The current control is becoming a challenging task for switched mode power supplies, while current sensorless control solutions can avoid the instantaneous current measurements that has been applied for mostly used power factor correction topologies. However, multilevel type of converters haven't been considered to use with current sensorless control (CSC). Hereby, the CSC is applied to three level neutral point clamped converter, where special volt-second balance is applied to inductor in order to keep average inductor's current value to track the reference signal during both discontinuous and continuous current modes. The explanation of post-fitting and pre-fitting current trajectories is done that are necessary for proper transition between voltage levels. Experimental results have confirmed the theoretical model. Keywords-sensorless control; current control; pulse width modulation inverters978-1-4799-6301-0/15/$31.00 ©2015 IEEE

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Abstract. Voltage source inverters connected to the grid in applications such as active power filters require synchronization with the grid voltage. Since in practice the grid voltage can be unbalanced and distorted, but the operation of the whole active filter control system is strongly dependant on precise estimation of grid voltage phase, the fundamental positive sequence phasor of the grid voltage has to be extracted. In this paper a system for smooth estimation of the position of the voltage phasor at the point of common coupling of a parallel active filter system is presented using a sinusoidal signal integrator and a simple software PLL. The performance of the proposed system is verified by simulation and experimental results. The proposed PLL scheme can also be used in other vector oriented control systems.

This paper is related to an alternative energetics microgrid with a wind generator and a hydrogen energy storage system. The main aim of this research is the development of solutions for effective use of the wind generators in alternative energetics devices, at the same time providing uninterrupted power supply of the critical loads. In this research, it was accepted that the alternative energetics microgrid operates in an autonomous mode and the connection to the conventional power grid is not used. In the case when wind speed is low, the necessary power is provided by the energy storage system, which includes a fuel cell and a tank with stored hydrogen. The theoretical analysis of the storage system operation is made. The possible usage time of the stored hydrogen depends on the available amount of hydrogen and the consumption of the hydrogen by the fuel cell. The consumption, in turn, depends on used fuel cell power. The experimental results suggest that if the wind generator can provide only a part of the needed power, the abiding power can be provided by the fuel cell. In this case, a load filter is necessary to decrease the fuel cell current pulsations.