DC-coupled microgrids are simple as they do not require any synchronization when integrating different distributed energy generations. However, the control and energy management strategy between the renewable energy sources and the energy storages under different operating modes is a challenging task. In this paper, a new energy management scheme is proposed for the grid connected hybrid energy storage with the battery and the supercapacitor under different operating modes. The main advantages of the proposed energy management scheme are effective power sharing between the different energy storage systems, faster DC link voltage regulation to generation and load disturbances, dynamic power sharing between the battery and the grid based on the battery state of charge, reduced rate of charge/discharge of battery current during steady state and transient power fluctuations, improved power quality features in AC grid and seamless mode transitions. The effectiveness of the proposed method is validated by both simulation and experimental studies.

A new zero voltage switching (ZVS) full-bridge DC-DC converter for battery charging is proposed in this paper. The proposed isolated DC-DC converter is used for the DC-DC conversion stage of electric vehicle charger. The primary switches in DC-DC converter turn-on at zero voltage over the battery charging range with the help of passive auxiliary circuit. The diode clamping circuit on the primary side minimizes the severity of voltage spikes across the secondary rectifier diodes which are commonly present in conventional full-bridge DC-DC converters. The main switches are controlled with asymmetrical pulse width modulation (APWM) technique resulting in higher efficiency. APWM reduces the current stress of the main switches and the circulating losses compared to the conventional phase-shift modulation (PSM) method by controlling the auxiliary inductor current over the entire operating range of the proposed converter. The steady-state analysis of auxiliary circuit and its design considerations are discussed in detail. A 100-kHz, 1.2-kW full-bridge DC-DC converter prototype is developed. The experimental results are presented to validate the analysis and efficiency of the proposed converter.

This paper presents an event-triggered model predictive control (ET-MPC) method for power converters. In the proposed method, the MPC scheme is triggered only when the state of the converter exceeds a preset threshold; otherwise, the MPC scheme is suspended and the control signal is held as constant. Therefore, compared to the conventional MPC with finite control set (FCS-MPC), the ET-MPC method has the advantages of less computational burden and less switching actions which contribute to lower switching losses, while ensuring satisfactory regulation performance. A buck converter prototype is adopted to validate the performance of ET-MPC. The results from the comparison with FCS-MPC demonstrate the effectiveness of the proposed ET-MPC method.

This paper presents a simple and effective deadbeat-based method for hybrid energy storage systems (HESSs), including batteries and supercapacitors, in DC microgrids. Inheriting from the nature of deadbeat control strategies, the proposed method can generate the optimal duty ratio in one control cycle, so that it can respond faster to the disturbance than various proportional-integral-based methods in previous works. With an appropriate reference assignment based on the characteristics of batteries and supercapacitors, this method can compensate the transient and steady-state power mismatches in DC microgrids while maintaining an excellent DC bus voltage regulation. Specifically, the high power density feature of the supercapacitor is fully utilized by the proposed method, and the burden on the battery can be relieved for a longer lifespan. A current observer is employed in the proposed method to eliminate the requirement of PV and load current sensors to reduce the system cost. A laboratorial setup of a DC microgrid including the HESS and photovoltaic (PV) emulator is built to validate the effectiveness of the proposed deadbeat-based method under various varying conditions in load power consumption, PV power generation and bus voltage reference. The performance of the proposed method is compared with that of the previous works to show its superiority in dynamic and steady-state responses

This paper proposes a hybrid control method based on model predictive control (MPC) and iterative learning control (ILC) for the hybrid energy storage system (HESS) in the application of islanded microgrid with photovoltaic (PV) generation. The hybrid method helps to deal with the sudden change in generation and load power demands. MPC aims to regulate the current of the battery and the supercapacitor (SC) to track the dynamic current references. An improved quadratic programming algorithm is proposed to reduce the iterations in online optimization. To compensate for the steady-state error caused by the power loss in the power electronic devices, a controller based on ILC is designed to correct the dynamic current references of HESS. Simulation results are used to verify the proposed algorithm. Validations using hardware experimental results substantiate the improved performance of the proposed control method in terms of reduced voltage regulations.

This paper proposes a new three-level DC/DC converter configuration for hybrid energy storage system (HESS) in DC microgrids. It effectively integrates different energy storage devices (ESDs), such as battery and ultracapacitor (UC), using one converter with bidirectional power flow. Furthermore, the proposed converter provides the flexibility of independent regulation of different ESDs with significantly reduced inductor current ripple due to the availability of three voltage levels. The voltage ratings of power semiconductors employed in this converter are also reduced. To further enhance the performance of HESS, a constant switching frequency based model predictive current control is employed for HESS regulation. The design guideline and operating principle of the proposed converter are discussed. Experimental results are presented to verify the efficacy of the proposed converter and control.