Development of a low-harmonic vector hysteresis current controller

Abstract

The increasing interest in the use of renewable energy sources for the generation of electrical energy makes it necessary to ensure that these type of installations do not jeopardize the global operation of the electrical system to which they are connected. Up until now, this safety has been achieved by imposing very strict limits to the percentage of “non-controllable” renewable energy that can be connected to the grid. In order to increase these limits, new control schemes must be developed, focusing in power quality and, if possible, in trying to help grid stability. The paper proposes two new control methods for the current injected by a variable-speed generation system and compares them to a traditional hysteresis control. The first one obtains a table by using an algorithm that calculates the switching state that minimises switching frequency. The commutation is determined by a single comparator applied to the error vector, achieving a circular error area. The use of this table, along with the selection of a circular error area for the current vector makes that the current error remains always inside the specified error area. The second method is a predictive one, based on the previous one, that decides the optimum switching vector in the precise time when the commutation occurs, taking into account the present state of the system.