Multi-Target Control Strategy of DFIG Using Virtual Synchronous Generator Based on Extended Power Resonance Control under Unbalanced Power Grid

Dan Sun,Jun Sun,Heng Nian,Yangming Wang,Tianlong Jiang,Xiaohe Wang

doi:10.3390/en13092232

Abstract

Virtual synchronous generator control is considered as an effective solution to optimize the frequency response characteristics of doubly fed induction generator. However, due to the insufficient control bandwidth of the original virtual synchronous generator, it has little control effect over the oscillating components of the power caused by the unbalanced grid voltage. Therefore, long-term unbalanced voltage will cause a series of problems, such as distortion of stator and rotor currents, as well as oscillations of power and electromagnetic torque, which seriously affect the power quality and the operating performance of the doubly fed induction generator. To solve these problems, the concept of extended power is introduced, and the second-order generalized integrator-based resonant controller is used to control the extended power and traditional power. Control targets of the extended power method are discussed and extended, so that the doubly fed induction generator system using extended power resonant control-based virtual synchronous generator control can realize three different control targets under the unbalanced grid condition. The three control targets are: balanced and sinusoidal stator current, sinusoidal stator current and constant active power, and sinusoidal stator current and constant reactive power and electromagnetic torque. The three control targets can also be flexibly switched according to the real-time requirements of the grid with unbalanced voltage. The simulation results verify the effectiveness of the control method.

Highlights

With the increase of renewable energy generation, the power electronic characteristics of the power system are more and more obvious [1]
For the widely adopted doubly fed induction generators (DFIG)-based wind power generation, when various vector control (VC) [2] or direct power control (DPC) strategies are used [3,4], the rotor speed of DFIG and the grid frequency are decoupled from each other, so the DFIG system cannot respond to the frequency disturbance of the grid, which will reduce the stability of the power system
The DFIG based on virtual synchronous generator (VSG) can have the same inertial characteristics as the SG; i.e., the synthetic inertia or virtual inertia can be given to the DFIG by the VSG control

Summary

Introduction

With the increase of renewable energy generation, the power electronic characteristics of the power system are more and more obvious [1]. In order to improve the equivalent inertia of the grid, virtual synchronous generator (VSG) control has been studied and considered as an effective solution for DFIG [5,6,7,8,9]. The VSG control imitates the operating mechanism of the conventional synchronous generator in order to obtain the same operating characteristics of inertia and frequency support. In VSG control of DFIG, the active power control loop simulates the rotor swing equation of the conventional. SG to realize the active power-frequency regulation in order to improve the frequency-response. Energies 2020, 13, 2232 characteristic, and the reactive power control loop simulates the excitation process of the SG to realize the reactive power-voltage regulation. In other words, when the grid frequency is disturbed, the mechanical rotational kinetic energy of the rotor can be used to provide dynamic frequency support for the grid, which completely changes the frequency response capability of the DFIG

Methods

Findings

Discussion

Conclusion