IRPTF-Simulation Update - nerc.com Resource Performance... · Modeling Objectives ... fast...

David Piper, PE

Presentation toNERC IRPTF

January 24, 2018

IRPTF-Simulation Update

UpdateThe studies subgroup has completed simulationsSome of the most severe fault/setting combinations have resulted in transient instabilitySystem response characteristics have been grouped for further analysis.

Momentary Cessation (Stable)1. Fault in Southern California

1. Inverters enter MC2. DC converters may block3. Inertial and Primary

frequency response (mostly from the Northwest)

4. Power swing magnitude depends on energy loss

2. Fault cleared1. DC converters resume2. Inverters resume3. System reaches

equilibrium

Magnitude of Energy Loss Matters

• Fault type and location increases the number of inverters that observe depressed voltage

• Vmc, Δsr, and Δrr settings have a direct impact on the total energy loss following a fault

Location of Spin Matters

Momentary Cessation (Unstable)1. Fault in Southern California

1. Excessive amount of inverters enter MC

2. DC converters block3. Inertial response (mostly from

the Northwest)4. Excessive power swing

2. Fault cleared1. DC converters resume 2. Inverters start to resume3. Voltages decline along

transfer paths4. Voltage collapse and/or

separation

Next StepsAnalysis will be completed on unstable cases to identify cause of instability.Studies subgroup will analyze the impact that a reallocation of spinning reserve may have on stabilityAnalysis of peak load casesProvide recommendation of real/reactive power priority

Questions?

Simulate Inverter Momentary Cessation

NERC IRPTF Updates

Songzhe Zhu, California ISO

David Piper, Southern California Edison

Ryan Quint, NERC

Modeling Objectives

• Existing inverter based generators Generic models shall be able to simulate the momentary

cessation and match the performance observed in the actual events

• Future inverter based generators Establish inverter performance guidelines

Generic models shall be examined for modeling capability against the inverter design under the performance guidelines

Illustration of Momentary Cessation

Momentary Cessation Modeling Requirement

• Cease active and reactive currents if voltage is below v1 or above v2

• Time delay between voltage is back to range [v1, v2] and recovery starts

• Ramp rate limit of active current during recovery• Control of reactive current during recovery• Priority between active and reactive current during

recovery

MC Modeling Capability of Generic RE Models

• Recommendation was to use reec_a model to simulate momentary cessationMeet most of the modeling requirements by carefully

setting up VDL1 and VDL2 blocks, voltage_dip and thld2

Does not simulate the reactive current recovery delay

Conversion of existing reec_b model to reec_a is a challenge

User-Written Model to Simulate MC

• Replaced in-run epcl with the user-written model for better control of model execution sequence, i.e. when the epcl is executed at each time step of integral.

• Interact with reec, pv1e and wt4e models to simulate zero current injection during cessation and recovery delay At the moment Vt_filt < V1 or Vt_filt > V2, set Imax = 0 At the moment V1 <= Vt_filt <= V2, start and recovery

delay timer. When the recovery delay timer has expired and voltage is still

within normal range, Imax is restored to the value in the dynamic model.

User-Written Model to Simulate MC (Cont.)

• Freeze state variables in reec models during recovery delay. During recovery delay, Iqmax and Iqmin are 0

to achieve zero current injection. S2 and s3 are winding up, which causes numerical distortion when the delay is over. Set all control gains to 0 to prevent this.

User-Written Model to Simulate MC (Cont.)

• Include a lock-out mechanism in the user-written model. After a certain number of successive MCs, the inverters are

tripped.

• The user-written model is invoked in the dyd file:

epcmod 10000 "12ST TAP" 46.00 "1 " : #9 "blockinv_epcmod.p" 8 "vblk" 0 "delay" 0 "rrpwr" 0 "lockout" 0

Output of the MC Model

• Report MC events

TIMEMODEL

TYPE BUS NOBUS

NAME ID EVENT EVENT DETAIL V

0.52917 reec_b xxxxx xxx 1 entering block state voltage outside of range 0.9-2 0.897255

0.570838 reec_b xxxxx xxx 1 entering delay state delay timer is 1 seconds 0.907237

1.570851 reec_b xxxxx xxx 1entering recovery state

unit will fully recover in 1.111111 seconds 1.036536

2.683346 reec_b xxxxx xxx 1entering normal state voltage inside of range 0.9-2 1.010558

BUS NO BUS NAME ID MC COUNTxxxxx xxx 1 1

Simulation Results – Pg of Solar PV

High Voltage ContextNERC Inverter-Based Resource Performance Task Force

Matthew Richwine

Dustin Howard

Min Lwin

Jason MacDowell

GE Energy Consulting

Schenectady, NY USA

Austin, TX

January 23-25, 2018

High Voltages - Classification

• For the sake of discussion, it’s separated into two groups:

• Fast Switching Transients

• “Spikes” lasting less than 1 cycle of the fundamental

• Typical of switching events

• Temporary Over-Voltages (TOV)

• Brief periods of high voltage lasting longer than 1 cycle to

~seconds

• Typical of fault-clearing

Fast Switching Transients

• Relevant factors in such events:

• Capacitors (both series and shunt)

• Point-on-wave timing

• Transformer saturation, capacitive coupling

• Grounding and transformer connection groups

• Often, there are many (typically damped) electrical resonances in

a system

• These resonances may be excited by switching events, causing

significant distortion in the voltage waveforms

• Control actions are not intended to operate in these time frames

• Equipment protection functions should be designed to ride

through these

Temporary Over-Voltages

• On fault recovery, voltage may overshoot for many cycles

• Degree and duration of overshoot is related to

• System characteristics – system strength (SCR after clearing),

X/R ratio, effective grounding (X0/X1, R1/X1)

• Equipment control actions

• Exacerbated by shunt capacitance, relative to equipment size

• Exacerbated by transformer saturation

Example Simulation – Line-Line Fault

~ Zeq GZcoll

System Equivalent

L-L Fault

Series CapStation Xfmr

Collector

Unit XfmrPlant

High Voltage Bus Voltages

Medium Voltage Bus Voltages

Time (50ms / division)Fault Onset

Fault Cleared

Example Simulation – Capacitor Switching

~ Zeq GZcoll

System Equivalent

Shunt Cap Station XfmrCollector

Unit XfmrPlant

High Voltage Bus Voltages

Medium Voltage Bus Voltages

Time (50ms / division)Cap switched in

(worst case point-on-wave)

Aspects of a specification

• Phase-phase, phase-ground, positive sequence voltages?

• Minimum or maximum of these?

• Duration?

• Applicable bus?

Conclusions

• Faults and switching events can excite existing resonances in the

system, which may produce significant voltage waveform

distortion and brief voltage spikes

➢May be mitigated through arrestors and plant design

• High voltages lasting many cycles to seconds often upon fault

clearing

➢May be mitigated through controls and plant design

Equipment protection functions must be designed to account for

fast switching transients and TOV to achieve selectivity and security

Questions?

Matt RichwineGE Energy ConsultingMatthew.Richwine@ge.com

Grounding and System Overvoltages

Effectively grounded vs. isolated systems

Voltage within reasonably safe range

when system is effectively grounded

System is effectively

grounded when 0<[X0/X1]<3

O U R M I S S I O N

Accelerate the world’s transition to sustainable energy

Location

Hornsdale, South Australia

Project Size100 MW | 129 MWh

Distributed Energy Resource

ApplicationsEnergy Arbitrage

Frequency Regulation

Contingency Reserves

CommissionedDecember 2017

1 . S O U T H A U S T R A L I A G R I D - S C A L E S T O R A G E

A ) O V E R V I E W

1 . G R I D - S C A L E S T O R A G E

B ) P S S / E A N D P S C A D A N A L Y S E S

• Tesla has developed detailed user-defined models that are a direct replica of the firmware running on the inverter and site controller

• The models have been validated against lab test results and actual site measurements

• Transmission level analyses studied for South Australia:

• PCC voltage control response time and setpoint change command tests

• Short duration, long duration, shallow, and deep single-phase, double-phase, and three-phase to ground fault ride

through for faults at the PCC and other grid buses

• Active and reactive power reference change

• Operation under different grid’s rate of change of frequency events

• Operation under weak grid conditions

• Multiple successive faults ride though

C ) R E S P O N S E T O F R E Q U E N C Y E V E N T S

D ) R E S P O N S E T O F R E Q U E N C Y E V E N T S

Source: http://reneweconomy.com.au

October 9 2017 Canyon 2 Solar Loss Disturbance

Rich BauerIRPTF updateJanuary 23, 2018

RELIABILITY | ACCOUNTABILITY2

220 kV line to line fault voltages

500 kV line to line fault voltages

WI frequency after 2nd fault

Solar PV Response during Canyon 2 Fire

• October 9, 2017 Canyon 2 Fire Smoke induced 2 transmission phase to phase faultso 220 kV line fault at 12:12:16 – normal clearing time ~3 cycleso 500 kV line fault at 12:14:30 – normal clearing time ~2.5 cycles

~682 MW solar reduction on first faulto No frequency tripping observedo ~773 MW Momentary Cessationo ~133 MW voltage tripping

~937 MW solar reduction on second faulto No frequency tripping observedo ~652 MW Momentary Cessationo ~400 MW voltage tripping

• No erroneous frequency tripping• Continued use of Momentary Cessation• Ramp rates on return from Momentary Cessation• Voltage tripping based on PRC-024 ride-through curve• Tripping on voltage transients• Voltage signal used for voltage protection measurement is

unfiltered• Recommend Alert 2…

Key Findings

• Phase Lock Loop Synchronization Issues• DC Reverse Current Tripping• Transient Interactions and Ride-Through Considerations

Key Findings

Various facilities output response

Take this out

Time [ms]

1.6 3.0 16.66 200.0

IEEE P1547 Transient Overvoltage LimitsFundamental Frequency Overvoltage Ride ThroughTransient Overvoltage Ride ThroughMomentary cessation is allowed in this region, and actually preferredRide-through under these conditions allows for momentary cessationRide-through under these conditions does not allow momentary cessationRide-through under these conditions does not allow momentary cessation

t of N

No Trip Zone

May Trip Zone*

Technical PointsRed Curve (Instantaneous) Blue Curve (RMS)

• Represents sub-cycle timeframe (not intended to be captured by PRC-024-2) less than 16.66 ms

• Clarifications• Inverse-time characteristic• Momentary cessation only allowed for very short,

high magnitude transient V• Protects IGBTs

• Inverter manufacturers have stated that 1.3-1.4 pu for less than 1 cycle is reasonable ride-through requirement

• Recent disturbances have shown 1.5-1.6 pu for 1/10th of a cycle (< 3 ms) – need to be able to ride through these types of fault voltages

• Peak/crest V above 1.7 pu for > 3 ms doesn’t seem all that feasible for sinusoidal AC voltage waveform…

• Mirrors PRC-024-2 after 16.66 ms• Clarifications

• Fundamental frequency voltage• Should be well filtered

• Inherently requires some period over the AC waveform

• Should be RMS quantity, not instantaneous

IRPTF Stability StudiesWestern Interconnection Resource Loss Protection CriteriaNERC IRPTF Update to NERC RS

NERC RS/IRPTF MeetingJanuary 2018

• The Blue Cut Fire Disturbance Report Recommendation 2ci states: “…Once a more detailed quantification of potential impact has been

determined, including the amount of momentary cessation and/or tripping as well as the inverter-based resources’ return from these conditions, the NERC Resources Subcommittee should consider whether any adjustments to the resource loss protection criteria are needed to protect interconnection frequency stability.”

• The NERC Resources Subcommittee (RS) requested the NERC Inverter-Based Resource Performance Task Force (IRPTF) investigate these impact via study

Background

• NERC IRPTF created a “Modeling and Studies” sub-group consisting of the following: WECC affected entities – Transmission Planners from throughout WECC

region Simulation and modeling experts Software vendors NERC and WECC staff

Background

Momentary Cessation

• Vmc: voltage threshold where momentary cessation occurs

• Δtsr: delay after voltage recovers before recovery in current injection

• Δtrr: ramp rate of recovery in current injection

• The IRPTF is recommending in its draft Reliability Guideline that momentary cessation…

1. Should not be used for future resources (resources should continue injecting current during ride-through events)

2. Should be mitigated, or minimized to the greatest extent possible, for existing resources

To Be Clear on Momentary Cessation…

PV Active Power Response

• Current generic models used in planning cases do not accurately represent all aspects of momentary cessation IRPTF developing recommendations and action plan to address this Some “modification” to off-the-shelf models required to perform this

assessment

• Modeling approach taken: Leave all as-provided models as-is to greatest extent possibleo These models do accurately represent the other aspects of the resources well

Develop user-defined model that “hooks into” these models and controls only the momentary cessation aspectso Rest of the model still in full control

• User-defined model controls commanded Ip and Iq by controlling specific parameter values only when MC occurs

Modeling Momentary Cessation

“Default” Momentary Cessation Settings

• Minimum load level case – ~85,000 MW Based on WECC historical data and planner input

• Transfers within known operating limits• All wind dispatched at 60-65% output• Solar dispatched at 95% output• Resource mix ~14.4 GW wind ~13.7 GW solar ~59.7 GW synchronous

Powerflow Setup

• For the purposes of these studies… Spinning Reserve: the amount of “unloaded generation that is

synchronized and ready to serve additional demand” that is modeled in the steady-state powerflow case. This generation may or may not be frequency responsive.

Online Frequency Responsive Reserve: the amount of unloaded generation that is synchronized and to the grid and responsive to changes in frequency. The model uses a baseload flag to disable, or block, governors response for units that are not responsive to frequency.

Online Frequency Responsive Reserve to UFLS: the amount of online frequency responsive reserve that would be deployable prior to reaching underfrequency load shedding (UFLS).

Online Contingency (Spinning) and Frequency Responsive Reserves

• All areas analyzed very closely

• Areas with higher HR% have must-run reqs

• Interconnection-wide: Spin = 7010 MW Spin % = 8.26% Headroom = 2538 Headroom % = 2.99% Based roughly on BAL-002-

WECC-2o Contingency Reserve > (3%

of Load + 3% of gen)

• FERC asked that the case be set up at absolute minimum demand level and reserve level 85,000 MW demand 3% online frequency responsive reserve

• This case DOES NOT reflect actual system operation and dispatch (under these conditions or other conditions) Entities expressed that the modeled reserve levels to not reflect historical

minimum reserve levels

• Therefore, IRPTF is calling this case “minimum requirements” case and not “expected minimum” case

Notes on Case and Reserves

• Dynamics data files as-provided• User-defined model added for momentary cessation• Composite load model included• UFLS relays disabled• Contingencies 2 Palo Verde 2 Diablo Canyon 3-Phase Normally Cleared Critical Contingencies

Dynamics Setup

“Critical Contingencies”

• Initial screening - each area with wind/PV penetration

• Key BPS substations that can trigger large momentary cessation

• Potential impacts upwards of 12,000 MW momentary cessation NOT tripping

Problem Statement: • Identify if the impacts of momentary cessation result in a more

severe frequency excursion than the Resource Loss Protection Criteria (RLPC) for the Western Interconnection.

• IRPTF to recommend to the RS, based on simulation results, whether any potential changes may need to be made

Reiterate problem statement

Benchmark Case2 Palo Verde + RAS

NOTES: • Due to min reserves, 2PV contingency

falls below UFLS (59.5 Hz)• Regardless, this is “benchmark” for all

momentary cessation simulations• No momentary cessation in 2PV

contingency

Sanity Check with 2 Diablo Canyon Comparison

NOTES: • No momentary cessation

with 2DC contingency• 2PV more severe than 2DC

“Default” Momentary Cessation Settings Results

0 2 4 6 8 10 12 14 16 18 20

Time [s]

NOTES: • With Delay = 0, all

simulation results stable• All frequency nadir

higher than 2PV• No need to change RLPC

0 2 4 6 8 10 12 14 16 18 202000

14000SOIP

0 2 4 6 8 10 12 14 16 18 20

Time [s]

60.1Fr

z]FMED

NOTES: • With Delay = 0.5s, all

stable cases have freqnadir higher than 2PV benchmark case

• Two cases unstable

0 2 4 6 8 10 12 14 16 18 202000

14000SOIP

• Frequency stability problem = system-wide energy loss issue Inability of system to dynamically balance gen and load sufficiently Declining frequency to the point of instability

• Transient stability problem = Δδ, Δω, ΔP issue Locational changes in power flow and angles Power swings and inter-area angular separation

Instability Drivers

0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7

Time [s]

Sensitivity StudiesUnderstanding Instability

NOTES: • Reduction of MW results in lower

frequency nadir – frequency stability issue

Settings sensitivity for MC ≠ 0.9

Sensitivity StudiesUnderstanding Instability

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

14000SOIP

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Time [s]

NOTES: • Initial drop of Solar P significantly larger• Unstable cases lose stability before

frequency declines – transient stability

Settings sensitivity for MC = 0.9

• Momentary cessation should not be used by inverter-based generating resources moving forward Use of momentary cessation should be eliminated for future resources Use of momentary cessation should be mitigated to the greatest extent

possible for existing resources

• Under current penetration levels, momentary cessation not expected to cause a frequency excursion more severe than the 2 Palo Verde RLPC in the Western Interconnection

Draft Findings and Recommendations

• Identified instability for “conservative expected” momentary cessation settings for certain contingencies – transient stability issue rather than lack of primary frequency response IRPTF still exploring simulated solutions – e.g., redispatch, increasing

spinning reserves in the South, operating limits, etc. These issues do not appear to be a BAL-003 issue – other related BAL

standards and potentially rethink other standards (TOP/FAC/etc.)

Draft Findings and Recommendations

• AC Machine : Power :: Inverter : Current We refer to response of inverter-based resources in terms of their current

injection

• While P is the focus of frequency response and stability, I is the focus on inverter controls Power is simply V*I

Current Control

IRPTF-Simulation Update - nerc.com Resource Performance... · Modeling Objectives ... fast...

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