Overload monitoring models are used to ensure Infeed Modules,
Bleeder Modules, Energy Storage Modules (ESM), Inverters and Motors
do not overheat when in an overload condition
(application value > continuous rated value)
for a prolonged duration. The continuous power and rms current and
torque values cover most conditions. However, if the cycle time is
very long, the rms and average values can be minimized. The
Overload Monitoring accounts for this situation, by applying an
exponentially weighted time factor to the overload value
(utilization factor, U).

- Inverter Rated Values
- Continuous current, Icont = 7.5A
- Peak current, Ipeak = 20A for 1s

- Application
- Cycle time = 20s
- 10A peak for 1.5s during accel
- 10A peak for 1.5s during decel

Therefore, the inverter utilization, U = 10A / 7.5A x 100% =
133%. Since U > 100%, the inverter is in an overload condition.
Worth noting is that 10A is only 50% of the inverter's maximum
output current. As shown in the chart below, in this particular
case, the Ixt value peaks at 84%, so the inverter will operate
below its maximum rated internal temperature.

Next, consider the same scenario as above, except that the accel
and decel durations increase from 1.5s to 3s. In this new scenario,
the inverter Ixt value exceeds 100% reaching a maximum value of
107%. This implies that the inverter will overheat. Either the
inverter must be upsized or the application requirements must be
reduced. The main point here is that the inverter is still
operating at 133% of its continuous current rating (utilization, U
= 133%). The difference is the duration of the overload
condition.

The actual Ixt model for the above scenario is shown below. With
U = 133%, the Ixt value reaches 100% at 2.9s, which is consistent
with the results above.