Leng Yue

Effectiveness analysis of determining the main harmonic source by harmonic active power direction method

Nowadays, harmonic active power direction method is the most widely applied method to judge the main harmonic source, but the power direction method is theoretically different from harmonic current superposition principle. In this paper, it has been got that the power direction method and harmonic current superposition principle are different through mathematical analysis, and the precise conditions which make harmonic active power direction method right has been got. On the basis of this, this paper analyzes the applicable area of the harmonic active power direction method. In practical engineering applications, this method does not require the exact values of the harmonic impedances of the two sides. Besides, the easy way to judge the location of the main harmonic source is obtained in this paper, which only depends on the measured angle value of the harmonic voltage and harmonic current at the PCC. It is convenient to the practical application in engineering.

A method for identifying the fault current of DC traction power supply system based on EMD approximate entropy

In this paper, an identification method of the oscillation current and the short-circuit fault current in DC traction power supply system based on empirical mode decomposition (EMD) and approximate entropy is proposed. The feeder current is decomposed by means of EMD technique, and the sum of the approximate entropy of each intrinsic mode function (IMF) is calculated. Thus, the characteristic value that reflects the running status information of DC traction network is obtained. According to the computed result, it can be found out that the feature extraction method combined EMD and approximate entropy can effectively distinguish the oscillation current and the short-circuit fault current of DC traction power supply system.

Fault current identification of DC traction power supply system based on LMD time-frequency entropy

In this paper, a method of identifying the short-circuit fault current in DC traction power supply system based on local mean decomposition (LMD) and time-frequency entropy is proposed. Firstly, the feeder current signal of DC traction power supply system is analyzed by means of LMD, by which the LMD time-frequency distribution can be obtained. Secondly, the LMD time-frequency plane is divided into time-frequency blocks with equal area. Finally, the time-frequency entropy of the time-frequency plane is obtained, which can serve as the feature vector to distinguish the oscillation current and the short-circuit fault current in DC traction power supply system. According to the simulation analysis, it can be found out that the simulation results conform to the theoretical analysis. Moreover, the calculation results of the measured data show that the proposed method is capable of distinguishing the oscillation current and the short-circuit fault current in DC traction power supply system.

A method based on 2DOF-IMC to voltage low-frequency oscillation suppression in high-speed railway traction network

Aiming at the low-frequency oscillation of traction network caused by the high-speed railway electric motor units (EMUs), when transient current control strategy (TCCS) based on traditional PI controller is adopted by the line-side converter (LSC) of the EMUs, by analyzing the PI controller parameter adjustment, it is found that this suppression measure has its limitations. In order to overcome the above problem, this paper brings internal model control (IMC) into the TCCS, and according to the internal model control principle, a two-degree-of-freedom (2DOF) internal model controller is designed to replace the traditional PI controller in the TCCS. Then comparing the performance characteristics of TCCS based on traditional PI controller with TCCS based on 2DOF-IMC. Finally, the EMUs adopting the two control strategies are applied to the time-domain simulation model of the train-grid respectively, it can be found that TCCS based on 2DOF-IMC provides better tracing and load disturbance regulation characteristics, in addition, it is able to suppress the low-frequency oscillation of high-speed railway traction network effectively.