DC to AC Motor Conversion: Retrofit, Vector Control and Payback

What the video shows

Convert a DC motor drive to AC, or keep the DC motor and renew the drive? In 8:01: on a DC motor, torque follows the armature current (T = k·Φ·I_a) and speed follows the armature voltage, with field weakening above base speed. The costs of DC: brush and commutator wear, a power factor that falls with speed on thyristor drives, ageing drives and commutator sparks. A closed-loop vector drive splits the stator current into I_d, which sets the flux, and I_q, which produces torque: full torque at zero speed, constant torque up to base speed and constant power above it, up to the AC motor's breakdown torque limit. Before you convert: torque at base speed and power at top speed, a separately driven fan for low-speed duty, mechanical fit, an encoder instead of an analog tacho; a four-quadrant DC drive regenerates to the grid, a standard AC drive with a diode rectifier cannot (braking resistor or active front end); shielded cable and insulated bearings. Worked example (the calculator's default inputs): 90 kW shaft power, 84 % vs 94 % efficiency, 6,600 hours a year → €10,532 energy, €35,532 total annual gain, 13.2 months payback on a €39,000 net investment.