Complete-period selective harmonic elimination pulse width modulation method without waveform symmetry characteristics

Abstract

The invention relates to a complete-period selective harmonic elimination pulse width modulation method without waveform symmetry characteristics. The method includes the following steps: generating an ideal inverter output waveform, carrying out Fourier analysis on the ideal inverter output waveform, and determining a DC component and a Fourier coefficient of the ideal waveform; making fundamental waves of a bipolarity SHEPWM wave and the ideal inverter output waveform be equal to the Fourier coefficients and the DC components of controlled harmonics to obtain a nonlinear equation set, and carrying out solution by using the nonlinear equation set to obtain a group of switch angles; and controlling the on-off of an inverter power device by the obtained switch angles so as to realize accurate control of the DC component and the fundamental wave of an inverter output signal, and the amplitudes and the phases of the controlled harmonics. According to the method provided by the invention, the 1 / 2 period or 1 / 4 period cycle symmetry constraints of the inverter voltage output waveform, the DC component and the fundamental wave of the inverter output waveform and the amplitudes and the phases of the controlled harmonics are accurately controlled to obtain waveforms meeting the requirements of output components.

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 a full cycle without waveform symmetry. 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 goal can be achieved, and has a direct and important impact on the output voltage, current waveform quality, reduction of system switching losses, and improvement of system efficiency. . [0003] With the rapid development of power electronics technology today, various PWM control strategies applied to inverters continue to emerge. In summary, they can be divided into three main categories: (1) Carrier Pulse...

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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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