Analysis of the thermal balance characteristics for multiple-connected Piezoelectric Transformers

Since the amount of power that piezoelectric transformer (PT) can handle is limited, the multiple connection of PTs is necessary for improvement of the PT-application power-capacity. In the connection, thermal imbalance between the PTs should be prevented to avoid the thermal runaway of each of the PTs. The thermal balance of the multiple-connected PTs are dominantly affected by the inherent thermal characteristics of each PT. In this paper, both the thermal balances of parallel-parallel and parallel-series connections are analyzed. For quantified analysis, the thermal-balance effects are estimated by the simulation of the mechanical loss ratio between the PTs using electrical model parameters. The analysis result shows that with similar characteristic PTs, parallel-series connection has better thermal balance performances due to the reduced mechanical loss of the higher temperature PT. For experimental verification of the analysis, a hardware-prototype test of C_s-L_p type 40W adapter system with real PTs has been performed.