2/23/26 Advanced Inverter Functions for Distributed Solar Integration. DOE Sunshot and state wide incentives for distributed solar. 2. Managing voltage fluctuations with smart inverters 3. The need for V to provide ride through and grid support 4. Evolution of IEEE Standard 547 5. On going research into V inverter functions and models Tom McDermott, tem42@pitt.edu ittsburgh IEEE ELS Chapter February 23, 26 Sponsors: State Net Metering olicies put the focus on distributed resources rather than transmission connected plants. 2/23/26 gh ELS: Advanced Inverter Functions 2 gh ELS: Advanced Inverter Functions
2/23/26 Net metering tiers can distort the interconnection; a 3 MW generator becomes three MW generators. Source: Neil LaBrake, Jr., National Grid 2/23/26 gh ELS: Advanced Inverter Functions 3 2/23/26 gh ELS: Advanced Inverter Functions 4 gh ELS: Advanced Inverter Functions 2
2/23/26 V Angle Effects may enhance (or degrade) the economics of a V interconnection. Best elevation depends on latitude and season Best azimuth depends on time of day 2/23/26 gh ELS: Advanced Inverter Functions 5 The inverter optimally matches the photovoltaic DC output voltage to the AC load via Maximum ower oint Tracking. 24 2 Ipv [Amps] 6 2 8 4 % 8% 6% 4% 2% 2 3 4 5 6 Vpv [Volts] 2/23/26 gh ELS: Advanced Inverter Functions 6 gh ELS: Advanced Inverter Functions 3
2/23/26 There are three main concerns with integrating VG on distribution systems.. Voltage Fluctuations a) Inverters can operate at fixed power factor 2. Fault Currents and Overvoltages a) Inverters contribute only. 2. times rated b) Inverters shut down quickly upon open circuit or short circuit conditions 3. Unintended Islanding a) Utility interactive inverters have built in antiislanding detection schemes to operate in 2 s 2/23/26 gh ELS: Advanced Inverter Functions 7 Sandia, NREL and ERI have promoted updates to the 5% screening criteria for no study V interconnects. Anti Islanding Screen DG > 2/3 of Min Load? No No Study Yes No Match within %? No Yes Synch Gen > 25% of DG? No roduct > 2/3 of DG? Yes Yes Detailed Study Coddington et. al.: Updating Interconnection Screens for V System Integration 2/23/26 gh ELS: Advanced Inverter Functions 8 gh ELS: Advanced Inverter Functions 4
2/23/26 Optimal (fixed) power factor dispatch alleviates voltage fluctuations, until vendors implement IEEE 547a Estimated % Voltage Change: V ( R jx )( j ) drop 2 n n U n dv U n 2 2 ( Re Vdrop ) (Im Vdrop ) (R, X in ohms, S n in MVA, U n in kv) 2/23/26 gh ELS: Advanced Inverter Functions 9 Basic Distribution Software Tasks have been limited to load flow and short circuit analyses. Current Flow and Voltage Drop Conductor Overload? Voltage Range? Overcurrent rotective Device Coordination R S Detected? R Trip First? Fuse Saving? 2/23/26 gh ELS: Advanced Inverter Functions gh ELS: Advanced Inverter Functions 5
2/23/26 uasi static Time Series (STS) Simulation addresses load and generation variability. Time stepping through a variable power profile Tap changers are active, with time delays Capacitor controls with time delays Controls remember state at next time But it s not a dynamic simulation: No inertia No numerical integration Simple RMS load flow solution at each time step 8 Aug eak Avg : 2: 4: 6: 8: : 2: 4: 6: 8: 2: 22: : [Hour of Day] Daily Load Variations) ower Output [kw] 7 6 5 4 3 2 3 6 9 2 5 8 2 24 Time [s] On/Off Status Combustion Turbine rofiles OffOnOff OnOffOn 8 36 54 Time [s] ercent Output 9 8 7 6 5 4 3 2 7 9 3 5 7 9 Hour of Day 4 minute Wind Conventional Generator Daily V (5 kw Unit) 2/23/26 gh ELS: Advanced Inverter Functions Intelligent Volt Var function attempts to hold a constant voltage using percent available VARs. Source: Common Functions for Smart Inverters, v3, ERI 322233, February 24 2/23/26 gh ELS: Advanced Inverter Functions 2 gh ELS: Advanced Inverter Functions 6
2/23/26 ercent available output means the physical slope [VARs/volt] varies. What was the intent? Available VARs implies whatever the DER is capable of providing at the moment, without compromising Watt output. In other words, Watt output takes precedence over VARs in the context of this function. Source: Common Functions for Smart Inverters, v3, ERI 322233, February 24, p. 9 3. 2/23/26 gh ELS: Advanced Inverter Functions 3 Dynamic Reactive Current function provides an eventbased response to changes in voltage. Source: Common Functions for Smart Inverters, v3, ERI 322233, February 24 Tested with a three phase high impedance fault in ERI 32227 2/23/26 gh ELS: Advanced Inverter Functions 4 gh ELS: Advanced Inverter Functions 7
2/23/26 Dynamic Reactive Current function provides reactive power in percent of rating. Source: Common Functions for Smart Inverters, v3, ERI 322233, February 24 2/23/26 gh ELS: Advanced Inverter Functions 5 Dynamic Reactive Current function uses a moving average to define the voltage set point. Source: Common Functions for Smart Inverters, v3, ERI 322233, February 24 2/23/26 gh ELS: Advanced Inverter Functions 6 gh ELS: Advanced Inverter Functions 8
2/23/26 A voltage control test circuit includes both grid voltage and solar output variability..5 Unity ower Factor.95 2 - -2 2/23/26 gh ELS: Advanced Inverter Functions 7 Intelligent Volt VAR mitigates fluctuation, but constrains operation (e.g. voltage reduction requires communication)..5 Unity ower Factor.5 Vreg=., Slope=5.95.95 2-2 - -2-2 2/23/26 gh ELS: Advanced Inverter Functions 8 gh ELS: Advanced Inverter Functions 9
2/23/26 The burden of choosing settings; detailed studies needed; the wrong choice makes things worse. vars (p.u. available) vars (p.u. available) Voltvar Response.5 -.5 -.94.96.98.2.4.6.8. Voltage (p.u.) Voltvar Response.5 -.5 -.94.96.98.2.4.6.8. Voltage (p.u.) Source: Abate, McDermott, Rylander and Smith, Smart Inverter Settings for Improving Distribution Feeder erformance, IEEE ES General Meeting, Denver, CO, July 25. 2/23/26 gh ELS: Advanced Inverter Functions 9 Adaptive Voltage Regulation provides the best of both intelligent volt VAR and dynamic reactive current. S - 2 2 rated out S - 2 2 rated out Vreg V e t 2/23/26 gh ELS: Advanced Inverter Functions 2 gh ELS: Advanced Inverter Functions
2/23/26 Adaptive Voltage Regulation mitigates fast voltage fluctuation while tracking slower grid voltage trends..5 Vreg=., Slope=5.5 Adaptive Vreg, Slope=5 Vreg.95.95 2-2 - -2-2 2/23/26 gh ELS: Advanced Inverter Functions 2 Dynamic Reactive Current performance may be close to Adaptive Voltage Regulation; Slope = 5..5 Adaptive Vreg.5 Dynamic Reactive.95.95 2-2 - -2-2 2/23/26 gh ELS: Advanced Inverter Functions 22 gh ELS: Advanced Inverter Functions
2/23/26 Dynamic Reactive Current and Adaptive Vreg tested with high impedance fault on clear day..5 Unity ower Factor.5 Dynamic Reactive.5 Adaptive Vreg.95.95.95.9.9.9 5 5 5-5 - -5-2 -5 - -5-2 -5 - -5-2 2/23/26 gh ELS: Advanced Inverter Functions 23 Voltage regulation set point and reactive power can be limited, if desired..5. < Vreg <.3.5 limited to 2 kvar Vreg.95 Vreg.95 2-2 - -2-2 2/23/26 gh ELS: Advanced Inverter Functions 24 gh ELS: Advanced Inverter Functions 2
2/23/26 Instead of attempting to regulate the grid voltage, dispatch reactive power (i.e. the bias point is not zero)..5 Supply 4 kvar.5 Absorb 4 kvar Vreg Vreg.95.95 2-2 - -2-2 2/23/26 gh ELS: Advanced Inverter Functions 25 Shorter Vreg time constants don t necessarily work better; the optimal value seems to be 2 seconds..5 Vreg Tau = 2 s Vreg.5 Vreg Tau = 3 s Vreg.95.95 2-2 - -2-2 2/23/26 gh ELS: Advanced Inverter Functions 26 gh ELS: Advanced Inverter Functions 3
2/23/26 Results from an actual feeder with.7 MW of V show that Adaptive Voltage Regulation performs well. 2/23/26 gh ELS: Advanced Inverter Functions 27 Volt Watt function can limit steady state voltage rise, especially with low X/R ratios (Hawaii uses this). Simplified Formula: V R X But do we really want to control V this way, even if has more leverage than? 2/23/26 gh ELS: Advanced Inverter Functions 28 gh ELS: Advanced Inverter Functions 4
2/23/26 A Frequency Watt function can help dampen system frequency swings. is the real power output [pu] pre is the pre disturbance real power output [pu] f is the disturbed system frequency [Hz] db is a single sided deadband (default to. Hz) k is the per unit frequency change corresponding to per unit power output change (defaults to.5) pre f (6 db) 6k 2/23/26 gh ELS: Advanced Inverter Functions 29 Conclusion Adaptive Voltage Regulation should be the default behavior of V inverters. The default settings work well (so far ): Slope = 3 Tau = 2 s.95 Vreg.5 [pu] Without smart grid communications No need for detailed coordination studies No wake up time for inverter s voltage response With smart grid communications Fail safe behavior Dispatch reactive power, just like shunt capacitors Default high frequency roll off as well 2/23/26 gh ELS: Advanced Inverter Functions 3 gh ELS: Advanced Inverter Functions 5
2/23/26 Bulk system planners have been concerned with losing large amounts of DG after a fault. Source: Mahendra atel, JM (shaded region has V < 5%) Source: Nick Miller, GE 2/23/26 gh ELS: Advanced Inverter Functions 3 Loss of DG events have caused problems in the European bulk power system. NERC IVGTF Task 7 Report 2/23/26 gh ELS: Advanced Inverter Functions 32 gh ELS: Advanced Inverter Functions 6
2/23/26 IEEE 547a 24 allows voltage regulation and requires more adjustability in voltage and frequency trip settings. 2/23/26 gh ELS: Advanced Inverter Functions 33 After more than years, IEEE 547 is in a full revision process to more fully address the issues. Before 22: a 5 year Life Cycle (if Reaffirmed ) Since 22: a year Life Cycle 75% Ballot Return and 75% Yes 2/23/26 gh ELS: Advanced Inverter Functions 34 gh ELS: Advanced Inverter Functions 7
2/23/26 An early draft of 547 clause 4.2 opens the door to technology dependent ride through requirements. Voltage (% of base) 5% 4% 3% 2% % % 9% 8% 7% 6% 5% 4% 3% 2% % C D E B %.. Cumulative Time (sec) A Mandatory Overvoltage Trip Clearing Time (default values) Mandatory Undervoltage Trip Clearing Time (Class I default values) Class II Low Voltage Ride through and Clearing Times (triangle markers) 2/23/26 gh ELS: Advanced Inverter Functions 35 One of shall do standards (547. 25) supports UL 74, which defines how single inverters are tested. 2/23/26 gh ELS: Advanced Inverter Functions 36 gh ELS: Advanced Inverter Functions 8
2/23/26 How to strengthen the provisions for intentional islanding (aka micro gridding) with new functions? 2/23/26 IEEE 547.4 2 gh ELS: Advanced Inverter Functions 37 What islanding detection methods will be reliable in multi inverter and high penetration scenarios? Xu et. al.: A ower Line Signaling Based Technique for Anti Islanding rotection of Distributed Generators art I: Scheme and Analysis Wang et. al.: A ower Line Signaling Based Scheme for Anti Islanding rotection of Distributed Generators art II: Field Test Results 2/23/26 gh ELS: Advanced Inverter Functions 38 gh ELS: Advanced Inverter Functions 9
2/23/26 itt and Duquesne Light are monitoring V output variability at multiple sites, on a second time scale. 295 June 7-8, 24 Volts RMS 29 285 : 6: 2: 8: : 6: 2: Time of Day 25 Amps RMS 2 5 5 : 6: 2: 8: : 6: 2: Time of Day 2 kw @ 6 Hz -2-4 kvar @ 6 Hz -6 : 6: 2: 8: : 6: 2: Time of Day - -5-2 -25 : 6: 2: 8: : 6: 2: Time of Day 2/23/26 gh ELS: Advanced Inverter Functions 39 OpenDSS running on a Web Browser enables engineers at FirstEnergy to simulate voltage fluctuations. GIS Feeder Extract (SL) GIS Data Server Browser (HTML5, Javascript) GIS extract files Model adjustments Simulation settings Web Server Server (Apache or IIS, H) Model Creation (ERL) User Local Machine Simulation results Visualizations Model export Feeder Simulations (OpenDSS) 2/23/26 gh ELS: Advanced Inverter Functions 4 gh ELS: Advanced Inverter Functions 2
2/23/26 The user can extract and analyze OpenDSS feeder models from the Geographic Information System. 2/23/26 gh ELS: Advanced Inverter Functions 4 Symmetrical components can work with V inverter sources, but results may be pessimistic? Z S ZT 2 Z L 2 Z L ZT 2 2Z Y B m 2Z Y 3Z N ZTH Z S ZT 2 Z L 2 Z L ZT 2 ZTH I X V.5pu S Z S Z T 2Z Y Bm 2Z I Y Y 2 Z L 2 Z L ZT 2 V DG Z NORT I DG.pu 2Z Y B m 2 2Z Y ZTH 2 I I I F F F 2 2/23/26 gh ELS: Advanced Inverter Functions 42 gh ELS: Advanced Inverter Functions 2
2/23/26 Detailed V transient models present issues with software licenses, proprietary data & learning curves. 4 SLGF TOV, 3 KVA Grounding,.6s Delay Vpcc [pu] 2.5.55.6.65.7.75.8.85.9.95 Ipcc [pu] 5 5.5.55.6.65.7.75.8.85.9.95 Ifdr [pu] 5.5.55.6.65.7.75.8.85.9.95 Simplified for OpenDSS Frequency [Hz] Spcc [pu] 64 62 6 58.5.55.6.65.7.75.8.85.9.95 2 -.5.55.6.65.7.75.8.85.9.95 Time [s] 2/23/26 gh ELS: Advanced Inverter Functions 43 Inverter open circuit and short circuit behavior testing to identify models for application studies. DC Output DC Input phs AC phs AC AC Output GND L3 L2 L 3phs AC phs AC phs AC N 2/23/26 gh ELS: Advanced Inverter Functions 44 gh ELS: Advanced Inverter Functions 22
2/23/26 Creating a better V inverter model for OpenDSS, using system identification. Hammerstein Weiner Modeling Framework iecewise Linear function representing input nonlinearity iecewise Linear function representing input nonlinearity Step Response of Linear Block iecewise Linear Function representing output nonlinearity 2/23/26 gh ELS: Advanced Inverter Functions 45 45 What can you do? The next 547 meeting will be in Juno Beach, FL, March 8 9. We need consistent participation! http://grouper.ieee.org/groups/scc2/ 2/23/26 gh ELS: Advanced Inverter Functions 46 gh ELS: Advanced Inverter Functions 23