2014 PV Distribution System Modeling Workshop: Determining Recommended Settings for Smart Inverters: Jeff Smith, EPRI

1. Jeff Smith, Matt Rylander, Huijuan Li
EPRI
EPRI Smart Inverter Workshop, Santa Clara, CA
5/7/2014
Determining Recommended Settings
for Smart Inverters

2. 2© 2014 Electric Power Research Institute, Inc. All rights reserved.
Overview
Objective Determine recommended settings for field site
demonstration
Evaluate the effectiveness of various smart inverter
functions and settings for improving feeder voltage
performance as load and PV vary over time
Approach Time-series simulations in OpenDSS comparing feeder
performance with and without smart inverter functions
Sites Three different feeders, each with unique characteristics and
overall objectives for use of smart inverters

3. 3© 2014 Electric Power Research Institute, Inc. All rights reserved.
Which Smart Inverter Setting is Most Appropriate for My
Situation?
0 5 10 15 20 25
1.024
1.026
1.028
1.03
1.032
1.034
1.036
1.038
1.04
1.042
1.044
Hour
Voltage(pu) Voltages with different voltvar settings
---- Voltvar
---- No PV
---- PV base
115 unique volt/var control settings

4. 4© 2014 Electric Power Research Institute, Inc. All rights reserved.
Site Characteristics
Site kWdc
(Panel
size)
kWac
(inverter
rating
Short-
circuit
MVA @
POI
X/R @ POI
J1 1900 1700 30-36* 1.8-2.6
E1 605 566 38 1.8
H1 1000 1000 71 1.7
*multiple POI

5. 5© 2014 Electric Power Research Institute, Inc. All rights reserved.
Overall Approach
• Solar variability conditions
– Clear day
– Overcast day
– Highly variable day
• Load variability conditions
– Peak load day
– Minimum load day
• Smart inverter settings
– Volt-var
– Volt-watt
– Off-unity power factor 0
2
4
6
8
10
12
1 3 5 7 9 11 13 15 17 19 21 23 25
Power (MW)
Local Time (Hour)
Offpeak
Peak
Sandia’s variability index (VI) and
clearness index (CI) to classify days
Consideration for Different Feeder Load Profiles

6. 6© 2014 Electric Power Research Institute, Inc. All rights reserved.
Smart Inverter Settings
Power Factor Settings (inductive)
0.99 0.98 0.97 0.96 0.95 0.94 0.93 0.92 0.91 0.9
Sample volt/var curves shown: see Video for complete set of curves
Similar range of curves used for volt/watt control

7. 7© 2014 Electric Power Research Institute, Inc. All rights reserved.
Feeder Model Validation
0.98
0.985
0.99
0.995
1
1.005
1.01
1.015
1.02
0
100
200
300
400
500
600
1
14
27
40
53
66
79
92
105
118
131
144
157
170
183
196
209
222
235
248
261
274
287
300
313
326
339
352
365
378
391
404
417
430
443
456
469
482
495
per‐unit voltage
P (kW)
P (kW)
V_model (pu)
V_measure (pu)
E1
J1 H1
0.98
0.985
0.99
0.995
1
1.005
1.01
1.015
1.02
0
200
400
600
800
1000
1200
1
16
31
46
61
76
91
106
121
136
151
166
181
196
211
226
241
256
271
286
301
316
331
346
361
376
391
406
421
436
451
466
481
496
per‐unit voltage
P (kW)
P (kW)
V_measure (pu)
V_model(pu)
0
50
100
150
200
250
1.02
1.03
1.04
1.05
1.06
1.07
0 50 100 150 200 250 300
PV (kW)
Voltage (Vpu)
Time (sec)
Measured
Simulated
PV (kW)

8. 8© 2014 Electric Power Research Institute, Inc. All rights reserved.
Smart Inverter Model Validation
OpenDSS Simulations
260
265
270
275
280
285
290
295
Voltage (Vln)
Time (s)
Measured
Simulated
‐400
‐300
‐200
‐100
0
100
200
300
400
Reactive Power (kvar)
Time (s)
Measured
Simulated

9. 9© 2014 Electric Power Research Institute, Inc. All rights reserved.
Selecting the “Best” Smart Inverter Settings
• Objectives
– Each feeder analysis has unique set of objectives
– Voltage
– Efficiency
– Control
• Metrics
– Approximately 20 conditions are monitored for each feeder
– Only daylight impact is analyzed
– Mean voltage at the point of common coupling (PCC)
– Voltage variability index at the PCC
– Tap operations
– Losses
• Rank objective impact based on the metrics for each scenario
– Solar
– Load
6 combinations all weighted equally (for now…)

10. 10© 2014 Electric Power Research Institute, Inc. All rights reserved.
Demo Site J1: Objectives & Metrics
Objective Metric Weight
1. Avoid overvoltage
conditions
100
2. Improve customer
efficiency
100
3. Reduce line regulator
tap changes
100
4. Combined 1, 2, and 3 33/33/33

11. 11© 2014 Electric Power Research Institute, Inc. All rights reserved.
Sample Plots
Clear Day Overcast day
Highly variable day
PCCvoltage
hour
PCCvoltage
hour
PCCvoltage
hour
0 5 10 15 20 25 30
1.02
1.025
1.03
1.035
1.04
1.045
1.05
0 5 10 15 20 25 30
1.02
1.025
1.03
1.035
1.04
1.045
1.05
0 5 10 15 20 25 30
1.01
1.02
1.03
1.04
1.05
1.06
1.07

12. 12© 2014 Electric Power Research Institute, Inc. All rights reserved.
Circuit Performance Characterization

13. 13© 2014 Electric Power Research Institute, Inc. All rights reserved.
Volt/Var Results
Demo Site J1
Lesson Learned
“best” settings can
be difficult to identify
1.01
1.015
1.02
1.025
1.03
1.035
1.04
1.045
1.05
1
9
17
25
33
41
49
57
65
73
81
89
97
105
113
Feeder Head Voltage
Max Feeder Head
Voltage (pu)
Min Feeder Head
Voltage (pu)
0
100
200
300
400
500
600
700
800
900
1
7
13
19
25
31
37
43
49
55
61
67
73
79
85
91
97
103
109
115
Reg/LTC Tap Operations
Tap Operations
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
1
8
15
22
29
36
43
50
57
64
71
78
85
92
99
106
113
Cap Operations
Cap Operations
1400
1450
1500
1550
1600
1650
1700
1
9
17
25
33
41
49
57
65
73
81
89
97
105
113
Feeder Losses (kWh)
Feeder Losses (kWh)
0.99
1
1.01
1.02
1.03
1.04
1.05
1.06
1.07
1
9
17
25
33
41
49
57
65
73
81
89
97
105
113
PCC Voltage
Max PCC Voltage (pu)
Min PCC Voltage (pu)
0
2
4
6
8
10
12
14
16
18
1
7
13
19
25
31
37
43
49
55
61
67
73
79
85
91
97
103
109
115
VI at PCC
VI at PCC
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
1.06
1.07
1
8
15
22
29
36
43
50
57
64
71
78
85
92
99
106
113
Feeder End Voltage
Max Feeder End
Voltage (pu)
Min Feeder End
Voltage (pu)
0
1000
2000
3000
4000
5000
6000
7000
1
9
17
25
33
41
49
57
65
73
81
89
97
105
113Time Above ANSI (sec)
Time Above ANSI (sec)
0.9
0.92
0.94
0.96
0.98
1
1.02
1.04
1.06
1.08
1
7
13
19
25
31
37
43
49
55
61
67
73
79
85
91
97
103
109
Overall Feeder Min/Max Voltage
Max Feeder Voltage
(pu)
Min Feeder Voltage
(pu)
Peak load day

14. 14© 2014 Electric Power Research Institute, Inc. All rights reserved.
Demo Site J1
Combined Objective 4 Best Settings
• Objective
– Avoids overvoltage
– Improves efficiency
– Reduces tap operations
• Metrics
– Lower mean voltage
– Flatter voltage profile
– Less tap operations
General trends in rank are due to
rolling through different setting
characteristics
Lesson Learned
Overall best settings
have similar curves

15. 15© 2014 Electric Power Research Institute, Inc. All rights reserved.
Sample Results – Volt/var control
Demo Site J1
‐1.2
‐1
‐0.8
‐0.6
‐0.4
‐0.2
0
0.95 0.97 0.99 1.01 1.03 1.05
% Avail vars
per‐unit voltage
1.01
1.02
1.03
1.04
1.05
1.06
1.07
0 5 10 15 20 25 30
per‐unit voltage
Hour
no_PV
PV base
voltvar
‐100
0
100
200
300
400
500
600
700
800
900
0 5 10 15 20 25 30
tap operations
hour
Tap_noPV
Tap_Pvbase
Tap_voltvar
‐1.5
‐1
‐0.5
0
0.5
1
1.5
0.95 0.97 0.99 1.01 1.03 1.05 1.07 1.09
Negative impact on voltage and line regulator operations
Positive impact on voltage and line regulator operations
1.01
1.02
1.03
1.04
1.05
1.06
1.07
0 5 10 15 20 25 30
per‐unit voltage
hour
no_PV
PV_base
Voltvar
Volt/var curve
Daily voltage profile
Regulator tap operations
Volt/var curve
Daily voltage profile
Regulator tap operations
0
100
200
300
400
500
600
700
800
0 5 10 15 20 25 30
tap operations
Tap_noPV
Tap_Pvbase
Tap_voltvar
Lesson Learned
Slight variation in
settings can yield
significantly
different responses

16. 16© 2014 Electric Power Research Institute, Inc. All rights reserved.
Demo Site J1
Trends in Volt/var Characteristics
Best curves begin absorbing
reactive power at 1.02 Vpu
Best curves have a steep volt-var
slope
Lesson Learned
Initial results
indicate trends can
be seen

17. 17© 2014 Electric Power Research Institute, Inc. All rights reserved.
Demo Site J1
Best Setting Impact for Objective 4
• Each smart inverter function has one “Best” setting
• Totalized metric for each “Best” setting in Objective 4 is
shown
• The Volt-var function and setting has the best impact for
each metric
PV volt/var volt/watt
power
factor
PCC Mean
Voltage (pu)
1.031 1.027 1.031 1.031
PCC VVI 18.88 8.39 15.56 8.41
Tap
Operations
675 418 603 523

18. 18© 2014 Electric Power Research Institute, Inc. All rights reserved.
Metric Improvement Based on Objective
PV volt/var volt/watt
power
factor
PCC Mean Voltage 1.031 1.027 1.031 1.031
PCC VVI 18.88 8.39 15.56 8.41
Tap Operations 675 418 603 523
PCC Mean Voltage 1.031 1.025 1.031 1.031
PCC VVI 18.88 30.21 15.56 14.18
Tap Operations 675 1727 603 485
PCC Mean Voltage 1.031 1.033 1.032 1.031
PCC VVI 18.88 6.02 9.92 8.41
Tap Operations 675 437 533 523
PCC Mean Voltage 1.031 1.034 1.032 1.032
PCC VVI 18.88 6.60 9.92 9.599
Tap Operations 675 401 533 485
Obj 4
Overall
Obj 1
Reduce
Overvoltage
Obj 2
Improve
Efficiency
Obj 3
Reduce
Taps

19. 19© 2014 Electric Power Research Institute, Inc. All rights reserved.
Demo Site J1 Best Curves
• Best volt/var and volt/watt curves
shown for each objective
• Each objective optimized with
different curve characteristics
Objective 1
Objective 2
Objective 3
Objective 4
Best Power Factor Setting
Objective 1 2 3 4
power
factor
0.90 0.97 0.94 0.97

20. 20© 2014 Electric Power Research Institute, Inc. All rights reserved.
Impact of Load Level on Best Settings
Peak Load
Offpeak Load

21. 21© 2014 Electric Power Research Institute, Inc. All rights reserved.
Sample Day – Comparing “Best” Setting
Responses
Offpeak day, highly variable solar
1.02
1.025
1.03
1.035
1.04
1.045
1.05
0 5 10 15 20
per‐unit voltage
hour
PCC Voltage
0
10
20
30
40
50
60
70
80
0 5 10 15 20
#
hour
Tap Operations
Lesson Learned
Power factor and
proper volt/var
settings can be
effective

22. 22© 2014 Electric Power Research Institute, Inc. All rights reserved.
Demo Site E1: Objectives & Metrics
Objective Metric Weight
1. Reduce voltage
flicker/voltage variations
100
2. Reduce losses 100
3. Combined 1 and 2 50/50

23. 23© 2014 Electric Power Research Institute, Inc. All rights reserved.
Sample Plots
0 5 10 15 20 25 30
0.975
0.98
0.985
0.99
0.995
1
1.005
1.01
1.015
0 5 10 15 20 25 30
0.985
0.99
0.995
1
1.005
1.01
1.015
0 5 10 15 20 25 30
0.975
0.98
0.985
0.99
0.995
1
1.005
1.01
1.015
Clear Day Overcast day
Highly variable day
PCCvoltage
hour
PCCvoltage
hour
PCCvoltage
hour

24. 24© 2014 Electric Power Research Institute, Inc. All rights reserved.
Demo Site E1 Best Curves
• 3 best volt/var and volt/watt
curves shown for each objective
• Each objective optimized with
different curve characteristics
Objective 1
Objective 2
Objective 3
Best Power Factor Setting
Objective 1 2 3
power factor 0.92 0.99 0.93

25. 25© 2014 Electric Power Research Institute, Inc. All rights reserved.
Metric Improvement Based on Objective
PV volt/var volt/watt
power
factor
PCC VVI 9.1787 7.4029 8.9498 6.8539
Losses (kWh) 3079 3038 3078 3124
PCC VVI 9.1787 7.0951 8.9498 6.8480
Losses (kWh) 3079 3082 3078 3129
PCC VVI 9.1787 7.4029 8.9498 8.1283
Losses (kWh) 3079 3038 3078 3091
Obj 3
Obj 1
Obj 2
power factor does not reduce losses

26. 26© 2014 Electric Power Research Institute, Inc. All rights reserved.
Demo Site H1: Objectives & Metrics
Objective Metric Weight
1. Flatter voltage and
improved customer
efficiency
50
50
2. Reduced LTC tap
changes
100
3. Combined 1 and 2 25/25/50

27. 27© 2014 Electric Power Research Institute, Inc. All rights reserved.
Demo Site H1: Best Curves
• 1 best volt/var and volt/watt
curves shown for each objective
• Each objective optimized with
different curve characteristics
Best Power Factor Setting
Objective 1 2 3
power factor 0.92 0.96 0.96
Objective 1
Objective 2
Objective 3

28. 28© 2014 Electric Power Research Institute, Inc. All rights reserved.
Metric Improvement Based on Objective
PV volt/var volt/watt
power
factor
PCC Mean Voltage 1.008 1.008 1.008 1.007
PCC VVI 11.5798 10.7196 11.0827 8.0583
Tap Operations 54 53 54 55
PCC Mean Voltage 1.008 1.006 1.008 1.007
PCC VVI 11.5798 11.0533 11.0827 8.0391
Tap Operations 54 57 54 55
PCC Mean Voltage 1.008 1.009 1.008 1.007
PCC VVI 11.5798 9.4340 10.1347 8.0583
Tap Operations 54 50 53 55
Obj 3
Obj 1
Obj 2

29. 29© 2014 Electric Power Research Institute, Inc. All rights reserved.
Summary
• Overall “best” setting depends
upon objective
– Improve voltage
– Increase efficiency
– Regulator operations
– Increase hosting
• Preliminary analysis indicates
trends in recommended settings
can be found
• Caution: Minor changes in settings
(volt/var) can have significantly
different impacts
• Less “aggressive” settings work
– Less risk, less potential benefit
(e.g., increasing hosting
capacity)
• Results shown today are based
upon site-specific conditions
• Future work for determining
recommended settings
– Other locations
– Other feeders
– Combined inverters

30. Jeff Smith, Huijuan Li
EPRI
EPRI Smart Inverter Workshop, Santa Clara, CA
5/7/2014
Potential Interaction Between Smart
Inverters

31. 31© 2014 Electric Power Research Institute, Inc. All rights reserved.
Overview
Objective Approach
Evaluating potential inverter interaction
Investigate possible inverter
interaction resulting from smart
inverter control on multiple PV
systems
Time-domain analysis in
Matlab/Simulink to investigate possible
inverter interaction

32. 32© 2014 Electric Power Research Institute, Inc. All rights reserved.
Studied System
PV1: 400 kW, 475 kVA
PV2: 1000 kW, 1235 kVA
20 s simulation widow
1.2 Mvar Cap is switched on at 10 s, which causes voltage rise

33. 33© 2014 Electric Power Research Institute, Inc. All rights reserved.
Interactions Between the Two Inverters
Single PV providing vars Both PVs providing vars
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
V1
V2
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
V1
V2
Oscillations
Observed !

34. 34© 2014 Electric Power Research Institute, Inc. All rights reserved.
What May Impact Var Control
Var control flow
VoltVar Curve
Inverter
Averaging
window
V
Reference Q
Average V
Q
PI
controller
(Kp Ki)
Switching
Command
Factors may impact var control:
• Volt-var curve parameters
• PI controller parameters: Kp and Ki
• Voltage average window length

35. 35© 2014 Electric Power Research Institute, Inc. All rights reserved.
Impact of Volt-var Parameters
Volt/var 1 Volt/var 2
% AvailableVars
voltage (pu)
‐100
Capacitive
100
Inductive
0.95 1.05
% AvailableVars
voltage (pu)
‐100
Capacitive
100
Inductive
0.99 1.01
Controller parameters for both cases:
Kp Ki
0.3 3

36. 36© 2014 Electric Power Research Institute, Inc. All rights reserved.
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
Volt/var 1
Voltages
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
V1 V1
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
V2 V2
Volt/var 2
High ratio may cause oscillations

37. 37© 2014 Electric Power Research Institute, Inc. All rights reserved.
Volt/var 1
4 6 8 10 12 14 16 18 20
-100
-80
-60
-40
-20
0
20
40
60
80
100
Time (s)
%ofAvailableVar
Actual var
Var reference
Vars
Var 1 Var 1
Var 2 Var 2
4 6 8 10 12 14 16 18 20
-100
-80
-60
-40
-20
0
20
40
60
80
100
Time(s)
%AvailableVars
Actual Var
Var reference
4 6 8 10 12 14 16 18 20
-100
-80
-60
-40
-20
0
20
40
60
80
100
Time(s)
%AvailableVars
Actual var
Var reference
4 6 8 10 12 14 16 18 20
-100
-80
-60
-40
-20
0
20
40
60
80
100
Time (s)
%AvailableVars
Actula var
Var reference
Volt/var 2

38. 38© 2014 Electric Power Research Institute, Inc. All rights reserved.
Impact of Controller Parameters
Volt/var 2 Volt/var 2: slower response
% AvailableVars
voltage (pu)
‐100
Capacitive
100
Inductive
0.99 1.01
Controller parameters for case 1:
Kp Ki
0.3 3 % AvailableVars
voltage (pu)
‐100
Capacitive
100
Inductive
0.99 1.01
Kp Ki
0.1 1
Controller parameters for case 2:

39. 39© 2014 Electric Power Research Institute, Inc. All rights reserved.
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
Volt/var 2
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)Voltages
V1 V1
V2 V2
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
Volt/var 2: slower response
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
Smaller control parameters, which means
smaller adjustments at each step, reduce
the oscillations

40. 40© 2014 Electric Power Research Institute, Inc. All rights reserved.
4 6 8 10 12 14 16 18 20
-100
-80
-60
-40
-20
0
20
40
60
80
100
Time(s)
%AvailableVars
Actual var
Var reference
Volt/var 2
4 6 8 10 12 14 16 18 20
-100
-80
-60
-40
-20
0
20
40
60
80
100
Time(s)
%AvailableVars
Actual Var
Var reference
4 6 8 10 12 14 16 18 20
-100
-80
-60
-40
-20
0
20
40
60
80
100
Time(s)
%AvailableVars
Actual var
Var reference
Vars
Var 1
Var 1
Var 2 Var 2
4 6 8 10 12 14 16 18 20
-100
-80
-60
-40
-20
0
20
40
60
80
100
Time(s)
%AvailableVars
Actual var
Var reference
Volt/var 2: slower response

41. 41© 2014 Electric Power Research Institute, Inc. All rights reserved.
Impact of Window Length of Averaging
Voltage
Volt/var 2 Volt/var 2: larger avg window
% AvailableVars
voltage (pu)
‐100
Capacitive
100
Inductive
0.99 1.01
% AvailableVars
voltage (pu)
‐100
Capacitive
100
Inductive
0.99 1.01
Controller parameters for both cases:
Kp Ki
0.3 3
Length of average window= 0.05s Length of average window= 1 s

42. 42© 2014 Electric Power Research Institute, Inc. All rights reserved.
Volt/var 2
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)Voltages
V1 V1
V2 V2
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
Volt/var 2: larger avg window
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
4 6 8 10 12 14 16 18 20
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
Time(s)
Voltage(pu)
Longer voltage averaging window
increases oscillation magnitude, but
improved dampening occurs

43. 43© 2014 Electric Power Research Institute, Inc. All rights reserved.
Volt/var 2
4 6 8 10 12 14 16 18 20
-100
-80
-60
-40
-20
0
20
40
60
80
100
Time(s)
%AvailableVars
Actual Var
Var reference
4 6 8 10 12 14 16 18 20
-100
-80
-60
-40
-20
0
20
40
60
80
100
Time(s)
%AvailableVars
Actual var
Var reference
Vars
Var 1 Var 1
Var 2 Var 2
Volt/var 2: slower avg window
4 6 8 10 12 14 16 18 20
-100
-80
-60
-40
-20
0
20
40
60
80
100
Time(s)
%AvailableVars
Actual var
Var reference
4 6 8 10 12 14 16 18 20
-100
-80
-60
-40
-20
0
20
40
60
80
100
Actual var
Var reference

44. 44© 2014 Electric Power Research Institute, Inc. All rights reserved.
Conclusions
• Interactions exist between the two close by inverters
• High ratio may cause oscillations
• Smaller adjustments at each step as a result of smaller
control parameters reduces oscillations
• Longer voltage averaging window increases magnitude of
oscillations, although dampening does occur