How MOSFET technology will boost the effectiveness solar energy installations

Photovoltaic inverters convert the DC current produced by photovoltaic arrays into an AC current with the appropriate line voltage and frequency that it can subsequently be fed into the grid (or alternatively used to power an off-grid network). Because they are straightforward to drive, power MOSFETs will normally form the basis of inverter switching functionality in solar energy installations. There are a series of important attributes that need to be considered when specifying MOSFET devices for this kind of application.

• Firstly devices should be rated at 600V or 650V, as this will generally provide more than adequate protection against the threat of high voltage transients.
• So that switching losses can be mitigated as much as possible and system efficiencies elevated, the inclusion of fast recovery diodes (FRDs) may be called for. The tuning of the body diode of the MOSFET as FRD can reduce the switching losses considerably.
• Thought must be given to how the balancing of MOSFET conduction and switching losses can affect system performance.
• Also the influence that the MOSFET’s gate charge (QG) has on its switching capabilities must be taken into account - with lower QG allowing high frequencies to be supported, but how this will conversely lead to higher RDS(ON) (on-resistance) values and thus increase power losses.