1.TECHNICAL FIELD
The present invention relates generally to wireless harvesting of maximum photovoltaic power, and, particularly but not exclusively, relates to maximum power point tracking of the photovoltaic power. This invention aims for a sophisticated way of transferring maximum solar power that can be used to recharge batteries of devices like wireless sensors, actuators, LEDs, etc. or power them up wirelessly, thus overcoming obstacles of cumbersome wiring or modifying existing ones. Nevertheless, we can recharge or provide solar power towards hermetically sealed devices where replacement of the battery is difficult and thereby fatigue, failures of connectors can be avoided effectively.
2. BACKGROUND OF INVENTION
Solar or photovoltaic energy, which can be converted into electrical energy using solar panels, is the most easily available and useable renewable source of energy. Solar panels can be installed easily on the rooftops of offices or buildings. The efficiency of the solar panel is low enough (»10% -16%) and electrical power characteristics of solar panel exhibit a peak power point. We need to operate the panel on that Maximum Power Point (MPP) to extract maximum renewable energy out of it using the Maximum Power Point Tracker(MPPT). A DC-DC converter is used along with solar panel to track the maximum power point.
Wireless power transfer (WPT) is the next generation way of transferring the power without using wires, and is widely used in many applications from low/mid power devices, such as medical implanted devices, charging of mobile, laptop, tablets and other portable device, to high power devices such as electric vehicle charging, etc. US 6,960,968 B2 provides a detailed design guidelines and characteristics of the planer resonator coil that can be used in WPT of compact and hermetically sealed devices. US 2010/0052811 A1 discloses features of two dimensional structure of transmitter and receiver resonators used in WPT.
Wireless sensors, actuators, LEDs, etc. that are mounted on the ceiling of buildings, are powered either by battery or by electrical wiring. In order to recharge or replace these power sources, we need to remove these devices from their existing mounting frames. Further installation or modification in the cable wiring to power up the device is quite difficult and leads to escalation of the cost towards the decoration of the room

and also create Untidy and hazardous wiring. Therefore, there is a requirement of

sophisticated way of transferring maximum solar power from rooftops that can be used to recharge the battery or as a power source for ceiling mountable devices overcoming the obstacles. This methodology is more suitable particularly where wiring is difficulty or no need to modify existing wiring. Thus fatigue, failures of connectors can be avoided effectively and leads to clean and green environment. WPT technology and MPPT technique is used for harvesting or use of maximum photovoltaic power wirelessly. The transmitter system consists of fast and efficient maximum power point tracker for photovoltaic module and a resonance inverter to transmit the solar power over obstacles. Using receiver at the receiving end, that is tuned with the transmitter, receives the transferred solar power. This power can be harvested and transferred to the storage device by the mode of non-intrusive charging or the harvested energy can be used to power up LEDs, wireless sensors or actuators, etc. Moreover, multiple receivers can utilize the power using the shared common flux.
3. OBJECTS OF THE INVENTION
The principal objective of this invention is to harvest and use maximum produced solar energy wirelessly. Our invention presents harvesting of maximum solar power as renewable source of energy and transfers that energy wirelessly to the target device overcoming the obstacles of unwieldy wiring and make for a clean and safe environment.
4. SUMMARY OF INVENTION
Wireless sensor/actuator devices, LEDs installed under roofs require a power source to charge its battery or power up itself. For installation of such devices, about 25% cost of the total budget and 75% time of project have to be invested in wiring. To overcome this scenario, such devices are powered up or recharged wirelessly where the power is transmitted from the rooftop through the obstacle. The renewable power like PV panels are installed on the rooftop and the maximum harvested power is transmitted to the target device. In this mode of transferring the power provides clean and tidy, hazard free environment for smart operation. More than one receiver can be installed in close distance to utilize the maximum amount of power. Use of shermetcally sealead device can also be possible as the connectors are removed.

5. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure I depicts Block diagram, equivalent circuit representation and operation point
Fig 1: Block diagram of complete system.
Fig 2: Equivalent circuit representation of 2-coil wireless power transfer block.
Fig 3: VI Characteristics of PV at MPP operation
3(a): At critical coupling condition of wireless power transfer devices. 3(b): At over coupling condition of wireless power transfer devices. Figure II depicts experimental waveform of the MPPT boost converter and wireless power transfer block
Fig 4(a): Experimental waveform of MPPT boost converter operated at
periodic mode condition.
Fig 4(b): Experimental waveform of MPPT boost converter operated at chaotic
mode condition.
Fig 4(c): Experimental waveform of full bridge resonant inverter used in
wireless power transfer block Figure III depicts experimental validation of the system with artificially illuminated PV panel
Fig 5(a): 2-coil wireless power transfer system (single transmitter and single
receiver)
Fig 5(b): Multi-coil wireless power transfer system (single transmitter and
multiple receiver)
6. DETAILED DESCRIPTION
The invention is related to a power processing of photovoltaic power and transfer of the processed maximum solar power wirelessly over the obstacle towards the target devices. In such a way renewable energy is harvested wirelessly to the target devices that leads to removal of untidy, hazardous wiring and make the environment green. Solar or photovoltaic energy is most easily available and useable renewable source of energy.
Fig 1 depicts the complete block diagram of the system where two separate systems are shown, wireless power transmitter and another is the wireless power receiver. These two systems are galvanically isolated and couple through the magnetic flux over the obstacle of distance 'd'. Transmitter block consists of a solar panel that will be instelled on the rooftop as photovoltaic characteristic shows a non-linear power

characteristic with a global peak power point at uniform insolation, so we have to use maximum power point tracking (MPPT) boost converter. The output of the boost converter is connected to the DC power bus of the H-bridge (Full bridge mode) inverter and thus the maximum power is transmitted from the transmitter end. In Fig.1 Gate pulse_1 is generated for a boost converter to track the MPP and Gate pulse_2 is complementary pulse generated for driving complementary switch of full bridge inverter. All gate pulses are generated simultaneously using a standalone microcontroller unit. The full-bridge inverter operates at resonance frequency to create inductive resonance and the maximum amount of magnetic flux lines are generated from the transmitter. The magnetic field lines are non-radiative in nature and does not interact with common object in daily uses. At the receiver end, the generated maximum flux lines are linked to pick-up coil of the receiver resonator which is installed on the ceiling. From the resonator we get raw high frequency AC power which can be processed to usable DC power using a high frequency rectifier or self-synchronous rectifier. That power may be further processed for harvesting with a DC-DC converter for charging of the battery or may be used to power up wireless sensor or actuator or light up LEDs, etc. The complete transmitter unit and receiver resonator can be compacted within a hermetically sealed, connector-less devices.
Solar or photovoltaic energy is easily available and useable renewable source of energy. The energy conversion device showing the photoelectric effect (from light energy to electrical energy) i.e. photovoltaic cell has non-linear P-V characteristics with a maximum peak power point at uniform insolation. In order to extract maximum power from the photovoltaic cell or solar panel we need to operate the panel at maximum peak operating point i.e. MPPT point. The MPPT point can be achieved by using an additional power processing unit called DC-DC converter and from the output of the DC-DC converter we can harvest the maximum amount of energy. In our system the output of the DC-DC converter is connected to the DC bus of full bridge inverter for wireless power so we need to track the MPP very fast with respect to the disturbance and accurately to minimize voltage fluctuation and obtain stiff regulation of bus voltage. Fast and robust tracking algorithm is implemented based on the ripple current and ripple voltage of the photovoltaic input as ripple dynamics is fast enough for any DC-DC converter, it is called ripple correlation control. The conventional hill climbing MPPT algorithm takes much time to reach maximum power

point (MPP) by varying the Duty ratio of the converter therefore the system lose its energy during off time of the switch of the converter, but in ripple co-relation based control, the switch remain on until the MPP reach and after reaching the MPP the switch is turned off to transfer the energy towards output side and oscillates around the MPP point. Fig 3(a) shows the limit cycle oscillation of the V-l characteristic of PV panel around MPP t and Fig 4(a) depicts the time domain waveform of the boost converter at a periodic mode of oscillation of boost converter. For any disturbance like insolation variation, change in coupling condition or load change at the receiving side of WPT system the operating point is drifted from the periodic orbit and moved to other aperiodic orbit in state space in order to balance the energy quickly and that leads to the chaotic mode of operation as shown in Fig 4(b). In Fig 4(b) aperiodic nature of gate pulse is shown. Due to aperiodic nature of converter, the output voltage of the boost converter Vs is given



The duty cycle is not the periodic in all over the range, so we need to consider the average value of duty cycle.
Fig.2 depicts an equivalent circuit representation of 2 coil wireless power transfer system, wherein Vs is the source voltage of the resonator i.e. output of the full bridge inverter. The peak-peak magnitude of the Vs is depends on the MPP tracked boost converter so also depends upon the solar insolation. rp-Tx and rp-Rx are the modelled equivalent series resistance for the transmitter and the receiver side respectively. LTX, CTX and LRx, CRx are the resonator at the transmitter and receiver side respectively. kTR is the coupling coefficient from transmitter to receiver and RL is the equivalent load resistance that produces the voltage VL at the receiver side. The input and output relation of the boost converter is given as (1) where vPV is the PV voltage at MPP point, and Vs is boosted according to the average duty cycle of the boost converter. Now applying circuital law on both transmitter side and receiver side of Fig. 1 gives

to derive a guideline in terms of design parameter, from tradeoff of the range-efficiency curve, the knee value of the critical coupling coefficient can be found from



Using Newman's mutual inductance formula, we can get the value of mutual inductance in terms of geometrical distance and from the mutual inductance we can find the coupling coefficient between transmitter and receiver in terms of distance as

Now the critical value distance in terms of design parameter of coil can be obtained


from (6) and (7)

where rTx.and rRx is the radius of the transmitter and the receiver coil respectively. The distance of power transfer depends upon the quality factor of the coil and the radius of the coil. In order to prevent frequency splitting of WPT system and operate between knee value of maximum efficiency and maximum power, the distance of operation should be slightly greater than dCrlt.
In Fig 1, in the transmitter unit MCU is shown that generates the gate pulse (Gate Pulse_1) for tracking the MPP of PV and Gate Pulse_2 to run the full bridge inverter in resonant mode. Fig 4(a),4(b) shows the time domain waveform of boost converter with PV current, voltage, gate pulse and clock, Fig 4(c) shows the waveform of the full bridge resonant inverter used in WPT, voltage waveform at the transmitter side, complementary gate pulses and voltage at receiver side is shown. Fig 5(a) shows complete transmitter and receiver module with different devices at in-house, artificially illuminated condition The flux generated from the transmitter can be shared among the multiple receiver resonator tuned at same frequency Fig 5(b) shows the condition of multiple receiver coupled with different load coupled to a single transmitter.

WE CLAIM:
1. A process of harvesting maximum produced solar energy wirelessly where in a Maximum Power Point Tracking (MPPT) controller is used for extracting maximum power and a wireless power transfer system is used for transferring the harvested power from transmitter side. At the receiving end, the power is picked up using one or multiple receiver and fed to target devices.
2. According to claim 1 the fast and robust MPPT controller comprising: photovoltaic(PV) array that generates PV output voltage vPV and PV output current iPV. A DC-DC boost converter is connected to PV array that can track maximum power point very quickly and the output of the converter produce DC link voltage of said wireless power transfer transmitter system.
3. According to claim 1 wireless power transfer transmitter comprising: a full bridge resonance inverter and at the receiving end the receiver system is tuned with resonance frequency of the transmitter.
4. Multiple receiver systems can be coupled with said single transmitter system to receive power.
5. The maximum PV power can be transferred wirelessly at the critical distance of coupling between the said transmitter and the said receiver.