FUNCTIONAL ANALYSES AND APPLICATION AND DISCUSSION REGARDING ENERGY STORAGES IN ELECTRIC SYSTEMS

INTRODUCTION

Electric power is the most popular form of energy because it is easy to produce, transformation (change its parameters), send and convert into other kinds of energy. Usually it is delivered to receivers through a power network. However, there are many cases where this power has to be accumulated for future use in certain conditions. This is a situation when storage items or devices are applied.

Electric power storages are systems that allow to accumulate power in any form (by changing electric power into other kind of energy or collecting it inside of a magnetic or electric field), and then, processing the accumulated power and delivering it at any moment in form of electric energy of given parameters [1-6]. Using energy storages is predominantly connected with issues of the correctness of electrical power system (especially in cases where renewable sources of energy are involved), with functioning of guaranteed power supply systems (that comprise mostly UPS devices), with powering of mobile systems, such as data communication systems, portable medical devices, consumer electronics as well as modern technologies of powering used in motor industry.

Energy storages in power industry make it possible to collect power in periods of its excess in the production-distribution system and then its effective utilization when a power shortage or receiving overload occurs. Moreover, they can be used as emergency sources during failures or momentary but intensive power fluctuation. They can also work together with ecological sources (photovoltaic, wind, etc.) as power buffer in stochastic operation conditions and also when these sources are overloaded. Therefore, it can be said that energy storages play the role of power supply system stabilizers in the power industry [1,6].

Power supply interruptions can be not only inconvenient to the receivers due to lack of electricity and impossibility of using certain devices, but may also have serious consequences, such as loss of data in IT systems, device damage, as well as the impossibility of providing heating in commercial premises (especially in winter). What constitutes a good solution to this type of issues is application of guaranteed power supply systems, such as UPS devices. In the stand-by operation mode (engaged in case of no mains power supply or incorrect parameters of the supply voltage) the electric power that has been accumulated in the storages is used in order to power secured receivers (most often the ones of very crucial importance). The functional properties of the energy storages influence the quality and effects of the guaranteed power supply systems’ operation, which, in turn, impacts safety and conditions in which the receivers operate.

Accumulating power is also relevant for power systems used in electric or hybrid vehicles. The discussion about such systems needs to include the following issue: the storages used in these vehicles have to provide high power density (that is high dynamics of receiving and returning of the electric charge) and, at the same time, they have to ensure high energy density (that is high efficiency or, in other words, the source’s capacity).

The paper examines possibilities of storing energy, with particular attention drawn to functional properties and comparison of batteries and supercapacitors. The analyses have been focused on application of these devices in guaranteed power supply systems (UPS) and in the motor industry. The analysis has been based on the functional properties of the following devices: UPS EVER SINLINE in battery module version and Evolution (with super capacitors) as well as the drive system of an electric car.

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AUTHOR:
dr inż. Karol Bednarek - EVER Sp. z o.o
dr inż. Leszek Kasprzyk - Poznań University of Technology