| With the growing demand for energy and the increasingly serious environmental pollution problem,changing the current energy structure and vigorously developing multi-energy complementarity has become the trend of energy development in the future.As a clean energy source,photovoltaic(PV)has gained widespread attention,and the installed capacity of domestic PV power plants is increasing year by year.However,due to the random,intermittent and fluctuating characteristics of PV plants,it brings difficulties to the scheduling of power grid,while hydropower has the characteristics of flexible operation regulation,fast starting speed and low operation and maintenance cost,which has great advantages in peak regulation,so the mode of hydro-PV complementarity is used to provide new ideas for peak regulation.However,with the increasing penetration of PV plants,the large-scale of them connected to hydropower system leads to low inertia and weak damping characteristics of the power grid.When the system suffers from disturbance,the traditional inverter control cannot support the safe and stable operation of the power system and is vulnerable to lowfrequency oscillations.In order to improve the stability of the system,Virtual Synchronous Generator(VSG)technology has emerged,which provides inertia and damping support for the system by simulating the external characteristics of Synchronous Generator(SG).Therefore,this paper explores the low-frequency oscillations suppression strategy based on VSG for hydro-PV complementary system with important practical and theoretical significance.Based on the existing research,the following elements are mainly studied in depth:Firstly,this paper analyzes the compensation ability of hydropower to PV in shortterm scheduling by combining the output characteristics of PV plants and hydropower;on this basis,it reveals the mechanism of hydro-PV complementary system and establishes the overall system architecture.By studying the working principles,mathematical models and corresponding control strategies of the hydropower plant,PV plant and energy storage units respectively,the overall small-signal model of the system is established,and the impact of VSG technology on the low-frequency oscillations of the hydro-PV complementary system is analyzed according to the small-signal model.Secondly,the low-frequency oscillation mechanism of the water-light complementary system is analyzed respectively from the hydropower side and the photovoltaic side,and the VSG technology is studied by referring to the SG mathematical model and working principle.The mathematical model of the VSG is established and virtual speed regulator and virtual excitation regulator are designed.By introducing VSG technology into the photovoltaic side inverter to enhance the equivalent inertia and damping of the system,and introducing additional damping control to enhance the equivalent damping of the system in the side speed regulating system of the hydropower unit,the low-frequency oscillation of the hydro-PV complementary system is suppressed.and the VSG technology is applied to the lowfrequency oscillations suppression of the hydro-PV complementary system,and the simulation is verified by PSCAD/EMTDC.Finally,this paper analyzes the influence of virtual inertia and damping coefficient on the dynamic performance of the system based on the small-signal model of VSG,by analyzing the power angle curve and angular frequency oscillation curve of SG,the relationship between virtual inertia and damping coefficient and system angular frequency deviation and angular frequency variation rate is determined.Based on the above analysis,the control parameters of the hydropower side and PV side are optimized based on the Particle Swarm Optimization(PSO)algorithm to achieve the overall optimization objective of the water-photovoltaic complementary system,and the effectiveness of the proposed control strategy is verified by simulation. |
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