Design and Development of an Efficient Multilevel DC/AC Traction Inverter for Railway Transportation Electrification

Abstract

This paper presents a new trend in the transportation industry to adopt the multilevel inverter-based propulsion systems and gives the design procedure of a new dc/ac 3-phase 6-level inverter for powering the rail metro cars. The proposed inverter is based on the multilevel converter as it possesses much lower component voltage stress compared with the pulse width modulated topologies. Space vector pulse width modulation (SVPWM) with Back-to-Back Clamped Diode (BBCD) voltage modulation operation is used to achieve voltage regulation and high efficiency at any loading condition. Zero Current Switching (ZCS) operation is achieved without using an auxiliary circuit, which leads to minimum switching losses. The novelty of the proposed inverter lies within the proposed control methodology, which uses a new switching pattern that guarantees a modified SVPWM to eliminate the unwanted harmonics from the output voltage. The new algorithm is developed using numerical iterative solution using Newton-Raphson technique, that was downloaded to the processor using digital signal processing (DSP) developed code. The mathematical model is simple but proven to be effective. As a result, a higher operating efficiency at full-load of 98.5% is achieved as compared to previous efficiency of 97%. Analytical, simulation and experimental results of a 1500Vdc/700Vac 400kW converter are presented to offer the proof of concept. The converter provides real estate savings for the train under floor layout, higher operating efficiency as well as better cost price than the conventional two level pulse width modulated (PWM) hard switched converters.

Multilevel Inverter Topology Using Current Path Change for Zero Current Switching

“…This comparison is calculated from Eqs. (2) and (3) under the conditions of Table 3. This result confirms that the proposed topology reduces the switching loss by realizing the zero current switching.…”

“…In general terms, multilevel inverters are categorized into three types by their topologies; Neutral Point Clamped (NPC), Flying Capacitor (FC) and Cascaded H-Bridge (CHB). The NPC inverters are used for high power AC motor drive applications, which have been studied to increase efficiency of trains (1) (2) . However, they have a disadvantage of the charge imbalance of capacitors, which need complicated modulation methods or extra circuits (3) (4) .…”

Fuzzy Logic Based Control of Multilevel Inverter for Railway Traction System

“…Recently, a bundle of research in the field of MLI has made, like applications such as Photo Voltaic System, STATCOM, Industrial drives and High Voltage Direct Current (HVDC) [1][2][3][4][5][6][7]. On the other hand, research work on Railway Traction Systems is relatively limited [8][9][10][11].…”

Comparison of Heat-Pipe Cooling System Design Processes in Railway Propulsion Inverter Considering Power Module Reliability

“…Most of them are based on electric railway systems that are an eco-friendlier system when compared to traditional diesel railway systems. Therefore, the propulsion system of an electric railway consists of a power conversion converter and electric motor [1][2][3][4]. At first, DC motors were used for railway systems, however, as technology advances, three-phase induction motors driven by a conventional two-level inverter with insulated gate bipolar mode transistor (IGBT) modules have replaced them [5][6][7].…”