Design and Control of a 2 kW Hybrid DC Micro-grid

The system proposed in this paper is a hybrid of two renewable sources of energy, solar power and wind power, to produce electricity to a small, independent (standalone) DC microgrid. In particular, it employs a 1 kW PV array and a 1 kW wind turbine system (WECS). This is aimed at achieving reliability of power supply by relying on both sources, as solar energy is best in sunny situations and wind energy can produce power at other times such as at night or even during bad weather. Both the solar and wind systems are made to generate as much power as possible at all times, even when the weather conditions are constantly varying. The solar (PV) system has a special controller known as Maximum Power Point Tracking (MPPT), which constantly modulates the operation of the panels so the panels can optimize the available energy regardless of the strength or weakness of the sunlight. In a similar fashion, the wind system operates a form of generator known as a Permanent Magnet Synchronous Generator (PMSG), which is powered by its own MPPT to change its operation according to wind speed. This enables the wind turbine to gain the maximum energy both at low and high wind speed. These intelligent control methods combined make the two energy sources effective and provide the optimum power output at different environmental conditions. To store additional energy and provide power on demand, a battery system with a voltage of 220 V is added. It is joined to the main DC line with a special device known as a bidirectional DC-DC converter, which is capable of regulating the direction of flow of electricity. This converter operates under two modes: in buck mode, it decreases the voltage (as in the case of charging the battery) and in boost mode, it increases the voltage (as in the case of the battery supplying power back to the system). It is due to this that the battery is able to store surplus energy produced by the solar and wind sources as well as offer energy during times of low generation. Meanwhile, it maintains the level of DC link voltage and also provides a smooth flow of energy between the energy sources, the battery and the load. The control system is meant to maintain everything at equilibrium with a change of condition. It constantly regulates the amount of power being produced by the solar and wind sources and the amount of power required by the load and then moderates the system to suit. The simulations are implemented in MATLAB and Simulink and the outcomes confirm with the simulation outcomes.