Abstract
Significant disadvantages in power quality especially the unbalance problem and neutral sections restrict the evolution of conventional traction power supply system. A new traction power supply system based on three-phase to single-phase converter is studied, which can transfer active power from three-phase grid to single-phase catenary. One catenary section could be utilized in the new traction power supply system instead of the multiple split sections in conventional system. Three-phase to single-phase converter is the core equipment of new traction power system. MMC (modular multilevel converter) structure of AC-DC-AC substation is proposed in this paper. To solve the problem of the capacitor voltage balancing in MMC, a parallel sorting algorithm based on field programmable gate array (FPGA) is studied. And the correctness and effectiveness of the algorithm are verified by experiments. In addition, it is inevitable that the AC grid voltage will be unbalanced caused by the fault in the new system. Therefore, this paper focuses on the analysis of the effect of the unbalanced grid voltage on the operating characteristics of the MMC system. Finally, the correctness of the theoretical analysis is verified by simulation.
Highlights
A traditional traction power system typically uses two split catenaries, as shown in Figure 1(a), so there is neutral section in one substation (SS) and between adjacent SS [1]
The scheme of one catenary line based on a power flow controller (PFC) was used, as shown in Figure 1(b); this scheme was called a cophase traction power supply system [5]
The algorithm uses the field programmable gate array (FPGA) hardware features with parallel computing and can be computed in four clock cycles, and the computation time does not vary with changes in the number of submodules
Summary
A traditional traction power system typically uses two split catenaries, as shown in Figure 1(a), so there is neutral section in one substation (SS) and between adjacent SS [1]. A traditional traction power system typically uses two split catenaries, as shown, so there is neutral section in one substation (SS) and between adjacent SS [1]. The scheme of one catenary line based on a power flow controller (PFC) was used, as shown in Figure 1(b); this scheme was called a cophase traction power supply system [5]. Based on the control strategy of singlephase converter proposed in this paper, the amplitude and phase of the output voltage of each traction substation can be ensured the same. The influence of negative-sequence current is analyzed in detail, and the unified control of positive and negative-sequence current is realized by using PR controller
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