Railway Static Power Conditioner Research Articles

Impedance Modeling and Mechanism Analysis of Low-Frequency Oscillations in Single-Phase MMC-RPC Integrated Vehicle-Grid Coupling System

The single-phase modular multilevel converter-based railway static power conditioner (MMC-RPC) has significant advantages in governing the power quality problems in the traction power supply system. The mechanism analysis of low-frequency oscillations (LFOs) in the MMC-RPC integrated vehicle-grid coupling system when electric multiple units are put into operation is a critical issue, which has been investigated in this article. The third-order ac admittance models of single-phase MMC-RPC and vehicle rectifiers are developed for the first time. To comprehensively study the small-signal stability of the MMC-RPC integrated vehicle-grid coupling system, this article proposes a modal analysis method based on modal phase margin and parameter sensitivity and combined with the generalized Nyquist stability criterion. It is found that LFOs around 10 Hz or 48 Hz are prone to occur due to the interactions of MMC-RPC or vehicle rectifiers with the traction power grid. To reveal the LFO mechanism, dominant modes and key parameters leading to LFOs in different working scenarios are clarified, and a series of guidelines are proposed for LFO elimination. Furthermore, the effects of control loops and power flow of MMC-RPC on system stability are revealed in detail. Finally, real-time hardware-in-the-loop experimental results validate the theoretical analysis.

Multi-Application Strategy Based on Railway Static Power Conditioner With Energy Storage System

With the rapid development of high-speed and heavy-load electrified railway, the peak impact and the regenerative braking energy content of traction load become increasingly significant, which has become an important problem affecting the construction and operation benefits of electrified railway. On the basis of comprehensively solving the power quality problems of electrified railway, a multi-application strategy based on the railway static power conditioner (RPC) with the energy storage system (ESS) is proposed in this paper to improve the economic benefits of the traction system. Through the implementation of the peak clipping and the recuperation and utilization of regenerative braking energy of traction load with the guidance of such strategy, the comprehensive economic benefits of the traction system can be improved. By analyzing the mathematical relationship between the comprehensive economic benefits and the parameters such as peak clipping rate and regenerative braking energy utilization rate of the system, an optimization model with the goal of maximizing the comprehensive economic benefits is established. Therefore, the optimal configuration capacity of the ESS is obtained. Finally, the experiments are carried out in MATLAB. The results show that, with the multi-application strategy, the peak load clipping and the recuperation and utilization of regenerative braking energy can be simultaneously realized. It is also demonstrated that the comprehensive economic benefits and environmental benefits can be improved while improving energy efficiency.

Supercapacitor Integrated Railway Static Power Conditioner for Regenerative Braking Energy Recycling and Power Quality Improvement of High-Speed Railway System

In order to increase the utilization rate of the regenerative braking energy (RBE), reduce the operation cost, and improve the power quality of traction power supply system (TPSS) in high-speed railway, a supercapacitor (SC)-based energy storage system (SCESS) integrated railway static power conditioner (RPC) is presented in this article. In this scheme, the SC is connected onto the dc link of the RPC via a bidirectional dc–dc converter. A hierarchical control strategy, with an energy management layer and a converter control layer, is presented. Four operation modes and transition conditions of SCESS-RPC are elaborated in detail in the energy management layer. To obtain rapid and stable control performance, in the converter control layer, a passivity-based control (PBC)-based nonlinear controller is designed for the RPC, and an optimal control strategy based on the linear quadratic regulator with integral action (LQRI) is adopted for the bidirectional dc–dc converter. By means of simulations and experiments, the feasibility of the proposed topology and control strategy are verified.

Flexible Fractional Compensating Mode for Railway Static Power Conditioner in a V/v Traction Power Supply System

Railway static power conditioner (RPC) is commonly used to improve the power quality (PQ) indices of the grid that supplies an electrified railway system (ERS). The main problem of the RPC is its high kilovoltampere rating, as it is intended to operate in a maximum compensating mode (MCM). This paper presents a flexible fractional compensating mode (FrCM) and its corresponding control system to mitigate the required rating of the RPC. The FrCM aims to fully utilize the available rating of the compensator for approaching the MCM. The FrCM not only reduces the kilovoltampere rating of the RPC but also maintains the grid-side PQ indices within their standard ranges and improves the performance of the dc-link voltage. The proposed method does not need any modification in power stages and adding extra circuit element(s); hence, this model can be used in both design and operating phases. Simulation and laboratory-scaled experimental results are presented to show the effective performance and rating reduction of the proposed method.

Reactive Power Compensation and Negative-Sequence Current Suppression System for Electrical Railways With YNvd-Connected Balance Transformer—Part I: Theoretical Analysis

This paper presents a new system for reactive power compensation and suppression of negative-sequence current for power quality improvement in electrical railways and the feeding three-phase utility grid, based on YNvd-connected balance transformer. Different from the conventional railway static power conditioner based compensation systems, this system integrates multiplex back-to-back converters (MBTBC) into phase- β side flexible taps through a cascade connection instead of into phase- β side feeder via a coupling transformer, thus the installation space and initial costs are reduced significantly. In addition, a new power distribution strategy with simple implementation is adopted in this paper, by which the compensation capacity of MBTBC can be decreased by 25%, compared with the commonly used full compensation scheme. As the first part of this topic, this paper focuses on the theoretical analysis, including the system topology, basic and partial compensation principles and its implementation method. While, the controller design on converter-level, stability analysis, and simulation and experimental verification are the main tasks of the second part of this topic.

Optimal electromagnetic hybrid negative current compensation method for high-speed railway power supply system

To achieve economical compensation for the huge-capacity negative sequence currents generated by high-speed railway load, an electromagnetic hybrid compensation system (EHCS) and control strategy is proposed. The EHCS is made up of a small-capacity railway static power conditioner (RPC) and a large-capacity magnetic static var compensator (MSVC). Compared with traditional compensation methods, the EHCS makes full use of the SVC’s advantages of economy and reliability and of RPC’s advantages of technical capability and flexibility. Based on the idea of injecting a negative sequence, the compensation principle of the EHCS is analyzed in detail. Then the minimum installation capacity of an EHCS is theoretically deduced. Furthermore, a constraint optimization compensation strategy that meets national standards, which reduces compensation capacity further, is proposed. An experimental platform based on a digital signal processor (DSP) and a programmable logic controller (PLC) is built to verify the analysis. Simulated and experimental results are given to demonstrate the effectiveness and feasibility of the proposed method.

Negative Sequence Current Optimizing Control Based on Railway Static Power Conditioner in V/v Traction Power Supply System

In order to bring railway static power conditioner (RPC) into full play in suppressing negative sequence current in the V/v traction power supply system, the reason of negative sequence current and compensation mechanism were analyzed, and the mathematical model with minimum negative sequence current under the constraint of voltage fluctuation, power factor, device capacity, transformer winding capacity, and energy conservation was set up. For solving the small-scale multidimensional nonlinear and constrained optimization problem, an intelligent algorithm based on sequential quadratic programming (SQP) method is proposed through a comparative analysis of existing optimization algorithms and the traditional analytical method. The proposed algorithm is capable to complete an optimizing computation process in several milliseconds with the precision of 0.1 A, and its computational efficiency and precision can meet the needs for real-time control of RPC. A self-adaption real-time optimization computing platform was built in combination with detectable analogue quantities of traction power supply system and RPC, including catenary network voltages, feeder currents, and compensation currents. Simulation and engineering experimentation results are provided to illustrate that the model and its computation are effective and feasible.

A New Railway Power Flow Control System Coupled With Asymmetric Double <italic>LC</italic> Branches

Facing the challenges of power quality problems and excessive neutral sections of conventional two-phase electric railway supply system, the way of adopting railway static power conditioner (RPC)-based single-phase supply system is a feasible solution. To enhance the cost-efficiency and reliability of RPC, a novel compensating system named asymmetric double LC -coupled railway power flow conditioner (ALC-RPFC) is proposed in this paper. The study indicates that compared with the conventional RPC, the proposed ALC-RPFC has an effective heavy-load compensating ability with lower power rating, which is benefit to enhance converter's operating efficiency and reliability. Besides, a design method for LC coupling branches mentioned in this paper is suitable for fluctuated railway loads, and is useful for designers of industrial applications as well. Finally, the good heavy-load compensating performance and power capacity decreasing ability of the ALC-RPFC are validated based on simulation and experiment results.

New Control Topology for Railway Static Power Conditioner

The traction power supply system of electric railway has the disadvantages of heavy unbalanced three phase, large harmonics and reactive power. Based on back-to-back converter, railway static power conditioner (RPC) can effectively balance the load between two arms, compensate the harmonic current and reactive power. As the conventional PI control is difficult to trace the waveform, a dual-loop control scheme was applied. The control scheme reduces the influences of the factors, such as sampling and calculation delay, dead-zone, parameters’ shift, on the system stability and enhances the robustness of the whole system. It can also eliminate the negative sequence current and three-phase voltage fluctuations of the primary side, improve the power factor and harmonic filter, so that electrified railway power quality problems can be resolved perfectly. The whole design was provided. Analysis and simulation results testify the effectiveness of the proposed control scheme.

A Simplified Power Conditioner Based on Half-Bridge Converter for High-Speed Railway System

With the rapid development of high-speed and high-power railway system in China, power quality such as the negative sequence current and harmonic current caused by electric locomotives becomes more and more critical. This paper proposes a half-bridge-converter-based railway static power conditioner (RPC) (HBRPC) which consists of two half-bridge converters connected by two capacitors in series. Compared with the traditional RPC, the HBRPC requires only a pair of power switch legs and two capacitors. Under the premise of accomplishing the same function of RPC, the proposed conditioner can reduce half of the power switches, which can make it with lower cost and hardware complexity. A double-loop control is proposed for HBRPC to keep the dc-link voltage stable and achieve the dynamic tracking of the current reference signals, while a balanced voltage control is proposed to eliminate the error of two capacitor voltages and maintain the normal operation of HBRPC. Finally, simulation and experiment results have verified the proposed structure and its control method effectively.

A Dual-Loop Control Strategy of Railway Static Power Regulator Under V/V Electric Traction System

For power quality in V/V traction system of the 350-km/h high-speed railway, a kind of railway static power conditioner (RPC) is discussed, which is used to carry out the comprehensive compensation of negative sequence and harmonic currents in the traction substation. In order to improve the control effect and performance of RPC, a dual-loop control strategy is constructed for RPC. Taking into account the disturbance and variation of electrified railway environment, a recursive proportional-integral control based on fuzzy algorithm is adopted to realize a fast and smooth tracking to the reference current. An energy-balance control is proposed to suppress the fluctuation of dc-link voltage and maintain the stability of RPC, which is an accurate and adaptive feedback control based on corresponding parameters. Finally, the correctness of the analysis proposed in this paper has been confirmed by the simulation and experiment results.

Voltage fluctuation compensator for Shinkansen

AbstractIn AC electric railways, three‐phase voltage is changed into the single‐phase circuit of two circuits with the Scott‐connected transformer. If unbalancing of the load between single‐phase circuits becomes large, voltage fluctuation becomes large on the three‐phase side. Railway static power conditioner (RPC) was developed for the purpose of controlling voltage fluctuation on the three‐phase side. An RPC is comprised of a pair of self‐commutated PWM inverters. These inverters connect the main phase and teaser feeding buses, coupled with a DC side capacitor such as a back‐to‐back (BTB) converter. In this way, the two self‐commutated inverters can act as a static var compensator (SVC) to compensate for the reactive power and as an active power accommodator from one feeding bus to another. 20 MVA/60 kV RPCs started commercial operation in 2002 at each two substations on the newly extended Tohoku Shinkansen for compensating voltage fluctuation on the three‐phase side caused by traction loads, absorbing harmonic current. The results of operational testing indicate that an RPC can accommodate single‐phase loads such as those of PWM‐controlled Shinkansen and thyristor phase‐controlled Shinkansen, and handle the exciting rush current of transformers, as well as compensate for harmonics successfully. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(4): 25–34, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20397

Voltage Fluctuation Compensator for Shinkansen

In AC electric Railway, three-phase voltage is changed into the single-phase circuit of two circuits with the Scott-connected transformer. If it becomes large unbalancing of the load between single-phase circuits, voltage fluctuation becomes large on three-phase side. Then, Railway Static Power Conditioner (RPC) was developed for the purpose of controlling voltage fluctuation on three-phase side. An RPC is comprised of a pair of self-commutated PWM inverters. These inverters connect the main phase and teaser feeding buses, coupled with a DC side capacitor such as a Back-To-Back (BTB) converter. In this way, the two self-commutated inverters can act as a static var compensator (SVC) to compensate for the reactive power and as an active power accommodator from one feeding bus to another.20MVA/60kV RPCs started commercial operation in 2002 at each two substations on the newly extended Tohoku Shinkansen for compensating voltage fluctuation on three-phase side caused by traction loads, absorbing harmonic current. The results of operational testing indicate that an RPC can accommodate single-phase loads such as those of PWM-controlled Shinkansen and thyristor phase-controlled Shinkansen, and handle the exciting rush current of transformers, as well as compensate for harmonics successfully.

Railway Static Power Conditioner Field Test

This paper reports on the basic configuration of the railway static power conditioner (RPC), a static voltage compensator for AC electric railways. 20 MVA / 60 kV RPCs started commercial operation in 2002 at each substations on the newly extended Tohoku Shinkansen. The results of operational test indicate that an RPC can accommodate single-phase loads such as those of PWM-controlled Shinkansen and thyristor phase-controlled Shinkansen, handle the exciting rush current of transformers, as well as compensate for harmonics. The voltage fluctuations on the three-phase side were succcessfully controlled by the RPCs.

A static voltage fluctuation compensator for AC electric railway using self‐commutated inverters

AbstractIn this paper, the authors describe the basic configuration of an RPC (Railway Static Power Conditioner), its compensation principles and successful test results (using a small model of RPC).An ac electric railway is placed under a rapidly changing single‐phase load. To avoid a voltage fluctuation under single‐phase loads, electric power is received from a large source. At a feeding substation, three‐phase electric power is transformed into two kinds of directional single‐phase feeding electric power.The authors have already proposed a static voltage compensator for the ac electric railway, called “RPC.” The RPC links a pair of feeding circuits, using two self‐commutated inverters.At the substation, the RPC accommodates an active power in the directional pair of feeding circuits to balance three‐phase power, and possess a reactive power to regulate a three‐phase voltage fluctuation. At a sectioning post, it can compensate for voltage drop using reactive power. It can also act as an active filter to compensate for harmonics.The authors have made a small model (220 V, 20 kVA) of the RPC, and report on the test results obtained using this small model under various conditions. The results indicate that the RPC can accommodate single phase loads, such as transformers and thyristors, can handle an exciter rush current from a transformer, can compensate for harmonics, and so on.