as the polarity of the instantaneous active power value, for example, when the torque current component is a driving current component of the induction motor 1, the polarity is “+”, and when the torque current component is a braking current component, the polarity is “−”. The no-load power measurement value is represented by “+” polarity. Therefore, the comparator 26 determines the magnitude relationship including the polarity of the both. That is, when the instantaneous active power value ≧ the no-load power measurement value, the “+” polarity is output to the vector control circuit 23 as the load polarity, and when the instantaneous active power value <the no-load power measurement value, the load polarity is “−”. The polarity is output to the vector control circuit 23.
[0023]
When the induction motor 1 is controlled at a variable speed by the inverter 21 and the vector control circuit 23, slip compensation of the induction motor is performed. At this time, the load polarity is determined as the “+” polarity, that is, the driving load. The slip frequency calculated in the vector control circuit 23 is added to the primary frequency command value commanded to the induction motor, and the voltage command corresponding to the added frequency is generated. When it is determined that the load polarity is “−” polarity, that is, a braking load, the slip frequency calculated in the vector control circuit 23 is subtracted from the primary frequency command value commanded to the induction motor. In addition, by generating the voltage command corresponding to the added frequency, the control accuracy of the rotational speed of the induction motor can be improved. Can.
[0024]
Further, when preventing the induction motor 1 driven by the inverter 21 from falling into a stalled state, it depends on whether the load of the induction motor 1 is a driving load (“+” polarity) or a braking load (“−” polarity). When the driving load is applied, the vector control circuit 23 is caused to reduce the primary frequency of the induction motor 1 and when the braking load is applied, the primary frequency is increased.
[0025]
FIG. 2 is a circuit configuration diagram of an induction motor driving apparatus showing a second embodiment of the present invention. Components having the same functions as those of the embodiment circuit of FIG. 1 are denoted by the same reference numerals.
[0026]
That is, the driving device 3 of the induction motor 1 shown in FIG. 2, the inverter 21, a current detector 22, a vector control circuit 23, the power calculator 24, in addition to the comparator 26, in place of the memory circuit 25, the induction As will be described later, the electric motor 1 includes a storage circuit 31 that stores the no-load power calculated during no-load operation as a no-load power calculation value.
[0027]
As the no-load power calculated value, the resistance value of the primary winding of a characteristic value of the induction motor as the induction motor 1, the induction motor, for example, substantially the primary current during no-load operation at rated speed (inverter 21 output current).
[0028]
That is, in the circuit configuration shown in FIG. 2, when the V / f constant control is performed on the induction motor, the magnetic flux of the induction motor is substantially constant, and therefore the no-load current is also constant. Therefore, the no-load loss (P ₀ ) derived from Equation 1 is a control method that focuses on the fact that the first term on the right side is dominant.
[0029]
FIG. 3 is a circuit configuration diagram of an induction motor driving apparatus showing a third embodiment of the present invention. Components having the same functions as those of the embodiment circuit of FIG. 1 are denoted by the same reference numerals.
[0030]
That is, the drive device 4 of the induction motor 1 shown in FIG. 3 includes a vector control circuit 23a instead of the vector control circuit 23, in addition to the inverter 21, the current detector 22, the power calculator 24, and the comparator 26. In place of the memory circuit 25, the induction motor 1 has a measured no-load power during no-load operation, as described later. And a storage circuit 41 for storing the load loss (P).
[0031]
[Expression 2]
P = P _Cu (I ² ) + P _ih (ω ₁ ) + P _ie (ω ₁ ² ) + P _M (ω ₁ )
= Α · I ² + β · ω ₁ + γ · ω ₁ ²
As apparent from the above equation 2, the induction motor 1 is operated without load at three different frequencies (for example, the rated frequency of the induction motor 1, the rated frequency × 0.5, and the rated frequency × 0.1). The coefficients α, β, γ are obtained from the current (I), frequency (ω ₁ ), and active power from the inverter 21. In addition, since eddy current loss (P _ie ) of iron loss is generally negligible, the third term on the right side is omitted at this time, and therefore two different frequencies (for example, the rated frequency of the induction motor 1, the rated frequency × 0.5) No load operation is required.
[0032]
That is, the comparator 26 determines the magnitude relationship including the polarity between the instantaneous active power value obtained by the power calculator 24 and the no-load power measurement value from the storage circuit 41. At this time, the storage circuit 41 The characteristics of the no-load loss (P ₀ ) with respect to the primary frequency from the inverter are obtained in advance by no-load operation at the different frequencies, and the no-load loss (P ₀ ) is obtained from the primary frequency and the characteristics. For example, the no-load loss (P ₀ ) is obtained from the coefficient (α, β, γ or α, β), the no-load current, and the primary frequency. However, since the no-load current is substantially constant if the magnetic flux of the induction motor 1 is constant, the average value is used for the current (I) when obtaining the coefficients α, β, and γ. In this way, the primary frequency from the vector control circuit 23a complements the no-load loss (P ₀ ) for the primary frequency with respect to the value of P obtained by the above equation ( ₂ ), thereby providing more accurate no-load power. It can be measured.
[0033]
In the description of the above embodiment, the instantaneous active power value calculated by the power calculator 24 is a product of the voltage command from the vector control circuit 23 to the inverter 21 and the detected value of the current detector 22 and its power factor. However, it may be obtained from the multiplication value of the detected value of the output voltage of the inverter 21 and the detected value of the current detector 22 and its power factor. Further, the instantaneous active power value can also be obtained from a value obtained by multiplying a voltage command value obtained by an internal calculation of the vector control circuit 23 and a current component in phase or opposite phase to the voltage command value, that is, a torque current component.
[0034]
【The invention's effect】
According to the present invention, based on the no-load loss value when the induction motor driven by the inverter is in a no-load operation, the polarity of the load that the induction motor is operating is more accurately derived, and the derived load polarity Based on the above, the control performance can be improved by performing variable speed control of the induction motor . Furthermore, since the above-described measurement of the no-load loss value can be performed by the inverter itself, it can also be derived by the measurement function added inside the above-described driving device without preparing a new measuring instrument. .
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram showing a first embodiment of the invention. FIG. 2 is a circuit configuration diagram showing a second embodiment of the invention. FIG. 3 is a circuit configuration showing a third embodiment of the invention. Figure [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Induction motor , 2, 3, 4 ... Drive apparatus, 21 ... Inverter, 22 ... Current detector, 23, 23a ... Vector control circuit, 24 ... Power calculator, 25 ... Memory circuit, 26 ... Comparator, 31, 41: Memory circuit.

Claims (7)

In the control method of the induction motor driven by the inverter,
From the magnitude relationship between the no-load loss value when the induction motor is in no-load operation and the active power value fed from the inverter, the polarity of the load during operation of the induction motor is derived,
A control method for an induction motor driven by an inverter, wherein the induction motor is subjected to variable speed control based on the derived polarity of the load. In the control method of the induction motor driven by the inverter according to claim 1,
A method for controlling an induction motor driven by an inverter, wherein the no-load loss value is corrected based on a no-load loss characteristic with respect to a primary frequency obtained from an inverter in advance . In the control method of the induction motor driven by the inverter according to claim 2,
From the inverter, an AC voltage is output so that the ratio of voltage to frequency is constant for a plurality of predetermined different frequencies, and the induction motor is operated with no load at these AC voltages. A control method for an induction motor driven by an inverter, wherein a corresponding no-load loss value characteristic is obtained. In the control method of the induction motor driven by the inverter according to claim 1 or 2,
The no-load loss value, the control method for an induction motor the induction motor is driven by an inverter, which comprises using the active power value measured during no-load operation. In the control method of the induction motor driven by the inverter according to claim 1,
The no-load loss value is driven by an inverter using an electric power value calculated from an output current of the inverter and a resistance value of a stator winding of the electric motor when the induction motor is in an unloaded operation. Induction motor control method. In the control method of the induction motor driven by the inverter according to any one of claims 1 to 5,
The active power value is driven by an inverter using an active power value derived from an output voltage command value and output current to the inverter and a phase polarity of the output current with respect to the output voltage command value. Induction motor control method. In the control method of the induction motor driven by the inverter according to any one of claims 1 to 5,
Control of an induction motor driven by an inverter, wherein the active power value uses an active power value derived from an output voltage and output current of the inverter and a polarity of the phase of the output current with respect to the output voltage Method.

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