改善独立微网频率动态特性的虚拟同步发电机模型预测控制

随着分布式能源在独立微网内的渗透率不断升高,系统惯量水平逐渐降低。虚拟同步发电机(VSG)由于能够模拟惯量,对系统频率的动态变化具有一定的阻尼作用,已逐步应用于微网中。针对新能源出力波动或负荷投切等导致微网内瞬时功率失衡,进而引起系统频率振荡甚至超过安全约束的问题,提出了基于模型预测控制(MPC)的VSG控制方法。建立了以频率变化率为约束,以频率偏差和VSG出力加权值为优化目标的预测模型。设计了根据系统频率及VSG输出电压—电流等物理量,利用预测模型计算所需功率增量,并据此改变VSG输入功率设定值的整体控制策略。同时,给出了预测模型的求解算法,并对算法收敛性进行分析,为关键参数的选取提供了依据。通过独立微网内负荷投切和分布式电源出力波动等典型工况下的仿真,验证了所提控制策略的正确性和有效性。

Model Predictive Control of Virtual Synchronous Generator to Improve Dynamic Characteristic of Frequency for Isolated Microgrid

With the continuous increasing penetration of distributed energy in isolated microgrid, the inertia of system is getting lower gradually. Virtual synchronous generator(VSG), which can simulate the inertia of synchronous generator and plays a vital role in damping dynamic frequency variations, has been gradually applied in microgrid. Frequency of island microgrid will oscillate severely and even may exceed its safety constraints when the power imbalance caused by fluctuations of renewable energy output or loads switching happens. To deal with these problems, a virtual synchronous generator control method based on model predictive control is proposed. Firstly, the predictive model, which aims at optimizing the weighted combination of frequency deviation and VSG output with frequency change rate as the constraint is established. Then, the systematic control strategy is designed according to physical quantities, such as frequency, VSG output voltage and current, the increment of active power needed is calculated for changing the power reference of VSG. Meanwhile, the solution of the predictive model is given, and the convergence of the algorithm is analyzed, which provides the basis for selecting key parameters. The correctness and effectiveness of the proposed control strategy are verified by the simulation results of two typical cases.