Power Flow Analysis of Electrostrictive Actuators Driven by Switchmode Amplifiers

Abstract

In this paper we analyze the power flow between stacked electrostrictor actuators and a pulse-width-modulated switching amplifier. The amplifier and actuator are analyzed as components of a smart skin whose function is underwater acoustic echo cancellation. An integrated model is developed which includes a dynamic structural model of the actuator, a dynamic model of the power electronics and a nonlinear electromechanical coupling mechanism of the electrostrictor actuation material. Using a linearized version of this model, the mechanical admittance of the actuator as seen by an external force is analyzed. It is shown that an outer acoustic control loop can modify this mechanical admittance and optimize the power coupling between the actuator and an external fluid medium by impedance matching. With the nonlinear model, the power flow between the electrical and mechanical systems is analyzed through simulation. The flow of power is traced from the power injected by the external force, through the amplifier and into the electrical bus. It is shown that effective power flow occurs only when the frequency of the external force is within the bandwidth of the amplifier. This analysis also reveals that the electrical power flow through the actuator is two orders of magnitude larger than the external mechanical power extracted by the actuator. This analysis shows that one main requirement on the amplifier design is to manage the charge flow through the actuator.

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