虚拟电容控制下并网型直流微网VSC多约束稳定运行边界

与传统交流电网相比，直流微电网不存在频率、相位同步及三相不平衡等问题，但其直流母线电压易受间歇性新能源及负荷的影响而失稳。端口换流器采用虚拟电容控制方法可以在控制层面为该问题的解决提供一种方案，且虚拟电容值大小可调，更增强了该控制方法的灵活可控性，但在该控制策略下虚拟电容在灵活调节时需满足多种约束条件以保证系统的稳定运行。据此，在研究电压源型换流器(VSC)灵活虚拟电容控制策略的基础上，分析影响虚拟电容调节的关键指标，考虑系统稳定性、动态特性、实际运行需求及可实现性约束条件，构建满足VSC多约束的稳定运行指标集，并给出了多指标约束下的稳定运行边界计算方法，以合理限制虚拟电容控制的灵活调节能力，使该控制方法在满足多项约束的基础上，尽可能地发挥其优势，为直流电网提供惯性支撑。最后，搭建了控制器级的硬件在环测试平台，验证了换流器灵活虚拟电容控制的有效性及多指标约束稳定运行边界的正确性。

Multi-constraint Stable Operation Boundary of Grid-connected Voltage Source Converter of DC Microgrid with Virtual Capacitance Control

Compared with traditional AC grids, the DC microgrid does not have problems such as frequency, phase synchronization and three-phase unbalance. However, the DC bus voltage is vulnerable to the impact of intermittent new energy sources and loads. The problem can be solved by adopting virtual capacitance control for converter at the control level. And the virtual capacitance value can be adjusted, which enhances the flexible controllability of the control method. However, the flexible adjustment of virtual capacitance with this control strategy needs to satisfy a variety of constraints to ensure the stable operation of the system. Therefore, based on the study of flexible virtual capacitance control strategy of voltage source converter(VSC), the key indicators affecting the regulation of virtual capacitance are analyzed. Considering the constraints of system stability, dynamic characteristics, actual operation requirements and realizability, the stable operation indicators satisfying multiple constraints of VSC are constructed, and the calculation method of stable operation boundary with multi-constraint is given. In this way, the flexible adjustment ability of virtual capacitance control can be reasonably limited, and the control method can give full play to its advantages as far as possible on the basis of satisfying multiple constraints, to provide inertial support for DC power grid. Finally, the hardware-in-loop test platform at the controller level is established to verify the effectiveness and correctness of the flexible virtual capacitance control of VSC and multi-constraint stable operation boundary.