Switching Performance Optimization of a High Power High Frequency Three-Level Active Neutral Point Clamped Phase Leg

This paper introduces a three-level neutral point clamped (NPC) converter as a high power renewable energy grid interface. The phase leg building block is carefully designed to achieve high switching frequency and high efficiency. Different operating modes and switching loops in the phase leg are identified. Switching characteristics of each loop is evaluated by a double pulse test. Various parameters are taken into consideration as influential factors to loss and stress. An in-depth analysis of some special switching transients is also given. The test shows significant switching performance variance for different switching loops. Performance for each switch is optimized separately considering loss and stress tradeoff. A detailed loss model is built based on the test to calculate system loss distribution and loss breakdown under different switching modes and different operating conditions. The ANPC phase leg can be used to avoid undesirable switching loop and to reduce system loss under certain operating modes. The high-frequency NPC phase leg is tested under full power and the high efficiency design objective is verified.