阅读说明：本技术 一种pwm谐波有效值计算方法 (PWM harmonic effective value calculation method ) 是由 符立梅 董立红 赵振民 于 2019-10-21 设计创作，主要内容包括：本发明属于电磁干扰领域,涉及一种PWM谐波有效值计算方法。本发明通过将PWM波构造成一种锯齿波,该锯齿波的频率与PWM波的载波频率相同,幅度是PWM波的幅度的2倍,利用发明方法,可以有效解决不能直接计算PWM波有效值的问题,使用本发明的PWM谐波有效值计算方法后,可以在后续仿真结果中直接得到各次谐波有效值,并且在电磁兼容仿真领域,利用锯齿波各次谐波独立性,直观的得到各个频点的有效值结果。(The invention belongs to the field of electromagnetic interference, and relates to a PWM harmonic effective value calculation method. According to the invention, the PWM wave is constructed into the sawtooth wave, the frequency of the sawtooth wave is the same as the carrier frequency of the PWM wave, and the amplitude is 2 times of the amplitude of the PWM wave, so that the problem that the effective value of the PWM wave cannot be directly calculated can be effectively solved by using the method disclosed by the invention.)

1. A PWM harmonic effective value calculation method is characterized in that a sawtooth wave is constructed according to a PWM wave.

2. The method according to claim 1, wherein the PWM wave is a result of a sawtooth carrier and a sine wave modulation.

3. A PWM harmonic effective value calculation method according to claim 1, wherein the PWM waves include unipolar PWM waves and bipolar PWM waves.

4. A PWM harmonic effective value calculating method according to any one of claims 1 to 3, wherein the step of causing the unipolar PWM wave to generate a sawtooth wave is as follows:

A. calculating the amplitude and frequency of the unipolar PWM wave;

B. constructing a sawtooth wave, wherein the frequency of the sawtooth wave is the same as the carrier frequency of the single-polarity PWM wave in the A, and the amplitude of the sawtooth wave is 2 times of the amplitude of the single-polarity PWM wave in the A;

C. carrying out FFT operation on the sawtooth wave to obtain each harmonic peak value;

D. by dividing the peak value of each harmonic by

5. A PWM harmonic effective value calculating method according to any one of claims 1 to 3, wherein the step of generating a sawtooth wave by the bipolar PWM wave is as follows:

A. calculating the amplitude and frequency of the bipolar PWM wave;

B. the sawtooth wave is constructed to have the same frequency as the carrier frequency of the bipolar PWM wave in a and an amplitude 2 times the amplitude of the bipolar PWM wave in a.

C. Carrying out FFT operation on the sawtooth wave to obtain each harmonic peak value;

D. by dividing the peak value of each harmonic by

6. The PWM harmonic effective value calculation method according to claim 1, wherein the slope of the sawtooth wave can be positive or negative.

Technical Field

The invention belongs to the field of electromagnetic interference, and particularly relates to a PWM harmonic effective value calculating method.

Background

In the field of power electronics, PWM is a common control method, and the waveform of PWM has periodicity macroscopically and duty cycle gradually changes microscopically. The frequency spectrum of the waveform often has main harmonics and more interharmonic waves, and the energy is distributed around each subharmonic, so that the effective value of each subharmonic is difficult to calculate.

In the electromagnetic interference category, a detector of a receiver has a certain bandwidth, energy in the bandwidth is received and a total effective value is detected, so that the effective value of each harmonic is important in interference calculation, and the harmonic effective value cannot be directly obtained through simple FFT (fast Fourier transform).

At present, the steps of calculating the effective value of each harmonic of PWM are: after the PWM wave is subjected to FFT conversion, because some harmonic interchannel waves are arranged near the main peak of each subharmonic wave, the energy of each subharmonic wave is relatively dispersed, and the effective value of each subharmonic wave is not convenient to directly calculate. In order to calculate the total effective value near each subharmonic, the band-pass filter is used to extract the spectrum energy near each subharmonic, and then the total effective value RMS is calculated, which is complex.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides an equivalent calculation method of each sub-harmonic effective value of PWM, namely a sawtooth wave is constructed, and each sub-frequency spectrum effective value of the sawtooth wave is consistent with the PWM.

A PWM harmonic effective value calculation method is characterized in that a sawtooth wave is constructed according to a PWM wave.

The PWM wave is the result of a sawtooth carrier and a sine wave modulation.

The PWM wave includes a unipolar PWM wave or a bipolar PWM wave.

The steps of the unipolar PWM wave to generate the sawtooth wave are as follows:

A. calculating the amplitude and frequency of the unipolar PWM wave;

B. the sawtooth wave is constructed so that its frequency is the same as the carrier frequency of the unipolar PWM wave in a and its amplitude is 2 times the amplitude of the unipolar PWM wave in a.

C. Carrying out FFT operation on the sawtooth wave to obtain each harmonic peak value;

D. by dividing the peak value of each harmonic by

To obtain the effective value of each harmonic of the unipolar PWM wave.

The steps of the bipolar PWM wave to generate the sawtooth wave are as follows:

A. calculating the amplitude and frequency of the bipolar PWM wave;

B. the sawtooth wave is constructed to have the same frequency as the carrier frequency of the bipolar PWM wave in a and an amplitude 2 times the amplitude of the bipolar PWM wave in a.

C. Carrying out FFT operation on the sawtooth wave to obtain each harmonic peak value;

D. by dividing the peak value of each harmonic by

Thus obtaining the effective value of each harmonic wave of the bipolar PWM wave.

The slope of the sawtooth wave may be positive or negative.

Has the advantages that: the invention provides an equivalent calculation method for effective values of each harmonic of PWM (pulse-width modulation), which can be used for abandoning complicated processes of editing a PWM generator and calculating effective values in the field of electromagnetic compatibility simulation, and intuitively obtaining effective value results of each frequency point by utilizing the independence of each harmonic of sawtooth waves.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is a schematic diagram of unipolar PWM generation according to the present invention;

FIG. 2 is a schematic diagram of a unipolar PWM spectrum and effective values of harmonics according to the present invention;

FIG. 3 is a schematic diagram of unipolar PWM and equivalent positive slope sawtooth waveforms in accordance with the present invention;

FIG. 4 is a schematic diagram of unipolar PWM and equivalent negative slope sawtooth waveforms in accordance with the present invention;

FIG. 5 is a schematic frequency spectrum diagram of the unipolar PWM conversion of the present invention into a sawtooth waveform;

FIG. 6 is a schematic diagram of bipolar PWM generation according to the present invention;

FIG. 7 is a schematic diagram of the bipolar PWM spectrum and the effective values of the harmonics according to the present invention;

FIG. 8 is a schematic diagram of a bipolar PWM and an equivalent positive slope sawtooth;

FIG. 9 is a schematic diagram of a bipolar PWM and an equivalent negative slope sawtooth waveform of the present invention;

FIG. 10 is a schematic diagram of the spectrum of the bipolar PWM converted to sawtooth wave according to the present invention.

Detailed Description

To further explain the technical means and effects of the present invention adopted to achieve the predetermined object, the following detailed description of the embodiments, structures, features and effects according to the present invention will be given with reference to the accompanying drawings and preferred embodiments.