The best of two concepts
As a result, the requirements the new family of devices had to fulfill were clear: an inverter that combined the benefits of both concepts. One that is both compact and light, offers all the benefits of galvanic isolation, and at the same time is more efficient than previous devices with transformers in this power class. “We achieved this primarily through the advancement of the HF topology,” says Sven Bremicker. Its basic idea is relatively simple: a transformer with the same power output becomes smaller and lighter, the higher the frequency of the alternating current flowing through it. If the direct current from the solar modules is initially converted into high-frequency alternating current, a significantly more compact transformer can be used as a result. Afterwards, the current is then rectified in order to convert it into alternating current with the usual grid frequency of 50 hertz.
Whereas the intermediate high-frequency circuit requires a series of additional semiconductor circuits, thus making the inverter’s design more complicated and also results in additional losses. “With the current state of technology, the additional electronics are not a problem – neither with regard to cost nor reliability,” explains Sven Bremicker, “and to increase efficiency, we rely on a really outstanding technological feature – resonant circuits.” The secret behind these circuits is something everyone who has ever sat on a swing is familiar with: the swing has a certain resonant frequency (also known as period of oscillation), which is determined by the length of the rope. By periodically applying a small amount of energy at just the right moment, it’s easy to generate a powerful and continuous swinging motion. This is much more efficient than moving a nonresonant object in alternation – and it also works with the semiconductor circuits in an inverter.