【正文】 ntroduced. Then the vector control of smallscale gridconnected wind power system including sensorless control, vector control of PMSG, singlephase PLL, vector control of gridside inverter are described in section III. Finally, in section IV, the simulation results and conclusion are given. Vector control strategy for smallscale gridconnected PMSG wind turbine converter Chunxue Wen, Guojie Lu, Peng Wang, Zhengxi Li Member IEEE, Xiongwei Liu Member IEEE, Zaiming Fan Student Member IEEE I 2II. THE PRINCIPLE OF FULL POWER BACKTOBACK PWM CONVERTER Typical topology model of directdriven PMSG wind turbine is shown in Fig. 1. Converters of the system adopt backtoback pairs of pulsewidth modulation (PWM) architecture. The generatorside converter controls the generator speed in order to achieve maximum capture of wind power, and the gridside inverter controls the stability of DCbus voltage and the power factor of the system. This topology can be a good way to improve performance, and the control method is flexible. Converters have fourquadrant operation function, which can fulfill the generator speed control and deliver the fine quality of electricity to the grid [7], [8]. Fig. 1. Topology of permanent mag directdriven wind power system III. THE VECTOR CONTROL OF SMALLSCALE GRIDCONNECTED DIRECTDRIVEN WIND POWER SYSTEM CONVERTER Fig. 2 shows the backtoback PWM voltage converter vector control block diagram. The machineside PWM converter controls the electromagic torque and stator reactive power (reactive power is often be set to 0) by adjusting the current of the daxis and qaxis of the machineside converter. This control mechanism helps the PMSG to operate in variable speed, so that the wind turbine can work with maximum power point tracking (MPPT) under the rated wind speed. The gridside PWM inverter stabilizes the DCbus voltage and acplishes active and reactive decoupling control by adjusting the current of the daxis and qaxis of the gridside. The gridside PWM inverter also controls the reactive power flow to the grid, usually at unity power factor condition. A. Sensorless control based on PLL The speed and position control is achieved through sensorless vector control of the machineside converter based on alldigital phaselocked loop. The phaselocked loop is designed to control the frequency of the DQ axis voltage through minimizing the difference of the output voltage phase angle and the given voltage phase angle, until the output voltage phase angle tracks the given voltage phase angle. As the phaselocked loop has frequency closedloop tracking mechanism, the generator voltage frequency and the angle between daxis voltage and rotor flux can be measured with this characteristic, then the generator speed and rotor position angle can be derived [2]. The control accuracy is generally good using this method, however some problems may occur when the generator operates at very low speed. The wind power system often works above the cutin wind speed, so this method can be applied to wind power generation system. Fig. backtoback PWM voltage converter vector control block diagram 3The actual rotor position of PMSG is indicated in the DQ coordinate system. The estimated location for ∧θ is the dq∧∧? coordinate system, αβ is the stationary coordinate system, as shown in Fig. 3. As the rotor position of PMSG is estimated rather than measured in the sensorless vector control system, there exists an error θΔ between the actual rotor position θ and the estimated location ∧θ . At the same time, the backEMF (electromotive force) generated by the rotor permanent mags generates two daxis and qaxis ponents in the estimated rotor position orientation coordinates, which are expressed as sde∧ and sqe∧respectively. Conventional PI controller can achieve zero error control, . sde∧ or θΔ can be adjusted to zero value. The PLL sensorless vector control schematic diagram is shown in Fig. 4, and the value of sde∧ and sqe∧ can be obtained from (1). sdsd s sd d q sq sdsqsq s sq q d sd sqdiuRiL LiedtdiuRiL Liedtωω∧∧∧∧∧∧?=+ ? ?????=+ + +?? (1) θθ?θΔαβdd?qq? Fig. 3. Presumed rotating coordinate system sKKiP+s1θΔω?θ?θ Fig. 4. Principle of PLL based sensorless vector control If we ignore the current differential items in (1), then we have sd s sd q sqsdsq sq s sq d sd?????arctan( ) arctan( )?????uRi Liee uRi Liωθω?+Δ= ? = ??? (2) where sdu , squ , sdi and sqi are the d, qaxis ponents of the output voltage and current of the generator stator。 ω is the generator electrical angular velocity of the generator。 Control Application, vol. 32, pp. 5357, 2020. Books: [3] Qingding Guo, Yibiao Sun, Limei Wang, Modern permanent mag AC servo motor system. China Electric Power Press, Beijing. In press. Papers from Conference Proceedings (Published): [4] S. Song, S. Kang, and N. Hahm, “Implementation and control of grid connected ACDCAC power