  In wireless power receiver systems, the buck converter is widely used to step
down the higher rectified voltage derived from the wireless receiver coil, to a
lower output voltage for the immediate battery charging process. In this work,
the presence and effect of the right-half-plane (RHP) zeros found in the
small-signal inductor-current-to-duty-ratio and output-voltage-to-duty ratio
transfer functions of the buck converter in the wireless power receiver system
on the control performance, are investigated. It is found and mathematically
proved that the RHP zeros are introduced by the current source nature of the
system attributed to the series-series compensation and finite DC-link
capacitance. The RHP zero not only results in non-monotonic open-loop dynamic
response but also complicates the design of feedback control and causes
potential closed-loop instability. Theoretical and experimental results are
provided to validate the presence of the RHP zeros and their effect on
open-loop and closed-loop dynamic responses.
