能量约束下电力电子并网装备的最优频率控制

大规模新能源并网导致现代电力系统的旋转惯量相对减少,频率动态特性变差。为支撑系统频率,通常要求新能源发电装备具备一定的惯量模拟或一次调频等附加控制功能,但目前在新能源的最优频率支撑方面研究较少。文中以最优控制为切入点,初步探讨了当参与调频的新能源存在能量约束时,作为并网接口的电力电子装备的最优功率支撑轨迹以及近似的最优控制结构。首先,从理论上推导并给出了多机系统的频率共模分量。该共模分量主导了电网的频率跌落特性。然后,基于高斯伪谱法研究了能量约束下电力电子装备在系统频率跌落时的最优支撑轨迹。最后,探索了电力电子并网装备支撑电网频率的最优反馈控制结构,指出虚拟惯量控制加下垂控制近似于最优的控制结构,且在可调用的能量较小时单独使用虚拟惯量控制优于下垂控制。仿真验证了理论分析和所讨论的频率最优控制结构的合理性。

Optimal Frequency Control of Grid-connected Power Electronic Devices with Energy Constraints

With the connection of large-scale renewable energy sources, the rotational inertia of modern power system decreases, and the dynamic characteristics of frequency are deteriorating. In order to support the system frequency, the power generation devices of renewable energy sources are usually required to have additional control functions, such as inertial simulation or primary frequency regulation. However, there is little research on the optimal frequency support of renewable energy sources. Based on the optimal control, this paper discusses the optimal power support trajectory and approximate optimal control structure of power electronic devices as grid-connected interfaces, when there are energy constraints on the renewable energy sources participating in frequency regulation. Firstly, the common-mode component of frequency for multi-machine system is deduced,which dominates the frequency drop characteristics of power grid. Secondly, based on the Gauss pseudospectral method, this paper studies the optimal support trajectory of power electronic devices with energy constraints when the system frequency drops. Thirdly, the optimal feedback control structure for grid-connected power electronic devices supporting power grid frequency is studied. It is shown that the control structure combined with virtual inertia control and droop control is close to the optimal control structure, and the virtual inertia control is better than the droop control when the available energy is small. Finally, the simulations verify the rationality of the theoretical analysis and the discussed optimal control structure of frequency.