Rail Traction System Research Articles

Stability Improvement of Adaptive Full-Order Observer for Sensorless Induction Motor Drives in Low-Speed Regenerating Mode

In the applications of high power induction motor railway traction systems, the switching frequency of power devices is relatively low. This restriction will severely reduce the accuracy and stability of conventional discrete model for adaptive full-order observer (AFO) in extremely high-speed region. What’s worse, due to the neglect of flux error during speed estimation derivation, the conventional AFO cannot maintain stability under low-speed regenerating mode. The above two reasons limit the application of AFO in rail traction systems for full speed range. To address this problem, this paper utilizes a high-accuracy discretization which is achieved in combined reference frames and feedback gains are designed in z-domain to ensure stability and dynamic performance of AFO. Moreover, a modified speed estimation mechanism with the error of d-axis current is developed to guarantee stability in extremely low-speed regenerating mode. Rigorous simulations and experiments are performed to verify that the proposed AFO model achieves excellent sensorless control performance in full speed range.

Urban Rail System Modeling and Simulation Based on Dynamic Train Density

To further improve the simulation calculation ability of urban rail traction systems during the peak operation period and provide an accurate and reliable simulation tool for the subsequent train schedule and energy storage system design, a multi-train circuit model with a bilateral power supply was established in this paper, and a power calculation algorithm based on dynamic train density was designed. The circuit topology in the model can be dynamically adjusted according to the number of trains to improve the operation rate. Based on the spatial and electrical data of a real section of the subway, the urban rail circuit model was built on the MATLAB platform, and the actual operation data of the subway was imported for verification. The experimental results show that the multi-train model can accurately reflect the influence of voltage fluctuations on the traction system under different train running conditions, and the results fit the actual operation conditions. By comparing the influence of different train intervals on the RBE (regenerative braking energy) utilization, the results show that the optimal RBE utilization rate can be achieved by adjusting the train interval in the peak period.

NPC-Based Multi-Source Inverters for Multimode DC Rail Traction Systems

The need for decarbonization has increased the interest in alternative propulsion systems for light rail vehicles, including fuel cells, batteries, and supercapacitors. These sources and storage devices can also be used in combination with an external supply to enable operation on both electrified and nonelectrified tracks. In traditional architectures, the sources are connected via dc/dc converters to a common dc-link that feeds the motor drives. This article addresses a new configuration where an NPC-based multisource inverter (MSI) is used for the integration of the dc sources to the traction motors in a single stage. First, a thorough analysis of the converter’s operation is carried out with reference to its state-of-the-art control. The conditions for full control of the dc sources and traction motors over the entire vehicle speed profile are derived. Second, a novel modulation technique is proposed to complement the baseline control and enable the stationary charging of the energy storage from the electrified line through the converter. Thus, the MSI can be operated to match all the functionalities of conventional multimode architecture, with the advantage of the reduced number of power converters. Validations are carried out by means of simulations and extensive experiments on a laboratory test bench.

Curving Motion Control of a Traction Rail Mover Using a Dual BLAC Motor Drive

This article presents an improved position control method of an overhang-type rail system considering a curved path. The designed system is driven by two BLAC (brushless ac) motors, and the moving position is controlled based on the signal from a simple Hall position sensor mounted on the motor without any absolute position sensors. The rail is composed of both linear and curved paths. For the linear rail, the two motors are controlled to rotate in the same speed. However, in a curved path, the two motors must have different moving distance according to the curvature. Generally, in order to determine the proper motion commands for both traction motors, the actual curvature state and position have to be detected by a potentiometer or an encoder equipped with linear position sensor, but this method significantly increases complexity and cost of the system. This article aims to solve this problem by using a low-cost semiconductor IMU (inertia measurement unit) to estimate the actual rail condition. The IMU will then estimate the heading angle variation to compensate the motion commands for the two BLAC motors without any additional external absolute sensors. As a result, a balanced and improved motion can be achieved for an arbitrary rail path. Practical experiments using an overhang-type rail traction system were performed to verify the effectiveness of the proposed control scheme. The results show the advanced control performance in both linear and curved path, and also a smooth transition between them both.

Anti-Disturbance Cooperative Fuzzy Tracking Control of Multi-PMSMs Low-Speed Urban Rail Traction Systems

Anti-Disturbance Cooperative Fuzzy Tracking Control of Multi-PMSMs Low-Speed Urban Rail Traction Systems

Motion control of the rail traction system by dual brushless AC motors using a disturbance observer

This study presents an accurate motion control scheme using a modified non-linear disturbance torque observer for a rail traction system driven by a dual brushless AC (BLAC) motor. The target application has two BLAC motors mounted on the top surface of the rail. The mover translation along the rail is handled solely by the traction motors without any external sensor. In the low-speed range, however, the conventional disturbance torque observer is unstable due to the resolution of the Hall sensor and speed detection delay. To solve this instability problem, a simple weight function with the synchronisation of torque current and the delayed speed feedback is added to the proposed torque observer. This way, zero output can be created in the selected speed region for stabilisation and torque current can be compensated. Furthermore, simple balance error compensation to synchronise both motors is added to the proposed speed and position model reference adaptive control scheme. The experiments were performed to verify the proposed control method. The results show advanced performance with reduced position and balance errors between the two BLAC motors and an improved overall control performance of the rail mover.

Modelling and numerical solution of ungrounded DC rail traction system load flow using ladder circuit – part II: solution method

Accurate solution of dc ungrounded rail power system load flow requires detailed modelling of negative path components, resulting in large numbers of circuit nodes and branches. Such modelling complexity incurs heavy computational burden and potential ill numerical conditions when solved by nodal voltage equations. Part I of this study presented a ladder-circuit model for traction network between substations and a power flow formulation adopted from ac distribution load flow. Part II presents the solution algorithm that harnesses the ladder circuit models to achieve efficient load flow computation and numerical robustness for the entire dc traction system by sequentially solving for power flows of individual substations and wayside ladder circuits. The proposed algorithm requires computational burden linearly proportional to the number of substations, much less than those by nodal voltage equations. The computation results from two transit lines in Taiwan illustrate that the proposed algorithm accomplishes the objectives of computational proficiency, numerical robustness and versatility to train load models and various traction circuit configurations such as branch lines.

Modelling and numerical solution of ungrounded DC rail traction system load flow using a ladder circuit – part I: circuit modelling

Accurate solution of DC ungrounded rail power system load flow requires detailed modelling of the negative path, resulting in large numbers of circuit nodes and branches. The solution of the associate nodal voltage equations not only requires a heavy computational effort, but could also encounter ill numerical conditions. This two-part study presents a novel methodology utilising the longitudinal configuration of rail traction power networks to derive a ladder-circuit model and to devise an efficient solution algorithm. This method belongs to the so-called sequential methods yet goes a step further to divide a DC traction power system into substations and ladder circuits between them. The modelling of individual substations makes it easier to incorporate detailed characteristics of receptive substations and various train load models, while the generic ladder-circuit topology paves the way for simple and efficient numerical solutions. The proposed load flow solution requires manipulation of small-dimensional matrices and equations, making it suitable for either manual or computer calculations of the DC portion of the sequential method for the load flow analysis of the entire traction system.

Failure analysis of BMC insulators used for third rail traction system

Bulk molding compound (BMC) or Glass Reinforced plastic (GRP) composite insulators are extensively used for the third rail electric traction system. The performance of these insulators primarily depends on the local environmental conditions that cause degradation over a period of time. Degradation leads to partial arcing which grow more severe and can generate combustion that ignites flammable debris, smoke including fires resulting in service interruptions and safety risks of the third rail traction system. In the present investigations, exhaustive analysis is conducted to understand the root cause of degradation and arcing on the field aged insulators rated for 750Vdc. Leakage current and surface resistance measurements are conducted under dry, wet and contaminated conditions. Further to better interpret Physico-chemical analysis are conducted using Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDAX) and Fourier Transform Infra-Red (FTIR) spectroscopy to investigate surface morphology and chemical changes in the samples, also Thermo-Gravimetric Analysis (TGA) is performed to find the thermal characteristics of the insulator. Interesting results obtained from the investigations clearly present evidence to loss of epoxy material from the bulk eventually leading to the exposure of glass fibers causing degradation, arcing and failure of the insulators. The study further highlights the essential procedures to be edopted to locate, isolate, and better anticipate failures of BMC insulators used in third rail traction system.

Estimation of current distribution in the electric railway system in the EMTP-RV

Current distribution in the electric traction system is an important factor regarding the electromagnetic influences on the surrounding metallic structures. The current value directly determines the magnetic field and consequently coupling of the systems. A single rail traction system can be equipped with return conductor. The return current flowing through return conductor has an opposite direction of supply current and decreases coupling and interferences.This paper presents the AC current distribution for both designs, with and without return conductor. Also, the soil resistivity is varied. The higher the soil resistivity, the higher is the amount of return current in rails and return conductor. The different construction of return conductor results in different impedance of return path. The relations of return conductor construction and return current value are analysed.Lightning can directly impact different traction system elements such as contact network, tower or return wire. The current distributions in several cases of lightning impacting different traction system elements are presented.

Inductive influence of 25 kV, 50 Hz electrified single rail traction system

The paper presents the methodology for calculation and measurement of induced voltage caused by railway system operation on the sensitive metallic structures. The arrangement and characteristics of railway system 25 kV, 50 Hz are provided. The procedures of short-circuit current calculation and supply current measurement in the railway system are described. The basic theoretic background of inductive interference is explained. The reduction factors of the communication cable, railway system and environment are mentioned and clarified. On a case study, the results of the induced voltage calculation and measurement is compared. It is proved that induced voltage directly depends of supply current or shortcircuit value.

Fault Current Detection and Dangerous Voltages in DC Urban Rail Traction Systems

In this paper, the electrical safety of dc urban traction systems is analyzed, with particular focus on fault current detection and on dangerous voltages which could arise in case of fault. For the discussion, the tram network of Turin, Italy, is used as a case study. First, the structure of the dc traction power supply is described, analyzing in detail the different components; then, the safety of the system is analyzed, examining possible types of fault. In particular, ground faults inside the substation and ground faults along the line are analyzed in detail. Fault currents and dangerous voltages are calculated, thanks to a simplified steady-state circuital model of the traction system. Finally, the consequent risks for the people are examined and some conclusions and possible solutions are presented.

Optimal harmonic filters design of the Taiwan high speed rail traction system of distributer generation system with specially connected transformers

This paper presents a method for combining a particle swarm optimization with nonlinear time-varying evolution and orthogonal arrays (PSO-NTVEOA) in the planning of harmonic filters for the high speed railway traction system of Distributed Generation (DG) system with specially connected transformers in unbalanced three-phase power systems. The objective is to minimize the cost of the filter, the filters loss, the total harmonic distortion of currents and voltages at each bus simultaneously. An orthogonal array is first conducted to obtain the initial solution set. The set is then treated as the initial training sample. Next, the PSO-NTVEOA method parameters are determined by using matrix experiments with an orthogonal array, in which a minimal number of experiments would have an effect that approximates the full factorial experiments. This PSO-NTVEOA method is then applied to design optimal harmonic filters in Taiwan HSR traction system, where both rectifiers and inverters with IGBT are used. From the results of the illustrative examples, the feasibility of the PSO-NTVEOA to design an optimal passive harmonic filter of Taiwan HSR system is verified and the design approach can greatly reduce the harmonic distortion. Three design schemes are compared that V–V connection suppressing the 3rd order harmonic and Scott connection for the harmonic improvement is better than those of V–V and Le Blanc connection.

Noise reduction strategies for a light metro rail traction system

Inside the paper the vibro‐acoustic characterization of a light rail vehicle is presented, with special reference to the traction noise emission identification. As a first step , on board measurements and pass by measurements, were performed in order to separate traction noise from rolling noise; these test revealed the electrical engine, as the most relevant sources at low speed. The electrical engine has then been characterized during specific laboratory test and innovative noise control solution were proposed to be tested. The first one could be a modification of inverter algorithm; this trying to reduce the influence of most relevant acoustic tones. This approach is essentially based on a software modification of the PWM algorithm through which modify the engine's spectral response. The second possible tested approach involved the enclosure of the engine in a sort of semi‐active skin panels co‐located at short distance from the engine; it has been demonstrated that this approach, by the merging of passive and active peculiarities, potentially lead to a wide frequency range application area. Following laboratory tests, the PWM solution was also decided to be implemented during "on board" test; a wide set of experimental results will be presented and discussed.

Wear mechanism of aluminum–stainless steel composite conductor rail sliding against collector shoe with electric current

In this paper, we developed a new tester by modifying the jigs and the control system of conventional pin-on-disc apparatus. The friction and wear characteristics of aluminum–stainless steel composite conductor rail and collector shoe used in subway third rail traction system were investigated on the tester with an electrical current applied across the sliding interface. The friction coefficient and wear volume loss were compared, and the morphologies of worn surfaces were observed and analyzed by means of scanning electron microscope and energy dispersive X-ray spectroscopy. Wear mechanisms with electric current were analyzed, and results were discussed based on electric contacts theory. Experiment results show that a threshold value of normal stress exists in friction and wear with electric current. If normal stress is larger than or equal to the threshold value, friction coefficients increase with the increasing of electric current, wear volume losses increase slightly with the increase of normal force, and contact resistance heat enhances mechanical wear. Further, if normal stress is smaller than the threshold value, friction coefficients decrease with the increasing of electric current, wear volume losses increase intensely with the decreasing of normal force, and arc heat induces arc erosion. Sliding wear with adhesion and abrasion are the major wear mechanisms of the frictional pair, but the material volume loss caused by arc erosion is much larger than those caused by the two kinds of wear mechanisms. For a certain velocity of train, the threshold value is an optimum normal stress. Working under the stress, mechanical wear and arc erosion are all much less, which makes electrical power supply stable and wear volume loss lower.

3-D Magnetic Field Analysis of Permanent Magnet Motor Considering Magnetizing, Demagnetizing and Eddy Current Loss

Rare-earth magnets, which have high energy product, have been widely used in several industrial applications such as voice coil motors for hard disk drives, MRI for medical devices and motors for electric vehicle. In order to realize a small and high performance device, the magnetic field analysis techniques are required. In this paper, we applied the magnetic field analysis to design the permanent magnet synchronous motors into the rail traction system. In the inverter fed motor drive, the eddy current loss in the permanent magnet increased. We simulated the effect that eddy current was decreased by using a divided permanent magnet. Furthermore, the permanent magnet tends to be demagnetized due to the effect of a demagnetizing field formed at high temperatures. However, according to our analysis, demagnetization does not occur within the range of our design specifications. Also, we performed magnetic field analysis assuming a pulse-type magnetization process and designed an optimal magnetizing coil.

Supervisory Takagi-Sugeno Fuzzy Fault-Tolerant Control of a Rail Traction System

This paper investigates the development of a supervisory control system with qualitative tasks at the upper level and simple quantitative models at the lower level to control complex non-linear systems. A new quantitative approach for the stability of non-linear fuzzy inference systems using Takagi-Sugeno (T-S) fuzzy models is presented. The necessary conditions for the assignability of eigenvalues to a region in the s-plane and the necessary conditions to guarantee the stability of fuzzy models for both T-S fuzzy observers and T-S fuzzy controllers together are derived. The problem is solved via the Linear Matrix Inequality (LMI) method. The paper demonstrates the feasibility of this system architecture through application to a fault-tolerant design for a railway traction system using DSP in a hardware test-rig.

Fault diagnosis and fault-tolerant estimation of a rail traction system via fuzzy observers

This paper studies the fault diagnosis and fault-tolerant estimation problems of a rail traction system. The main idea is to use a bank of fuzzy observers to detect faults and to isolate failed sensors. Once the failed sensor is isolated, the fuzzy observer driven by healthy sensors provides reliable torque and flux estimates which are used for the control purpose. The concept and design procedures for fuzzy observers are presented in this paper. A fuzzy observer is able to produce accurate state estimations and generate robust residuals for non-linear dynamic systems such as a rail traction system. The fault diagnosis and fault-tolerant estimation scheme proposed for the rail traction system is demonstrated using simulations.

Reply: Iterative techniques for the solution of complex rail-traction systems including regenerative braking

Reply: Iterative techniques for the solution of complex rail-traction systems including regenerative braking

Design of a high-voltage GTO chopper for traction drive

A chopper operating at 4000 V and 800 A RMS using two large series-connected GTOs (4500 V, 2500 A) is designed. The series connection of GTOs is considered, including criteria for the selection of GTOs, design of snubbers, and adaption of GTO controls. The advantages and drawbacks of the strategies used are discussed. Detailed experimental results concerning the GTOs' commutations and the snubber circuits are presented. The influence of important parameters, such as the load current on the transient voltage distribution on the GTOs is discussed. Because series connection of GTOs is liable to be used in the high-voltage converters of rail traction systems, two industrial realizations are proposed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>