Multilevel cascaded transformerless inverter for connecting distributed-generation sources to network

There are many types of distributed-generation (DG) sources that cannot be connected to the network directly and use an inverter-based interface. In harmonic compensators [like active power filters (APFs)], the coupling transformer disrupts the compensation capability, therefore the transformerless inverter schemes have grown up in recent years. A new cascaded multilevel transformerless inverter topology is introduced in this study to connect the DG sources to power utility. The proposed circuit of this study can compensate the current harmonic of the non-linear load (as in APF) and inject maximum possible active power as a DG source interface, simultaneously. A fixed gain called K_C is obtained based on the load nature, and is used to adjust the set point of the inverter between two operating modes. Proposed scheme has been simulated in Matlab/Simulink to evaluate the circuit performance both in the maximum active power injection mode and the load harmonic compensation mode. Then a 2.2 kW single-phase prototype of the circuit is used for experimental evaluation of the study. Both simulative and experimental results prove that such a circuit minimises the total harmonic distortion of the source side current to an acceptable margin, while injecting the maximum possible active power.