JP2001153899A - Method of operating digital sine wave for power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a required data volume without lowering angular resolution when a digital sine wave is generated. SOLUTION: A relation between angles A, B and a prescribed number g is expressed as A=g.B, where A>B and cos A≈1 are satisfied. When a sine of the sum of an angle nA and an angle mB is found by an addition theorem using an optional number n and an optional number m selected from 0 to g, cos(mB)≈1 is satisfied becuase of mB<=A, and an expression sin(nA+mB)≈sin(nA)+cos(nA).sin(mB) is provided thereby. For example, the data volume of values of sin(mB) is 250 words in m=250, the respective data volumes of values of sin(nA) and cos(nA) are 360 words in n=360, and sine values from 0 degree up to 360 degree are computed at 0.004 degree of pitch.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital sine wave calculation method for a power conversion device for obtaining a sine wave as a waveform reference of the power conversion device by digital calculation.

[0002]

2. Description of the Related Art As an example of a power converter, a digitally controlled PWM inverter for converting DC power into AC power by pulse width modulation control will be described in detail as an example. When a digitally controlled PWM inverter converts input DC power into AC power, it is necessary to generate a digital sine wave command in order to control voltage and current.

FIG. 4 is a circuit diagram showing a first conventional example for generating a digital sine wave command. A voltage signal having a sine waveform output from a power supply 1 is supplied to a comparator 2 and a PLL (phase locked loop) circuit. The data is taken into the computer 5 via the counter 3 and the counter 4. When the angular frequency ω and the time t are determined, the sine value can be calculated by the equation y = sin ωt. When the time signal t is supplied from the counter 4 to the computer 5, the sine value can be calculated because the angular frequency ω is known. Alternatively, if the output of the counter 4 is given to the computer 5 as an address, the desired sine value can be obtained by reading the sine value data stored in the memory in advance. However, the digital sine wave command is generated by the latter method. Is common.

[0004]

In order to generate a digital sine wave command by the latter method, data for one cycle, that is, 360 degrees, must be stored in the sine wave table. The amount of minute data depends on the accuracy of the generated sine waveform. To improve the accuracy of the sinusoidal waveform, it is necessary to improve the angular resolution as much as possible. However, improving the angular resolution, that is, subdividing the angle, makes the memory area even larger. This has the disadvantage of having to be done.

FIG. 5 is a table map diagram of a conventional table for storing sine value data. For example, if the angular resolution of a sine wave is 0.004 degrees, one cycle is 360.
Therefore, a large data amount of 360 / 0.004 = 90000 (words) is required. Therefore, the sign table 6 needs the ability to store 90000 words of data.

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the amount of data required for generating a digital sine wave without lowering the angular resolution.

[0007]

According to a first aspect of the present invention, there is provided a method for calculating a digital sine wave of a power converter, comprising an angle A, an angle B, and a predetermined number g. , If they are in a relationship of A = g · B, then A> B
It is. Here, the angle A is determined so that cosA ≒ 1. If n is an arbitrary number and m is an arbitrary number between 0 and a predetermined number g, the sine of the sum of the angle nA and the angle mB can be obtained by the addition theorem, but mB ≦ A. Therefore, cos (mB) ≒ 1. Therefore, the angle nA
And the sine of the sum of the angle mB can be expressed by the following equation 1.

[0008]

## EQU1 ## sin (nA + mB) = sin (nA) .cos (mB) + co
s (nA) · sin (mB) ≒ sin (nA) + cos (nA) · sin (mB) The value of sin (mB) shown in Equation 1 is stored in the first sine table as first sine value data, and Sin (n)
The value of A) is stored as second sine value data in the second sine table, and the value of cos (nA) shown in Expression 1 is stored as first cosine value data in the cosine table. The second sine value data is added to the product of the one sine value data and the sine value at the desired angle is calculated.

In the second aspect, the angle A and the number n are determined so that the maximum value of the angle nA becomes 360 degrees. In the third invention, there are an angle A, an angle B, and a predetermined number g. If these are set to A = g · B, then A> B. here
The angle A is determined so that cosA ≒ 1. If p is an arbitrary number and m is an arbitrary number between 0 and a predetermined number g, the sine of the sum of the angle pA and the angle mB can be obtained by the addition theorem, but mB ≦ A. From the first
Cos (mB) ≒ 1 as in the case of the invention of FIG. Therefore the angle p
The sine of the sum of A and the angle mB can be expressed by Equation 2 below.

[0010]

## EQU2 ## sin (pA + mB) ≒ sin (pA) + cos (p
A) · sin (mB) Then, the value of sin (mB) is stored as first sine value data in the first sine table, and the value of sin (pA) in the range of 0 degrees ≦ pA ≦ 360 degrees is set to the third sine value. It is stored as third sine value data in the table. Cos (pA) = sin (pA +
90 degrees), the value of sin (pA + 90 degrees) read from the third sine table is expressed as cos (p
The second cosine value data of A) is used. However, when the angle calculation value of pA + 90 degrees exceeds 360 degrees, pA + 90 degrees−
The second cosine value data is obtained by using the calculated angle value of 360 degrees. The third sine value data is added to the product of the second cosine value data and the first sine value data to calculate a sine value of 0 to 360 degrees.

In the fourth invention, there are an angle A, an angle B, and a predetermined number g. If these relations are A = gB, A
> B. Here, the angle A is determined so that cosA ≒ 1. If q is an arbitrary number and m is an arbitrary number between 0 and a predetermined number g, the sine of the sum of the angle qA and the angle mB can be obtained by the addition theorem, but mB ≦ A Therefore, cos (mB) ≒ 1 as in the first invention. Therefore, the sine of the sum of the angle qA and the angle mB can be expressed by the following Equation 3.

[0012]

[Equation 3] sin (qA + mB) ≒ sin (qA) + cos (q
A) · sin (mB) Then, the value of sin (mB) is stored in the first sine table as the first sine value data. Although the fourth sine value data stored in the fourth sine table is used for the value of sin (qA) in the range of 0 degrees ≦ qA ≦ 180 degrees, 180 degrees ≦ qA ≦ 360
The value of sin (qA) in the range of degrees is used by adding a minus sign to the fourth sine value data.

Cos (qA) in the range of 0 degrees ≦ qA ≦ 90 degrees
Is used as third cosine value data using fourth sine value data corresponding to an angle obtained by adding 90 degrees to qA, and 90 degrees ≦
The value of cos (qA) in the range of qA ≦ 270 degrees is obtained by using a value obtained by adding a negative sign to the fourth sine value data corresponding to the angle obtained by subtracting 90 degrees from qA as the third cosine value data.
The value of cos (qA) in the range of degrees ≦ qA ≦ 360 degrees is qA
The fourth sine value data corresponding to the angle obtained by subtracting 270 degrees from is used as the third cosine value data.

The sine value data is added to the product of the third cosine value data and the first sine value data to calculate a sine value at a desired angle.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS When 1 degree is adopted as the angle A,
cosA = cos1 ^O = 0.9998477 ≒ 1. If the predetermined number g = 250, the angle B becomes 0.004A. Therefore, if the number m is any integer between 0 and 359 and the number m is any integer between 0 and 249, then n
By calculating A + mB, an angle from 0 degrees to 360 degrees can be obtained in 0.004 degree steps. Therefore, the sine value of this can be obtained by substituting A, B, m, and n into the above-described equation (1).

FIG. 1 is a first table map diagram showing a first embodiment of the present invention. When calculating the sine value of the desired angle by the above-described formula 1, the first sine value data is used as the value of sin (mB).
1 to 249, the amount of data stored in the first sine table 11 is 250 words as shown in FIG. The second sine value data is used as the value of sin (nA).
Since the values are integers up to, the amount of data stored in the second sine table 12 is 360 words as shown in FIG. 1B. Further, the first cosine value data is used as the value of cos (nA). The amount of data stored in the cosine value table 13 is 360 words as shown in FIG. 1C. Therefore, the total amount of data stored in the three tables is 970 words, and the resolution is 0.004 as in the conventional example although the data amount can be significantly reduced as compared with 90000 words in the conventional example. The degree can be secured. FIG. 2 is a second table map diagram showing a second embodiment of the present invention. When calculating the sine value of the desired angle by the above-described formula 2, the first sine value data is used as the value of sin (mB). The number m is between 0 and 249 as in the first embodiment. And the first sine table 11
The amount of data to be stored in the storage area is, as shown in FIG.
Is a word. The second sine value data is used as the value of sin (pA). Since the number n is an integer between 0 and 359, the amount of data stored in the third sine table 21 is as shown in FIG. ) Is 360 words as shown in FIG.
In addition, since there is a relationship of cos (pA) = sin (pA + 90 degrees), sin read from the third sine table is used.
The value of (pA + 90 degrees) is set as the second cosine value data of cos (pA). However, when the angle calculation value of pA + 90 degrees exceeds 360 degrees, the second cosine value data is obtained using the angle calculation value of pA + 90 degrees-360 degrees. That is, since the second cosine value data is obtained from the third sine table 21, the cosine table is unnecessary. Therefore, the total amount of data stored in the two tables is 610 words, and although the data amount can be greatly reduced from 90000 words in the conventional example, the resolution is 0.004 degrees in the same manner as in the conventional example. Can be secured. FIG. 3 is a third table map diagram showing a third embodiment of the present invention. When calculating a sine value of a desired angle by the above-described Expression 3, sin (m
Although the first sine value data is used as the value of B), the number m is an integer between 0 and 249 as in the first embodiment, and the amount of data stored in the first sine table 11 is shown in FIG. 3
There are 250 words as shown in FIG. 0 degrees ≤ qA ≤
The fourth sine value data is used as the value of sin (qA) in the range of 180 degrees, but in the range of 180 degrees ≦ qA ≦ 360 degrees.
The value of sin (qA) is used by adding a negative sign to the fourth sine value data. Therefore, since the number q is an integer between 0 and 179, the amount of data stored in the fourth sine table 31 is 180 words as shown in FIG. 3B.
Further, since there is a relationship of cos (qA) = sin (qA + 90 degrees), cos (qA) in the range of 0 degrees ≦ qA ≦ 90 degrees
The value of A) is obtained by using the fourth sine value data corresponding to the angle obtained by adding 90 degrees to qA as the third cosine value data,
The value of cos (qA) in the range of degrees ≦ qA ≦ 270 degrees is qA
The value obtained by adding a minus sign to the fourth sine value data corresponding to the angle obtained by subtracting 90 degrees from the second sine value data is used as the third cosine value data.
The value of cos (qA) in the range of 70 degrees ≦ qA ≦ 360 degrees is
The fourth sine value data corresponding to the angle obtained by subtracting 270 degrees from qA is used as the third cosine value data. That is, since the third cosine value data is obtained from the fourth sine table 31, the cosine table is unnecessary. Therefore, the total amount of data stored in the two tables is 430 words, and the resolution is 0.004 as in the conventional example although the data amount can be significantly reduced from 90000 words in the conventional example.
The degree can be secured. A proposal for calculating the value of a trigonometric function using the addition theorem is disclosed in Japanese Patent Laid-Open No.
No. 135, which uses the additive theorem to obtain an AC sine waveform,
It has nothing to do with the reduction in the amount of data that the present invention is directed to.

[0017]

Conventionally, a desired resolution (for example, 0.004
In order to obtain 360-degree sine value data (in increments of degrees), a data amount of, for example, 90000 words was required. However, in the present invention, in order to obtain the same resolution, the angles A and 0 in increments of 1 degree are required. A sine value in the range of 0 to 360 degrees is calculated using the addition theorem by combining the angles B in increments of .004 degrees. At this time, since the cosine value of the angle A is almost 1,
The total amount of data stored in the sine table and the cosine table can be significantly reduced as compared with the related art.

Further, by utilizing the relationship of cos α = sin (α + 90 degrees), the sine value data of the predetermined angle range stored in the sine table is used as the cosine value data of the same angle range, thereby omitting the cosine table. Therefore, the effect of further reducing the data amount can be obtained.

[Brief description of the drawings]

FIG. 1 is a first table map diagram showing a first embodiment of the present invention.

FIG. 2 is a second table map diagram showing a second embodiment of the present invention.

FIG. 3 is a third table map diagram showing a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a first conventional example for generating a digital sine wave command;

FIG. 5 is a table map table of a table storing conventional sine value data.

[Explanation of symbols]

 Reference Signs List 1 power supply 2 comparator 3 PLL circuit 4 counter 5 computer 6 sine table 11 first sine table 12 second sine table 13 cosine table 21 third sine table 31 fourth sine table

Claims (4)

[Claims] 1. An angle A whose cosine value exhibits a value very close to 1.
An angle B obtained by dividing the angle A by a predetermined number, and first sine value data corresponding to an angle obtained by multiplying the angle B by an arbitrary number m are stored in a first sine table. The second sine value data corresponding to the angle obtained by multiplying the number n by the angle A is stored in the second sine table, and the first cosine corresponding to the angle obtained by multiplying the arbitrary number n by the angle A Storing the value data in a cosine table; adding the second sine value data to a product of the first cosine value data and the first sine value data to calculate a sine value at a desired angle; Is used as a waveform reference of the power conversion device. 2. The method according to claim 1, wherein the angle A and the number n are determined so that the product of the angle A and the number n becomes 360 degrees at the maximum. A digital sine wave calculation method for a power converter. 3. An angle A at which the cosine value exhibits a value very close to 1.
An angle B obtained by dividing the angle A by a predetermined number, and first sine value data corresponding to an angle obtained by multiplying the angle B by an arbitrary number m are stored in a first sine table. The third sine value data corresponding to the angle (360 degrees at the maximum) obtained by multiplying the number p by the angle A is stored in the third sine table, and is obtained by multiplying the arbitrary number p by the angle A. Calculates an angle obtained by adding 90 degrees to the angle (however, if the addition result exceeds 360 degrees, an angle obtained by subtracting 360 degrees from the addition result), and adds the third sine value data corresponding to the angle after the addition operation before the addition Calculating the sine value of the desired angle by adding the third sine value data to the product of the second cosine value data and the first sine value data; Is used as a waveform reference of the power converter. Digital sine wave calculation method for converter. 4. An angle A whose cosine value exhibits a value very close to 1.
An angle B obtained by dividing the angle A by a predetermined number, and first sine value data corresponding to an angle obtained by multiplying the angle B by an arbitrary number m are stored in a first sine table. The fourth sine value data corresponding to the angle obtained by multiplying the number q by the angle A and the angle A (up to 180 degrees) is stored in the fourth sine table, and the angle of the product of the arbitrary number q and the angle A is 0 degrees ≦ qA ≦ 180
If it is in the range of degrees, the fourth sine value data corresponding to this angle is used as sine value data, or if the angle of the product of the arbitrary number q and the angle A is in the range of 180 degrees ≦ qA ≦ 360 degrees, The fourth sine value data corresponding to the angle obtained by subtracting 180 degrees from qA is used as a sine value data with a minus sign, and the angle of the product of the arbitrary number q and the angle A is 0 degree ≦ qA ≦ 90 degrees , The fourth sine value data corresponding to the angle obtained by adding 90 degrees to qA is used as the cosine value data, or the angle of the product of the arbitrary number q and the angle A is 90 degrees ≦ qA ≦ 27.
If it is in the range of 0 degrees, the fourth sine value data corresponding to the angle obtained by subtracting 90 degrees from qA is used as a cosine value data by adding a minus sign, or the angle of the product of arbitrary number q and angle A If 270 degrees ≦ qA ≦ 360 degrees, the fourth sine value data corresponding to the angle obtained by subtracting 270 degrees from qA is used as the cosine value data, and the product of the cosine value data and the first sine value data is A digital sine wave operation method for a power converter, wherein the sine value data is added to calculate a sine value at a desired angle, and the calculated sine value is used as a waveform reference for the power converter.