Which device converts DC to variable frequency AC?

Which device converts DC to variable frequency AC?

• A. DC traction motor
• B. Inverter
• C. Battery system
• D. AC traction motor

Answer: (B)

Converting DC to variable frequency AC is done by an inverter. In rail power systems, DC may come from rectified lines or onboard storage, but to drive an AC traction motor you need AC power whose frequency can be adjusted. The inverter uses switching electronics to turn the DC into a three‑phase AC waveform and controls the output frequency (and voltage) to set motor speed and torque. The motor speed is tied to the output frequency, so changing the frequency directly controls how fast it runs. A DC traction motor would run on direct current, a battery system provides DC power, and an AC traction motor is the load—not the device that creates the variable-frequency AC.

Converting DC to variable frequency AC is done by an inverter. In rail power systems, DC may come from rectified lines or onboard storage, but to drive an AC traction motor you need AC power whose frequency can be adjusted. The inverter uses switching electronics to turn the DC into a three‑phase AC waveform and controls the output frequency (and voltage) to set motor speed and torque. The motor speed is tied to the output frequency, so changing the frequency directly controls how fast it runs. A DC traction motor would run on direct current, a battery system provides DC power, and an AC traction motor is the load—not the device that creates the variable-frequency AC.