Railway vehicles have a large number of 380VAC powered components, such as air conditioners, air pumps, and motors, which require inverter modules to convert the DC voltage output by the DC/DC converter into a 50Hz AC voltage. Generally, 1200V power devices are used in 2-level or T-type 3-level topologies.
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To ensure the uninterrupted power supply to critical loads, such as lighting, a certain number of batteries are deployed for emergency power supply. The input voltage for these batteries are generally low, for example 110V. Therefore, they cannot be directly charged by the DC/DC module, and require a charger module to step down the DC voltage output by the DC/DC module to a suitable voltage. Generally, 1200V power devices are used in half-bridge topology.
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The output voltage of the BOOST stage is relatively high. To further lower down the voltage and implement the isolation between the power supply side and the load side, a DC/DC module is usually deployed at the output of the BOOST module. This module typically uses full-bridge LLC converter and high-frequency transformer for gavanic isolation, stepping down the DC voltage to 600V-800V. Generally, 3300V or 1200V high-current power devices are used.
As affected by load fluctuation on the lines, the power supply voltage of the vehicle fluctuates quite distinctly. To avoid the impact of voltage fluctuation on the system, a BOOST module is usually deployed on the DC bus input side. The module generally uses BOOST conversion to stabilize the DC voltage, using 3300V or 1200V power devices in 2-level or I-type 3-level architecture.
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