Analysis on the Contribution of Virtual Synchronous Generator Controlled Energy Storage System to Primary Frequency Modulation

Virtual Synchronous Generator (VSG) control has been applied to the Energy Storage System (ESS) to improve its frequency response characteristics. However, the influence mechanism of the control parameters of the VSG controlled ESS on the primary frequency modulation has not been analyzed in depth. An analysis method of the influence of the control parameters of the VSG controlled ESS on the primary frequency modulation is proposed in this paper. The VSG control scheme of the ESS is briefly introduced and then the exact differential equation for the primary frequency modulation of the power system is established. By solving this differential equation, the complete frequency response curve in the primary frequency modulation process of the power system is obtained. Therefore, it is possible to further analyze the influence of different control parameters on the frequency response during a frequency modulation process. Moreover, when the State of Charge (SOC) of the ESS reaches the limit during charging and discharging, it will cause a secondary change in frequency. This phenomenon is also analyzed and the corresponding solutions is given. Finally, the simulation results verify the effectiveness of the analysis method proposed in this paper.

I. Introduction

Renewable energy sources such as wind energy and solar energy use converter interfaces to replace traditional mechanical switches for grid connection. As its penetration rate in the power system continues to increase, the system inertia continues to decrease, and the primary frequency modulation capability decreases, which is not conducive to system frequency stability [1] –[3]. There are usually two ways to solve this problem: one is to improve the control algorithm of new energy power generation, so that it has inertial support and primary frequency modulation capability; the other is to install the energy storage system (ESS) in the power grid and utilize the charge and discharge characteristics of it to maintain the grid frequency stability. The control methods of the ESS include vector control, droop control, virtual synchronous generator (VSG) control, etc. Among them, VSG has been a research hotspot since it was put forward. VSG realizes grid connection by simulating the characteristics of synchronous generators, so that grid stability analysis and management are consistent with traditional synchronous generators. It is also beneficial to the stability of the control and management of the grid system [4–5].