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In this paper, a space vector pulse width modulation (SVPWM) algorithm is proposed, which is in α β frame with dclink capacitor voltage equalization for diode-clamped multilevel converters (DCMC). The α β frame is a coordinate system similar to αβ frame. In this frame, some original complex calculations are substituted by integer additions, integer subtractions, and truncations, etc.. It brings the time and area efficiency to fix-point digital realization, especial for the application in field programmable gate array. Meanwhile, a minimum energy property of multiple dc-link capacitors is applied as the basic principle for voltage equalization based on a capacitor current prediction algorithm. By evaluating the redundant vectors in each pulse dwelling period, the balancing algorithm chooses an optimal vector, generates the optimal PWM signals, and sustains the voltage stable. After that, an arbitrary multilevel SVPWM intellectual property (IP) core is designed and analyzed in the α β frame. At the end of this article, a 5-level DCMC-based static synchronous compensator is built and tested. The experimental results the balancing algorithm and the system steady-state and dynamic performances.Index Terms-Space vector pulse width modulation (SVPWM), voltage equalization, diode-clamped multilevel converter (DCM-C), static synchronous compensator (STATCOM).

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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 singlephase 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.Index Terms-Automatic current-sharing control, multilevel converter, power quality, three-phase to single-phase converter, traction power supply.

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Abstract:The advanced traction power supply system (ATPSS) is a new directional development for traction power supply systems, which can totally remove the neutral sections and effectively promote power quality. However, the existing converters suffer from small substation capacity. In this paper, a new configuration based on a three-level neutral point clamped (3L-NPC) three-phase to single-phase cascade converter in a substation is proposed for ATPSS, which can be used to match the capacity of the converter for high voltage and large power applications. The control strategy of the proposed converter is analyzed in depth, and the phase disposition sinusoidal pulse width modulation (PD-SPWM) with phase shift carrier SPWM (PSC-SPWM) is employed in the inverters. Then, the inductance equalizing circuit is applied for the voltage balance on the DC-link. Besides, a LC filter circuit is designed to eliminate the double line-frequency ripple of DC voltage. Afterwards, a simulation model and an experimental prototype are developed, respectively. The simulation results show that the proposed converter in this paper can not only meet the requirements of voltage and capacity for the traction network, but also improve power quality. Finally, the experimental results verify the correctness and feasibility of the proposed control strategy. OPEN ACCESSEnergies 2015, 8 9916