Research On Parameters Design And Internal Resonance Suppression Strategy Of Co-phase Compensation Device Output Filter

As a new traction power supply method,co-phase power supply can not only convert three-phase electricity into single-phase electricity as traction power,but also solve the power quality problem.Using co-phase compensation device(CPD)can compensate the harmonics generated by the locomotive,which is a significant approach to ensure the stability,safety and high-efficient of the co-phase power supply system.However,due to the high harmonic current generated by CPD,it is necessary to select an appropriate output filter for processing.The LCL output filter has the advantages of strong harmonic attenuation,low cost and simple structure,so it is used to filter the harmonic generated by CPD.But the LCL output filter is a third-order system,and there is a resonance problem.It is of great significance to research LCL parameter designing method and resonance suppression strategy to co-phase power supply system.In view of the situation above,the following researches are carried out in this thesis.(1)Based on the working principle of LCL output filter,this report establishes the mathematical model under the situation of three-phase static coordinate system and discrete state.Then the constraint problem in the design of CPD output filter LCL is provided.It lays a foundation for the research on parameter design and resonance suppression strategy theoretically.(2)To solve the problem of high frequency harmonics in the co-phase power supply system,an output filter LCL parameter design method which aims at the current of minimum total harmonics distortion(THD)at grid side is proposed.First,based on the overall perspective of locomotive current,grid side inductance,and output current from CPD,this thesis deduces the relationship among THD of current at grid side,ripple attenuation factor(RAF)of CPD,and the inductance of grid side,the capacitance of LCL,the total inductance of LCL,and the total inductance distribution ratio of LCL.Then,the range of parameter is determined by making CPD compensation current meeting fast tracking ability,switching ripple current meet the inhibition requirement,and LCL fundamental reactive power loss meet the restriction conditions.The minimum THD is the objective function and RAF is the constraint.The dividing rectangle algorithm(DIRECT)is applied to solve the problem and find the parameter of LCL with the minimum THD.(3)Because of the resonance problem of output filter LCL,this thesis emphasize on damping strategy of the output filter LCL.Firstly,the reason of output filter LCL resonance is analyzed.Then the performance of four different damping topologies is discussed for passive damping method.It is found that resistor series/parallel in capacitor branch of output filter LCL are more suitable for CPD system.Finally,the two damping modes above are discussed and verified by simulation in three aspects: system stability margin,harmonic attenuation characteristics and active power loss.For the active damping method,the single-state variable feedback and the virtual resistance method are analyzed separately.An improved active damping strategy is proposed.Finally,the effectiveness of the three active damping methods is verified by simulation with the co-phase power supply system.