Iason Vittorias

A bidirectional battery charger for electric vehicles with V2G and V2H capability and active and reactive power control

A bidirectional battery charger using a three-phase voltage source inverter (VSI) is presented to be employed in plug-in electric vehicle applications enabling Vehicle-to-Grid (V2G) and Vehicle-to-Home (V2H) functionality with simultaneous active and reactive power control. The charger is controlled by a grid supervising unit with voltage droop control, providing it with P (active) and Q (reactive) power requests, and is responsible of reporting back its available power reserves (apparent power). In V2G mode the grid voltage is observed and a current controller on the d-q coordinate system together with the three phase inverter can transfer energy in both directions. Also reactive power compensation, inductive or capacitive, is possible. Asymmetries on the grid load can also be compensated by slight modifications of the control regime. Further, in V2H mode, the charger system can be seen as the master grid-forming generator responsible to provide a stable voltage at the network frequency. A proper synchronization strategy is presented as well, to guarantee smooth reconnection with the power grid. The proposed architecture is modeled in Simulink and aims the realization in existing electric vehicle and smart grid prototypes of the Siemens AG.

A novel piezohydraulic actuator as artificial muscle in robotic applications

Modern robotic applications involve close contact to the human and consequently, require apart from performance a high degree of safety from their actuators. Further, the dexterous manipulation abilities of a human are not yet inherently realized by technical media. In this work a novel piezohydraulic actuator is presented aiming at a) high power density, b) human-like force/velocity characteristic, c) intrinsic passive safety and low reflected inertia, and d) high robustness. It is shown why the piezohydraulic actuation principle is appropriate to mimic the behavior of a human muscle and, as a consequence, desirable for robotic applications. A model of the actuator is also presented together with simulation and experimental results.