The Design and Control of a Battery-Supercapacitor Hybrid Energy Storage Module for Naval Applications

Abstract

As the Navy transitions to a more electrical fleet, the electrical architectures must adapt to the changing load profiles. With the introduction of electrical propulsion and new types of electrical energy based weapons, load profiles have become higher power and more transient than ever seen before – especially during directed energy weapon operation. One issue that has become apparent with the introduction of these transient loads is the ability of traditional generation sources, such as fossil fuel generators, to power them. Generators are stiff sources of power which suffer efficiency losses when they deviate from operating at a constant maximum load. The logical answer to this problem is to create a low-pass filter on the power flow by inserting an energy storage device that is capable of both sinking and sourcing energy in order to keep the power demand constant. In a Naval setting, the traditional approach to energy storage devices would be lead acid batteries, but with recent developments in lithium-ion chemistries, it would be preferable to utilize energy dense lithium-ion batteries to save precious space and weight on board the ship. Although lithium-ion batteries offer many benefits, one issue they face is a degradation of lifetime when the battery is cycled at high rates. One solution that might come to mind is to simply use a power dense device that is relatively unaffected by high rate usage such as a capacitor, but these devices typically do not possess enough energy density to accommodate the system for long periods of time – even sourcing power for periods of time where there may be a deficiency in generation. One proposed method of overcoming these challenges is the integration of both energy dense and power dense devices into a single module, referred to as a hybrid energy storage module. In the case of a battery-supercapacitor hybrid energy storage module, the voltage of each device is proportional to the energy stored. If these devices were simply placed in parallel, as energy is drawn from the module, the voltage will drop on the capacitor quicker than it will from the battery, leading to a situation where the battery will source the majority of the current due to voltage dominance. In order to minimize the current batteries, power electronic converters are placed in front of the battery to actively control the amount of current flowing in and out of it. There are many challenges when designing this type of system – especially when considering how to integrate this into existing shipboard systems using commercial-off-the-shelf components. The research presented here will delve into the design and control of a hybrid energy storage module. The work presented here will present the mathematical model of a hybrid energy storage module, it will show the simulation of this system using the SimPowerSystems toolbox within MATLAB/Simulink, it will build this system up on a tabletop testbed to validate the simulation results, and finally it will evaluate the integration of this components using commercial-off-the-shelf components to mimic a real-life implementation of such a system.