A Contactless Power Station (CLPS) is a new breakthrough to transmit power without wires in electronic devices such as cellular phones. Power transfer capability of a CPLS system can be increased if the system is designed to operate under resonance condition. The power transfer is then controlled by controlling the inverter frequency. In order to ensure that the power transfer is maximum, a maximum power point tracker is employed to control the CLPS. Several simulated and experimental results are included

Pekik Argo, Dahono

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page 1 of 6  A CONTACTLESS POWER STATION FOR CELLULAR BATTERY CHARGER  Okuli Agunaldo, Rama Dhani Wahono, Rachma …., and Pekik Argo Dahono School of Electrical Engineering and Informatics Institute of Technology Bandung  Jl. Ganesa No. 10 Bandung 40132 Tel. 62-22-2503316 Fax. 62-22-2508132 Email:  ramadhani.wahono@gmail.com  Abstract – A Contactless Power Station (CLPS) is a new breakthrough to transmit power without wires in electronic devices such as cellular phones. Power transfer capability of a CPLS system can be increased if the system is designed to operate under resonance condition. The power transfer is then controlled by controlling the inverter frequency. In order to ensure that the power transfer is maximum, a maximum power point tracker is employed to control the CLPS. Several simulated and experimental results are included.  Key Words: resonance, contactless power station, maximum power point tracker I. INTRODUCTION Wireless charging technology development was developed so that the electronic devices can be charged without any physical contacts. Many types of wireless or contactless power transfer strategies and applications have been reported in the literature [1]-[4]. One application of wireless power transfer is wireless battery charger, the one that is discussed in this paper, Contactless Power Station (CLPS). At first, the general design and construction of wireless battery charger is discussed in this paper. As the energy is transferred through air core transformer, a volt-ampere power supply is needed to transfer the required energy. In order to solve the problem, a resonance concept is proposed in this paper. By operating the system under resonance condition, the voltage drops across the leakege inductances air core transformer are cancelled. Thus, a large volt-ampere power supply is not needed anymore. As the transformer leakage inductances vary with the secondary winding position in relative to the primary winding, the inverter frequency must be changed continuously to ensure that the power transfer is maximum. Thus, a maximum power tracker must be designed to control the inverter to ensure that the power transfer is maximum. Several simulated and experimental results are included in this paper. It is shown that the designed system is successfully operated to transfer the required battery charger power. II. DESIGN OF CLPS SYSTEM Essentially, a CLPS system can be divided into two parts; primary and secondary.  The primary side of the system is made up of a high-frequency inverter, series resonance capacitor, and the primary coil.  This inverter produces a high frequency sinusoidal current in the coil.  The secondary side (or ‘pickup’) has a smaller coil, a series resonance capacitor, and a rectifier. The scheme of the system is shown in Fig. 1. Step by step proceses of designing the CLPS system are described below:  1. Determine the spesification of charging object. 2. Determine the design of the coil, both primary and secondary, as the core of CLPS system.  3. Measure the coil’s inductance and the coupling coefficient between the primary and secondary.  4. Determine capacitance value, in the primary and secondary side, so that the CLPS system works in resonance.  5. Wireless power transfer experiment and  measurement.  6. Simulation of the CLPS system to validate the experiment results.  7. Determine the power transfer characteristic of the designed CLPS system.  air gapINVERTERAC Power SupplyRECTIFIERMagnetic fieldDC Power Supply to DevicePrimary CoilSecondaryCoil Figure 1. Basic CLPS system  The device that will be the charging object are a cell-phone with battery spesification as in Table 1. In designing  the primary coil, the dimention are determined by the type of power transfer in this CLPS system. After several trials it has been found that a CLPS system with several primary coil that smller than secondary coil, has a better efficiency in case involving a moving charge object. High number of coil turns are required to increase the power transfer. The secondary coil must fit in the device, page 2 of 6  however,  can not be so thick to be fitted in the electronic device and, therefore 7 layer was selected. As for the primary, the main considerations are to get the highest inductance as possible, so 10 layer was choosed. Fig. 2 shows the realization of the coils. The next step was to measure the inductance of coils and then, determine the required resonance capacitors.  An LCR meter was used to measure the  coil’s inductances.   Table 2 shows the results. Resonance capacitors can be  determined from this data, knowing the system was designed to operate at 100 kHz. Table 3 shows the calculated results. Table 1. Battery Spesification Charge (Q) 600 mAh Nominal Charge Voltage (V) 3.7 Volt Maximum Charge Voltage (V) 4.2 Volt Power 2.2 Watt Load Impedance (for experiment) 5 Ω   Fig.  2. Secondary and primary coils. Table 2. Inductance Measurement Results Coil L (µH) XL (Ω) Primary 138 86.7 Secondary 48 30.16  Table 3. Resonance Capacitors Coil Capacitance (nF) Primary 18.3 Secondary 52.7   III. MAXIMUM POWER TRANSFER  As the coil inductances varies with the object (secondary coil) positions, the resonance frequency also varies with the position. Thus, the inverter frequency must be controlled to ensure that the power transfer is maximum. In order to investigate the inductance variations, three extreme positions are investigated as shown in Fig. 3. Under these positions, the inverter frequency is varied to determine the maximum power transfer. The results are shown in Table 4. The results are also plotted in Fig. 4.  In order to ensure that the power transfer is maximum, an MPPT strategy is developed. The proposed method is based on the perturb and observe method as described as follows:            Fig. 3.  Relative positions primary to secondary coils. Table 4. Voltage, current, and power for several frequency for each configuration  Position Primary  1  f (kHz)  V (V)  I (A)  P (Watt)     89  38  0.56  6.95     94  48  0.7  10.13     100  68  1  17.8     107  68.8  0.92  15.5     114  48.7  0.6  7  2  85  43  0.6  7     91  54  0.7  11     95  67  0.95  16.2     98  80.2  1.1  21.2     106  63.5  0.8  11     113  48  0.56  6.2  3  83  43  0.6  5.5     89  67  0.9  13.4     94  101  1.3  26     100  89  1.1  20     106  62  0.7  10    Fig. 4. Power vs frequency for each positions SekunderSekunderPrimerPosisi 1SekunderPrimerPosisi 2SekunderPrimerPosisi 3page 3 of 6   1. Determining the initial value for the frequency and measure the value of power at the f value. 2. Raise and lower reference frequency and measure its value 3. Calculate sign(∆P) and sign(∆f) 4. ( )* ( )*ref ref stepf f sign f sign P f     5. Back to step (3) until maximum point found.  The curve in Fig. 5 below illustrates the movement of tracking point to get the optimum point.   Fig. 5.  Algorithm illustration.  IV. SIMULATED AND EXPERIMENTAL RESULTS In order to verify the proposed concept, the whole system is first simulated. The scheme of the simulated system is shown in Fig. 6. The secondary coil is loaded by a fixed resistor.  Fig. 7 shows the simulated and experimental results under the same conditions. The results show that the simulation gave a good result and can be used for further investigation.   ViALpVIpVpAVIsVo RoutLsCp Cs Fig. 6.  The scheme of the system.  The proposed MPPT algorithm is then simulated by using Simulink.  Initial reference frequency value used in the simulation is 110 kHz with a level of change in frequency of 100Hz (fstep). The simulated results are shown in Fig. 8. The results show that the proposed MPPT able to control the CLPS system successfully.    (a) Simulated.  (b) Experimental. Fig. 7. Simulated and experimental primary coil voltage.  (a) Position 1.  (b) Position 2. Fig. 8. Frequency variation to find the maximum power.    page 4 of 6   Table 5 shows comparison between simulated and experimental results. Once again, the results show that the system has been worked as expected.   Table 5. Simulation vs experiment  k Simulation results Experimental results Frequency  (kHz) Voltage  (V) Current (A) Frequency (kHz) Voltage (V) Curretn  (A) 1 99.50 64.15 0.85 100.20 69.10 1.0 2 97.50 78.75 1.10 98.23 80.50 1.1 3 93.15 98.34 1.30 94.16 101 1.3    V. CONCLUSION  A CLPS system for cellular battery charger has been proposed in this paper. An MPPT strategy has also been proposed. Under resonance condition, the power transfer can be controlled by controlling the inverter frequency. Simulated and experimental results have shown that the proposed system has been working as expected.   VI. REFERENCES  [1] Adachi,Shin-ichi, Fumihiro Sato, Shinki Kikuchi, Hidetoshi Matsuki. Consideration of Contactless Power Station with Selective Excitation of Moving Robot. IEEE Transactions on Magnetics, VOL 35, No 5, September 1999. [2] Spies, Peter, Philip Babel. Wireless Energy Transmission System for Low Power Devices. IEEE Sensors  Conference, 2008. [3] Coup, Robert. 2003. Project Report : An Inductively Coupled Universal Battery Charger. The University Auckland. [4] Spies, Peter, Philip Babel. Wireless Energy Transmission System for Low Power Devices. IEEE Sensors  Conference, 2008.     

A CONTACTLESS POWER STATION FOR CELLULAR BATTERY CHARGER

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