Modulation method for cascaded PWM (pulse-width modulation) rectifier

Abstract

The invention discloses a modulation method for a cascaded PWM (pulse-width modulation) rectifier. The modulation method for the cascaded PWM rectifier comprises the following steps of: extracting the modulation signal of each H bridge unit in real time; calculating to obtain the carrier wave phase updating value of a cascading unit; updating the carrier wave phase; and taking the updated value as the practical carrier wave signal of the unit. Because each unit load of the cascaded PWM rectifier can not be completely consistent, each H bridge modulation model can not be completely consistent according to the power equivalence principle, and therefore, the corresponding switching subharmonic can not be offset when a traditional carrier wave phase-shifting algorithm is adopted. On the basis of the novel modulation algorithm adopted by the modulation method disclosed by the invention, influence on net side current due to inconsistent modulation signals can be effectively lowered, and primary harmonic and the WTHD (weighted total harmonic distortion) value of the net side current are lowered.

Description

technical field [0001] The invention relates to a modulation method of a cascaded PWM rectifier, which belongs to the technical field of high voltage and high power power electronics. Background technique [0002] With the continuous advancement of smart grid construction, high-voltage and high-power power electronic devices have been more and more widely used in power systems. The voltage balance control technology is the key technology for the safe and reliable operation of the cascaded PWM rectifier. The overvoltage of a DC side capacitor caused by voltage imbalance will cause the device to malfunction or even be damaged. Therefore, in recent years, many literatures have proposed new solutions to the voltage imbalance problem. According to different modulation algorithms, these voltage balance control methods can be mainly divided into two categories: the first category is based on the selection of harmonic elimination technology, by changing the phase shift angle of eac...

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Problems solved by technology

[0004] However, no matter what kind of balance control method is used, they all have certain contradictions with the premise of the carrier phase-shift modulation algorithm. Therefore, when the number of cascaded units is N, 2Nf c The following carrier sideband harmonics will not be completely eliminated, causing an increase in the weighted total harmonic distortion index (WTHD) of the output voltage

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