Comprehensive Guide: How to Determine Energy in Wireless Charging Systems

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Wireless charging systems have become increasingly popular in recent years, offering a convenient and cable-free way to power up our electronic devices. However, accurately determining the energy in these systems is crucial for optimizing their performance and efficiency. In this comprehensive guide, we will delve into the various factors that contribute to the energy determination in wireless charging systems, providing you with a detailed and technical understanding of the subject.

Understanding the Fundamentals of Wireless Charging

Wireless charging systems operate on the principle of electromagnetic induction, where a transmitter coil in the charging station generates a magnetic field that induces a current in the receiver coil within the device being charged. The efficiency of this power transfer is influenced by several factors, including the coupling between the coils, the quality of the coils, and the compensation topology used.

Measuring Power in Wireless Charging Systems

how to determine energy in wireless charging systems

  1. Power Measurement Techniques:
  2. The power transferred to the load in a wireless charging system can be measured using a method that does not require any metrologically certified measurement instrumentation on the receiver side.
  3. This method is based on the measurement of AC parameters in the circuit of the transmitting (primary) coil.

  4. The systematic error of the power assessment does not exceed 0.7% for serial-serial (SS) and 1.1% for serial-parallel (SP) topologies when the coupling coefficient is in the range of 0.05 to 0.4 and the quality factor of the resonant system is in the range of 100 to 800.

  5. Coil Coupling Coefficient:

  6. The coil coupling coefficient is a measure of the strength of the magnetic coupling between the transmitter and receiver coils.
  7. It plays a crucial role in determining the efficiency and power transfer capability of the wireless charging system.

  8. The systematic error of the power assessment does not exceed 0.7% for SS and 1.1% for SP topologies when the coupling coefficient is in the range of 0.05 to 0.4.

  9. Coil Quality Factor:

  10. The coil quality factor is a measure of the coil’s efficiency in storing electrical energy relative to the energy lost as heat.
  11. A higher quality factor indicates less energy loss and better efficiency.

  12. The systematic error of the power assessment does not exceed 0.7% for SS and 1.1% for SP topologies when the quality factor of the resonant system is in the range of 100 to 800.

  13. Current and Voltage Quantization Resolution:

  14. The resolution of current and voltage quantization affects the accuracy of power measurement.

  15. Higher resolution leads to more accurate power assessment.

  16. Compensation Topology Type:

  17. The compensation topology type, either serial-serial (SS) or serial-parallel (SP), influences the power transfer efficiency and systematic error of the power assessment.

  18. The systematic error of the power assessment does not exceed 0.7% for SS and 1.1% for SP topologies when the coupling coefficient is in the range of 0.05 to 0.4 and the quality factor of the resonant system is in the range of 100 to 800.

  19. Transferred Power:

  20. The power received at the secondary coil affects the assessment error of the method.
  21. The active transferred power assessment error does not exceed 0.7% in the SS compensation topology and does not exceed 1.1% in the SP compensation topology if 16-bit resolution analog-to-digital conversion is used for current and voltage quantization.

Theoretical Considerations

  1. Electromagnetic Induction Theory:
  2. The wireless charging process is based on the principle of electromagnetic induction, where a time-varying magnetic field generated by the transmitter coil induces a voltage in the receiver coil.
  3. The induced voltage is proportional to the rate of change of the magnetic flux, as described by Faraday’s law of electromagnetic induction.

  4. The magnetic flux is determined by the coupling coefficient between the transmitter and receiver coils, as well as the current flowing through the transmitter coil.

  5. Resonant Circuit Theory:

  6. Wireless charging systems often employ resonant circuits to enhance the power transfer efficiency.
  7. The resonant frequency of the transmitter and receiver circuits should be matched to achieve maximum power transfer.

  8. The quality factor of the resonant circuits, which is a measure of the ratio of stored energy to dissipated energy, plays a crucial role in determining the overall system efficiency.

  9. Power Transfer Equations:

  10. The power transferred from the transmitter to the receiver in a wireless charging system can be expressed using the following equation:
    P_transferred = (k^2 * Q_1 * Q_2 * V_1^2) / (R_1 + R_2)
    where:

    • k is the coupling coefficient between the transmitter and receiver coils
    • Q_1 and Q_2 are the quality factors of the transmitter and receiver coils, respectively
    • V_1 is the voltage applied to the transmitter coil
    • R_1 and R_2 are the resistances of the transmitter and receiver coils, respectively

Practical Considerations and Examples

  1. Wireless Charging System Design:
  2. Consider a wireless charging system with the following parameters:
    • Transmitter coil inductance: 20 μH
    • Receiver coil inductance: 15 μH
    • Coupling coefficient: 0.2
    • Transmitter coil quality factor: 500
    • Receiver coil quality factor: 400
    • Transmitter coil voltage: 12 V
    • Transmitter coil resistance: 0.5 Ω
    • Receiver coil resistance: 0.3 Ω

  3. Using the power transfer equation, the power transferred from the transmitter to the receiver can be calculated as:
    P_transferred = (0.2^2 * 500 * 400 * 12^2) / (0.5 + 0.3) = 18.43 W

  4. Efficiency Optimization:

  5. To improve the efficiency of the wireless charging system, the following strategies can be considered:

    • Increasing the coupling coefficient by optimizing the coil geometry and alignment
    • Improving the quality factor of the coils by using high-permeability materials and minimizing losses
    • Reducing the resistive losses in the coils by using thicker conductors or low-resistance materials
    • Employing advanced compensation topologies, such as the LCC-C topology, to enhance the power transfer efficiency

  6. Experimental Validation:

  7. Experimental measurements can be conducted to validate the theoretical calculations and assess the accuracy of the power determination methods.
  8. Measurements can be performed using high-precision power analyzers or custom-built measurement setups that capture the relevant electrical parameters, such as voltage, current, and phase.
  9. The experimental results can be compared with the theoretical predictions to evaluate the systematic error and validate the power assessment techniques.

Conclusion

In this comprehensive guide, we have explored the various factors that contribute to the determination of energy in wireless charging systems. By understanding the principles of electromagnetic induction, resonant circuit theory, and power transfer equations, you can accurately assess the energy in these systems and optimize their performance. The practical considerations and examples provided offer a hands-on approach to applying the theoretical knowledge in real-world scenarios. With this guide, you are now equipped with the necessary tools and techniques to become an expert in determining energy in wireless charging systems.

References

  1. Scosche. (n.d.). Assessing Wireless Charging Speeds: Factors and Considerations. Retrieved from https://www.scosche.com/blog/post/assessing-wireless-charging-speeds-factors-and-considerations
  2. Jiang, C., Chau, K. T., Liu, C., & Lee, C. H. (2017). An Overview of Resonant Circuits for Wireless Power Transfer. Energies, 10(7), 894. https://doi.org/10.3390/en10070894
  3. Power Electronic Tips. (2019). Measuring Wireless Charging Efficiency in the Real World. Retrieved from https://www.powerelectronictips.com/measuring-wireless-charging-efficiency-in-the-real-world/
  4. Huang, X., Li, S., Li, Q., & Khaligh, A. (2019). A New Wireless Power Transfer System Using Magnet Array Coupled Resonators for Electric Vehicles. IEEE Transactions on Vehicular Technology, 68(5), 4467-4478. https://doi.org/10.1109/TVT.2019.2904305