PhD Defence_yoy_Print

Advanced Control Strategies to
Enable a More Wide-Scale Adoption of
Single-Phase Photovoltaic Systems
Yongheng YANG
Supervisor: Prof. Frede BLAABJERG
PhD Dissertation Defense
Pontoppidanstraede 101, Aalborg, August 20, 2014

2 | August 20, 2014
Acknowledgement
Prof. Frede Blaabjerg, AAU, Denmark
Prof. Claus Leth Bak, Prof. Jorma Kyyrä, Prof. Toshihisa Shimizu, and
Prof. Stig Munk-Nielsen
Prof. Prasad Enjeti, TAMU, TX, Dr. Keliang Zhou, Uni. of Glasgow, UK
Assist. Prof. Huai Wang, Assist. Prof. Ke Ma, Assist. Prof. Xiongfei Wang
My family, my girlfriend, members of CORPE, all the colleagues at the
Department of Energy Technology, and all my friends

3 | August 20, 2014
Outline
I. Introduction
 Background and motivation
II. Methods
 Power control method of single-phase PV systems
 Mission profile based evaluation approach
III. Advanced Control Strategies
 Harmonic control
 Low voltage ride-through
 Constant power generation concept
 Thermal optimized control strategy
IV.Conclusions
 Summary and outlook

4 | August 20, 2014
Introduction
DCàDC
Photovoltaic Panels
DCàAC
Power Electronics System
vdc
vg
Converter Inverter
vdc
vpv
vg
Power Grid
C
Solar
Irradiance
Transformer
vpv
I. Introduction
 Background and motivation
II. Methods
IV.Conclusions

5 | August 20, 2014
Background and Motivation
Introduction
Germany, 25.8%
China, 13.3%
Italy, 12.8%Japan, 9.9%
USA, 8.7%
Spain, 4.1%
France, 3.3%
Australia, 2.4%
Belgium, 2.2%
United Kingdom, 2.1%
Rest of the world, 14.8%
Source: EPIA
Total: 136.7 GW
PV cumulative installation capacity world-wide share in 2013 (%)
Opportunities enabled by PV systems

6 | August 20, 2014
Introduction
Codes/requirements evolution for PV systems
Generator Level (PV modules) –
Efficiency, Cost, Safety, …
Converter System Level (LV) –
Voltage rise, Fault ride-through (V and/or f),
Anti-islanding, Efficiency, Cost, Reliability,
Power controllability, Power factor,…
Distribution Level (HV, MV) –
Local stability (voltage), Power flow,
P/Q provision to HV, …
Transmission Level (EHV, HV) –
Response to faults, Grid stability,
Power quality, Reactive power, …
Monitoring, Forecasting, and Communication

7 | August 20, 2014
Introduction
Demands (challenges) for a grid-connected PV system
Challenges brought by further increasing PV capacity
▪ Power optimization
▪ DC voltage / current
▪ Panel monitoring &
diagnose
P P
Q
▪ High efficiency
▪ Temp. management
▪ Reliability
▪ Monitoring & safety
▪ Islanding protection
▪ Communication
▪ Power quality (THDi)
▪ Voltage level
In case of large-scale:
▪ Freq. – Watt control
▪ Volt – Var control
▪ Fault ride-through
PV side Grid side
2/3
DC DC AC
Power Electronics

8 | August 20, 2014
Introduction
What else benefits to the grid and the costumers ?
− How to better fulfill the requirements (grid and customer demands)?
− Any solutions to further reduce the cost of PV energy?

9 | August 20, 2014
Introduction
Suggestions on grid requirement modifications:
 Active power control (power curtailment)
 Reactive power control (Volt-VAR control)
 Freq. control through active power control (Freq.-Watt control)
 Dynamic grid support (fault ride-through capability)
 High reliability
 High efficiency
…
Y. Yang, P. Enjeti, F. Blaabjerg, and H. Wang, “Suggested grid code modifications to ensure wide-scale adoption of
photovoltaic energy in distributed power generation systems,” IEEE Ind. Appl. Mag., in press, Sept.-Oct. 2015.

10 | August 20, 2014
Methods
DCàDC
Photovoltaic Panels
DCàAC
vdc
vg
Converter Inverter
vdc
vpv
vg
Power Grid
C
Solar
Irradiance
Transformer
vpv
I. Introduction
II. Methods
 Power control method of single-phase PV systems
 Mission profile based evaluation approach
IV.Conclusions

11 | August 20, 2014
DCàDC DCàAC
vdc
vg
Converter Inverter
vpv
Input power Output power
ipv ig
Main Control
Feedforward Feedback
Internal feedback Control output
Power Profiles
(reference command)
according to grid/customer demands
PV Panel/Plant MonitoringMPPT
Grid Support (V, f, Q) Energy Storage
Advanced Functions (Ancillary Services)
PV System Specific Functions
Basic Control Functions
Current/Voltage Control
Fault Ride Through
Grid SynchronizationVdc Control
Anti-Islanding Protection
Harmonic Compensation Flexible Power Control Reliability
DCàDC DCàAC
vdc
vg
Converter Inverter
vpv
Input power Output power
ipv ig
Feedforward Feedback
Internal feedback Control output
Power Control Method
Methods
Power profiles for single-phase PQ control

12 | August 20, 2014
Power Control Method
Methods
Single-phase PQ control
P
Controller
Q* Q
Controller
*
P
Q
MPPT DC-Link
Controller
Q* Q
Controller
vdc
Q
vdc
*igq
*igd
P*
*igq
*igd
vpv
ipv
Power Profiles
ig
Gc(s)
vinv* *ig
vg
vinv
ig
Ls+R
1
1+1.5Tss
1
vgα+vgβ
2 2vgα
vgβ
P
Q
Plant (PWM delay and filter)Current
controller
PI
controllers
Gp(s)
Gq(s)
Tdevice
vg
fg
ig
ipv
vpv MPPT
LVRT
Temp. Control
Power Curtailment
Q Comp.
etc.
P
Q
*
*
Y. Yang, H. Wang, and F. Blaabjerg, “Reactive power injection strategies for single-phase photovoltaic systems
considering grid requirements,” IEEE Trans. Ind. Appl., vol. 50, no. 6, in press, Nov.-Dec. 2014.

13 | August 20, 2014
Mission Profile based Evaluation Approach
Methods
Mission profile based analysis/evaluation method
Energy Yield
Topology
Lifetime
Thermal Model Electrical Model
Evaluation
(efficiency, reliability, leakage
current rejection, etc.)
Lifetime
Estimation
Energy
Production
Thermal Behavior
(Tjmax,ΔTj)
System Model
Output
Electrical Behavior
(Ptot,η,vCMV)
Ambient Temperature Solar Irradiance
Losses
Temp.
Thermal Model
Tj
P tot ( S )
Ptot (D )
Tc
Th
Ta
ZthS (j-c)
Z thD (j-c)
Z th ( c-h )Z th ( h- a )
Rth1 Rth 2 Rth 3 Rth 4
Tj Tc
C2 C3 C4
Zth( j-c )
C1
Foster Model
S1 D1
S3 D3
S2
D2
S4
D4
vpv vinv
DC-BypassSwitches
AC-BypassSwitches
Leakage
Current
Y. Yang, H. Wang, F. Blaabjerg, and K. Ma, "Mission profile based multi-disciplinary analysis of power modules in
single-phase transformerless photovoltaic inverters," in Proc. of EPE ECCE Europe, pp.1-10, 2-6 Sept. 2013.

14 | August 20, 2014
Methods
ΔS
MissionProfile
time
ts
MissionProfile
time
MissionProfile
time
decompose
A
Detailed Analysis
Structure
B
Look-up Table
based
Analysis Structure
Original profile
Short-term
MP1
ts
MP2
MP2
MP1
Ploss
Tj
Pin
Thermal
Model
PV
Models
Tj
LifetimeLife
Model
Grid
Pout
Electrical System
Tj
MPPT
Power losses
Power lossesLook-up Table
based
Compound
Model LifetimeLife
Model
Power
Converters
Leakage current
vCMV
A B
MP Decomposition
Mission profile (MP) decomposition for the multi-disciplinary evaluation approach

15 | August 20, 2014
Methods
Application (results) of the evaluation approach
FB-Bipolar H6 HERIC
B
A
00:00 12:00 24:00 00:00 12:00 24:00 00:00 12:00 24:00
S1-4
S5,6 S1-4
S1-4 S5,6
-20
0
40
80
Tjmax(ºC)
20
60
10/11 03/12 09/12
-20
0
40
80
10/11 03/12 09/12 10/11 03/12 09/12
Tjmax(ºC)
S1-4
S1-4
S1-4
S5,6
S5,6
20
60

16 | August 20, 2014
Advanced Control Strategies
DCàDC
Photovoltaic Panels
DCàAC
vdc
vg
Converter Inverter
vdc
vpv
vg
Power Grid
C
Solar
Irradiance
Transformer
vpv
I. Introduction
II. Methods
 Harmonic control
 Low voltage ride-through
 Constant power generation concept
 Thermal optimized control strategy
IV.Conclusions

17 | August 20, 2014
Harmonic Control
Harmonic emissions from PV inverters
Y. Yang, K. Zhou, and F. Blaabjerg, "Harmonics suppression for single-phase grid-connected PV systems in
different operation modes," in Proc. of APEC, pp.889-896, Mar. 2013.
0 4 8 16 20 2412
0
2
4
6
8
10
12
14
16
Time of a day (hour)
PVoutputcurrent(A)
0
2
4
6
8
10
12
14
16
0 0.000250.00050.000750.0010.001250.00150.001750.0020.002250.00250.002750.003
Inverterinputcurrent(A)
Time of a day
Ppv = 3 kW
PV power weather-dependency
0
2
4
6
8
10
12
14
16
-80 -60 -40 -20 0 20 40 60 80
AverageTHD(%)
Power Angle φ ( )
Ig = 6 A
Ig = 2 A
Ig = 10 A
-80 -60 -40 0 20 40 60 80-20
0
2
4
6
8
10
12
14
16
Power angle φ (º)
CurrentTHD(%)
Proportional resonant control
Harmonic emissions from PV inverters

18 | August 20, 2014
Harmonic Control
Harmonic control – current controllers in the αβ-frame
Current controllers for single-phase PV inverters with or w/o harmonic compensation

19 | August 20, 2014
Harmonic Control
Harmonic control – current controllers
100
40
Frequency (Hz)
Magnitude(dB)
101
102
103
20
0
-20
RC
5×103
60
80
100
120
PI
PR+MRC
PR+RCPR
3rd
5th
7th
DB+RCDB
ω0/2π
Magnitude responses of different current controllers

20 | August 20, 2014
Harmonic Control
Harmonic control – current controllers
DB DB+RC
PR PR+MRC
PR+RC IEC 61727
4
Frequency (Hz)
Mag(%offundamental)
100 1000
2
0
5000
6
8
10
3rd
5th
7th
500
Harmonic distributions of the grid current using different current controllers

21 | August 20, 2014
Harmonic Control
Test results – harmonic comp. in single-phase inverters
THDig= 7.70%
ig
7th
11th
Y. Yang, K. Zhou, and F. Blaabjerg, "Harmonics suppression for single-phase grid-connected PV systems in
different operation modes," in Proc. of APEC, pp.889-896, Mar. 2013.
Y. Yang, K. Zhou, H. Wang, F. Blaabjerg, D. Wang, and B. Zhang, "Frequency adaptive selective harmonic control
for grid-connected inverters,“ IEEE Trans. Power Electron., DOI: 10.1109/TPEL.2014.2344049, in press, 2015
PR w/o HC
ig
THDig= 3.55%
7th
11th
ig
THDig= 3.90%
7th
11th
PR with MRC PR with RC

22 | August 20, 2014
Low Voltage Ride-Through
LVRT requirements
Time (s)
VoltageLevel(p.u.)
0
1.0
Anti-Islanding
Protection
t1 t3 t4t2 t5
LVRT
Stay connected
v3
v2
v1
0
May disconnect
short-term islanding
Must
disconnect
Normal operation
Compatible implementation of low voltage (and zero voltage) ride-
through and anti-islanding requirements

23 | August 20, 2014
LVRT implementation - 1
Implementation possibilities of LVRT in single-phase PV inverters
C Grid
IPV VPV
MPPT DC
DC
3. Energy Storage System
2. DC Chopper
1. MPPT Control
C
DC
AC
FilterInverterPV Panels
Mission
Profiles

24 | August 20, 2014
P
Q0
PPV,MPP
VNImax
Q*
2
VIN
2PPV
Q
VNIm
2
LVRT implementation - 2
Implementation of LVRT by modifying the MPPT control
Y. Yang, F. Blaabjerg, and Z. Zou “Benchmarking of grid fault modes in single-phase grid-connected photovoltaic
systems,” IEEE Trans. Ind. Appl., vol. 49, no. 5, pp. 2167–2176, Sept.-Oct. 2013.

25 | August 20, 2014
igvg
Q
P
Sag Duration Sag Duration
t1 t2 t1 t2
t [40 ms/div]t [40 ms/div]
Tests of single-phase FB inverters in LVRT
Y. Yang and F. Blaabjerg, “Low voltage ride-through capability of a single-stage single-phase photovoltaic system
connected to the low-voltage grid,” Int’l J. Photoenergy, vol. 2013, pp. 1 - 9, 2013.
Y. Yang, F. Blaabjerg, and H. Wang, “Low voltage ride-through of single-phase transformerless photovoltaic
inverters,” IEEE Trans. Ind. Appl., vol. 50, no. 3, pp. 1942–1952, May-Jun. 2014.

26 | August 20, 2014
Tests of single-phase transformerless inverters in LVRT
Y. Yang, F. Blaabjerg, and H. Wang, “Low voltage ride-through of single-phase transformerless photovoltaic
inverters,” IEEE Trans. Ind. Appl., vol. 50, no. 3, pp. 1942–1952, May-Jun. 2014.
0
1
2
3
4
5
6
0 0.2 0.4 0.6 0.8 1 1.2
AverageCurrent(A)
VoltageLevel(p.u.)
FB-Bipolar IGBT1-4
FB-DCBPIGBT1-4
FB-DCBPIGBT5-6
HERICIGBT1-4
HERICIGBT5-6
1
2
3
4
5
6
AverageCurrent(A)
FB-Bipolar IGBT1-4
FB-DCBPIGBT1-4
FB-DCBPIGBT5-6
HERIC IGBT1-4
HERIC IGBT5-6
FB-Bipolar S1~4
H6 S1~4
H6 S5~6
HERIC S1~4
HERIC S5~6
IIIIII
Voltage level (p.u.)
0 0.2 0.4 0.6 0.8
0
1
2
3
4
5
6
Averagecurrent(A)
1.0 1.2
Current stress vs. voltage level (transformerless inverters)

27 | August 20, 2014
Reactive Power Injection (RPI) requirements
0 0.5 1.10.9
vg (p.u.)
100
20
DeadBand
Iq/IN(%)
LVRT- Support voltage
k = 2 p.u.
k = 3 p.u.
30
Full reactive
current injection
Reactive current profile during LVRT Inverter Q capability
P
Q
0
VgnImax
2
PMPP= Sn
Qmax
Smax=
S
φ
Q
LVRT- Support voltage

28 | August 20, 2014
Reactive power injection strategies (proposed)
0.00
0.50
1.00
1.50
2.00
2.50
0.00 0.20 0.40 0.60 0.80 1.000
Voltage Level (p.u.)
0.2 0.4 0.6 0.8 1.0
0
0.5
1
1.5
2
2.5
Igmax/IN(p.u.)
0.5 0.9
kd = 1 p.u.
Solid line k = 2 p.u.
Dashed line k = 4 p.u.
2.24
Imax = 1.5IN
kd = 0.5 p.u.
0.72
Wider range
0
0.5
1
1.5
2
2.5
0 0.2 0.4 0.6 0.8 1
0
0.2 0.4 0.6 0.8
0
0.5
1
1.5
2.0
2.5
Igmax/IN(p.u.)
0.5 0.9
Const.-Id
(m = 1 p.u.)
Const.-P
(kd = 1 p.u.)
Imax = 1.5IN
Full reacitve
power injection
0.72 1.0
Const.-Igmax
(n = 1 p.u.)
0
0.5
1
1.5
2
2.5
0 0.2 0.4 0.6 0.8 10
0.2 0.4 0.6 0.8 1.0
0
0.5
1
1.5
2
2.5
Igmax/IN(p.u.)
0.5 0.9
m = 0
Solid line k = 2
Dashed line k = 3
m = 0.5 p.u.
m = 1 p.u.
Imax = 1.5IN
Const. - P Const. - Id Const. - Igmax

29 | August 20, 2014
RPI tests of single-phase PV inverters in LVRT
Qig
vg
time [40 ms/div]
vg
time [40 ms/div]
vg
time [40 ms/div]
time [40 ms/div]
P
Q
time [40 ms/div]
P
Q
time [40 ms/div]
P
ig
ig
igmax
igmax
igmax
Const. - Igmax
Const. - Id
Const. - P
(20 % drop)
(45 % drop)
(45 % drop)

30 | August 20, 2014
Constant Power Generation Concept
Challenges increase with an even wide-scale PV adoption:
 Overloading at peak power generation (voltage rise, transformer saturation)
 Limited utilization of PV inverters
 High temperature peaks and variations due to intermittency
Y. Yang, H. Wang, F. Blaabjerg, and T. Kerekes, “A hybrid power control concept for PV inverters with reduced
thermal loading,” IEEE Trans. Power Electron., vol. 29, no. 12, pp. 6271 - 6275, Dec. 2014.
Overloading !

31 | August 20, 2014
CPG – one of the Active Power Control (APC) functions
Y. Yang, F. Blaabjerg, and H. Wang, "Constant power generation of photovoltaic systems considering the
distributed grid capacity," in Proc. of APEC, pp. 379-385, 16-20 Mar. 2014.
Extend the CPG function for WTS in Denmark to wide-scale PV applications?
Gradient
production
constraint
Time
ActivePower
Possible active power
MPPT
control
MPPT
control
Delta production
constraint
Absolute (constant)
production constraint
Power ramp
constraint

32 | August 20, 2014
0 20 40 60 80 100
0
20
40
60
80
100
Power limit (% of peak feed-in power)
Energreduction
(%ofannualenergyyield)
20 % reduction of
feed-in power
6.23 % energy
yield reduction
Feasibility of CPG for PV systems
Energy reduction vs. limiting feed-in power

33 | August 20, 2014
Implementation of CPG in single-phase PV systems - 1
 Energy “reservoir” – storage elements
 Power management/balancing control
 Modifying the MPPT
Total Power Power Limitation (Plimit)
C
P1 P2 PnP3
Power
Pm
P1* * P3* Pm* Pn*P2
Plimit Central Control Unit
Communication

34 | August 20, 2014
Implementation of CPG in single-phase PV systems - 2
Time
Power
Pmaxn
I III V
Po
Energy yield
t0 t1 t2 t3 t4 t
II IV
PPV
Plimit
Rated peak PV power
Pow
er-Voltage
Pmaxn
vpv1 vpv2
Current-Voltage
ipv1
ipv2
Po=Plimit
L H
M
N
Plimit
Po=P'max

35 | August 20, 2014
Boost
ipv vpv
vg
ig
Inverter LCL-filter
vdc PWMinvPWMb
Grid
Zg
C
LoadInverter
Control
*
L
Cdc
PV Panels
L1 L2
Cf
vdcMPPT Control
Boost
ipv vpv
vg
ig
Inverter LCL-filter
vdc PWMinvPWMb
Grid
Zg
C
LoadInverter
Control
*
L
Cdc
PV Panels
L1 L2
Cf
vdc
MPPT/CPG
Control
Plimit
Entire implementation of CPG in double-stage systems
MPPTvpv
ipv
Ppv
Plimit
PWMb
Ppv < Plimit
Ppv ≥ Plimit
Proportional
Controller
kcpg

36 | August 20, 2014
Operation examples of CPG control - 1
PVpower(kW)
1
1.5
2
2.5
3
200 250 300 3500.5 1 1.5 2
PVpower(kW)
1
1.5
2
2.5
3
2.4 kW
PV Power
Power to Grid
MPPTMPPT CPG
2.5
SolarIrradiance(kW/m2
)
0.4
0.6
0.8
1
1.2Solar Irradiance
(Ambient temp.: 25 ºC)
PVvoltage(V)
200
250
300
350
0.5 1 1.5 2.5 32
Time (s)
0.5 1 1.5 2.5 32
Time (s)
PVcurrent(A)
3
6
9
12
PV voltage (V)Time (s)
MPPTMPPT CPG MPPTMPPT CPG
CPG
Solar irradiance:
1 kW/m2
Solar irradiance: 0.5 kW/m2
MPPT
Solar irradiance:
0.7 kW/m2
(Ambient temp.: 25 ºC)
(Ambient temp.: 25 ºC) (Ambient temp.: 25 ºC)

37 | August 20, 2014
Operation examples of CPG control - 2
MPPT-CPG
0
Time of a day (hours)
0.5
2.5
MPPT
4 8 12 16 20 24
1.5
3.5
CPG
20
0
5
10
15
25
0 4 8 12 16 20 24
0.5
1.5
2.5
3.5
kWh
0
0.4
0.8
1.2
0
0.4
0.8
1.2
0
10
20
30
0
10
20
30
kWh
2 samples/h12 samples/h 2 samples/h
12 samples/h
2 samples/h12 samples/h
2 samples/h12 samples/h
2400 W
MPPT-CPG
Time of a day (hours)
MPPT
CPG
CPG
20
0
5
10
15
25
2400 W

38 | August 20, 2014
Reduced thermal loading enabled by CPG control
Mission
profile
Plimit
C
PV
Model
S
Ta
Boost
Converter
Ppv
PV
Inverter
Pin Po
Grid
Losses ó Thermal
Model
ÚÙ
Tj
Look-Up Table based Model
CPG control control
vdc*
Ploss Temp.
Rebuilt
mission
profile
PV
Model
S
Ta
Boost
Converter
Ppv
PV
Inverter
Pin Po
Grid
Losses ó Thermal
Model
ÚÙ
Tj
Look-Up Table based Model
MPPT control control
vdc*
Ploss Temp.
C
Direct CPG
Rebuilt MP

39 | August 20, 2014
Results – thermal loading with and w/o CPG control
MPPT control
CPG control (80%)
Thermalloading(ºC)
-10
10
30
50 53 ºC
70
Oct.
Nov.
Dec.
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.
Thermalloading(ºC)
-10
10
30
50
70
62 ºC
Oct.
Nov.
Dec.
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.

40 | August 20, 2014
10-1
100
101
102
103
104
105
106
107
0 5 25 35 45 55 65 75 85
MPPT
MPPT-CPG
MPPT
MPPT-CPG
10-1
100
101
102
103
104
105
106
-25 155-5 25-15 35 6545
NumberofCycles
NumberofCycles
ΔTj (ºC) Tjm (ºC)
5515 95
Reduced temperature-
cycle number
107
Results – reliability (application of the evaluation approach)
MPPT
MPPT-CPG
Most LC region
0
0 5 25 35 45 55 65 75 85
NormalizedLC(%)
ΔTj (ºC)
15
1
3
2
5
4
6
Accumulated LC in
MPPT-CPG mode:
3.08%
MPPT
MPPT-CPG
0
NormalizedLC(%)
1
3
2
5
4
6
Accumulated LC in
MPPT-CPG mode: 3.08%
2s 1m 1d 7d 30d
Cycle Period ton
1h

41 | August 20, 2014
Benefits from CPG control
Energy yield and lifetime improvement (single device)
under different power limits (CPG control)
0 20 40 60 80 100
0
20
40
60
80
100
Power limit (% of peak feed-in power)
Energyield(%ofannual
energyyieldinMPPTmode)
20 % reduction of
feed-in power
100
101
102
103
Normalizedlifetime(LF)
93.77 %
energy yield
5.62Energy yield
Normalized LF

42 | August 20, 2014
Thermal Optimized Control Strategy
High efficiency and high reliability are important
Efficiency à Transformerless inverters, optimization, etc.
Reliability à Considering rated power, packaging technologies, severe users,
and harsh operation conditions, e.g. voltage sags.
Grid
Cf
ig vg
ipv
D1 ig
PV
ipv
vpv
L1
S1
S2 Rs
RL
Sag Generator
Zg
Inverter
S2
D3
D4
Current
Controller
PWM ig P
Q
P*
Q*
Power
Reference
Generation
vg
vpv
Power
Controllers
ig
*
C
L2
LCL Filter
Tref
Control Structure
vpv
S1
D2
S3
S4
C
Mission
profile
Y. Yang, H. Wang, and F. Blaabjerg, “Reduced junction temperature control during low-voltage ride-through for
single-phase photovoltaic inverters,” IET Power Electron., vol. 7, no. 8, pp. 2050 - 2059, Aug. 2014.

43 | August 20, 2014
Coupled relationship between junction temp. and losses
Tc Th
Zth(j-c)
Zth(c-h) Zth(h-a)
vdc vinv
Pin Pout
Power Losses
Device
Temperature
Tj
Electrical Domain
Thermal Domain
Ta
(Ploss=Pin -Pout)
   j m
β
β βT β
f j ONN α T e t i
 
2
1 3 4
  , , , , ,...j a s lossT f i v T f p

44 | August 20, 2014
Tjmax, set = f (Pj, Qj) ?
Principle of the T-optimized control
Tjmax,set
Fault?
vg
Reliability demands
(Pj1, Qj1, Pj2, Qj2, ...) MPPT
NO
YES
Look-up table
Power reference
(P1, Q1, P2, Q2, ...)* * * *
Power optimization
(optimization objectives:
e.g., P = max{P1, P2, ...}. )
P, Q* *
* **
Grid requirements
(PL, QL, Eq. (2) and (3))

45 | August 20, 2014
Power references of the T-optimized control in LVRT mode
Tjmax,IGBT(ºC)
50
100
150
200
250
Tjmax,IGBT(ºC)
50
100
150
200
250
0.2 0.4 0.6 0.8 1 1.2
0.2 0.4 0.6 0.8 1 1.2
Q= 0% Q= 20% Q= 40% Q= 60% Q= 80% Q= 100%Q = 0 Q = 20% Q = 40% Q = 60% Q = 80% Q = 100%
0.2 0.4 0.6 0.8 1 1.2
0.2 0.4 0.6 0.8 1 1.2
Tjmax,IGBT(ºC)
50
100
150
200
250
Tjmax,IGBT(ºC)
50
100
150
200
250
Allowable Tjmax = 125 ºC Allowable Tjmax = 125 ºC
Allowable Tjmax = 125 ºCAllowable Tjmax = 125 ºC
Tjmax_d = 80 ºC Tjmax_d = 80 ºC
Tjmax_d = 80 ºCTjmax_d = 80 ºC
P = 80 %
P = 40 % P = 20 %
P = 60 %

46 | August 20, 2014
Power references of the T-optimized control in LVRT mode
JP*
1
QJ1
NormalOperationMode
A
B
C
*
0 0.2 0.6 0.9 10.4 0.8
0
0.2
0.4
0.6
0.8
1
1.2P*
(black)andQ*
(red)(p.u.)JJ
Const. T

47 | August 20, 2014
Results of the T-optimized control in LVRT mode
LVRT – Const. P Const. T
60
80
100
120
0.8
0.5
1.0
Time (s)
1.0 1.5 2.5
Time (s)
1.0 1.5 2.5
Junctiontemp.(ºC)Power(p.u.)
Active power
Reactive power
Active power
Reactive power
Achieved constant
junction temperature
D2
S1
D2
S1
ΔTj1
ΔTj2
Voltage sag Voltage sag

48 | August 20, 2014
Experiments of the T-optimized control
R
L
½vdc
+
-
½vdc
vdc
NPC Inverter
Load+
-
C1
C2
Sp1
Sp2
Sp3
Control signal
(modulation index)
dSPACE
Test No. 1 Test No. 2 Test No. 3

49 | August 20, 2014
Loss comparison (experiments) with other RPI strategies
Normal
Grid
Normal
Grid
Voltage Fault
(vg = 0.55 p.u.)
0
10
20
30
40
70
DeviceTotalPowerLoss(W)
Const.-P
(kd = 1 p.u.)
50
60
T-Optimized
Const.-Id
(m = 1 p.u.)
Const.-Igmax
(n = 1 p.u.)
No LVRT Control
(P = 1 p.u.,
Q = 0 p.u.)

50 | August 20, 2014
Conclusions
I. Introduction
II. Methods
IV.Conclusions
 Summary and outlook
DCàDC
Photovoltaic Panels
DCàAC
vdc
vg
Converter Inverter
vdc
vpv
vg
Power Grid
C
Solar
Irradiance
Transformer
vpv

51 | August 20, 2014
Summary
Conclusions
 Comprehensive comparison of transformerless inverters
 Proposed grid code/requirement modifications
 Proposed reactive power injection strategies
Developed advanced control strategies
− Harmonic control
− Low voltage ride-through control
− Constant power generation control
− Thermal optimized control strategy
Main contributions of this project
Ultimate Solutions?

52 | August 20, 2014
Outlook
Conclusions
Research perspectives enabled by this project
 Evaluation of grid-side filters (also power losses) and current controllers in different
operation modes
 Reactive power injection (thermal performance and cost of reactive power)
 System integration with e.g. storage systems and electrical vehicles, and thus grid
code modifications
 More detailed investigations of the constant power generation control
 Developing analytical method/model of the junction temperature control (thermal
optimized control)
 Application of advanced power devices (SiC, GaN) in those inverters
Ideas for Future PV Systems

53 | August 20, 2014
Selected Journal Papers
1. Y. Yang, K. Zhou, H. Wang, F. Blaabjerg, D. Wang, and B. Zhang, “Frequency adaptive selective harmonic control for
grid-connected inverters,” IEEE Trans. Power Electron., DOI: 10.1109/TPEL.2014.2344049, in press, 2015.
2. Y. Yang, P. Enjeti, F. Blaabjerg, and H. Wang, “Suggested grid code modifications to ensure wide-scale adoption of
3. Y. Yang, H. Wang, and F. Blaabjerg, “Reactive power injection strategies for single-phase photovoltaic systems
4. K. Zhou, Y. Yang, F. Blaabjerg, and D. Wang, “Optimal selective harmonic control for power harmonics mitigation,”
IEEE Trans. Ind. Electron., DOI: 10.1109/TIE.2014.2336629, in press, 2014.
5. Y. Yang, H. Wang, F. Blaabjerg, and T. Kerekes, “A hybrid power control concept for PV inverters with reduced thermal
loading,” IEEE Trans. Power Electron., vol. 29, no. 12, pp. 6271-6275, Dec. 2014.
6. Y. Yang, H.Wang, and F. Blaabjerg, “Reduced junction temperature control during low-voltage ride-through for single-
phase photovoltaic inverters,” IET Power Electron., vol. 7, no. 8, pp. 2050-2059, Aug. 2014.
7. Y. Yang, F. Blaabjerg, and H. Wang, “Low voltage ride-through of single-phase transformerless photovoltaic inverters,”
IEEE Trans. Ind. Appl., vol. 50, no. 3, pp. 1942–1952, May-Jun. 2014.
8. Y. Yang, F. Blaabjerg, and Z. Zou, “Benchmarking of grid fault modes in single-phase grid-connected photovoltaic
systems,” IEEE Trans. Ind. Appl., vol. 49, pp. 2167–2176, Sept.-Oct. 2013.
9. Y. Yang and F. Blaabjerg, “Low-voltage ride-through capability of a single-stage single-phase photovoltaic system
connected to the low-voltage grid,” International Journal of Photoenergy, vol. 2013, Article ID 257487, 9 pages,
2013. DOI:10.1155/2013/257487.

54 | August 20, 2014
Future
Face the future with what I have learnt from all of you.
All the best for our future.
‘‘Prediction is very difficult,
especially about the future’’
Niels Bohr
Danish physicist (1885 - 1962)

PhD Defence_yoy_Print

Recommended

Recommended

More Related Content

Viewers also liked

Viewers also liked (15)

Similar to PhD Defence_yoy_Print

Similar to PhD Defence_yoy_Print (20)

PhD Defence_yoy_Print