For physically understanding the dynamic response of the photovoltaic (PV) integrated power system for electromechanical oscillations damping, firstly, this paper develops the linear mathematical model of a single machine infinite bus system integrated by the PV grid-tied inverter under the electromechanical time scale. Then, based on the electric torque analysis method, and the functional route of the PV grid-tied inverter variable active power control (P -control) and reactive power control (Q-control) with the power angle or grid frequency feedback as the input control signal, the key factors and influence laws of the integrated system inertia, damping level and synchronization capability are investigated. The developed model shows that enlarging the proportional-integral-derivative (PID) controller parameters of P and/or Q-control loop can effectively change electromagnetic power distribution to suppress the imbalance power, and equivalently improve the system damping level, synchronization capability and inertial effect, respectively, contributing to actively adjust the grid frequency oscillation amplitude, period and recovery speed to maintain the system control stability according to the grid code demand. Besides, under the same inverter capacity constraint, P -control mode is proved more advantageous than Q-control mode to damp electromechanical oscillations. Finally, the correctness of the physical mechanism analysis is verified by MATLAB simulations and RT-LAB experiments.

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Given the increasing penetration of wind power generation, the power system faces great challenges in frequency regulation due to reduction in system inertia. This paper proposes an adaptive power compensation based frequency regulation (FR) strategy of the wind turbine system (WTS). In a frequency transient event, the proposed strategy exploits power excitation method to estimate the disturbance level, which enables the WTS to timely and accurately participate in FR. After the system frequency and the rate of change of frequency meet their requirements, the droop control is adopted to smooth the WTS out of the FR mode and further improve the frequency quality. By analyzing the operation mode and determining the switching logic, detailed implementation of the proposed strategy is developed. Its excellent frequency response performance is verified via results of hardware-in-the-loop experiment and MATLAB/Simulink-based simulation.

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