Checks whether a candidate VFD is a reasonable match for a given motor: voltage compatibility, how heavily the motor's FLA loads the drive's rated output current, the motor's base V/Hz ratio (the flux-defining constant a V/Hz drive maintains from 0Hz up to base frequency), synchronous speed, and slip.
Standards followed
Ns = 120×f/P (synchronous speed); slip% = (Ns−N)/Ns × 100; base V/Hz ratio = rated voltage / rated frequency
What it can do
- Voltage match check (VFD rated voltage ≥ motor rated voltage, within a practical +10% window).
- Current loading of the drive by the motor's FLA, with a WELL MATCHED → PARAMETER MISMATCH grading.
- Base V/Hz ratio, synchronous speed, and slip from motor nameplate frequency/poles/speed.
Example problem
Motor: 400V, 65A FLA, 50Hz, 1480rpm, 4-pole. VFD: 400V, 75A rated output.
- Voltage match: 400V ≥ 400V and ≤440V — OK
- Current loading = 65/75 × 100 ≈ 86.7% — ADEQUATE band
- Ns = 120×50/4 = 1500rpm; slip = (1500−1480)/1500 × 100 ≈ 1.33%
- Base V/Hz = 400/50 = 8.0 V/Hz
ADEQUATE match — 86.7% current loading, 1500rpm sync speed, 1.33% slip.
This is a nameplate-compatibility screen, not a full drive commissioning study — motor cable length/dV-dt filtering, carrier frequency derating, and the specific VFD's overload/duty rating (e.g. variable-torque vs constant-torque) all need separate confirmation against the drive manufacturer's application data.