1. Frankfurt (Germany), 6-9 June 2011 Pyeongik Hwang School of Electrical Engineering Seoul National University Korea Hwang – Korea – RIF Session 4a – 0324 A control method of distributed generators in smart distribution system considering system loss and voltage

2. Frankfurt (Germany), 6-9 June 2011  Increased installation of distributed generations(DGs) The characteristics of the distribution system is changed  Voltage profile, system loss, power flow, etc.  Introduction of the smart distribution system The status of the distribution system can be measured and calculated more accurately The power output of DGs can be controlled using the communication infrastructures.  Chance to more effective operation using DGs Hwang – Korea – RIF Session 4a – 0324 Introduction

3. Frankfurt (Germany), 6-9 June 2011  The objectives of the proposed method Minimize the system loss Maintain the system voltage within its limit - Minimize - Subject to Hwang – Korea – RIF Session 4a – 0324 DG control problem formulation

4. Frankfurt (Germany), 6-9 June 2011  Relationship among loss, voltage, and output of DGs is highly non-linear Formulated DG control problem is a non-linear optimization problem  Sequential Linear Programming(SLP) method is adopted Optimal solution is calculated by solving series of linear programming (LP) problem linearized at the operation point Operation point is determined at the previous iteration Hwang – Korea – RIF Session 4a – 0324 Sequential Linear Programming

5. Frankfurt (Germany), 6-9 June 2011  Sub-functions of SLP LP formulation Step size adjustment Convergence test  Decision variable for LP Hwang – Korea – RIF Session 4a – 0324 SLP application to DG control

6. Frankfurt (Germany), 6-9 June 2011  Linearized Optimization problem -Minimize -Subject to Hwang – Korea – RIF Session 4a – 0324 LP formulation Loss sensitivity matrix Voltage sensitivity matrixInjection power sensitivity matrix

7. Frankfurt (Germany), 6-9 June 2011  Differences between distribution system and transmission system Existence of mutual impedance in line parameter Unbalanced connection of DGs  Bus admittance matrix with mutual line impedance Used for calculation of loss and voltage sensitivity matrices A : bus incidence matrix, [y] : primitive admittance matrix. Hwang – Korea – RIF Session 4a – 0324 LP formulation

8. Frankfurt (Germany), 6-9 June 2011  Differences between distribution system and transmission system Existence of mutual impedance in line parameter Unbalanced connection of DGs  Bus admittance matrix with mutual line impedance Used for calculation of loss and voltage sensitivity matrices A : bus incidence matrix, [y] : primitive admittance matrix. Hwang – Korea – RIF Session 4a – 0324 LP formulation

9. Frankfurt (Germany), 6-9 June 2011  Injection power sensitivity matrix calculation method Hwang – Korea – RIF Session 4a – 0324 LP formulation A=zeros(N, M) for i=1:1:M switch connection topology of P(Q) controllable DG i case : single phase A(bus #, i)=1 case : two phase A(bus # 1, i)=1/2; A(bus # 2, i)=1/2 case : three phase A(bus # 1, i)=1/3; A(bus # 2, i)=1/3; A(bus # 3, i)=1/3

10. Frankfurt (Germany), 6-9 June 2011  Step size adjustment Prevent oscillation in SLP  Convergence test Hwang – Korea – RIF Session 4a – 0324 SLP application to DG control

11. Frankfurt (Germany), 6-9 June 2011  Flow chart of the proposed method Hwang – Korea – RIF Session 4a – 0324 Proposed method

12. Frankfurt (Germany), 6-9 June 2011 DG 1 A-B-C phase DG 2 A-B phase DG 3 B-C phase  IEEE 37 node test feeder system with three DGs Hwang – Korea – RIF Session 4a – 0324 Case Study

13. Frankfurt (Germany), 6-9 June 2011  Under voltage violation is occurred in case 2 and case 3 Hwang – Korea – RIF Session 4a – 0324 Initial voltage vs. voltage limit Under Voltage

14. Frankfurt (Germany), 6-9 June 2011  The proposed method is implemented as a Matlab code Matlab provided function “linprog” is utilized as the LP solver  Comparing with results of the function “fmincon” Maximum error is less than 0.1% Proposed method is at least 90 times faster than fmincon Hwang – Korea – RIF Session 4a – 0324 Performance of the proposed method Method System loss(kW)Time(sec) Case 1Case 2Case 3Case 1Case 2Case 3 SLP78.9985.5189.851.283.151.29 Fmincon78.9685.5189.77142285290

15. Frankfurt (Germany), 6-9 June 2011  The system loss is reduced about 19 %(97kW  78 kW)  Operation cost can be reduced by minimizing the loss Hwang – Korea – RIF Session 4a – 0324 Case 1 ( V min = 0.97 p.u., V max = 1.03 p.u. )

16. Frankfurt (Germany), 6-9 June 2011  Without proposed method, tap position of OLTC must be changed to eliminate the voltage violation Increasing operation cost  With proposed method, Under violation is eliminated without tap changing  System operation cost can be reduced by preventing the tap changing of OLTC  System stability can be improved by maintaining system voltage within its limit Hwang – Korea – RIF Session 4a – 0324 Case 2 ( V min =0.98 p.u., V max =1.02 p.u.)

17. Frankfurt (Germany), 6-9 June 2011  System voltage Hwang – Korea – RIF Session 4a – 0324 Case 2 ( V min =0.98 p.u., V max =1.02 p.u.)

18. Frankfurt (Germany), 6-9 June 2011  Tap changing to eliminate the under voltage violation  New over voltage violation is occurred Hwang – Korea – RIF Session 4a – 0324 Case 3 ( V min =0.985 p.u., V max =1.015 p.u.) Over voltage

19. Frankfurt (Germany), 6-9 June 2011  System voltage can be maintained within its limit  Power quality can be enhanced by controlling the voltage more tightly Hwang – Korea – RIF Session 4a – 0324 Case 3 ( V min =0.985 p.u., V max =1.015 p.u.)

20. Frankfurt (Germany), 6-9 June 2011  DGs control problem was formulated as a non-linear optimization problem.  Sequential Linear Programming (SLP) based DGs control method was proposed  Effects of the proposed method were identified Operation cost reduction System stability improvement Power quality enhancement Hwang – Korea – RIF Session 4a – 0324 Conclusions

21. Frankfurt (Germany), 6-9 June 2011 Hwang – Korea – RIF Session 4a – 0324 Thank You ! (hpi@powerlab.snu.ac.kr)