In our Tulip field irrigation system, we have 3 phase BLDC water pumps. They spin at 8000rpm to pump water. (that's 400Hz bridge transistor switching frequency).....this is the maximum frequency that the bridge can switch at, and so even when the pump suddenly runs dry, the BLDC speed cannot increase....therefore, how does the BLDC inverter controller know that it must reduce the PWM duty cycle of the bridge transistors when the pump suddenly runs dry...after all, the motor speed does not increase?