Delta Electronics VFD-M manual

Chapter 4 Parameters
Pr. 119	Differential Time (D)	Unit: 0.01sec
	Settings 0.00 to 1.00 sec	Factory Setting: 0.00

This parameter determines the damping effect for the PID feedback loop. If the differential time is long, any oscillation will quickly subside. If the differential time is short, the oscillation will subside slowly.

Pr. 120 Integration’s Upper Bound Frequency
Settings 00 to 100 %	Factory Setting: 100 %

This parameter determines the integration’s upper frequency limit while operating in the PID feedback loop. (Limit = Pr.03×Pr.120). During a fast Integration response, it is possible for the frequency to surpass a reasonable point. This parameter will help limit this frequency spike.

Pr. 121 One-Time Delay

Unit: 0.1sec Factory Setting: 0.0

Settings 0.0 to 2.5 sec 0.0 disable

PI Control: When controlled by P action only, deviations cannot be eliminated entirely. To eliminate residual deviations, the P + I control is generally utilized. If PI is used, it could eliminate the deviation caused by set-point changes and external interferences. However, if the I-action is excessively powerful, it will delay the response to the variation. The P-action could solely be used on a loading system that possesses integral components.

PD Control: when a deviation occurs, the system immediately generates some operational load that is greater than the single load generated by the D-action in order to restrain the increment of the deviation. If the deviation is small, the effectiveness of the P-action decreases as well. In some cases, control systems include integral component loads, which are controlled by the P action only, and sometimes, if the integral component is functioning, the whole system will be vibrating. In such cases, a PD control could be used to lower the P- action’s vibration and to stabilize the system. In other words, this control is good for use if the loads have no braking functions over the process.

PID Control: Uses the I-action to eliminate the deviation and the D-action to restrain the vibration, and combine with the P action to construct the PID control. The PID control method normally determines a control process with no deviations, high accuracy and very stable.

4-78 Revision May 2008, ME14, SW V3.04