Power Technology Issue 102. Comparison of Conventional and Elementary Block Method of Handling Transfer Function Blocks in PSS E Dynamic Models

Transcription

1 SEMENS Power Tranmiion and itribution Power Technology ue 102 Comparion of Conventional and Elementary Block Method of Handling Tranfer Function Block in PSS E ynamic Model Jay Senthil Senior Staff Software Engineer Siemen PT jayapalan.enthil@iemen.com Leonardo G. Lima Senior Staff Conultant Siemen PT leonardo.lima@iemen.com Sallehhudin Yuof Preident Advanced Power Solution alleh@ap-my.com Abtract At PSS E-31, a new feature called Elementary Block wa introduced for handling of variou tranfer function in PSS E dynamic model. Thi article how the comparion of the conventional and the elementary block method of creating PSS E dynamic model. General Tranfer function are commonly ued in dynamic model and are uually preented in the block diagram of the variou PSS E dynamic imulation model. n general, thee block diagram decribe complex model in term of impler (firt or econd order) tranfer function. The following tranfer function are commonly encountered: BLOC TRANSFER FUNCTON PSS E ELEMENTARY BLOC FUNCTON NAMES ntegrator 1 T NT_MOE1 NT_MOE2 NT_MOE3 ntegrator with non-windup limit T 1 NWNT_MOE1 NWNT_MOE2 NWNT_MOE3 Firt order (lag) filter 1 T LAG_MOE1 LAG_MOE2 LAG_MOE3

2 Firt order (lag) filter with nonwindup limit 1 T NWLAG_MOE1 NWLAG_MOE2 NWLAG_MOE3 Wahout Lead-lag Lead-lag with non-windup limit 1 T 1 T 1 T 1 2 V max 1 T 1 T 1 2 WSHOUT_MOE1 WSHOUT_MOE2 WSHOUT_MOE3 LLG_MOE1 LLG_MOE2 LLG_MOE3 NWLLG_MOE1 NWLLG_MOE2 NWLLG_MOE3 Proportional-integral (P) controller Proportional-integral (P) controller with non-windup limit V min P P P_MOE1 P_MOE2 P_MOE3 NWP_MOE1 NWP_MOE2 NWP_MOE3 Proportional-integral-derivative (P) controller Proportional-integral-derivative (P) controller with nonwindup limit P P 1 T 1 T P_MOE1 P_MOE2 P_MOE3 NWP_MOE1 NWP_MOE2 NWP_MOE3 Page 2

3 Second order tranfer function () U 2 A 2 B C E F OR2_MOE1 OR2_MOE2 OR2_MOE3 One common approach in handling the tranfer function block i to write the tate equation. n PSS E implementation, the dynamic model calculate the derivative of the tate (called STATE), which are then ued to calculate the tate variable (called STATE in PSS E) uing the Modified Euler integration method. The computation of STATE involve writing the appropriate equation. Since there could be everal way of formulating the STATE equation, the expreion for initializing the STATE variable and the equation involved in obtaining the STATE could alo vary. n addition, implementation of non-windup limit could alo prove to be tricky. n order to provide for an eay and a conitent method of handling of tranfer function STATE and STATE equation along with the aociated non-windup limit, the concept of Elementary Block wa introduced in PSS E-31. Simply tated, the elementary block are imply a library of function (provided with PSS E) that can be invoked in dynamic model to initialize the model STATE, for the calculation of STATE, to impoe non-windup limit (if any), and to calculate the tranfer block output. The decription given below how an AVR model implementation a it i done conventionally compared with the Elementary Block method of achieving the ame end. Since the Elementary Block method applie only to the PSS E imulation MOE (i.e., MOE 1, 2 & 3), the relevant code for thee three MOE only are preented below. Page 3

4 Comparion of Conventional and Elementary block The AVR model ued for illutrating the ue of Elementary Block i hown in Figure 1. V R E C 1 1 T R E S V E A 1 T A V MAX E F V S V MN Figure 1 - Simplified AVR (EMOEX) The variou tep involved in writing a PSS E model EMOEX are a follow: 1. dentify the CON, T R = CON(J) A = CON(J1) T A = CON(J2) V RMAX = CON(J3) V RMN = CON(J4) 2. dentify the tate, E S = STATE() E F = STATE(1) 3. At initialization (MOE = 1), we need to calculate input of each block from the known output and input. n cae of EMOEX, the known output i E F and the known input i E C (in PSS E thi i E COMP ), Conventionally we would write, E F /V E = A, and V E = E F / A Since at the tart E S = E C V R = V E E S -V S STATE(1) = EF STATE() = EC VR = STATE(1)/A STATE() Uing elementary block, V E = NWLAG_MOE1( A, T A, V RMAX, V RMN, E F, 1, ERR ) E S = E C VNP = LAG_MOE1( 1.0, T R, E S,, ERR ) V R = V E E S -V S n the above, ERR i the error code (for variou value of ERR, ee PSS E -31 Program Application Guide, volume, chapter on Elementary Block for Handling Tranfer Function in PSS ynamic Model ). Page 4

5 4. For calculating the derivative (in MOE=2), one need to etablih the firt differential equation for each tate, Uing conventional method (where i the Laplace operator), E S = (E C E S )/T R, or STATE() = (EC STATE())/CON(J) V E = V R V S - E S, or VE = VR VS STATE() E F = ( A x V E E F )/ T A, or STATE(1) = (A*VE STATE(1))/CON(J2) We need to apply non-windup limit F (STATE(1).GE. VRMAX.AN. STATE(1).GT. 0.0) THEN STATE(1) = 0.0 ELSEF (STATE(1).LE. VRMN.AN. STATE(1).LT. 0.0) THEN STATE(1) = 0.0 Uing the elementary block, in MOE=2, uing the appropriate function, we will provide input to get the block output a follow: E S = LAG_MOE2(1.0, T R, E C, ) V E = V R V S - E S VOUT = NWLAG_MOE2( A, T A, V RMAX, V RMN, V E, 1) 5. n MOE=3, we will calculate the output or tate, Baed on conventional method, we would write, EF = STATE(1) Uing the elementary block, we will need to write, E S = LAG_MOE3(1.0,T R,E C,) V E = V R V S - E S VOUT = NWLAG_MOE3( A, T A, V RMAX, V RMN, V E, 1) EF=VOUT Comparion Table The comparion table below illutrate the difference between the conventional method veru the Elementary Block approach Page 5

6 Conventional Uing Elementary Block F (MOE.EQ. 1) THEN STATE(1) = EF() STATE() = ECOMP() VR = STATE(1)/A STATE() F (MOE.EQ. 1) THEN VE = NWLAG_MOE1(A,TA,VRMAX,VRMN,EF(),1,ERR) ES = ECOMP() VOUT = LAG_MOE1(1.0,TR,ES,,ERR) VR = VE ES VS F (MOE.EQ. 2) THEN STATE() = (ECOMP() STATE())/CON(J) VE = VR VS STATE() STATE(1) = (A*VE STATE(1))/CON(J2) F(STATE(1).GE.VRMAX.AN.STATE(1).GT.0.0) THEN STATE(1) = 0.0 ELSEF(STATE(1).LE.VRMN.AN.STATE(1).LT.0.0) THEN STATE(1) = 0.0 F (MOE.EQ.2) THEN ES = LAG_MOE2(1.0,TR,ECOMP(),) VE = VR VS - ES VOUT = NWLAG_MOE2(A,TA,VRMAX,VRMN,VE,1) F (MOE.EQ. 3) THEN EF() = STATE(1) F (MOE.EQ.3) THEN ES = LAG_MOE3(1.0,TR,ECOMP(),) VE = VR VS - ES EF() = NWLAG_MOE3(A,TA,VRMAX,VRMN,VE,1) Page 6

7 Concluion Siemen PT ha implemented function to handle the PSS E calculation aociated with ome elementary tranfer function often ued a building block of complex dynamic model in PSS E. Thee function provide a implification in the proce of writing new model for PSS E and alo enure a conitent definition of thee tranfer function and, more important, the application of non-windup limit. Several new model in PSS E have already been implemented uing thee elementary block function, including the new model aociated with the EEE Std (2005) EEE Recommended Practice for Excitation Sytem Model for Power Sytem Stability Studie. Siemen PT conider that thee function are very ueful and ha made them acceible (via the NCLUE of COMON4.NS) for uer writing new PSS E dynamic model. Pleae refer to the PSS E -31 Program Application Guide Vol. Chapter 22 for detailed documentation about thee function. The ue of the elementary block would greatly implify the proce of writing PSS E dynamic model, and in addition, the application of non-windup limit would be conitent with the EEE recommendation. Page 7