Abstract
In order to improve stability of the microgrid operation connected to distribute network, the power flow fluctuations are smoothed. In this paper, a kind of flexible interconnection interface was studied in this paper, based on voltage source converter low voltage direct current(VSC-LVDC) containing energy storage. According to the mathematical model of VSC-LVDC and battery, a dual vector decoupling three-loop control strategy consisted of stages charging is proposed, and the battery charging and discharging switch control is offered, for charging and discharging of the energy storage, the bidirectional power transmission and suppressing power fluctuations. A simulation model is built that microgrid connected to distribute network using the flexible interconnection interface, and the conditions of power fluctuation, battery charging and discharging switch and the short-circuit fault at the microgrid side AC bus are simulated. The simulation results show that the control strategy effectively suppresses the power fluctuations of point of common coupling(PCC), guarantee the stability of the power flow.
Highlights
a kind of flexible interconnection interface was studied in this paper
a dual vector decoupling three⁃loop control strategy consisted of stages charging is proposed
The simulation results show that the control strategy effectively suppresses the power fluctuations of point
Summary
柔性直流输电 ( voltage source converter⁃low voltage direct current,VSC⁃LVDC) 技术是一种新型的 输电技术,具有功率双向传输,可向无源网络供电, 易于构成多端直流系统等优点,在对输送的有功功 率进行快速控制的同时还能动态补偿无功功率,稳 定交流母线电压,提高故障穿越能力,非常适用于微 网并网[11⁃14] 。 因此将 VSC⁃LVDC 与储能装置结 合 用于微网并网,既实现平滑 PCC 点处的功率波动, 又维持了配网的功率潮流分布,还可提高故障穿越 能力[15⁃17] 。 柔性并网接口系统由配网侧换流器( VSC1) 、微 网侧换流器( VSC2) 和储能单元组成,如图 1 所示, 换流器采用三相两电平结构。 图中,Ls1,s2 为滤波电 感,us1abc 为配网三相交流电压,is1abc 为配网侧三相交 流电流,uc1abc 为换流器 VSC1 交流侧三相电压,us2abc 为微网三相交流电压,is2abc 为微网侧三相交流电流, uc2abc 为换流器 VSC2 交流侧三相电压,uB 为蓄电池 组端电压,iB 为流经蓄电池的电流,SOC 为储能单元 荷电状态( state of charge,SOC) 。 系统工作时,通过 控制 VSC1 可以实现配网 PCC 点处的功率大小与方 向的恒定,控制 VSC2 实现储能单元充放电与功率 传输,平抑微网功率波动,维持微网内的功率平衡。 且不饱和,两侧 VSC 参数相同,且控制独立,因此两 侧换流器可以看成 2 个独立且相似的系统,可只对 一侧系统进行分析,图 2 为配网侧换流器具体结构, 图中,udc[1] 为 VSC1 直流侧电压,idc 为 VSC1 直流侧电 流,ic 为流经电容的电流,id 为流经直流母线的 电流。 对(1) 式进行 Clark 和 Park 变换,可得到 dq 坐标系
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