Soft switching: Better efficiency for high power inverters
Inverters turn direct current into alternating current; they are used in three-phase drives, grid feeds in photovoltaics and wind energy, for uninterruptible power supplies and for active mains filters. In particular the three-stage pulse inverters are increasingly regarded as a promising technology. Typically, the inverters used in this context are operated in a switching mode with high slope steepness. The switching losses associated to this switching behaviour however negatively impact the energy efficiency.
At the Konstanz university, a team around professor Manfred Gekeler has developed an alternative. The Soft-Switching Three Level (S3L) inverter solves the problem of energy losses by simply adding a snubber circuit, which due to its principle avoids the drawbacks of usual circuitries; efficiency is increased significantly. Even better: The snubber circuit consists of a few simple passive components, combining the multi-level inverter topology with the technique of soft switching.
The S3L inverter features high efficiency and favourable even with standard silicon semiconductors such as IGBT, OGCT or GTO transistors. Nevertheless, the principle can also be applied to SiC and GaN-based circuits. In this case however, not reducing the losses is the dominating factor but instead limiting the slope steepness (du/dt) and voltage surges – an aspect of particular relevancy for motor controls.
The S3L inverter is a pulse width modulated inverter enabling switching frequencies in excess of 30kHz and thus AC output frequencies up to about 500 Hz. The harmonics content has been tested for grid feed inverters in photovoltaic applications and meets the tough requirements in this field. What’s more, the circuit can be operated at all load angles from 0 to 360 degrees – in other words it can operate as an inverter as well as a rectifier. Another interesting aspect is the capability of the circuit to limit the slew rate (du/dt). As a consequence, external du/dt filters are redundant.
Benefits of the S3L topology are in the first place low losses and the potential if implementing very high switching frequencies. This translates into a cost-effective de-warming, in other words, the S3L inverter contents itself with relatively small, compact and cheap heat sinks, fans and power chokes.
More information: Technologie Lizenz Büro (TLB)
If you enjoyed this article, you will like the following ones: don't miss them by subscribing to :
