Analysis of Single Area System |
This is known as free governor operation.DPL, the change in load demand. Let us consider a simplesituation in which the speed changer has a fixed setting (DPref, the change in speed changer setting, and DThe work showsthat there are two important incremental inputs to the load frequency controlsystem - In the given condition, theblock diagram will be simplified as Considering Ts < TTG << TP 1, the dynamic response which is giving thechange in frequency as a function of the time for a step change in load can beobtained as follows@and KSKTG where G(s) = KP/(1+sTP ) and H(s) =1/R. Therefore, we can say that the LFC system possesinherently steady state error for a step input of load change provided that thereference setting remains unchanged. Consider now the steady effect of changing speed changersetting with load demand remaining fixed. Similar to the previous condition,letting Ts < TTG << TP 1, the simplified block diagram and transferfunction becomes@and KSKTG Where G(s) = KP/(1+sTP) and H(s) =1/R Following the same procedure as case A, the steady statechange in frequency due to change in reference setting will have similarexpression: PL, the steady state frequency change is obtained by superposition,i.e.DPref while the load demand changes by DIf the speed change setting is changed by According to the above equation, thefrequency change caused by load demand can be compensated by changing thesetting of the speed changer, i.e. f =0.D, for f is fed through an integrator to thespeed changer resulting in the block diagram configuration shown below.DTherefore, for this purpose, a signal from Now, the analysis on input-output relationresults Neglecting TS and TTG /both have << 1, the above equation becomes,@Tp/ and KSKTG.