基于虚拟单位线路阻感比的改进解耦下垂控制策略研究

IMPROVED POWER DECOUPLED DROOP CONTROL STRATEGY BASED ON VIRTUAL UNIT IMPEDANCE RATIO

微电网中,传统下垂控制会引起功率耦合,并且线路阻抗不平衡会影响功率均分精确度,进而引起系统环流。该文在多台分布式单元(distributed generation,DG)并联运行基础上,提出基于虚拟单位线路阻感比的改进功率解耦控制方法。通过加入虚拟阻抗,使发电单元等效系统阻抗为单位阻感比(R/X=1或-1)且各发电单元等效阻抗一致,该控制策略不仅可使发电单元输出功率得到解耦,增强系统稳定性,而且还可解决传统功率解耦控制下实际输出功率不能均分的问题。对比等效阻感比为1或-1的策略,两种控制会对系统产生不同的影响。此外,该方法可提高电压控制精度,且适用于任意线路阻感比的微电网系统。仿真和实验均可验证控制策略的可行性和有效性。

In the microgrid, the conventional droop control can produce power cou）ling, and the inconsistent line impedance from inverter will affect the power sharing accuracy, thereby resulting in circulation current of system. The improved decoupled power control strategy was proposed based on virtual unit impedance ratio for the system consisted of multiple distributed generation （DG） units operating in parallel. The control strategy not only couht decouple the outpnt power of the power generation unit and enhance system stability by adding the virtual impedance so that the equivalent system impedance of the power unit was the unit impedance ratio （R/X=1 or-1 ） and the equivalent impedance of each power unit was uniform, but also could solve the problem which the actual output power could not be equally divided under the traditional power decoupling control. In contrast to the strategy with an equivalent resistance ratio of I or - 1, the two controls would have different effects on the system. Furthermore, the method could improve control precision of the voltage, and can be applied to microgrid systems with any ratio of line impedance The simulation and experiment results verify the validity and feasibility of the proposed control strategy.