Abstract
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.
Highlights
Low frequency electromechanical oscillations are regarded as one of the major limiting factors in active power transfer over the long transmission lines, and frequently trigger the related frequency protection relays, adversely affecting the power system stability [1]
This paper reveals in detail the physical mechanisms of system inertia, damping and synchronization capability under typical control strategies with different detection signal feedback modes, including the effect of PID controller gain and PV grid-tied position on the integrated system dynamic characteristics, which provides theoretical support for damping strategies optimization
Regulation capacity ratio (RCR) indicator developed in this paper proves that P-control has a stronger ability than Q-control for the PV suppressing electromechanical oscillations
Summary
Low frequency electromechanical oscillations (usually 0.1– 2.5 Hz) are regarded as one of the major limiting factors in active power transfer over the long transmission lines, and frequently trigger the related frequency protection relays, adversely affecting the power system stability [1] To this end, previous works have developed different measures for electromechanical oscillation damping. Few work has investigated the related physical mechanisms, especially the influence of power control modes, control parameters and inverter location on the power system dynamic characteristics, which contributes to design more effective PV control strategies to improve the system inertia and damping. This paper reveals in detail the physical mechanisms of system inertia, damping and synchronization capability under typical control strategies with different detection signal feedback modes, including the effect of PID controller gain and PV grid-tied position on the integrated system dynamic characteristics, which provides theoretical support for damping strategies optimization.
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