Simulation of Synchronized-Switching Method Energy Harvester Including Accurate Piezoceramic Nonlinear Behavior

Synchronized-switching techniques have significantly enhanced the harvested energy from semipassive and active surrounding ambient mechanical vibration harvesters. They have allowed a large improvement of vibration-control efficiency using piezoelectric devices. Unfortunately, for such techniques, dielectric limitations appear as soon as the piezoceramic operates under external solicitation of higher amplitudes and frequencies. Under extreme conditions, active materials exhibit nonlinear behavior related to dielectric hysteresis that significantly reduces their performance. In this work, we focus on this nonlinear behavior and its consequences in terms of system efficiency. We apply a realistic model including accurate material laws. In such models, a constant piezoelectric coupling d 31 is not suitable as a coefficient anymore and it should be replaced by a function depending on the polarization level through the active material. The response of more realistic systems including hysteresis was taken into account and compared with the basic model, where a constant d 31 was considered.

Clamping system for series connected IGBTs to avoid transient breakdown voltages

<p>IGBTs (Insulated Gate Bipolar Transistor) can be used for power DC-DC converters at higher voltages. A series connection is needed due to the blocking<br />capability limit of 6500V. The voltage must be shared among the IGBTs both dynamic when switching and blocking mode. A non-synchronized switching creates transient voltage that might damage the IGBT. The non-synchronized switching comes from different delays in the gate drivers and deviation in the IGBT parameters. This paper investigates in theory and practice a solution<br />contains of clamp circuit, dynamic and static circuit. Turning on process of the stack of three IGBTs are in focus in a buck converter design. An operating<br />voltage closer to the IGBT limit is used in order to press the system. For the simulations (Pspice) and experimental tests, fast IGBTs (1200V /30A IXYH40N120C3) are used to show the good dynamic of the chosen solution. The Lab tests also show that because of the deviation in parameters preadjustment of the gate signals is needed. The experimental tests have been carried out in different clamp voltage to finally have clamp voltage close to<br />the blocking voltage of the IGBTs and maximum 2A as output current. Examples of wave forms for voltages are given and discussed.</p>