May 2010

Doc ID 17056 Rev 1

1/17

AN3152

Application note

The right technology for solar converters

Introduction

Following a short overview of types of solar power systems and converters, this application

note introduces a fully working, grid-connected solar inverter prototype suitable for rooftop

applications. This solar inverter has been equipped with STMicroelectronics’ MDmesh™

and silicon carbide (SiC) devices to allow evaluation of these products in “green”

technologies.

Thanks to ST’s newest technologies (MDmesh™ V and SiC) and a new converter

philosophy, a 650 V fast power MOSFET can be used to boost performance and reduce the

size of the converter. A stage-by-stage explanation is presented here, as well as the

topologies adopted, and a detailed analysis of the front-end stage of the inverter is

discussed. The BOOST stage is used as a case study to validate the performance of the

new power MOSFETs and diodes.

Everyone is thinking “green’ these days. Adding to the new green conscience are the

increasing costs of fossil and nuclear fuels, prompting the market to turn to creative

technologies that use renewable resources to produce energy. Energy produced from

renewable resources are becoming an important contribution to the world’s total energy

demand and will increase in the next decades. Solar photovoltaic technology represents one

of the most promising energy resources, due to its low environmental impact and high

reliability. Every photovoltaic (PV) system consists of a module array and an inverter. The

inverter module is mandatory on all grid-connected applications, in order to amplify the low

DC voltage generated by the module to the higher AC level required by the grid. If several

modules are connected in series it might not be necessary to include amplification, but in

any case a maximum power point tracking (MPPT) function is required.

This prototype has a wide operating input voltage range (from 200 V to 400 V), and 3 kW of

maximum power output, since it is intended for rooftop applications. Total efficiency must be

at least 97%, and an MPPT function is implemented in order to enable panels to work at

their highest efficiency. In fact, the PV module (or modules, if connected in series) changes

its maximum power point continually during normal operation due to the variances in solar

radiation caused by shade or weather.

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