Transcript Part 2

Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Overview of Distributed Power
Generation Systems (DPGS) and
Renewable Energy Systems (RES)
Marco Liserre
[email protected]
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Outline

Introduction to distributed power generation and renewable energy
systems

World energy scenario (including renewable energy)

Outlook on wind and photovoltaic energy

Integrating renewable energy sources with the future power system

Wind systems

Photovoltaic systems
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Distributed power generation


Relatively small generating units and storage
technologies
Either be interconnected
with the electric grid or
isolated from the grid in
"stand- alone"
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

Provide electric
capacity and/or
energy at or near
consumer sites to
meet specific
customer needs
The location value is important to the
economics and operation
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
60
40
20
0
Cost of electricity (¢/kWh)
1980
1985
1990
1995
10
8
Geothermal
6
4
2
0
1980
1985
1990
Cost of ethanol ($/gal)
Photovoltaics
1995
Biomass
3
2
1
0
1980
Cost of electricity (¢/kWh)
80
1985
1990
Solar Thermal
20
10
0
1980 1985
1990
40
1995
Wind
30
20
10
1995
40
30
Cost of electricity (¢/kWh)
4
100
0
1980
Cost of electricity (¢/kWh)
Cost of electricity (¢/kWh)
Renewable energy systems
1985
1990
1995
20
15
Biomass Electric
10
5
0
1980
1985
1990
1995
Source: Billman, Advances in Solar Energy submission, 1/8/99
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
World energy consumption

The growth of energy demand in 2007 remained high despite high
energy prices

China has surpassed the EU
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
World energy production

The relative market share of oil is decreasing respect coal and gas
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Renewable Energy scenario

In 2007 the world renewable energy production share has been calculated as
19 %.

However 16 % is due to hydraulic energy production, hence wind and
photovoltaic (the most promising renewable sources) energy production is still
very modest.

The goal of the European Community is to reach 20 % in 2020, however the
EU-27 energy is only 17% of world energy.

USA with 22% of energy share may adopt similar goals under the pressure of
public opinion concerned by environmental problems (in California the goal is
20 % in 2010).
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Renewable Energy scenario

However the policies of Asia and Pacific countries, with 35% of energy share,
will be probably more important in the future energy scenario.

In fact countries like China and India require continuously more energy (China
energy share increases 1 point every year from 2000).

The need for more energy of the emerging countries and the environmental
concerns of USA and EU will drive the increase of the renewable energy
production: the importance of renewable energy sources in the future energy
scenario is not anymore under discussion !

The needed technology is available and it benefits of continuous improvement
due to academic and industrial research activity

Knowledge transfer to industry on the basis of international conferences and
workshops and educational programs.
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Renewable Energy scenario

Wind energy – highest development

Solar energy – next highest development

Wave energy – largely unexplored

Tidal energy – largely unexplored

Small hydro (<10MW), 47GW used, 180 GW untapped (70% in developing
countries). Oldest technology (not covered)

Biomass 18GW used (2000), largely unexplored. Used in CHP
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind energy
Bigger and more efficient !
3.6-6 MW prototypes running (Vestas, GE, Siemens Wind, Enercon)
Danish Vestas and Siemens Wind stand for over 40% of the worldwide
market
2 MW WT are still the "best seller" on the market!
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind energy
 Wind energy can benefit of huge investments in research and education.
 Some of the most relevant goals of the research can be briefly summarized
as:
 to increase the power production of each wind turbine (over 5 MW),
 to increase the penetration of small wind turbine systems (under 50 kW)
 to create wind plants (preferably off-shore) that can behave similarly to
standard oil & gas power plants respect to the grid (due to wind forecast
and proper control strategies).
 Educational investments are mainly done by universities to prepare a future
category of engineers for the wind industry but also by leader wind companies
that want to form highly specialized engineers through specific PhD programs
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Photovoltaic energy
 The cost of PV electricity will reach the break-even point soon in many
countries
Optimistic ! Silicon shortage has slowed
the price reduction
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Photovoltaic energy
 Despite the silicium shortage in the last years the PV industry is growing at more than 30%
 PV Module technology is also developing fast toward higher efficiency and lower cost of 4-5
€/Wp, expected 3€/Wp in 5 years. From experience 7%/year fall
 String technology is dominating. Multi-string for residential applications
 Mini-central three-phase inverters 8-15 kW are emerging for modular configuration in medium
and high power systems (commercial roof-tops)
 Central inverters are available for plants up to MW range (1MW – SMA)
 Reliability is increased now 5 years but extended 20 years (not free!)
 Increase functionality available (built-in logger, communication, grid support, etc)
 Cost is still high (400- 500€/kWp) and high efforts are done in order to reduce it to 250-300
€/kWp in the next 5 years by:
 mass production
 better topologies with fewer components
 design-to-cost
 PV electricity cost is expected to reach the break-even cost around 2015 where mass PV
penetration is expected
Marco Liserre
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Photovoltaic energy
 The most relevant goals of photovoltaic energy are 40% cost reduction of
photovoltaic panels and of the power converter stage in 5 years and the
increase of the efficiency of both and the reliability of the latter considerably.
 These goals are driving the research towards several directions such as:
 maximum power extraction algorithms,
 advanced anti-islanding algorithms for higher safety levels
 higher efficiency of the power converter (98 % efficiency is the goal for
transformerless topologies)
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Power system evolution
 Active distribution grids with a significant
amount of medium-scale and small-scale
generators (ranging from hundreds of kW to
tens of MW), involving both conventional and
renewable technologies, together with storage
systems and flexible high-voltage
transportation systems connecting those grids
with lower cost and ROW (Right Of Way)
restrictions.
The importance of storage in the overall
scenario is crucial
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Smart micro-grids (SMG)
 Within active grids, generators and loads can both play a role as operators in electricity markets
 Distribution grids have to be equipped with protection systems and real-time control systems
leading to smart micro-grids (SMG) usually operated in connection to distribution grids but with
the capability of automatically switching to a stand-alone operation if faults occur in the main
distribution grid, and then re-connected to the grid.
 The safe operation in any
condition (grid-connected or
stand-alone) relies also on
good simulation tools to
predict the behavior of the
overall system considering
the specific operation of the
renewable energy sources.
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Information Technology Networking
The operation of a SMG can result in
higher availability and quality compared
with strictly hierarchical management of
power generation and distribution. The
security of the system can be improved
by the ability of feeding final users,
reacting to demand variations in a short
time by redispatching energy thanks to
smart systems. This allows to reduce
risks and consequences of black-outs,
avoiding the increase of the global
production.
Photovoltaic systems
highly integrated in the
buildings
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Hydrogen distribution
network
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Information Technology Networking
problems . . .
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Information Technology Networking
possible solutions . . .
Color-based indication of grid status
Automated Demand Response
from Dr. Peter Palensky’s contribution to IEEE – IECON 2008 Panel Discussion
Session On Industrial Electronics for Renewable Energy
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind systems
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind turbine systems
Doubly-fed induction generator - wounded rotor
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



Limited speed range (-30% to +20%, typical)
Small-scale power converter (Less power losses, price)
Complete control of active Pref and reactive power Qref
Need for slip-rings
Need for gear
Doubly-fed
induction generator
Grid
Gear
Pitch
DC
AC
DC
Pref
AC
Qref

Producers: Vestas, Gamesa, NEG Micon, GE Wind, Nordex, REpower Systems,
DEWind

Power range: 0.85 MW to 4.2 MW
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind turbine systems
Induction generator - Squirrel cage rotor






Full speed range
No brushes on the generator
Complete control of active and reactive power
Proven technology
Full-scale power converter
Need for a gear
Induction
generator
Gear
AC
DC
DC
Pitch
Pref
AC
Qref

Mainly for low power stand-alone

Producers: Verteco (converter rated for 50% power), Neg Micon, Siemens

Power range: 0.66 MW to 3.6 MW
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind turbine systems
Synchronous generator - External magnetized







Full speed range
Possible to avoid gear (multi-pole generator)
Complete control of active and reactive power
Small converter for field
Need of slip-rings
Full scale power converter
Multi-pole generator may be big and heavy
inverter
or
diode-bridge + chopper
DC
AC
VII
Synchronous
Generator
Gear
AC
DC
Pitch

Producers: Enercon, Largey,

Power range: 0.6 MW to 4.5 MW
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Pref
Grid
DC
AC
Qref
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind turbine systems
Synchronous generator - Permanent magnets








Full speed range
Possible to avoid gear (multi-pole generator)
Complete control of active and reactive power
Brushless (reduced maintenance)
No power converter for field (higher efficiency)
Full scale power converter
Multi-pole generator big and heavy
Permanent magnets needed
inverter
or
diode-bridge + chopper
PM-synchronous
Generator
Multi-pole
Grid
AC
DC
DC
Pitch
Pref

Producers: Largey, Mitsubishi, Pfleiderer Wind Energy

Power range: 0.6 MW to 4.5 MW
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AC
Qref
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
SG Example 1
20 kW mini-WT multipolar permanent
magnet synchronous generator with axial
flux produced by JONICA IMPIANTI
(JIMP)
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
SG Example 2
from “WindBlatt 02/03”
WT Enercon
300 kW multipolar synchronous
generator installed in Antartica
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
SG Example 3
Multibrid WT
5 MW multipolar synchronous
generator (Multi) with ibrid gear
(brid) for offshore applications
Prokon Nord
synchronous generator with
permanet magnets surface
mounted and radial flux
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3 kV NPC converter from
Alstom or ABB
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Trends
2002
no
gear-box
Design Concept
Fixed speed (Stall or active stall regulation, fixed
speed operation, gearbox, pole-switchable
asynchronous
Dynamic slip control (Limited variable speed, pitch
regulation, gearbox, pole-switchable asynchronous
generators with variable slip)
Doubly-fed generator (Variable speed operation,
pitch control, gearbox, double-fed generator utilizing
power electronics in the inverter)
Direct-driven variable speed synchronous
(generators with large-diameter synchronous ring
generator, including pitch control, but no gearbox,
utilizing power electronics in
the inverter)
Total
World-Market Share
28%
5%
47%
20%
100%
- Power electronics is now in wind turbines
- Direct-driven genertaor market share is growing
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind turbine systems control
Basic power conversion and control:
Mechanical power
Electrical power
Wind power
Rotor
Gearbox (obtional)
Power converter
(obtional)
Generator
Supply grid
Consumer
Power conversion &
power control
Power transmission
Power conversion &
power control
Power conversion
Power transmission
Electrical control
Power control
Pref
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Qref
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind turbine systems control
Basic demands:
Electrical:
• Interconnection (conversion, synchronization)
• Overload protection
• Active and reactive power control
Mechanical:
• Power limitation (pitch)
• Maximum energy capture
• Speed limitation/control
• Reduce acoustical noise
Control loops with different bandwidth
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind turbine systems control
Induction
generator
DC
AC
Gear
DC
Pitch
vra,vrb ,vrc
ira,irb ,irc
sra,srb ,src
Power control
Grid
AC
sga,sgb ,sgc
vga,vgb ,vgc
i ,igb ,igc
ga
Grid control
- Controllers (internal)
- Modulation
- Overall system control
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind turbine systems control
Control of permanent magnet synchronous generator system
CARATTERISTICA DI CONTROLLO
6000
5000
60/(2*pi)
1
T*
Coppia [N*m]
4000
1
wm
14 m/s
3000
12 m/s
2000
10 m/s
9 m/s
1000
8 m/s
4 m/s
0
0
20
40
60
80
5 m/s
100
6 m/s
7 m/s
120
140
160
180
200
Velocità rotore [rpm]
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind turbine systems control
Control of synchronous generator system
C
PWM
controller
i


i*

PLL
Voltage
controller
vdc


vdc*
- Control of active and reactive power
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind turbine systems control
Control of doubly-fed induction generator system
Transformer
DFIG
vra,vrb ,vrc
ira,irb ,irc
Rotor
converter
Grid
converter
AC
DC
sga,sgb ,sgc
Grid control
Rotor control
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Qref
AC
DC
sra,srb ,src
Pref
vga,vgb ,vgc
i ,i ,i
ga gb gc
vDC
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Detailed example
Operating range
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Wind turbine systems control
Control of doubly-fed induction generator system (generator-side)
P
a s
e
m
PI
cont
ol
r
er

P
f
e
r
PI
cont
ol
r
er
i
Ps  
3 Lm
 vs irq 
2 Ls
i
i
i

3 Lm  vs
Qs 
vs 
 ird 
2 Ls  2 fLm

v
q
r

k
+ k
Ts
·
k
+k
T·
s
q
r
2
a
r
b
r

3
c
r

s
s
s
r
a
r
b
r
c

i
Q
e
r
f

k
+ k
T·
s
Q
e a
m
s
PI
cont
ol
r
er

d
r
v
d
r
k
+k
T·
s
PI
cont
ol
r
er

- Complete control of active and reactive
power
Marco Liserre
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Detailed example
Basic power flow
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Photovoltaic systems
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
PV Inverter Topologies
on the LF side
with isolation
with boost
on the HF side
transformerless
PV
Inverters
without boost
(central inverters)
transformerless
• PV dc voltage typical low for string inverters  boost needed for low power
• For high power (>100 kW) central PV inverters w/o boost, typical threephase FB topologies with LV-MV trafo
• Galvanic isolation necessary in some countries
• LF/HF transformer (cost-volume issue)
• A large variety of topologies
• The optimal topology is not matured yet as for drives
• Transformerless topologies having higher efficiency are emerging and the
grid regulations are changing in order to allow them
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
PV inverters with boost converter and isolation
DC
PV
Array
DC
PV
Array
Grid
DC
AC
Filter
Boost without trafo
Filter
FB inverter
S1
S5
D1 S3
Filter LF Trafo Grid
S2
D2
S4
PV Array
D3
D5
AC
DC
Grid
AC
DC
AC
On high frequency (HF) side
On low frequency (LF) side
PV Array
DC
Filter
FB boost with HF trafo
S5
D5 S7
D7
Filter
FB inverter
S1
D1 S3
Filter
Grid
D3
L
L
N
N
D4
S6
D6 S8
D8
S2
D2
S4
D4
VPE
VPE
Boosting inverter with LF trafo based on boost converter
Boosting inverter with HF trafo based on FB boost converter [2]
Both technologies are on the market! Efficiency 93-95%
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Transformerless PV inverters with boost
DC
PV
Array
DC
Grid
DC
AC
•FB inverter + boost
• Typical configuration
•Time
sharing
configuration
Filter
Filter
FB inverter
Boost without trafo
PV Array
PV Array
Filter
Boost without trafo
Filter
FB inverter
S1
S5
D1 S3
Filter
S1
D3
L
D5
Filter
S5
D1 S3
D3
L
D5
N
N
S2
VPE
Leakage circulating current
• Efficiency >95%
•Leakage current problem
•Safety issue
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S2
D2
S4
Grid
Grid
D4
VPE
D2
S4
D4
Leakage circulating current
•Efficiency > 96%
•Extra diode to bypass boost when Vpv > Vg
•Boost with rectified sinus reference
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Frequency analysis of voltage to earth Vpe for
FB with UP and BP PWM switching
VAB, VPE and IPE for FB-UP
Spectrum of voltage to earth
Spectrum of leakage current
Based on ICp and VCp and different frequencies the leakage capacitance was calculated at:
Cp=13.6nF (7.06nF/kWp). Cp is useful in high-frequency analysis and in damping resonances
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
High efficiency topologies derived from Hbridge FB with Bipolar PWM Switching
PV Array
Filter
Basic FB inverter
D1 S3
S1
Filter Grid
PV Array
Filter
D3
VPV
L1
A
Vg
VAB = VPV
S2
D2 S4
A
L
Vg
VAB = - VPV
CPV
L2
B
D3
S3
L1
CPV
D1
S1
VPV
Filter Grid
Basic FB inverter
N
L2
B
D4
D2 S4
L
N
D4
S2
VPE
S1 + S4 = ON
S1 + S4 and S2 + S3 are switched complementary at high frequency.
VPE
S2 + S3 = ON
S1 + S4 and S2 + S3 are switched complementary at high frequency.
 S1 + S4 and S2 + S3 are switched complementary at high frequency (PWM)
 No 0 output voltage possible
 The switching ripple in the current equals 1x switching frequency  large filtering needed
 Voltage across filter is bipolar  high core losses
 No common mode voltage  VPE free for high frequency low leakage current
 Max efficiency 96.5% due to reactive power exchange L1(2)<-> Cpv during freewheeling and due to the
fact that 2 switched are simultaneously switched every switching
 This topology is not suited to transformerless PV inverter due to low efficiency!
Marco Liserre
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Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
PV Array
High efficiency topologies derived from H-bridge FB with
Unipolar PWM Switching
Basic FB inverter
Filter
S1
D1 S3
Filter Grid
PV Array
Filter
Vg
D2 S4
N
S2
VPE
Vg > 0, Ig >0. S2, S4 and D2 = ON
Basic FB inverter
S1
D1 S3
Filter Grid
Filter
L1
D1
S1
L
Vg
VAB = 0
N
VPE
Filter Grid
D4
D2 S4
S2
N
L2
B
D4
D2 S4
Basic FB inverter
D3
D3
L
Vg > 0, Ig > 0. S1 and S4 = ON
PV Array
D1 S3
CPV
L2
B
D4
Vg
VAB = VPV
CPV
L2
Filter Grid
A
L
VAB = 0
B
Filter
S1
A
CPV
PV Array
Basic FB inverter
Filter
VPV
L1
A
VPE
PV Array
D3
VPV
L1
S2
D1 S3
S1
D3
VPV
Filter Grid
Basic FB inverter
Vg > 0, Ig >0. S1, S3 and D3 = ON
PV Array
Basic FB inverter
Filter
S1
D3
D1 S3
Filter Grid
D3
S3
VPV
VPV
L1
L1
A
L1
A
A
Vg
L
VAB = 0
CPV
D2 S4
Vg
VAB = - VPV
CPV
L2
B
S2
VPV
N
D2 S4
D4
Vg
N
L2
B
D4
L
VAB = 0
CPV
L2
B
L
S2
D2 S4
N
D4
S2
VPE







Vg < 0, Ig <0. S1, S3 and D1 = ON
VPE
Vg < 0, Ig < 0. S2 and S3 = ON
VPE
Vg < 0, Ig < 0. S2, S4 and D4 = ON
Leg A and Leg B are switched with high frequency with mirrored sinusoidal reference
Two 0 output voltage states possible: S1 and S2 = ON and S3 and S4 = ON
The switching ripple in the current equals 2x switching frequency  lower filtering needed
Voltage across filter is unipolar  low core losses
VPE has switching frequency components  high leakage current and EMI
Max efficiency 98% due to no reactive power exchange L1(2)<-> Cpv during freewheeling
This topology is not suited to transformerless PV inverter due to high leakage!
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
High efficiency topologies derived from H-bridge FB with
Hybrid PWM Switching
PV Array
Filter
Filter Grid
Basic FB inverter
D1
S1
S3
PV Array
Basic FB inverter
Filter
S1
D3
VPV
L1
A
A
Vg
VAB = VPV
CPV
L
N
S2
D1
S1
D4
D2 S4
VPE
Vg > 0, Ig >0. S1, S3 and D3 = ON.Leg A switched at 50 Hz, Leg B at 16 kHz
Filter Grid
Basic FB inverter
L
N
L2
B
D4
D2 S4
VPE
Vg > 0, Ig > 0. S1 and S4 = ON. Leg A switched at 50 Hz, Leg B at 16 kHz
Filter
Vg
VAB = 0
CPV
L2
B
PV Array
D3
VPV
L1
S2
D1 S3
Filter Grid
PV Array
Basic FB inverter
Filter
S1
D3
D1 S3
Filter Grid
D3
S3
VPV
VPV
L1
L1
A
A
Vg
VAB = - VPV
CPV
D2 S4
Vg
D4
L
VAB = 0
CPV
L2
B
L
N
L2
B
S2
D2 S4
N
D4
S2
VPE
Vg < 0, Ig < 0. S2 and S3 = ON. Leg A switched at 50 Hz, Leg B at 16 kHz
VPE
Vg < 0, Ig < 0. S2, S4 and D4 = ON. Leg A switched at 50 Hz, Leg B at 16 kHz
 Leg A is switched with grid low frequency and Leg B is switched with high PWM frequency
 Two 0 output voltage states possible: S1 and S2 = ON and S3 and S4 = ON
 The switching ripple in the current equals 1x switching frequency  high filtering needed
 Voltage across filter is unipolar  low core losses
 VPE has square wave variation at grid frequency  high leakage current and EMI
 High efficiency 98% due to no reactive power exchange L1(2)<-> Cpv during freewheeling and due to
lower frequency switching in one leg.
 This topology is not suited to transformerless PV inverter due to high leakage!
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
High efficiency topologies derived from H-bridge H5 (SMA)– ηmax=98%
PV Array
Filter
S5
D5
Filter Grid
H5 FB inverter
D1 S3
S1
PV Array
Vg
L
S5
VAB = 0
CPV
VPE
Vg > 0. S5 and S4 = OFF, S1 and D3 =ON
S5 and S4 are switched at high frequency. S1 is switched at line frequency
Filter Grid
PV Array
Filter
S5
D5
D5
D1 S3
S1
D4
D2 S4
S2
D3
Filter Grid
H5 FB inverter
D1 S3
S1
D3
VPV
VPV
L1
L1
A
A
Vg
VAB = - VPV
CPV
L
CPV
L2
D2
S4
N
D2
S4
D4
D4
VPE
VPE
L
N
S2
S2
Vg
VAB = 0
B
L2
B
N
L2
B
D4
H5 FB inverter
L
Vg
VPE
Vg > 0. S5, S1 and S4 =ON
S5 and S4 are switched at high frequency. S1 is switched at line frequency
Filter
L1
N
L2
D2 S4
D3
A
VAB = + VPV
B
D1 S3
S1
D5
A
CPV
Filter Grid
H5 FB inverter
VPV
L1
S2
S5
D3
VPV
PV Array
Filter
Vg < 0. S5, S2 and S3 = ON
S5 and S2 are switched at high frequency. S3 is switched at line frequency
Vg < 0. S5 and S2 = OFF, D1 and S3 = ON
S5 and S2 are switched at high frequency. S3 is switched at line frequency
 Extra switch in the dc link to decouple the PV generator from grid during zero voltage
 Two 0 output voltage states possible: S5 = OFF, S1 = ON and S5 = OFF, S3 = ON
 The switching ripple in the current equals 1x switching frequency  high filtering needed
 Voltage across filter is unipolar  low core losses
 VPE is sinusoidal with grid frequency component  low leakage current and EMI
 High max. efficiency 98% due to no reactive power exchange as reported by Photon Magazine for SMA
SunnyBoy 4000/5000 TL single-phase
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
High efficiency topologies derived from H-bridge HERIC
(Sunways)-ηmax=98%
PV Array
Filter
Filter Grid
HERIC FB inverter
D1
S1
S3
PV Array
Filter
D1 S3
S1
VAB = + VPV
D3
VPV
VAB = 0
D3
L1
A
D+
S+
Vg
L
S+
D+
D-
S-
Vg
L
CPV
CPV
S-
D-
S2
D2
N
L2
B
D4
S4
HERIC FB inverter
D3
S4
Filter
HERIC FB inverter
VAB = - VPV
VPV
D1 S3
L1
A
A
S+
D+
D-
S-
Vg
L
B
S4
D+
D-
S-
Vg
L2
B
L2
S+
L
CPV
CPV
D2
VAB = 0
D3
VPV
L1
S2
Filter Grid
Filter Grid
S1
D1 S3
S1
D4
Vg > 0. S1 and S4 =OFF. S+ and D- = ON
VPE
S5 and S4 are switched at high frequency. S+ is switched at line frequency
PV Array
Filter
D2
N
L2
B
S2
VPE
Vg > 0. S1 and S4 =ON, S+ = ON
S1 and S4 are switched at high frequency. S+ is switched at line frequency
VPE
Filter Grid
VPV
L1
A
PV Array
HERIC FB inverter
N
N
S2
D2
S4
D4
D4
Vg < 0. S2 and S3 =ON. S- = ON
S2 and S3 are switched at high frequency. S- is switched at line frequency
Vg < 0. S2 and S3 =OFF. S- and D+ = ON
VPE
S2 and S3 are switched at high frequency. S- is switched at line frequency
 Two 0 output voltage states possible: S+ and D- = ON and S- and D+ = ON
 The switching ripple in the current equals 1x switching frequency  high filtering needed
 Voltage across filter is unipolar  low core losses
 VPE is sinusoidal has grid frequency component  low leakage current and EMI
 High efficiency 98% due to no reactive power exchange as reported by Photon Magazine for Sunways AT
series 2.7 – 5 kW single-phase
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
High efficiency topologies derived from H-bridge FB – DC Bypass
(Ingeteam)-ηmax=96.5%
Filter Grid
FB inverter
Filter DC Bypass
PV Array
S5
S1
D5
D1 S3
D3
L1
D+
D3
Vg
S2
Vg
VAB = - VPV
B
DS2
D6
L
N
L2
CPV2
D4
D2 S4
A
L
B
D-
D+
N
L2
CPV2
L1
VPV
A
VAB = VPV
D4
D2 S4
D6
VPE
S6
Vg > 0. S5, S6,S1 and S4 = ON
S5 and S6 are switched at high frequency, S1 and S4 at line frequency
Filter Grid
FB inverter
Filter DC Bypass
S6
Vg < 0. S5, S6,S1, S2 and S3 = ON
S5 and S6 are switched at high frequency, S2 and S3 at line frequency
PV Array
Filter Grid
FB inverter
Filter DC Bypass
S5
S5
S1
D5
D1 S3
D3
S1
D5
CPV1
D1 S3
D3
CPV1
L1
VPV
D+
Vg
L2
CPV2
S2
D2 S4
D+
Vg
VAB = 0
N
L2
CPV2
S2
D6
L
N
B
D-
D4
S6
Vg > 0. S1 and S4 = ON
S5 and S6 are switched at high frequency, S1 and S4 at line frequency
A
L
B
D-
L1
VPV
A
VAB = 0
VPE
D1 S3
CPV1
VPV
PV Array
S1
D5
CPV1
VPE
Filter Grid
FB inverter
Filter DC Bypass
PV Array
S5
D2 S4
D4
D6
VPE
S6
Vg < 0. S2 and S3 = ON
S5 and S6 are switched at high frequency, S2 and S3 at line frequency
 Two extra switches switching with high frequency and 2 diodes bypassing the dc bus. The 4 switches in FB
switch at low fsw
 Two 0 output voltage states possible by “natural clamping# of D+ and D The switching ripple in the current equals 1x switching frequency  high filtering needed
 Voltage across filter is unipolar  low core losses
 VPE is sinusoidal and has grid frequency component  low leakage current and EMI
 High max efficiency 96.5% due to no reactive power exchange as reported by Photon Magazine for Ingeteam
Ingecon Sun TL series (2.5/3.3/6 kW, single-phase)
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
High efficiency topologies derived from H-bridge REFU
ηmax=98% PV DC Link L Boost DC Link H
Array
VDC
HB Boost Bypass
Grid
PV DC Link L Boost DC Link H
Array
VDC
VAB = + VPV/2
S3
S1
AC Bypass Filter
VPV
VPV
Vg
S-
AC Bypass Filter
Grid
S-
S2
VPE
PV DC Link L Boost DC Link H
Array
VDC
S2
HB Boost Bypass
VPE
Grid
VPV
PV DC Link L Boost DC Link H
Array
VDC
Vg
S-
HB Boost Bypass
VPE
Grid
PV DC Link L Boost DC Link H
Array
VDC
L
S-
HB Boost Bypass
S2
VPE
L
A
L
Vg
B
S+
S-
L
S+
N
S4
Vg < 0, VPV < |Vg| Ig < 0. S4 and S- =ON
S2 is switched at high frequency. S- is switched at line frequency
Grid
VAB = 0
S3
N
S4
AC Bypass Filter
VPV
Vg
B
S4
S1
L
A
S+
Vg < 0,VPV > |Vg| Ig < 0. S2 and S- =ON
S2 is switched at high frequency. S- is switched at line frequency
S+
Vg > 0, Ig > 0. S+ =ON
S+ is switched at line frequency
VAB = - VDC/2
S3
N
S2
VPE
AC Bypass Filter
L
N
S2
VPV
L
B
S-
S4
S1
A
Vg
S+
Vg > 0, VPV < |Vg|, Ig > 0. S3 and S+ =ON
S3 is switched at high frequency. S+ is switched at line frequency
VAB = - VPV/2
S3
S1
AC Bypass Filter
L
N
S4
Vg > 0, VPV < |Vg|, Ig > 0. S1 and S+ =ON
S1 is switched at high frequency. S+ is switched at line frequency
VAB = 0
S3
B
N
Grid
A
L
Vg
B
AC Bypass Filter
VPV
L
L
HB Boost Bypass
S1
A
S+
PV DC Link L Boost DC Link H
Array
VDC
VAB = + VDC/2
S3
S1
L
A
B
HB Boost Bypass
S2
VPE
S4
Vg < 0, Ig < 0. S- =ON
S- is switched at line frequency
 Three-level output. Requires double PV voltage input in comparison with FB but it include time-shared boost
 Zero voltage is achieved by shortcircuiting the grid using the biderectional switch
 The switching ripple in the current equals 1x switching frequency  high filtering needed
 Voltage across filter is unipolar  low core losses
 VPE without high frequency component  low leakage current and EMI . No L in neutral!
 High max efficiency 98% due to no reactive power exchange, as reported by Photon Magazine for Refu Solar
RefuSol (11/15 kW, three-phase)
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
High efficiency topologies derived from Hbridge Summary
• Actually both HERIC, H5, REFU and FB-DCBP topologies are converting the 2 level FB (or
HB) inverter in a 3 level one.
• This increases the efficiency as both the switches and the output inductor are subject to
half of the input voltage stress.
• The zero voltage state is achieved by shorting the grid using higher or lower switches of
the bridge (H5) or by using additional ac bypass (HERIC or REFU) or dc bypass (FB-
DCBP).
• H5 and HERIC are isolating the PV panels from the grid during zero voltage while REFU
and FB-DCBP is clamping the neutral to the mid-point of the dc link.
• Both REFU and HERIC use ac by-pass but REFU uses 2 switches in anti- parallel and
HERIC uses 2 switches in series (back to back). Thus the conduction losses in the acbypass are lower for the REFU topology.
• REFU and H5 have slightly higher efficiencies as they have only one switch switching with
high-frequency while HERIC and FB_DCBP have two.
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
High efficiency topologies derived from NPC
Half Bridge Neutral Point Clamped (HB-NPC)-ηmax=98% PV Array
Filter
NPC inverter
Filter
S1
Grid
PV Array
D1
CPV1
S2
D+
D1
S2
D2
VPV/2
VAB = + VPV/2
VPV
S1
CPV1
VPV/2
Filter
NPC inverter
Filter
VAB = 0
VPV
D2
D+
L1
B
CPV2
D-
D3
CPV2
D-
Filter
S1
CPV1
VPV
S2
D+
VPE
N
Grid
D4
Filter
NPC inverter
Filter
S1
D1
S2
D2
CPV1
VPV/2
VAB = - VPV/2
D+
L1
B
A
S3
CPV2
D-
D3
D-
S3
L
D3
VPV/2
Vg
S4
D4
Vg < 0, Ig < 0. S3 and S4 =ON, S1 and S2 = OFF
S4 is switched at high frequency. S3 is switched at line frequency
A
CPV2
Vg
S4
VPE
L1
B
L
VPV/2
Grid
VAB = 0
VPV
D2
N
Vg > 0, Ig > 0. S2 =ON, D+ = ON, S1, S3 and S4 = OFF
S1 is switched at high frequency. S2 is switched at line frequency
PV Array
D1
VPV/2
D3
Vg
S4
NPC inverter
L
VPV/2
D4
Vg > 0, Ig > 0. S1 and S2 =ON, S3 and S4 = OFF
S1 is switched at high frequency. S2 is switched at line frequency
Filter
A
S3
Vg
S4
PV Array
B
L
VPV/2
VPE
L1
A
S3
Grid
N
VPE
D4
Vg > 0, Ig > 0. S3 =ON, D- = ON, S1, S2 and S4 = OFF
S4 is switched at high frequency. S3 is switched at line frequency
N
 Three-level output. Requires double PV voltage input in comparison with FB. Typically needs boost.
 Two 0 output voltage states possible: S2 and D+ = ON and S3 and D- = ON. For zero voltage during Vg>0,
Ig<0, S1 and S3 switch in opsition and S2 and S4 for Vg<0, Ig>0
 The switching ripple in the current equals 1x switching frequency  high filtering needed
 Voltage across filter is unipolar  low core losses
 VPE is equal –Vpv/2 without high frequency component  low leakage current and EMI . No L in N!
 High max efficiency 98% due to no reactive power exchange, as reported by Danfoss Solar TripleLynx series
(10/12.5/15 kW)
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
High efficiency topologies derived from NPC
Conergy NPC -ηmax=96% -
PV Array
Filter
Clamping Switch HB inverter Filter
S1
PV Array
Grid
Filter
S1
D1
CPV1 VPV/2
Clamping Switch HB inverter Filter
D1
CPV1 VPV/2
VAB = VPV/2
VPV
Grid
VAB = -VPV/2
VPV
S+
D+
L1
B
S-
D-
L1
B
A
CPV2 VPV/2
S+
D+
A
S-
D-
CPV2 VPV/2
Vg
S2
VPE
N
Vg > 0, Ig > 0. S1 =ON, S+, S- and S2 = OFF
PV Array
Filter
Clamping Switch HB inverter Filter
S1
CPV1 VPV/2
Vg
S2
D2
VPE
D+
L1
D-
CPV2 VPV/2
S-
D1
S+
L1
B
A
A
D-
S-
Vg
Vg
S2
VPE
S2
D2
Vg > 0, Ig > 0. S+ =ON, S-, S1 and S2 = OFF
Grid
VAB = 0
VPV
D+
S+
B
CPV2 VPV/2
Clamping Switch HB inverter Filter
CPV1 VPV/2
VAB = 0
VPV
Filter
S1
D1
N
Vg < 0, Ig > 0. S2 =ON, S+, S- and S2 = OFF
PV Array
Grid
D2
N
VPE
D2
Vg < 0, Ig < 0. S- =ON, S+, S1 and S2 = OFF
N
 Only 4 switches needed with 2 of them (S+ and S-) rated only Vpv/4
 Three-level output. Requires double PV voltage input in comparison with FB. Typically needs boost.
 Two 0 output voltage states possible using the bidirectional clamping switch (S+ and S-)
 The switching ripple in the current equals 1x switching frequency  high filtering needed
 Voltage across filter is unipolar  low core losses
 VPE is equal –Vpv/2 without high frequency component  low leakage current and EMI . No L in N!
 High max efficiency 96.1% due to no reactive power exchange, as reported by Conergy IPG series (2-5 kW
single-phase)
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
High efficiency topologies derived from NPC
Summary
• The classical NPC and its “variant” Conergy-NPC are both three-level topologies featuring
the advantages of unipolar voltage across the filter, high efficiency due to disconnection of
PV panels during zero-voltage state and practical no leakage due to grounded DC link midpoint.
• Due to higher complexity in comparison with FB-derived topology, these structures are
typically used in three-phase PV inverters with ratings over 10 kW (mini-central).
• These topologies are also very attractive for high power in the range of hundreds of kW)
central inverters) where the advantages of multi-level inverters are even more important.
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
PV Inverter Topologies -Conclusions
• The “race” for higher efficiency PV inverters has resulted in a large variety of
“novel” transformerless topologies derived from H-Bridge with higher efficiency and
lower CM/EMI (H5, HERIC)
• Equivalent high-efficiency can be achieved with 3-level topologies (ex NPC)
•Today more than 70% of the PV inverters sold on the market are transformerless
achieving 98% max conversion efficiency and 97.7% “european” (weighted)
efficiency
• Further improvements in the efficiency can be achieved by using SiC MosFets. ISE
Fraunhofer-Freiburg reported recently 98.5% efficiency (25% reduction in switching
+ conduction losses)
• For 3-phase systems the trend is to use 3 independent controlled single-phase
inverters like 3xH5 or 3xHERIC but 3FB-SC and 3NPC (not proprietary) are also
present on the market. 3NPC achieve higher efficiency 98%
•The general trend in PV topologies is “More Switches for Lower Losses”
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Control Structure Overview
L
+
PV Panels
String
dc-ac
PWM-VSI
dc-dc
boost
C
LCL
Low pass
filter
Trafo
&
Grid
N
PWM
Vdc
PWM
IPV
VPV
Vdc
Control
Ig
Grid
Synchronization
Current
Control
Vg
Basic functions (grid conencted converter)
MPPT
Anti-Islanding
Protections
Grid /PV plant
Monitoring
PV specific functions
Active filter
control
MicroGrid
Control
Grid support
(V,f,Q)
Ancillary functions
Basic functions – common for all gridconnected inverters
Grid current control
THD limits imposed by standards
Stability in case of grid impedance
variations
Ride-through grid voltage
disturbances (not required yet!)
DC voltage control
Adaptation to grid voltage variations
Ride-through grid voltage
disturbances (optional yet)
Grid synchronization
Required for grid connection or reconnection after trip.
Marco Liserre
PV specific functions – common for PV
inverters
Maximum Power Point Tracking – MPPT
Very high MPPT efficiency in steady state
(typical > 99%)
Fast tracking during rapid irradiation
changes (dynamical MPPT efficiency)
Stable operation at very low irradiation
levels
Anti-Islanding – AI as required by standards
(VDE0126, IEEE1574, etc)
Grid Monitoring
Operation at unity power factor as
required by standards
Fast Voltage/frequency detection
Plant Monitoring
Diagnostic of PV panel array
Partial shading detection
Ancillary Support – (future?)
Voltage Control
Frequency control
Fault Ride-through
Q compensation
DVR
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Introduction to Maximum Power Point Tracking
- MPPT
The MPP is affected by temperature and
irradiance.
0
0
All algorithms are based on the fact that,
looking at the power characteristic, at the
left of the MPP the dP/dV > 0, at the right
dP/dV < 0 and at MPP dP/dV = 0
Pcel l [W]
2
1.5
15 o C
40 o C
o
75 C
600 W/m 2
2
2.5
The MPPT is a nonlinear and time-varying
system that has to be solved.
1000 W/ m2
4
I cell [A]
The task of MPPT is to track this MPP
regardless of weather or load conditions
so that the PV system draws maximum
power from the solar array.
6
200 W/m 2
0.1
0. 2
0.3
0.4
Cell voltage [V]
0.5
0.6
o
15 C
o
40 C
75 o C
0.7
MPP
1
0.5
0
0
0.1
0. 2
0.3
0.4
Cell voltage [V]
0.5
0.6
0.7
dP/dV = 0
P
dP/dV > 0
MPP
dP/dV < 0
dP/dV = 0, MPP
Marco Liserre
V
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
MPPT Comparison

Most common methods:






Perturb&Observe – PO
Incremental Conductance – IC
Constant Voltage
Preliminary results indicate that IC method compares favorably
with PO and CV methods
Still PO is preferred due to implementation simplicity
Combined PO+CV is best!
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Typical control structure for dual-stage PV
inverter
 The MPPT is implemented in the dc-dc boost converter.
 The output of the MPPT is the duty-cycle function. As the dc-link
voltage VDC is controlled in the dc-ac inverter the change of the dutycycle will change voltage at the output of the PV panels, VPV as:
VDC  K
VPV
1 D
 The dc-ac inverter is a typical current controlled voltage source
inverter (VSI) with PWM and dc-voltage controller.
 The power feedforward requires communication between the two
stages and improves the dynamics of MPPT
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Typical control structure for single-stage PV inverter
Vac
I pv
V pv
MPPT
*
V pv


PV
array
dc voltage
controller
Iˆr

PLL
Iˆref
sin 
I ref
current
controller

PWM
dc-ac
inv
I
Ppv
VacR MS
Ppv  2
Iˆ*ref
VacRMS
 In these topologies -which are becoming more and more popular in
countries with low grid voltage (120V) like Japan and thus the voltage from
the PV array is high enough- the MPPT is implemented in the dc-ac inverter
 Also in topologies with boost trafo on ac side (SMA)
 The output of the MPPT is the dc-voltage reference. The output of the dcvoltage controller is the grid current reference amplitude. The power
feedforward improves the dynamic response as MPPT runs at a slow
sampling frequencies (typ. 1 Hz).
A PLL is used to synchronize the current reference with the grid voltage
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Practical PV inverter control implementation
Dual-stage full-bridge PWM inverter with LCL filter and grid trafo
Ipv
+
L
U
Ig
PV
P anels
String
V pv
D C/D C
C onverter
F ull- bridge
Inverter
V SI- P W M
V dc
C
LC L
Low pass
filter
V
Vg
Isolation
Transform er
Grid
N
Ipv
PW M
MPPT
Vpv
Vdc
V d c ref

dc
Gdc
+
PW M
ˆI
r
dc  1
2

Ir e f
+
s in
+
-
Ig
GC
*
V ac
 dc  1
2
dc
Vdc
P LL
Control structure
Vg
•The current controller Gc can be of PI or PR (Proportional Resonant) type
•Other non-linear controllers like hysteresis or predictive control can be used
for current control
•The dc voltage controller can be P type due to the integration effect of the
typical large capacitor
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
PV Inverter Control Structures - Conclusions







The most typical control structure is the current controlled voltage source
inverter with PWM
Typically boost dc-dc converter is required
The MPPT is a necessary feature in order to extract the maximum power
from a panel array at any conditions of irradiation and temperature.
PO and INC are the most used ones. PO+CV is also possible
According to the topology (dual- or single-stage) the MPPT is implemented
in the dc-dc converter or in the dc-ac inverter
PR current controller better than PI control for sinusoidal references
PLL is typically required for synchronization
Marco Liserre
[email protected]
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES)
Acknowledgment
Part of the material is or was included in the present and/or past editions of the
“Industrial/Ph.D. Course in Power Electronics for Renewable Energy Systems –
in theory and practice”
Speakers: R. Teodorescu, P. Rodriguez, M. Liserre, J. M. Guerrero,
Place: Aalborg University, Denmark
The course is held twice (May and November) every year
Marco Liserre
[email protected]