Fujun Ma

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.

Railway Static Power Conditioners for High-speed Train Traction Power Supply Systems Using Three-phase V/V Transformers

In order to eliminate the negative-sequence and harmonic currents in the high-speed train traction systems with three-phase V/V transformers, a compensation strategy based on the railway static power conditioners (RPC) is proposed in this paper. An RPC contains two converters that are connected back to back by sharing the same dc link. In this paper, the structure and principle to compensate negative-sequence currents for the RPC with a three-phase V/V transformer are explained, and a strategy to provide the compensation references for negative-sequence and harmonic currents is proposed. Also, a method to separate active current, reactive current, and harmonic current references from the total negative-sequence and harmonic current references is given. Moreover, a controller is proposed to maintain the dc-link voltage and to compensate the negative-sequence and harmonic currents. Simulation and experimental results are provided to demonstrate that the proposed strategy is very effective.

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.

A Railway Traction Power Conditioner Using Modular Multilevel Converter and Its Control Strategy for High-Speed Railway System

With the development of high-speed and high-power electrified railway, power quality of traction power grid becomes more serious. In order to achieve three-phase balance of traction power grid, a modular multilevel converter (MMC)-based railway traction power conditioner (RTPC) is studied, which is characterized by modular multilevel cascaded structure. The RTPC consists of four H-Bridge links and output filter inductors, which can be connected to 27.5-kV traction feeders in co-phase supply system directly. This conditioner can be used for different kinds of traction system, especially suited to Scott traction system. According to the analysis of equivalent electrical model and power balance of RTPC, a hierarchical control strategy is put forward aiming to balance the submodule capacitor voltages, which ensures the safety and stability of system. Finally, the structure and its control strategy are verified by the simulation and experiment effectively.

Hierarchical Direct Power Control of Modular Multilevel Converter for Tundish Heating

In this paper, the full bridge-based modular multilevel converter (MMC) is discussed for the application of tundish induction heating power supply (TIHPS). TIHPS features three-phase to single-phase ac/ac conversion and variable output frequency, and has intense demand for the power transmission stability and output current control precision. MMC is suitable for this application and especially the bulky and costly transformer and ac filter in the conventional topology can be dispensable. Therefore, it is interesting to investigate the applicable control method for MMC-TIHPS. According to the instantaneous power theory, a hierarchical direct power control based on the improved deadbeat current control is presented to assure the energy balance inside and outside MMC-TIHPS and reduce the sensitiveness of the current controller to parameter uncertainties. The proposed control strategy dispenses with the phase-locked loop, and does not exist the coupling among control variables of internal and external currents. Then, parameters design of energy controller is studied for stability analysis. Finally, MMC-TIHPS and proposed control method are verified by experimental results of a down-scaled physical prototype.

Multilevel Power Conditioner and its Model Predictive Control for Railway Traction System

In the rapid development process of a high-speed electrified railway, power quality problems in traction power grid have become increasingly deteriorative. In order to ensure a three-phase balanced traction power grid, a modular multilevel converter based railway traction power conditioner (RTPC) is presented. The RTPC consists of four H-Bridge clusters and filter inductors, and it can be directly connected to traction feeders in a co-phase traction system without insulation transformers. According to the equivalent circuit analysis of RTPC system, it can be considered as four single-phase inversion systems. Based on the equivalent control model of each single-phase cluster, the relationship between the multilevel output voltage and current slopes in a control period is analyzed, and an improved model predictive control is proposed. Moreover, a linear combination of two different output levels is proposed to improve tracking performance of cluster current control, and enhance the waveform quality of ac current. Finally, both simulation and experiment results are presented to verify the effectiveness of the structure and its control method.

Analysis and Comparison of Modular Railway Power Conditioner for High-Speed Railway Traction System

With the rapid development of modern electrified railway, negative-sequence current minimization is one of the most important considerations in the high-speed railway traction system. In the past, many multiple or multilevel topologies with high compensation capacity have been introduced for railway power conditioner (RPC). This paper presents a simplified quantitative comparison of five previous modular RPC topologies for negative sequence compensation in V/V and SCOTT traction systems, aiming for an optimal selection of the compensators. Performance criteria such as transformer requirement, voltage stress and current stress of a power switch, numbers of the power switches and capacitor are derived by analytical methods. Moreover, the numerical comparison of operating controllers is completed for modular RPCs. In addition, power losses of five modular RPCs are obtained by theoretical analysis, IPOSIM calculation as well as PSIM simulation. These calculations are validated via simulations results in PSIM. The main conclusion is that presented modular RPCs can be divided into general purpose RPC and special purpose RPC in terms of the behavior and efficiency. It is helpful to choose the appropriate topology for specific applications.

Development and Application of the Two-Phase Orthogonal Power Supply for Electromagnetic Stirring

This paper presents a three-leg voltage-source inverter topology for two-phase orthogonal power supply used for driving electromagnetic stirring. Compared with the conventional two two-leg inverter, the three-leg structure reduced the loss of power module and switching. The improved structure has an inductor in series between two-phase orthogonal power supply and the common phase of electromagnetic stirring, which make it possible to apply deadbeat current control method to two-phase orthogonal power supply, thus the controller design is simplified, the current adjustment speed is enhanced, and the current waveform is improved. A control strategy with reactive power compensation is proposed for enhancing the utilization rate of a three-phase pulsewidth modulation (PWM) rectifier in two-phase power supply, which makes it possible that the three-phase PWM rectifier not only operating rectification status but also operating reactive power compensation status. Hence, the reactive compensation cost of enterprises will be decreased. At last, simulation and industrial application results are provided to verify the effectiveness of the proposed topology and control strategy.

The Development of High-Current Power Supply System for Electrolytic Copper Foil

A 6.5 V/50 kA high-frequency switching power supply (HSPS) system composed of 10 power modules is developed to meet the requirements of copper-foil electrolysis. The power module is composed of a two-leg pulse width modulation (PWM) rectifier and a DC/DC converter. The DC/DC converter adopts two full-wave rectifiers in parallel to enhance the output. For the two-leg PWM rectifier, the ripple of the DC-link voltage is derived. A composite control method with a ripple filter is then proposed to effectively improve the performance of the rectifier. To meet the process demand of copper-foil electrolysis, the virtual impedance-based current-sharing control method with load current full feedforward is proposed for n-parallel DC/DC converters. The roles of load current feedforward and virtual impedance are analyzed, and the current-sharing control model of the HSPS system is derived. Virtual impedance is used to adjust the current-sharing impedance without changing the equivalent output impedance, which can effectively reduce current-sharing errors. Finally, simulation and experimental results verify the structure and control method.

Reactive Power Strategy of Cascaded Delta-Connected STATCOM Under Asymmetrical Voltage Conditions

Cascaded static synchronous compensator (STATCOM) is an effective solution for reactive power support in middle/high voltage conditions, and it has been widely employed to control reactive power in photovoltaic (PV) plants, wind farms, and industrial occasions. In this paper, reactive power control strategy of cascaded delta-connected STATCOM under asymmetrical voltage conditions is investigated. A new phase current reference calculation method is proposed to support reactive power continually under abnormal voltage conditions considering cluster voltage balancing control and phase current limitation. Constrains between voltage and current phasors of STATCOM are deduced. Then, the analytical expressions of phase currents and circulating current references are solved. Therefore, reactive power support and the safe operation of STATCOM can be obtained simultaneously by limiting the peak value of the phase current references. Furthermore, the reactive power support capability of cascaded STATCOM under asymmetrical voltage conditions is explored and compared by combining the proposed references calculation method with the three generalized current references calculation strategies. Finally, simulation and experimental results have been given to verify the theoretical studies.