SCMIC: Single cell module integrated converter system

• Research unit: EU RFP
• Project number: 95.0207-1

Key words (English)

Photovoltaics; module integrated converter system; single cell; low voltage converter; renewable energy; maximum power tracking; power pulsation

Alternative project number (English)

EU project number: JOR3-CT95-0029

Research programs (English)

EU-programme: 4. Frame Research Programme - 5.1 Nonnuclear energies

Short description (English)

See abstract

Partners and International Organizations (English)

Fraunhofer-Institut für Solare Energiesysteme
(FhG-ISE), Freiburg (D),
NAPS France S.A., Lens (F),
Enecolo AG, Mönchaltorf (CH), Alusuisse-Lonza Services Ltd., Neuhausen am Rheinfall (CH)

Abstract (English)

The kick-off meeting of the project took place on the 11th of April 1996.
We investigated the power converter and its control. The aim was to prove the feasibility of a power converter with an input voltage of 1.. 2V and up to 1 00A input current. Further simple and effective control strategies had to be developed.
The special requirements of the single cells application call for an optimised and specially designed converter. The developed converter takes a well smoothed input current out of the solar cell, but it needs no smoothing reactor on the high-current side and only a small input filter capacitor. An additional transistor allows to control the input current of the converter from the low current side and to operate the high current stressed input transistors at zero current switching conditions, which strongly reduces the switching losses of the input power stage.
A first hardware prototype proved the feasibility of the power converter and confirmed that efficiencies of 80% and more are achievable over a wide operating range of the converter. Our power converter has a very good behaviour at partial load conditions. The efficiency can be increased by putting more semiconductors in parallel on the low voltage high current side.
The final hardware prototype of the boost stage is characterised by an increased efficiency compared to the first prototype. The boost stage reaches efficiency peak values of 93%! As most important improvement, a completely new design of the low voltage high current part of the converter allows to use standard etching process techniques for the converters fabrication.
The single phase mains converter is characterised by its 100Hz AC-power pulsation. The power flow controller avoids any power pulsation on the solar panel. The highlight of our control strategy is that there is no need for large electrolytic capacitors in the power circuit. The maximum power tracking causes no power variations on the mains side and guarantees on this way a sinusoidal mains current. Our solution minimises the number of measurements because the different control loops share the dc-link voltage as reference signal. The fast current control is realised by analogue circuits. The power flow, the maximum power tracking and the mains synchronisation are implemented on a low cost microprocessor.
Extended investigations on the power circuit of the inverter stage have shown that there is a remarkable optimisation potential for this stage in a power range of 200W. By optimising the power circuit as well as the gating of the power semiconductors the efficiency of the inverter stage can be increased up to 97%.
Our investigations have shown that a power converter with an overall efficiency in the range of 90% is feasible for the single cell application. Compared to 200W converters for conventional solar cells the main differences of the single cells low voltage converter are not concerning the achievable conversion efficiency but are its additional costs of about 30%.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 95.0207-1