Texas Instruments has developed a reference design for an 800 V, 11 kW three-level, three-phase inverter using gallium nitride (writes Nick Flaherty).

The inverter uses a 6.6 kW active neutral-point clamped (ANPC) inverter design with a 600 V LMG3422R030 GaN FET. This enables a switching frequency of 100 kHz to reduce the size of the magnetics and increase the power density to 2.57 kW/litre. Its peak efficiency is 98.5%.

Multi-level topologies enable the use of lower voltage switching devices, but come with certain limitations including more devices resulting in lower reliability and the need to drive more switches and the need to avoid overvoltage, even during abnormal operation.

The design shows how to address all 18 power devices in the power stage of the design with the limited number of pulse width modulation outputs available from a common C2000 microcontroller, as well as how to implement the hardware-based interlocking protection needed to avoid device overvoltage under all operating conditions without the use of additional components.

Another requirement that is becoming more prevalent for inverter power stages is the need for bidirectional power transfer. The ANPC’s power stage is inherently capable of bidirectional operation – only software is required for it to operate as or inverter or power factor controller (PFC).

The modular design allows for easy replacement of power switching devices to enable easy comparisons between them. It consists of a motherboard with the filter, sensing electronics, bias power, switching relays and cooling fans, a TMDSCNCD280049C control card to support the DSP and six power cards switching at 100 kHz containing GaN power switching devices and isolated bias power supplies.

Three power cards switching at 100 and 120 Hz contain silicon power switching devices, gate drivers and isolated bias power supplies. Although the board can accept 12 V bias power from an external power supply, it has provision for adding an auxiliary power supply that can run from the high-voltage DC bus.