Reseach On Circulation Control For Parallel Inverters On Grid Side In Double-fed Wind Power System

With more and more attention of renewable energy, wind energy is paid moreattention to in recent years, development and utilization of wind energy has becomethe most practical green energy electricity generation technology now. As a importantpart of green energy, wind energy is inexhaustible, pollution-free. Meanwhile, windfarm construction period is short, operating costs is low and after the completion,maintenance workload is small.High-power doubly-fed wind power system is one of the most popular windpower systems currently. In the double-fed VSCF wind power system, due to windspeed varying, the frequency and amplitude of voltage and current generated isdifferent with time. In order to get qualified stator voltage, the excitation current ofslip frequency is injected into double-fed generator rotor windings by back to backPWM converter. Grid side converter and rotor side converter operate together toachieve two-way flow of energy.Along with the international wind power technology development trend, WTGcapacity is more and more big, the mainstream models of land wind generators about1.5MW or2MW singly, offshore wind generators about3MW or5MW singly. WithStandalone capacity increasing, solo converter is already far cannot meet itsrequirements. If the higher power level device used, cost will be more expensive, soconverter running parallelly become ever more important. Muitiple converters paralleloperation can not only improve the power level, improve the system reliability andflexibility, but also will bring circulation in parallel converters.This paper mainly studies circulation of parallel converters in doubly-fed windpower generation system. This paper analyses control strategy of zero sequencecomponent of three-phase current in grid side converter in rotating coordinate, andproposes addition of a zero sequence current loop to control the circulation of zerosequence based on the traditional control strategy.This paper firstly introduces the current research status of wind powertechnology, analyzes the operating principle of variable speed constant frequencydoubly-fed wind turbines system. Then, establishes the mathematical model ofdoubly-fed wind power system, analyzes the basic structure of PWM converter,deduces the control strategy of grid side standalone converter as well as parallelconverters, and gets control mode of doubly-fed wind generators side converter based on the stator field-oriented. Finally, construct simulation and experimental platform;verify theory related with the variable speed constant frequency doubly-fed windpower system. Simulation and experiment results show the effectiveness of thecontrol strategy.