Re Reso sour urce ces s with with & & with withou - - PowerPoint PPT Presentation

Managed by UT-Battelle for the Department of Energy

Impac Impacts ts of Var

• f Varying

ying Pen Penet etra ration tion of Distr

• f Distribut

ibuted ed Re Reso sour urce ces s with with & & with withou

• ut

t Vo Volt/Va lt/Var r Co Cont ntro rol: l: Cas Case e Stu Study dy of Var

• f Varying

ying Lo Load ad Typ Types es

• D. Tom Rizy1, Senior Member,

Huijuan Li2, Member, Fangxing Li1,3, Senior Member, Yan Xu1, Member, Sarina Adhikari3, Student Member, Phil Irminger2, Student Member 2011 IEEE PESGM July 26, 2011

1ORNL, Power & Energy Systems Group 2Oak Ridge Associated Universities 3University of Tennessee, Knoxville

2 Managed by UT-Battelle for the Department of Energy

Background

 Follow-up to 2010 paper “Properly Understanding the Impacts of Distributed Resources (DR) on Distribution Systems”  Addresses how DR impacts vary in regards to both DR voltage regulation capability and load mix  Focuses on impacts to distribution capacity, losses and voltage regulation with DR penetration  Comparison of DR with and without volt/var control

• n 10MVA feeder example with two DRs

 Inverter-based volt/var controls based on ORNL R&D work at the DECC Lab.

3 Managed by UT-Battelle for the Department of Energy

Impacts Of Distributed Resources (DR) On Distribution System

The connection of DR systems to the distribution system will have an impact on  Feeder Capacity  Line Losses  Voltage Regulation  System Protection  Safety A steady-state analysis of DR impacts may not be adequate for addressing the full impacts of DR in a distribution system.

4 Managed by UT-Battelle for the Department of Energy

Dynamic versus Steady-State Analysis

• f DR Impacts

 Standard approach is to use a power-flow-based program to calculate the network voltages with different DR sizes, penetration and feeder loadings.  Used to be quite difficult to dynamically model a small system not to mention a large distribution system.  However, new tools such as EMTP-RV make the modeling of large systems possible along with their dynamic behavior.

5 Managed by UT-Battelle for the Department of Energy

Issues that Merit Consideration for DR Impact Assessment

 Voltage Sensitivity of the Feeder Loads

• Impacts on feeder capacity, losses and voltage regulation

depend on feeder load voltage sensitivity.

• To what degree?
• Load mix and distribution for each phase may be important.

 Variable Distributed Resource (DR) Output

• Concern with the variability of renewable DR (i.e., wind and

PV) that does not have an energy storage component.

• May not be a concern with penetration level lower than 10%
• Penetration level of 20% or greater, intermittent DR may

quickly change the feeder voltage profile.

6 Managed by UT-Battelle for the Department of Energy

Issues that Merit Consideration for a DR Impacts Assessment (cont.)

 Representation of Multiple DR

• A big question is a usable and accurate aggregation model.

 Protection Changes with DR

• Not expected to be an impact at low DR penetration (i.e. 10% or

less)

• Becomes a concern at higher DR penetration especially if the

DR type is a generator-based system.

• Inverter-based DRs are inherently current limited; but may need

new modeling and protection methods for high penetration.

 DR with Reactive Power Capability

• DRs not allowed (i.e., per 1547) to regulate voltage on the

distribution system unless authorized by the utility.

• Being amended by both IEEE Standards (1547.8) and NIST

(P2030).

7 Managed by UT-Battelle for the Department of Energy

Advantages of Allowing DR to Provide Volt/Var Control

 Provides reactive power locally instead of delivery over transmission lines from central power plants.  Provides reactive power needed to maintain a steady voltage profile at the load.  Respond to voltage transients (i.e., motor starts or load step changes) to maintain voltage.  Improves feeder capacity by reducing reactive current flow from substation to load.  Reduces line losses along with line flows due to local reactive power injection for voltage regulation.

8 Managed by UT-Battelle for the Department of Energy

Impacts Study Approach

 DR with and without voltage regulation capability

• No regulation – only active power injection from DR
• Regulation – both active and reactive power injection (to

maintain voltage reference)

 Distribution feeder impacts with increasing DR levels

• Total line flow (used capacity)
• Line losses
• Voltage profile

 Repeated for different feeder load compositions

• Constant Power – served as the benchmark
• Constant Impedance
• Constant Current
• ZIP – equal combination of the previous ones

9 Managed by UT-Battelle for the Department of Energy

Example Used to Evaluate DR Impacts on Distribution System

 Inverter-based DR controls1 used to compare impacts of DR with and without voltage regulation capability.  DR penetration level (% of total DR output to feeder capacity) varied to analyze impacts.  Repeated for the four different loading cases.

1Developed and tested by ORNL

Substation bus

1 3 2 4

INVERTER I CONTRO LLER

DE INVERTER CONTROLLER

6 5

INVERTER I CONTRO LLER

DE INVERTER CONTROLLER

DR1 DR2

10MVA Feeder Total Load: 5.1MW, 3.7MVar, 0.8pf

10 Managed by UT-Battelle for the Department of Energy

Inverter-Based DR Voltage Control

Power System (Controlled System)

Voltage Reference

Controller Compare Error

Voltage (Controlled Variable)

Measure vc

DR: Distributed Energy Resource Control variable: the PCC voltage Reference: the desired value of the PCC voltage Error: difference between reference and measured PCC voltage  Fixed control: PI control with Kp and Ki fixed Kp and Ki typically by trial & error Incorrect gains result in under- performance, oscillation, or instability  Adaptive control: Kp and Ki values are initially conservative but adjusted in real- time to achieve desired system response time Voltage stability is ensured

Load Controller

ic vdc

switching signals

vt (PCC) is il Lc ic vc is vt vdc il Ls Rs vs

DE

DR

11 Managed by UT-Battelle for the Department of Energy

DECC Lab interfaced with Actual Distribution System Supports Volt/Var Control Development and Testing.

DECC Lab

12 Managed by UT-Battelle for the Department of Energy

Voltage Regulation with both Fixed and Adaptive Gain Control

(b) Voltage regulation with fixed gains. (a) No voltage regulation. (c) Voltage regulation with adaptive gains.

 Response to two- volt (2V) local voltage transient.  Tested on ORNL distribution system at DECC Lab.  Faster voltage regulation achieved with adaptive gains.

The voltage scales are different since under different distribution system operating conditions on different days.

13 Managed by UT-Battelle for the Department of Energy

0% 5% 10% 15% 20% 25% 30% 35% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55%

% Output by Each DR Total DR Penetration Level (%)

DR1 % DR 2 %

Study Assumptions

 10MW Radial Feeder with 63% used capacity  DR penetration from 5% to 55% in 5% increments  Feeder load is fixed for each loading case  DRs provide -1.5MVAr to 1.5MVAr to regulate voltage

• 0.980pu for DR at bus 4
• 0.975pu for DR at bus 6

 Capacitors both at substation and on circuit assumed to be fixed  DR active power scaled up instead of adding more DRs

14 Managed by UT-Battelle for the Department of Energy

Voltage Feeder Profiles for the Constant Power Load Case

 Voltage profiles with increasing DR without voltage regulation  Voltage profiles with increasing DR with voltage regulation

0.960 0.965 0.970 0.975 0.980 0.985 0.990 0.995 1.000 1.005 Bus 1 Bus 2 Bus 3 Bus 4 Bus 5 Bus 6

Voltage (per unit) Substation to End of Feeder

0% 5% 10% 20% 25% 30% 35% 40% 45% 50% 55%

DR Penetration Levels 0.960 0.965 0.970 0.975 0.980 0.985 0.990 0.995 1.000 1.005 Bus 1 Bus 2 Bus 3 Bus 4 Bus 5 Bus 6

Voltage (per unit) Substation to End of Feeder

0% 5% 10% 20% 25% 30% 35% 40% 45% 50% 55%

DR Penetration Levels

Direction of Increasing DR Penetration

15 Managed by UT-Battelle for the Department of Energy

DR Impacts on Distribution Losses for Constant Power load

 Active power losses with and without DR voltage regulation  Reactive power losses with and without DR voltage regulation

40 50 60 70 80 90 100 110 120 130 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60%

Active Power Losses (kW) DR Penetration Level (%)

No Regulation Regulation

40 50 60 70 80 90 100 110 120 130 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60%

Reactive Power Losses (kVAr) DR Penetration Level (%)

No Regulation Regulation

Dashed line shows where DR with voltage regulation compared to DR without voltage regulation no longer provides benefit. Losses increase.

16 Managed by UT-Battelle for the Department of Energy

DR Output with Voltage Regulation for the Load Cases

 DR active/reactive power with increasing penetration  DR power factor with increasing penetration

0.0 0.5 1.0 1.5 2.0 2.5 3.0

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5 2.0 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60%

Active Power Output (MW) Reactive Power Output (MVar) DR Penetration Level (%)

Q_CP - VR Q_CI - VR Q_CZ - VR Q_ZIP - VR P_ALL

Injecting Reactive Power Absorbing Reactive Power

0.0 0.2 0.4 0.6 0.8 1.0 1.2 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60%

DR Power Factor DR Penetration Level (%)

CP_pf CI_pf CZ_pf ZIP_pf Injecting Reactive Power Absorbing Reactive Power

Dashed line shows where DR with voltage regulation absorbs reactive power instead of injecting reactive power.

17 Managed by UT-Battelle for the Department of Energy

2.0 2.5 3.0 3.5 4.0 4.5 5.0 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60%

Reactive Power Line Flow (MVar) DR Penetration Level (%)

CP - No VR CP - VR CI - No VR CI - VR CZ - No VR CZ - VR ZIP - No VR ZIP -VR

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60%

Active Power Flow (MW) DR Penetration Level (%)

CP - No VR CP - VR CI - No VR CI - VR CZ - No VR CZ - VR ZIP - No VR ZIP -VR

DR Impacts on Distribution Power Flow for the Load Cases

 Active power flow with and without DR voltage regulation  Reactive power flow with and without DR voltage regulation

Dashed line shows where DR with voltage regulation compared to without voltage regulation no longer provides benefit. Reactive load increases.

VR No VR

18 Managed by UT-Battelle for the Department of Energy

Voltage Profiles for the Four Different Load Cases

5% DR Penetration 35% DR Penetration 20% DR Penetration 55% DR Penetration

VR No VR VR No VR VR No VR VR No VR

19 Managed by UT-Battelle for the Department of Energy

Results

 Observed slight differences in distribution impacts for the four load cases.  Most difference was in losses - maximum variation of 8.3% between load cases.  Maximum variation of 6.0% for line flows between load cases.  Similar voltage responses for the four load cases.  Reach a point of diminishing return using high penetration DR to provide local voltage regulation.

20 Managed by UT-Battelle for the Department of Energy

Results (cont.)

 At 35% or greater DR penetration:

• Active power from DR causes mode change.
• DR voltage regulation mode reverses from

injecting to absorbing reactive power.

• DR becomes additional reactive load.

 Penetration trigger point could be higher if voltage references are allowed to be higher.  However at 30%, reactive power losses increase above no regulation case.  Analysis is based on our specific example and on fixed DR voltage references.

21 Managed by UT-Battelle for the Department of Energy

Summary

 A number of distribution system impacts merit consideration for DR interconnection (i.e., losses, feeder capacity, voltage regulation, protection and safety).  If some DRs can provide reactive power in addition to active power, they can provide voltage regulation and support.  If voltage regulation is dynamic, DRs can respond to a voltage transient in 0.5 or less and be transparent to system voltage controls.  Local voltage regulation done correctly can lower feeder line flows and losses and increase capacity.  Standards are being developed to determine when DR volt/var control is appropriate.

22 Managed by UT-Battelle for the Department of Energy

Possible Future Considerations

 Impacts as loading and distribution is varied (rather than fixed) with high DR penetration.  Impacts of intermittent DR (i.e., PV) penetration.  Impacts of air-conditioning stall and DR impacts together.  Impacts of multiple inverter-based DR control to address possible interaction.  More complex distribution network.

Managed by UT-Battelle for the Department of Energy

Q&A

24 Managed by UT-Battelle for the Department of Energy

OAK RIDGE NATIONAL LABORATORY

Managed By UT-Battelle for the Department of Energy

• D. Tom Rizy, Research Staff

Power & Energy Systems Group Energy & Transportation Science Division One Bethel Valley Road, MS-6070 Oak Ridge, Tennessee 37831-6070 (865) 574-5203 Voice, 575-7643 Fax (865) 207-6769 Cell Email: rizydt@ornl.gov www.ornl.gov, www.ornl.gov/sci/decc