Electric railway vehicles now use regenerative braking for normal operation from the top speed to almost zero. For regenerative braking, the terminal voltage of the traction motor cannot be exceeded in the limited catenary voltage and the withstand voltage of semiconductor device. Therefore, the electrical brake force in the high-speed range is smaller than that at medium or low speed and the total brake force in the high-speed range mainly depends on the mechanical brake. By inserting rheostats between the inverter and traction motors, the regenerative brake force can be increased in the high-speed range without increase of the rated power and current of inverter. We studied the possibility of increasing the regenerative brake force by rheostats. The effectiveness of the proposed method is verified by test-bench experiments.
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