Geometric Duty Cycle Trajectory-Based Smooth Mode Transition Strategy in Four-Switch Buck-Boost Converters

Four-Switch Buck-Boost (FSBB) converters are widely adopted in renewable energy systems and electric vehicles due to their wide voltage conversion range. However, conventional multi-mode control strategies face critical limitations: single-mode operation generates excessive current ripple, while dual-mode schemes exhibit discontinuous voltage gain during transition intervals, thereby degrading system stability. This paper proposes an enhanced three-mode control strategy. By optimizing geometric duty cycle trajectories in Buck-Boost mode, the proposed method eliminates voltage gain discontinuities and reduces the number of mode transitions. Theoretical analysis reveals reduced inductor current stress and suppressed output ripple. Experimental results validate seamless transitions between Buck, Boost and Buck-Boost modes, demonstrating improved stability and efficiency under dynamic operating conditions.