|
Copyright
©Denis Lenardic 2001-2010 All Rights Reserved
Thursday
11th Mar, 2010
07:02
This page was last time updated on
7th Mar, 2010
|
Inverters
"When wealth is lost, nothing is lost; When health is lost, something is lost;
When character is lost, all is lost."
(German proverb)
Photovoltaic inverters produced by Siemens (courtesy:
Siemens).
Where are you: Home > Inverters
Inverters are used for DC voltage to AC voltage conversion. According to output
voltage form they could be rectangle, trapezoid or sine shaped. The
most expensive, yet at the same time the best quality inverters,
output voltage in sine wave. Inverter input voltage depends on inverter power,
for small power of some 100 W the voltage is 12 or 24 V, and 48 V or even more for higher powers. Large inverters could be connected in
parallel when higher powers are required. For large systems 3-phase inverters are available in the market. Inverters connecting a PV
system and the public grid are purposefully designed, allowing energy transfers to and from the public grid. According to working principle
we have many different types of inverters, such as central inverters for wide power range from 1 kW to up to 100 kW or even more, string
inverters and module inverters. Central inverters are used in large applications. Many times they can be connected according to the
"master-slave" criteria, when the succeeding inverter switches on only when enough solar radiation is available or in case
of main inverter malfunction. Inverters connected to module strings are used in wide power range applications allowing for more reliable
operation. Module inverters are used in small photovoltaic systems. Such solutions are applicable to larger systems, however, in practice
cheaper, and less reliable solution of central inverter or string inverters are used. Special design inverters are available for the
purposes of hybrid systems. In most cases a powerful inverter includes charge regulator electronics, and not only the inverter.
Modern inverters are the most sophisticated electronic devices implemented in photovoltaic systems. On top of high reliable
electronics, which must be used, great care should also be taken on lightning protection. Inverters are based on microprocessor circuits,
classic or RISC, and on power MOS or IGBT transistors.
Other topics:
Monitoring & control >
Charge controllers >
Batteries
|
|
|
Inverters - features and applications
|
|
Technical parameters
The most important inverter parameters are rated DC and AC power,
MPP Voltage range, maximum DC/AC current and voltage and rated DC/AC current and voltage.
Other parameters are power in standby mode, power in sleeping (night) mode,
power factor, distortion, noise level etc.
The following parameters can usually be found in inverter data sheets:
Rated DC voltage - VDC
MPP voltage range - VMPP
Maximum DC voltage - VDCmax
Switch off voltage - VDCoff
Rated AC voltage - VAC
Rated DC current - IDC
Maximum DC current - IDCmax
Rated AC current - IAC
Maximum AC current - IACmax
Rated DC power - PDC
Maximum DC power - PDCmax
Rated AC power - PAC
Maximum AC power - PACmax
Power factor - cos φ
DC power Off - PDCoff
DC power On - PDCon
Standby DC power - PDCStandBy
Night mode DC power - Pnight
Noise level - dBA
Temperature range - T
Total Harmonic Distortion - k
Inverters are most sophisticated widely used electronic devices. SMA's inverter
electronic control section is presented on the picture above (courtesy:
SMA Solar Technology AG).
Inverter - main parts
Main parts of an inverter are presented on the picture below - example of a 2100TL
SMA's inverter without output transformer:
Input, MPP unit, DC/DC converter, switching
bridge, output inductance, output DC current detection (protection function), ENS protection.
Control functions includes grounding monitoring, optional display, thermal and overvoltage protection,
communication ports (RS232, RS485, wireless etc.).
Input stage of a grid-tied inverter
is usually buck or similar converter. With appropriate MPP algorithm
conversion in at maximum power can be attained. For more information about
MPP algorithms and MPP trackers see literature section below.
Inverter efficiency
Inverter efficiency is a ratio of AC power and DC power:
η = PAC / PDC
To make comparison of different inverters and/or inverters that are operating under
different climatic conditions possible, "Euro η" efficiency was defined:
ηEURO = 0.03×η5% +
0.06×η10% +
0.13×η20% +
0.1×η30%
0.48×η50% +
0.2×η100%
Voltage and current in line-commutated (top) in PWM self commutated inverters (middle) and in cascade
inverters (bottom)
|
Inverter technologies
There are various types of inverters used in photovoltaic systems.
In line-commutated inverters thyristors as switching elements are used.
Line-commutated inverters are not suitable for use in standalone systems because
AC voltage is required to turn off thyristors. Second group are
self-commutated inverters which can operate without AC grid voltage. In this inverters IGBT,
MOSFET or GTO (Gate Turn Off) thyristors are used.
According to the inverter operation, voltage and current control scheme are distinguished.
Because of some advantages in grid-connected inverters in most cases current control scheme
is applied. Advantages are higher power factor, better transient current suppression, short
circuit current is limited to rated AC current. AC current of a line-commutated inverter is
a simple rectangle form which must be filtered with low pass output filter. AC current of a
self-commutated inverter is most common PWM signal and in cascade inverters sum of partial
rectangle forms which together represent quite good reconstruction of sine current as shown
in the picture.
More about inverter technologies
IEA-PVPS:
Grid-Connected Photovoltaic Power Systems: Survey of Inverter and related Protection Equipment;
Report IEA PVPS T5-05: 2002, December 2002 (800 kB).

Thyristor and MOSFET bridge as switching element. Thyristor bridges are used
in line-commutated inverters. In self-commutated inverters MOSFETs, IGBTs or GTO thyristors are most common switching elements used.
Inverter - main parts
Main parts of an inverter are presented on the picture below - example of a 2100TL
SMA's inverter without output transformer:
Input, MPP unit, DC/DC converter, switching
bridge, output inductance, output DC current detection (protection function), ENS protection.
Control functions includes grounding monitoring, optional display, thermal and overvoltage protection,
communication ports (RS232, RS485 for example). For more information about MPP operation please see
charge regulators section.
SB 2100TL inverter (source/copyright:
SMA Solar Technology AG)
Islanding and line disconnect
Islanding operation can be detected or monitored by passive or
active islanding detection method. Passive method includes detecting rate of change
of frequency, voltage phase jump and three-phase voltage drop monitoring. With active
islanding operation detection method frequency shift, active frequency drift - AFD,
ENS (impedance measurement), and reactive power fluctuation are detected and monitored.
ENS disconnect unit is a standalone unit which disconnects inverter from the grid.
ENS = Selbsttätig wirkende Freischaltstelle mit zwei voneinander unabhängigen Einrichtungen
zur Netzüberwachung mit zugeordneten allpoligen Schaltern in Reihe.
Other description for such kind of protection is:
MSD = Mains Monitoring Units with Allocated All-pole Switching
Devices.
Multi string inverter - each string is connected to its own input (source/copyright:
SMA Solar Technology AG)
|
|
Inverters - interconnection and control
|
|
Centralized or distributed inverter solutions: central inverter, "master-slave"
string inverters, "PSC" or "Teamkonzept" connection.
|
|
Test reports available on-line
|
|
Several comprehensive test reports are available on-line. For detailed test reports about some Fronius, SMA, Sputnik and Sunways inverters
please visit web site of PV Labor der HTI Bern, Switzerland. Reports are available as pdf files (about 70 pages each)
in german language.
|
|
Fronius: IG 30,
IG 40
|
|
|
SMA:
SunnyMiniCentral 6000,
SunnyMiniCentral 8000TL
SunnyBoy 3800,
|
|
|
Solar-Fabrik:
Convert 6T
|
|
|
Sunways:
NT 4000
|
|
|
Sputnik Engineering:
SolarMax 2000E,
SolarMax 3000E,
SolarMax 6000E,
SolarMax 6000C,
SolarMax 25C
|
|
|
Inverters - companies
|
|

|
Siemens - a solar power pioneer.
With over 25 years experience Siemens producing and offers PV Inverter in over 20 power ranges,
junction boxes, monitoring software, container solutions, medium voltage transformers and switches.
Languages:
|
|

|
SMA -
SMA Solar Technology AG has been successfully producing
industrial computers, photovoltaic (PV) inverters,
and energy supply systems for 20 years.
Languages:
|
|

|
Conergy -
produces inverters, modules and mounting structures.
Languages:
|
|

|
Fronius -
Fronius has been engaged in solar electronics since 1992,
in particular in the development and production of photovoltaic
inverters for both grid-connected and independent power supplies.
Languages:
|
|

|
SolarEdge Technologies
- SolarEdge provides next generation power conversion electronics that effectively remove
the known system constraints across the photovoltaic energy space. Smart DC ASIC technology
and active electronics enable increased production of clean, grid-ready energy at a lower
cost per watt than any other competitive offering.
Languages:
|
|

|
Solar Max -
Inverters produced by Sputnik Engineering.
Languages:
|
|

|
Elettronica Santerno -
Elettronica Santerno S.p.A., a worldwide leading company in designing and
manufacturing drives, electric motors and frequency converters for industrial
automation and solar inverters for renewable energies.
Languages:
|
|
|
Kaco new energy -
KACO new energy is a powerful partner for system solutions in the field
of current inverters, power electronics and photovoltaics.
Languages:
|
|
|
PV Powered -
Headquartered in Bend, Oregon, PV Powered designs,
manufactures and markets utility interactive photovoltaic inverters for the renewable energy
marketplace. PV Powered's one-of-a-kind StarInverter product line offers PV solutions for
the residential and commercial markets.
Languages:
|
|
|
Xantrex -
Xantrex Technology develops, manufactures and markets advanced
power electronic products. The Xantrex's products
convert raw electrical power from any central,
distributed, or backup power source into high-quality
power required by electronic and electrical equipment.
Languages:
|
|

|
AnswerDrives -
The AnswerDrives SolarGate inverter family has expressly been projected to convert
the direct current electric energy made by photovoltaic panel, in alternating current,
for the directly introduction in the electric net.
Languages:
|
|

|
OutBack Power Systems -
OutBack Power Systems is an engineer-owned, customer focused, power systems
equipment manufacturer.
Languages:
|
|
|
Mastervolt -
Mastervolt is one of the leading manufactures of high quality electrical
systems for marine, mobile, industrial and solar applications in
Europe and beyond.
Languages:
|
|
|
power one -
Magnetek, Inc. produces power control products and systems for communications,
data processing and storage, medical electronics, consumer products,
industrial automation, transportation, energy management and other applications.
Languages:
|
|
|
Centrosolar -
inverter series ranging from 1 to 6 kW, using the latest technology.
Languages:
|
|
|
Panelektron -
Company Panelektron located in Hungary produces
sine wave inverters, solar charge controllers, switch mode power converters,
mains battery chargers and other electronic equipment.
Languages:
|
|
|
Grupo Ingeteam -
Ingeteam Group is made up of 26 companies, all of which are at the technological
forefront in their respective areas.
Languages:
|
|
Inverters - research topics
|
|
|
PV Labor der HTI Bern -
PV laboratory was founded in 1988 and focuses on PV system
technology, mostly on grid-connected PV systems, but also
on stand alone systems. The laboratory is active in education
and in research and development.
Languages:
Webmaster's choice - one of the best inverter research related web sites.
Detailed inverters test reports and monitoring data available on-line. Detailed plant descriptions and
comprehensive literature section.
|
|
Inverters - electronics, application notes
|
|
|
Texas Instruments - Solar Power Inverters
DSC application notes for power inverters.
Languages:
|
|
Literature and more information
|
|
Inverters - general topics
Zacharias, P. (Editor): Use of Electronic-Based Power Conversion for Distributed and
Renewable Energy Sources, ISET Kassel, 2008.
Häberlin, H.: Photovoltaik, Strom aus Sonnenlicht für Verbundnetz und Inselanlagen; VDE Verlag, 2007, ISBN 978-3-8007-3003-2.
Castañer, L., Silvestre, S.: Modelling Photovoltaic Systems Using PSpice®, John Wiley&Sons, 2002, ISBN 0-470-845279.
Inverters - efficiency
Häberlin, H., Schaerf, Ph.: New Procedure for Measuring
Dynamic MPP-Tracking Efficiency at Grid-Connected PV Inverters, 24th European
Photovoltaic Solar Energy Conference, Hamburg, Germany, Sept. 2009.
Valentini, M., Raducu, A., Sera, D., Teodorescu, R.:
PV inverter test setup for European efficiency, static and dynamic MPPT efficiency evaluation,
Optimization of Electrical and Electronic Equipment, 2008. OPTIM 2008, May 2008.
Bower, W. et al:
Performance Test Protocol for Evaluating Inverters Used in Grid-Connected Photovoltaic Systems,
Institute for Sustainable Technology. 2004.
Valentini, M., Raducu, A., Sera, D., Teodorescu, R.: PV Inverter Test Setup
for European Efficiency, Static and Dynamic MPPT Efficiency Evaluation;
Aalborg University, Institute of Energy Technology,
11th International Conference on Optimization of Electrical and Electronic Equipment, 2008.
MPP Tracking
Esram, T., Chapman, P.L.: Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques
IEEE Transactions on Energy Conversion, Vol. 22, No. 2, June 2007.
Salas, V., Olías, E., Barrado, A., Lázaro, A.:
Review of the maximum power point tracking algorithms for stand-alone
photovoltaic systems;
Solar Energy Materials and Solar Cells, Elsevier, January 2006, article available on-line (597 kB).
Koutroulis, E., Kalaitzakis, K., Voulgaris, N.C.: Development of a Microcontroller-Based,
Photovoltaic Maximum Power Point Tracking Control System; IEEE Transactions on Power Electronics, Vol. 16, no. 1, January 2001, p.46-54.
Other
Cramer, G.:
PV-System-Technik Entwicklungsstand und Trends in der dezentralen Elektrifizierung;
SMA Solar Technology AG (518 kB).
Cramer, G., Kleinkauf, W., Ibrahim, M.:
Modulare Systemtechnik für die Netzeinspeisung mit Photovoltaikanlagen;
SMA Solar Technology AG, Institut für Elektrische Energietechnik, Universität Kassel (148 kB).
Cramer, G.:
Dezentrale Netzeinspeisung mit String-Wechselrichtern für das 1 MWp-PV-Dach der Fortbildungsakademie in Herne;
SMA Solar Technology AG (249 kB).
IEA-PVPS:
Grid-Connected Photovoltaic Power Systems: Survey of Inverter and related Protection Equipment;
Report IEA PVPS T5-05: 2002, December 2002 (800 kB).
IEA-PVPS:
International Guideline for the Certification of Photovoltaic System Components and Grid-Connected systems;
Report IEA-PVPS T5-06: 2002, February 2002 (1272 kB).
IEA-PVPS:
Probability of Islanding in Utility Networks due to Grid-Connected Photovoltaic Power Systems;
Report IEA-PVPS T5-07: 2002, September 2002 (1422 kB).
IEA-PVPS:
Risk Analysis of Islanding of Photovoltaic Power Systems within Low Voltage Distribution Networks;
Report IEA PVPS T5-08: 2002, March 2002 (805 kB).
IEA-PVPS:
Evaluation of Islanding Detection Methods for Photovoltaic Utility Interactive Power Systems;
Report IEA PVPS T5-09: 2002, March 2002 (1413 kB).
IEA-PVPS:
Impacts of Power Penetration from Photovoltaic Power Systems in Distribution Networks;
Report IEA-PVPS T5-10: 2002, February 2002 (657 kB).
IEA-PVPS:
Grid-Connected Photovoltaic Power Systems: Power Value and Capacity Value of PV Systems;
Report IEA-PVPS T5-11: 2002, February 2002 (830 kB).
IEA-PVPS:
Utility Aspects of Grid-Connected Photovoltaic Systems;
Report IEA-PVPS T5-01:1998, December 1998 (1948 kB).
|
|
Mathematical background and new sollutions
|
|
Chiasson, J., Tolbert, L.M., McKenzie, K., Du, Z.:
Elimination of Harmonics in a Multilevel Converter using the Theory of Symmetric Polynomials and Resultants;
IEEE Transactions on Control Systems Technology, Vol. 13, No. 2, March 2005 (414 kB).
Mariethoz, S., Rufer, A.:
Resolution and efficiency improvements for three-phase cascade multilevel inverters;
35th Annual IEEE Power Electronics Specialists Conference, Aachen, 2004 (410 kB).
Tolbert, L.M., Cheng, P.F., Chiasson, J., Cunnyngham, T.:
Charge Balance Control Schemes for Cascade Multilevel Converter in Hybrid Electric Vehicles;
IEEE Transactions on Industrial Electronics, Vol. 49, No. 5, October 2002 (291 kB).
Tolbert, L.M., Cheng, P.F., Habetler, T.G.:
Multilevel PWM Methods at Low Modulation Indices;
IEEE Transactions on Power Electronics, Vol. 15, No. 4, July 2000 (222 kB).
|
|