Research On Hydrodynamic Speed Regulation System For Variable-Speed Constant-Frequency Wind Turbines

Due to the problems of energy shortage and environmental pollution,the development and utilization of renewable energy has been widely concerned in the world.Among various renewable energy technologies,wind turbine technology is becoming mature and the cumulative capacity of wind turbines is increasing.In traditional variable-speed constant-frequency(VSCF)wind turbines,it is necessary to use the frequency converter to generate electricity.Moreover,VSCF wind turbines involve the high failure rate of the gear box and the complex frequency conversion technology.However,the reliability of wind turbine is low and the MTTR(Mean time to Repair)is long.The installation and maintenance costs of wind turbines are increasing with the increase in the failure frequency.Traditional VSCF wind turbines face the bottleneck in manufacturing,installation,and maintenance.In order to avoid the high failure rate of the gear box and the complex frequency conversion technology,meet the increasingly stringent grid connection requirements of wind turbine,and improve the reliability of wind turbine and prolong its service life,new VSCF wind turbines are developed based on hydrodynamic speed regulating technology.The hydrodynamic speed regulation device of the wind power generator can realize the constant generating frequency of the generator,and directly generate high quality electric energy by adjusting the adjustable guide vanes.The hydrodynamic torque converter with adjustable guide vanes has the control and damping effect in the whole transmission chain,thus decreasing the dynamic torque ripple and inhibition peak load of the transmission system.Wind turbines with hydrodynamic speed regulation device are characterized by the small size,light weight,low cost,and high reliability.This paper is based on the project of “study on hydromechanical speed adjusting system with adjustable guide vanes of wind turbine” of special foundation project of ministry of education(20100061120057).The hydrodynamic speed regulation device for VSCF wind turbine is further studied.The main results and relevant conclusions in the paper are summarized as follows.1.The hydrodynamic torque converter with adjusting guide vanes is the core control component of VSCF wind power system.In order to study the internal characteristics of hydrodynamic torque converter with adjusting guide vanes,a new transparent hydrodynamic torque converter with adjusting guide vanes was designed and manufactured.The computational fluid dynamics(CFD)method was used to calculate the internal fluid flows at different openings under working conditions.Based on the testing results of particle tracking velocimetry(PTV),the CFD simulation result was proved to be accurate and reliable.Based on the CFD calculation,the internal characteristics,external characteristics,and regulation characteristics of the adjustable guide vanes were obtained,thus providing the foundation for the application of the hydrodynamic torque converter with adjusting guide vanes as the control element in the hydrodynamic speed regulation device.2.Based on the VSCF wind turbines,the hydrodynamic speed regulating transmission system in wind turbines was analyzed.According to the speed and torque equation of the hydrodynamic speed regulation device,the overall transmission efficiency and the ratio of the transmission power of the hydrodynamic torque converter with adjusting guide vanes to the input power of the hydrodynamic speed regulation device are obtained.For the purpose of power ratio less than 30%,a hydrodynamic speed regulation device with the rated power of 300 k W was designed by theory of power split.The hydrodynamic torque converter with adjusting guide vanes with a circular diameter of 425 mm was designed.According to the results of the CFD numerical simulation,the original characteristics under different openings were obtained and its mathematical model was established.3.With the same original characteristics,the hydrodynamic torque converter with adjusting guide vanes was scaled up from the effective circulating circle diameter of 425 mm to 800 mm.Based on the mathematical model of the hydrodynamic speed regulation device with the planetary parameters as 1?=2 and 2?=4,the operating characteristics of the 2 MW VSCF wind turbines were obtained.According to its operating characteristics,the speed range and efficiency of the hydrodynamic speed regulation device was analyzed with the planetary parameters and the effective diameter of circular circle.Finally,the principle for the selection of parameters was given and optimized parameters for the hydrodynamic speed regulation device in the 2 MW wind turbine was 1?=2 and 2?=5,and D=750 mm.4.According to the operation characteristics of 2 MW VSCF wind turbine,combined with open and close loop control,a dual-mode speed control system based on frequency switching strategy was proposed and designed.The simulation model of the control system of hydrodynamic speed regulation device in the 2 MW wind turbine was established.According to the same theory and method,the operating characteristics of the 300 k W hydrodynamic speed regulating function prototype were analyzed.Based on the prototype parameters,its control system simulation model was established and simulated.The simulation results show that the dual mode control system can accurately control the speed of synchronous generator,and allow a faster response speed.5.In order to test the speed regulation performance of the hydrodynamic speed regulation device and verify the actual control effect of the new designed dual mode control system,the 300 k W hydrodynamic speed regulating function prototype was tested.Under three different control algorithms(open-loop,closed-loop and dual-mode control),the effects of variable input speed and constant output speed of the hydrodynamic speed regulation device were tested.The testing results showed that the dual-model control algorithm could combine the open-loop control with closed loopcontrol,thus improving the control speed and precision of the control system and realizing the high output speed and accurate control of wind power hydrodynamic speed regulation device.Testing results of speed the regulation device were compared with simulation results to verify the correctness and reliability of the control system simulation model.