Abstract
Currently, high-performance power conversion requirements are of increasing interest in microgrid applications. In fact, isolated bidirectional dc-dc converters are widely used in modern dc distribution systems. The dual active bridge (DAB) dc-dc converter is identified as one of the most promising converter topology for the mentioned applications, due to its benefits of high power density, electrical isolation, bidirectional power flow, zero-voltage switching, and symmetrical structure. This study presents a power management control scheme in order to ensure the power balance of a dc microgrid in stand-alone operation, where the renewable energy source (RES) and the battery energy storage (BES) unit are interfaced by DAB converters. The power management algorithm, as introduced in this work, selects the proper operation of the RES system and BES system, based on load/generation power and state-of-charge of the battery conditions. Moreover, a nonlinear robust control strategy is proposed when the DAB converters are in voltage-mode-control in order to enhance the dynamic performance and robustness of the common dc-bus voltage, in addition to overcoming the instability problems that are caused by constant power loads and the dynamic interactions of power electronic converters. The simulation platform is developed in MATLAB/Simulink, where a photovoltaic system and battery system are selected as the typical RES and BES, respectively. Assessments on the performance of the proposed control scheme are conducted. Comparisons with the other control method are also provided.
Highlights
The dual active brigde dc-dc converter is used in order to interface the dc bus with distributed energy resource (DER) and battery energy storage system (BESS)
In the proposed power management strategy, the system can seamlessly switch between the battery discharging mode, battery charging mode, and battery standby mode in order to ensure the power balance in the dc microgrid under study
Since the SoC of the battery is considered in the power management algorithm, the BESS can intelligently switch its control algorithm based on its SoC and the system information without the communication involved
Summary
Power electronic systems have been considered to be a solution for high efficiency power conversion systems, such as renewable power integration, energy storage interfaces, solid-state transformer, electric vehicles, and microgrids [1,2,3,4,5,6]. There are in total four degrees-of-freedom (DoF) to control the power flow of the DAB converter Such DoF are composed of two internal phase-shift, corresponding to the primary bridge (D1 ) and secondary bridge (D2 ), respectively, an external phaseshift between two ac voltages (φ) and the switching frequency ( f s ). This study addresses the operation and control of a dc microgrid in stand-alone operation, which is comprised of a PV generation system and a battery energy storage system (BESS), which are enabled with the common dc bus through DAB converters. An explanation to control the power flow in DAB dcdc converter under SPS modulation scheme and the proposed power management control is introduced.
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