Efficiency Optimization of Four-Switch Buck-Boost Converter Using Frequency-Domain Analysis

A bidirectional four-switch buck-boost (FSBB) converter offers more control variables than a classical buck-boost converter and can thus achieve higher power efficiencies through appropriate control. Traditionally, efficiency is optimized by reducing the inductor current rms value (or conduction loss) obtained through time-domain analysis. However, it is extremely difficult to use this time-domain approach to include converter switching losses in the efficiency optimization for all possible modulation modes. To solve this problem, this article proposes a frequency-domain analysis to estimate switching losses and establish a comprehensive loss model that allows for the efficiency to be optimized using a Gaussian quantum-behaved particle swarm optimization (GQPSO) algorithm. The switching frequency is then used as an additional optimization variable to improve the efficiency over a much wider range of operating conditions. The proposed method is verified experimentally, using 600 and 1500 W rated laboratory prototypes, and compared with existing methods. Results demonstrate the effectiveness of the proposed technique in increasing converter efficiency over the whole range of load conditions.