Abstract: Reducing the DC bus capacitor of variable frequency controller is an effective means for cost reduction and increasing power density, which is also of great significance for low carbon, environmental protection, energy saving and emission reduction. Currently, many air conditioning companies are trying to reduce the DC bus capacitor. However, this would enlarge DC bus voltage fluctuation, which further deteriorates the life and reliability of system. To solve this problem, deeply analyzing the mechanism of DC bus voltage fluctuation for air conditioner’s variable frequency controller. Based on the energy change of both input side’s PFC and output side’s compressor, and the principle of instantaneous energy balance, the mechanism of DC bus voltage fluctuation is proposed, which provides effective theoretical basis for research and realization of DC bus voltage fluctuation reduction.

Key words: DC bus voltage fluctuation, Variable frequency controller, Air conditioner