Performance Analysis of the Frequency-Adjustable Current Pulse Charger for LFP Battery

Performance Analysis of the FrequencyAdjustable Current Pulse Charger for LFP Battery Wen-Yeau Chang*1, Po-Chuan Chang2, Jheng-Syuan He3 Department of Electrical Engineering, St. John’s University, 499, Sec. 4, Tam King Road, New Taipei City, Taiwan

*1,3

Department of Electronics Engineering, National Chiao Tung University, 1001 University Road, Hsinchu, Taiwan

2

changwy@mail.sju.edu.tw; 2bcchang5836@yahoo.com.tw; 3100m05007@stud.sju.edu.tw

*1

Abstract This paper presents the performance analysis of a frequency-adjustable current pulse charger for LiFePO4 (LFP) battery. The charger uses frequency-adjustable current pulse charging circuit which contains rectifier, buck DC/DC converter, microprocessor, voltage detecting interface, current detecting interface, keyboard, LCD display and control software. The user can adjust the frequency of charging current pulse by controlling the pulse width modulation (PWM) signal. With a microprocessor integrated, the charger is capable of digital control to improve the system reliability. To demonstrate the performance analysis of the frequency-adjustable current pulse charger, the field practical operations of the prototype charger were studied in accordance with the conditions for the different charging modes. The performance is evaluated based on two indexes, namely, charging time and charging capacity.

Keywords LFP Battery; Frequency-Adjustable Current Pulse Charger; Performance Analysis

Introduction The gradual shortage of oil and worldwide awareness of environmental issues highlights the exploitation of energy storage systems. The battery is one of the most attractive energy storage systems because of its high conversion efficiency, low cost and low pollution. There are several kinds of batteries currently being used in industry: leadacid battery, Ni-MH battery, Ni-Cd battery, lithium-ion battery and LFP battery. Of these, LFP batteries are being rapidly developed as the primary power source in hybrid electric vehicles, energy storage system and industrial applications, because of their low pollution and low self-discharge rate [1].

The frequency-adjustable current pulse charge method is to provide the LFP battery a varied pulse charging current, instead of conventional constant current (CC) or constant voltage (CV) charge method, and provide a rest period for the Li ions to diffuse and neutralize [2]. The current pulse charging method can increase the battery life cycle and reduce the battery charge time, and thus, it is widely used in advanced battery charger.

The frequency of current pulse in the frequency-adjustable current pulse charger is the major factor of charger performance [3]. In fact, the frequency of current pulse in battery pulse charge system is always determined by a try-and-error method or empiricism. In order to increase the charge speed and charge efficiency of charger, the performance analysis of the different frequency is proposed in this paper.

In this paper, a performance comparison of the frequency-adjustable current pulse charger for LFP battery is presented. To verify the performances of the proposed frequency-adjustable current pulse charger, a prototype charger has been tested on practical LFP battery. The field practical operations of the prototype frequencyadjustable current pulse charger were studied in accordance with the conditions for the different charging modes.

Configuration of the Frequency-Adjustable Current Pulse Charger The configuration of the proposed frequency-adjustable current pulse charger is illustrated in Figure 1. The control core of the charger is the micro processor. The charging circuit is formed by the current pulse charging circuit at International Journal of Engineering Practical Research, Vol. 4 No. 1-April 2015 2326-5914/15/01 075-04 © 2015 DEStech Publications, Inc. doi: 10.12783/ijepr.2015.0401.15

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Wen-Yeau Chang, Po-Chuan Chang, Jheng-Syuan He

which the PWM signal control the charging pulse.

The architecture of the proposed current pulse charging circuit is illustrated in Figure 2. The current pulse charging circuit integrated rectifier, buck DC/DC converter, micro-processor, terminal voltage detecting interface, current detecting interface, keyboard, LCD display and control software. The user can adjust the frequency of charging pulse by controlling the PWM signal.

110V AC Source

Frequency-Adjustable Charging Circuit

Charge Current

Battery

Voltage Detect Interface

Charge Control Program

Frequency Adjustable PWM Control Program

Input Program

LCD Display Program

PWM Signal

Current Detect Interface

Frequency Adjust Cmmand

LCD Display

LCD Signal

Keyboard Micro Processor

FIGURE 1. CONFIGURATION OF THE PROPOSED FREQUENCY-ADJUSTABLE CURRENT PULSE CHARGER. Buck DC/DC Converter

Rectifier

Power Transistor

Current Signal Voltage Signal

Frequency Adjustable PWM Signal

Battery

110V AC Source

Keyboard

Power Transistor Driven Circuit

Voltage Detect Interface

Micro Processor

Current Detect Interface

FIGURE 2. ARCHITECTURE OF THE PROPOSED CURRENT PULSE CHARGING CIRCUIT.

Experimental Results To verify the proposed the frequency-adjustable current pulse charger and compare the performance of different frequencies, experiments were conducted to demonstrate its effectiveness of the proposed charger. A prototypical charger for LFP battery was set up in the laboratory. The charger employed in the tests consisted of a current pulse charging circuit with 10 kinds of frequencies of charging adjusted modes, the frequency of charging pulse is adjusted from 10Hz to 100Hz. In the experiment, the amplitude of charging current is fixed, and the duty cycle of charging pulse is fixed.

In the adjust frequencies current pulse charging test, the testing LFP batteries have nominal voltage of 3.2V, and nominal capability of 10 Ah. The testing results show that the proposed charger can adjust the frequency accurately. Figures 3~7 show the experimental results obtained with charging current amplitude is 10A, duty cycle is 50%, and the frequency are 10Hz, 30Hz, 50Hz, 80Hz and 100Hz, respectively. In Figures 3~7, Channel 1 denotes

Performance Analysis of the Frequency-Adjustable Current Pulse Charger for LFP Battery

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the PWM control signal (20 V/div), Channel 3 incates the waveform of the charging pulse current (5 A/div)i, and Channel 4 depicts the waveform of battery terminal voltage (2 V/div). Table 1 presents the performances analysis of 10 kinds of frequencies of pulse charge currents.

FIGURE 3. EXPERIMENTAL WAVEFORMS OF THE 10Hz CURRENT FIGURE 4. EXPERIMENTAL WAVEFORMS OF THE 30Hz CURRENT PULSE CHARGING TEST. PULSE CHARGING TEST.

FIGURE 5. EXPERIMENTAL WAVEFORMS OF THE 50Hz CURRENT FIGURE 6. EXPERIMENTAL WAVEFORMS OF THE 80Hz CURRENT PULSE CHARGING TEST. PULSE CHARGING TEST.

FIGURE 7. EXPERIMENTAL WAVEFORMS OF THE 100Hz CURRENT PULSE CHARGING TEST. TABLE 1 THE PERFORMANCES ANALYSIS OF 10 KINDS OF FREQUENCIES OF PULSE CHARGE CURRENTS

Performance index Charging time (hr:min:sec) Charging capacity (mAh)

100Hz

90Hz

80Hz

02:24:3 8354.6

01:56:1 8040.9

02:09:1 8185.2

Frequencies of pulse charge currents 70Hz 60Hz 50Hz 40Hz 02:10:1 8227.0

02:04:0 8143.8

01:58:5 8797.4

02:14:1 8288.2

30Hz

20Hz

10Hz

02:07:4 8430.3

02:03:1 8432.6

02:08:5 8377.2

Comparing the nine kinds of duty cycles of charging adjusted modes, a general conclusion that may be drawn from the obtained results is that the frequency-adjustable current pulse charger can be effective for fast charging a LFP battery. In what relates to the comparison between ten modes, one may generally conclude that the 50Hz frequency achieve shorter charging time and has better performance in charging capacity.

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Conclusions This paper has proposed a frequency-adjustable current pulse charger for LFP battery. Experimental results have been used to verify the effectiveness of the proposed frequency -adjustable current pulse charger. The performance analysis of the different frequency has been presented in this paper. The experimental results show that the frequency-adjustable current pulse charger can be very effective for fast charging a LFP battery. The experimental results also show that the the 50Hz frequency achieve shorter charging time and has better performance in charging capacity. The directions of future research of the adjustable current pulse charger can be described as follows: To further improve the performance of current pulse charger, the current pulse charger based on both duty-adjustable and frequency-adjustable will be investigated.

ACKNOWLEDGMENT

The authors would like to express their acknowledgements to the Ministry of Science and Technology of ROC for the financial support under Grant MOST 103-2632-E-129 -002 -MY3.

REFERENCES

[1] Chang, Wen-Yeau. “Estimation of the State of Charge for a LFP Battery Using a Hybrid Method That Combines a RBF Neural Network, an OLS Algorithm and AGA.” International Journal of Electrical Power and Energy Systems 53(2013): 603611.

[2] Chang, Wen-Yeau. “Design and Implementation of the Multifunction Fast Charger for LiFePO4 Battery.” Applied Mechanics and Materials 577(2014): 568-571.

[3] Chen, Liang-Rui. “A Design of an Optimal Battery Pulse Charge System by Frequency-Varied Technique.” IEEE Transactions of Industrial Electronics, 54(2007): 398-405.