Design and Analysis of Wireless Power Transfer Charger for Electric Vehicles

Electric Vehicle
By Majdi EL Fahem | 28/07/2022

What is Behind the Wireless Power Transfer (WPT)?

In simple terms, wireless power transfer is the transmission of electric power without any direct physical wire or cable connections. The power transfer is usually based on the technology that utilizes electric, magnetic, or electromagnetic fields. WPT happens by creating an alternating magnetic field on the transmitter coil. This magnetic flux is then converted into an electrical current in the receiver coil.  The generated electrical current depends on the amount of flux generated by the transmitter coil, and how much of a percentage the receiver coil can capture. The distance, size, and position of the receiver coil relative to the transmitter coil decide the “coupling factor or coupling coefficient” of the two coils.

Ever since the concept of WPT became popular, scientists and engineers begins to develop various techniques to realize this concept. These techniques are mainly classified based on the transmission distance, maximum power, and method used to achieve power transmission. Therefore, WPT can be categorized into the inductive coupling, capacitive coupling, magnetic coupling, and electromagnetic radiation. Moreover, based on the energy encryption and WPT technique, broadly we can divide it into three sections such as near field, medium field, and far field. The comparison among these techniques, their advantages - disadvantages, and applications are tabulated below.

Comparison between Near, Medium, and Far Fields of WPT [1]
Aspect The Near Field The Medium Field The Far Field
  The Energy Efficiency High High Low
  The Performance of power transfer High High Low
 The characteristics of distance, frequency, and number of turns Easier to transfer power Easier to transfer power More complex to transfer power

Advantages and Disadvantages of WPT Techniques [1]
WPT technique Advantages Disadvantages Applications
  Inductive Coupling  Simple safe, high efficiency in short range   Short transmission distance, needs accurate alignment   Electric toothbrush and razor battery charging, induction stovetops, and industrial heaters
  Capacitive Coupling   Simple structure of couplings, lightweight, low cost, position flexibility, and high frequency   Small power density of the small coupling capacitance   Charging portable devices, power routing in large-scale integrated circuits, Smartcards
  Magnetic Resonant Coupling   Long transmission distance, no radiation   Difficult to adjust resonance frequency for multiple devices   Cars charging
  Electromagnetic Radiation   Very high transmission percent over long distance   Radiation needs line of sight   Implement in biomedical

Why WPT is in High Demand?

  • Fewer wires and connectors
  • Lower risk of sparks
  • Ability to charge cars while they are inroads 
  • Convenient, safe, and effective way to transfer power 
  • Environmentally friendly - Does not harm or injure a human or any living being.
  • Enhancing the quality of life and reducing the risk of infection and other complications caused by maintenance or replacement of implantable medical devices

What are their Drawbacks?

  • Low efficiency and higher losses
  • Expensive
  • Higher maintenance costs
  • Not suitable for high power delivery.
  • Power drastically decreases with misalignment and higher air gap distance. 

How Can FEA Simulation Help in Designing an Efficient WPT of an Electric Car?

The graph below shows the main design issues that an engineer needs to tackle while designing and developing a wireless power charging system for electric vehicles. The same graph demonstrates how EMWorks solution can be used to solve these problems. The main key parameter of a WPT system is the coupling coefficient which is affected mainly by the distance and the alignment of transmitter and receiver. It is also impacted by the geometry of these coils. Different scenarios and designs can be investigated to come up with an efficient design iteration that provides higher transmitter energy. Resonant wireless power transfer is a considerably great solution to improve further the efficiency of the charging system. 
Through their different magnetic modules, with parametric and multi-configuration features, EMWorks software help to test and solve different iterations and design scenarios. In addition to this, the circuit simulator of EMWorks tools is used to model the power system including different resonant circuit topologies and loads to provide better efficiency and performance of the WPT charger. 

Wireless Charger of an Electric Vehicle

Smartphone Wireless Charger 

Pacemaker Wireless Charger

Case Study: Different Topologies of a WPT Charger used in Electric Vehicles

Both circular and rectangular coil-based wireless chargers are commonly utilized in electric cars. DD coil, DDQ coil, and bipolar coil are some topologies that are used in wireless charging systems for electric vehicles. These topologies provide certain improvements in terms of coupling coefficients, and they allow more tolerance for misalignment. They can come with ferrite to better direct the magnetic flux and aluminum shielding.
EMS, which is a 3D multi-purpose electromagnetic simulation software, generates plots of the magnetic fields density and current distribution, etc. Different post-processing options including fringe, vector, and lines are overall available through EMWorks FEA software. The plots of the magnetic fields allow us to explore the strength of the magnetic field and its distribution from the transmitter to the receiver and in the air gap region. This can help to optimize the design by maximizing the receiver flux and minimizing the field leakage around the system.