Research On System Simulation And Design For Variable Speed And Fixed Frequency Controller Of Doubly-fed Shaft Generator

Ship shaft generator can be an optional choice for the reason that it can berunning both as generator or motor, it not only fully uses the residual power of mainengine but also can support propulsive force when needed as motor, which will helpthe ship to get out of emergency operating mode. The capability of switchingoperating mode definitely improves ship reliability.During voyage, the speed of ship and load of propeller are changeable, thetraditional speed-compensated solution is aimed to compensate the generator’s speedto make its speed constant with some kind of machinery. This solution generallydoesn’t have high efficiency or large enough speed range. On the other hand, thefrequency-compensated solution is on the base of modern power electronics technic,which has higher efficiency、large enough speed range and less devices. Its aim is tocompensate the frequency of generator power to get constant-frequency AC or DCpower. This solution includes the form with transducer, the form with controllersilicon inverter and synchronous compensator, the form with full power converter, theform with DFIG (Doubly-fed induction motor) and so on. Among them the last twosolutions are now hot research spot. This paper will study the form with DFIG for theadvances of DFIG.DFIG (Doubly-fed induction motor) has a special structure that makes it perfectfor application of variable speed situation. The exciting voltage of DFIG is the kind ofthree phase of AC voltage, whose amplitude、phase and frequency all can be adjustedto make sure that the stator of DFIG can produce amplitude-needed andfrequency-needed power. Specifically for the DFIG, converter is connected to therotor side, capacity of converter is just on the base of slip power which is small part ofnormal power of motor. That advantage absolutely decrease converter’s capacity、weight and costs. This paper is aimed to research on the DFIG and try to make acontroller to control it to get needed power when speed is variable.Firstly the paper compare the DFIG with other synchronous motor orasynchronous motor when used in variable-speed field. Then this paper established one dynamic math model for DFIG, analyzed the relationship between severaldifferent physical quantity. At the same time, this paper analyzed the structure andcontrol strategy of converter which included rectifier and inverter, simulating resultscertifies the analysis above. Then this paper try to design the hardware and programthe software for the controller of DFIG on the base of analysis of needed functions.The main body of this paper is research of characters and control strategy ofDFIG, on the process this paper proposed to establish one P.U. math model for DFIG,improve the observer of flux, simplify the method of detect rotor angle, add protectcircuits for controller to make the controller perform better.Restricted by time and locate condition, this paper just made test to the controlleritself, which proves the controller can meet the requirement.On the other hand, this paper try to analyze the power flow when DFIG isoperating at different mode. On the base of this analysis this paper discussed twodifferent control strategies for two different application of DFIG. One is that DFIG isoperating at stand-alone mode, the other is at grid-connected mode. Both operatingmode are simulated through Simulink.