直流微电网二次调压系统设计

母线电压恒定是直流微电网正常运行的关键。针对直流微电网下垂调压方式不能实现无差调节,双闭环调压方式不能实现各微源根据自身容量灵活调节出力、效率低的问题,整合两种调压方式设计了直流微电网二次调压系统。当微电网功率不平衡导致母线电压偏离额定值时,首先由下垂调压系统进行一次调压,将直流母线电压调节至稳定工作区;然后根据微网工作模式,孤岛模式下由钒电池(Vanadium Redox Battery,VRB)系统与锂电池储能系统配合进行二次调压,并网模式下由钒电池系统与并网变换器配合进行二次调压,将母线电压进一步调节至额定值;此时,若微网再次出现较大功率波动,系统重新回到一次下垂调压,重复上述过程。一次调压、二次调压协调配合,灵活切换,实现母线电压高效调节。该调压系统在保留下垂控制高效、灵活优点的同时,能够实现母线电压无差调节,提高了微网运行效率。仿真及实验验证了所提出调压系统的有效性和可行性。

Design of secondary voltage regulation system of DC Microgrid

The bus voltage stability is the key to the normal operation of DC micro-grid.In a DC microgrid adopting droop control,zero-error regulation of DC bus voltage can't be achieved.When adopting double closed loop control,micro-sources cant adjust their output power according to their own capacity flexibly,thus leading to the low efficiency of the microgrid.To deal with this problem,a secondary voltage regulation system was designed through integrating these control methods above.When the DC bus voltage deviates from the rated value,the primary voltage regulation is conducted by the droop-control system firstly.The DC bus voltage is regulated to the stable working range.Then,the secondary voltage regulation is conducted by the vanadium redox battery (VRB) storage system,with the cooperation of the lithium battery in island mode or the grid-connecting converter in grid-connected mode.The DC bus voltage is regulated to the rated value.If a large power fluctuation occurs in this time,the DC micro-grid returns to primary voltage regulation again.The processes above are repeated.The primary and secondary voltage regulations cooperate with each other,switch flexibly and achieve the efficient regulation of the bus voltage.The proposed voltage regulation system realizes the zero-error regulation of DC bus voltage,while retaining the high efficiency and flexibility advantages of droop control.Thus,the efficiency of micro-grid is improved.The validity and feasibility of the proposed voltage regulation system were verified by simulations and experiments.