JPH033695A - Method of reducing audible electromagnetic sound of inverter driven motor - Google Patents

Abstract

PURPOSE:To suppress an audible electromagnetic sound generated from a motor by variably controlling the frequency of a triangular wave carrier signal for a sine wave control signal within a suitable varying width of a frequency of an integral multiple of the frequency of the control signal. CONSTITUTION:A 3-phase sine wave control signal generator 1 inputs a fre quency command fs of a predetermined output of an inverter and a voltage command, and outputs 3-phase sine wave control signal voltages Vsu-Vsw having a frequency fs and a phase difference at each 120 degrees. An aural controller 2 inputs a central value fco of frequency of a triangular carrier wave for modu lating a sine wave control signal of frequency fs, and outputs a voltage signal Vf of a frequency varying in a triangular wave state and being an integral multiple of the frequency fs with, the maximum fluctuation width of the signal vf being the difference between a maximum value and a minimum value. Specifications regarding to the frequency varying in a triangular state are so suitably determined as to effectively suppress the electromagnetic sound of a motor. Thus, a harmful motor electromagnetic sound in an audible fre quency band can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of generating switching signals for main circuit switching elements of a PWM inverter device for reducing audible electromagnetic noise generated by a driving AC motor.

[Conventional technology]

As a conventional method for generating a PWM switching signal in this type of inverter device, the frequency of the triangular wave carrier signal is set to an appropriate fixed frequency over the entire phase range of the sine wave control signal, and the reduction of audible electromagnetic noise is achieved by changing the frequency of the triangular wave carrier signal to an appropriate fixed frequency over the entire phase range of the sine wave control signal. It is known that changes are made.

[Problem to be solved by the invention]

The electromagnetic noise from the AC motor as described above is caused by harmonic components contained in the inverter output voltage applied to the motor, and the harmonic components are concentrated in an integral multiple range of the carrier frequency.

Therefore, in the conventional method as described above, even if the fixed carrier frequency is changed, it is difficult to reduce audible electromagnetic noise unless harmonic components generated in integral multiples of the fixed carrier frequency fall into the inaudible range. Even in the case of changes, the gradual changes had the potential to cause frequency jitter, accompanying fluctuations in the tunable electromagnetic noise, and excessive current fluctuations in the load motor.

In view of the above, an object of the present invention is to provide a PWM switching signal generation method that reduces the audible electromagnetic noise by avoiding concentration of harmonic components in a specific region as described above.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a method for reducing audible electromagnetic noise in an inverter-driven motor, which includes a method for generating a switching signal for a main circuit switching element of a PWM inverter device that drives an AC motor at a variable speed. Regarding a triangular wave carrier signal with a constant peak value that modulates a sine wave control signal having a frequency equal to the output frequency and whose amplitude is proportional to the required output voltage of the inverter device, The sum of the center frequency and a frequency variation that has a specific relationship with the phase angle of the sine wave control signal and that fluctuates at a frequency that is an appropriate integral multiple of the frequency of the sine wave control signal, with the maximum range of variation being constant. Alternatively, instead of keeping the maximum fluctuation width of the carrier signal frequency constant as described above, it is the ratio of the deviation between the maximum and minimum frequencies to the maximum frequency in the fluctuation of the carrier signal frequency. The frequency of the carrier signal is variably controlled so that the frequency modulation ratio of the carrier signal decreases linearly as the output frequency of the inverter device increases.

[Effect]

As mentioned above, the electromagnetic noise generated by an AC motor driven by an inverter is caused by harmonic components included in the output voltage of the inverter, and furthermore, the harmonic components are sine waves that form the basis of the inverter output voltage. The control signal is concentrated in an integer multiple range of the frequency of the triangular carrier signal that modulates the control signal.

Therefore, by modulating the frequency of the carrier signal at a frequency that is an appropriate integer multiple of the frequency of the sine wave control signal during constant fluctuation and changing it in an appropriate relationship with the phase angle of the sine wave control signal, The frequency range that is an integer multiple of the carrier signal frequency is also expanded and dispersed to avoid concentration in a specific frequency range. Avoiding concentration in the audible frequency range is particularly effective in reducing harsh motor electromagnetic noise.

Furthermore, the variation of the carrier signal frequency is variable, and the variation in the low frequency range of the sine wave control signal is larger than that in the high frequency range, and is linear with respect to the frequency of the sine wave control signal. By changing the frequency to , it is possible to suppress the occurrence of frequency jitter and smoothly reduce the motor electromagnetic noise over the entire required change range of the sine wave control signal frequency.

The present invention provides the sine wave control in such a manner that the frequency of the carrier signal is changed, for example, in a triangular wave shape having a frequency that is an integral multiple of the frequency of the sine wave control signal and whose maximum fluctuation range, that is, the peak value is constant. By changing the phase angle in a certain relationship with the phase angle of the signal, it is possible to avoid concentration of harmonic components generated as integral multiples of the carrier signal frequency in a specific frequency range, and furthermore, to increase the frequency of the carrier signal. During the fluctuation, for example, the peak value of the triangular wave change is made variable, and the frequency modulation ratio, which is the ratio of the deviation between the maximum and minimum frequencies to the maximum frequency of the carrier signal frequency, is the sine wave with the inverter output frequency axis. The carrier signal frequency is variably controlled so as to decrease linearly as the control signal frequency increases, thereby avoiding concentration of harmonic components in a specific frequency range and suppressing frequency jitter. .

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

1 and 3 are block circuit diagrams of a switching signal generation circuit for three-phase inverter main circuit switching elements showing an embodiment of the present invention, and FIGS. FIG. 3 is a signal operation waveform diagram in the circuit.

In Fig. 1, ■ is a three-phase sine wave control signal generator, which inputs the frequency command f3 of the required output of the inverter and the voltage command, and receives a three-phase sine wave having the frequency f and a phase difference of every 120 degrees. Control signal voltage■,. .

Output V 3y, V 314. Reference numeral 2 denotes an auditory controller, which inputs the central value fco of the frequency rc of the triangular wave carrier signal modulating the sine wave control signal whose frequency is f, and calculates the difference f between the maximum value f c + emx and the minimum value f cmin. csmx f c,in is the maximum fluctuation width, and the frequency n is an integer (n) times the frequency f.
-f, which outputs a voltage signal V having the frequency fc that changes in a triangular wave shape, and the above-mentioned specifications regarding the frequency fc are appropriately determined so as to effectively suppress the electromagnetic noise of the motor. 3 is a V/F converter which converts the voltage signal (2) into a pulse voltage signal VCp of frequency f.

Reference numeral 4 denotes an integrator which integrates the voltage signal VC9 and outputs a required variable frequency triangular wave carrier signal voltage V. 5, 6, and 7 are comparators, and the signal voltages V SLI + V 3V, V 3W, and ■
It calculates the voltage difference between This provides the required PWM switching signal for the device.

FIG. 2(A) shows the operating waveform diagram of each phase voltage signal V Iu, V 3y, V 3H of the three-phase sine wave control signal, and FIG. 2(B) shows the operation waveform diagram of the carrier signal frequency ". FIG. 3 is an operational waveform diagram showing the characteristics of the sine wave control signal with respect to the phase angle ω,·t, and shows the case where the integer n is selected to be 6 with respect to the frequency of the change.

FIG. 3 shows the auditory controller 2 and V/V in FIG. 1.
The functions of the F converter 3 and the integrator 4 are combined to form a frequency modulator 8, and in order to perform the above-described modulation regarding the frequency rC, an input field for the frequency command f to the modulator 8 is provided. It is something.

FIG. 4(a) illustrates a variation pattern of the modulation ratio (α) of the frequency f with respect to the frequency command f,
α=α at 0≦f, ≦f31. (constant).

α is α when fil≦f and ≦fsTl. It decreases linearly to zero, and α=0 when f≧rsz. Note that α is 0≦
α≦1.

FIG. 4(B) shows the fluctuation pattern of the frequency fc corresponding to the change in the modulation ratio α shown in FIG. 4(A). f c@i
n= f CIemX+ f c= f cmmx, and the carrier frequency f becomes the fixed frequency of f coax.

〔Effect of the invention〕

According to the present invention, regarding a method of generating a PWM switching signal for an inverter main circuit switching element, the frequency of a triangular wave carrier signal relative to a sine wave control signal is adjusted to a frequency that is an appropriate integer multiple of the frequency of the control signal during an appropriate fluctuation. By performing variable control, it is possible to avoid concentration of harmonic components generated in a frequency range that is an integral multiple of the carrier signal frequency in a specific range, and to effectively suppress audible electromagnetic noise generated from an AC motor driven by an inverter. Furthermore, by variably controlling the fluctuation of the triangular wave carrier signal frequency with the modulation ratio according to the control signal frequency as described above, fluctuations in audible electromagnetic noise due to frequency jitter and fluctuations in the inverter load motor can be suppressed. Excessive current fluctuations can be avoided.

[Brief explanation of drawings]

1 and 3 are block circuit diagrams showing an embodiment of the present invention, and FIGS. 2 and 4 are signal operation waveform diagrams in FIGS. 1 and 3, respectively. DESCRIPTION OF SYMBOLS 1... Sine wave control signal generator, 2... Auditory controller, 3... V/F converter, 4... Integrator, 5
~Modulation ratio and soil force variation diagram 4

Claims (1)

[Scope of Claims] 1) In a method for generating a switching signal for a main circuit switching element of a PWM inverter device that drives an AC motor at variable speed, the switching signal has a frequency equal to the output frequency of the inverter device and an amplitude of the inverter device. Regarding a triangular wave carrier signal with a constant peak value that modulates a sine wave control signal with a value proportional to the required output voltage of the device, the frequency of the carrier signal has a specific relationship with its center frequency and the phase angle of the sine wave control signal. an inverter-driven electric motor, characterized in that the maximum fluctuation width is kept constant and the inverter-driven motor is variably controlled as the sum of a frequency fluctuation component that fluctuates at a frequency that is an appropriate integral multiple of the frequency of the sine wave control signal. Audible electromagnetic noise reduction method. 2) In the audible electromagnetic noise reduction method for an inverter-driven motor according to claim 1, instead of keeping the maximum variation width of the carrier signal frequency constant as described above, An inverter characterized in that the frequency of the carrier signal is variably controlled so that the frequency modulation ratio of the carrier signal, which is the ratio of the minimum deviation between frequencies, decreases linearly as the output frequency of the inverter device increases. A method for reducing audible electromagnetic noise of a drive motor.