Tag Archives: LiFePO4 accumulator

1141–1151 V. Papez and S. Papezova,
Optimization of the balancer for LiFePO4 battery charging
Abstract |
Full text PDF (415 KB)

Optimization of the balancer for LiFePO4 battery charging

V. Papez¹ and S. Papezova²,*

¹ Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Electrotechnology, Technicka 2, CZ166 27 Pague 6, Czech Republic
² Czech University of Life Sciences in Prague, Faculty of Engineering, Department of Electrical Engineering and Automation, Kamycka 129, CZ165 21 Prague 6 ˗ Suchdol, Czech Republic
*Correspondence: papezovas@etf.czu.cz

Abstract:

Balancers of various constructions are currently used for the operation control of the batteries connected in series. Unidirectional balancers ensure proper charging of all battery cells in a way that the first loaded cells should not be overcharged. Active balancers distribute the power, supplied to already-charged cells, to other cells; the power is further consumed by the passive balancers. Bidirectional balancers enable distributing the power between the cells during the discharge process, as well. This process thus protects the fastest discharging cells against the deep discharge. Passive balancers are most often used in batteries charged by the currents up to 20 A. If there are not big differences between individual cells in the battery, passive balancers reduce the efficiency of the charging process by only a few percent. They are the cheapest and most reliable. Optimally adjusted balancers with very low internal resistance deteriorate the efficiency only by about 1%. Commercially available balancers, working on the principle of a switch, periodically connecting the load resistor to the cell, deteriorate the efficiency to a greater extent, by about 5%. Optimized balancers, whose construction is described in the paper, work on a principle of a linear feedback controller. They can work with a maximum charging current up to 20 A, they have very low dynamic resistance of about 1 mW, and are absolutely stable. Their properties are further compared both with previously used circuits and commercial circuits.

Key words:

, ,



1212–1221 S. Papezova and V. Papez2
Automated Measuring Station for Accumulator Testing
Abstract |
Full text PDF (1 MB)

Automated Measuring Station for Accumulator Testing

S. Papezova¹* and V. Papez2

¹Czech University of Life Sciences in Prague, Faculty of Engineering, Department of Electrical Engineering and Automation, Kamycka 129, CZ 165 21, Prague 6 ˗ Suchdol, Czech Republic
2Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Electrotechnology, Technicka 2, CZ 166 27 Pague 6, Czech Republic
*Correspondence: papezovas@tf.czu.cz

Abstract:

The paper describes the design and implementation of the system allowing the testing of the lithium-iron-phosphate (LiFePO4) cell parameters during long-term loading. Manufacturers and retailers, in particular, accentuate their beneficial properties – the possibility of charging and discharging by high currents, minimum influence of the discharge time on capacity, long durability. At the same time, their operational conditions are a lot more strictly defined than those for other types of accumulators. The proposed testing system enables loading the accumulators, consisting of several cells, by periodic discharging and charging processes with various operating currents and various levels of cell discharging. The charging and discharging process control is fully automated; the measuring of the cell operational state is performed automatically during charging and discharging. The data is recorded, and continuously evaluated for the purposes of process management. The measurements enable the comparison of the catalogue data with the parameters of the real products. The testing system design is based on the application of a digital control block, which is completed with an analog control block. The core of the digital control unit is a control computer equipped with a multifunctional input-output card and an array of logically controlled circuit breakers. An accumulator management algorithm, implemented as a control program of the computer, ensures the operation of the accumulator in subsequent charging and discharging periods. The actual accumulator control is based on the evaluations of voltage levels at the cell terminals. 

Key words:

, , ,



1200–1211 V. Papez and S. Papezova
Optimization of a solar power station with LiFePO4 accumulators
Abstract |
Full text PDF (989 KB)

Optimization of a solar power station with LiFePO4 accumulators

V. Papez¹ and S. Papezova²*

¹Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Electrotechnology, Technicka 2, CZ 166 27 Pague 6, Czech Republic
²Czech University of Life Sciences in Prague, Faculty of Engineering, Department of Electrical Engineering and Automation, Kamycka 129, CZ 165 21, Prague 6 ˗ Suchdol, Czech Republic; *Correspondence: papezovas@tf.czu.cz

Abstract:

The paper describes the design and construction of an isolated solar power station supplying energy at weekends to a remote location. The system comprises two parts: a photovoltaic system generating electric energy in sunlight, and an accumulator accumulating energy to be permanently available and to be able to supply a peak power of several kW. The design of the system optimized with respect to maximum reliability, ease of operation and minimum purchase costs. The control circuits were therefore constructed by means of simple analog circuits. To use microcomputers, which are nowadays used in battery management systems most often available on the market, is not appropriate. Such a system, compared with a simpler analog system, is less reliable. Power circuits are again designed in order to ensure minimum complexity of the system. The resulting design is absolutely different from conventional designs offered by suppliers of photovoltaic systems. The photovoltaic part of the system is designed for optimum adaptation of the load characteristic of the photovoltaic generator to the charging characteristic of the accumulator. By selecting photovoltaic panels with appropriate parameters and their appropriate interconnection, possibly by an automatic change of their interconnection during the charging cycle, it is possible to achieve more effective utilization of the charging power of the photovoltaic generator than by using charging DC/DC converters. The accumulator used in the system is formed by an assembly of LiFePO4 accumulators which thanks to their outstanding durability in spite of their high price currently show the lowest cost per accumulated kWh. 

Key words:

, ,