A New High Speed Superconducting Maglev Traction Converter Topology and Modulation Strategy

High speed maglev transportation fills the speed gap of high-speed railway and civil aircraft, and is suitable for medium and long-distance transportation. Traction power supply is one of the key components of maglev systems. This paper focuses on the topology and control strategy of high-speed superconducting maglev high-power traction converters. Regarding the superconducting maglev train, the Yamanashi Line in Japan has set a world record for a speed of 603 kilometers per hour and is currently constructing commercial line. However, there are two main disadvantages to existing superconducting maglev traction converters. Firstly, in order to improve the DC bus voltage, thyristor rectifier and GTO PWM rectifier are used on the rectifier side, resulting in high harmonics on the grid side. Secondly, the disadvantage is that the two level H-bridge topology based on device series connection of the inverter side, causing high inverter harmonics and complex series voltage equalization algorithm, resulting in large losses in the maglev long stator linear motor. This paper proposes a high-power traction converter topology that can operate in four quadrants multi-level topology. The rectifier side adopts a three-level active neutral point clamp (ANPC) circuit, and the DC side adopts a common bus structure, the braking energy can feedback to the power grid to improve energy utilization efficiency. The existing high-speed superconducting maglev converter system has a cascaded H-bridge circuit based on device series connection on the inverter side. This paper proposes a five-level ANPC H-bridge topology on the inverter side, which increases the output level of the submodule from two levels to five levels, reducing output harmonics and improving the operating efficiency of the superconducting maglev long stator linear motor. The topology proposed in this paper adopts active midpoint clamping topology for both the rectifier side and inverter side submodules. By reasonably allocating the redundant level switching method in the topology, balanced control of all switching device losses in the converter can be achieved. Compared with traditional converter, the new topology is more conducive to the heat dissipation design of high-power converters, and the output power can be increased from 3SMVA to 4SMVA, with higher energy utilization efficiency.