A Pulse Width Modulation Method for Selective Harmonic Elimination without Waveform Symmetry in Full Period

Abstract

The invention relates to a selective harmonic elimination pulse width modulation method with no waveform symmetry characteristics in the full cycle. The method includes the following steps: generating an ideal waveform output by an inverter and performing Fourier analysis on it, and determining the direct current of the ideal waveform. components and Fourier coefficients; the nonlinear equations obtained by making the bipolar SHEPWM wave and the fundamental wave of the ideal waveform output by the inverter and the Fourier coefficients and DC components of each controlled harmonic are equal, using the nonlinear A set of switching angles can be obtained by solving the equations; by using the obtained switching angles to control the on and off of the inverter power device, the DC component, fundamental wave and each controlled harmonic amplitude of the inverter output signal can be realized. Precise control of phase. The present invention cancels the symmetrical constraints of the phase voltage output waveform of the inverter being 1 / 2 cycle or 1 / 4 cycle, and precisely controls the amplitude and phase of the inverter output waveform DC component, fundamental wave and each controlled harmonic, A waveform meeting the output component requirements can be obtained.

Description

technical field [0001] The invention belongs to the technical field of inverters for power electronic equipment, and specifically relates to a selective harmonic elimination pulse width modulation (Selective Harmonic Eliminated Pulse Width Modulation, SHEPWM) method with respect to the full-cycle non-waveform symmetry feature. Background technique [0002] With the development of power electronic technology, inverters have been widely used in various power electronic devices. The PWM control method is a key technology in inverter research, which directly determines whether the power conversion target can be realized, and has a direct and important impact on the output voltage and current waveform quality, the reduction of system switching loss and the improvement of system efficiency. . [0003] Today, with the rapid development of power electronics technology, various PWM control strategies applied to inverters are emerging. In summary, they can be divided into three categ...

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Problems solved by technology

[0005] Theoretically, the inverter output waveform analyzed by the SHEPWM method can be arbitrary, but in practice, in order to control the harmonics and simplify the equations, it is usually assumed that the inverter phase voltage output waveform has a 1 / 4 cycle symmetry, which A limited condition simplifies the establishment method and solution process of nonlinear equations, but at the same time it also limits the applicable space of the solution, for example, the control of the even harmonic amplitude and the phase angle of each harmonic cannot be realized

Later, the researchers relaxed the symmetry constraints, and took the inverter voltage output waveform as 1 / 2 cycle symmetry, and obtained a wider solution space than that under the condition of 1 / 4 cycle symmetry, but only realized the phase of odd harmonics. Angle control, unable to control even harmonic amplitude and phase angle

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