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PERFORMANCE OF MPPT CHARGE CONTROLLERS
A STATE OF THE ART ANALYSIS
Michael Müller
1
, Roland Bründlinger
2
, Ortwin Arz
1
, Werner Miller
1
, Joachim Schulz
2
, Georg Lauss
2
1. STECA ELEKTRONIK GMBH, Mammostr. 1, D-87700 Memmingen, Germany, Tel.: [phone], Fax:
[phone] E-Mail: [e-mail], Internet: http://ww.stecasolar.com
2. AIT Austrian Institute of Technology GmbH, Giefinggasse 2, A-1210 Vienna, Austria, Tel.: [phone],
Fax: [phone], email: [e-mail], Internet: http://www.ait.ac.at
ABSTRACT
Maximum Power Point Tracking (MPPT) charge
controllers have recently become increasingly popular
not only for off-grid PV applications.
MPPT Charge Controllers not only promise to
increase the energy yield of the PV generator, they also
allow to use low cost PV modules designed for grid-
connected applications (between 40-70 cells) which
normally could not be used in off-grid installations due
to their high MPP voltage. Therefore DC-DC converters
(typically step-down converters) are used to match the
output voltage of the PV generator to the battery voltage.
Those products commonly use MPPT-algorithm to track
the maximum power point (MPP) of the PV generator.
According to recent estimtations, about 30 to 50 MW of
MPPT Charge Controllers are installed per year. Among
the variety of products 60 A MPPT charge controllers
dominate the market?
In the absence of standard testing procedure
dedicated to DC battery charging MPP-trackers only
part of grid connected PV-inverter tests can be applied
1
.
However, due to expensive and complex test
requirements it is not possible for customers to evaluate
the actual performance and quality of a certain product.
This paper summarizes the results of the TESCABI
2
project which is part of the EU DERri initiative
(www.der-ri.net). Within the project, a set of test
procedures for performance characterization of MPPT
charge controllers have been defined. Using the
procedures, extensive laboratory tests were made at the
AIT PV inverter laboratory with a world-wide market
representative set of 9 different MPPT devices. Based
on the results, recommendations for manufacturers as
well as customers have been formulated to select the
appropriate product for a certain application.
1. DEVELOPMENT OF TEST PROCEDURES
FOR MPPT CHARGE CONTROLLERS
The developed test procedure takes into account the
experience of testing PV-grid tied inverters and
switching (non-MPPT) battery charge controllers. It is
divided into 6 categories, which define the test
procedure.
1.1 Installation and usage
The first category deals with the construction of the
product and checks the most important technical data.
It evaluates the mechanical robustness of the
enclosure and the ease of installation in terms of the
design (e.g. if there is enough room for the cables, easy
to reach terminals, etc).
1.2 Night-time and stand-by consumption
The 2
nd
category deals with the self consumption of
the MPPT controller. In all off-grid systems it is of
crucial importance to have extremely low self
consumption during the night and periods of low
irradiation.
1.3 DC-DC conversion efficiency
Similar to grid connected inverters, the DC-DC
conversion efficiency is one of the most relevant
performance parameters of MPPT charge controllers.
Today, manufacturers typically show only the
maximum (peak) efficiency in their datasheets which
however does not reflect the real operating conditions in
field. In practice a number of external factors influence
the conversion efficiency: Actual battery voltage, actual
input voltage, temperature and the power output of the
device.
To characterize the conversion efficiency of MPPT
charge controllers, the basic test procedure from the
EN 50530
1
has been extended to take into account the
additional aspects of the specific devices (e.g. influence
of the battery voltage)