Choosing Proper Membership Function of PI-Fuzzy Controller for DC-Link Voltage

The generation of energy from solar and wind sources has witnessed a growing interest in recent years due to their advantages as clean and renewable sources of energy. However, in order to use these sources in large scale, they have to be connected to the electric grid. This process is challenging as it is important to match the output power from, e.g. the solar panels, to that of the electric grid. This is achieved through the use of suitable DC/DC and DC/AC converters. Within a solar energy system connected to the electric grid, the DC-link voltage forms an essential intermediate stage between the DC/DC and DC/AC converters. Due to the voltage fluctuations and current disturbances, a controller should be suitably designed to maintain the DC-link voltage well stabilized. In   this paper, a comprehensive study for choosing the proper membership function type is presented for the proposed PI-fuzzy controller. Simulation results show that the trapezoidal membership function is the best choice for 3×3 PI-fuzzy controller, while the bell-shaped membership function is the best choice when a 5×5 PI-fuzzy controller is used.