A: There are 4 parameters P22.19~P22.22 are used for setting the conditions of add motor:
1. P22.19 pressure allowance 100% is corresponding with P09.02.
2. If variable frequency motor runs frequency reach P22.20, and PID feedback [P17.24] < (PID given[17.23] – Pressure allowance [P22.19]), this status keep time reach P22.21, meet condition of add motor.
3. P22.20 a limit frequency to add motor. Also when reduced a motor, VFD also output this setting frequency, then adjust by PID, avoid pipe pressure fluctuation.
4. when the feedback pressure are not satisfied, motor-added logic as followings:
a. Add variable frequency motor: switch current variable frequency motor to power frequency, start new variable frequency motor.
b. Add power frequency motor: RO operate to add power frequency motor, at the same time, current variable frequency motor reduce to setting frequency
5. P22.22 After meet add motor condition, if next motor is variable frequency, the current motor will switch to power frequency, because the contactor operation have delay time(P22.26, P22.37), in order to reduce the pipe pressure fluctuation, before switch to power frequency, VFD will output a high frequency, then switch to AC power, this high frequency is the switch frequency P22.22.

Switch process: VFD reach switch frequency firstly, then stops output, switch-off variable frequency contactor, switch-on power frequency contactor.