| Summary: | 碩士 === 國立臺灣大學 === 電機工程學研究所 === 106 === Design of a model predictive auxiliary frequency controller and maximum power tracking compensator for a doubly-fed induction generator (DFIG) in a microgrid is investigated in this thesis. When there’s frequency change in a microgrid, the conventional approach is to rely on the inertia control, primary control, and secondary control of synchronous generators to stabilize the system frequency. With the increasing need of green energy, some of the traditional synchronous generators are replaced by wind turbine generators. If the wind turbine generators are not provided with auxiliary frequency controller mechanism, satisfactory frequency response can not be achieved. Therefore, the wind turbines must be designed with the auxiliary frequency controller in order to improve system frequency response.
In a doubly-fed induction generator (DFIG), the auxiliary frequency controller is usually installed on the rotor side converter (RSC) and frequency regulation is achieved through a droop control signal which is proportional to frequency deviation and the torque reference command of the RSC is modulated through this droop control input. In previous works, the gain of the auxiliary frequency controller was fixed. However, a fixed-gain auxiliary frequency controller is not able to provide satisfactory frequency response when there is a change in generator parameter or wind speed. Moreover, underfrequency load shedding must be enforced when the frequency deviation exceeds the preset value.
In the present work, a model predictive auxiliary frequency controller is designed for the DFIG in order to improve frequency response in a microgrid. The plant predictive model will change when there is a change in generator parameter or wind speed. As a result, better frequency response can be achieved with the adaptive control provided by the proposed model predictive auxiliary frequency controller. Furthermore, underfrequency load shedding can be avoided with the implementation of state variable (frequency) constraint in the model predictive auxiliary frequency controller.
When there is a change in system frequency, the auxiliary frequency controller of the wind turbines would provide the needed active power to the system timely. In the dynamic process, the rotating speed of the wind turbine would decrease. As a result, the maximum power tracking control and frequency compensation are affected. Therefore, the investigation of maximum power tracking compensator is required. The research results show that, with maximum power tracking compensator, the frequency response in the dynamic process can be improved.
In order to demonstrate the effectiveness of the proposed model predictive auxiliary frequency controller and maximum power tracking compensator, MATLAB/Simulink dynamic simulation are performed on a microgrid in central Taiwan which comprises conventional synchronous generators and off-shore wind farms.
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