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1598 JOURNAL OF COMPUTERS, VOL. 8, NO. 6, JUNE 2013 Figure 5. Power complement controller diagram The active switch S 2 is driven by gating signal V GS2 to control the input current from PV array. For the control loop of grid power, the main object is to deliver the complement power for remaining smooth current to the LED lighting module. Therefore, the load current I o is fed back and needs to be regulated to the load current command I o * which is decided by the normal operating current of LED module. Then the active switch S 1 will be driven by the gating signal V GS1 to control the input grid power for complementing the power demand. IV. EXPERIMENT RESULTS To evaluate the performance and validity of proposed converter, a prototype with a 45W PV array for a 36W LED lighting module is constructed as shown in Fig. 6. The controlled is implemented by a microprocessor, HT46R23, and relative electrical parameters are shown in Table I. The input current from PV array and load current are sampled by hall sensors. Fig. 7 shows the waveforms of the grid input current, PV input power and the load condition. In Fig. 7(a), it can be seen that firstly the load demand is only provided by the grid because the PV power is unavailable. Then, the PV power is started to provide its maximum power, but the available PV power is still not enough for the load. Therefore, the converter is automatically changed into hybrid supply mode for delivering the complement power from the grid. Once, the maximum PV power is higher than the load demand, there is no complement power required from grid. As a result, the output power for the LED module as shown in Fig. 7(b) can then be wellcontrolled at 36W/24V/1.5A. Fig. 8 shows the waveforms of the capacitor C 1 while the converter is operated in hybrid supply mode with 50% PV power and 50% grid power. It can be seen that the current ripple and peak current are reduced because of adopting the interleave phase shift technique. Fig. 9 shows the efficiency of the proposed converter in single power supply mode with PV power or Grid power input. The efficiency in hybrid power supply mode is measured and shown in Fig. 10, and the definition of the efficiency η is given as following: PO η = (1) P + P PV Grid Table I. PARAMETERS OF PROTOTYPE SYSTEM Input - V Grid =110VACrms, 60 Hz V MPPT ≈45 V, I MPPT ≈1 A Output - V O =24 V, I O =1.5 A Frequency - 38.4 kHz Ferrite core Transformer Component - - EI-33 L T1P /L T1S =425μH / 35.8μH A gip ≈ 0.29 mm N T2P /N T2S =32N / 16N Inductance L 1 =460μH - Component L 2 =525μH C 1 =6μF Capacitor Component - C 2 =1μF C 3 =220μF Figure 6. Prototype of proposed dual-input power converter © 2013 ACADEMY PUBLISHER
JOURNAL OF COMPUTERS, VOL. 8, NO. 6, JUNE 2013 1599 (a) grid input current I GRID Figure 10. Measured Efficiency of the proposed converter in hybrid power supply mode (b) output voltage V o , output current I o and output power P o Figure 7. Measured waveforms in hybrid power supply mode The comparison of system cost between stand-alone PV power system and the proposed hybrid power system is shown in Table II. For a 36W office lighting power system with 85% efficiency works 8 hours a day, the minimum required power capacity is 340Wh. However, the rated power of PV array is only available in 2~3 hours a day [19]. The minimum PV array installed capacity for a 36W stand-alone power system is 120W. Compared with the stand-alone system, the required capacity of PV array in the proposed system is only 36W. Moreover, the energy storage device is not required neither. It is seen that the installing and maintenance cost can then be greatly reduced. Table II. THE POWER SUPPLY SYSTEM COST COMPARISON (8HOURS/DAY AT 36W) Stand-Alone Proposed system PV System Loading 36W 36W PV Array 120W 36W Battery bank 720Wh — Cost High Low Figure 8. Waveforms in different supply modes (V GS1&GS2 : 20V/DIV, V C1 : 5V/DIV, I C1 :4A/DIV) Figure 9. Measured Efficiency of the proposed converter in single power supply modes V. CONCLUSION This paper proposed an isolated dual-input power converter for grid/PV hybrid power conversion systems which can be operated in single power supply mode or hybrid power supply mode. The power complement controller composed of two independent control loops for the grid and the PV power. Once the available PV power is insufficient for the load demand, the power flow from the grid would automatically be controlled to complement the output power. Finally, a prototype for a 36W LED lighting module is constructed to evaluate the validity and performance of the proposed converter. From the experimental results, it is seen that even while the PV power is unstable, the proposed converter can provide a smooth 24V/1.5A output power for the LED module. © 2013 ACADEMY PUBLISHER
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Journal of Computers ISSN 1796-203X
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Corn Moisture Measurement using a C
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Page 261: Call for Papers and Special Issues
Page 264: (Contents Continued from Back Cover
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