Jianqiang Liu

Energy Harvesting for the Electrification of Railway Stations: Getting a charge from the regenerative braking of trains.A

An enormous amount of energy is generated by railway cars when applying regenerative braking in train stations. This article discusses the methods for absorbing, storing, and using the energy produced by regenerative braking. Two methods are proposed: 1) regenerative energy is fed back to the distribution grid for supplying stationary loads at train stations and 2) regenerative energy is used to charge railway car-mounted storage containers, which can also supply stationary loads or be transported elsewhere for supplying remote loads. The working principles and topological structures of the two methods are introduced. In addition, main circuits and corresponding control systems are simulated, and analyses are conducted to validate the proposed methods for train stations in China.

Harmonic analysis of traction networks based on the CRH380 series EMUs accident

The harmonic component introduced by the high-speed electric multiple units(EMUs) can cause resonance phenomenon in traction networks. A similar resonance accident occurred when the novel CRH380 Series EMUs were running in the Beijing-Shanghai high-speed railway. According to the operation parameters, this paper built the chain network model of the traction power supply system and analysed the influence of harmonic current using the matrix calculation function of MATLAB. The model was based on the uniform transmission lines analysis and combined the characteristics of the multi-conductor transmission. The reason of the accident was analyzed and a reliable strategy to solve the resonance problems was proposed.

A Modified Gain Model and the Corresponding Design Method for an LLC Resonant Converter

In this paper, a modified gain model and the corresponding design method for an LLC resonant converter are proposed. To derive the gain model, two important factors—resonant factor and load factor are considered and discussed in detail by combining time domain and frequency domain. Compared with fundamental harmonic approximation (FHA) method, the accuracy of the gain model is highly improved. Referring to the modified gain model, the corresponding design method is also obtained that can inherit conciseness and practicability of the FHA method. Thus, the design method can be used to replace the FHA method in practical design procedures. Finally, the simulation results are given and a prototype of the LLC resonant converter used for power electronic traction transformer is built to verify the accuracy and validity of the proposed gain model and the corresponding design method

Reliability evaluating for traction drive system of high-speed electrical multiple units

Based on the structure parameter and operating principle of the traction drive system for high-speed electric multiple units (EMUs), the reliability block diagram(RBD) models of traction drive system are established. According to the theory of system reliability and the failure statistic datum of the traction drive system in CRH3 high-speed EMUs which running in Beijing-Tianjin and Wuhan-Guangzhou high-speed railway, the law of reliability about components in the traction drive system are proved. At the same time, the methods of calculation about reliability evaluation indexes are given, the failure rate and the reliability of the various components are calculated. Based on the RBD model of the traction drive system, the reliability of the whole traction drive system in Beijing-Tianjin and Wuhan-Guangzhou high-speed railway are evaluated. The research results provide reference for safe utilization and maintenance and repair of the traction drive system of CRH3 high-speed EMUs.

Voltage Balance Control Based on Dual Active Bridge DC/DC Converters in a Power Electronic Traction Transformer

In this paper, a voltage balance control strategy based on dual active bridge (DAB) dc/dc converters in a power electronic traction transformer (PETT) is proposed. Based on this strategy, the output-parallel DAB converters can be equivalent to an input-series-output-parallel system. Furthermore, a PETT starting control method is put forward, which can effectively avoid risks of overcurrent and overvoltage in the PETT starting process. In order to carry out the controller design and system stability analysis, three different kinds of mathematical models of DAB converters are set up. The first model is related to a single DAB converter, the second model reflects the equivalent relation between an output-parallel DAB system and a single DAB converter in terms of the output-voltage control loop, and the third model indicates that the voltage balance control system based on DAB converters is a multiinput-multioutput system. Due to the nonzero off-diagonal elements of the controlled plant, there is a mutual effect between different control loops, which is defined as “interaction” in the multivariable feedback control theory. The stability of the voltage balance control system is made up of two parts, including the stability of each single-input-single-output (SISO) control loop and the influence of the interaction on the system stability. The research is carried out to measure the intensity of the interaction in this paper, and a criterion directly based on the controlled plant is proposed to predict the influence of the interaction, which can obviously simplify the system stability analysis. Considering the particular traction onboard application, a new control structure toward the voltage balance controller is introduced. Based on the new structure, the controller is designed and the stability of the SISO system is analyzed. Finally, a five-cell PETT prototype with rated power of 30 kW is taken to carry out further research, and the experiment results verify the effectiveness and correctness of the proposed algorithms.

Current adaptive resonant loop soft switching PWM converters

In light loading mode, most of the existing soft switching techniques have higher switching loss than their hard switching counterparts as the amplitude of the current in the resonant loop is greater than the load current of the switching instant point. To solve this problem, in the paper, a class of Current Adaptive Resonant Loop (CARL) soft switching PWM converters are proposed, in which, not only all power switches and diodes operate with zero current switching (ZCS), the resonant current amplitude also self adaptively tracks the value of the switching instant point of load current value, at both turn-on and turn-off durations. Compared to their hard switching counterparts, the CARL soft switching PWM converters add only three auxiliary components including one auxiliary switch device, one resonant capacitor and one resonant inductor. The advantages of the proposed CARL soft switching PWM converters are verified by the experimental results of a buck converter.

Improved Fault-Tolerant Method and Control Strategy Based on Reverse Charging for the Power Electronic Traction Transformer

Power electronic traction transformer (PETT) is a new topology for a traction drive system, which can realize the high voltage and power conversion through multilevel converters and high-/medium-frequency transformer link. Reliability becomes a key issue for PETT adopting the module-cascaded structure. In this paper, an improved fault-tolerant method based on reverse-charging control of dual active bridge is proposed, which is suitable for PETT and other two-stage structure converters. The control strategy and operating process of an improved fault-tolerant method are introduced. Comparisons among improved and traditional fault-tolerant methods are also presented. Simulation and experimental results are provided to show the correctness and effectiveness of the improved fault-tolerant method.