The Control Of Output Power For Variable-Speed Direct-Driven Switched Reluctance Generator Based Wind Turbine

As a clean renewable energy,wind generation is gaining great popularity,the wind power technologies also become research hotspot of many countries's scholar.The wind generator is a key component determining the performance of the wind generation system.At present,many existing wind generator systems mainly use standard squirrel-cage induction generators(SCIG),doubly fed induction generators(DFIG) or synchronous generators.The speed of SCIG is close to a constant value,thus the wind energy utilization factor cannot be maintained at the optimal value during wind speed variation.And also a gear box is required which results in reduced system reliability, extra energy losses and more maintenance works.The DFIG can change its operating speed and has better utilization of wind energy than SCIG.However,the structure of DFIG is complex and a multi-stage gearbox is still necessary in the drive train because the speed range for DFIG is far from a common turbine speed.To reduce the gearbox, many manufacturers provide low-speed high-torque synchronous generators,include electrically excited synchronous generators(EESG) and permanent magnet synchronous generators(PMSG).But its material cost is high and more efforts are required to further improve its performance and reliability,reduce its cost and size.The developing trends of wind generator systems may be variable-speed direct-driven concept,so a new type of generator should be developed.The switched reluctance generator(SRG) offers a number of advantages compared to other types of generators,such as simple and robust machine structure,convenience of control,high efficiency in a wide speed range,high fault tolerance and high power density.These features make it very suitable for application to variable-speed direct-driven wind turbines.The application of SRG in wind generation was proposed early in the 1990s,but so far only laboratory results were presented.This paper mainly focuses on the control of output power for switched reluctance generator in wind generation,and has done all-around study,from simulation to experiment,from theory to field practice.The detailed research works include:(1) This paper summarized and analyzed the present wind generator and relative techniques based on a large number of referenced materials,presented the several advantages of SRG in wind generation system,and further made the significance of developing the switched reluctance wind generator(SRWG) system clear. (2) The control principles of SRG output power is proposed.The mathematical model of SRG.output power is built,turn-on and turn-off angles,DC bus voltage level and shaft speed of the switched reluctance generator have been identified as design parameters and control variables affecting output power.Iterative simulation of the generator model on the range of design parameters and control variables has been used for finding output power profile.The simulation and test results validate the control principles of switched reluctance generator for the range of control variables.(3) A variable-step maximum power point tracking(MPPT) algorithm for switched reluctance wind generator system is proposed.At present,the existing MPPT algorithms were torque demand control strategy and speed feedback control strategy,basically these control schemes depend on the characteristics of a wind turbine,which means the turbine characteristics have to be obtained either before or during the execution of these control algorithms,and sometimes an anemometer is needed to measure wind speed which will bring more cost.This paper proposed a variable-step Hill-Climb algorithm to track maximum power point for SRWG system,its advantages are that no knowledge of the wind turbine characteristics or measurement of the wind speed is required.(4) The model of SRWG system was built and simulated in Matlab.The MPPT algorithm proposed in this paper was simulated and discussed in details,the results of simulation were used to prove its feasibility.(5) SRG controller is developed.Using TMS320LF2407A(DSP for motor control, made in TI Corp.) as the control-core,this paper design a suit of SRG controller,the hardware design and the software design were all listed clear.(6) Switched reluctance wind generator simulator is established.Due to the uncontrollable natural characteristic of wind speed,it is very difficult and sometimes impossible to do the experimental study of control strategy for wind generation system in field.In this paper a wind turbine simulator is established using the DC motor and its controller,PC and torque meter.Using this method,wind turbine can be simulated easily in the laboratory.(7) A 10kW SRWG system is designed and built in the field.The field test results prove the SRG based wind generation system is feasible and has many advantages over conventional wind generation technology.Simulation and Experimental results validated the control principles of SRG output power and the proposed MPPT algorithm for SRWG system.The proposed MPPT algorithm is independent of wind turbine characteristics,low cost without any measure device and can be realized easily,which can satisfy the requirement of field engineering. Field test results prove the SRWG system can generate electricity in very low wind speed, can be driven directly in a wide wind speed range,and its application has obviously significance for the improvement of wind energy conversion.