Improved Short-Circuit Current Calculation of Doubly Fed Wind Turbines With Uninterrupted Excitation

Jun Yin

doi:10.3389/fenrg.2021.686138

Abstract

With the enlarging scale of a doubly fed induction generator (DFIG) connected to a power system, the influence of short-circuit current on the system relay protection could not be ignored. Setting and configuring relay protection would be affected by an imprecise short-circuit current calculation. However, some existing studies only consider the condition that the input is the Crowbar and the rotor excitation is blocked. China's new network standard requires the output reactive support current of a DFIG and will change the characteristics of short-circuit current. To solve this problem, on the basis of analyzing the characters of the transient equivalent potential of a DFIG, the transient model of a DFIG with uninterrupted excitation is provided. Based on the characteristics of a non-abrupt change of flux linkage and the requirement of a new grid standard reactive support current, the short-circuit current calculation method of a DFIG with uninterrupted excitation is put forward. Based on the real-time digital simulator (RTDS), a digital-analog experimental platform containing the actual control unit of the DFIG converter is founded, the proposed short-circuit current root mean square (RMS) value calculating method is validated.

Highlights

In recent years, as represented by wind power, new energy sources have been developing rapidly in China
In order to solve this problem, based on analyzing the equivalent potential characteristics of a doubly fed induction generator (DFIG) during the fault, this paper firstly proposes a DFIG transient equivalent model DFIG under continuous excitation
The control units of the rotor converter are designed by using the field-programmable gate array (FPGA) chips, which are the controller core, the DFIG, and an real-time digital simulator (RTDS)-built grid model

Summary

Introduction

As represented by wind power, new energy sources have been developing rapidly in China. In 2019, there are 26.79 million kilowatts wind power newly installed in China. The grid connected wind power capacity has reached 270 million kilowatts. With rapid development in the generation of wind power, its impact on the power grid has become more and more obvious. In China, doubly fed induction generators (DFIGs) were widely used in MW-class wind turbines whose converter capacity is only about one-third of the rated capacity. They have the advantages of low cost and the decoupled control of active and reactive power. With a continuous increase in the capacity of a DFIG, its short-circuit current can no longer be neglected in the

Methods

Results

Conclusion