Unified Discrete-time Modeling and Digital Control of Bidirectional Chopper Converter

Bidirectional DC/DC converter is widely used in battery charge/discharge systems. The traditional state space average analysis method is not accurate enough when digital control is adopted. The separate analysis of the circuit from charge and discharge modes and design two sets of controllers will evidently reduce reliability and increase complexity of the system. Based on the discrete time modelling method, this paper establishes a unified discrete time model for current reversible chopper circuit. Then based on bilinear transformation method, design digital PI controller that can be directly applied according to the frequency domain index. By utilizing a unified current controller, accurate, fast and stable constant current charging/discharging control and switch can be realized. Voltage controller is used to realize constant voltage charging control. Finally, the validity and accuracy of the unified discrete-time model, unified current control strategy and digital controller design method proposed in this paper are further verified by simulation and experiments.