Control strategy of a solar power inverter (analysis of a fifth order system III)

In power inverter applications coupled to power grids a dedicated reactive filter is unavoidable to interface the generator to the power grid. This is necessary to fulfill the EMC requirements of switched mode inverters, and to ensure the required output characteristics (current source). In this paper the output stage of an inverter in conjunction with the matching filter section and the main impedance is analysed. The topology used here leads to a structure of sixth order which was difficult to control (due to its high system order) and problematic to realize due to unknown varying mains impedance behaviour. To overcome the resulting limitations of the low damped system and to reach the goal of an always stable and robust system here a special compensator is used. It is shown, that the optimal adaptation of the presented structure leads to a simple, insensitive, easy to use and very robust solution. The presented concept is well-suited for mains-coupled power inverters, especially solar inverter applications.