Research On The Frequency Regulation Control Strategy For Direct-driven Permanent Magnet Wind Power Generation System With Flywheel Energy Storage Unit

As the increasing penetration of the wind power in the power system, the windpower generation systems are influencing the grid continuously and increasingly. Thedemand for wind power generation systems which integrated to the grid is gettingstrictly. Due to the intermittent, randomness and fluctuation of wind power, the activepower injected to the grid generated by wind power systems is always fluctuating,which may decrease the frequency stability. At present, most of the countries whichhave quantities of wind power generation systems have raised the claims to wind powersystems under the circumstance of non-ideal power system frequency. On one hand, thewind power systems are required to keep connecting to the grid during the period ofnon-ideal grid frequency. On the other hand, wind power systems are required togenerate frequency regulating power like traditional power generators. Therefore, inorder to provide the stable frequency regulating ability of wind power systems in allworking conditions and improve the power quality of wind power connected systems,this paper studies the frequency regulation control strategy of direct-driven permanentmagnet synchronous generator (D-PMSG) with flywheel energy storage unit(FESU).This research has important practical significance to improve the grid frequencystability of wind power grid and grid-friendly wind farm construction.In this paper, considering the widely use of direct-driven permanent magnetsynchronous generator, the following studies were carried out after mastering itsworking principle and control strategy.①The mathematical model of the direct-driven permanent magnet wind powergeneration system with flywheel energy storage unit is established. The steady-statecontrol strategies for the generator-side converter (MSC), grid-side converter (GSC) andflywheel-side converter (FSC) are proposed and the performance of the steady statecontrol strategy is verified by simulation results. This work builds the foundations forthe investigation of D-PMSG with FESU frequency regulation control strategy.②The power system frequency regulation model including D-PMSG with FESUis analyzed and established. In order to increase the equivalent inertia and damping ofpower system to improve the frequency regulation ability in all working conditions andimprove the system frequency stability, this paper proposes the frequency controlstrategy based on traditional proportional-derivative controller (PD controller). A simulation system based on micro-grid including direct-driven permanent magnetsynchronous wind power generator, traditional synchronous generator and flywheelenergy storage unit is built. The simulation results show that the proposed controlstrategy can realize the control target of stable frequency regulation ability in allworking conditions, and effectively improve the grid frequency stability.③After qualitatively analyzing the influence of different equivalent inertia anddamping to different frequency fluctuation conditions, in order to decrease theamplitude of frequency fluctuation, increase the recover speed of frequency, as well asthe precisely of frequency recovering, this paper proposes a fuzzy PD controller todynamic regulate equivalent inertia and damping. In order to verify the stability of afteradding the proposed fuzzy PD controller, a small-signal analysis model including GSC,MSC and FSC, which taking grid frequency fluctuation into consideration, isestablished. The results of small-signal analysis show the stability of system, which arehelpful to finding the appropriate fuzzy controller output range. The simulation resultsverify the adaptability and effectiveness of proposed fuzzy PD frequency regulationcontrol strategy.