Smart Grid Application of Optimal Transmission Switching

Transcription

1 Smart Grid Application of Optimal Transmission Switching By, Kory W. Hedman, et al.* University of California, Berkeley INFORMS Annual Meeting Washington, DC October 15, 2008 *Dr. Richard P. O Neill (Chief Economic Advisor, FERC), Emily B. Fisher (Ph.D. Student, Johns Hopkins University), and Dr. Shmuel S. Oren (Professor, UC Berkeley)

2 Motivation Co-optimize transmission topology and generation dispatch Efficiency improvements with no reliability degradation Smart grid application by flexible reconfiguration Proof of concept: ISONE 5000, IEEE 118, and IEEE 73 (RTS 96) bus model 2

3 Overview Introduction Optimal transmission switching and transmission planning Transmission switching DCOPF and N-1 DCOPF formulations Results Practical implications revenue adequacy Current and future work Conclusions References 3

4 Introduction Control of transmission assets not fully utilized today Transmission assets are seen as static in the short term Currently operators change transmission assets states on ad-hoc basis Personal communication with Andy Ott, VP, PJM Network redundancies Required for reliability but not required for every market realization Redundancies may cause dispatch inefficiency 4

5 Introduction continued Smart grid application of co-optimizing transmission and generation With appropriate switching technology, backup transmission can be kept offline (just in time transmission) DCOPF Optimal Transmission Switching Model If not, enforce N-1 standards with transmission switching N-1 DCOPF Optimal Transmission Switching Model FERC order 890 calls for economic transmission - makes transmission switching 5 relevant

6 Introduction continued Electric Transmission Network Flow Problem Optimal Power Flow (OPF) Alternating Current Optimal Power Flow (ACOPF) With contingency constraints: N-1 ACOPF Direct Current Optimal Power Flow (DCOPF) Linear Approximation of the ACOPF With contingency constraints: N-1 DCOPF 6

7 Example: Introduction continued 7

8 Optimal Transmission Switching and Transmission Planning Transmission planning Long run problem A line need not be beneficial for every hour A line may not be necessary to meet reliability standards for every hour Long investment cycle leaves room for efficiency improvements by topology reconfiguration Optimal transmission switching Short run problem Does not necessarily indicate inefficient transmission planning 8

9 Traditional DCOPF Formulation Minimize: Total generation cost Constraints: Bus angle constraints Generator min & max operating constraints Node balance constraints Line flow constraints Line min/max thermal constraints No generation unit commitment We do not use PTDFs rather: 9

10 Optimal Transmission Switching Z k : Binary variable DCOPF Formulation State of transmission line (0 open, 1 closed) Update line min/max thermal constraints: Original: New: Update line flow constraints: Original: New: 10

11 Optimal Transmission Switching DCOPF Formulation continued 11

12 IEEE 118 bus model Results DCOPF 25% savings found by Fisher et al. ISONE 5000 bus model (includes NEPOOL, NYISO, NB, NS costs for NEPOOL only) 5% to 13% savings of $600,000 total cost for NEPOOL for one hour (feasible solutions) Does not include reliability constraints 12

13 Optimal Transmission Switching N-1 N-1 standards: DCOPF Formulation Demand must be satisfied even if any single element (transmission line or generator) is lost due to a contingency Optimal transmission switching N-1 DCOPF formulation Repeat OPF constraints for each contingency Create binary parameters representing the state of each element in the system Optimal topology and generation dispatch solution must satisfy steady-state constraints and all N-1 contingency constraints 13

14 Results N-1 DCOPF Savings while including reliability constraints IEEE 118 Bus Model Up to 16% savings with N-1 DCOPF transmission switching (feasible solutions) IEEE 73 (RTS 96) Bus Model Up to 8% savings with N-1 DCOPF transmission switching (feasible solutions) 14

15 Practical Implications Revenue Adequacy Revenue adequacy not guaranteed with transmission switching Social welfare will not decrease There may be wealth transfer issues due to Financial Transmission Right (FTR) settlements 15

16 Current Optimal Transmission Switching Research Generation unit commitment Speed up B&B by introducing valid inequalities that exploit the problem structure Explore heuristic techniques, separation techniques, etc. Benders decomposition Analyze various sub-problem formats Research local branching approach 16

17 ACOPF Future Optimal Transmission Switching Research MINLP very difficult Research heuristic techniques Revenue adequacy & FTR settlement Can revenue adequacy be maintained with transmission switching? Do we need a compensation scheme to offset the impact on FTR settlements? 17

18 Conclusions DCOPF for ISONE networks ranged from 5% to 13% savings (without N-1) N-1 DCOPF for IEEE 118 & RST 96 system showed savings from 1% to 16% Substantial results for off-peak and peak Increases social welfare Transmission switching can be beneficial even with well planned networks and adds another level of control 18

19 References [1] E. B. Fisher, R. P. O Neill, and M. C. Ferris, Optimal transmission switching, IEEE Trans. Power Syst., vol. 23, no. 3, pp , Aug [2] K. W. Hedman, R. P. O Neill, E. B. Fisher, and S. S. Oren, Optimal transmission switching sensitivity analysis and extensions, IEEE Trans. Power Syst., vol. 23, no. 3, pp , Aug [3] K. W. Hedman, R. P. O Neill, E. B. Fisher, and S. S. Oren, Optimal transmission switching with contingency analysis, IEEE Trans. Power Syst., to be published. 19

20 References continued [4] K. W. Hedman, R. P. O Neill, and S. S. Oren, Analyzing valid inequalities of the generation unit commitment problem, PSCE 2009, to be published. [5] K. W. Hedman, R. P. O Neill, E. B. Fisher, and S. S. Oren, Optimal transmission switching applied to ISO networks, working paper. [6] K. W. Hedman, M. C. Ferris, R. P. O Neill, E. B. Fisher, and S. S. Oren, Optimal multi-period generation unit commitment and transmission switching with N-1 reliability, working paper. [7] K. W. Hedman, R. P. O Neill, and S. S. Oren, Optimal transmission switching using Benders decomposition, working paper. 20