JPH0851792A - Equipment and method for controlling pwm inverter - Google Patents

Abstract

PURPOSE:To provide an equipment and a method for controlling a PWM inverter which allows a noise generated from a motor to be easily heard even when the condition of a load of the motor or the installation environment of the motor changes. CONSTITUTION:A carrier wave variation width controlling circuit 13 sets a width of a carrier wave frequency according to the central frequency of a carrier wave from a command circuit 12 which commands the central frequency of the carrier wave. A carrier wave controlling circuit 14 changes the carrier wave frequency by the variation width in point of time. A signal having the central frequency commanded by the command circuit 12 of the central frequency of the carrier wave and a pattern signal from the carrier wave controlling circuit 14 are added by an adder 11 and then a PWM frequency command signal which changes cyclically around the central frequency is generated. A carrier wave generating circuit 4, receiving the PWM frequency command signal, makes a carrier wave which changes in point of time by the variation width set just around the central frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PWM inverter control device and a control method thereof, and more particularly to improvement of noise generated from an electric motor driven by the PWM inverter.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional example.
It is a block diagram which shows the structure of the PWM inverter shown by 79959 publication. 1 is a rectifying bridge, 2 is PWM
Inverter 3, carrier wave control circuit, 4 carrier wave generator circuit, 5 comparator, 6 output voltage pattern generator circuit, 7 AC motor, 8 gate circuit, 9 three-phase AC power supply, 10
Is a carrier center frequency setting circuit, and 11 is an adder.

Next, the operation will be described. The rectification bridge 1 converts alternating current from the three-phase alternating current power supply 9 into direct current and supplies it to the PWM inverter 2. The carrier wave control circuit 3 generates a pattern signal for periodically changing the frequency of the carrier wave, and the carrier wave center frequency setting circuit 10 generates a constant signal for setting the center frequency of the carrier wave. Then, these signals are added by the adder 11 to become a PWM frequency command that periodically changes around the center frequency, and the carrier wave generation circuit 4 creates a carrier wave whose frequency changes. The carrier wave and the modulated wave generated by the output voltage pattern generation circuit 6 become a PWM signal in the comparator 5, are amplified in the gate circuit 8, control the PWM inverter 2, and drive the AC electric motor 7.

Therefore, since the frequency of the harmonic component contained in the output voltage of the PWM inverter 2 is periodically changed, the harmonic of the same frequency is not continuously applied to the AC motor 7, This prevents certain noise from being emphasized.

[0005]

In the conventional PWM inverter control device and control method therefor, the carrier frequency is fixed to a single value, and the carrier frequency is changed periodically based on the center frequency. Is also fixed, so when the load condition of the motor or the installed environment changes, the frequency characteristics of the noise that requires the dispersion effect change, making it easier to hear the noise generated by the motor. The effect was not sufficiently obtained.

This generation is made in order to solve such a problem, and the control of the PWM inverter makes it easy to hear the noise generated from the electric motor even when the load condition of the electric motor or the installed environment changes. The purpose is to obtain a device and a control method thereof.

Further, by using the frequency analysis result of the noise of the electric motor, a specific large noise generated due to the electric motor and its load is avoided, and the noise generated from the electric motor is easily heard.
The purpose is to obtain a controller for a WM inverter.

[0008]

PWM according to the present invention
In the inverter control method, when the output frequency is constant, the frequency of the carrier that determines the frequency of the PWM signal is temporally changed before and after the center frequency of the carrier, and the change width of the frequency of the carrier is set to the center frequency. It changes according to.

Further, the control device for the PWM inverter has a command means for commanding the center frequency of the carrier wave for determining the frequency of the PWM signal when the output frequency is constant, and a change width of the frequency of the carrier wave according to the center frequency. And a carrier wave control unit that temporally changes the frequency of the carrier wave by the change width.

Further, noise measuring means for measuring the noise of the electric motor driven by the PWM inverter, noise analyzing means for identifying the maximum frequency component from the noise data, and a change range of the carrier frequency of the maximum frequency component Carrier change range setting means for setting the frequency larger than 1/2 of the frequency,
It is provided with.

[0011]

In the control method of the PWM inverter according to the present invention, when the output frequency is constant, the frequency of the carrier wave that determines the frequency of the PWM signal is temporally changed before and after the center frequency of the carrier wave and the frequency of the carrier wave is changed. By changing the variation width according to the center frequency, not only the center frequency of the carrier wave but also the temporal variation width of the carrier frequency is set according to the usage environment.

Further, in the control device of the PWM inverter,
Command means for commanding the center frequency of the carrier wave for determining the frequency of the PWM signal when the output frequency is constant; carrier change width control means for changing the change width of the frequency of the carrier wave according to the center frequency; The carrier control means for temporally changing the frequency of the carrier by the width sets not only the center frequency of the carrier but also the temporal change width of the carrier frequency according to the usage environment.

Further, noise measuring means for measuring the noise of the electric motor driven by the PWM inverter, noise analyzing means for identifying the maximum frequency component from the noise data, and the variation range of the carrier frequency are the frequency of the maximum frequency component. 1 / of
The carrier change range setting means set to be larger than 2 avoids specific noise generated due to the AC motor and its load according to the noise analysis result.

[0014]

【Example】

Example 1. 1 and 2 show an embodiment of the present invention. FIG. 1 is a block diagram showing the configuration of a PWM inverter.
FIG. 2 is a carrier frequency change width pattern diagram showing a pattern of the carrier frequency change width with respect to the carrier center frequency. In the figure, the same reference numerals indicate the same or corresponding parts, and 12 is a command circuit for commanding the center frequency of the carrier wave, 1
Reference numeral 3 is a carrier wave change width control circuit that sets the change width of the carrier wave frequency according to the center frequency of the carrier wave, 14 is a carrier wave control circuit that temporally changes the carrier wave frequency by a specified change width, and 21 is the noise of the AC motor 7. Sound level meter for measuring 2
Reference numeral 2 is a noise analysis circuit that frequency-analyzes noise data to identify a component caused by a carrier wave, and 23 is a carrier change range setting circuit that calculates a range in which the carrier wave should change from the noise analysis result and determines the center frequency of the carrier wave.

Next, the operation of changing the variation width of the carrier frequency according to the center frequency of the carrier will be described. Here, a description will be given mainly of the part of the operation different from the conventional example, that is, the operation until the signal supplied to the adder 11 is generated. The carrier wave change width control circuit 13 stores the change width pattern of the carrier wave frequency shown in FIG. The pattern of FIG. 2 is, for example, 1 KHz to 3 KH as a frequency region (fc1 to fc2) that is easily perceived by human ears.
z is set, and in this frequency range, the change width is set to the maximum, for example, k3 = 1.5 and k4 = 0.5 in order to increase the dispersion effect of the carrier frequency and make noise easier to hear. Further, in the low frequency region (fc1 or less), the carrier frequency dispersion effect is not so necessary, and the change width is small to reduce the possibility of resonance with the natural frequency of the load, for example, k1 = 1.1, k2 = 0. It is set to 9. Since the audible frequency range is exceeded even in the high frequency range (fc2 or higher), the dispersion effect of the carrier frequency is not necessary so much, and the change width is small, for example, k1 = 1.1,
The k2 is set to 0.9.

When the center frequency of the carrier wave is set by the command circuit 12, the carrier wave change width control circuit 13 determines the time change width of the carrier wave frequency according to the change width pattern shown in FIG. The carrier wave control circuit 14 changes the carrier wave frequency in a change width designated by the carrier wave change width control circuit 13, for example, periodically or using a random number table. Then, the signal related to the center frequency from the command circuit 12 and the pattern signal from the carrier control circuit 14 that temporally changes by the specified change width are the adder 1
1 and added there to create a PWM frequency command that varies periodically around the center frequency.

Here, it is assumed that the center frequency of the carrier wave is set lower than fc1 and the AC motor 7 is PWM-driven. In this case, the noise generated by the AC electric motor 7 is lower than the audible frequency range, so that the noise is not a problem for human ears. However, AC motor 7
When the installation state changes, the noise caused by the carrier wave may be annoying due to the resonance phenomenon. In order to avoid this phenomenon, it is necessary to increase the center frequency of the carrier wave sufficiently to deviate from the resonance phenomenon. For example,
If the center frequency of the carrier wave is set between fc1 and fc2, an increase in noise due to the resonance phenomenon can be avoided, but this time, a large carrier frequency dispersion effect is required due to the audible frequency range. That is, as shown in FIG. 2, a pattern having a change width larger than the change width when the center frequency of the carrier wave is lower than fc1 is required.

In the change width pattern of FIG. 2,
The range of change is set to a narrow range of 0.9 to 1.1 when the center frequency of the carrier wave is fc1 or lower and fc2 or higher, but in some cases, it is possible to set k1 = k2 = 1 and not change temporally.

As described above, since the carrier wave change width control circuit 13 changes the time change width of the carrier wave in accordance with the center frequency of the carrier wave, the audible frequency range (fc1 to fc1).
In fc2), the variation width can be widened to maximize the dispersion effect of the carrier frequency, and in the low frequency region (fc1 or less), the variation width is small, so resonance with the natural frequency of the load is possible. Since the change can be reduced and the change width is reduced even in the high frequency region (fc2 or more), useless control can be omitted.

Example 2. An embodiment in which the carrier frequency is controlled by using noise measurement data will be described with reference to FIG. First, when the center frequency of the carrier wave set by the parameters or the like is commanded from the command circuit 12, the PWM inverter 2 is controlled and the AC motor 7 is driven by the same operation as described in the first embodiment. At this time, the noise generated by the AC motor 7 due to the carrier frequency, for example, fc, generally has the most dominant frequency component of twice fc. Now, let us consider a case where this frequency component resonates with the AC electric motor 7 and the load driven by the AC electric motor 7, and becomes a large noise above a set level. When the noise data from the sound level meter 21 is sent to the noise analysis circuit 22, the noise analysis circuit 22 identifies the frequency component of this largest noise, for example, 2fc.
The carrier change range setting circuit 23 uses the information of the change width pattern of the carrier frequency of FIG. 2 which is known in advance for the 2 fc data, and the change range of the carrier frequency that changes with time indicates the frequency fc. The center frequency of the carrier is determined so as not to include it.

When the center frequency of the carrier wave determined by the carrier wave change range setting circuit 23 is, for example, fc0 and the change width is, for example, ± dfc0, the time change range of the carrier wave frequency is (fc0-dfc0) and (fc0 + dfc).
It will be between 0). Generally, the resonance frequency due to the AC motor 7 and the load driven by the AC motor 7 is low, and therefore the lower limit (fc0-dfc0) of the carrier frequency is set to be larger than 1/2 of the frequency component 2fc of the loudest noise. .

As described above, the noise analysis circuit 22 includes the sound level meter 21.
Frequency analysis is performed on the noise data from and the frequency component of the largest noise above a certain set level is identified. The carrier change range setting circuit 23 determines that the change range of the carrier frequency over time is 1/2 of the largest frequency component of noise.
Since the center frequency is determined so as to be larger, it is possible to automatically avoid generation of large noise that is amplified due to resonance caused by the AC motor 7 or a load that drives the AC motor 7.

In this embodiment, the carrier change range setting circuit 23 is based on the analysis data from the noise analysis circuit 22.
Shows an example in which the center frequency for avoiding a noise larger than the designated level is determined and is fed back to the command circuit 12 to automatically avoid generation of a large noise. However, instead of feeding back the signal of the carrier change range setting circuit 23 to the command circuit 12, a person may change the command value of the command circuit 12 by looking at the signal of the carrier change range setting circuit 23.

[0024]

Since the present invention is constructed as described above, it has the following effects.

When the output frequency is constant, the frequency of the carrier wave that determines the frequency of the PWM signal is temporally changed before and after the center frequency of the carrier wave, and the change width of the frequency of the carrier wave is changed according to the center frequency. Therefore, not only the center frequency of the carrier wave, but also the temporal change width of the carrier wave frequency can be set according to the usage environment, and the effect of increasing the dispersion effect of the noise frequency distribution and making it easier to hear the noise generated by the motor .

Further, when the output frequency is constant, command means for instructing the center frequency of the carrier wave for determining the frequency of the PWM signal, and carrier wave change width control for changing the change width of the carrier wave frequency according to the center frequency. And a carrier wave control unit that temporally changes the frequency of the carrier wave by the change width, so that not only the center frequency of the carrier wave but also the time change width of the carrier frequency is adjusted according to the usage environment. This can be set, and the effect of dispersing the frequency distribution of noise is enhanced, and the noise generated from the electric motor can be easily heard.

Furthermore, noise measuring means for measuring the noise of the electric motor driven by the PWM inverter, noise analyzing means for identifying the maximum frequency component from the noise data, and the variation range of the carrier frequency are the frequency of the maximum frequency component. 1 / of
If a carrier change range setting means for setting the value larger than 2 is provided, specific noise generated due to the AC motor and its load can be avoided by the noise analysis result, and the frequency distribution of the noise can be avoided. It has the effect of enhancing the dispersion effect of, and making it easier to hear the noise generated from the electric motor.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a PWM inverter according to first and second embodiments of the present invention.

FIG. 2 is a variation pattern diagram of a carrier frequency according to the first and second embodiments of the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional PWM inverter.

[Explanation of symbols]

2 PWM inverter, 4 carrier wave generation circuit, 6 output voltage pattern generation circuit, 7 AC electric motor, 12 carrier wave center frequency command circuit, 13 carrier wave change width control circuit, 14 carrier wave control circuit, 21 sound level meter, 22 noise analysis circuit, 23 Carrier change range setting circuit.

Claims (3)

[Claims] 1. A method of controlling a PWM inverter, comprising:
When the output frequency of the PWM inverter is constant, the frequency of the carrier wave that determines the frequency of the PWM signal is temporally changed before and after the center frequency of the carrier wave, and the change width of the frequency of the carrier wave is changed according to the center frequency. A method for controlling a PWM inverter, characterized in that 2. In a control device for a PWM inverter,
Command means for instructing the center frequency of the carrier wave for determining the frequency of the PWM signal when the output frequency of the PWM inverter is constant, and carrier change width control means for changing the change width of the frequency of the carrier wave according to the center frequency, And a carrier wave control unit that temporally changes the frequency of the carrier wave by the change width. 3. A noise measuring means for measuring noise of an electric motor driven by a PWM inverter, a noise analyzing means for specifying a maximum frequency component from noise data of the noise measuring means, and a change range of a carrier frequency as the main range. 3. The control device for the PWM inverter according to claim 2, further comprising a carrier change range setting unit that sets the frequency component frequency to be greater than ½ of the frequency.