IPT STATION FOR STATIC AND DYNAMIC CHARGING OF ELECTRIC VEHICLES Nikolay D. Madzharov(1), Anton T. Tonchev(2)

(1)Technical University of Gabrovo H.Dimitar str. 4, 5300 Gabrovo, Bulgaria, e-mail:madjarov@tugab.acad.bg (2) Technical University of Gabrovo H.Dimitar str. 4, 5300 Gabrovo, Bulgaria, e-mail: anton_tonchev@abv.bg

Abstract

The present research report examines the key aspects in the design and implementation of contactless charging station for electric vehicles 30kW@9cm. Its main purpose is a representation an alternative method of charge. At the same time, provides an opportunity for quick charging of electric vehicle batteries. Modes of charge, which are part of functional properties of the system are both when stationary and during motion of electric vehicle. The basic units of the Charging converter are described, the circumstances of their design, advantages and disadvantages.

1. Topology and construction

The developed and presented converter for contactless charging of electric vehicles, both in static and dynamic mode demonstrates practical aspects of the application of this technology as well as some of its drawbacks to this moment (Fig.1). An interesting characteristic is the maximum power transfer system which the system provides - over 30 kW in continuous operating mode. In practice such levels of transferred power makes this prototype forefront of the competition along with many companies producing systems for contactless charging of electric vehicles as: SIEMENS, PRIMOVE, NISSAN, WAMPFLER etc. [2,3,4,5,12].

Figure 1. Power Electronics Topology of the on-route charging of EVs

In figure 1 is presented a topology of the power electronics of the converter. As the prototype is designed for testing and demonstration of static and dynamic mode (at the time of motion) an advanced model of a standard full bridge converter is used [1,8,9,10,11]. For this purpose one leg of the converter runs constantly (both in static and dynamic charge) while the remaining four are connected with each of the inductive power transfer (IPT) coils. The main advantage of this type of full bridge modification is the decreasing the total number of IGBT modules – from four separate converters, each with two modules the total amount is 5 modules. Instead of using four separate full bridge inverters the designed prototype uses only one modified five leg inverter. Of course, the major unit in the IPT station is the loosely coupled equivalent power transformer. The design process of such transformer is focused on the specifics of geometry and dimensions, range of misalignment change, mechanical construction, concentration and orientation of the electromagnetic field etc. Figure 2 presents influence of the aluminum shield of the IPT coils – results based on electromagnetic computer simulations. The main goals of this simulation are to find the level of influence of the electromagnetic field to the nearby objects, according to the ICNIRP requirements.

Figure 2. Electromagnetic field distribution with and without (below) AL shield

Figure 3. IPT Coil construction

The construction of the prototype transmitting coil and distribution mock-up of the ferrite bars are shown on figure 3. Basic role for the efficiency is played by the effective current density in the coil conductor (copper losses) and material type of the ferrite bars. Moreover the weight of the receiving coil (on the EV) is also connected with the overall efficiency. On table1 are shown the main parameters of developed IPT transformer and their change for different values of the air gap and at frequency that ensures ZCS of the IGBTs. The measured values are measured by connecting the primary and secondary coils in series - in one direction (LSER) and opposite (LPAR) [6].

� = ��. ���

��� =

�����������

� (1) � =

�

���.�� (2)

��� = �� − �� (3) ��� = �� − �� ���

��� (4)

���� = �� + �� + 2� (5) ���� = �� + �� − 2� (6)

Table 1. IPT parameters

ZCS Frequency 14,4 kHz 13,8 kHz 13,3 kHz 13,0 kHz

Vertical Gap 55 mm 65 mm 75 mm 85 mm

N2 / N1 1,63 1,63 1,625 1,63

Coupling coefficient, K 0,613 0,556 0,508 0,465 M , µH 83,65 73,7 66 59,43

L1, µH 79 76,7 75 73,6

L2, µH 236 229,4 225 221,9

L1+L2 (LSER), µH 482 453,2 431 413,8 L1-L2 (LPAR), µH 147,4 158,4 167 176,1

Lm , µH 51,48 45,35 40,62 36,57

L11, µH 27,52 31,35 34,38 37,03

L22, µH 152,4 155,7 159 162,5

2. Output power regulation techniques

The frequency shift control method of the converter enables a wide range of variation of the output parameters in dependence of the air gap between the coils and their axial displacement. The condition for power control of continuous load circle is given by the following expressions:

��� =��.�√�

� (7)

��� =���.��� �

� (8)

� =���

�.���� �

� (9)

� =���

�

�.

�

������

���

���

�� , (10)

where: Vd – DC supply voltage of the converter; VHF – high frequency voltage; IHF – high frequency current; ω – angular control frequency of the converter; ω0 – angular resonant frequency of the AC circuit.

In combination of simple PWM or Phase Shift PWM regulation technique the expression for power regulation is:

� =[���.(���)]�

�.

�

������

���

���

�� , where D – pulse width coefficient (11)

Another option for output power control with variable coupling factor between the coils is to change the parameters of compensation components [7,8]. On Figure 4 and 5 are shown the achieved characteristics and simulation model for changing the values of secondary inductance L5 or secondary capacitor C3. Switching process between different sets of capacitors (C3) or different sets of chokes (L5) can be achieved using a pairs of electronic switches - MOSFET or IGBT modules [1,2,9,11].

Figure 4a. Output DC Voltage vs. Frequency characteristics - C3 variable, L5=const

Figure 4b. Output DC Voltage vs. Frequency characteristics - L5 variable, C3=const

Figure 5. Simulation model for IPT transformer and output compensation

Another key feature of the developed system is its ability to transfer energy while running (“on-route” charging). Figure 6 shows the main parameters describing the process of dynamic charge of the battery pack. The length of the path in which the system does not transfer energy is:

���� = (����� − ���) + ����� (12)

Transferred energy during the movement is proportional to the speed and EPT area (±80mm):

��� = ��� . ∫ ����������

����� , (13)

where: EPT - represents the area of effective transfer of energy, wherein the efficiency of the

system is above 80%. It determines the maximum speed during dynamic charge along with the time constants of switching the inverter.

PT represents the area of energy transfer, but with significantly lower efficiency.

CSAREA (coil switching area) is used for starting point for the coils switching algorithm.

Figure 6. Dynamic charging parameters

This method is very useful when it is necessary to test the actual performance of the system under various operating scenarios, but not suitable for use in real charging process (only for tests).

3. Converter parameters and results

Table 2 shows the main geometrical and electrical parameters of the designed IPT system. Figure 7. shows the current and voltage waveforms of the AC-Bridge diagonal at 85mm vertical air gap.

Table 2. IPT Converter parameters

Parameter Value

Nominal Input Power 30kVA / 75A / 400V

Peak Input Power 45kVA @ 1min

Efficiency, [%] up to 92%

Converter Freq., [kHz] 20kHz ÷ 12kHz

Coil dimensions, [kg] 700mm x 800mm x

90mm

Converter Control Technique

Frequency shift, Phase shift

Gap, mm 70 ÷ 90mm

Horizontal misalignment, mm

ΔX=ΔZ= ± 100mm

Figure7. Current and Voltage waveforms of the AC-Bridge diagonal

The dependence of the resonant characteristics of the converter according to the change of the air gap between the coils is shown in figure 8. It is clearly seen the need for a preliminary choice of the variation of the air gap range, the choice of a different kind of compensation circuit (mixed) or ability to change any of the compensating elements (output capacitor C3, for example) in order to obtain the optimum operating point of the converter.

Figure 8a. Output IPT Power Vs. Resonant frequency at different vertical air gap

Figure 8b. Primary IPT coil voltage Vs. Resonant frequency at different vertical air gap

Figure 9 shows the first prototype of the movable pick-up coil (the DC load at power of 30kW is not shown). It can be seen the transmitting and receiving coils, used for the demonstration of "on route" charging process. For this purpose special sensorless algorithm is used for primary coils switching. In figure 10 are shown HF converter prototype and the main components of the DC/AC inverter – figure 11.

Figure 9. The first prototype of the IPT mock-up for static and on-route charging of EVs

The main components of the HF inverter are shown in figure 11: 1. Dual channel IGBT Drivers with embedded SMPS – 5 pcs. 2. IGBT Modules – 200A / 1200V with the copper heat sink – 5 pcs. 3. Primary Matching transformers, based on E100 cores –two connected in parallel for

each Transmitting Coil – 8 pcs. 4. 3 phase bridge rectifier and DC Current Measurement module – 1pc. 5. DC Capacitor Bank – 1pc.

Figure10. HF converter prototype Figure11. HF inverter “DC/AC section” view

The test results of the mock-up charging station are satisfactory both in the DC/AC inverter operating mode and in terms of the change in the air gap. The next steps of this work will continue to improve the magnetic coupling between the windings and efficiency by optimizing the IPT configuration and the parameters of its core.

Conclusion

The theoretical and experimental studying of the developed IPT charging station is very important for the general assessment of the possibility of practical implementation. The content of work carried out in this aspect can be summarized as follows:

- Analysis of the physical aspects, important in the design of IPT system. - Implementation of the prototype - transfer of 30kW through air gap of 7÷9 cm and

90% efficiency of the process. The achieved results are encouraging and one of future direction is to develop a production model of the charging station for the static and on-route charging of electric vehicles operating in real urban environments [6], which is in line with the objectives of the project FastInCharge under the FP7 program.

References

[1] Madzharov N.D. Resonant Power Supplies with Energy Dosing and PLL Control System, PCIM’08,Power Conversion, Nurnberg, Germany, 2008.

[2] Patent WO 2009/021979, Self-configuring induction sealing device for use to produce pourable food product packages, Donati Andrea (Tetra Pak, Italy), Madzharov Nikolay (TU,BG), Melandri Antonio (Tetra Pak, Italy), Siginolfi Fabrizio (Tetra Pak, Italy).

[3] Patent WO 2006/048441, Sealing Device For Producing Sealed Packages of a Pourable Food Product, Valentin Nemkov (Fluxtrol, USA), Nikolay Madzharov (TU, BG)

[4] Patent WO2007138372 AB, Sealing Device and Method for Producing Sealed Packages of Pourable Food Product, Valentin Nemkov (Fluxtrol USA), Nikolay Madzharov (TU Gabrovo, BG), Gerhard Gnad (Herrmann, Germany)

[5] Madzharov N.D, Ilarionov R.TBattery Charging station for electromobiles with inverters with energy dosing, PCIM’11,Power Conversion, Nurnberg, Germany, 2011.

[6] Mohd Zaifulrizal ZAINOL Design and analysis of contactless transformer using series resonant converter, UMPEDAC, University of Malaya

[7] “Innovative fast inductive chargingsolution for electric vehicle” - Smart infrastructures and innovative services for electric vehicles in the urban grid and road environment, part of 7th Framework Program of EU, www.fastincharge.eu

[8] Kraev G., N. Hinov, L. Okoliyski, “Analysis and Design of Serial ZVS Resonant Inverter”, Annual Journal of Electronics,V5,B1,TU Sofia, Faculty of Electronic Engineering and Technologies, ISSN1313-1842, pp.169-172, 2011.

[9] Kraev G., N. Hinov, D. Arnaudov, N. Ranguelov and N. Gradinarov, „Multiphase DC-DC Converter with Improved Characteristics for Charging Supercapacitors and Capacitors with Large Capacitance”, Annual Journal of Electronics, V6,B1,TU of Sofia, Faculty of EET, ISSN 1314-0078, pp.128-131, 2012.

[10] Bankov, N., Al. Vuchev, G. Terziyski. Operating modes of a series-parallel resonant DC/DC converter. – Annual Journal of Electronics, Sofia, 2009, Volume 3, Number 2, ISSN 1313-1842, pp.129-132.

[11] Bankov, N., Al. Vuchev, G. Terziyski. Control characteristics of a transistor LCC resonant DC/DC converter with a capacitive output filter.-Annual Journal of Electronics, Sofia,2011, V 5, Number 1, ISSN 1313-1842, pp.204-207.

[12] Madzharov N.D., Tonchev A.T., Contactless Charging System For Electric Vehicles., International Scientific Conference PCIM2012, Nuremberg, Germany.