基于虚拟同步电机的微电网二次调频技术

Secondary Frequency Regulation Technique Based on Virtual Synchronous Generator for Microgrid

传统虚拟同步发电机属于一次调频技术,在负载功率波动后,频率无法恢复至额定值,严重时影响微电网系统的安全性,为消除大幅度负载波动时频率稳态误差,提出了一种基于虚拟同步电机技术的二次调频方案。首先,将频率外环计算得到的频率偏差通过PI控制器自动产生前馈功率,对频率—有功下垂控制器输出的参考机械功率进行补偿,并将它们共同作为同步电机机械方程的输入;其次,参考电力系统二次调频的机理与应用场合,定义了频率偏差界限的概念,仅当负载扰动较大且引起超过界限的频率偏差时,执行二次调频算法,消除稳态误差,不影响系统在低负载扰动时的动态性能。仿真和实验验证了所提的二次调频技术的有效性。

Traditional virtual synchronous generator(VSG)is a primary frequency regulation technique. After load power changes,the frequency of microgrid cannot return to the rated level,influencing the safety of the microgrid in a severe condition. In order to avoid steady-state errors under large load fluctuations,a secondary frequency regulation technique based on VSG was proposed for microgrid. First,the frequency error calculated in the outer control loop was used to automatically generate the feedforward power by the use of a PI controller,which is used to compensate the output mechanical power of the frequency-active power(f —P)droop controller. The sum of the two parts of power was treated as the input of the mechanical equation of the synchronous generator. Then,referring to the mechanism and applications of the secondary frequency regulation techniques used in power systems,a concept of frequency error threshold was defined. Only when the load power disturbances are large enough to cause a large frequency error,the secondary frequency regulation algorithms are executed. In this case,the steady-state errors will be avoided without influencing the system dynamics in the low load disturbance situations. Both simulation and experiment were carried out to verify the effectiveness of the proposed secondary frequency regulation method.