ABSTRACT
In this, a comprehensive voltage control loop design for a dual active bridge (DAB) DC-DC converter is proposed using the sliding mode control (SMC), where the coefficients are formed to ensure both small signal and large signal stability of the system. The major objectives of the proposed SMC are to enhance the converter dynamics and attain a tight output voltage regulation under fast load fluctuations or during start-up. In addition, dynamic performance of the system is examined considering the steady state error and overshoot. The proposed control method is capable of achieving soft-switching operation by determining the effective duty phase displacement range. The simulation work is carried out using MATLAB/Simulink.
INTRODUCTION
In recent years, the DAB DC-DC converter [1], [2] has drawn much attention for high power applications, i.e. electric vehicle charger, energy storage system. It has the advantages of galvanic isolation, high efficiency and wide range output voltage. Moreover, the power inductor of the DAB converter can be integrated as the leakage inductor in the transformer [3], which leads to the reduction in cost and volume. Many researches have been conducted in the DAB converter, including the topological variations, control and system optimization [4]–[9]. Aiming at the optimization of the minimum conduction loss and copper loss, a set of closed-form expressions for the optimal control parameters are derived and implemented in [4] to facilitate the direct application to a given DAB converter. The paper further presents the properties of the proposed modulation scheme with respect to the switching loss. Moreover, a comprehensive triple-phase-shift control method is proposed in [9] to reduce the current stress and achieve soft switching, where all effective switching modes are investigated. In terms of the DAB converter control, it is fundamentally examined using different methods and models, to achieve the minimum conduction loss, low transformer ringing, low component current/voltage stress, extended soft-switching range and efficiency optimization over wide input/output voltage range [4], [9]–[12]. However, most of them are mainly focused on the power flow management and steady state performance of the DAB converter, which may have limited dynamic response performance. In most cases, PI compensators are adopted [13] as the controllers. However, they fail to achieve the desired performance under large parameter variations and load disturbances [14]. Another choice is to implement the sliding mode controllers on DAB converter for better dynamic performance. In [15], a SMC based control technique is proposed for modular DAB converters, which is aimed to balance and regulate the output voltage. However, it does not cover the details of synthesizing procedure among the control and power stages, and the system stability is not clear.