Abstract
•DC micro-grid is modeled, controlled and operated under different conditions.•Natural frame control for grid-side converter shows excellent performance.•MPPT control techniques are used for both PV and WECS systems.•Fuel cell supplies power only whenever there is a power shortage from DGs.
This paper presents modeling, control and performance of a DC micro-grid connected to the utility under variable load demand and different environmental conditions. This micro-grid consists of 60kW wind turbine (WT) energy conversion system, 40kW photovoltaic (PV) panel and 40kW fuel cell (FC) module, in addition to, DC and AC loads. The WT energy conversion system is controlled by the indirect field orientation control (FOC) method to extract maximum power from the wind. The PV module is controlled to generate the available maximum power using P&O MPPT control considering environmental conditions. The fuel cell, with a current controlled DC/DC boost converter, supplies power only when the load demand exceeds the total power of the WT and PV systems. A bidirectional 6-pulse PWM converter connects the micro-grid to utility using the natural frame control (NFC) technique. It controls the DC bus voltage, power and reactive power transfer to/from the utility according to the available power from the DG units and the total load demand. The various control algorithms are presented to harness the maximum power from the renewable energy sources at different operating modes. In addition, voltage stability and smooth power transfer between the micro-grid and utility are maintained.