Huan Xia

Modeling and state of charge-based energy management strategy of ultracapacitor energy storage system of urban rail transit

Applying ultracapacitor to store regenerative braking energy in urban rail transit can achieve good effects on energy efficiency and voltage regulation. But when multiple devices distributed in one rail line, it cannot be coordinated by current energy management strategy, which leads to higher power dissipation and voltage stress. The paper firstly establishes models of train, traction power grid and energy storage system combined with characteristics of ultracapacitor. Then operating features are analyzed under constant voltage-based energy management strategy, in view of the analysis a state of charge-based energy management strategy is proposed, which can be sufficiently utilize the configuration capacity of all ultracapacitors, lower the power dissipation and the voltage stress and help to extend the service life of the ultracapacitors. Finally, simulation and experiment results show the correctness of the model and the effectiveness of the proposed energy management strategy.

An overview on braking energy regeneration technologies in Chinese urban railway transportation

In order to prevent the failure of regeneration and reduce energy consumption, making full use of regenerative energy has been widely recognized as an important issue by Chinese urban railway transportation community. This paper provides an overview on the technologies of regenerative energy braking in China. It is first explained that why the ground resistor is popular in China in order to prevent the failure of regeneration. Alternative technology using regenerative inverter and ground supercapacitor is then introduced including main circuit, working mechanism and existing problems. Next, the simulation, status quo and experimental results of the ground supercapacitor energy storage system are discussed in detail for a 200kW prototype system developed in China. Finally, future improvements are mentioned for Chinese braking energy regeneration technology.

Variable gain control of supercapacitor energy storage system of urban rail transit considering system parameters variation

Using supercapacitor store surplus regenerative braking energy in urban rail transit traction power supply system can achieve good effects on energy efficiency and voltage regulation. Firstly, the traction power supply system characteristics and train braking characteristics are analyzed. Then the model of supercapacitor energy storage system based on bidirectional Buck/Boost converter is established. Combing with voltage-current double closed loop control strategy, the influence of grid voltage and duty cycle on dynamic performance of the system is discussed. The relationship between the inner loop gain and grid voltage, and the relationship between the outer loop gain and duty cycle are discussed. Based on this, the control strategy of variable gain is proposed, which can offset the influence of grid voltage and duty cycle on dynamic performance of the system by changing the gain of inner loop and outer loop, making the system maintain good dynamic performance when the parameters variation in a wide range. Finally, the effectiveness of the proposed control strategy is verified by simulation.

Thresholds modification strategy of wayside supercapacitor storage considering DC substation characteristics

Wayside supercapacitor based energy storage system (ESS) for urban rail transit can reuse the braking energy and reduce energy consumption. Most ESSs switch over from charging to discharging states based on voltage of DC bus. But open circuit voltage of DC power supply in subway system always changes, which would influence the normal operation of ESS. This paper will show the output characteristic of substation and the basic structure of supercapacitor based ESS. At the same time, influences of substation output voltage fluctuation on ESS will be analyzed. And then, a control strategy for eliminating the influence will be come up with. Finally, this paper will present the experiment results of 200kW supercapacitor based ESS prototype field test in Beijing subway.