Development of a converter to interface ultra-capacitor energy storage to an alternate energy resource

Abstract

Alternate energy resources such as Solar PV, Wind, Fuel Cell, Micro-turbine generators etc have become important and have the potential for development due to the growing energy demand, increasing global environmental issues, and depleting energy resources (coal, oil and gas). The energy conversion to electricity from such resources normally requires some form of electrical energy storage that requires rapid charging and discharging of the storage device. Electrical energy storage is normally used for back-up power but in distributed generation it is used for "toppingup" power during sudden change in load demand or required for peak power conditions for short duration of time. The output of the alternate energy resource can be controlled and adjusted to meet the load demand so the storage device only needs to satisfy the transient energy required while the generator power is adjusted. Batteries have traditionally being used for such purposes. However batteries are heavy, bulky, and occupy a large space. They have a low cycle (charging and discharging) life which means that they need to be replaced quite frequently. Ultracapacitor is a good option for an alternative to batteries for short-term duration electrical energy storage because ultracapacitor have several advantages, like high power density (5kw/kg), long lifecycle and very good charge/discharge efficiency. Ultracapacitors also have more cycles of charging and discharging (> 100000 cycles) during its lifetime. They can also provide large transient power instantly, thus capable of providing energy during sudden change in load demand or peak power conditions for short time duration. However, ultra-capacitor voltage varies quite significantly when charging and discharging. Therefore an interface is needed to connect ultra-capacitor to another alternate energy resource. In this research, the various converter topologies and various control techniques to interface an alternate energy resource to an Ultracapacitor Module are studied. The Converter approach uses a Bidirectional DC-DC Converter, where converter current can flow in two directions. A converter to interface ultra capacitor energy storage to another alternate energy resource is designed and developed. The Design of Converter is modelled and simulated by MATLAB-Simulink simulation to verify the performance of the proposed approach. Control System of the proposed converter also has been carried out. Then a hardware prototype is developed to verify and analyze the effectiveness of the proposed control method. Finally, the performance of the developed converter control system is tested base on the charging and discharging capabilities of the ultra-capacitor module.