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How electricity works without wires (CHAPTER III)

3.1 Main Parts of WPT (Wireless Power Transfer) System

There are 3 main parts in this wireless power delivery system, including:
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Figure 3.1 Schematic of Wireless Power Transfer (WPT)
  1. DC voltage source that will supply voltage to the oscillator.
  2. The transmitter/transmitter circuit consists of a high-frequency alternating current voltage generator circuit and an LC circuit as a magnetic resonance frequency generator that will send electrical power to the receiver circuit.
  3. Receiver circuit, consisting of an LC circuit with a resonant frequency equal to or close to the transmitter circuit, as a magnetic resonance induction catcher from the transmitter circuit to receive electrical power to be channeled to the load.
Based on the scheme in Figure 3.1 above, the author makes a plan for a wireless power transfer system consisting of a design on the sending side and the receiving side as described in the following sub-chapter.

      Based on the scheme in Figure 3.1 above, the author makes a plan for a wireless power transfer system consisting of a design on the sending side and the receiving side as described in the following sub-chapter.

      3.2 Design of Cordless Electric Power Transfer System

      An explanation of the design process of each part of a wireless electric power delivery system with the principle of magnetic resonance induction will be explained in the following sub-chapter.

      3.2.1 DC 15 V, 1.2 A Regulator As Source On Transmitter Side

      This direct current source regulator is used to regulate the DC voltage of the system in order to obtain a DC voltage source that is stable and able to withstand a large enough current. In this final project, the author will use an input voltage of 15 V with the maximum current limit that can be held is 1.2 A. The picture of the regulator that will be the source of the transmitter circuit can be seen in Figure 3.2 below.

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      Figure 3.2 Power Supply DC 15V, 1.2 A

      3.2.2 Circuit on the Sender Side

      In a wireless power delivery system, the transmitter circuit is a very important circuit in the process of generating magnetic resonance. As previously explained, the transmitter circuit consists of a high-frequency alternating current-producing circuit and an LC circuit that functions as a resonant frequency generator or commonly called an Oscillator Circuit.

      In the transmitter circuit, all components are designed to achieve a certain resonant frequency, in order to transmit electrical power properly. The following is a picture of the transmitter circuit design planned by the author.

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      Figure 3.3 Oscillator Circuit 65–976 kHz

      The picture above is an LC oscillator circuit with a resonant frequency between 651–976 kHz. The frequency of the AC voltage generated by this circuit will depend on the L and C values used. There are 8 capacitors in this circuit. To get the working frequency from the range mentioned above, then one or more of the Capacitors C3–C9 must be ON/OFF from the circuit. This circuit uses a DC 15 V, 1.2 A power supply as a source. Resistor R1 in this circuit is worth 5.6 kΩ. This circuit uses the BD139 transistor. The L value that has been set to achieve the maximum frequency of 967 kHz is 14.2 H, where the inductance (L) value is determined by the author himself using an L meter measuring instrument. In theory, this circuit will resonate at the resonant frequency given by:

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      3.2.3 Design of sending coil

      The coil that will be designed by the author in this final project is made of copper wire with a cross-sectional area in the form of a short cylindrical air core with N turns. With the inductance value of the sending coil is 14.2 H, the number of turns required can be found using Equation (3.1) below.

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      The provisions of the coil on the sending side are given in Table 3.1 below:

      Description of the dimensions of the sending coil:

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      With the provisions in Table (3.1) above, the number of turns used on the sending side can be found by Equation (3.1), namely:

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      Thus, the theoretical number of turns required by the sending circuit is 14 turns.

      3.2.4 Design on the receiving side

      The circuit on the receiving side consists of LC components which are connected in parallel. Then as an indication of the presence or absence of received power, the receiving side is also connected to an LED as an indicator. The shape, size, and inductance value of the L3 winding do not have to be exactly the same as the sender, the most important thing is the resonant frequency value between each, namely the sender and receiver are the same or close to each other.

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      Figure 3.4 Design on the receiving side

      3.2.5 Design of receiving coil

      To get better performance, the self-resonant frequency in the receiving coil must be equal to or close to the coupling resonant frequency in the transmitter circuit. The shape, size, and value do not have to be the same or identical, as long as the coupling resonant frequency requirements are met. The dimensions of the receiving coil are made the same as the dimensions of the sending coil. Because the basic principle of this tool is the same as that of the transformer, the equations used in the transformer are also used in this tool. As the equation used to find the number of turns on the receiving side, namely:

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      3.2.6 WPT system testing

      The equation to find the efficiency of power transfer and system is as follows.

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      3.2.7 Testing using LED load

      To prove the presence or absence of energy transfer on the receiving side, several LEDs are installed in the receiver circuit in parallel as shown in Figure 3.8 below.

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      Figure 3.5 Testing Using Parallel LEDs

      In addition, the test will also be carried out using a voltmeter and an oscilloscope to show the voltage value that can be received by the receiving coil and observe the frequency received on the receiving coil.

      3.3 Component Installation

      The process of assembling this wireless electric power transfer device will be explained in the following sub-chapter.

      3.3.1 Order of Component Installation

      The order of installation of components is as follows:
      1. Checking the connection between the lines to avoid short circuits in the circuit
      2. Test all existing components to get components that have the desired characteristics
      3. Components that are damaged/not in accordance with the desired characteristics must be replaced to avoid operation failure
      4. Installing components
      5. Doing soldering with a solder whose power is not too big, which is about 30 Watts. This is done to avoid overheating, especially in the active component.

      3.2.3 Sequence of Assembling Components

      The sequence of the tool assembly process is:

      1. Connecting printed circuit boards to one another using connector cables
      2. Re-checking whether or not the circuit is incorrectly connected between one component and another.