Technique to improve IGBT converter efficiency and transient response

For medium to large power converters (1 kW to 100 MW) the switching frequency is limited to ensure acceptable losses at the cost of converter performance (bandwidth). A technique is presented that dynamically changes the switching frequency to maintain a low average switching frequency but for transient events shorter than the thermal time constant of the device, the switching frequency and bandwidth are increased. Relationships between the switching frequency and bandwidth are developed, and a method for determining when and how to change bandwidths is introduced. The technique is shown to give improvements in THD compared to a fixed frequency system of the same average switching frequency (same losses) in a harmonic filter application.