Study On Three-phase/single-phase Negative Sequence Control Of Electrified Railway Based On Impedance-matching Balance Transformer

With the rapid development of electrified railways,it also brought a series of power quality problems such as negative sequence and harmonic,which caused serious damage to the power system.The large number of AC-DC-AC electric locomotives are used in high-speed electrified railways,which has reduced the harm of harmonics,but the problems of negative sequence and neutral section have become more serious.The co-phase power supply system with traditional railway power conditioner(RPC)is an effective solution,however,the required capacity of the active part of the compensation system is relatively large and the cost of the entire device is high.Based on the above background,this paper proposes a hybrid railway power conditioner system(H-RPC)suitable for the co-phase power supply system,the main work is as follows:At first,the structure of the impedance-matching balance transformer is introduced,and the specific relationship that the transformer parameters must meet to achieve three-phase to two-phase symmetrical transformation by impedance matching control is analyzed,also,the voltage and current relationship of the impedancematching balance transformer is analyzed;this paper also describe the basic structure of the traditional RPC and analyze the principle of the compensation,and the relationship of the compensation current is given.Then,in order to reduce capacity and improve economy,a hybrid railway power conditioner system(H-RPC)suitable for the co-phase power supply system was proposed.Firstly,this paper analyze the topology structure of H-RPC and point out the difference between H-RPC and the traditional RPC.Then the compensation principle of the H-RPC and the current and voltage characteristics of the converter are analyzed.The design of the H-RPC coupling branch parameters is also proposed.Moreover,based on this design principle,the design method of coupling branch parameters is given.Finally,the maximum port voltages of H-RPC and traditional RPC were calculated respectively,and the capacity of the two systems was analyzed in theory,the theoretical results show that the design capacity of H-RPC will be 30% lower than that of traditional RPC under the same compensation task,and it prove that H-RPC will have excellent capacity-saving performance.Next,this paper is introduce the control strategy of H-RPC.A detection method for H-RPC command current is proposed based on the improvement of ip-iq method.Then,the control strategy of H-RPC is proposed: a double closed-loop control strategy of current inner loop and voltage outer loop.The voltage outer loop use complex PI control to ensure the stability of the DC voltage.The current inner loop use triangle carrier or hysteresis current control to ensure the real-time tracking of the compensation current and the command current.Finally,a simulation model of H-RPC and traditional RPC was built.The steady and transient characteristics of the two systems were compared and analyzed,at the same time,the capacity of the two systems was simulated and compared.