Research On Robust Fuzzy Control Strategies For Single-phase Voltage Source Converter Of The High-speed Train

Electric transportation has seen a rapid expansion partly due to flexibility for commuters and carbon emission reduction.However,transportation electrification creates severe power quality problems in the utility grid.Single-phase voltage source traction converter(VSTC)plays a vital role in high-speed train operation.However,it is partly blamed for injecting instability into the vehicle-grid coupling systems(VGCSs).Therefore,understanding the function of VSTC and complying with various grid codes and technical standards for VGCSs is essential.Furthermore,the grid-connected VSTC must comply with strict safety standards such as IEEE Std.519,and IEEE Std.16.However,with hundreds or thousands of literature available,it is difficult to choose an effective control method that meets all the requirements.Furthermore,electric multiple units(EMUs)or electric locomotive uses the rectifying load connected to a single-phase feeder,which consumes imaginary or quadrature power and injects negative sequence current into VGCS.The interaction between the EMUs and VGCS created serious power quality issues.This problem is associated with a four-quadrant VSTC.Furthermore,EMUs use VSTC as anterior rectifiers because they can pull energy from the VGCS or inject energy back into the VGCS in the event of regenerative braking.VSTC ensures a nearly sinusoidal alternating current and unity power factor on the vehicle side.However,their operation under sinusoidal pulse-width modulation may generate sideband harmonics around the carrier frequency.If some of the negative sequence currents injected into the VGCS accidentally coincide with the resonant frequency of the VGCS,an LFO could be excited.LFO creates unwanted distortion in both voltage and current.It also interferes with communication channels and activates protective devices,resulting in traction blockade.Consequently,to illustrate a clear picture of the development of effective mitigation strategies,this dissertation focuses on control techniques,mainly for harmonics rejection and LFO,and stabilizing the effects of constant power loads(CPLs).This work intends to address the above problems by proposing robust fuzzy control solutions to mitigate LFO,stabilize the system and eliminate the effects of incremental negative resistance induced by the CPLs.Takagi-Sugeno fuzzy model(TSFM)law is utilized.Moreover,the TSFM model effectively combines convexity theory,linear control theory,and nonlinear systems.That is to say,instead of employing complex fuzzy algorithms to create global linear controllers,the TSFM modeling methods use simple basic control concepts to create piecewise linear controllers.Therefore,we first proposed a fuzzy-observer-based control(FOC)algorithm to improve the efficiency of VSTC and address the instability issues.Furthermore,the proposed observer can check for errors in the system model by estimating the system premise variables,and the fuzzy controller then accurately compensates for the estimated variables.To further study the application of fuzzy-based control solutions,a robust fuzzy nonlinear control is proposed for VSTC feeding CPLs.The negative incremental resistance characteristics of the trains due to CPLs are first investigated.Then,utilizing the TSFM and parallel distributed compensation approach,a robust stabilizing controller is constructed to ensure the asymptotic descent of the dynamic system state trajectories toward the equilibrium position.Moreover,using linear matrix inequalities,the intended control gain can be automatically computed.The critical adjustment time of the controller and total harmonic distortions of the line currents are selected to measure and compare the transient and dynamic stability of other state-of-the-art controllers and the designed controller.The suggested technique not only maintains global stability in the face of considerable changes in the CPLs but also offers a fast dynamic reaction time and precise tracking over a wide operating range.Finally,a simulation model is formed in SIMULINK,and the waveforms are checked with other state-of-the-art control techniques.The proposed methods can achieve better performance,such as fast transient,more damping,and small overshoot.Furthermore,the methods can maintain stability when the system is subjected to external disturbance.In the end,hardware-in-the-loop experiments are performed to validate the proposed control algorithm.Moreover,future trends on control strategies for VSTC,considering the recent advancements in artificial intelligence,are extensively discussed.