Optimal Design of Nested Current and Voltage Loops in Grid-Connected Inverters

This paper presents a method to optimally design the nested control loops of a grid-connected converter. Conventionally, the inner loop is designed to be at least several times faster than the outer loop such that its dynamics can be ignored when the outer loop is designed. In the proposed method, this condition is relaxed by adding additional feedback paths from the inner loop to the outer loop. Moreover, all the gains of the inner and outer controllers are designed using optimal control theory. The results show that the proposed converter enjoys a more robust performance during severe operating conditions such as large and fast power jumps or weak grid conditions.