Design And Grid-connected Control Of 12MW Permanent Magnet Direct-drive Wind Generator

Wind power technology has broad application prospects.Direct-drive permanent magnet wind generators occupy an important position in offshore wind power generation due to their simple structure,long maintenance cycle and the possibility of high power generation.The purpose of the thesis is to study and design a 12 MW high-power permanent magnet direct-drive wind generation.The research is conducted in three parts: the motor’s electromagnetic design solution,the efficiency and cogging torque optimization of the permanent magnet generator,and the high-power permanent magnet generator network connection and control strategy.In this thesis,the parameters of permanent magnets,silicon steel sheet material,main dimensions,air gap length and stator structure are firstly determined,and the advantages of the outer rotor structure are combined with the comparison of four pole-slot matching schemes: 132 pole 594 slot,132 pole 624 slot,140 pole 480 slot and 132 pole 432 slot.The preliminary design basically meets the design requirements,but there is still room for optimization in terms of motor cogging torque and efficiency.Secondly,a combination of Taguchi method and response surface method is applied to the optimal design of the motor.Firstly,the analysis is carried out by Taguchi method,and the cogging torque and motor efficiency are selected as the optimization objectives,and the slot torque and motor efficiency are selected as the optimisation targets,and the air gap length,the thickness of the permanent magnet,the pole arc coefficient,the stator slot width and the stator internal diameter are selected as optimisation factors for the multi-objective optimisation of efficiency and slot torque.The three main factors affecting the generator efficiency and slot torque were determined according to the weight of the optimisation parameters on the motor performance: the polar arc coefficient,the permanent magnet thickness and the air gap length.The response surface function is then obtained using the response surface method to derive the optimal combination of parameters and to verify the feasibility of this method in the optimal design of the motor.Ansoft Maxwell was used to model the 12 MW generator based on the field-circuit coupling principle,and the optimised motor was modelled and simulated for its operating characteristics at no load and rated load,as well as for the permanent magnet’s resistance to demagnetisation under extreme conditions.The simulation results verify that the optimised electromagnetic design is reasonable and does not suffer from irreversible demagnetisation.Finally,it presents the control methods of the machine side converter and the network side converter.The machine side converter uses a speed-current dual closed loop control strategy,aiming to achieve the control goal of maximum power tracking.The net-side converter selects the traditional voltage-directed vector control method to fulfill the constant bus voltage and the uncoupling of active and reactive power.The optimized control model for grid-connected permanent magnet synchronous generator is built in Matlab/Simulink for simulation and analysis.The simulation results show that the optimization strategy can output stable voltage and current to meet the grid-connected requirements and grid-connect the permanent magnet wind generator effectively.