AN-2116 Datasheet, PDF (1/8 Pages) National Semiconductor (TI) – SolarMagic™ ICs in Microinverter Applications

SolarMagic™ ICs in
Microinverter Applications
National Semiconductor
Application Note 2116
Perry Tsao
May 4, 2011
Introduction
Microinverters are a growing and rapidly evolving part of the
photovoltaic (PV) system. Modern microinverters are de-
signed to convert the DC power from one PV module (solar
panel) to the AC grid, and are designed for a max output
power in the range of 180W to 300W. Compared to conven-
tional string or central inverters, microinverters have advan-
tages in ease of installation, localized max power point
tracking, and redundancy that provides robustness to failure.
Since this area of power electronics is seeing such rapid in-
novation, there are many different topologies and variations
being developed. This article explores some of the prevalent
topologies used in microinverters today, and the use of So-
larMagic™ ICs in these demanding applications. In particular,
the use of the SM72295 Photovoltaic Full-Bridge Driver will
be highlighted.
SolarMagic Renewable Energy
Grade Components
The environment for electronics in PV systems is a very de-
manding one due to the extremes in temperatures and re-
quirements for long-lifetime. The ambient temperature behind
a photovoltaic module can range from below freezing in the
winter to over 90°C on a summer day. With this in mind Na-
tional Semiconductor created the Renewable Energy Grade
line of SolarMagic ICs that are all rated for operation from -40°
C to +125°C and have all been screened and tested to stan-
dards appropriate for products that are designed for a 25 year
lifetime. This line of products includes MOSFET gate drives,
PWM controllers with integrated switches, LDO regulators,
amplifiers, and many other ICs necessary for photovoltaic
electronics. All of the ICs recommended in this article are be-
ing made available as Renewable Energy Grade compo-
nents.
Single-Stage Microinverters
There have been a multitude of microinverter topologies de-
veloped [1], and these topologies can be broken up into two
broad categories. The first category depicted in the block di-
agram of Figure 1 employs a DC/DC converter and controls
the converter output voltage to have the shape of a rectified
sinusoid. This rectified sinusoid waveform is then inverted into
a full sinusoidal waveform using an “unfolding bridge” that in-
terfaces to the grid voltage. Though perhaps not the most
accurate name, this category of microinverter topologies is
often referred to as a “single-stage microinverter” because the
boosting of the panel voltage and shaping of the AC waveform
is accomplished in a single stage.
A more formal categorization of microinverter topologies [2]
refers to this as a PV-side decoupled topology because the
input capacitors decouple the AC power variation. The most
widespread topology of this category is a quasi-resonant in-
terleaved flyback, however, there are other variants such as
interleaved flyback (not quasi-resonant) and interleaved for-
ward converter. The unfolding inverter is generally imple-
mented with 4 SCR’s (silicon controlled rectifiers) that switch
at the grid frequency.
30150101
FIGURE 1. Block diagram of a microinverter using a single-stage topology. The DC/DC stage can be implemented as
a quasi-resonant interleaved flyback or another topology.
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