Co-phase Traction Power Supply Research Articles

A Multi-timescale Energy Management Strategy for Advanced Cophase Traction Power Supply System with PV and ES

A Multi-timescale Energy Management Strategy for Advanced Cophase Traction Power Supply System with PV and ES

Arm Current Deviation Minimizing Method for Co-phase Traction Power Supply System Using Direct AC/AC Full-bridge Modular Multilevel Converter

Arm Current Deviation Minimizing Method for Co-phase Traction Power Supply System Using Direct AC/AC Full-bridge Modular Multilevel Converter

Impedance Modeling and Stability Analysis in Co-Phase Traction Power Supply System

Impedance Modeling and Stability Analysis in Co-Phase Traction Power Supply System

Cophase Traction Power Supply System Based on Improved MMC-STATCOM-Vv Wiring

Cophase Traction Power Supply System Based on Improved MMC-STATCOM-Vv Wiring

Thermal Constrained Energy Optimization of Railway Cophase Systems With ESS Integration—An FRA-Pruned DQN Approach

This paper investigates the railway co-phase traction power supply system (TPSS) with a power flow controller (PFC) to address the power quality and neutral section issues. To collect the regenerative energy and achieve a more flexible power flow, the energy storage system (ESS) is integrated into the co-phase system. As the key components, the reliability of power electronics modules in PFC and battery cells in ESS is highly related to their thermal performance. It is therefore vital to consider their operational thermal dynamics, leading to the proposal of a deep Q network (DQN) based thermal constrained energy management strategy in this paper. Firstly, the system power flow model and electrothermal models for power electronics modules and battery cells are all established. Then, a DQN method is adopted to learn an optimized policy for peak power shaving while meetings thermal constraints. Finally, an FRA-based pruning method is proposed to reshape the agent to become more compact without sacrificing its performance. Case studies confirm that the proposed strategy can effectively reduce the peak traction power supply by up to 42.0%, and achieve up to 94.1% thermal reduction. The FRA-based pruning can achieve up to 89.9% agent size reduction and 87.2% computation savings.

A Novel Co-phase Traction Power Supply System in Electrified Railway

The electrified railway has power quality problems such as three phases seriously unbalanced, large harmonics, and reactive power. In addition, the neutral section exists at each power supply section, which restricts the development of the high-speed and heavy-haul railway. This paper proposes a novel co-phase traction power supply system (TPSS) based on a YNvd balanced transformer, which can not only solve the above problems but also save one single-phase coupling step-down transformer, thus reducing the cost and space of the whole system. In addition, the voltage level of the converter switching device can be reduced by the rational design of the transformer tap position, which enhances the reliability and feasibility of the system. The compensation principle and control strategy of the co-phase TPSS based on the novel YNvd balanced transformer are analyzed in detail in this paper, and the compensation current detection and integrated power flow controller (IPFC) control methods are given. Simulation and analysis show that the proposed topology structure and control method are correct and feasible.

FPGA-based Digital Implementation of Flexible Power Control for Three-phase to Single-phase MMC-based Advanced Co-phase Traction Power Supply System

FPGA-based Digital Implementation of Flexible Power Control for Three-phase to Single-phase MMC-based Advanced Co-phase Traction Power Supply System

Bi-hierarchy capacity programming of co-phase TPSS with PV and HESS for minimum life cycle cost

Co-phase traction power supply system (TPSS) with photovoltaic (PV) and hybrid energy storage system (HESS) is a promising way to improve the utilization of regenerative braking energy (RBE) and power quality. However, despite co-phase TPSS with PV and HESS being beneficial from the perspective of technology, how to coordinate the operation strategies of various devices to ensure system economy is a key issue in practical engineering applications. Therefore, this paper proposes a bi-hierarchy capacity programming strategy of co-phase TPSS to minimize life cycle cost. In the upper layer, the integrated lifetime evaluation model of HESS and PFC (HESS-PFC) is proposed for the lower long-term investment cost. Remarkably, the PFC reliability assessment and the HESS degradation process are analyzed. Meanwhile, the capacity of HESS-PFC is obtained, and the lifetime of HESS-PFC is extended. In the lower layer, the power flow of co-phase TPSS is optimized to minimize short-term operating cost under satisfying three-phase voltage unbalance standards. Traction load peak-shaving and valley-filling are achieved by coordinating HESS-PFC and PV. And it is formulated as a mixed integer linear programming model based on efficient linearization methods. Whale optimization algorithm with GUROBI solver embedded is employed to solve this bi-hierarchy model. Finally, case studies show that the proposed model can achieve 23.26% cost reduction and 63.82% PFC lifetime extension, while the voltage unbalance is within an allowable range of 2%.

Study on resonance characteristic of continuous co‐phase traction power supply system

In order to solve the power quality problems and eliminate the neutral sections in the railway, the implementation of the continuous co-phase traction power supply system (CCTPSS) is the development trend of the future. However, various parameters of the compensator in CCTPSS have a huge impact on the resonance, which will possibly change the original resonance characteristic of the railway. Therefore, the parameters design of the compensator has become a difficult problem to be solved. An optimization mode method is proposed in this paper to obtain the influence of the compensator on the resonance characteristic of CCTPSS and the optimal solution of each parameter is obtained with the goal of suppressing resonance and minimizing the cost. Firstly, the impedance analysis and transfer function analysis are used to establish models for CCTPSS. It is found that the equivalent harmonic impedance of the traction substation decreases after adding the compensator, which will inevitably cause the resonance frequency to increase. By comparing the resonance points of the original traction power supply system (TPSS) and CCTPSS, the results show that the parameters of the compensator have a greater influence on the resonance point in CCTPSS. At last, taking the CCTPSS based on LCL-type reactive power comprehensive compensator (RPCC) as an example to carry out the optimization mode method, the result proves that this method is not only beneficial to the suppression of harmonic resonance, but also helpful for reducing the cost of the RPCC.

Dynamic Voltage Unbalance Constrained Economic Dispatch for Electrified Railways Integrated Energy Storage

The cophase traction power supply system (CTPSS) is a promising solution in the smart electrified railways to effectively eliminate the neutral section, improve regeneration braking energy (RBE) utilization and mitigate voltage unbalance (VU). It works by coordinating the power flow distribution (PFD) among the energy storage (ES), power flow controller, and traction transformer. However, the conventional dispatch considering VU mitigation may result in increasing extra operation costs and accelerating ES aging. Therefore, driven by the day-ahead forecasted information, a dynamic VU regulation strategy is proposed to draw up the VU compensation schedule (VU-CS), which can satisfy the probabilistic limitations of power quality standards. Consequently, a Copula-based VU dependence model is developed to transform the VU-CS into the PFD constraint set of CTPSS. Meanwhile, an ES degradation model is introduced to quantify the system operation cost within different scenarios. Taking the PFD as a VU regulation constraint, an economic dispatch scheme of CTPSS is established to obtain a minimum operation cost and maximum RBE utilization. Finally, case study tests verify the efficiency of the proposed approach. The results show that scheme can improve ES cycle life and decrease cost under the probabilistic limitations of VU.

Analysis and Comparison of MMC-Based Co-Phase Traction Power Supply Topology for Auto-Transformer Power Supply System

As high-speed railways develop rapidly worldwide, the problems of neutral section and power quality are becoming increasingly prominent. These problems affect the normal operation of the power grid and the electric locomotives. The co-phase power supply schemes were proposed by researchers, which can solve these problems well. Among them, the MMC-based scheme (MMC-5 L) is a representative one. The existing scheme, when applied to the auto-transformer (AT)-fed system which is usually adopted by high-speed railways, needs to install an auto-transformer on the output side. To eliminate the auto-transformer and to obtain the more suitable and superior co-phase power supply schemes to AT-fed system, two improved schemes are proposed in this paper based on the novel MMC-based scheme (MMC-6 L) we proposed before. While establishing the mathematical model, creating the control system, and carrying out simulation verification of the proposed schemes, the proposed schemes are compared with MMC-6 L and MMC-5 L in terms of topological characteristics, control system complexity, power loss, and functionality. The results show that while the proposed schemes can fulfill the functions of the co-phase power supply scheme well like the MMC-5 L and MMC-6 L, they are more suitable and superior for the AT-fed system in terms of control system complexity and power loss. Among them, MMC-5L1CB performs best in power loss, and MMC-4L2CB performs best in control system complexity.

Improved Coordinated Control Strategy for Reliability Enhancement of Parallel PFCs With LCC Restriction

Power flow controllers (PFCs), which adopt high voltage and large power converters, are the significant device of cophase traction power supply systems (TPSSs); therefore, it is important to enhance the reliability of PFCs. Due to the limited capacity of power semiconductor switches, parallel connection of PFC units has been encouraged, and system reliability can be enhanced by configuring standby PFC units. However, while the increase in the number of redundant modules is accompanied by higher investment, the reliability improvement also has a saturation effect. In addition, among the control techniques of parallel PFCs, one of the commonly employed methods is current-sharing control, but the thermal stress of converters is increased at low loads. Therefore, in this article, a PFCs’ cost model is built based on life cycle cost (LCC) theory, and the number of basic, redundant PFC units is determined with the constraint of the minimum average annual cost. Furthermore, an improved coordinated control strategy that can alleviate thermal stress is proposed. Under a high load, all the PFC units are operated simultaneously, while, under a low load, the units are operated by turns. Moreover, to ensure consistent reliability and maximize system reliability, the rotation working time of each unit and the load demarcation point are optimized considering negative sequence compensation constraints. Case studies show that the given control strategy can extend the life span up to 26.30% and achieve a 19.11% cost reduction.

Cophase Traction Power Supply System Based-MMC-Vv Wiring

A new homogeneous traction power supply scheme based on Vv wiring transformers and modular multilevel converters (MMC) is proposed, which due to address the electrical power quality problems and the negative effects of power splitting on locomotives in electrified railways. The three-phase converter in this paper adopts MMC-based active power compensator (APC), which can eliminate the bridge arm of one phase converter and the step-down isolation transformer compared with the conventional single-phase back-to-back structure converter. The compensation relationship of each port of APC is derived, and the dynamic compensation control strategy of APC is established, and the equalization control and phase shifting carrier techniques are applied to control them and achieve the compensation target. Finally, MATLAB/Simulink is employed as a platform to build a model for simulation, and the experimental results verify the feasibility of the compensation strategy.

Negative Sequence Current and Reactive Power Comprehensive Compensation for Freight Railway Considering the Impact of DFIGs

To solve the power quality problems caused by freight railways in weak grids with high penetration of wind generation, this paper proposes a comprehensive control method for negative sequence current (NSC) suppression and reactive power compensation. Firstly, a co-phase traction power supply system (CTPSS) is introduced, and its compensation principle is analyzed. Secondly, to bring a doubly fed induction generator (DFIG) into full play in suppressing voltage unbalance (VU) in the grid, a VU compensation model of stator is developed. Moreover, a comprehensive compensation method is presented to achieve the dynamic compensation of VU and reactive power. Finally, the effectiveness of the proposed approach is demonstrated using a simulation, which can fully solve the power quality issues and effectively reduce the capacity of the CTPSS.

Prototype Model for High Speed Railway Power Supply System Suitable for Indian Traction Sub Stations using Multi Modular Converter

As on 2020, India does not have any globally proven railway lines running with high-speed standards as above 250 km/h. Indian Railways looking at the prospect of high speed rail networks also known as bullet rail network in India. With the present Indian traction supply system which is based on the phase splitting or phase shifting method is not suitable for the high speed railway network unless we eliminate neutral sections as well as mitigating the power quality issues such as voltage unbalance, harmonics and high reactive power drawn from the utility grid. In this paper, Co-phase traction power supply system with zero neutral sections is proposed. Modular multilevel converter based three phase to single phase catenary system through a DC Link has been designed, simulated and laboratory prototype is made. A MATLAB simulation of the suggested method and droop characteristics based on load sharing between the two single phase parallel inverters had executed. The obtained results were satisfactory and shows that the proposed system is very much suitable for high speed railway.

Modelling on Novel Cable Traction Power Supply System and Power Distribution Analysis

Novel cable traction power supply system (NCTPSS) is a kind of long distance co-phase traction power supply system (TPSS), it can effectively solve problems caused by train's passing through electrical phase separation and improve utilization rate of regenerative energy in system, which is an ideal traction power supply mode. However, its structure is relatively complex due to cable power supply pattern, and internal power flow distribution mechanism still needs further study. In order to establish train-network coupling power flow calculation model, in this paper, two-port network model of each system component is established at first, then equivalent solid circuit model of the system is built by external cascade strategy and tearing nodal method. Then, power flow, the change of traction transformer power output and network voltage are analyzed under the condition that trains work in traction and regenerative braking condition, based on actual train operation schedule. The research shows that the proposed model can accurately calculate and detailed reflect electrical characteristics of NCTPSS, traction transformer capacity is effectively decreased compared with that needed in existing TPSS; Regenerative power can feed back to entire cable traction network and be reused by traction trains with high utilization rate inside NCTPSS.

A lifetime extension strategy to increase the reliability of PFC in Co-phase TPSS

Co-phase traction power supply system (TPSS) is proposed to solve the problems of neutral section and power quality in electrical railways. As the key component of co-phase TPSS, the lifetime of the power flow controller (PFC) largely relies on the power module (PM)’s reliability. The PMs’ lifetime is affected by junction temperature, including average temperature and temperature fluctuation. In this paper, a lifetime extension strategy is presented for junction temperature management, which combines switching frequency conversion with modulation changes. Firstly, in the low-load area, switching frequency conversion is utilized to minimize temperature fluctuation; in the high-load area, an optimized single-phase space vector pulse width modulation (SVPWM) is introduced to reduce the average temperature. Secondly, the particle swarm optimization with constriction factor is applied to solve the load partition point, as well as optimize switching frequency for PFC. Finally, the validity of the proposed lifetime extension strategy is verified by case studies, the result is shown that the failure rate of IGBT module can be reduced by 39.01% and the mean time to failure (MTTF) of the PFC is prolonged by 16.28%. The optimization algorithm can effectively improve the reliability of PFC.

Robust Energy Management of High-Speed Railway Co-Phase Traction Substation With Uncertain PV Generation and Traction Load

Co-phase traction power supply system provides the insights for solving the existing power quality and electrical sectioning issues in high-speed railways, and the flexible control of co-phase traction substation (CTSS) with the integration of photovoltaic (PV) and hybrid energy storage system (HESS) attracts widespread attention. However, the strong volatilities and uncertainties of PV and traction load introduce challenges to the reliable and economic operation of CTSS. In this study, the energy management of CTSS aims at minimizing the operating cost of CTSS by coordinating PV, HESS, power flow controller (PFC) and the energy transactions with the power grid, where the three-phase voltage unbalance constraint is taken into account in particular. Furthermore, to handle the uncertainties of PV and traction load, a two-stage robust optimization model is proposed. The first stage determines the operating status of HESS and energy transaction status with grid, and the second stage aims at finding the optimal scheduling power of CTSS and the worst-case scenario with maximized operating cost of CTSS. A column-and-constraint generation algorithm is employed to solve this robust optimization model, along with efficient linearization approaches for the formulation of mixed-integer linear programming. The proposed methodology is tested with a real high-speed railway line case in China.

A Co-Phase Traction Power Supply System Based on Asymmetric Three-Leg Hybrid Power Quality Conditioner

Single-phase 25kV AC traction power supply system (TPSS) is widely used for electric power feeders in high-speed rail. Modern locomotives draw a large amount of unbalanced, inductive power from two phases of the grid through the traction transformer and lead to severe problems of voltage unbalance and reactive power existence. These problems are mitigated in the promising co-phase TPSS with the equipment of Railway Power Conditioner (RPC) or Hybrid Power Quality Conditioner (HPQC), in which HPQC can operate with a lower voltage and cost. However, HPQC installation involves the adoption of a bulky and expensive coupling transformer. In this paper, a co-phase TPSS employing asymmetric back-to-back modular multilevel converter (MMC) is proposed and it is named asymmetric three-leg hybrid HPQC (ATHPQC). Through the simulation verifications in this research work, the proposed design can effectively remove the additional and costly step-down coupling transformer, which is required by symmetric HPQC. For comprehensiveness of the ATHPQC design, internal circulating current modeling and analysis are investigated. Control system is implemented, including external compensating current control, internal balancing control and PWM module. ATHPQC is a promising alternative TPSS for next-generation high-speed rail.

Improvement of Quadruple Structure and Optimization of Control Algorithm for Co-Phase Traction Power Supply System

Co-phase power supply is one of the key technologies to solve the technical bottlenecks such as electrical phase separation zone, poor power quality and defects in structure and control algorithms in traditional traction power supply systems and single co-phase power supply schemes, and an inevitable way to realize the development of electrified railways in the direction of safety, high speed and heavy load. Based on the single co-phase power supply technology, a novel quadruple co-phase power supply scheme with negative sequence elimination and to suppress reactive power and harmonic better for the two aspects of the system structure improvement and control algorithm optimization is proposed by combining the technologies of power system flexible transmission grid-connected and multiple inverters. Finally, the simulation model for the novel co-phase traction power supply system was designed and built, and the present method was verified by a set of simulation experiments so as to obtain the expected results.