An established research institute of a Swiss university of applied sciences has invented a new topology for highly efficient switched mode power converters with low electromagnetic interferences (EMI). Along with the right method of control, this topology allows to reduce the power losses by approximately 50% compared to conventional switched mode power converters, which allows very high energy savings. Thus, conversion efficiency of 99% or more can be achieved. Despite the superior performance, the topology is simple and easy to drive. This is a major benefit compared to other low-loss converter topologies (such as resonant converters).
The proposed topology is based on the classic dc-to-dc-converter topologies of the buck-, boost- or buck-boost-converter. Two such converters, each consisting of an inductor, a power switch and a diode, are being operated in parallel mode. However, the chopper voltages of the two sub-converters are connected with a small coupling capacitor. With the right method of control, zero-current / zero-voltage switching is achieved. Consequently, switching losses are almost completely eliminated and electromagnetic interferences are considerably reduced.
To achieve zero-current / zero-voltage switching, the sub converters are being operated in discontinuous conduction mode. At the begin of each switching cycle, the power switches of both sub-converters are being turned-on simultaneously. Because of the discontinuous conduction mode, this turn-on happens at zero-current and is therefore lossless. After activation of the switches, the inductor currents of both sub-converters rise with a near-linear slope. As soon as the desired peak inductor current is reached, the switches are being turned-off, but not simultaneously. Instead, there is a slight time delay between the turn-off of the power switches of the first and second sub-converter. This leads the inductor current in the first moment after turn-off of the power switch to be redirected into the coupling capacitor. The result is a soft switching slope and nearly zero-voltage switching. After both power switches have been turned-off, both inductors transfer their energy into the converters output and the inductor currents fall back to zero. To avoid an undesired charge of the coupling capacitor during the currentless phase of the converter, there is a small bypass-switch in parallel to the coupling capacitor which is activated when both diodes are conducting and deactivated during the on-phase of the power switches in the next switching cycle.
To clarify the function of the invention, the figure below shows the topology of a boost-converter based on the described principle and the corresponding timing diagram. Buck- and buck-boost-converters based on the same principle can be realized by changing the locations of the switches, diodes and inductors. Moreover, by replacing the diodes with another pair of power switches, bidirectional operation can be achieved. Even though the basic function of these topologies is dc-to-dc-conversion, by modulation of the output voltage, dc-to-ac conversion is possible as well.
Fields of application:
This allows the realization of numerous topologies for inverters and synchronous rectifiers in many fields of application such as:
- Photovoltaic inverters
- Traction inverters
- Battery chargers
- Uninterruptible power supplies
The inventors of this new topology have designed, realized and tested a prototype of a bidirectional dc-to-dc-converter with a rated power of 2kW. The device has a peak efficiency of >99.4%. Even though there are no components for EMI suppression present, the conducted emissions of the prototype are below 80dBμV (0.15-30MHz). These very good results prove the feasibility of the invention.
The institute is now looking for partners for licensing or partnerships for further development of this new technology. The prototype can be demonstrated on request.