Research On Control Strategy Of Statcom For Voltage Fluctuation In Wind Energy Conversion Systems

A major challenge for any wind turbine is how to manage the large variation in wind speeds. This variation in output contributes to deviations in power exchange, which will lead to affect the power quality of the imbedded grid. With the development of the Flexible AC Transmission System (FACTS) technology, this problem of voltage instability can be solved by using dynamic reactive power compensation. Shunt FACTS devices, such as the Static Synchronous Compensator (STATCOM), have been widely used to provide high performance steady state and transient voltage control at the Point of Common Coupling (PCC). Multilevel converters are well suited to, and thus are increasingly used in high-voltage high-power applications, for it provides 1) higher ac-side voltage levels and 2) improved waveforms in terms of harmonic distortion, especially in utility power transmission and distribution systems. Since the introduction of Diode Clamped Multilevel Converters (DCMC), various modulation and control strategies have been developed to control these converters. This paper deals with the application of the Multi-level NPC–VSC.This paper introduces a general space-vector modulation algorithm for three-level STATCOM. Space-vector modulation (SVM) stands out because it offers significant flexibility to optimize switching waveforms, and because it is well suited for implementation on a digital computer. However, regardless of its advantages, SVM for more than three-level converters is still mostly unexplored. This is largely the consequence of increasing computational difficulties for converters with a higher number of levels. So this paper introduces a hexagonal coordinate system and another method of Simplification of a three-level space–vector diagram. These algorithms simplify greatly the computation of switching states and the process of the switching sequence generation. They are used in the strategy of five-level STATCOM too.A technical challenge in the application of NPC is to maintain the balance of the dc-side capacitor voltages. This paper explores the fundament of neutral-point voltage balancing problem, and then introduces the simple methods used in three-level and five-level neutral point balancing control. This paper presents a new neutral point balancing strategy for the five-level diode clamped converter (DCC) which can be used in STATCOM of wind energy conversion systems (WECS). The simulation results demonstrate the capabilities of the proposed strategy to effectively maintain voltage balance of the dc link capacitors. The mathematic model in ABC three-phase stator coordinate and DQ coordinate frame of the inverter is set up. The automatic voltage control mode with the direct voltage droop is used to control the output of the STATCOM.The voltage stability characteristic of wind turbine is analyzed. The STATCOM mode including induction generator based wind turbine models were implemented in Matlab/Simulink and PLECS co-simulation platform. The simulation results demonstrate that the STATCOM can provide reactive power support, and the improve the stability of the power network.