Home » Wiki » VFD acceleration and deceleration ramps

VFD acceleration and deceleration ramps

Just as we have acceleration and deceleration lanes on and off highways, VFDs have acceleration and deceleration ramps. These drives ramps are used to limit the motor starting current. They act as integrators in the loop dynamics. The variable frequency drive default setting usually is 5 sec. to 10 sec., a typical flow loop reset value. If the integrator in the PI or PID controller is set faster than the variable frequency drive ramp, the resulting closed-loop performance will exhibit a limit cycle. This cycle isn't due to reset windup or saturation but, rather, occurs because the controller integrator is acting faster than the load can respond. Many controllers offer a feature that allows the reset action to be changed based on actual valve travel. Configure an auxiliary variable frequency drive output signal proportional to the actual load to the controller function block to eliminate the limit cycle.

Another factor is the process time constant. For VFD-powered liquid flow control loops, the process time constant is larger during start up; in contrast, flow control loops with control valves have a smaller time constant. The loop will perform sluggishly during start up compared to a flow loop with a control valve and pump powered by an induction motor without a VFD.

Always check the VFD's deadband setting, which is used to reduce the reaction to noise. If not carefully adjusted, it can add deadtime and cycling.

Post a Comment:

Plz Calculate (9 - 8) =
(Your comment will show after approved.)

You may also like:

Featured Articles
Variable frequency drive Rectifier Variable frequency drive RectifierTo understand variable frequency drive (VFD) better, it's necessary to explain some of the main parts of the variable frequency ...
VFD controlled Induction motor ... VFD controlled Induction motor Efficiency measurementThis paper presents a procedure to measure the efficiency on an induction motor fed by a VFD by the all operation range to speed ...
VFD: Pulse Width Modulation (PWM) VFD: Pulse Width Modulation (PWM)Pulse Width Modulation (PWM) VFDs provide a more sinusoidal current output to control frequency and voltage supplied to an AC ...
Variable frequency drive Advantages & ... VFDs are good for variable speed, in a water pump this is used to maintain a steady pressure, they will smooth out variances in ...
Variable frequency drive Energy saving Variable frequency drive Energy savingEnergy can be saved in a VFD by reducing the losses in the electric motor or by reducing the energy consumption of the variable ...
Variable Frequency Drive Service
VFD manufacturers
Variable Frequency Drive Sales Email buy@vfds.org
Variable Frequency Drive Support Email tech@vfds.org