Control Strategies Of PMSG-based Wind Turbines And Application To The Power System In Bac Lieu, Viet Nam

Wind power is growing rapidly,from a small number to a large number,from onshore to offshore,from an alternating current transmission line to a direct current transmission line.The increased continuous penetration of wind power into the electrical network system makes the decreased continuous proportion of electricity from traditional electricity sources(thermoelectricity and hydroelectricity)which brings some concerns about the operation of the electrical network system.The incident which occurres the electrical grid,requires to follow that the wind farms,however its need to have the control strategies to contribute to the control of the electrical parameters in the system.This present thesis evaluate the communication free control strategy to allow the high voltage direct current(HVDC)system connecting the offshore WF and the onshore AC networks and to ensure respectively:(1)Fault Ride-Through(FRT)capability,(2)Elements in the system which are not damaged when the incident occures long-term on the electrical grid,(3)Incidents with small fluctuations in the system.The thesis consists of three main parts:1.Control strategy Fault Ride-Through for offshore wind farm connected to the main electrical grid via High Voltage Direct Current.The purpose of the control strategy is to combine the AC voltage reduction method and chopper resistor.A cascading control scheme was designed to allow offshore wind farms to respond to AC mainland faults.Its strategy is to adjust the offshore AC grid voltage corresponding to the DC voltage variation.Through this control strategy,the offshore wind turbine will have to reduce the AC voltage at its terminals,reduce transmission active power to the offshore converter.The new point of this control strategy is not to put chopper resistor in the conventional way.The conventional approach is that the chopper resistor is connected in parallel on the DC side of the onshore conversion station.In this control strategy,with the PMSG wind generator,use a chopper resistor mounted at wind turbine tower,and connected to the back-to-back converter DC link.In order to promote the desired active power reduction,the chopper resistors also control the magnitude of the DC voltage increase at the DC busbar.2.Control strategy for the HVDC grids when the incident occurring long-term on the electrical gridWhen the incident occurring long-term on the electrical grid,the solution given is hybrid strategy which combined the two control methods:(1)Reduction the active power by heat dissipation through the chopper resistors.(2)Adjustation of the pitch angle in order to reduce the output power of the wind turbine.This phase ensures a long-term energy balance on the DC grid.This combination method has the advantage to calculate directly the power reduction from the wind turbine based on the reduction of the offshore AC voltage,to avoid the communication delay.3.Utilization of artificial neural network for the controller design of the machine side converter in the PMSG wind turbineAn artificial neural network is trained to replace traditional PID controllers.The principle of the design of this neuron controller is: to run the initial program,especially take the input and output data of the PI controller.Afterwards,obtain this data set to train the neural network and then use the neural network to replace the old PI module.If the data set is obtained in a interference condition means the system has problems and the linear PI module can not be processed,the neural network will study,adapt by itself so it keeps the system stable and reduces the harmonic coefficient.The simulation results indicate that the new system is more stable,higher performance.The error between the control signal and the reference signal is also much smaller than the traditional PID controller.Particularly,the training of artificial neural networks in accordance with the actual data sets has helped the system to work well with the actual conditions,expressed by the Total Harmonic Distortion(THD)of the AC grid voltage decreased from 39.21% to 13.6%,thus significantly reducing the high harmonic components.The simulation results show the effectiveness of the proposed strategies.Applying with the current situation in Vietnam,when the wind energy source is still in the development process,the qualification of engineers is still low,the choice of artificial neural network method is most suitable.This is a method that is not too complicated,does not require a very high level of engineers and still ensures technical requirements.