Enhanced transient response and voltage stability by controlling ultra-capacitor power in DC micro-grid using fuzzy logic controller

In a DC micro grid, storage units are used to balance the load-generation mismatch. Battery is used as a primary unit of storage, but it cannot meet the transient demands of the load which can cause DC bus voltage fluctuations. For this reason, an ultra-capacitor is used along with the battery to meet the transient demand of the grid. The controller used to regulate the power converter to feed power from ultra-capacitor to grid must respond very quickly in order to ensure fast response of power from ultra-capacitor. In this paper, a novel control strategy is proposed based on the fuzzy logic controller, which gives faster response and ensures reduced voltage fluctuations as compared to conventional strategies. The voltage of the DC bus is sensed and passed through the fuzzy rules to generate the reference pulse current to meet transient power demand. In the proposed scheme, converter output current sensing is not required. Hence, the need of one current sensor is obviated. It also does not use HPF/LPF filters in the control loop, which reduces the complexity and processing time. Moreover the fuzzy logic controller design is simple as it does not involve estimation of the mathematical model of the converter.