Parallel connection of piezoelectric transformers

The behavior of parallel connected piezoelectric transformers (PTs) was analyzed by applying the generic PT model to represent the combined network in the most general way. The influence of a deviation in each of the PT parameters was examined with respect to total output and losses in each PT. It was found that the requirement for identity in the equivalent circuit parameters R_m and C_o in the two PTs is not strong. The most critical parameter for equal loss in the PTs is ω_r - the mechanical resonant frequency of PTs, which has to be equal in the parallel units, even though the values of the parameters C_r and L_r can be slightly different. Since the resonant LCC type inverters are practically identical to the equivalent electrical circuit of PTs, the results of this study are relevant to combined connected LCC inverters. The analytical results of this study were verified by SPICE simulation and experiments. The experiments were done on parallel-connected PTs (Tl-2, Face Co., VA, USA) and LCC inverters built by passive elements.