A Combination Control Strategy of VSC-HVDC with Wind Farms Based on Virtual Synchronous Generator of Voltage Drop Method

Large-scale wind farms can supply power to the AC power grid through the HVDC based on voltage source converter (VSC-HVDC). This paper proposes a combination control strategy based on virtual synchronous generator (VSG) of voltage drop without relying on communication for the case of small disturbances and large shifts in the frequency on the AC power grid. Firstly, the improved virtual synchronous machine technology is added on the grid side VSC (GSVSC) of the DC side to selectively provide an effective inertial response for the frequency disturbance of the receiving-end power grid. Secondly, the wind farm VSC (WFVSC) adopts an improved frequency conversion control strategy and selectively responds to the frequency control according to the voltage fluctuation level of the DC side. At the same time, the doubly-fed wind turbines of the wind farms use virtual synchronous machine technology to adjust the rotating speed, rather than the traditional maximum power tracking mode. Finally, simulation experiments on PSCAD/EMTDC simulation software verify the correctness and effectiveness of the proposed control strategy.

I. Introduction

The VSC-HVDC is a typical structure of the long-distance large-scale wind farms accessing to the AC grid [1]. However, it decouples the connection between the wind farms and the AC grid, and it does not have the inherent rotational inertia and damping components of the traditional motor. The increasing capacity of wind turbines will lead to a reduction in the equivalent inertia of the power system. When the load disturbance is relatively small or there is a jamming signal, the power system does not need to adjust the frequency; but in the case of relatively large load changing and system faulting, it will seriously affect the power system stability [2]. At this time, the DC system needs to participate in the frequency response.