Topologies and Operation Modes of Rail Power Conditioners in AC Traction Grids: Review and Comprehensive Comparison

Abstract

Electric locomotives in AC traction power systems represent a huge single-phase non-linear load and, detrimentally, affect the power quality and the efficiency of the three-phase power grid. Nevertheless, along the last decades, power electronics are being used to mitigate power quality problems in the three-phase power grid. In particular, Rail Power Conditioner (RPC) helps to increase the loading capacity of traction substations and improve the power quality of three-phase power grids. As the main characteristics, an RPC can supply reactive power, suppress current harmonics and overcome currents imbalance of the three-phase power grid. On the other hand, the traction substations may be constituted by different types of power transformers. For instance, single-phase power transformers and open-delta (V/V) power transformers are widely used, while Scott power transformers are less frequently used, since they are more complex and expensive. In this framework, this work presents a review study of RPC topologies, including their operation modes, and a comprehensive comparison between the characteristics of the RPC topologies when using different types of AC traction substations and power transformers. This helps to ensure the correct selection of the RPC topology for a specific application, according to the main structure of the traction substation. Consequently, and based on the established review, it is possible to sort and allocate each RPC topology for limited or wider applications.

A Review on Power Electronics Technologies for Electric Mobility

“…Another possibility is to consider a power converter connected to the single-phase traction power system (TPS), where the rail power conditioner (RPC) is used for the purpose of power quality improvement in the ac electrified railways. The RPC structure contains two single-phase back-to-back converters with a single dc link in between and two coupling transformers, as shown in Figure 28b [263]. The STATCOM device is a three-phase converter, whereas the RPC is composed of two back-to-back single-phase converters.…”

“…It is worth mentioning that this interface converter between two traction substations is only able to transmit power between traction substations and has no ability to accomplish power quality Another interface converter between two traction substations is presented in Figure 31. This converter is used to interface between two phases (with different out-of-phase angles) for the purpose of power transmit from two substations instead of only one substation [263]. In other terms, it is possible to shift the active power from one substation to another.…”

“…The system started the operation in 2015 and is designed to shift active power from one substation to another, including the energy resulting from the regenerative braking of the trains. It is worth mentioning that this interface converter between two traction substations is only able to transmit power between traction substations and has no ability to accomplish power quality improvement [263].…”

“…The primary converters are important to perform the power conversion and to use the power resulting from the regenerative braking of the three-phase traction electric machines. In light railway applications, such as suburban and regional trains, the dc link voltage is selected in the range of 1500 V dc, whereas in high-speed ac railway the dc link voltage is selected in a range between 1500 V and 3600 V [263].…”

A Novel Co-Phase Power-Supply System Based on Modular Multilevel Converter for High-Speed Railway AT Traction Power-Supply System

“…However, it can only eliminate the neutral section at the substation but cannot eliminate the neutral section in the entire traction network. This kind of co-phase power-supply schemes includes China's first co-phase power-supply unit, which is put into operation at the Mershan substation in 2010 [10] and the first single three-phase combined co-phase power-supply unit at the Shangyu substation in 2014 [15], as well as the Active Power Compensator (APC) [16], the Railway Power Conditioner (PRC) [17,18], the Hybrid Power Quality Conditioner (HPQC) [19][20][21][22], and the Hybrid Electrical Magnetic Power Quality Compensator (HEMPQC) [23]. The through co-phase power-supply schemes can simultaneously and completely solve the power quality problems and eliminate all neutral section of the whole traction network, making the traction network whole line through, e.g., the schemes based on the Cascaded H-Bridge (CHB) converter in [24,25] and the schemes based on the Modular Multilevel Converter (MMC) in [26].…”