| In the field of renewable energy,wind power generation is one of the power generation forms with the most mature technology,the most large-scale development conditions and commercial prospects.Offshore wind power achieved large scale development due to several advantages,such as abundant wind resources,no occupation of land resources,friendly gird connection and power consumption and so on.However,the cost of offshore wind power construction and maintenance is expensive.In view of the specific characteristics of offshore wind power operation and maintenance,rigorous requirements are put forward for the reliability of products and the rapid replacement of generator components.The key ways to reduce Levelized Cost of Energy(LCoE)of offshore wind power are increasing rated capacity and implementing modular design.With increasing of unit wind turbine capacity,there are higher requirements of electrical drive system reliability,modular design,high power density generator and so on.In this dissertation,further analysis and research about questions mentioned is carried out.The main contents of this dissertation are as followings:First,the reliability analysis of typical wind turbine electric drive system is carried out,focusing on the stability of permanent magnet direct drive modular electric drive system in the fault-tolerant operation mode.Based on the analysis of difference of air gap flux density and torque characteristics between four winding operation and single winding operation,a control strategy of fault-tolerant operation of electric drive system is proposed.The test results show that the method can effectively eliminate the 6-fold frequency vibration of the generator,and the total vibration acceleration of the generator can be reduced from 0.047 g to 0.025 g.Aiming at the problems of rotor loss and torque ripple caused by multi-poles and few slots modular generator tooth harmonic,an electromagnetic field calculation model of 10 poles and 12 slots unit generator is established.Also,the optimization of tropology is carried out with target of rotor loss and torque ripple.The study results show that implementing the structure of the rotor core yoke can effectively reduce the rotor loss and torque ripple.Compared with the solution that increasing the gap between stator core modules,the first harmonic is reduced by 40%,the core loss is reduced by 64%,the average electromagnetic torque is increased by 8.9%,and the torque ripple is reduced by 49%.Secondly,the influence of different rectification modes on the electric drive system is studied,which is aimed at collaborative design of permanent magnet direct drive wind turbine generator and convertor,and it was found that there was an over-voltage phenomenon caused by over compensation of shunt capacitor with passive rectifier.However,a closed loop control strategy of controllable rectification mode can be used to flexibly adjust generator torque and terminal voltage,it also can realize power factor correction according to design requirements.Meanwhile,the short circuit characteristics of generator port and convertor rectifier are studied.The results show following findings: the maximum torque of the motor increases to 1.4 times of the rated torque when there is a two-phase short circuit at the generator port or a single bridge arm short circuit at the rectifier side of the converter,and the maximum short circuit is about 3.8 times of the rated current when there is a single bridge aim short circuit at the rectifier side of the converter.Moreover,a three-dimensional fluid-thermal coupling model of permanent magnet direct drive wind turbine was established,the fluid and thermal fields study of 10 MW modular generator was carried out.The results show that the difference between winding temperature and that of maximum and minimum temperature along core axial direction is only 2.4K,the temperature difference between core and winding is only 0.2K,which is very small.There is a significant variation of flow distribution in 16 radial ventilation channels,the maximum flow is about 34.7% higher than the minimum flow.By establishing electromagnetism-fluid-thermal multi physical field coupling calculation model,the optimal design of 3.35 MW modular permanent magnet direct drive wind turbine principle prototype was completed.Taking the voltage and current limits required by electric drive system as constraints,the generator topology optimization with loss reduction as the objective is achieved.Meanwhile,the topology optimization of generator ventilation cooling is carried out.The results show that ventilation air flow volume can be increased up to 13% by using 11 k W cooling fan compared to the 7.5k W cooling fan and the maximum temperature of winding can be reduced by 5?,which proves that the temperature rise of generator winding can be reduced by increased the power of cooling fan.Also,it was found that temperature rise of generator is minimum under conditions of keeping the number and height of ventilation spacer fixed and the radial width of ventilation channel steel is 35-40 mm.A mathematical model is established,which considers fluid and heat transfer of permanent magnet direct drive wind turbine ventilation spacer.The flow field and thermal field of 36 kinds of ventilation channel steel with different structures are analyzed.The results show that the best winding scheme can achieve 11.2K highest temperature reduction,which reduce from 102.6? to 91.4?.The ventilation and cooling experiment platform is the key to optimize the design of the highefficiency ventilation and cooling system.In this paper,a ventilation and cooling experiment platform for single-layer winding was built to carry out experimental tests on two ventilation spacer schemes with high technical and processing feasibility.The results show that the optimized channel steel can reduce the generator temperature rise by 3.9K.Finally,in order to verify the effectiveness of the design scheme of 10 MW permanent magnet direct drive wind turbine,a 3.35 MW prototype is designed and developed,and a special full power back-to-back test bench was set up to test the key parameters of the prototype,such as open circuit characteristic,noise characteristic,vibration characteristic and temperature rise..The test results show several findings.First,no-load voltage,load voltage,load current and other parameters are in good agreement with the design results.Second,there is no abnormal noise in the full rotating speed range under no load and load conditions.Third,the temperature rise of motor is 96.5k and that of permanent magnet is 48.4k under rated power,which verifies the accuracy of magnetic circuit topology with concentrated winding,modular structure and forced ventilation cooling technology.All these results provide a technical foundation for the development of 10 MW or larger capacity wind turbines. |
PDF Full Text Request