Accurate estimation of the capacitance between the transmitter and receiver plates is critical for the design of capacitive wireless power transfer systems used in electric vehicle charging. Classical capacitance formulas typically assume that the plate dimensions are much larger than the separation distance between them—an assumption that fails for CPT systems in EV applications, where the air gap is often comparable to the plate dimensions. Furthermore, a closed-form analytical expression for finite-size coplanar plates is unavailable in the literature. This article addresses both these gaps by deriving analytical expressions for (i) the mutual capacitance between facing Tx and Rx plates, and (ii) the self-capacitance formed between coplanar plates on the same side (either Tx or Rx), assuming a uniform charge distribution. The derived expression is validated against Finite Element Analysis (FEA) simulations. Additionally, experimental measurements obtained from a laboratory-scale CPT prototype are compared with both the analytical model and FEA results to assess accuracy and applicability.
