Variable switching frequency PWM control method suitable for single-phase MMC

Abstract

The present invention discloses a variable switching frequency PWM (Pulse Width Modulation) control method suitable for a single-phase MMC (modular multilevel converter). The method comprises the steps of: regulating the carrier frequency of a single-phase MMC, and regulating the switching period duration of the PWM pulses generated based on comparison of the carrier signals to control the switching frequency of the single-phase MMC driven by the PWM pulses and allow the switching frequency of the single-phase MMC to be changed with the change of the load current, wherein the switching frequency is continuously changed near the fixed switching frequency, a mean switching frequency is unchanged, the mean switching frequency is the same as the fixed switching frequency, when the load currentis zero, the switching frequency is the maximum, and when the load current is the maximum, the switching frequency is the minimum. For large-power application occasions for the MMC, the optimizationof the switching loss is taken as a target to control the switching frequency of the inverter system, on the premise of maintaining the mean switching frequency unchanged, the switching loss of the system is reduced; and moreover, relative to the PWM algorithm of the fixed switching frequency, the current harmonic spectral distribution is wider so as to effectively reduce the system conduction EMI(Electromagnetic Interference).

Description

Technical field [0001] The present invention relates to the field of power electronics technology, and more specifically, to a variable switching frequency pulse width modulation (Pulse Width Modulation, PWM) control method suitable for a single-phase modular multilevel converter (MMC). Background technique [0002] Compared with the traditional multi-level inverter, the modular multi-level inverter MMC shows many excellent performances. It adopts a modular structure, is easy to expand, has high reliability, and has good output waveform quality. It is suitable for high voltage Power applications. At present, modular multi-level inverters have obtained preliminary applications in the field of flexible direct current transmission, and have good prospects in high-voltage power electronic applications such as high-power motor inverters. [0003] The main goal of modular multi-level modulation technology is to form more level steps in the output voltage of the AC side to be closer to t...

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Problems solved by technology

[0005] In view of the defects of the prior art, the purpose of the present invention is to solve the problem that the existing MMC switching frequency is fixed, so that the current harmonics are distributed in a relatively narrow frequency spectrum, resulting in a relatively high EMI peak value of the system, and the MMC switching frequency is fixed without considering the load current. Factors, leading to technical problems with large switching losses

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