Dynamic analysis and control of wind energy conversion systems

Abstract

Research on wind energy conversion systems (WECS) has been steadily expanding, driven by the global push to achieve net-zero carbon emissions. Enhancing the efficiency of wind turbines remains a critical focus, despite the theoretical limitation of 59.3 % for extracting the maximum power from the wind. Beyond this constraint, turbines encounter challenges such as varying wind conditions, mechanical losses, and inefficiencies during energy conversion stages. One effective way to improving turbine efficiency is the use of advanced generator control systems that maximize power conversion while managing these dynamic factors. However, using a physical wind turbine for research can be impractical due to high costs and space limitations, making laboratory-based WECS emulators a more viable alternative.

This thesis focuses on the design and modelling of a WECS emulator in MATLAB Simulink, implementing a suitable control mechanism for the generator, and analysing the system’s performance under desired dynamic conditions in a software-based environment. The emulator available at Tampere University represents a small-scale type 4 wind turbine, and this study is tailored to the specifications of this emulator. The modelling process involves appropriately scaling the wind turbine emulator and developing models for the generator and its converter. The generator's machine-side converter control operations are designed to manage maximum power point tracking (MPPT) using the optimum tip speed ratio control algorithm, in conjunction with the maximum torque per ampere (MTPA) control mechanism. The MPPT mechanism is chosen to accommodate the lower inertia of the emulated wind turbine, compared to conventional large-scale wind turbines. The MTPA implementation offers the advantage of controlling electromagnetic torque using the minimum required stator currents, since the generator used in this setup is an interior permanent magnet synchronous machine.

By utilizing small-signal stability analysis, the study demonstrates the process used to design and analyse the speed and current controllers for the generator control operations. This analysis identifies the open-loop transfer functions for the linearized system to achieve the desired system dynamics. Linearisation is performed using the Taylor's approximation method, while the controllers are tuned using the loop-shaping technique, guided by Bode plots.

The software simulation presents the performance of the system, incorporating the designed controllers, under varying wind speed conditions. The control system has proven effective, successfully maintaining system stability for both increasing and decreasing wind speeds. The results also confirm that the MPPT and MTPA techniques function as intended, validating that the software-based implementation can be applied to the physical system.