A Decentralized And Cooperative Control Strategy For DC Microgrid

With the increasing energy crisis and environmental pollution, this paper concentrates on the energy management and power control of DC microgrid due to its advantage in the utilization of renewable energy resources (RES). However, the traditional centralized control relies heavily on communication since the distribution of most RES is scattered, and the communication failures may cause serious control error, therefore, a distributed and cooperative control strategy without communication is proposed for DC microgrid in this paper.A DC microgrid comprising multiple photovoltaic cells (PV), energy storage unit (ESU) and load is introduced in this paper, and it can operate in grid-tied or islanding mode according to different bus regulating units, besides, transition mechanisms between different operating states have been designed respectively for the local control of each PV, ESU, load and Utility Grid in order to achieve the modes transition of the whole microgrid, which finally ensure the power balance among PV, ESU and load. In addition, unlike the conventional constant voltage control, a power reduction control based on successive approximation theory is presented for PV to achieve off-maximum power point tracing (off-MPPT) control, namely, the PV output voltage is adjusted by the DC bus voltage to decrease the output power, so facility cost would be significantly saved and a smooth handover between off-MPPT and MPPT control can be achieved. What’s more, an adaptive and decentralized current sharing method based on state-of-charge (SoC) is proposed for ESUs to maintain the stability of dc bus voltage and achieve the storage balance among multiple ESUs simultaneously through reasonable current sharing, that is, the output current of each ESU is regulated by its SoC and bus voltage, which eliminates the dc bus voltage deviation, simultaneously guarantees the SoC of each ESU trends to be equal.The proposed strategy not only maintains the bus voltage and power balance in a cooperative way through the regulation of each micro-sources, but also solves the unbalance problem between ESUs, meanwhile, this method is suitable for DC microgrid with multiple PVs and ESUs since the communication is not necessary, which is benefit for the plug and in of micro-sources. Finally, some simulation models are built on Matlab/Simulink platform, and the performance of suggested solution is verified through a set of simulation experiments, the result turns out to be good and confirms our expectation.