Development of a multi-cell inverter topology for driving nonlinear piezoelectric load

Abstract

This report presents the design and development of a five cell multicell inverter for driving a piezoelectric load. The multicell inverter was chosen for this application as it became evident that it would be more suitable for driving piezoelectric transducers due to its high apparent switching frequency. The multicell inverter was designed using DirectFET’s as this type of FET has a high current switching ability in a very small package. A positive and negative bootstrap power supply was incorporated in the design to reduce the number of supplies to power the gate drive circuits of the multicell inverter. Three compensation networks were designed and constructed to investigate which one would transfer the most energy to the piezoelectric transducer. It was also important to investigate whether these compensation networks were able to reduce the harmonic content produced by the multicell inverter. This is necessary in order to excite the transducer correctly. It was found that the Q-Matching compensation network reduced the harmonic content applied to the load the most. Experiments were also conducted to determine if the advantage of the apparent frequency of the multicell inverter would mean that the piezoelectric load could be driven directly with the multicell inverter without any damage to the transducer. It was however required to increase the applied apparent power to the transducer to compensate for the reactive component of the load in order to melt the plastic which was used as the load to the transducer. Experiments were conducted to determine if the charge on the cell capacitors of the multicell inverter would stay balanced while driving a non linear load such as a piezoelectric transducer. The results showed that the voltages stayed balanced when driving the piezoelectric transducer.