2016_An Automated Impedance Estimation Method in Low-Voltage Distribution Network for Coordinated Voltage Regulation

1 An Automated Impedance Estimation Method in Low-Voltage Distribution Network for Coordinated Voltage Regulation Sekyung Han, Daisuke Kodaira, Soohee Han, Bokyu Kwon, Yasuo Hasegawa & Hirohisa Aki Daisuke Kodaira

Problem: Voltage violation HV line (22.9 kV) LV line (220 V) Normal Power Flow 1 Fixed Voltage due to the transformer 10 2 9 3 4 5 8 7 6 Reverse Power Flow Voltage Voltage upper limit Voltage lower limit 1 House # 10

3 Objective Voltage regulation requires line impedance, however, which is not recognized. ? ? ? NODE 3 ? ? NODE 2 NODE 1 • Why impedance have not been recognized so far? Without DERs on the network, accurate impedance is not necessary; because there is no requirement for voltage regulation. Objective Impedance estimation for voltage regulation

User A 𝑍𝐴𝐵 ? User B 𝑉𝐴 ∶ 50~60𝐻𝑧 User C Voltage Constraints 𝑉𝐶 , 𝐼𝐶 , 𝑃𝐶 𝑉𝐶 , 𝐼𝐶 , PC 𝑉𝐵 , 𝐼𝐵 , 𝑃𝐵 𝑉𝐴 , 𝐼𝐴 , 𝑃𝐴 𝑉𝐵 , 𝐼𝐵 , 𝑃𝐵 Time Frequency = 1/50 =0.02[sec] Required sampling rate = 0.02/2 = 0.01[sec] 𝑉𝐴 , 𝐼𝐴 , 𝑃𝐴 Smart Meter （Meter metrology + communication module） Measured values are shared Measuring data including the phase difference between several points needs sophisticated GPS system Constraint: Estimate impedance without phase difference information 4

Model J-node 5 = ZJ45 Z 𝑇5 ZT4 ZT3 T-node 5 T-node 4 𝑆𝑇5 𝑆𝑇4 𝑉𝑇5 , 𝐼𝑇5 𝑉𝑇4 , 𝐼𝑇4 J-node 3 ZJ34 J-node 2 ZJ23 ZT2 ZT1 T-node 1 𝑆𝑇3 T-node 2 𝑆𝑇2 𝑉𝑇3 , 𝐼𝑇3 𝑉𝑇2 , 𝐼𝑇2 𝑉𝑇1 , 𝐼𝑇1 T-node 3 J-node 1 ZJ12 Pole-trans T-node indicates a household J-node 4 𝑆𝑇1 • The power (S), voltage (V), and current (I) are measured at each node • Impedance are estimated based on circuit theory principle. Voltage of J-node 5 can be described in the two ways: 1. 𝑉𝐽5 = 𝑉𝑇5 + 𝑍𝑇5𝐼𝑇5 2. 𝑉𝐽5 = 𝑉𝑇4 + 𝑍𝑇4𝐼𝑇4 Both equations should be equal ∴ 𝑂𝑏𝑗𝑒𝑐𝑡𝑖𝑣𝑒 𝑓𝑢𝑛𝑐𝑡𝑖𝑜𝑛: 𝑉𝑇5 +𝑍𝑇5𝐼𝑇5 − 𝑉𝑇4 + 𝑍𝑇4𝐼𝑇4 = 0 The solution to impedance estimation can be expressed as nonlinear equations

Result: impedance • Real part has small errors as less than 1%. • Imaginary part has relatively larger error rate than real part. This is because the original value of imaginary part is smaller. With these acceptable error values, our algorithm proofs the efficacy for voltage regulation. ZT1 Technical specification (Ω) 0.0436 + 0.0020i Estimated Impedance (Ω) 0.0436 + 0.0018i ZT2 0.0436 + 0.0020i 0.0437 + 0.0024i 0.2 20.0 ZT3 0.0436 + 0.0020i 0.0433 + 0.0027i 0.7 35.0 ZT4 0.0436 + 0.0020i 0.0437 + 0.0026i 0.2 30.0 ZT5 0.0948 + 0.0287i 0.0953 + 0.0280i 0.5 2.4 ZJ12 0.0512 + 0.0267i 0.0508 + 0.0267i 0.8 0.0 ZJ23 0.0512 + 0.0267i 0.0511 + 0.0269i 0.2 0.7 ZJ34 0.0512 + 0.0267i 0.0514 + 0.0263i 0.4 1.5 ZJ45 0.0512 + 0.0267i 0.0509 + 0.0269i 0.6 0.7 Error(%) Re Imag 0.0 10.0

Coordinated Voltage Regulation Individual Inverter Capacity Reactive Power Coordinated The rest of inverter ΔPloss Active power User1 User2 User3 User1 User2 User3 Voltage Specific Range House # House # All users share the Reactive Power supplies to avoid restricting Active Power 7

Result: Coordinated voltage regulation • Objective function: Maximize σ𝑛𝑖=1 𝑃𝑖 (𝑛: 𝑡ℎ𝑒 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 ℎ𝑜𝑢𝑠𝑒ℎ𝑜𝑙𝑑𝑠) Generaton loss during the simulation period (120 secs) [Wh] • Constraint： voltage capacity of inverter Vlower_limit < 𝑉𝑖 < 𝑉𝑢𝑝𝑝𝑒𝑟_𝑙𝑖𝑚𝑖𝑡 2 𝑃𝑖2 + 𝑄𝑖2 < 𝑆𝑚𝑎𝑥 120 CVR : Coordinated voltage control 100 80 IVR : Individual voltage control 60 40 T-node2, 3, 5 and 6 have PVs. 20 0 IVR CVR IVR CVR IVR CVR IVR CVR IVR CVR T node 2 T node 3 T node 5 T node 6 total Total active power loss is reduced by almost 80% in CVR. 8