Traction motors, particularly modern railway 3-phase types, are controlled by precisely managing the electrical power supplied to them.
The fundamental way a modern railway 3-phase traction motor is controlled is by feeding in three AC currents which interact to cause the machine to turn. This interaction creates a rotating magnetic field within the motor, which drives the rotor.
The Role of the Inverter
To achieve this control, a key component is used:
- Inverter: The three phases with the necessary characteristics are most easily provided by an inverter.
The inverter's function is crucial because it doesn't just supply a fixed AC current. It provides variable voltage, variable frequency (VVVF) motor inputs.
Variable Voltage, Variable Frequency (VVVF) Control
This VVVF control is essential for managing the motor's performance. By changing the voltage and frequency of the AC currents supplied by the inverter, operators can control:
- Speed: Adjusting the frequency directly changes the speed of the rotating magnetic field and thus the motor's speed.
- Torque: Varying the voltage and frequency allows for control over the motor's torque output, enabling acceleration, deceleration, and pulling power adjustment.
This modern control method offers significant advantages over older DC motor systems, including higher efficiency, better reliability, and more precise control over acceleration and braking.
In summary, modern traction motor control relies on electronic inverters to supply variable voltage and frequency three-phase AC power, which directly influences the motor's speed and torque.
