JPH02241370A - Calculating method for pwm waveform of inverter control - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an inverter control method used in air conditioners, etc., and more specifically, even if the control ratio exceeds 1, the current waveform of the compressor motor is The present invention relates to a method of calculating a PWM waveform for inverter control without distortion.

[Conventional example] Conventionally, in calculating PWM waveforms using this type of inverter control, three-phase sine wave waveforms are shifted by 120 degrees from each other to form U, V, and W phases, and a triangular fundamental wave (carrier). At this point, PWM waveform data is obtained based on the magnitude relationship between the sine wave of each phase and the carrier. For example, to explain the U phase of the sine wave 1 shown in FIG. 5 as an example, the portion of the U phase shown in FIG.
/OI+, the pulse train shown in FIG. 2(b) is obtained.

Here, as shown in Fig. 6, when the operating frequency of the compressor is 81.0)(z, the control rate is 1.050, and the number of carriers is 33, the pulse trains of U phase, V phase, and W phase are shown in FIG. The voltage waveforms shown in (d) to (f) in the same figure are applied to -V, V-V, and w-u, respectively, but due to these phase voltages and the inductance component of the motor coil, the three-phase motor A sinusoidal current will flow.

Therefore, the pulse trains shown in FIGS. 6(a) to (Q) are obtained for each operating frequency, and the signal train (
A voltage pattern storage method is generally used in which a three-phase motor is controlled at a predetermined operating frequency by storing the pattern in a storage unit as a pattern (Pw waveform data) and switching the pattern to be read out according to an operating frequency command.

[Problem to be Solved by the Invention] By the way, when calculating the above PWM waveform, since the phase-to-phase voltage of the three-phase motor is determined by the amplitude ratio (control rate) of the sine wave and the carrier, it is necessary to calculate the output voltage to the three-phase motor by If an attempt is made to increase it, the control rate will exceed 1, and the vicinity of the peaks of the three-phase sine waves will each become higher than the carrier, resulting in a decrease in the number of pulses in the pulse train. That is, as shown in FIGS. 6(a) to (c), there is a range (U) corresponding to the crest of the sine wave, and a range (U, W) corresponding to the trough of the sine wave, respectively.
), the number of pulses is smaller than when the control rate is 1 or less. As a result, the number of switching operations of the switching power transistor decreases, distortion occurs in the current waveform of the three-phase motor, and harmonic components increase, causing noise and vibration in the three-phase motor.

Therefore, the control rate must be limited to 1 or less, and this limitation may become an obstacle when attempting to utilize inverter control in various ways.

This invention was made in view of the above problems, and its purpose is to provide a method for calculating a PWM waveform using inverter control, which prevents distortion from occurring in the current waveform of a three-phase motor even if the control rate exceeds 1. It's about doing.

[Means for Solving the Problems] In order to achieve the above object, the present invention uses a carrier of a predetermined frequency (a fundamental wave of a triangular wave) when calculating a PWM waveform for inverter control of a load such as an air conditioner. In a method for calculating a PWM waveform in inverter control, in which three-phase sine waves having a phase shift of 120 degrees are superimposed on each other, and the PWM waveform data is obtained based on the magnitude relationship between the sine waves of each phase and the carrier. , while distorting the vicinity of the peak of the sine wave to a value smaller than its peak value,
The difference between the distorted portion and the above sine wave is added to each other sine wave and distorted to obtain a three-phase distorted wave, and the three-phase distorted waves are superimposed on the carrier to obtain the above PTM waveform waveform -
The main point is that the data is calculated.

[Function] Since the above method is adopted, the three phases superimposed on the above carrier (
When the peaks of the distorted waves (U phase, ■ phase, W phase) are made lower than the peak of the conventional sine wave, the lowered amount is added to the other two phase waves. The three phases obtained in this way (U phase,
Since the distorted waves of the three-phase sine waves (phase II, phase W) exhibit the same relative relationship as the conventional three-phase sine wave, they do not affect the correlation waveform obtained from the three-phase distorted waves, and moreover, the calculation of the correlation waveform is It's easy.

Furthermore, since the peak values of the three-phase distorted waves are lowered, even if the control ratio (sine wave peak/carrier peak) exceeds 1, the number of pulses of the phase voltage waveforms does not decrease. Therefore, even if the output voltage is increased, distortion does not occur in the current waveform of the compressor or the like and harmonic components do not increase, so it is possible to prevent noise from the compressor.

[Example] Hereinafter, an example of the present invention will be described based on the drawings. In FIG. 1, the same parts as in FIG. 5 are designated by the same reference numerals, and redundant explanation will be omitted. Further, the phases of the 1°6.7 sine waves are shifted from each other by 120°.

In Figure 1, there are three distorted waves (U phase, ■ phase.

)3 and 4.5 of the W phase have the same shape and are 1
The phase is shifted by 20 degrees. Those three-phase distorted waves 3, 4
．． 5 can be obtained as follows.

First, in the range of 60 degrees to 120 degrees, the distorted wave 3 has a shape that is lower than the peak value of the sine wave 1 by a predetermined value t, for example, a straight line 3a. On the other hand, the difference δa between the sine wave 1 and the straight line 3a is added to the sine waves 6 and 7 (indicated by the arrow in the figure).

Then, the sine waves 6 and 7 are distorted within the range of 60 degrees to 120 degrees corresponding to the difference. That is,
Maximum (1) at 90 degrees, 60 degrees and 120 degrees
This is because the difference δa which is the minimum (0) in the range is added to the sine waves 6 and 7 corresponding to that range.

Subsequently, within the range of 0 degrees to 60 degrees, the ■ phase distorted wave 4 is made into a straight line 4a that is higher than the peak (valley) value of the sine wave 6 by a predetermined value t. On the other hand, the sine wave 6 and the straight line 4a
The difference δa between the sine waves 1 and 7 is added to the sine waves 1 and 7. Therefore, the sine waves 1 and 7 are distorted within the range of 0 degrees to 60 degrees corresponding to the difference as described above. Also, from 120 degrees to 1
Within the range of 80 degrees, the W-phase distorted wave 5 forms a straight line 5a that is higher than the peak (valley) value of the sine wave 7 by a predetermined value t. on the other hand.

The difference δa between the sine wave 7 and the straight line 5a is added to the corresponding sine waves 1 and 6, respectively. Therefore, sine wave 1,
6 is distorted within the range of 120 degrees to 180 degrees corresponding to the difference.

In this way, the U-phase, V-phase, and W-phase distorted waves 3°4.5 each have a straight line near the peak, and the other parts are distorted according to the difference δa from the straight line, and these U-phase The distorted waves 3° 4.5 of phase, V phase and W phase are sine waves 1, 6 .
It can be said that the value is relatively the same as 7.

And, as shown in FIGS. 2(a) and (b),
By superimposing the U-phase distorted wave 3 on the carrier 2, the U-phase voltage waveform (pulse train) at that point can be obtained. At this time, U-phase, V-phase and W-phase distorted waves 3 and 4
, 5 are relatively the same as the sine waves 1, 6.7, PVM data calculation for obtaining the phase voltage waveform can be easily performed. By the way, as shown by the broken line in FIG. 2(a), when the control rate exceeds 1 and the wave superimposed on carrier 2 is sine wave 1, the U-phase voltage waveform (pulse train) has pulses. Pa is not included. Further, the V-phase and W-phase voltage waveforms of the V-phase and W-phase sine waves under the same conditions as the U-phase sine wave 1a do not include a pulse corresponding to the pulse Pa. Such U phase and V phase with a small number of pulses
u-v, v-w obtained by phase and W phase voltage waveforms
, When the w-u interphase voltage waveform is applied to the three-phase motor of the compressor (shown in Figures 6(d) to (f)), the current waveform of the motor will be distorted, and the noise of the three-phase motor will be increased. This can cause vibrations and vibrations.

However, in this invention, even under the above control rate condition, the pulse Pa is Obtainable.

Here, as shown in FIG. 3, under the same conditions as in FIG. 6, carrier frequency 81. To explain the case of OHz, number of carriers 33, and control rate 1.050, first of all, the same Wi
In the U-phase voltage waveform in (a), a pulse is obtained in the range Ua corresponding to the pulse Pa. That is, that U
As shown in FIG. 6(a) of the conventional example, the phase voltage waveform does not reduce the number of pulses even at the same control rate of 1.050, and has the same number of pulses as when the control rate is 1 or less. become. Furthermore, the range V of the V-phase voltage waveform shown in FIG.
a, and the range W of the W-phase voltage waveform shown in FIG.
A pulse is similarly obtained at point a. therefore,
As shown in (d) to (f) of the same figure, those U phases,
Due to the V-phase and W-phase voltage waveforms, the phase-to-phase voltage waveform, U-■
Since the phase-to-phase, V-W, and phase-to-U voltage waveforms are applied to the three-phase motor, the current waveform of the three-phase motor becomes a sinusoidal current waveform with little distortion, as in the case where the control rate is 1 or less.

Next, a modification of the above embodiment will be explained based on FIG. 4. In addition, in the figure, the same parts as in FIG. 1 are given the same reference numerals, and redundant explanation will be omitted.

In this figure, the U-phase distorted wave 8 superimposed on the carrier 2 has a curved arc 8a within a range of 60 degrees to 120 degrees, and an arc 8b that is symmetrical to this arc 8a and a 90 degree line. In addition, the peak position of the sine wave 1 has a predetermined value t. On the other hand, although not shown, the V-phase and W-phase distorted waves each have an arc 8a, as in the previous embodiment.

The difference between 8b and sine wave 1 is added to the sine waves corresponding to the V phase and W phase.

Although not shown, in the range of 0 degrees to 60 degrees,
The distorted wave of phase (2) has the shape of a curved arc and an arc that is symmetrical to the 90 degree line, and has a predetermined value t at the peak (valley) position of the chord wave.

On the other hand, the W-phase and U-phase distorted waves are obtained by adding the difference δa between the arc and the sine wave to the sine waves corresponding to the U-phase and W-phase. That is, as shown in Figure (a), U
In the case of phase distortion 8, the difference δa is added to the sine wave 1 in the range of 0 degrees to 60 degrees. Also, W
The same applies to phase distortion waves. Furthermore, the same processing as described above is performed for the range of 120 degrees to 180 degrees,
U-phase, V-phase, and W-phase distorted waves are obtained.

In this way, by shifting the U-phase distorted wave 8 in the figure by 120 degrees, three-phase U-phase, V-phase, and W-phase distorted waves can be obtained.2. However, it can be said that the U-phase, ■-phase, and W-phase distorted waves are relatively the same as the sine waves 1, 6.7 (shown by the broken line in FIG. 1).

Here, as shown in FIG. 2B, by superimposing the U-phase distorted wave 8 on the carrier 2, the U-phase voltage waveform (pulse train) at that point can be obtained. That is, as in the previous embodiment, a pulse pb is obtained in the U-phase voltage waveform at a location corresponding to the vicinity of the peak of the sine wave 1. On the other hand, other areas of the U-phase distorted wave 8, 0 degrees to 60 degrees, 1
In the range of 20 degrees to 180 degrees, the value does not become larger than the peak value of 60 degrees of sine wave 1, so the number of pulses of the U-phase voltage waveform does not decrease even in those regions. In addition, the V-phase and W-phase voltage waveforms obtained by the V-phase and W-phase distorted waves are the same as the U-phase voltage waveforms, and the peaks of the sine waves (
A pulse is obtained at a position corresponding to a peak or valley. Therefore, based on these U-phase, V-phase, and W-phase voltage waveforms, the interphase voltage waveforms applied to the three-phase motor, υ−■ interphase,
The voltage waveforms between the V-W phase and between the W-U phase are similar to those shown in FIGS. 10(d) to 12(f), and the current waveform of the three-phase motor has little distortion as in the case where the control rate is 1 or less.

Note that the shape of the distorted wave in the above embodiment is not limited to the above two types, but may be any shape as long as it does not exceed the peak value near the peak of the sine waves 1 and 6.7. good.

[Effects of the Invention] As explained above, according to the method of calculating a PWM waveform by inverter control of the present invention, three-phase distorted waves superimposed on a carrier and shifted by 120 degrees from each other are calculated relative to a three-phase sine wave. Pt
Since the 1M waveform is calculated, even if the control rate exceeds 1, the number of pulses of the phase voltage waveform (pulse train) will not be reduced.
Distortion of the current waveform of the three-phase motor can be reduced, and factors that cause noise and vibration of the three-phase motor can be suppressed. Further, according to the present invention, the control rate may exceed 1, and there is an effect that inverter control can be used in various ways.

[Brief explanation of drawings]

1 and 2 show an embodiment of the present invention, and are diagrams for explaining a method of calculating a PVM waveform by inverter control, and FIG. 3 shows three-phase voltage waveforms and their phase relationship by calculating the PWM waveform. A voltage waveform diagram, FIG. 4 shows another embodiment of the present invention, and is a diagram for explaining a method of calculating a PWM waveform by inverter control, and FIG. 5 explains a method of calculating a Pt1M waveform by conventional inverter control. FIG. 6 is a diagram showing three-phase voltage waveforms and their phase-to-phase voltage waveforms based on conventional PWM waveform calculations. In the figure, 1, 6.7 are sine waves, 2 is carrier (triangular wave),
3.8 is a U-phase distorted wave, 4 is a V-phase distorted wave, 5 is a W-phase distorted wave, 3a and 3b are straight lines (of U-phase distorted wave 3), and 4a. 4b is a straight line (of V-phase distorted wave 4), 5a and 5b are straight lines (of W-phase distorted wave 5), and 8a and 8b are arcs (of U-phase distorted wave 8). Patent applicant: Fujitsu General Co., Ltd. Representative, Patent attorney: Takuya Ohara Figure 2 Figure 3

Claims (3)

[Claims] (1) When calculating a PWM waveform for inverter control of a load such as an air conditioner, a carrier of a predetermined frequency (
PWM in inverter control in which three-phase sine waves with a phase shift of 120 degrees are superimposed on a triangular fundamental wave), and data of the PWM waveform is obtained based on the magnitude relationship between the sine waves of each phase and the carrier. In the waveform calculation method, the vicinity of the peak of the sine wave is distorted to a value smaller than its peak value, and the difference between the distorted portion and the sine wave is added to each other sine wave to create a three-phase distorted wave. The three-phase distorted waves are superimposed on the carrier to generate the PW.
A method for calculating a PWM waveform in inverter control, characterized in that data of an M waveform is calculated. (2) The method for calculating a PWM waveform in inverter control according to claim (1), wherein the three-phase distorted waves are straight lines near the peaks of the sine waves. (3) The method for calculating a PWM waveform in inverter control according to claim (1), wherein each of the three-phase distorted waves is formed into an arc near a peak of a sine wave.