JPS63257497A - Operation controlling method and device for ac motor - Google Patents

Abstract

PURPOSE:To retain the energy efficiency of a system to be high, by setting switching pulse fed to an inverter main-circuit to be always optimum one. CONSTITUTION:An inverter main-circuit 22 is provided with six switching elements 26, which are controlled by switching pulse from a PWM controlling circuit 28. By a motor controlling circuit 10, based on signal from an input power arithmetic circuit 34 and an output power arithmetic circuit 40, a specified arithmetic is performed, and the carrier frequency of the switching pulse is controlled so that energy efficiency in a system may be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for controlling the operation of an AC motor, and particularly to improving energy efficiency in a drive system for an AC motor.

[Prior Art] Conventionally, a system that combines an inverter main circuit has been used as a drive system for an AC motor. .

In such a system, switching elements in the inverter main circuit are sequentially turned on and off, that is, switched, based on a current or voltage command from a controller to supply a predetermined drive power to an AC motor.

As a control method for such switching, P
There is a WM (pulse width variable: A) control system.

In this PWM control method, while keeping constant the carrier frequency of the switching pulse that normally controls switching in the inverter main circuit, the width of the pulse, that is, the time of energization 181, is varied to control the rotation of the AC motor.

In addition, in this PWM control method, in order to generally supply current or voltage to the AC motor according to the command, the command is compared with a triangular wave, and a switching pulse with a predetermined switching pulse width is generated. Controls on/off of switching elements.

Therefore, an example of this switching pulse generation circuit will be explained based on FIGS. 3 to 5.

The motor control circuit 10 supplies the adder 12 with a clock pulse having a constant frequency F. The adder 12 repeats the operation of sequentially adding 1 from 0 each time the clock pulse F is supplied, and returning to 0 when the addition result reaches, for example, FF.

The adder 12 then supplies the addition result to the triangular wave pattern map 14. The triangular wave pattern map 14 is
A triangular wave pattern as shown in FIG. 4 is stored inside. Then, the input numerical value of the addition result is made to correspond to the address as it is or after a predetermined conversion, and the corresponding amplitude data is output.

This data is input to 16 D/A converters.

The D/A converter 16 generates a triangular wave from the amplitude data of each input clock pulse and outputs it.

The PWM pattern generator 18 is supplied with a triangular wave from the D/A converter 16 and a current or voltage command from the motor control circuit 10, as shown as input signals in FIG. This current or voltage command corresponds to a three-phase alternating current waveform shifted by 120 degrees. By processing this command and the triangular wave, U and V as shown in FIG.

Three-phase switching pulses of W are formed.

This switching pulse is supplied to the inverter main circuit,
By performing the switching, a predetermined drive power is supplied to the AC motor.

[Conventional Problems] In such conventional AC motor operation control, the efficiency of the AC motor drive system could not be maintained sufficiently high for the following reasons.

Generally, energy loss in an AC motor drive system changes depending on the carrier frequency of the switching pulse. This relationship is shown in FIG.

In this way, the energy loss in the AC motor is smaller as the carrier frequency is higher, and the energy loss in the switching element is larger as the carrier frequency is smaller. Therefore, the energy loss in the entire system is
There is a highest carrier frequency at which this becomes a minimum. and,
By setting the carrier frequency to this optimal carrier frequency, the energy efficiency of this system can be maximized.

However, this optimum carrier frequency changes depending on the rotational speed and load of the AC motor. In conventional systems, the carrier frequency is kept constant, making it impossible to maintain high energy efficiency of the system.

This invention constantly monitors the carrier frequency and
It is an object of the present invention to provide an operation control method and device for an AC motor that can control this so as to always optimize the energy efficiency of an AC motor drive system.

[Related technology] Note that changing the carrier frequency of switching pulses supplied to the inverter main circuit is disclosed in Japanese Patent Laid-Open No. 55-10.
It is shown in the 0087 publication.

JP-A-55-100087 discloses a technique for pulse width modulation control of the rotation speed of a non-commutated motor, in which the carrier frequency of the switching pulse is increased when the rotation speed of the motor is low. .

The effect of this is that when the rotation speed is small,
The purpose is to prevent excessive current from flowing through the switching elements.

In this way, JP-A-55-100087 discloses a technique of changing the frequency of switching pulses, but the feature of this invention is to constantly monitor the energy efficiency and carrier frequency of the system, and improve the energy efficiency. No technique has been shown to change the carrier frequency so that it is always kept high.

[Means for Solving the Problems] The AC motor operation control method according to the first aspect of the present invention is characterized in that the inverter main circuit that supplies predetermined driving power to the AC motor can be changed in carrier frequency and pulse width. A method for controlling the operation of an AC motor using modulated switching pulses, which includes the steps of: detecting the input power to the inverter main circuit; and detecting the output power of the AC motor that is driven by receiving power from the inverter main circuit. a step of calculating energy efficiency from the input power and output power; a step of calculating the amount of change in the energy efficiency; a step of detecting the amount of change in the carrier frequency of the switching pulse; The method is characterized by comprising a step of changing the carrier frequency so as to increase the energy efficiency by comparing the positive and negative of the amount of change in efficiency and the positive and negative of the amount of change in the carrier frequency.

The AC electric drive control device according to the second aspect of the present invention includes an inverter main circuit that includes a plurality of switching elements and supplies drive power to the AC motor, and a predetermined pulse width and a predetermined pulse width for sequentially turning on and off the switching elements. a pulse width modulation control circuit that supplies switching pulses having a carrier frequency to the inverter main circuit; an input power detection circuit that detects input power to the inverter main circuit; and a rotation speed sensor that detects the rotation speed of the AC motor. a torque sensor that detects the torque of the AC motor; and an output power detection circuit that detects the output power of the AC motor based on the rotation speed obtained by the rotation speed sensor and the torque obtained from the torque. - A circuit that detects the amount of change in the switching pulse, calculates the energy efficiency from the above human power power and the above output power, compares the amount of change in this energy efficiency with the amount of change in the carrier frequency, and responds to the result. and a motor control circuit that controls the carrier frequency of the switching pulse in the bipedal pulse width modulation control A1 circuit so that the energy efficiency increases. In this method of controlling the operation of an AC motor, input power input to an inverter main circuit and output power of the AC motor are detected. Then, the energy efficiency of this system is determined from the ratio of the two, and then the amount of change in this energy efficiency is determined.

On the other hand, the carrier frequency is monitored and the amount of change in this carrier frequency is also detected. Then, by comparing the amount of change in energy efficiency and the carrier frequency, the direction of change in carrier frequency that increases energy efficiency is determined,
Change carrier frequency. By repeating this change and comparison, the carrier frequency is always optimized and the energy efficiency of the system is kept high.

In the operation control device for an AC motor, which is the second aspect of the present invention, power is supplied to and driven the AC motor by sequentially turning on and off switching elements of an inverter main circuit.

Here, the input power to the inverter main circuit is detected by the input power detection circuit. Further, the rotation speed of the AC motor is detected by a rotation speed sensor, the torque is detected by a torque sensor, and the output power of the AC motor is detected by an output power detection circuit from the detected values.

And these input power and output power are the motor I
II Input to g9 circuit. In the motor control circuit, energy efficiency is determined by comparing human power and output power, and the amount of change in this energy efficiency is also determined. Also,
The carrier frequency of the switching pulses supplied to the inverter main circuit is monitored, and the amount of change in this carrier frequency is also determined.

Then, by comparing the amount of change in energy efficiency and the amount of change in carrier frequency, the carrier frequency is changed in a direction that increases energy efficiency. By repeating this process, the energy efficiency of the system is kept high at all times.

[Example] An example of the present invention will be described based on FIG. 1 and FIG. 2.

FIG. 1 is a block diagram showing the overall configuration of an AC motor drive system of the present invention.

AC motor 20 is supplied with power for driving from an inverter main circuit 22 . Electric power is supplied to this inverter main circuit 22 from a DC power supply 24, and the inverter main circuit 22 converts this into AC. The inverter main circuit 22 has six switching elements 2'6, and input terminals 26a of the switching elements 26 are supplied with switching pulses from the PWM control circuit 28, respectively. Then, by sequentially turning on and off the switching elements 26, the power from the DC power supply 24 is converted to AC.

Here, the voltage supplied to the inverter main circuit 22 is detected by a voltmeter 30, and the current supplied to the inverter main circuit 22 is detected by an ammeter 32.

These detection results are then manually input to the input power calculation circuit 34. This human power an circuit 34 calculates input power by multiplying the detected voltage and current. The calculated human power is supplied to the motor control circuit 10.

Furthermore, a rotation sensor 36 and a torque sensor 38 are attached to the AC motor 20 to detect the rotation speed and torque, respectively. The rotation speed and torque detected in this way are inputted to the output power calculation circuit 40, where they are multiplied.
The output power of the AC motor is calculated. This output power is also input to the motor control circuit 10.

The motor control circuit 36 performs predetermined calculations based on the manually input power and output power, and controls the carrier frequency of the switching pulse so that the energy efficiency in the system increases.

Here, the input power calculation circuit 34 and the output power calculation circuit 40
A specific example of control in the motor control circuit 36 will be explained based on FIG. 2.

First, input terminal I and input voltage V to inverter main circuit 22 are input to input power calculation circuit 34, and rotation speed ω and torque T of AC motor 20 are input to output power calculation circuit 40 (data manually).

The input power calculation circuit 34 calculates the input power Pi by multiplying the human power current 1 and the input voltage V (input calculation).

The Pi-V/engineering output power calculation circuit 40 calculates the output power Po by multiplying the rotational speed ω and the torque T (output calculation).

Po-ω conflict T The motor control circuit 10 calculates the energy efficiency η of the system by dividing the input output power Po by the input power Pi. Also, the current energy efficiency η
The amount of change Δη in the energy efficiency is determined from the difference between the energy efficiency ηn−1 at the time of the previous calculation and the energy efficiency ηn−1 (energy efficiency calculation).

η-P o / P i Δη-η. -ηn-1 Next, in the present invention, the carrier frequency of the switching pulse is changed so that this energy efficiency is maintained high.

Here, the same switching pulse generation circuit as shown in FIG. 3 is used. The carrier frequency of the switching pulse is the frequency of the triangular wave here. Then, in order to change the frequency of the triangular wave, the frequency F of the clock pulse input to the adder 12 is changed.

In other words, as the frequency of the clock pulse increases, the reading speed of the triangular wave address increases, and the frequency of the output triangular wave also increases in proportion to the speed.

Therefore, in this embodiment, the frequency of the clock pulse is controlled, and the carrier frequency is indirectly controlled.

The current frequency F of the clock pulse is compared with the frequency Fn-1 used in the previous calculation, and the change amount ΔF is calculated (clock pulse change amount calculation).

ΔF−F −Fo.

Next, it is determined whether the amount of change in energy efficiency Δη is positive or negative (Δη>0?).

If the amount of change in energy Δη is positive, the energy efficiency of this system has increased, and the direction in which the clock pulse has been changed is correct. Therefore, the frequency of the clock pulse is changed by a predetermined amount in the same direction.

That is, when Δη>0, the frequency F of the next clock pulse is changed as follows.

n+1 If ΔF>0, F −F + ΔF n+1　　n If ΔF≦0, F -F - to ΔF n+1　　n shall be.

Furthermore, if the amount of change in energy efficiency Δη is negative, either the direction of the change in the clock pulse was wrong or the amount was too large, so the frequency of the clock pulse is changed in the opposite direction.

That is, when Δη≦0, the frequency Fn+1 of the next clock pulse is changed as follows.

If ΔF≧0, F −F − to ΔF n+1　　n If ΔF<0, F - F + - ΔF H+l　　n shall be.

Here, k is a coefficient for determining the magnitude when changing the frequency of the clock pulse. Although not shown in FIG. 2, it is preferable to make this coefficient k variable.

For example, regarding energy efficiency η, store a predetermined high efficiency value η, compare this with η obtained by a x , and if this difference is large, adopt a value of 1 or more as the value of k, When this difference is small, it is preferable to adopt a value of 1 or less. If this difference is less than a predetermined small value, 0 is output as a coefficient, the clock pulse frequency is not changed, and the minimum change in the clock pulse frequency change point in the predetermined direction is performed. Δ the amount
F.

l n You can also keep it as .

Next, in order to prevent destruction of the switching element 26 of the inverter main circuit 22, upper and lower limits are set for the carrier frequency. In this example, an upper limit value F 1 and a lower limit value F are provided for the frequency of the clock pulse corresponding to this carrier frequency to prevent the HL LL frequency of the clock pulse from changing any further.

In other words, the frequency Fn+ of the next clock pulse and F
%F is compared, F is in this range I HL
If it is outside the LL n+1 range, set the clock pulse frequency F to the nearest upper limit value or lower limit value (FLn+1 <F <F).

L n+1 HL If F <F <F, then set F to L
L n+1 HL n+1 output.

If F<F, output F.

n+1 LL LL If F>F, output F.

n+1 HL HL In this way, the next F is output (n+1), and the process returns to the next data input and repeats this (Fn+1 output).

The output clock pulse of frequency F 2 is inputted to the n+1 PWM control circuit 28 . This PWM control circuit 28 has the configuration shown in FIG. 3 as described above, and a clock pulse of frequency Fn+1 is input to this adder 12.

This changes the frequency of the triangular wave, that is, the carrier frequency.

In this way, the carrier frequency is always changed to optimize the energy efficiency of the system, so the energy efficiency of the system can be kept high.

Note that the upper limit of the energy efficiency η of the system is roughly known, so this η is compared with a predetermined high efficiency value, and if it is within the predetermined range, the above calculation is omitted and the previous state is changed. It may also be retained.

Furthermore, the difference between the value of this predetermined high efficiency energy efficiency and the value of the current energy efficiency η may be taken into consideration in the control. For example, if this difference is small, the magnitude of the above-mentioned coefficient may be set to a relatively small range, and if this difference in energy efficiency is large, the magnitude of the coefficient may be increased.

Furthermore, the temperature of the AC motor and the switching element may be monitored and used as information for controlling the carrier frequency of the switching pulse.

In other words, since heat generation is related to energy loss, it is preferable to change the carrier frequency in a direction that reduces energy loss when overheating occurs. Furthermore, in the case of heating, the above-mentioned coefficient k may be increased to increase the amount of change in carrier frequency.

[Effects of the Invention] As described above, according to the AC motor operation control method and device of the present invention, the switching pulses supplied to the inverter main circuit can be always optimized, thereby increasing the energy efficiency of the system. Can be retained. Furthermore, good energy efficiency means that there is less energy loss, that is, less heat generation, which also makes it possible to prevent overheating of the AC motor and switching elements.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the overall configuration of an AC motor drive system to which an embodiment of the present invention is applied, Fig. 2 is a flow sheet diagram explaining the operation of the embodiment, and Fig. 3 is a PWM control A block diagram showing an example of the circuit, Fig. 4 is a waveform diagram showing an example of a triangular wave, and Fig. 5 is a PW
FIG. 6, a waveform diagram showing the signals of the M control circuit, is a characteristic diagram showing the relationship between the carrier frequency and the energy loss of the system. 10...Motor control circuit 20...AC motor 22...Inverter main circuit 24...DC power supply 26...Switching element 28...PWM control circuit 34...Input power calculation circuit 40... - Output power calculation circuit.

Claims (2)

[Claims] (1) In an operation control method for an AC motor in which an inverter main circuit that supplies a predetermined drive power to an AC motor is controlled by a switching pulse whose carrier frequency is changeable and whose pulse width is modulated, a step of detecting input power; a step of detecting output power of an AC motor driven by receiving power from the inverter main circuit; a step of calculating energy efficiency from the input power and output power; The energy efficiency is calculated by calculating the amount of change in efficiency, detecting the amount of change in the carrier frequency of the switching pulse, and comparing the positive and negative of the amount of change in the energy efficiency and the positive and negative of the amount of change in the carrier frequency. A method for controlling the operation of an AC motor, comprising: changing the carrier frequency so that the carrier frequency increases. (2) An inverter main circuit that has a plurality of switching elements and supplies drive power to the AC motor, and a switching pulse having a predetermined pulse width and a predetermined carrier frequency that sequentially turns on and off the switching elements to the inverter main circuit. a pulse width modulation control circuit to supply; an input power detection circuit that detects input power to the inverter main circuit; a rotation speed sensor that detects the rotation speed of the AC motor; and a torque sensor that detects the torque of the AC motor. and an output power detection circuit that detects the output power of the AC motor based on the rotation speed obtained by the rotation speed sensor and the torque obtained by the torque, and a circuit that detects the amount of change in the switching pulse. The energy efficiency is determined from the input power and the output power, the amount of change in this energy efficiency is compared with the amount of change in the carrier frequency, and the pulse width modulation control circuit is configured to increase the energy efficiency according to the result. An operation control device for an AC motor, comprising: a motor control circuit that controls the carrier frequency of the switching pulse;