PERFORMANCE ENHANCEMENT OF VARIABLE SPEED WIND ENERGY CONVERSION SYSTEM

Abstract

As a result of the world consciousness about environmental issues and to decrease the nuclear power demand, wind power becomes a competitive energy source that rivals the conventional power sources. However, the interconnection of the variable speed wind generator system (VSWG) with the network suffers from a lot of technical challenges, in terms of power quality and availability. The variable-speed wind turbine (VSWT) generator systems have various merits that make them more prevalent in wind energy production. Some of these features are its capability to control, lower quantities of ripples, and higher power density compared to the fixed. There are various types of these machines used in the VSWT, Such as the permanent-magnet synchronous generator (PMSG). Which is featured by gearless construction, higher efficiency, small size, high reliability, and self-excitation. The interconnection of the VSWT-PMSG and the electrical network is carried out by utilizing the fully rated frequency converter (FC). The FC composes of generator- and grid- side converters with an intermediate DC link capacitor (CDC). The generator-side converter (GSC) has the responsibility to extract the maximum power from the wind to the grid at a unity power factor. The grid-side inverter (GSI) is applied to control the DC-link voltage and the terminal voltage as well, at a desired value adjusted by the operator. The CDC is protected by an over-voltage protection scheme (OVPS). The cascaded control scheme is utilized to control both GSI and the GSC. This control strategy can utilize various types of controllers such as proportional-integral-derivative (PID), proportional-integral (PI), and fuzzy logic controller (FLC). The PD and PID are not more attractive to be used in the industry due to the demerits of derivative control action, where it amplifies the input frequency of any harmonics to the system, and to avoid this problem; a designed filter should be used. Therefore, PI is commonly used. The main feature of the PI controllers is their wide stable responses. However, these controllers have a high sensitivity to variation of parameters and system non-linearity.