Simulation Research On Harmonic Suppression Device In Electric Railway

The characteristics of random fluctuation and nonlinear of traction load make electric railway have many power quality problems,such as harmonics,reactive power and so on.These problems increase potential risk and seriously restrict development of electric railway.In order to achieve the "Thirteenth Five-Year Plan for Development of Railways" and move electric railway forward economically and environmentally,we must take measures to treat the electric railway's power quality problems.Active compensation devices as an effective measure,are impacted by step-down transformers and multiple-converter technique.For this reason,this paper adopts H-bridge cascaded active power filter(APF)straight hanging on traction network to manage electric railway's power quality problems,and studies the whole control strategy of cascaded APF according to the traction load's characteristics.Simulation models of traction power supply system and electric locomotives are built so as to research the harmonic distortion of traction power supply system.The simulation result of traction power supply system's harmonic content in different situation reflects that compensating and treating the electric railway's harmonics is urgent and necessary.On the basis of the existing power quality improving methods,cascaded APF is adopted.Cascaded APF's operating principle,mathematical model,the design of main circuit parameters and carrier phase shifted modulation technique are analyzed.Cascaded APF's control strategy is the key to compensation performance.Reference current detection method chooses adaptive algorithms on the basis of traction load's nonlinear because it can work even distord traction network voltage.Based on several kinds of variable step size algorithm,Sigmoid-tanh switching variable step size algorithm is proposed which improves traditional adaptive algorithms' problems of steady accuracy and response speed;Current control adopts improved dead-beat(DB)control which can predict command current of the next two beat and correct output curren because conventional DB control's delay and current samping error will reduce system stability;Voltage control includes DC voltage PI control and Shifting the modulatin wave DC voltage balancing control which is simple because it saves the trouble of time-consuming and complicated parameters setting.Single-phase cascaded APF simulation model is established in the MATLAB/Simulink environment.The control strategy is validated by simulation experiments.In the end,cascaded APF is hanged straightly on traction network's simulation model.Simulation result in steady and transient conditions reflects that the cascaded APF has good compensation performance...