DC-DC converter

Topics: Transformer, Photovoltaics, Switched-mode power supply Pages: 27 (6054 words) Published: February 5, 2014

TECHNICAL SCIENCES, Vol. 59, No. 4, 2011
DOI: 10.2478/v10175-011-0061-7

Review and comparison of high efficiency high power boost
DC/DC converters for photovoltaic applications
Faculty of Electrical Engineering, Department of Automatic Control Engineering and Electronics, Bialystok University of Technology, 45D Wiejska St. 15-351 Bialystok, Poland
Abstract. Recent environmental issues have accelerated the use of more efficient and energy saving technologies in renewable energy systems. High power high efficiency boost DC/DC converters for the use in photovoltaic, fuel cell systems are discussed in this paper from the viewpoint of power losses and efficiency. State of the art converters with switching frequency within the range of 25 kHz with IGBTs to 100 kHz with power MOSFETs and the highest efficiency close to 98%, depending on the load conditions, is considered. A comparison and discussion of the highest efficiency high power DC/DC boost converters is also presented in this paper. Key words: boost DC/DC converters, high efficiency, high power, photovoltaic systems, renewable energy.

1. Introduction
In many renewable energy applications high efficiency, high
power, high voltage boost DC/DC converters are required as
an integral interface between the available low voltage sources and the output loads, which operate at higher voltages. Examples are energy storage components such as batteries, and ultracapacitors which are used in the power trains of hybrid electric vehicles, electric vehicles, and fuel cell vehicles. In the modern power drive, the voltage levels of the energy storage devices are predominantly low when the motors of the vehicles are driven at much higher voltages. In the computer industry and in the telecommunication batteries with low voltage levels are utilized as a back-up power source .

Another example is automotive headlamps which use
high-intensity discharge lamp ballasts. The DC/DC converter
is required to boost the low voltage of the car battery to much higher voltage during start-up and normal operation. Examples of recent applications are photovoltaic cells that require high-gain dc voltage conversion. In all of these applications, non-isolated boost DC/DC converters can be used but they

should operate at high efficiency while conducting high currents from low-voltage dc sources at their inputs. The duty cycle of a conventional boost converter increases
with the increase of the voltage gain. For applications requiring high voltage gain (8 or higher) it becomes a problem to maintain high efficiency because of the high duty cycle. In
practical applications it causes additional voltage stresses and necessitates the use of switches with a high blocking voltage rating, thus introducing more losses.
Low input voltage results in large currents flowing through the switches. While working at maximum duty cycle current
spikes of high amplitude flow through output capacitors and output diodes causing serious problems with diode reverse
recovery. They also increase switching and conduction loss∗ e-mail:

es. High Ron resistance of the switches increases conduction losses and the reverse recovery problem can reduce efficiency. Moreover the parasitic components introduce additional voltage overshoots creating the necessity to use switches with higher blocking voltages, which further increases losses.

The demand for power converters working with low voltage sources has increased in the last decade, especially in the area of renewable energy sources, including photovoltaic systems.

2. Structures of a photovoltaic system
The main parts of a photovoltaic system (PV) are: photovoltaic panels (also called photovoltaic cells), DC/DC and/or DC/AC converters, energy storage and control systems and
control-measuring devices.
DC/DC and DC/AC converters are a main part of
a network-connected photovoltaic system. The main task for

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