Step wave pulse width modulation method based on nonlinear programming

Abstract

The invention relates to a step wave pulse width modulation method based on nonlinear programming. The step wave pulse width modulation method comprises the following steps of: correspondingly calculating the number of sub-modules in a part to be added or cut according to increase or decrease of a modulation degree so as to reach required alternating current voltage output; secondly, establishing a nonlinear programming mathematical model of the modulation method with a goal that the approximate error of a fundamental wave component in the step wave outputted by a current converter is minimum relative to a given modulation wave on the basis of a theoretically output step waveform Fourier transform result by selecting an initial value of a triggering angle; finally obtaining the solution of the triggering angle under a corresponding level number and modulation degree. The step wave pulse width modulation method based on the nonlinear programming, disclosed by the invention, overcomes defects of a specific sub-harmonic elimination method that calculation amount is huge and on-line real-time calculation cannot be carried out. A switch device is only switched on and off once in one cyclic wave, the remarkable advantage of small switching loss is achieved. The step wave pulse width modulation method based on the nonlinear programming, disclosed by the invention, has better expandability, can theoretically finish trigger impulse control tasks of voltage source current converters with any quantity of levels, has stronger transportability, is suitable for modularized multi-level converters and is also suitable for cascaded H-shaped bridge type voltage source current converters with a large quantity of levels.

Description

technical field [0001] The invention belongs to the field of high-voltage direct current transmission and FACTS based on a voltage source converter (Voltage Source Converter, VSC), and specifically relates to a modular multilevel converter (Modular Multilevel Converter, MMC) or a cascaded H-bridge voltage source converter. Direct Pulse Width Modulation (DPWM) technology of converters, especially a step wave pulse width modulation method based on nonlinear programming. Background technique [0002] In 1990, Boon-Teck Ooi and others from McGill University in Canada first proposed the concept of DC transmission using a voltage source converter (Voltage Source Converter, VSC) and PWM modulation technology based on fully controlled power switching devices. This new generation of DC transmission technology based on voltage source converters, turn-off devices and pulse width modulation (PWM) technology is officially called VSC-HVDC by CIGRE and IEEE, the authoritative academic orga...

AI Technical Summary

Problems solved by technology

Its disadvantage is that the calculation of the trigger angle is based on the Fourier series of the steady-state waveform, which is obtained by solving a series of transcendental equations

Therefore, for higher level converters (such as MMC for DC transmission and reactive power compensation), the order of the corresponding nonlinear transcendental equations is higher than the number of levels, and sometimes it is almost impossible to solve

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