PREDICTIVE DIRECT POWER CONTROL OF VOLTAGE SOURCE CONVERTER (VSC) IN MICROGRIDS

Abstract

In recent years, electricity generation from standard fossil fuel resources originate critical influence on the environment. Moreover, fossil fuel resources are evacuating day by day. Therefore, the microgrid is an effective way of integrating current power system and renewable energy resources. A microgrid is a type of grid that has local distributed generators (DGs) and it is connected to the national grid but also able to work independently and have effective control. Hybrid AC/DC microgrid, DC microgrid and AC microgrid and are the three categories of microgrid. The generally used configuration in the AC microgrid because it provides a straightforward way for the integration of DG modules and existing network utilities with minimal modifications. Although maximum distribution networks are AC, ESS units, addition of DC modules and DG-based loads is included. More characteristics include opening the entryways of distribution networks which are based on DC. The features of both AC and DC are combined in hybrid AC/DC microgrid. In hybrid microgrid, the three phase AC/DC bidirectional converter is required for power conversion. It can operate both in rectification mode and inverter mode. In rectification mode, it can regulate power on the DC side or it can maintain voltage on the DC side. In inverter mode, it can further operate in two modes, islanded mode and grid connected mode. In grid connected mode, national grid controls the frequency and voltage of the microgrid while power is control by the DG. In the islanded mode, DG control the frequency and voltage of a microgrid and also fulfill the local demand. Bidirectional Voltage Source converter (VSC) is an essential component in hybrid microgrids. The challenges in bidirectional converter are; control of power flow in both directions while maintaining stability, efficient transitions between the modes and efficient control of nonlinearity. This study proposes the FCS–MPC control scheme for the bidirectional converter in hybrid microgrid. In the proposed scheme, future value of the system at each sampling instant is forecasted for every switching states using system’s mathematical model. After this, for the next sampling instant optimum action is applied using cost function. Converter switching frequency is reduced using tow-step horizon-based cost function (CF). The proposed MPC model for bidirectional converter is verified for its robustness and effectiveness using MATLAB/SIMULINK.