The increasing penetration of the distributed energy sources and the increasing load on the AC grid demands for integration of DC grids in AC distribution network. This has resulted in the requirement of power electronic converters such as DC/AC converters. For different operating conditions of the DC/AC converter it is not recommended for the converter to operate in open loop. Hence, while designing the control for the converter there are challenges such as the presence of unbalance on the grid leading to higher losses, offsetting of AC voltages at the output and grounding of the converter leading to higher common mode voltage and currents. This thesis explores the control strategy that can be implemented on the converter to mitigate the unbalance in different operating conditions and compares different modulation techniques to reduce the common mode voltage and currents.
To begin with the islanded operation is considered for the converter and the voltage control is implemented on this type of converter. Further a modification on this type of control is proposed for the operation of converter under overcurrent scenario. Subsequently the control strategy for grid connected operation is analyzed such that the issue of unbalanced currents on the grid is mitigated. Three different operating modes are considered under grid connected operation for validating the control strategy proposed. Following the controlled operation in islanded and grid connected scenario, the active methods for reducing the common mode voltage are reviewed by comparing different modulation techniques.
On the discussed control strategies for different operating conditions of the DC/AC converters, an optimized implementation of the control on the microcontroller is presented. Other functionalities such as protection of the converter against unwanted actions is investigated through implementation of state machine. The results of the controlled DC/AC converter operating in islanded operation is presented and modifications in the existing PCB are discussed to make it compatible to operate under grid connected condition. The operation of control strategies implemented is validated for the real time application of the converter with unbalanced load conditions.