The inner current-loop in double-loop digital control of 400 Hz inverter based power supply under low switching frequency condition

For voltage source inverter based 50 Hz or 60 Hz power supplies, it is conventionally assumed that double-loop control with an inner current-loop performs better than single-loop methods. However, this paper analyzes the role of the inner current-loop in double-loop digital control of 400 Hz inverter under low switching frequency condition. The results show that the inclusion of an inner current-loop with the common linear regulators, such as proportional (P), resonant (R) or proportional plus resonant (PR) controllers will not increase the control bandwidth, but will reduce it. Therefore, for control of 400 Hz inverter based power supply in high-power applications, single-loop control is superior to double-loop control if the popular linear regulators are employed. Simulation results show validity of these analyses. Meanwhile, the single-loop method is also tested experimentally and show good consistence with the simulation and theoretical analyses.