Qunzhan Li

Single-Phase Back-To-Back Converter for Active Power Balancing, Reactive Power Compensation, and Harmonic Filtering in Traction Power System

An active power compensator (APC) based on single-phase back-to-back power converter is proposed in this paper to solve problems of power quality of electric railway power supply system. This system adopts a single-phase feeding connection, which is called cophase power supply scheme. In this scheme, APC connects the balance transformer between feeding phase for power supply and another phase for compensation. It has some characteristics, such as active power balancing, reactive power compensating, and harmonics filtering. In order to achieve these characteristics, the control scheme requires seven combination models. In this paper, a multifunctional control algorithm is proposed to realize every conceivable model. A cophase system with APC based on field programmable gate array (FPGA) and YNvd balance transformer is also designed and evaluated. The experimental results obtained from this prototype illustrate that the compensating ability is extremely high in steady-state and dynamic responses, and the power quality of a substation with distorted loads can be improved integrally.

Digital Detection, Control, and Distribution System for Co-Phase Traction Power Supply Application

Unbalance and reactive power currents of electric railway will result in poor power quality of three-phase industrial power grid. A co-phase traction power supply system is introduced in this paper to solve these problems by adopting single-phase ac-dc-ac converter. The converter is connected between two secondary windings of traction transformer with abilities of active power transmission and reactive power compensation. Because of the power conversion, the co-phase supply system can utilize single-phase feeding connection scheme instead of traditional two-phase feeding scheme. An actual 10 MVA/27.5 kV co-phase system with impedance-matching balance transformer is designed, developed, and tested. Its real-time detection, control, and distribution algorithms with field programmable gate array-based implementation are introduced. Some test running results validate the performance of the digital controller and demonstrate the feasibility of the proposed co-phase power supply system.

Development and Implementation of a Prototype for Co-phase Traction Power Supply System

Poor power quality of single-phase electric railway systems with industrial three-phase power supply will result in extra line losses, under-voltage at the terminal of contact wire, and unbalanced current of utility grid, etc. To address all of the above problems, a co-phase power supply system is adopted and an active power compensator (APC) based on electronic power converter is proposed in this paper. APC has the ability of balancing the current of the transformer, compensating reactive power, and filtering harmonics of the load. The performance of the co-phase power supply system is validated by the experimental results of a prototype.

Optimized Design and Performance Evaluation of New Cophase Traction Power Supply System

The traction power supply system of electric railway has the disadvantages of heavy unbalanced three phase, large harmonics and reactive power, needing neutral section insulator in every supply sector, which conditions the improvement of high speed and heavy-haul railway. New cophase traction power supply system can solve these problems radically. In this paper, connection type of traction transformer and the optimum matching topology of comprehensive power flow controller (CPFC) are discussed based on the mathematic model. The cophase direct and AT power supply models are set up, and the properties are analyzed. The control modes and operating performance of system are demonstrated, and the modes can be switched according to system status. Compared with the existing system, the economy of new cophase traction power supply system is evaluated. These studies have great significance on the design and application of new cophase traction power supply system. Keywords-cophase traction power supply system; mathematical model; design; evaluation

Simultaneous Coordinated Tuning of PSS and FACTS Damping Controllers Using Improved Particle Swarm Optimization

This paper deals with the simultaneous coordinated tuning of the power system stabilizer (PSS) controllers and the flexible ac transmission system (FACTS) power oscillation damping controllers in power system. A new particle swarm optimization approach is proposed for the design of optimal PSS and FACTS power oscillation damping (POD). Simulation results of multi-machine power system validate the efficiency of this approach.

Co-phase power supply system for HSR

Poor power quality and phase splitting are the main issues in electric railway. Co-phase traction power supply system is adopted in electrified railway for active power balance, reactive power compensation and harmonic filter. The research development and application of co-phase traction power supply system in China are depicted detailed in this paper. Experiments and pilot project proved that good power quality, feasible, reliable and economical traction power system can be implemented in co-phase traction power supply system.

Co-Phased Traction Power System Based on Balanced Transformer and Hybrid Compensation

Power quality pollution to power system and locomotives discontinued current collection are caused by two phase traction power supply system in electrical railway. Cost-effective co-phased traction power systems (CTPS) consisted of balanced transformer, active power flow controller device (APFC) and passive compensation device (PCD) was presented to reduce power quality pollution and guarantee locomotives current collection continuously by canceling neutral section. Two schemes of CTPS were compared, parameter calculating method of PCD and control strategy of APFC are analyzed. CTPS and its control strategy have been verified based on MATLAB simulation.

Impedance Calculations for AT Power Traction Networks with Parallel Connections

The modes of power traction networks are various, such as direct mode, BT (boost transformer) mode and AT (auto-transformer) mode. A new mode of AT power traction networks with parallel connections (PC) is applied on high-speed electrified railways in China. The impedance of normal AT power traction networks was analyzed in many documents with some methods, such as generalized method of symmetrical components, equivalent circuit method. AT power traction networks with parallel connections is a new power supply mode. According to the characteristic of this power supply mode, the impedance was analyzed and calculated in this thesis based on generalized method of symmetrical components (GMSC). The impedance characteristic was shown with graph in briefly based on the parameters of one AT power traction networks. The method is simple and is a good tool to analyze AT power traction networks with parallel connections. At last, suggestion about relay protection and fault location for this power supply mode is put forward.

The Design of Comprehensive Compensation in Traction Substation Based on Measured Data

An adjustable reactive power compensation scheme is given in this paper to overcome the defect of the fixed parallel capacitor compensation used in present traction substation. Based on actual measured data, a method to deploy the compensation capacity of compensation devices is given. At last, the compensation scheme of the third fixed filter, the third adjustable filter and the adjustable reactors set at the two phases is designed. According to the analysis of technical specification , its effectiveness and feasibility are validated.

Mathematic Model and Operating Performance of YNvd Transformer

The YNvd transformer, which is one kind of three- phase three-winding balance transformer, has several properties and can be used in traction power system of electric railway. Based on the magnetomotive force balance equations, winding connection equations, output-port equations and voltage transfer equations, the mathematical model of the YNvd transformer is set up. The performance of transformer in different grounding mode is discussed. The two-phase equivalent circuit in secondary side is obtained with the source impedance of the power system taken into account. The short-circuit current calculation formulae are deduced when variety kinds of short-circuit failure appear in the traction power substation, and the voltage losses of bus bars are calculated. These studies have great significance on the application of YNvd transformer.