Frequency Inverter DF51... - Moeller.com.tr

04/07 AWB8230-1541GB BrakingPK PD: differential <strong>com</strong>ponentDifferential control increases the value of K and therefore the rateof change while reducing system deviation. If the reference valuesis static, it does not issue a control signal. D-control is thereforeused only in <strong>com</strong>bination with P- or PI control.eIK PT N x d+++DFigure 20: D-controlK P T V x dFigure 17: PID controle: system deviation (difference between actual value and referencevalue)u: manipulated variable for the frequency inverterK P : proportional-action coefficient (gain)hT N : reset timeT V : derivative action timex d : control differenceIn practice, PI control is often used next to PID control.P: proportional <strong>com</strong>ponentProportional control responds without delay and proportional toany system deviation but can not fully match the reference valueso that a deviation always remains. Small values of K (normalizingconstant) dampen the control action (i.e. reduce the rate ofchange), while large values result in instability.K PT VuT VPID control represents an “ideal” <strong>com</strong>bination, allowing fast,accurate <strong>com</strong>pensation of system deviations. In variable speedcontrol, PID controller are used mainly for controlling speed,pressures and flow rates. In all cases, an actual value sensor isrequired, which must provide the frequency inverter with asuitable signal (0 to 10 V or 4 to 20 mA).PID-control for frequency inverters is not suitable forsystems with a response time below 50 ms.Figure 18:P-controlI: integral <strong>com</strong>ponentIn integral control, the rate of change is proportional to the systemdeviation. This avoids fluctuations in the actual value due toovershoot but can not cope with rapid changes. With I-control,zero deviation (actual value = reference value) can be achieved.Figure 19:I-control27