Design Considerations for a 10kW Single-Phase Cascaded Inverter Based on TI GaN FETs

Figure 1. Schematic diagram of a hybrid series inverter connected to the power grid

Comparison between IGBT and GaN FET

String inverters are composed of power switches, such as insulated-gate bipolar transistors (IGBTs). These power devices suffer from issues such as tail current and diode reverse recovery, which result in high switching losses. Additionally, these phenomena are affected by temperature, leading to higher power losses, especially when using static cooling solutions. Therefore, these power devices need to operate at low frequencies, requiring larger passive components and heat sinks. The typical switching frequency range is 5 kHz to 15 kHz.

Wide-bandgap power switches such as gallium nitride (GaN) do not exhibit minority carrier phenomena, thereby reducing switching losses. With reduced switching losses, the switching frequency can be increased while maintaining constant system losses, thereby reducing the number of passive components. On average, the switching frequency can be increased by a factor of six.

This paper proposes a 10kW series inverter based on GaN field-effect transistors (FETs). We will also explore the advantages of GaN and highlight the benefits of building such systems for residential solar applications.

Design considerations for GaN-based series inverters

Figure 2 shows a 10kW single-phase series inverter reference design based on GaN and equipped with a battery energy storage system, including all active and passive components.

Figure 2. 10kW single-phase reference design based on GaN devices

Figure 3 shows the schematic diagram of the converter.

Figure 3. Block diagram of single-phase series inverter reference design

This reference design includes four power conversion systems operating at different switching frequencies:

• Two boost converters for two independent series inputs, each with a rated power of 5kW (134kHz).
• One interleaved bidirectional DC/DC converter with a rated power of 10kW (67kHz).
• One grid-connected bidirectional DC/AC converter with a rated power of 4.6kW (89kHz).