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Converter Fed Microgrids:
Challenges & Solutions
Presenter: Charles Sao, PhD Candidate, ECE Dept., U. of Toronto
Contact Info: [email protected]
Supervisor: Prof. Peter Lehn
Microgrids: Power Network with Loads and DGs that
operate as a Single Controllable System.
Grid Connected
Mode
VSC 1
it1d it1q
L1
jX1
Power
Grid
Epcc pcc
Loads
L2
jX2
 Current Mode Control: Dynamic Current Control
 Synchronized to PCC Voltage: Fast P and Q Control
 Grid Provides PCC Voltage and Frequency Control
it2d it2q
VSC 2
Microgrids: Challenges
Intentional
Islanding Mode
VSC 1
it1d it1q
L1
Epcc , pcc =?
L2
jX1
Loads
jX2
it2d it2q
VSC 2
 Identical Topology and Control as Grid Connected Mode
 Lose Control of PCC Voltage and Frequency
 PQ Supply does NOT equal Demand
Operate Like
Conventional Gen?
VSC 1
VSC 2
P1 Q 1
L1
Epcc , pcc
L2
P2 Q2
it1 =?
jX1
Loads
jX2
it2=?
E1,1
withDroop
E2,2
withDroop
 Voltage Source with Regulated Voltage & Frequency
 Frequency & Voltage Droop to Share Real & Reactive Power
 No Dynamic Control of Current– Risk Burn-out (or)
 Conventional P & Q Control - Slow
Solution & Results
VSC 1
Epcc , pcc
L1
it1d it1q
jX1
Loads
E1dq
L2
it2d it2q
VSC 2
*
E pcc
*pcc
jX2
i*t1 Current E 1
Voltage &
Plant
Control
Frequency Control
E2dq
Epcc pcc
it1
 Identical Topology as Grid Connected Mode
 Regulates PCC Voltage and Frequency
 Fast Control of Current and Power to meet Demand
Step Responses of the Voltage Control Loop
Step Responses of the Frequency Control Loop
65
96
92
Frequency (Hz)
Voltage (V)
94
Volt Mag Ref
Volt Mag-Lab
90
60
Freq Ref
Freq-Lab
88
86
80
100
120
140
160
Time (ms)
180
200
55
80
100
120
140
160
Time (ms)
180
200
E pcc
pcc
Load Sharing of 2 Converters
VSC 1
Epcc , pcc
L1
it1d it1q
jX1
Real Power Sharing
4
P of VSC 1
P of VSC 2
Q of VSC 1
Q of VSC 2
2
1
0
-1
2
1
0
-1
0
500
Time (ms)
1000
-2
Instantaneous P Sharing During Load Switching
4
P of VSC 1
P of VSC 2
3
P1 (kW), P2 (kW)
3
Q1 (kVAr), Q2 (kVAr)
3
VSC 2
E2dq
Reactive Power Sharing
4
P1 (kW), P2 (kW)
it2d it2q
jX2
Loads
E1dq
-2
L2
2
1
0
-1
0
500
Time (ms)
1000
-2
0
50
Time (ms)
100
Grid Connection Transient
Response of the Frequency Control Loop to Grid Connection
90
Freq Ref
Freq-Lab
85
Response of the Voltage Control Loop to Grid Connection
100
Volt Mag Ref
Volt Mag-Lab
Frequency (Hz)
80
96
94
75
70
65
60
92
55
90
0
100
200
300
Time (ms)
400
500
50
-20
0
20
Change in Total Converter Power Output
4
Real Power
Reactive Power
3
P (kW), Q (kVAr)
Voltage (V)
98
2
1
0
-1
-2
0
100
200
300
Time (ms)
400
500
40
60
Time (ms)
80
100
120
Islanding Transient
Responses of the Voltage Control Loop to Islanding
Responses of the Frequency Control Loop to Islanding
95
60
Frequency (Hz)
85
Volt Mag Ref
Volt Mag-Lab
80
75
50
Freq Ref
Freq-Lab
40
30
70
65
0
20
40
60
Time (ms)
80
100
20
0
120
20
Change in Converter Power Output due to Islanding
4
3
P (kW), Q (kVAr)
Voltage (V)
90
Real Power
Reactive Power
2
1
0
-1
-2
0
20
40
60
Time (ms)
80
100
120
40
60
80
Time (ms)
100
120
Summary
Project Summary:
 Identical Controls in Island & Grid Connected Modes
 Regulate V & Freq., Manage P and Q
 Dynamic Current Control to Protect Converters
Other Research Projects:
 Autonomous Load Sharing of Voltage Source Converters
 Computing Lightning Exposure of Wind Turbines (with Dale Dolan)
 Benchmark System for Time Domain Simulation of D-STATCOMs
Selected Industrial Projects (at BC Hydro):
 Stability study of the North Coast 500 kV Line
 Effect of non-linear loads on reactive power metering
 CEA Power Quality Survey Coordination in BC