Frequency response enhance control method based on two-step MPC for VSG

Virtual synchronous generator (VSG) technology is ideal for inverter friendly access to the power grid. With the large-scale connection of grid-connected inverters to the grid, the frequency response of the power system has attracted more and more attention in recent years. In this paper, a two-step predictive control method based on model predictive control (MPC) is proposed, which can accurately predict the data of the next two sampling moments. The frequency response and dynamic mechanism of the system are studied by establishing a micro-grid system with VSG grid-connected inverter. In this method, the current system frequency is sampled to establish the reference frequency trajectory of VSG and realizes the accurate tracking of system frequency. Compared with traditional predictive control, two-step predictive control method can effectively reduce the adverse effects caused by system feedback error or external interference. Simulation results demonstrate that the frequency response of the proposed method has good dynamic characteristics, which verifies the correctness and effectiveness of the presented method.

I. Introduction

With the increasingly prominent global energy crisis and environmental problems, distributed generation technology and micro-grid technology have received more and more attention [1]–[3]. At the same time, modern power system is gradually evolving into electronic power system characterized by high permeability of power electronic equipment. The frequency in the traditional power system is determined by the rotor speed of the synchronous generator, and the rotor rotary inertia of the synchronous generator is very large, which determines the small fluctuation of the system frequency under disturbance, and this rotary inertia can provide active power support for the system, so the traditional power system has very good frequency response characteristics [4]. However, with the continuous increase of power electronic equipment permeability, the proportion of synchronous generators gradually decreases, and the power system gradually loses the inertia to maintain the system frequency. The result will be that the frequency fluctuation of the power system becomes larger under disturbance, the frequency stability becomes worse, and the ability to resist large disturbance decreases greatly [5]. In particular, when the inverter adopts constant power control, it can be regarded as a power source. At this time, it cannot participate in the frequency regulation of the system or provide frequency support [6], thus presenting "unfriendly" grid-connected characteristics.