Dr. Ing. Heribert Schmidt invented a new circuit for a solar inverter, achieving a new world record for inverter performance with his HERIC technology. Image: Dirk Mahler |
A
switching trick makes it possible to cut the losses of a
series-production inverter in half and increase the efficiency from 96
to 98%. The HERIC-topology makes it possible to achieve a world-record
efficiency of more than 99%.
“It
was a matter of minutes,” says Dr. Heribert Schmidt as remembers the
day in spring of 2002 he made his discovery. To find opportunities for
improvement, he had often pondered about the switching plan of an
inverter while in his office at the Fraunhofer Institute for Solar
Energy Systems ISE in Freiburg, Germany. According to Schmidt, he had a
flash of inspiration and a solution that was ingeniously simple came to
his mind. He immediately went to get an inverter from the laboratory,
laid a few new strips and installed two additional semiconductor
switches.
“Then it required only a little bit of work on the controls–and we already had the proof!” he says.
The
electrical engineer described the revolutionary step in brief: the
losses could be halved and the degree of effectiveness could be
increased from 96 to 98%.
After
the solar generator, the inverter is the second key component of a
grid-linked photovoltaics system. Solar modules generate direct current.
If the current is to be fed into the public grid, then it must be
converted into grid-compatible alternating current. The inverter handles
this task. Single-phase feed inverters consist of three essential
parts: the buffer capacitor at the input which provides intermediate
storage for the direct current from the solar generator; the inverter
bridge with four semiconductor switches that “chop up” the direct
current by rapidly switching on and off and as a third component, the
inductor at the output that converts the alternating current into a
perfect sinus current.
Schmidt
knew that a large portion of the losses are caused by the return of
current between the output inductor and the input capacitor. The
question therefore was how to prevent this.
“That‘s easy,” says Heribert Schmidt after a sudden inspiration.
“If
I decouple the capacitor and the inductors completely from each other
at certain intervals, then it is impossible for a return current to
flow, and electromagnetic disturbances cannot occur at the input as a
result of voltage spikes,” he says.
He
immediately had his invention patented as HERIC topology and began to
develop a new series of devices with the SUNWAYS company in Konstanz,
Germany. An encompassing patent has been awarded to the basic idea and
the Fraunhofer-Gesellschaft is in negotiations with additional
licensees.
Heribert
Schmidt – who has been with the Fraunhofer Institute for Solar Energy
Systems ISE since 1988 – is an experienced inventor with more than 20
awarded patents. The HERIC patent provided the institute with lucrative
licensing agreements – and Heribert Schmidt with the Fraunhofer Prize.
