Frequency Response Primary Frequency Response Assessment of Energy Storage Potential Problem Formulation Simulation Results Key Findings References

Presentation Outline

Frequency Response

Point A: pre-disturbance frequency Point B: maximum excursion point Point C: settling frequency of the Interconnected system

Frequency response characteristics during loss of generation

Frequency response is the swift equilibrium between generation and demand provided by system, or elements of system, at time of frequency deviation [1]-[2]

Based upon the definition –

( )_BA

Generation lost MWNadir based Frequency responseFrequency Frequency

=−

( )

CA

Generation lost MWFrequency responseFrequency Frequency

=−

S. No.

Response type

Time frame Control objectives Function

1 Inertial response 0-5 secs

Power balance and transient frequency dip minimization

Transient frequency control

2 Primary control, (governor)

1-20 secs Power balance and transient frequency recovery

Transient frequency control

3 Secondary control, (AGC)

30secs -15 mins

Power balance and steady-state frequency Regulation

4 Tertiary Control

5 - 30 mins

Power balance and economic-dispatch

Load following and reserve provision

India [3]

Primary Frequency Response

Primary frequency response is of prime concern for system security and reliability (FERC, NERC)

FERC in Feb 2018, by order no. 842 mandates the PFR in all LGIA and SGIA[4]

FERC make PFR, an essential service in ensuring the reliability and resilience of the North American Bulk Power-System

Less PFR would lead to frequent events of frequency falling [5], [6]

PFR prevents the grid frequency from falling below the first stage of under frequency load shedding (“UFLS”) set points

Traditionally, PFR can be provided via Governor employed in conventional generators

9

Transition towards Low-Carbon Systems

10

Assessment of Energy Storage Potential

Intermittency and uncertainty associated with renewable energy sources such as solar and wind would create generation load imbalances

These impacts lead to recurring events of frequency deviation followed by inevitable contingencies

The initial frequency deviation can be arrested by SI and PFR

With an ability of high energy density and power density, PHES comes out as a viable solution for PFR to stabilize post fault frequency dynamics

Generation scheduling is performed for the day-ahead, to estimate the PFR adequacy

Problem Formulation

Objective function

Generator scheduling constraints Minimum-up and down time Ramp-up and ramp-down The line power flow is limits

2, ,min . . .

.C . ,, , , , t

g t g tI T Tu dTC a P b P c C C VOLL LSti t t

PV T W Tcur cur cur curP P C g tpv t pv t w t wpv t w t

= + + + + +∑∑ ∑

+ + ∀∑ ∑ ∑ ∑

PFR Constraints System Inertia Rate of change of frequency Frequency nadir and nadir time Steady-state frequency

Simulation Results

Case- Study[7]-[12] New England test system

Hourly data of wind speed and PV irradiance for a day

The frequency data

Nominal frequency (=60 Hz)

Rate of change of frequency (=2 Hz/sec)

Governor dead band (=36mHz)

Maximum steady-state frequency deviation (=0.2Hz)

Load damping rate (=1%)

Under frequency load shedding bound as (=59.1Hz)

Total installed capacity is 8840 MW and peak demand of 5748 MW

The system PFR requirement is assumed to be 50% of the system largest generator

The capacity of PHES takes as 200MW

PHES fixed operating cost is assumed as 18$/Kw-h yearly

PV and wind curtailment cost as 0.7$/MWh and 1$/MWh, respectively

Largest generator outage is consider at t5

System Performance

Cases

Limit on RoCoF and Fnadir

No Limit on RoCoF and Fnadir

Without

PHES Operating

Cost ($) With PHES Operating

Cost ($) Base case √ 2606027 - -

Case -ii √ 2037064 √ 2032000

Case- iii √ 1665598 √ 1661624

Case- iv × - √ 1232391 Case- v × - √ 961442

Fig. gives the hourly load, wind and PV generation profile for 24 hr

Wind and PV power generation shown is at 10% integration

Fig. shows the PFR contribution from conventional units PFR requirement in most of the instances is increased on

RES integration The same is reduced on PHES integration

Limit on Frequency Security Parameters

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24Time (Hrs)

-2

-1.5

-1

-0.5

0

RoCo

F (H

z/sec

)

Base case

30% RES

30% RES + PHES

Impact on RoCoF with 30% RES integration with constraint on frequency parameter

Bound of 2Hz/sec is imposed on RoCoF RoCoF is within range and well behaved with PHES

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (Hrs)

0

200

400

600

800

Syste

m In

ertia

(Mw-

sec/H

z)

Base Case

20% RES

30% RES

40% RES

50% RES

The variation of SI under different RES integration is plotted

Due to low availability of wind power and decreasing profile of PV power around t15, additional CG are committed to meet the load

Increases SI in these hours

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (Hrs)

55

56

57

58

59

60

Freq

uenc

y Na

dir (

Hz)

Base case

40% RES

PHES at 40% RES

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (Hrs)

55

56

57

58

59

Freq

uenc

y Na

dir (

Hz)

Base case

50% RES

PHES at 50% RES

1 2 3 4

Cases of RES integration

0

500

1000

1500

SI an

d PF

R fro

m P

HES

PFR

SI

Case 1 shows results at 20% RES integration, next at 30% integration up to 50%

There is no RES curtailment at 20% and 30%; however, curtailment increases on large integration

Key Findings

At low RES integration, conventional units are adequate for PFR

RES integration at 40% and above, response from conventional units is limited and fails to maintain frequency in range

PHES stabilizes post-fault frequency dynamics-RoCoF, frequency nadir and steady-state frequency

PHES reduces additional commitment of conventional units for PFR

Results in reduction in overall system operating cost Large scale RES integration and power flow limits ->

RES curtailment and requires storage proper allocation

References

1. Wind speed anChallenges and Opportunities for the Nordic Power System,” 2016.

2. H. Bevrani, “Robust Power System Frequency Control”, New York, NY, USA: Springer, 2009.

3. Central Electricity Regulatory Commission 2017, “Report of Expert Group to review and suggest measures for bringing power system operation closer to National Reference Frequency”, [Online]. Available: http://cercind.gov.in/2018/Reports/50%20Hz_Committee1.pdf

4. FERC Revises Requirements for Provision of Primary Frequency Response, 2018, Available: https://www.ferc.gov/media/news-releases/2018/2018-1/02-15-18-E-2.asp

5. O.I. Elgered, Electric energy system theory: An introduction, 2nd edn , Mcgraw- Hill, New York,1982, pp. 55-60.

6. Joseph H. Eto, John Undrill, Peter Mackin, Ron Daschmans, Ben Williams, Brian Haney, Randall Hunt, Jeff Ellis, “ Use of Frequency Response Metrics to Assess the Planning and Operating Requirements for Reliable Integration of Variable Renewable Generation”, Ernest Orlando Lawrence Berkeley National Laboratory, Dec. 2010

7. D. Krishnamurthy, W. Li, and L. Tesfatsion, “An 8-zone test system based on ISO New England data: development and application,” IEEE Trans. Power Syst., vol. 31, no. 1, pp. 234–246, 2016.

8. d PV irradiance data, [Online]. Available: http://www.soda-pro.com/.

9. Report on “Pinnapuram integrated renewable energy with storage project, IRESP.

10. [Online].Available: http://environmentclearance.nic.in/writereaddata/Online/TOR/16_Apr_2018_13182853391O82IHRPinnapuramPFRFinalToR.pdf

11. "Updated Capital Cost Estimates for Utility Scale Electricity Generating Plants." Information Administration, Energy, U. S, 2013.

12. V. Trovato, A. Bialecki, and A. Dallagi, “Unit commitment with inertia-dependent and multi-speed allocation of frequency response services,” IEEE Trans. Power Sys., vol. 34, no. 2, pp. 1537-1548, 2018.