Abstract
This chapter describes two methods whose purpose is to estimate the coupling factor k for the inductive coupling of an experimental prototype designed for the contactless battery charging of electric vehicles. The air gap that separates the two square-shaped coils of the inductive coupling is 150 mm. The first method is analytical and provides an expression with which to calculate the mutual inductance between both coils by solving Neumann's formula, from which k readily follows. The second approach is empirical and combines data from waveforms of currents that were obtained both experimentally and from PSpice simulations, where k is a model parameter, under different loading conditions. The agreement between the analytical and the empirical method is good, as they both yield coupling factor figures that are equal to 0.197 and 0.200, respectively. Both techniques could, therefore, be applied in order to determine the coupling factor of the constructed inductive coupling for other air gaps near to 150 mm, which are also of practical interest in electric vehicle charging.
TopBackground
On-board chargers that are present in conductive charging schemes have a number of disadvantages that are conveniently addressed by WPT systems, some of which are: the need for a robust wired connection terminated with a plug charger, a galvanic isolation of the on-board electronics, the dimensions of the charger, and the need to ascertain safety considerations that are relevant when the vehicle is operating in wet conditions. A number of WPT manufacturers supply their chargers to members of the automotive industry, such as Audi, BMW, Chrysler, Daimler, Ford, GM, Honda, Mitsubishi and Toyota. Some of these WPT suppliers are Conductix-Wampfler, Evatran, HaloIPT (Qualcomm), Momentum Dynamics and WiTricity. Research initiatives exploring the potential of WPT technology are not limited to manufacturers; universities, government facilities and R&D centers worldwide are, at present, also actively involved in further developing this technology. Relevant examples of such institutions can be found in (Musavi & Eberle, 2014).
Key Terms in this Chapter
Ideal Transformer: A transformer that is characterized by a perfect magnetic coupling, in which the coupling factor equals unity.
Vehicle-to-Grid (V2G): A system that allows EVs to return electricity to the grid, according to a scheme in which EVs can act not only as loads for the grid but also as generators.
MOSFET: Metal-oxide-semiconductor field-effect transistor. A voltage-controlled device characterized by a high input impedance at its gate and very short switching times (that is, a very high switching speed).
Compensation Capacitor: A capacitor whose purpose is to be connected either in series or in parallel with a coil in a circuit. The resulting LC circuit acts as a resonator at a certain frequency denominated as the resonant frequency of the circuit, in which the reactances of the capacitance and the inductance cancel each other out.
Reflected Impedance: In an inductive coupling, this is the equivalent impedance of the secondary side of the coupling (including the load impedance) as seen from the primary side.
Leakage Inductance: An inductance parameter that is useful as regards modeling loosely-coupled coils, which accounts for the fraction of the magnetic flux generated by one of the coils that does not reach the other coil.