Research on supraharmonic emission characteristics and influence factors of two-stage single-phase frequency converter

Abstract

PWM converters, switching power supply, and other power electronic equipment inject a large quantity of supraharmonics into the power distribution network when they are connected to the network on a large scale, resulting in more and more serious power quality problems. In this paper, a two-stage single-phase frequency converter is selected and studied in depth about its supraharmonic emission characteristics and influence factors. First, a Fourier series equation of the grid side current of the frequency converter is derived using switching function method, which shows great simplicity and convenience in the theoretical analysis. The equation shows that the grid side current supraharmonics include odd supraharmonics and sideband supraharmonics related to the input and output frequencies of the frequency converter. Then, the supraharmonic ratio is calculated and it can be found that the ratio is associated with the output power of the frequency converter and the capacitance of the filter capacitor. The existence of the power system impedance also affects the supraharmonic ratio. Finally, the correctness of the theoretical analysis is verified by simulations on Matlab. An experiment of actual equipment was also carried out to prove theoretical results, which measured the conducted emission of a compact fluorescent lamp electronic ballast with load. The study will provide a reference for quantification, detection, and monitoring of supraharmonics in the power distribution network.

Keywords

• Single-phase frequency converter
• Switching function
• Supraharmonic
• Emission characteristic
• Harmonic ratio