Dynamic Control of Grid Assets

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1 Dynamic Control of Grid Assets Panel on Power Electronics in the Smart Grid Prof Deepak Divan Associate Director, Strategic Energy Institute Director, Intelligent Power Infrastructure Consortium School of Electrical Engineering Georgia Institute of Technology

2 Power Delivery - Major Challenge for Sustainable Energy US wind (blue) and solar (brown/yellow) resource map. Wind at price parity with natural gas, retail price parity imminent for solar PV. Binding RPS mandates of 1-4% in 27 states. To meet current reliability standards, new solar/wind plants need energy storage, back-up fossil plants & spinning reserve. EVs require spinning reserve and back-up generation. Excessive new T&D buildout with RPS and EVs to meet energy delivery requirements.

3 Impact of Renewable Generation on Transmission Grid DOE study shows LMP impact of 2% wind in eastern interconnect with existing transmission. 37.8% curtailment of wind generation; revenues unable to support wind generation without market-distorting make-whole payments, $33B/yr in congestion GA Tech study of simplified IEEE 39 Bus system with 4 control areas, operation simulated for 2 years, 2% RPS phased in over 2 years, sufficient transmission capacity added each year to eliminate curtailment of renewable generation (renewable generation lean, transmission heavy scenario) BAU case requires upgrade of 3 inter-regional paths, for a total of 186, MW-MILES. Smart Grid case uses Controlled Energy Flows to route power along underutilized paths, 36, MW-miles of new lines needed, only 2% of BAU. Generation-weighted LMP for 2% Wind Scenario (source DOE, Eastern Wind Integration and Transmission Study, 21) IEEE 39 Bus System Partitioned into 4 Control Areas

4 Smart and Dynamically Controllable Grid To achieve energy sustainability will require integration of renewable energy, electric vehicles, price based electricity demand, load-following generation, energy storage results in tremendous spatial and temporal variability. This will need to be solved through increased smarts, communications, and control. Existing breaker based controls will be prohibitively costly, and will require dynamic controls that can enhance asset utilization without compromising system reliability. At a societal level, the Smart and Controllable Grid is the key to achieving costeffective energy sustainability by using assets more effectively and minimizing the build of new transmission and distribution infrastructure. Utilities are wary of power electronics because of cost and reliability. Transmission and sub-transmission systems have 99.99% reliability, higher than most power conversion systems. Also, single point of failure can reduce system capability just at the time the capability is needed. Even though power electronics based FACTS devices have been available for 2 years, penetration has been poor (except in applications for point-to-point power delivery over distances HVDC or HVDC Light).

5 Dynamic Grid Control using FACTS Devices Dynamic grid control using Flexible AC Transmission Systems (FACTS) Lumped solution that is added to the existing system, with single point of failure Dynamic control of voltage and power flow is required. Power Flow Control Voltage Control Control of power flow and voltage magnitude Voltage Magnitude Control Impedance-based FACTS Devices lower cost, only Q control Voltage Source Converter (VSC) improved P/Q/H control Response Time Cost Control capabilities Complexity Physical size

6 Thin AC Converters Dynamic Control of Grid Assets The concept of Thin AC Converters lies in utilizing existing grid assets to provide additional functionality, i.e. making the dumb asset smart. GRID ASSET Layer the existing asset with a direct ac converter use the existing asset as the bulk energy storage element at the fundamental frequency Reflect the dynamically controlled asset value on the grid. No additional stresses. The converter has a Fail Normal mode, where failure of the converter restores normal function of asset on the grid.

7 Thin AC Converters MULTI-LEVEL DIRECT AC CONVERTERS VIRTUAL QUADRATURE SOURCES THIN AC CONVERTERS Possible Applications Smart Wires Controllable Network Transformers Inverter-less STATCOMs Transmission Lines LTC Transformers Shunt VAR Capacitors

8 Smart Wires Dynamic Control of Line Impedance Distributed Static Series Compensator (DSSC) or Distributed Series Reactance (DSR) modules that clip on to existing conductors and change line impedance as needed Low-cost zero-footprint distributed solution that can change line impedance by 2%. Power flow control has substantial impact on system capacity and for enhancing system utilization, even under contingencies. Demonstrated at 161 kv level, with pilot demonstration underway. Power Line Transformer X M Power Supply DSR S M S 1 Control

9 Increase in Network Utilization With DSR Modules 39 G1 G MVAR MVAR 8 7 G G2 IEEE 39 Bus System MVAR G MVAR 9.15 MVAR MVAR G MVAR 19 G4 24 G MVAR MVAR G6 G7 Line Currents (%Thermal Limit) Increase in Transfer Capacity from 194 MWs (59%) to 2542 MWs (93.3%) - congested corridors are shown in red Would require 9 additional lines to realize capacity increase, capacity utilization stays at 63% With (N-1) contingency, capacity is decreased to 1469 MW (46%), and increased to 23 MW with DSR modules without building additional lines Line2_3 Line6_5 Line Current (KA) Line6_7 Line9_39 Generator Taken Off Network Performance With CLiC Line1_13 94 A Line12_11 Line13_14 Line19_16 Power Lines Line22_21 Line23_24 Current Profile With CLiC Modules Line currents with CLiC Line currents without CLiC CLiC Active Time (s) Line25_26 Line26_27 Line29_26 Current Without CLiC Modules 94 A Current With CLiC Modules 643 A Line29_28

10 Switch C Inverter-less STATCOM With Active Filter Function Boost configuration TACC v S i DCAP TACC L F i X C F S 3 S 2 S 1 i C Fail Normal Switch Increases VARs as voltage decreases S 4 C + v C -- Duty Function: Virtual Quadrature Sources (VQS) d K K4 sin(4 t 4) K6 sin(6 t 6) If: d f (,2,4,...) Then: i f, 3,5,7,... DCAP VAR Injection K 2 sin(2 t ) 2 Active Filter Provide dynamic VARs and active harmonic filtering in one single integrated unit without any bulk energy storage elements! Control utilizes Virtual Quadrature Sources at the 3 rd and fundamental frequency.

11 Harmonic Control of Dynamic Capacitor Using VQS Boost mode of operation shows increase in VARs at lower line voltage - STATCOM A multi-level direct ac/ac converter is used to realize up to 2.4 kv New techniques had to be developed for scaling design to realistic levels Three phase D-Cap in Active Filter mode. Three-Phase Control Architecture V, A A Duty 2 Line Voltage Line Current Load Current D-CAP current time, s Mag. Mag. Fundamental (6Hz) = 7.3, THD = 17.65% 15 1 Load Current Fundamental (6Hz) = 61.23, THD =.62% 15 1 Line Current Harmonic Number

12 Controllable Network Transformer Voltage & Power Flow TACC: Converter is rated at ~2% of line power, attached to LTC transformer Scalable to sub-transmission, transmission level using multi-level ac-ac converter or dc/ac inverter based system Provide +/-1% voltage control and phase angle control power flow control Fail Normal mode allows CNT to revert back to a simple transformer in case of power electronics failure No line outage, thus system reliability not compromised 13.8 kv 1 MW CNT demonstration unit is being built in the lab. V OUT V IN Thin AC Converter

13 CNT Applications: Power Flows Between Control Areas Control direction and magnitude of Real and Reactive power Convert a transformer in a tieline into a dispatchable element Prevent unwanted loop flows at flow gates, implement firm power transaction contracts. Provide real and reactive power as needed during contingencies Scalable to high power levels, lower cost than B2B and UPFC Real & Reactive Power Control by CNT P > Q < Varying K 2 Varying K P (Real Power) Q (Reactive Power) MW or MVAR 1 5 P > Q > P < Q < P < Q > Time (secs)

14 Conclusions The existing electricity infrastructure has to be upgraded to a smart and controllable grid in order to meet RPS mandates, allow increased EV penetration, and to reduce GHG emissions helping make the energy infrastructure sustainable. Dynamic control on the grid has typically required FACTS devices may be too expensive and pose reliability issues Dynamic control of grid assets can provide a cost-effective method for improving system controllability, reliability and utilization. Smart Wires, Inverterless STATCOMs, Dynamic Capacitors (D-CAP) and Controllable Network Transformers (CNT) show examples of Dynamic Grid Asset Control.