考虑负荷动态变化的孤岛微电网二次频率控制

Secondary frequency control of isolated microgrid with consideration of dynamic varying loads

传统虚拟同步发电机(virtual synchronous generator,VSG)二次调频策略未考虑负荷动态变化时频率偏差持续变化引发的积分器不断累加,易导致VSG调频效果不佳甚至引发频率振荡问题。针对此问题,提出了一种基于负荷扰动模态辨识和VSG自适应调整的孤岛微电网二次频率控制策略。首先,分析了传统VSG二次调频策略在负荷动态变化场景中存在的问题。然后,利用负荷功率特征数据实时辨识负荷扰动模态;当判定负荷扰动属动态变化模态后,以一二次调频阈值与有功变化阈值为边界,根据系统频率偏移量自适应调整VSG参数与虚拟调速器结构,实施微电网频率的跟踪调节。之后,通过建立小信号模型分析了积分器引入及VSG参数自适应调整情况下的系统稳定性。最后,仿真测试结果验证了所提频率控制策略的可行性。在相同条件下,相比于几种已有策略,所提策略将微电网二次频率波动范围限制在0.0173 Hz以内,在减小频率偏移量方面更具优势。

In the scenario with dynamic varying loads,for the traditional VSG secondary frequency modulation strategy,the integrator continuously accumulates due to the continuous change of frequency deviation,which may lead to poor frequency adjustment effect and even frequency oscillation.For improvement,a secondary frequency modulation method of isolated microgrid,which based on the identification of load disturbance modes and adaptive adjustment of VSG,is proposed in this paper.Firstly,the issues in the traditional VSG secondary frequency regulation strategy of dynamic varying loads are analyzed.Then,the power characteristic data is used to discern the modes of load disturbances in real time.When the secondary frequency modulation is requisite for the microgrid,and the load disturbance is classified the mode of dynamic change,the parameters and virtual governor structure of VSG are changed by an adaptive adjustment.The adjustment is predicated on the deviations of frequency and bounded by the thresholds of secondary frequency regulation and active power change,thus enabling the frequency tracking in the microgrid.Further,a small signal model is constructed to evaluate the implications on system stability prompted by the incorporation of an integrator and the flexible adjustment of VSG parameters.Finally,the feasibility of the proposed frequency modulation strategy is verified by the results of simulation testing.When compared with the other existing strategies under the same conditions,the proposed strategy limits the range of secondary frequency fluctuation of microgrid within 0.0173 Hz,which exhibits significant merits in decreasing the magnitude of frequency offsets.