Research On The LVRT Control Of Direct-drive PMSG Wind Power System Based On Three-phase CSC

With the rapid development of grid-connected wind power systems, LowVoltage Ride Through(LVRT) technology plays an important role in wind powersystem. Most of the topology of direct drive permanent magnet synchronousgenrator (PMSG) wind power systems are voltage source converters, and theresearch of current source converter is still relatively uncommon. This paperfocuses on LVRT control of direct-drive PMSG wind power system based on threephase current source converter (CSC). The main contents of the paper are:Firstly, according to the analysis of every components of permanent magnetdirect-drive wind power generation system based on three phase current sourceconverter. This chapter build the mathematical model of each part, includes windturbine, DC link，permanent magnet synchronous generator and current sourceconverter, which provides some part of theoretical support for the low voltage ridethrough.Secondly, because of the phase-locked loop performance plays an importancerole in the control of LVRT, by analyzing the advantages and disadvantages ofseveral conventional method of PLL such as hardware PLL, dq transformation PLLand DSC PLL and so on, the double dq transformation phase-locked loop method isadapted in the paper. Simulation results show that this method can quickly andefficiently extract the fundamental frequency, magnitude and phase of the positiveand negative sequence components of grid voltage in the case of symmetric gridfault and asymmetric grid fault.Thirdly, the operation of PMSG when the grid voltage symmetrical drop andasymmetric drop is analyzed. By comparing the conventional method of LVRT andcombined with the characteristics of current source converter, this paper presents aLVRT method with fast limiting PMSG output power. This method uses directpower control in the PMSG side, which can quickly limit output power when thegrid drop, and uses dc current closed loop for the grid side to control dc currentstable with PMSG side power fed-forward control method. When the grid voltageasymmetric drop, unbalanced control method is used to control the positive and negative sequence current to stabilize the DC current shock. This method does notneed additional equipment and reduce the cost of the system, without switchmethod when the grid drop, which reduces the complexity of the control system.Finally, a simulation model for the system is set up by Matlab. The simulationresults show the feasibility of the proposed LVRT control method presented in gridvoltage symmetrical drop and asymmetric drop.