Inexpensive Ancillary Service from Automated Tuning of Continuously Variable Loads

Transcription

1 Inexpensive Ancillary Service from Automated Tuning of Continuously Variable Loads Pre-conference workshop, IEEE CDC, Dec 2013, Florence, Italy Ancillary service from flexible loads to help the electric grid of the future Prabir Barooah Mechanical and Aerospace Engineering, University of Florida in collaboration with Prof. Sean Meyn, Yashen Lin (UF) He Hao (formerly UF, now UCB) Tim Middelkoop (formerly UF, now UMissouri) Physical Plants

2 Operating the grid is a control problem,.. (non- contingency) balancing currently achieved by > feedforward : scheduling and dispatching generation to match predicted load > feedback : frequency regulation Power (GW) Day-ahead forecast Hourly schedule Power (GW) Hour ahead forecast Total dispatch Residual Load following Power (GW) Realized load Total dispatch Regulation Time (h) Time (h) Time (h) slow, large generators: energy small, fast ramping generators: ancillary services

3 .., it needs actuators to provide energy and ancillary services BP Gas Nuclear Turbine Σ Control C BP BP BP BP Coal Batteries gas turbines Water Pump HVAC Actuation Power Grid H Measurements: Voltage Frequency Phase slow, large generators: engine small, fast ramping generators: flaps

4 The trouble(?) with solar and wind Potential for tremendous societal benefit : 33% energy from solar and wind will reduce carbon emissions by ~30%, and save ~7 billion $ per year (NREL western wind and solar integration study, phase 2, Sept. 2013) Potential for headache: (Germany, U.S. Pacific Northwest,...) not controllable, (i) Volatile (time varying), (ii) Unpredictable Regulation requirement Load- following requirement Hellman, Resources and transmission planning to achieve a 33% RPS in CAISO..., 2010

5 Automated Load Tuning to obtain Inexpensive Ancillary Services build more gas turbines? giant batteries? Now: dispatchable generation meeting demand Future: tune demand to meet volatile generation* Enabling resource: flexible loads Task: tune loads to provide ancillary service, without causing inconvenience to consumers the loads serve has to be inexpensive to the grid as well as to the consumer has to respect capacity and bandwidth (time- scale) constraints of loads 1. Flexible loads = short- term storage 2. Load Tuning = Demand Response 3. FERC 755 *1980: Schweppe et al.

6 Automated Load Tuning Intelligence at the nodes grid operator option 1: Hierarchical control architecture C Grid G C C C low bandwidth loads medium bandwidth loads high bandwidth loads option 2: fully distributed (not in this talk)

7 #1 Source of flexible loads: buildings HVAC systems in commercial buildings: approx 20% of national electricity consumption (U.S.) Large thermal inertia, so small and fast variation in air flow has little effect on indoor climate Buildings with VAV (variable air volume) systems : power consumption can be varied continuously between 0 and max, not just on/off continuously variable loads: ex: Variable Speed Drives in commercial building HVAC

8 primer on VAV (Variable air volume) systems chiller VSD VSD Electricity consumers in order: 1. chiller 2. fans 3. pumps (4/2/1) heating

9 Case study #1: obtain high frequency ancillary service, in [1/(5 min) 1/(8 sec)] Regulation Signal r Fan Controller Regulation Controller + fan speed command u r Fan fan speed v p b+r Desired air flow Building + climate controller Air flow building control system

10 Case study #1: obtain high frequency ancillary service, in [1/(5 min) 1/(8 sec)] Grid operator Regulation Signal band pass filter r Fan Controller Regulation Controller + fan speed command u r Fan fan speed v p b+r Desired air flow Building + climate controller Air flow Band pass filter to ensure the climate control unit doesn t fight the regulation command

11 Band pass filter to prevent fight between controllers Magnitude (db) Regulation Command to Fan Speed Regulation Command to Temperature /600 1/8 Frequency (Hz) power 10 0 Regulation Signal BP filter r Fan Controller Regulation Controller + fan speed command u r Fan fan power v p b+r Desired air flow Building + climate controller Air flow

12 Excellent tracking with little impact..... as long as you maintain frequency (time scale) separation Simulation results: 5 Regulation Actual Estimation Power (kw) Time (h) Temperature ( o C) Time (h)

13 Implementation : Pugh UF AHU 2: serves auditorium System identification (sine sweep) 0 10 H (db) H (deg) H : input: disturbance w (speed command) output: VDS power f (Hz)

14 Implementation: controller architecture Feedback control used for robustness to plant uncertainty High Pass Filter: subtracts baseline...since baseline power consumption is of low frequency! Bandwidth separation also helps in estimating actual service provided: power - baseline power Ack: PPD, TM, Yashen,...

15 Experimental results : Pugh UF Reference: PJM regd, bandpass filtered [1/(10 s) 1/(30 s) ] gain chosen to ensure regulation reference is within +/- 1.5 kw regulation control on for 20 minutes Power (kw) 4 Fan power Reference signal Measured power deviation Power (kw) Temp ( o F) Room temperature Time (min) Time (min) 1. Tracks reference command in the high frequency range. 2. Has little effect on indoor climate

16 How much can this help? A LOT! Resource 35 kw fan motor Ancillary service potential 5 kw 46,000 sq.ft bldg, 75 kw fan power 11 kw All buildings in the U.S. with VAV HVAC systems 6.6 GW 70% of the regulation capacity needed by the US in 2012, in the high frequency range ( ~1/1 min) Inexpensive! 1. software add on, no change in equipment 2. non disruptive to consumer service > Economic incentive? FERC oder 755 (2011) > Load aggregation? Ref: Ancillary Service for the Grid Via Control of Commercial Building HVAC Systems, He Hao, Anupama Kowli, Yashen Lin, Prabir Barooah, Sean Meyn, American Control Conference, June, 2013

17 Case study #2: obtain medium frequency ancillary service, in [1/(60 min) 1/(5 min)] Medium frequency variation in air flow will affect (i) fan power and (ii) chiller power consumption Good : much more ancillary service! Bad : 1. delay, more complex dynamics, 2. lack of direct actuation ability (typically not run by VSDs) u fan power [τ 1 τ 2 ] chiller u fan air flow rate m m T la T la small P chiller high freq. variation in air flow rate P chiller! d " low freq. variation in air flow rate

18 Indirect actuation of chillers without VFDs P r P d To handle transport delay in chiller: 1. Predict reference command (Kalman filter), 2. delay tolerance with Smith predictor Band-pass Filter + Scaling m az Indoor Climate Controller Kalman Predictor P dp Smith Predictor m ar m ad Fan/Duct/Damper Dynamics m a T Zone Dynamics Power (KW) T (F) Real Reference Real Baseline P b P Power Model Regulation Controller Tmix Wmix Closed-loop Building Dynamics Approx 80 GW of ancillary service in the medium frequency [1/(60 min) - 1/(5 min)] range, with about 1 o F temperature deviation ma (kg/s) Time (h) Real Baseline Ref: Low Frequency Ancillary Services from Commercial Building HVAC Systems, Yashen Lin, Prabir Barooah, Sean Meyn, IEEE Smart Grid Comm, October, 2013, Vancouver, Canada

19 Continuously variable loads 1. Building HVAC systems that are variable speed a. Already equipped with VAV systems b. VSD equipped chillers (not common) c. Variable speed residential air conditioners 2. Industrial loads: water and gas pumps 3. Manufacturing ex: Alcoa, IN: 70 MW of frequency regulation service since 2009 by using low- pass filtering property of Aluminum smelter Key requirement: Process the load serves must have low pass property so that high frequency variation in power consumption doesn t affect service as long as average power is maintained over time Q: What s the total capacity of such loads to provide service: AS (f,...)? Q: Risk to consumers? AS (f,c) C = constraints ex: equipment life reduction? Q: What incentives are needed to recruit loads to provide AS?

20 Parting Comments A sustainable energy future with a high renewable energy portfolio requires substantially large amounts of inexpensive ancillary service Tuning of a large number of loads offers a vast and untapped source of inexpensive ancillary service Continuously variable loads, e.g., motors with VSDs, are particularly convenient In principle, can be solved through appropriate automation Many, many, many open research questions: 1. technological 2. social- science related 2. economic Financial support from National Science Foundation, DOE (EPAS, CPS)

21 References (AS from continuously variable loads) 1. How demand response from commercial buildings will provide the regulation needs of the grid, He Hao, Timothy Middelkoop, Prabir Barooah and Sean Meyn, invited paper, 50th Allerton Conf., Oct Ancillary Service for the Grid Via Control of Commercial Building HVAC Systems, He Hao, Anupama Kowli, Yashen Lin, Prabir Barooah, Sean Meyn, American Control Conference, June, Ancillary Service to the Grid through Control of Fans in Commercial Building HVAC Systems, He Hao, Anupama Kowli, Yashen Lin, Prabir Barooah, Sean Meyn, IEEE Transactions on Smart Grid, under review 4. Low Frequency Ancillary Services from Commercial Building HVAC Systems, Yashen Lin, Prabir Barooah, Sean Meyn, IEEE Smart Grid Comm, October, 2013, Vancouver, Canada Acknowledgements: National Science Foundation, DOE (EPAS, CPS)