Four-switch buck-boost (FSBB) converter has the capability of bidirectional voltage step-down and step-up, which has attracted attentions in the fields of energy storage and solar energy. However, it faces the challenges in multimode operation and smooth mode transition, which rely on the complex mode detection scheme and cumbersome parameter tuning. In this article, the inherent limitation is analyzed through inconsistent frequency response and noncontinuous duty cycle operation region aspects. Then, a model predictive control (MPC) method characterized by tuning-free cost function is presented to achieve multimode control and smooth transition simultaneously. With the goal of ensuring the reference current tracking under inconsistent frequency response, a duty cycle and current ripples prediction are presented for all switching combinations. Then, a tuning-free cost function is utilized to overcome the gaps in noncontinuous duty cycle operation region and a smooth mode transition is achieved. Further, the robustness of the current tracking capability is analyzed mathematically considering the inductance variation and stray resistance variation. Finally, a comparative experiment proves the effectiveness. And it shows that the method can improve the efficiency by 0.4% compared with the traditional four-mode control. 

Model Predictive Control for Four-Switch Buck–Boost Converter Based on Tuning-Free Cost Function With Smooth Mode Transition

Four-switch buck-boost (FSBB) converter has the capability of bidirectional voltage step-down and step-up, which has attracted attentions in the fields of energy storage and solar energy. However, it faces the challenges in multimode operation and smooth mode transition, which rely on the complex mode detection scheme and cumbersome parameter tuning. In this article, the inherent limitation is analyzed through inconsistent frequency response and noncontinuous duty cycle operation region aspects. Then, a model predictive control (MPC) method characterized by tuning-free cost function is presented to achieve multimode control and smooth transition simultaneously. With the goal of ensuring the reference current tracking under inconsistent frequency response, a duty cycle and current ripples prediction are presented for all switching combinations. Then, a tuning-free cost function is utilized to overcome the gaps in noncontinuous duty cycle operation region and a smooth mode transition is achieved. Further, the robustness of the current tracking capability is analyzed mathematically considering the inductance variation and stray resistance variation. Finally, a comparative experiment proves the effectiveness. And it shows that the method can improve the efficiency by 0.4% compared with the traditional four-mode control.

The non-inverting buck-boost (NIBB) converter is a non-isolated converter with bidirectional step-up and step-down capabilities. To realize the continuous regulation of output voltage, four-mode modulation is preferred. However, there are various pulse position allocation strategies, and their differences are rarely discussed. In this article, four different pulse width modulation (PWM) methods are introduced. Then, their effects on the characteristics of inductor current are discussed, including average value, ripple value and root-mean-square (RMS) value. Analytical solutions are given and compared to guide the converter design and inspire future research. Finally, the analysis and comparison are verified on a 200V, 400W output prototype. Experimental results show that there is about 0.2% efficiency difference when using different modulation methods. 

Analysis and Comparison of Inductor Current Characteristics for Non-Inverting Buck-Boost Converter With Four-Mode Modulation

Four-switch buck-boost converter (FSBB) has received extensive attention in the fields of power battery test and energy storage because of its bidirectional buck and boost capabilities, which are suitable for wide-range voltage changes. However, due to its complex mode detection and disturbance brought by mode transition, it faces great challenge of operating mode selection and also has difficulty in achieving smooth mode transition. In this paper, a mode selection and transition strategy based on predictive control strategy is proposed, and the traditional three modes of FSBB are expanded to four modes, which reduces the sudden change of duty cycle resulted from control dead zones. The predictive control method is used to select the best working mode and ensure smooth transition of working mode. The simulation results demonstrate that the proposed method can successfully accomplish the aforementioned functions and exhibit strong dynamic performance when the input voltage and output are almost equal. 

Predictive Control Strategy for Four-switch Buck-Boost Converter with Mode Smooth Transition

Four-switch buck-boost converter (FSBB) has received extensive attention in the fields of power battery test and energy storage because of its bidirectional buck and boost capabilities, which are suitable for wide-range voltage changes. However, due to its complex mode detection and disturbance brought by mode transition, it faces great challenge of operating mode selection and also has difficulty in achieving smooth mode transition. In this paper, a mode selection and transition strategy based on predictive control strategy is proposed, and the traditional three modes of FSBB are expanded to four modes, which reduces the sudden change of duty cycle resulted from control dead zones. The predictive control method is used to select the best working mode and ensure smooth transition of working mode. The simulation results demonstrate that the proposed method can successfully accomplish the aforementioned functions and exhibit strong dynamic performance when the input voltage and output are almost equal.

The H-bridge buck–boost converter shows better efficiency compared to all other buck–boost converter variants due to the ability to work in buck and boost modes. The existence of dead-zone in voltage gain during mode transition due to the maximum and minimum duty limitations results in instability and oscillations in output voltage. This dead-zone is eliminated by overlapping the buck and boost gate signals, which results in efficiency decrement due to high switching loss. Using a common compensator in all the modes in the H-bridge buck–boost converter results in poor dynamic performance. In this article, dead-zone free control (DZFC) scheme with increased efficiency and improved dynamic performance is proposed to mitigate the dead-zone during mode transition. In the proposed DZFC scheme, dead-zone elimination is independent of the values of mode boundaries, which reduce the transition mode duration. The proposed DZFC scheme improves the efficiency during transition modes by reducing the switching loss, a generalized small-signal model valid for the buck, boost, and transition modes and a control design is proposed for improved dynamic performance. The proposed DZFC scheme is verified experimentally on a hardware H-bridge buck–boost converter prototype.

Akhilesh K

Papers

Dead-Zone Free Control Scheme for H-Bridge Buck–Boost Converter