Dynamic Control of Grid Assets

Transcription

1 Dynamic Control of Grid Assets ISGT 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 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! The cost of Business As Usual is too high, and consumers are not willing to pay more for energy (definitely in the US). 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 power delivery HVDC or HVDC Light).

3 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. FACTS DEVICES Power Flow Control Voltage Control Control of power flow and voltage magnitude Series Injection Shunt Injection Series-Shunt Injection TCSC Thyristor Controlled Series Capacitor SVC Static VAR Compensator TCPAR Thyristor Controlled Phase angle Regulator SSSC Static Synchronous Series Compesator STATCOM Static Synchronous Compensator Voltage Magnitude Control UPFC Unified Power Flow Controller 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

4 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. THIN AC CONVERTER (TACC) FAIL NORMAL S 3 FAIL NORMAL GRID ASSET C f2 ASSET CONTROL GRID ASSET V s L f S 1 GRID C f1 S 2 ASSET A 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.

5 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

6 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. Line Current Main transformer Current feedback Power supply V Filter PWM Inverter Control Communic. Module DC Capacitor

7 Line Current (KA) Line2_3 Line6_5 Line6_7 Line9_39 Line1_13 Line12_11 Line13_14 Line19_16 Line22_21 Line23_24 Line25_26 Line26_27 Line29_26 Line29_28 Line Currents (%Thermal Limit) Increase in Network Utilization With DSR Modules G8 IEEE 39 Bus System Network Performance With CLiC 39 G1 G MVAR MVAR G MVAR G MVAR 9.15 MVAR MVAR G MVAR 19 G4 24 G MVAR MVAR G6 23 G A Power Lines Current Profile With CLiC Modules Line currents with CLiC Line currents without CLiC Current Without CLiC Modules 94 A 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 Generator Taken Off CLiC Active Time (s) Current With CLiC Modules 643 A

8 Switch C Inverter-less STATCOM With Active Filter Function Boost configuration TACC C F S 3 S 2 v S L F S 1 i C i X i DCAP Fail Normal Switch TACC C 1 pu Lagging VAR Current Line Voltage Controllable Range Leading VAR Current 1 pu 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.

9 ILSTATCOM Experimental Results Boost mode of operation shows increase in VARs at lower line voltage 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 V c V cf I L I in Test data at 24 volts input

10 Duty Mag. A Mag. V, A Duty Mag. A V, A Mag. Harmonic Control of Dynamic Capacitor Using VQS 2 Line Voltage Line Current Single-Phase Control Architecture Load Current D-CAP current time, s Three-Phase Control Architecture Fundamental (6Hz) = 66.6, THD = 19.68% 15 1 Load Current Fundamental (6Hz) = 49.73, THD = 1.3% 15 1 Line Current Harmonic Number 2 Line Voltage Line Current Load Current D-CAP current time, s Fundamental (6Hz) = 7.3, THD = 17.65% 15 1 Load Current Fundamental (6Hz) = 61.23, THD =.62% 15 1 Line Current Harmonic Number

11 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

12 MW or MVAR 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) 1 5 P > Q > P < Q < P < Q > Time (secs)

13 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.

14 Smart and Dynamically Controllable Grid Dumb Use Smart Use: Smart meters, real time pricing, demand side management, EV charging, net metering, energy efficiency, LED lighting, transaction management, energy appliances, smart homes, data centers Dumb Asset Smart Asset: Adding intelligence & control to the T&D network and components, power flow control, wind and solar integration, system protection, dynamic voltage control, improved asset utilization, energy storage, Dynamic OPF, enabling bidirectional power flows, system protection, enabling market functions Reactive Response Proactive Response: Improved situational awareness, wide area coordination, massive data streams into actionable information, load/source forecasting and optimization, coordinated operation, operating under electrical and communications contingencies. Key Technologies: Transmission & Distribution, Solar PV, Wind, DG, Energy Storage, Power Electronics, Sensors, Cyber-Security, Transaction Management, IT Infrastructure, Energy Efficiency, Smart Appliances, EV/PHEV Dumb Grid Smart & Dynamically Controllable Grid: EPACT 25, EISA 27, ARRA 29, all move the system towards the Smart Grid requiring dynamic control capability. A new smart grid is too expensive! Prioritize.