Catenary-free Trams Research Articles

Fault Tolerable Cooperative Control for Charging Supercapacitors of Catenary-Free Trams

Fault Tolerable Cooperative Control for Charging Supercapacitors of Catenary-Free Trams

Optimal Sizing of On-Board Energy Storage Systems and Stationary Charging Infrastructures for a Catenary-Free Tram

This paper introduces an optimal sizing method for a catenary-free tram, in which both on-board energy storage systems and charging infrastructures are considered. To quantitatively analyze the trade-off between available charging time and economic operation, a daily cost function containing a whole life-time cost of energy storage and an expense of energy supplies is formulated for the optimal sizing problem. A mixed particle swarm optimization algorithm is utilized to find optimal solutions for three schemes: (1) ultracapacitors storage systems with fast-charging at each station; (2) battery storage systems with slow-charging at starting and final stations; (3) battery storage systems with fast-swapping at swapping station. A case study on an existing catenary-free tramline in China is applied to verify the effectiveness of the proposed method. Results show that a daily-cost reduction over 30% and a weight reduction over 40% can be achieved by scheme 2, and a cost saving of 34.23% and a weight reduction of 32.46% can be obtained by scheme 3.

Optimisation of a Catenary-Free Tramline Equipped With Stationary Energy Storage Systems

Catenary-free trams powered by on-board supercapacitor systems require high charging power from tram stations along the line. Since a shared electric grid is suffering from power superimposition when several trams charge at the same time, we propose to install stationary energy storage systems (SESSs) for power supply network to downsize charging equipment and reduce operational cost of the electric grid. To evaluate the trade-off between component cost and operational cost, an optimisation problem, which integrates type selection, sizing, energy management and different installation configurations of the SESSs, is introduced and formulated in terms of an annual cost. Disciplined convex modelling is applied to obtain a computationally tractable solution for a case study on an existing line in China. Results show that the optimal solution may reduce tramline cost by 11.48%.

Optimal Charging Scheduling for Catenary-Free Trams in Public Transportation Systems

Catenary-free tram with supercapacitor for short-distance travel is an emerging and energy-efficient way of urban transportation. However, a large number of decentralized and high-power charging loads from Catenary-free trams bring new challenges to the power system. In addition, frequent and high-voltage charging may result in a shorter lifetime of the supercapacitor. Thus, how to coordinate the charging processes of Catenary-free trams considering the power system constraint and the operation costs of the transportation system is an important open issue, especially as the charging requirements are time-varying. In this paper, we design a charging scheduling system to manage the charging processes of Catenary-free trams. Then, based on the historical and estimated operation data of Catenary-free trams, we propose a day-ahead optimal charging scheduling scheme to arrange their charging processes and report to the power system on the upper bound of the charging loads. Thereafter, we propose a real-time optimal charging scheduling scheme according to the real-time operation information to update the real-time charging loads of Catenary-free trams, such that a trade-off among the electricity cost, operation reliability, and battery lifetime is made to minimize the total operation costs. Finally, simulations have been conducted to evaluate the performance of the proposed charging scheduling schemes and show that the proposed algorithms can reduce the total operation cost by about 28%.

A Cooperative Charging Protocol for Onboard Supercapacitors of Catenary-Free Trams

Catenary-free trams with an onboard supercapacitor have been an emerging and energy-efficient way for urban rail transportation. However, the high-power charging load from catenary-free trams brings a new challenge to the design of charging systems. The traditional single-module charging system typically suffers from a high power and thermal pressure, which reduces the reliability of the charging system. In this paper, we propose a multimodule charging system to improve the system reliability by decomposing power pressure to multiple charging modules. Specifically, a cooperative charging protocol is proposed to improve the dynamic performance of the charging system by suppressing the current imbalance and avoiding the current overshoot during the startup process. First, we mathematically model the multimodule charging system using the state-space averaging method and graph theory. Second, the cooperative charging protocol is designed using the leader–follower consensus algorithm, where the virtual leader represents the desired charging current for each module with a warm-start mechanism. Third, multiple-input multiple-output root locus technique is exploited to characterize the dynamic performance of the charging system. Both simulation and experiment results show that the proposed protocol effectively suppresses the imbalance and avoids the overshoot during the startup of the charging system.

Model Predictive Control for Real-time Position Tracking of a Catenary-free Tram

Automatic Train (or Tram) Operation (ATO) systems have been widely studied in the last decade to guarantee energy-efficient operation. Speed profiles and timetables are derived by applying optimization methods geared towards finding the optimal trade-off between journey time, emissions and energy efficiency. An on-board controller is required to track such optimal trajectories, despite model uncertainties. Due to the non-linear dynamics and non-holonomic constraints on both inputs and outputs, the tracking of such trajectories represents a difficult task. This paper deals with the design of the tracking algorithm, for a catenary-free tram, with regenerative braking. A Model Predictive Control (MPC) approach is used to track the optimal position profile. Thanks to the ability to easily deal with multivariable systems, make use of the references and disturbances preview, and enforce time-varying input/output constraints, MPC is the perfect candidate to fulfill this task. The proposed MPC formulation is simple enough to be implemented in real-time, with a quadratic programming solver. Results show that the algorithm tracks the position reference, and guarantees punctuality and comfort, while enforcing time-varying constraints on vehicle velocity, electrical machine and friction forces. The results are also confirmed in the case of operation with model mismatch.