Presentation from the EPRI-Sandia Symposium on Secure and Resilient Microgrids: Practical Implementation of Microgrid Control, Protection, and Communications, presented by Scott Manson, SEL, Baltimore, MD, August 29-31, 2016.

1. Practical Implementation
of Microgrid Control,
Protection, and
Communications
Scott Manson
Technology Director, SEL

2. Control Cost, Quality, Features
Hardware-in-the-Loop Testing
Both Mechanical and Electrical Systems
Must Be Modeled Accurately!
Controller
Inputs
Controller
Status
Controls
Dynamic
Simulation
System
Outputs
0.96
1.0
Power
(pu)
Frequency
(pu)
1.0
Steady-State
Droop Line
3
2
1
Transient Governor
Behavior
Governor Frequency
Set Point

3. Factory Acceptance Tests Improved With
Hardware-in-the-Loop Testing
66
65
64
63
62
61
60
59
0 10 20 30 40
Time (s)
Frequency(Hz)
Field
Simulation

4. Inverter-Based Generation Has Limited
Overload Capacity
Short-Term
Capacity Limit
Long-Term
Capacity Limit
Inverter-Based
Generation
Q
P
Rotating Generators
Q
P

5. Load Balancing Must Happen Faster
With Inverter-Based GenerationPower,Frequency
Time
Rotating Generation Power
Rotating Generator Frequency
Power
Frequency
Load
Inverter-Based Power
Inverter-Based Frequency

6. FAST Load Shedding Prevents
Blackouts
Grid-Tied
Operation
Islanded
Operation
Synchronization
Systems
Automatic
Decoupling
Load
Shedding
Subcycle
FAST
Controller
Relay
Status Trip

7. PF Deadband
–PF
+PF
–P +P
–PF
+PF
+Q
–Q
Enlargement of Origin
–100 +100
–50
+50
Deadband
Control
Boundary
+28.9
PFsp1, sp2
PFactual1
PFactual1
+0.5PF
–0.5PF+0.5PF
–0.5PF
Power Factor
Control Limits
Must Be
Considered
Carefully!

8. Frequency and Voltage Define
Power System Resilience
1/f
t
f
V
V
2V
63
57
Rotating
Generator
Sets
1.3 0.7
Generation Shedding
Load Shedding
Allowable Operation
65
1.2 0.8
55
Inverter
Technology

9. A
CB2 CB1
57
60
63
f (Hz)
B
Reliability Improved With Several
Load-Balancing Techniques
CB1 Opens:
Contingency
Load Shedding Island
Generator
Autobalancing
Aka “AGC”
CB2
Opens
Underfrequency Load Shedding
Overfrequency
Generation Runback

10. How Much “Responsive” Generation Is
Required to Ensure Stability?
Step 1: Identify grid time constants
+
–
–
DER Frequency/
Droop Controller
Steady-State
Electrical Load
Frequency
+ –
Simplification
Frequency
1
JS
1
R
2
R
1 S 
DER Frequency/
Droop Controller
Power System 2 (seconds)
Utility 0.5 to 1.2
Microgrid 0.25 to 2.5

11. How Much “Responsive” Generation Is
Required to Ensure Stability?
Step 2: Tabulate Incremental Reserve Margins (IRM)
DER Rating (kW) IRM(%) IRM(MW)
PV 200 0 0
Battery (SLOW) 1000 5 50
Battery (FAST) 1000 100 1000
Steam Extraction
Turbine 1200 0 0
CHP 900 10 90
Gas Turbine 1500 40 600
Diesel Genset 1000 40 400
Totals 6800 31.5 2140

12. How Much “Responsive” Generation Is
Required to Ensure Stability?
Step 3: Compare Total IRM to Largest Disturbance
Event kW
Small Motor 200
LCI drive 2000
Large Feeder 5000
Small Feeder 800
Available IRM 2140
50
49.4
49
48
Hz
DERs will trip

13. Macrogrid
Power
Frequency
Microgrid
Power
Frequency
Load
Frequency(Hz)
47
48
49
50
51
52
53
54
55
0 50 100 150 200 250 300
Time (seconds)
Unstable Microgrid
Governor Controls must be Adapted for
Changing load Composition
Load Responses Are Different
for Islanded Microgrids

14. Intelligent Relays Are Used to Adapt
DER Controllers
Turbine
Electric
Generator
Valve
Turbine
Controller
Microgrid
Macrogrid
Relay
Microgrid
Controller
Relay
Relay
Relay
Relay
Relay
Relay
Relay Relay
Relay
It’s an Island !

15. Protection Must Adapt to Changing
Fault Conditions
 Fault levels
 Grounding
 Directions
 Impedances
DER
t
I
Relay
20,000
20,000
2,000
2,000

16. Fault Current Independent Protection
Schemes Are Preferred
 Line current differential
 Transformer differential
 Bus differential
 Time domain (future)

17. Security for Critical Infrastructure
• Avoid OS and software
• Made in the USA
• Mature Processes
• Vertical Integration
• Cyber Security

18. Conclusions
 Testing reduces installation and maintenance costs
 Fast control systems prevent outages
 Reliable load balancing maintains stability
 Adaptive protection saves lives
 Security in depth is mandatory