【目的】针对储能变流器由离网模式切换至并网模式过程中的过渡问题,本文研究了一种基于虚拟同步机(VSG)控制的预同步策略。【方法】对离网运行模式、预同步控制模式以及并网运行模式分别建立了详尽的动态数学模型。在并网切换前,需引入预同步环节,用以补偿逆变器输出与电网母线之间的电压幅值及相位偏差。将预同步比例积分(PI)调节器引入原离网模型后,系统整体的数学模型阶次由原有的二阶上升为三阶。应用劳斯稳定判据对系统进行稳定性分析,并给出预同步控制环节中控制参数可行选取准则。进一步地,采用根轨迹法研究了加入预同步控制之后闭环系统根轨迹随关键参数变化的规律。所考虑的参数包括虚拟惯量、阻尼系数以及预同步控制的比例和积分增益等,通过分析根轨迹与虚轴的交点以及主导极点对的移动趋势,系统地归纳了各参数对系统稳定性、响应速度的影响。【结果】研究结果表明,在预同步控制过程中,VSG的惯性时间常数对响应速度的影响相对有限;阻尼系数以及预同步PI控制器的比例增益与积分增益,则构成了决定系统动态响应品质的关键因素。仿真工况系统性地覆盖了不同虚拟惯量、阻尼系数及预同步PI参数组合下的典型运行场景。仿真结果不仅印证了虚拟惯量对响应速度的影响较弱,也定量展示了阻尼系数和PI参数对响应时间、超调量等调控效果。【结论】本文所建立的理论模型与分析方法可为微电网平滑并网控制策略的工程参数整定提供理论依据与实践指导。

[Objective] To address the transition issue during the switching process of an power conversion system from off-grid mode to grid-connected mode, this paper studies a pre-synchronization strategy based on virtual synchronous generator (VSG) control. [Methods] Detailed dynamic mathematical models were established for the off-grid operation mode, the pre-synchronization control mode, and the grid-connected operation mode, respectively. Before the grid-connection transition, a pre-synchronization link was introduced to compensate for the voltage amplitude and phase deviations between the inverter output and the grid bus. After incorporating the pre-synchronization proportional-integral (PI) regulator into the original off-grid model, the overall order of the system’s mathematical model was increased from the original second order to third order. The Routh stability criterion was applied to analyze the system stability, and feasible selection guidelines for the control parameters in the pre-synchronization control loop were provided. Furthermore, the root locus method was adopted to investigate the variation of the closed-loop system’s root locus with key parameters after the addition of pre-synchronization control. The considered parameters included virtual inertia, damping coefficient, and the proportional and integral gains of the pre-synchronization control. By analyzing the intersection points of the root loci with the imaginary axis and the movement trends of the dominant pole pairs, the influences of each parameter on system stability and response speed were systematically summarized. [Results] The research results indicated that during the pre-synchronization control process, the inertia time constant of the VSG had a relatively limited impact on the response speed. In contrast, the damping coefficient, along with the proportional and integral gains of the pre-synchronization PI controller, constituted the key factors determining the quality of the system’s dynamic response. The simulation scenarios systematically covered typical operating conditions under different combinations of virtual inertia, damping coefficients, and pre-synchronization PI parameters. The simulation results not only confirmed that the virtual inertia had a weak influence on response speed, but also quantitatively demonstrated the regulation effects of damping and PI parameters on response time, overshoot, and other performance metrics. [Conclusion] The theoretical models and analytical methods established in this paper provide a theoretical basis and practical guidance for the engineering parameter tuning of smooth grid-connection control strategies for microgrids.

国家自然基金(52007111)