Controlled Power Point Tracking for Grid Connected and Autonomous Operation of PMSG based Wind Energy Conversion System

Khandelwal, S (2014) Controlled Power Point Tracking for Grid Connected and Autonomous Operation of PMSG based Wind Energy Conversion System. Masters thesis, Indian Institute of Technology, Hyderabad.

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Abstract

With continuous depletion of conventional sources of energy, Wind Energy Conversion Systems (WECS) are turning out to be one of the major players with immense potential to meet the future energy demands. It is one of the most preferable source, as it can be installed onshore as well as offshore. But with the increasing penetration of wind energy into power system, wind energy conversion systems (WECSs) should be able to control the power flow for limited as well as maximum power point tracking. Apart from tracking desired power, there are some other issues which needs to be addressed for stable and reliable operation of WECS in grid connected as well as islanded mode. In the grid connected mode synchronization of the system to the grid and maintenance of dc-link voltage in absence of ESS are the main control requirements apart from controlled power extraction from the wind turbine. Unlike the grid connected mode, where most of the system level dynamics are imposed by the grid and hence load voltage magnitude an frequency are dictated by the grid itself, in the autonomous operation of WECS the load voltage magnitude and frequency control comes in as additional control requirements other than controlled power extraction from Wind Turbine. However the usage of batteries in the system is unavoidable due to stability and reliability issues. In contrast to the traditional pitch angle control, this work focusses on field oriented speed control of permanent magnet synchronous generator (PMSG) for controlling the active power flow based on the wind turbine characteristics. A back to back AC/DC/AC topology is implemented for interfacing the WECS to the distribution network with various power electronic interfaces providing the necessary control over the power flow. By maintaining the dclink voltage constant and by deploying PLL, power balance and grid v synchronization are attained respectively in grid connected operation of WECS. For the standalone operation of WECS, however the ideology for controlled power extraction from WECS remains same but the load voltage magnitude and frequency control are attained by carrying out the analysis and design exercise in synchronously rotating reference frame so that linear control techniques can be employed easily and sinusoidal command following problem gets transformed to an equivalent dc command tracking thus yielding desired performance with zero steady state error. The motive behind using batteries in the system is to facilitate transient stability and enhance reliability. Proper decoupling and feed forward techniques have been deployed to eliminate crosscoupling and mitigate the effect of load side disturbances. Simulations are carried out under varying load demand as well as changing weather conditions to demonstrate the applicability and effectiveness of the proposed control strategies for grid connected as well as standalone WECSs. Overall, the project work involves study, design, modelling and simulation of grid connected as well as standalone Wind Energy Conversion System.

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