The Soft Start Controller based on Duty Cycle Presetting on Low Cost Analogue Devices

The linear compensator is a widely used controller with the merits of easy implementation and design in power converters. The controller could make a good compromise in the system stability and dynamic transient. However, during the startup in the bidirectional buck/boost converter, the traditional linear controller usually generate large inrush current due to its saturation characteristics. In this paper, a startup method with duty cycle presetting circuit for bidirectional buck/boost converters is proposed. The proposed controller reuses the linear compensator to build the duty-cycle closed loop, which eliminates the saturation before converter startup. The duty cycle presetting reduces the hard current inrush and the startup transient is fast. The method is easy to implement on the low cost analog devices with very compact frame, meanwhile provides significant improved startup performance. It is suitable for bidirectional applications such as battery charging and phase-shedding occasions. The simulations and experiments have proved the improvement brought by the new controller.