Zeliang Shu

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.

Steady-State and Dynamic Study of Active Power Filter With Efficient FPGA-Based Control Algorithm

A new approach using field-programmable gate array (FPGA) to implement a fully digital control algorithm of active power filter (APF) is proposed in this paper. This FPGA-based controller integrates the whole signal-processing function of an APF, including synchronous-reference-frame transform, low-pass filter, three-phase phase-locked loop, inverter-current controller, etc. By case studies on the principle, performance, and architecture, these control blocks are implemented in real-time and synthesized into a medium-scale FPGA chip by adopting some useful digital-signal-processing techniques, such as pipelining, folding and strength reduction, with respect to minimization of hardware resource and enhancement of operating frequency. As a result, the whole algorithm needs around 5000 logic elements and can run at synchronous system-clock rates of up to 65 MHz. Experimental results on a laboratory prototype are given to demonstrate performance of the proposed approach during steady-state and dynamic operations.

An Efficient SVPWM Algorithm With Low Computational Overhead for Three-Phase Inverters

A compact algorithm of space vector pulsewidth modulation (SVPWM) for three-phase inverters is proposed and developed in this paper. Simplified by the proposed method, the conventional SVPWM is decomposed into fast integer operations entirely by using an intermediate vector, which will properly counteract the redundant calculations of the remaining procedures. This concept can not only simplify a two-level scheme, but is also suited for multilevel implementation. Since it can be implemented without any multiplier or divider, the fast algorithm is especially suitable for field programmable gate array applications. Then, an area- and speed-efficient IP-core based on this algorithm is built and tested. It ensures lower hardware resource usage, and at the same time, operates several times faster than some reported examples. Finally, experimental results obtained from a dc-ac inverter prototype are presented to verify the viability and effectiveness of the proposed algorithm.

Voltage Balancing Approaches for Diode-Clamped Multilevel Converters Using Auxiliary Capacitor-Based Circuits

An auxiliary capacitor-based balancing approach is adopted in this paper to equalize the dc-link capacitor voltages of a diode-clamped multilevel converter (DCMC). Four balancing circuits, including the generalized, one-level-capacitor, one-capacitor, and simplified one-capacitor-based configurations are discussed for a five-level DCMC system. These configurations are different in connection of the auxiliary circuits and numbers of the capacitors and switches, but they work on the same principle called ping-pong operation by utilizing the auxiliary capacitor as an equalizer between the capacitors of different voltages. The unbalance phenomenon, ping-pong principle, circuit configurations, and their switching schemes are analyzed, respectively. The superiorities of the proposed approach include balancing operation regardless of load power factor and modulation index, control simplicity, and independence from main circuits when compared to the traditional approaches. Simulations and experimental results verified the performances using the proposed balancing circuits and control strategies.

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.

Advanced Cophase Traction Power Supply System Based on Three-Phase to Single-Phase Converter

An advanced cophase traction power supply system is proposed to solve the power quality problems of the traditional traction power supply system, such as unbalance, reactive power, and harmonics to three-phase industrial grid. The three-phase to single-phase converter-based substation is adopted in this system, which can transfer active power from three-phase grid to single-phase catenary and compensate reactive power and harmonics of the locomotives. One catenary section could be utilized in the advanced cophase system instead of the multiple split sections in traditional system. The neutral sections and problems caused by them in traditional system could be avoided. In this paper, the characteristics of the advanced cophase system and the automatic current-sharing control algorithm of three-phase to single-phase converter are studied and analyzed. The simulation and experimental results verify the viability and effectiveness of the proposed 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.

Predictive Harmonic Control and Its Optimal Digital Implementation for MMC-Based Active Power Filter

An optimal active power filter (APF) based on modular multilevel converter (MMC) without load current and lower arm current sensors is proposed. Its control algorithm mainly includes predictive harmonic current control, fundamental frequency control, and dc voltage control. Comparing to direct current control, the first two subcontrollers transfer the harmonic and fundamental active/reactive power current to voltage references, which are suitable to generate the modulation signals to MMCs as well as two-level converters. Their full digital optimization structures combined with the MMC voltage and current control are detail discussed and implemented on field programmable gate array. The synthesis result indicates a low hardware resource utilization and calculation delay of the designed controller. The experimental results on an MMC-based APF prototype verified the static and dynamic performances of the proposed algorithm.

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.

Advanced Co-phase Traction Power Supply Simulation Based on Multilevel Converter

Serious power quality and neutral sections disadvantage restrict the evolution of traditional traction power supply system. An advanced co-phase traction power supply system is proposed in this paper based on three-phase to single-phase converter as the key equipment in substation. This converter adopts multi-module diode clamped multi-level algorithm, connects between industrial grid and feeder line without using output transformer. It transfers active power from three-phase grid isolated to one-phase traction line, and provides the frequency, phase and amplitude controlled output voltage. Then, the feeder line between different substation can be connected directly, and constructs an ideal co-phase traction supply system in the same phase. The performance of the converter is validated by the discussion and simulation results in this paper.