当逆变型分布式电源(distributed generation,DG)以T接的方式接入高压配电网时,仅依靠提高电流纵联差动保护的整定值可能导致保护拒动。首先分析了逆变型DG的接入对电流纵联差动保护带来的影响。然后,利用线路母线电压互感器的信息,提出了以线路两端正序补偿电压的差值作为辅助判据的解决方案,并利用正序补偿电压和正序差动电流的相位关系消除动作死区。该方案简单易行,能够实现全线速动,并且不受DG容量、过渡电阻及两侧系统电势相角差等因素的影响。最后,基于PSCAD仿真平台搭建了含逆变型DG的110 k V高压配电网模型,对传统的电流纵差保护及改进的纵差保护进行了对比,验证了改进后保护方案的可靠性和有效性。
In this paper, the dynamic behavior analysis of the electromechanical coupling characteristics of a flywheel energy storage system (FESS) with a permanent magnet (PM) brushless direct-current (DC) motor (BLDCM) is studied. The Hopf bifurcation theory and nonlinear methods are used to investigate the generation process and mechanism of the coupled dynamic behavior for the average current controlled FESS in the charging mode. First, the universal nonlinear dynamic model of the FESS based on the BLDCM is derived. Then, for a 0.01 kWh/1.6 kW FESS platform in the Key Laboratory of the Smart Grid at Tianjin University, the phase trajectory of the FESS from a stable state towards chaos is presented using numerical and stroboscopic methods, and all dynamic behaviors of the system in this process are captured. The characteristics of the low-frequency oscillation and the mechanism of the Hopf bifurcation are investigated based on the Routh stability criterion and nonlinear dynamic theory. It is shown that the Hopf bifurcation is directly due to the loss of control over the inductor current, which is caused by the system control parameters exceeding certain ranges. This coupling nonlinear process of the FESS affects the stability of the motor running and the efficiency of energy transfer. In this paper, we investigate into the effects of control parameter change on the stability and the stability regions of these parameters based on the averaged-model approach. Furthermore, the effect of the quantization error in the digital control system is considered to modify the stability regions of the control parameters. Finally, these theoretical results are verified through platform experiments.
电压不平衡和电压暂降是微电网中突出的电压质量问题。针对含单公共连接点(point of common coupling,PCC)和多PCC的微电网,提出一种基于下垂控制的面向多分布式电源(distributed generation,DG)的分区电压质量控制(zonal-voltage quality control,ZVQC)策略,将二次电压控制的思想引入DG的本地控制,不仅改善了微电网正常运行时PCC的电压质量,还可在微电网故障导致电压平衡跌落和不平衡跌落时能够支撑PCC电压并改善其不对称度,实现微电网区域及全网电压质量改善。此外,给出微电网ZVQC的原则,讨论DG附加容量的规划方法,并给出ZVQC的实施方案。最后在PSCAD/EMTDC中建立IEEE P1547.4典型微电网拓扑,仿真验证了所提方案的有效性和可行性。
