Sijia Hu

A New Integrated Hybrid Power Quality Control System for Electrical Railway

This paper presents an integrated hybrid railway power quality control system (HRPQC) to deal with the power quality problems in the electrical railway supply system. The prominent advantage of HRPQC is that, in the premise of adopting a hybrid compensating scheme for better performance, it can integrate the active system with the main transformer without other expensive low-frequency high-power auxiliary transformers. HRPQCs mathematical model, control idea, and transforming relationship in harmonic frequency are first presented. Second, the harmonic-suppressing mechanism and the resonance characteristics are analyzed in detail. Finally, simulation and experimental results verify the effectiveness of the proposed compensating system.

A Virtual Impedance Comprehensive Control Strategy for the Controllably Inductive Power Filtering System

In this letter, a virtual impedance comprehensive control (VICC) strategy is proposed for the controllably inductive power filtering (CIPF) system with a new filtering mechanism. This control strategy aims to satisfy the zero-impedance design precondition of the inductive power filtering system, and can dampen the harmonic resonance at the grid side. By the proposed zero-impedance control, the quality factor of the passive power device can be adjustable, and the single-tuned filter can be multituned. First, the main circuit topology for implementing the VICC-based CIPF is presented. Then, on the basis of the multipurpose control, the VICC strategy is designed. Furthermore, by means of the established equivalent circuit model and the corresponding mathematical model, the principles of the harmonic damping and the zero-impedance realization are revealed. Finally, the experimental results verify that the proposed control strategy can weaken the harmonic amplification effectively, and improve the filtering performance significantly.

A New Half-Bridge Winding Compensation-Based Power Conditioning System for Electric Railway with LQRI

Facing the challenges brought by the negative sequence current (NSC) pollution in power supply system of electric railway, a new topology named half-bridge winding compensation-based railway power conditioner (HBWCRPC) without auxiliary step-down transformer is proposed to suppress the NSC injected into the public networks. It has the advantages of high integration, low losses, and more functions. The compensation principle is discussed, and its physical interpretation is presented. Besides, the mechanism of the voltage perturbation and its various representations in steady state are analyzed. Considering the complexity of voltage perturbation, an optimal control method is adopted to improve the robustness of the control system, and a linear quadratic regulator with integral action, which is applicable for this system, is designed. Finally, simulation and experiment results validate the HBWCRPC system and its control method.

A New Railway Power Flow Control System Coupled With Asymmetric Double LC 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 converters 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.

A Power Factor-Oriented Railway Power Flow Controller for Power Quality Improvement in Electrical Railway Power System

Focusing on the freight-train dominant electrical railway power system (ERPS) mixed with ac-dc and ac-dc-ac locomotives (its power factorε[0.70,0.84]), this paper proposes a power factor-oriented railway power flow controller (RPFC) for the power quality improvement of ERPS. The comprehensive relationship of the primary power factor, converter capacity, and the two-phase load currents is built in this paper. Besides, as the main contribution of this paper, the optimal compensating strategy that suited the random fluctuated two-phase loads is analyzed and designed based on a real traction substation, for the purposes of satisfying the power quality standard, enhancing RPFCs control flexibility, and decreasing converters capacity. Finally, both the simulation and the experiment are used to validate the proposed conceive.

A Y-D Multifunction Balance Transformer-Based Power Quality Control System for Single-Phase Power Supply System

This paper proposes a Y-D multifunction balance transformer (YD-MFBT)-based power quality control system (MBT-PQCS) to deal with the power quality problems in the single-phase power system. The MBT-PQCS mainly consists of a YD-MFBT and a three-phase full-bridge converter (FBC). It fully explores the inherent negative sequence current (NSC) suppressing the ability of YD-MFBT, which makes the power flow transformed by FBC less than that of the conventional transformer-based compensating system. In addition, since the YD-MFBT exits three-phase output ports in relatively low-voltage level, FBC can directly connect with the main transformer via the output ports, without using the auxiliary step-down transformer. Therefore, the initial investment cost, installing difficulties and covering space of the whole compensating system, can be reduced significantly. In this paper, the current transforming relationship and the compensating principle of MBT-PQCS are presented, and the detection and control methods are given as well. Both the simulation and the experiment are used to verify the effectiveness of the proposed system.

An Inductively Filtered Multiwinding Rectifier Transformer and Its Application in Industrial DC Power Supply System

In this paper, a new industrial direct-current (dc) power supply system with the four-winding inductively filtered rectifier transformer (FW-IFRT) is proposed based on an inductive filtering (IF) method, which can effectively solve the power quality problems generally existing in the high-power rectifier system, such as high energy consumption, serious harmonic pollution, low power factor, and so on. The single-phase equivalent circuit model of such a new system is established based on the multiwinding transformer theory, and then its operating characteristics are investigated in detail. The harmonic suppression factor is proposed, and the influences of system and transformer impedances on the harmonic suppression characteristic are revealed. Finally, the simulation and experimental case studies are used to verify the effectiveness of the proposed system on the comprehensive improvement of power quality and operating efficiency.

Reactive Power Compensation and Negative-Sequence Current Suppression System for Electrical Railways With YNvd-Connected Balance Transformer—Part II: Implementation and Verification

This part mainly focuses on the implementation and verification of the reactive power compensation and negative-sequence current suppression system with YNvd-connected balance transformer, by means of simulation and experiment. The system model is presented, and a current control method, which explores the dissipation characteristic of the proposed system under two-phase rotating frame, is analyzed. Then, a stability analysis of this control is made, considering the deviations of system parameters and the time delay caused by the low-pass filter. Besides, dc-link overall control and balance control are investigated, and the self-balance ability of multiple dc links is briefly discussed. Both the simulation and experimental results verify the effectiveness of the proposed system topology, compensation strategy, and control 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.

A Balance Transformer-Integrated RPFC for Railway Power System PQ Improvement With Low-Design Capacity

This paper gives the fundamental aspects of a power distribution scheme on railway power flow controller (RPFC) for the grid connection compatibility improvement in planning stage railway power system (RPS) via neatly adjusting the value and rotation direction of the primary three-phase current phasors for every given power factor and random load point. This method not only leads RPS to satisfy the relevant grid connection standards, but also can make RPFC have minimum designing capacity and high operating efficiency to decrease its costs in system planning stage. The analytic design method and the experimental results validate the correctness of the conception. The method of using this idea in more challenging serviced RPS will be discussed in another companion volume.