Purpose -This paper aims to integrate cascaded multilevel converters in the static compensator (STATCOM) systems in order to assure dynamic compensation of the reactive power absorbed by fixed speed wind turbines. Design/methodology/approach -The cascaded multilevel converter topology is incorporated as a variable source of reactive power required by the wind farm. The evaluation of reference reactive currents is assured by the technique of instantaneous power theory. Thus, the STATCOM, with its appropriate control strategy, continuously compensates the reactive currents. Findings -A developed non-linear state representation makes possible the analysis of static and dynamic behaviour of the proposed system. The STATCOM-based cascaded multilevel converter is able to provide continuous compensation and proves highly dynamic under steady state and transient operating conditions. Practical implications -The paper formulates a mathematical model which includes all parameters describing the system composed by a medium voltage network, a wind farm and a STATCOM-based cascaded multilevel converter. The study may help to develop new control methods of such power systems containing non-linearities and an extended number of parameters. Originality/value -Since there are few studies on comprehensive and complete models of power systems, the paper contributes to make both a study and a simulation based on a developed non-linear state model which perfectly describes the state and transient behaviour of the proposed system.

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The performance of photovoltaic system is affected by solar radiation, temperature, shading and cells configuration. This paper presents a suggested solution to cure the problems of the shade, by the use of the cascaded multilevel inverters adapted to the situation of non-identical continuous DC PV sources and commended by an appropriated PDPWM control.