I have a typical problem with my allen-bradley make powerflex 525 vfd. the vfd capacity is 7.5 kw which is used for spedd control of two 3.7kw each motor (950RPM, 6 pole) in a lime stone vibrofeeder application. the direction of motor is opposite to another one & that is done by swapping R/Y for one motor. the VFD always gets forward command. vital point, the distance between vfd & motor is around 300 meters, vfd is having DV/DT filter as per the selection guideline of Powerflex 525 accessories. speed is control by analog input 4-20mA.
now, the problem is, when I am giving the drive a command frequency, it is increasing the output frequency properly throughout the speed range 5 hz to 50 hz & goes upto command frequency, but if the commanded frequency is above 45 hz & at this situation I try to speed down, then output frequency stuck at its running value & does not follow command frequency. DC bus voltage is normal (around 570VDC) during the operation, running current is under set FLC, VFD/MOTOR temperature is normal, mode is set V/F (SVC was also tested but same result, moreover as it is multimotor so I avoided SVC), bus regulation checked with both enable & disable option, slip compensation is checked with both enable & disable it. even, at this condition, if I command a stop, then VFD is unable to decelerate & after some time it is showing Motor stalled fault, but motors are running smoothly. now I have to set the Maximum frequency upto 44.9 Hz so as there is no problem.
I need your suggestion to achieve full 50 Hz range, my production sometimes needs full speed of motor.