LLC Resonant Converter based Electric Vehicle...

SEEE DIGIBOOK ON ENGINEERING & TECHNOLOGY, VOL. 01, MAY 2018 ALTERNATE ENERGY TECHNOLOGIES

978-81-933187-0-6 © 2018 SEEEPEDIA.ORG Society for Engineering Education Enrichment

E. Sarangapani, [email protected] Dr. N. Narmadhai, [email protected]

LLC Resonant Converter based Electric Vehicle Battery

charger using LabVIEW

E. Sarangapani, Dr. N. Narmadhai Government College of Technology, Coimbatore, India

[email protected], [email protected]

Abstract— This projects presents a performance analysis of LLC resonant converter based electric vehicle battery charger using labVIEW. New LLC resonant converter with two transformers in parallel for the electric vehicle battery charger. This topology achieves the zero-voltage switching for main switches in the entire charging profile. In addition, the zero-current switching for output rectifier diodes is extended under charging condition. The proposed charger provides a wide range output voltage for the battery system because charge equalization algorithm used to achieving higher efficiency for battery charging system. Moreover, in order to maintain the high efficiency under charging, the charger adopts a bidirectional switch. At low-output power condition, the charger uses one transformer to transfer the energy. Finally, the design procedure is provided and implemented in a prototype charger with the input DC link 230 V and the output voltage of 12–24 V. Experimental results are presented to demonstrate the system performance. peak efficiency is as high as 93.6%. Index Terms— LLC Resonant converter, LABView, Charge equalization algorithm, electric vehicle battery system.

I. INTRODUCTION Recently, battery technology has been improving in the applications of electric vehicles (EVs). Thereby the EVs battery chargers are critical for the applications of high-power density and high efficiency[1]. A typical EVs battery charger consisted of an electromagnetic interference (EMI) filter, an AC/DC converter and a DC/DC converter as shown in Fig. 1. Generally, the front stage AC/DC converter adopts a boost topology for power factor correction (PFC) . At the end stage, the DC/DC converter transforms the voltage to charge the battery. Traditional pulse-width modulation (PWM) converters suffer from high-switching losses and greater EMI. Among various DC/DC converters, LLC resonant converter has gained popularity. An LLC resonant converter has the advantage of (i) the main switches operate with zero-voltage switching (ZVS) over wide load ranges, (ii) the output rectifier diodes can achieve zero-current switching (ZCS), (iii) the output filter is formed by only a capacitor instead of the conventional inductor and capacitor and (iv) high efficiency and low EMI

II. PROPOSED SYSTEM

The proposed battery charger, as shown in Fig., consists of a conventional LLC resonant converter[1], two transformers T1 and T2 in parallel, and one bidirectional switch S3. To facilitate the analysis of the proposed system, the FHA

approach is used to simplify the LLC resonant converter circuits, the voltage gain of the LLC resonant tank is expressed and the circuit parameters are shown in fig. On the basis of the FHA approach, the voltage gain curves with different Q are shown in Fig, in which the conditions of from the heavy load to the light load are included. The boundary between ZVS and ZCS regions is also shown in this figure. The Qmax is indicated for the proposed charger at the maximum output power. Basically, there are three operation regions for the LLC resonant converter in Fig.. In Region 1, the resonant tank impedance is capacitive. In general, the LLC resonant converter should avoid operating in this region to prevent high reverse recovery loss and device failure. In region 2, the switching frequency fr2 < fs < fr1, the resonant tank impedance is inductive so that it is easy to achieve ZVS for the main switches. Maximum voltage gain is achieved in this region. In addition, the magnetizing inductor Lm can join the resonance with the resonant inductor Lr and resonant capacitor Cr. Hence, when the rectifier diodes are reverse biased, ZCS can be achieved for the rectifier diodes. In region 3, the switching frequency above fr1, Lm does not join the resonance, though the resonant tank impedance is inductive. The LLC resonant converter can achieve ZVS under all load conditions, but cannot realize ZCS in region 3. Therefore, the switching loss in region 2 is lower than that in region 3. The converter

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operating in region 2 has high efficiencies. shows the characteristics of system in regions 2 and 3. Fig(1). Circuit diagram III. Battery Charge Equalization system: The battery charge equalization[2] is necessary to equalize the battery charge level of overcharged cell by transferring the excess energy to cell back or to equalize that of undercharged cell by feeding the required charge from the cell pack. The proposed battery charge equalization algorithm development is divided into two parts, a master board which comprises the microcontroller and flyback DC-DC converter and the module board that consists of the measurement and the cell monitoring device with battery cells and bidirectional cell switches as shown in Fig.1. The microcontroller communicates with the monitoring IC where the IC monitors the cell status and switches on/off the bidirectional cell switches. Based on the cell status, the microcontroller executes the charge equalization algorithm and generates regulated PWM signal for the flyback DC-DC converter to protect and equalize the battery cell by discharging the overcharged cell or by charging undercharged cell accordingly. The flyback DC-DC converter provides the channel of current flow during charging or discharging process. The cell switch allows a specific cell to be connected through flyback DC-DC converter to cell pack for discharging or charging based on the cell condition as overcharged or undercharged respectively. National Instrument (CRIO) compact rio is the centrol control unit of this battery charge equalization algorithm.

fig(2) Block diagram

IV .Charge Equalization Algorithm: The modularization method is an active equalization method[2]. The monitoring IC is the sensor to make measurements on the status of the battery cell. The monitoring IC reads the voltage level of the cells and communicates with the microcontroller. The microcontroller collects data from monitoring IC, then estimates SOC and compares the result with the threshold value set, detects the unequalized cell and sends instruction to the monitoring IC to activate the bidirectional switch of the corresponding detected cell and the operation of flyback DC-DC converter to carry out charge equalization according to the proposed algorithm. The flowchart of the proposed charge equalization algorithm is shown in Fig.4. The charge equalization algorithm makes decision based on the SOC of battery cells’ voltage readings obtained from the monitoring IC. The charge equalization algorithm[2] is included the charge equalization for overcharged and undercharged battery, and the unbalanced charge in battery string. The following steps are used for the proposed charge equalization algorithm.

Fig (3) Charge Equalization algorithm.

Start

System Initialization

Check the cell status

Cell monitoring and communication

Overcharge modularization

Cell status normal?

Charge balanced?

Undercharge modularization

Over-/under-charged? ( V cell V > max /V cell < V min )

Cell equalization

Balancing with discharge/charge?

SOC estimate

Bidirectional MOSFET switch

control

Stepup flyback DC-DC converter

control

PWM control

Bidirectional MOSFET switch

control

Stepdown flyback DC-DC converter

control

PWM control

Yes

No

Discharge Charge

Overcharged Undercharged

Yes No

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1. Initialize the system. Record the voltage readings, Vi of the battery cells and sort in descending order, V1 to V8, 2. Check the cells’ status whether they are normal or abnormal. if cells are operated at normal goto step2 else ; a cell is found as abnormal. goto next 3. Check the condition of cell if V1>Vmax ; a cell is found as overcharged. 4. Execute overcharge modularization and goto step7. if V8<Vmin ; a cell is found as undercharged. 5. Execute undercharge modularization and goto step7. 6. Start the cell equalization process. 7. Estimate SOCi corresponding to the cells. 8. Check the SOC value for discharge balancing. if SOC1>OSOC ;the respective battery cell of SOC1 is classified as overcharged battery, where SOC1 is the highest SOC reading of the battery cells and OSOC is the threshold value of the overcharged battery SOC which is corresponding to Vmax. 9. Execute the discharge mode 10. Control the bidirectional MOSFET switch corresponding to detected battery cell, generate the PWM signal for discharging the overcharged battery cell, control the stepup flyback DC-DC converter, and allow the equalization current for discharging. 11. Check the balancing of discharging cell. if |SOC1-SOCavg|>2%; the respective cell is unbalanced, where SOCavg is the average SOC of all battery cells and |SOC1-SOCavg| is ∆SOC. goto step7 else ; the cell is balanced. goto step2 12. Check the SOC value for charge balancing. if SOC8<USOC ;the respective battery cell of SOC8 is classified as undercharged battery, where SOC8 is the lowest SOC reading of the battery cells and USOC is the threshold value of the undercharged battery SOC which is corresponding to Vmin. 13. Execute the charge mode 14. Control the bidirectional MOSFET switch corresponding to detected battery cell, generate the PWM signal for charging the undercharged battery cell, control the stepdown flyback DC-DC converter, and allow the equalization current for charging. 15. Check the balancing of charging cell. if |SOC8-SOCavg|>2%; the respective cell is unbalanced, where |SOC8-SOCavg| is ∆SOC. Goto step7 else ; the cell is balanced. Goto step2 The algorithm repeats to maintain the continuous execution of the battery charge equalization process. V. Simulation Results A) Input pulse circuit the multisim simulation doesnot providing individual pulse control. So with the help of LabVIEW software used for co

simulation of multisim power circuit to achieve the linear control of switching circuit.

Fig (4) Pulse generation circuit. B) Simulation Power Circuit:

Fig (5) Simulation power circuit. This is the simulation circuit for proposed llc resonant converter. Switching control from labview tool. VI. Simulated Algorithmic Block The Battery charge equalization Algorithmic simulation diagram is shown in fig. The below algorithmic diagrams are subdivided into three conditions. Condition -1-(Checking for battery voltage equal to 12v) Condition-2–(Checking for battery voltage less than or greater then, if less than battery voltage the cells excess charge can be added to this cells) Condition -3-(Checking for battery voltage greater than or lesser than, if greater than battery cell voltage the cell excess charge can be sent to the lowest cells)

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A) Condition-1

Fig(6)-Charge equalization algorithm-1 B) Condition-2

Fig(7)-Charge equalization Algorithm-2 C) Condition-3

Fig(8)-Charge equalization Algorithm-3

VII. Output Result for Battery charging

Fig (9) Battery output Result. Initial input voltage is 230 dc link with getting output of battery voltage varies from 12 to 24 voltage output. Voltage Varying depends on input voltage tabulation is shown in below

S.NO Input voltage(ac) Battery Output voltage(dc) 1 210 11.20 2 220 11.55 3 230 12.00

Table (1) - Different input voltage ratings. VIII. CONCLUSION A LabVIEW Based new LLC resonant converter for EV battery chargers has been presented in this paper. ZVS for main switches and ZCS for all rectifier diodes are achieved. The features of the new LLC resonant converter include the resonant tank consisting of two transformers in parallel. The proposed design can achieve a gain adjustment with small frequency change for the charger at the CC stage. In the CV stage, the charger has higher efficiencies than the conventional LLC converter. In addition, the charge equalization algorithm is provided to achieve a wide range output voltage for the battery system. Finally, the simulation

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results are given to demonstrate the system performance including the charging waveforms and the charging profile. In the battery charger with Vin = 230 V and Vo = 12–24 V, the measured efficiency is 93% and the measured peak efficiency is up to 94.6%. REFERENCES [1] Chih-Chiang Hua1, Yi-Hsiung Fang2Cheng Wei Lin LLC

Resonant converter for electric vehicle Battery chargers, IET POWER ELECTRONICS, Research articles.

[2] M A Hannana*, M M Hoqueb, S E Pengb, M N Uddinc Lithium- ion Battery charge Equalization Algorithm for electric vehicle Application, IEEE Transaction on industry application.

[3] Hu, H., Fang, X., Chen, F., et al.: ‘A modified high-efficiency LLC converter with two transformers for wide input-

voltage range applications’, IEEE Trans. Power Electron., 2013, 28, (4), pp. 1946–1960

[4] Ma, G., Qu, W., Yu, G., et al.: ‘A zero-voltage switching bidirectional DC–DC converter with state analysis and soft switching-oriented design consideration’, IEEE Trans. Ind. Electron., 2009, 56, (6), pp. 2174–2184

[5] M. M. Hoque, M A Hannan, and A. Mohamed, “Voltage Equalization Control Algorithm for Monitoring and Balancing of Series Connected Lithium-Ion Battery,” J. Renewable Sustainable Energy, vol. 8, no. 025703, pp. 1-15, Mar. 2016.

[6] M. A. Hannan, M. M. Hoque, A. Mohamed, and A. Ayob, “Review of energy storage systems for electric vehicle applications: Issues and challenges,” Renewable and Sustainable Energy Reviews, vol. 69, pp. 771–789, Mar. 2017.

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LLC Resonant Converter based Electric Vehicle...

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