JPH01136572A - Pwm inverter - Google Patents

Abstract

PURPOSE:To eliminate noise offensive to the ear, by employing a means for determining respective PWM periods based on random numbers. CONSTITUTION:A drive signal generating section 4' for generating a drive signal to be used for ON/OFF control of a switching element in an inverter main circuit section comprises main components, i.e. a frequency setter FR, a reference wave generator SWB, a modulated wave generator TWV for producing triangular wave and the like, a comparator CMP and a random number generator RDM. PWM periods are determined based on outputs from the random number generator RDM such that the time intervals T1-T2'' will be different. When a means for providing different PWM periods is employed, noise of motor can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter motor drive device, and particularly to a PWM inverter that reduces motor noise by controlling the cycle of pulse modulation.

[Prior art]

A PWM inverter (pulse width modulation inverter) is commonly used as a motor drive device.6 Figures 7 and 8 show the basic concept of a PWM inverter, where 1 is a DC power supply, 2 is an inverter circuit 13 is an induction motor (hereinafter simply referred to as an electric motor), 4 is a drive signal generation section, and 5 is a drive circuit section. Further, Sl is a voltage reference waveform shown as a sine wave example, 8 is a modulation wave shown as a triangular wave example, and Sl is a drive signal s8.
4 is PWM waveform 1. is a sine wave approximation curve.

Here, the inverter main circuit section 2 includes a switching element SW
I*8W! , 8W@, 8W4, 8Wi,
8W6 forms the three-phase bridge shown in the transistor example, and flywheel diodes DI en, I Ds l D4 + are connected antiparallel to these switching elements.
Da + Da are connected.

Further, since the PWM waveform output method is well known, a detailed explanation will be omitted, but the drive signal generating section 4 generates a voltage reference waveform S1 and a modulated wave S! After comparing, inverter main circuit section 2
Drive signal S3 that controls on/off control of the switching element of
The drive circuit section 5 drives the inverter main circuit section 2 based on the drive signal Ss.

In this type of PWM inverter, the PWM period TU is generally as shown in the waveform shown in FIG.
P3 indicates that TU, , Ti, etc. are almost constant over time.

[Problem that the invention seeks to solve]

When a motor is driven by such a conventional PWM inverter, the noise emitted from the load such as the motor 3 (mainly due to vibrations caused by magnetostriction) is extremely loud.

This electric motor noise has a tone of 1 beep,
Depending on the frequency, it can be very audible.

Note that when the inverter output frequency is variable, the PWM period is also usually variable, and if it matches the natural frequency of the motor, the noise level will further increase.

[Means for solving problems]

In view of the above-mentioned points, the present invention has been developed in the conventional PWM inverter. In order to randomize the chopping frequency, the present invention is characterized by having a means for determining each PWM period by employing random numbers.

It is. Furthermore, this is a white noise
It has the effect of producing a pleasant sound.

[For production]

Therefore, the present invention employs a means for determining each PWM period by employing random numbers, specifically, in a drive signal generating section as described above, a modulated wave, which is one of the comparison signals, is used as a signal sent out by a random number generator or A preferable motor noise is obtained by controlling the period of pulse modulation based on the output signal of the random number generation program means.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

〔Example〕

1 and 2 are summary configuration diagrams and partial waveform diagrams thereof shown as hardware configuration examples to facilitate understanding of the present invention, and 4' is a drive signal generating section 4 shown in FIG. 7.
a drive signal generation section that generates a drive signal that controls on/off of the switching elements of the inverter main circuit section 2 in the same manner as the above;
'r11 'r, IT□' + rr, / ITl
", T3" is time.

That is, only the drive signal generation section is shown here;
The main components of the drive signal generator 4' are a frequency setter FR, a reference wave generator 8WB, a modulation wave generator 'rwv' that generates a triangular wave, etc., a comparator OMP, and a random number generator RD.
It is equipped with M.

In Figures 1 and 2, when determining the PWM period, especially the time 'r, , 'r + Tl' * T2'
It is assumed that the output of the random number generator RDM is used to determine e Tl' + 'r,'' which are different from each other.In other words, in the modulated wave generator TWVIm, (1) the control input 801 is the inverter output frequency; and P
There may be no difference from the conventional method, such as setting the WM frequency in a proportional relationship.

(2) It is assumed that the control input So2 is randomly controlled so as to have no periodicity with the PWM frequency.

Therefore, the modulated waveform 5l11' is input to these control inputs 801.
It is clear that the period can be controlled by +802.

This will be further explained with reference to a specific example.

3, 4, and 5 are shown to explain one embodiment to which the present invention is applied. FIG. 3 shows the main part configuration, and FIGS. 4 and 5 show waveforms. It shows the concept of generation and its partial operation flow.

In FIGS. 3 to 5, the part mainly composed of a CPU, a comparator, and a flip-flop (FF) corresponds to the drive signal generating section 4 shown in FIG. The main supply signals are to give a preset value to the latch board and a time signal to the comparator, and the FF has a drive signal S as in Fig. 1.
3 will be generated.

The basic technology for generating PWM waveforms is well known and the details are omitted here, but in FIG. 4, the PWM period TU,
, the voltage reference waveform S1 is determined by determining the line from point A to point B in the modulated waveform S2 by the random number signal.
As shown in the example below.

Furthermore, such a time T1 is obtained, and the time P-
It is clear that 7 Tz is required.

Next, PWM with such times 'r, I 'r,
When the period is determined in terms of pulse width for easier understanding, the flow is illustrated in FIG. 5. Here, it goes without saying that the constants a and b need to be selected so that they have no periodicity in practice.

〔Effect of the invention〕

As described in detail above, if a method is used in which the PWM cycle is set to a different cycle, the problem of motor noise can be solved. This is clear from the fact that the following effects were obtained in actual machine tests.

That is, a frequency analysis of the inverter output is shown in FIG. 6. Here,
(a) shows a case where the PWM cycle is constant as a conventional product, and (b) shows a case where the PWM cycle according to the present invention has no periodicity.

[Brief explanation of the drawing]

1 and 2 are main part configuration diagrams and partial waveform diagrams thereof, showing an example of a hardware configuration, and FIG. 3. 4 and 5 are explanatory diagrams showing an example to which the present invention is applied, in which FIG. 3 shows the main part configuration, and FIGS.
The figure is a conceptual diagram of waveform generation and a partial operation flow diagram. Furthermore, FIG. 6 is a frequency analysis explanatory diagram of an inverter output shown for detailed explanation of the present invention, and FIGS. 7 and 8 are a configuration diagram and a signal waveform diagram showing the basic concept of a PWM inverter. 2... Inverter main circuit section, 3 is induction motor (
Electric motor), 4.4'...Group/Drive signal generation part%8.・・・
...Voltage reference waveform, 8B + 8! '・・・・・・
Modulated wave% s, e 8B'... Drive signal, 8
01 e 802"""Control inputs TUl e TU
l” song PWM period, Tl, Tz, T□r +
r, / l T Engineering I1. T, “Scream...Time.

Claims (1)

[Claims] In a PWM inverter that drives a motor by a drive signal generation section that generates a pulse width modulated drive signal, the drive signal generation section includes a random number generation device, and the PWM period of the drive signal is controlled by obtaining the output of the random number generation device. A PWM inverter characterized by: