How silicon carbide helps to get the best from a solar PV system: Page 2 of 3

August 01, 2018 //By Jonathan Dodge
How silicon carbide helps to get the best from a solar PV system
When working with the design of solar inverters, meeting a certain efficiency specification was mandatory to be competitive in the market.  This is a challenge, especially with 1200 V IGBTs, and required attention to every detail, from bus bar thickness to inductor core material. 

A Typical Inverter Topology

A common topology for a solar inverter feeding into a three-phase 400 VAC mains system (typical European installation) uses IGBTs in a ‘Transistor Neutral Point Clamped’ (TNPC) arrangement (Figure 1). This runs off a DC link of 600 to 800 VDC, boosted as needed from the solar panel voltage, and achieves better than 98% peak efficiency when switching in the audible range (15 kHz or less).  Including the booster, there are 13 switch positions with IGBTs, six rated at 600V and seven at 1200V.  Each IGBT needs a parallel fast diode (arguably except the booster).  With low frequency operation the inductors are large and heavy to avoid magnetic saturation.  Increasing the operating frequency would reduce their size approximately in proportion but the IGBT switching losses would quickly become unbearable.

Figure 1. Typical solar inverter arrangement

To reduce complexity, the IGBTs Q1-6 could be omitted but the volt-seconds in the output inductors L2, 3, 4 would double, substantially increasing their physical size again.

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