An improved finite control set model predictive control for power converters in distributed generations/microgrids

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This thesis focuses on finite control set model predictive control (FCS-MPC) of power converters in distributed generation (DG) and microgrids. In any network with an adequately high number of DG units, a hierarchy of control is one of the approaches to coordinate the system. Developments in the control of microgrids increase their potential to interact more efficiently with the main grid. Hierarchical control of the microgrid includes four levels: the component (zero) level, primary, secondary, and tertiary controls. The FCS-MPC uses an internal model of the plant to predict the future progress of the controlled variables over the next prediction interval. An objective function is minimized via an exhaustive search to acquire the optimal control input sequence. While FCS-MPC carries some benefits, the algorithm needs to be reformed for various applications, mostly due to the variety of the plant characteristics that cause some challenges for the design. The thesis is divided into two parts: The first part is devoted to theory and algorithms of FCS-MPC for power converters in DGs at the component (zero) level of the grid-connected microgrid, whereas the second part tackles power sharing, at the primary control level of microgrid, among DGs in the grid-connected microgrid. The first part, Chapters 3, 4, and 5, investigate the main concerns of FCS-MPC algorithm with respect to implementation in terms of delay time compensation, computational burden in longer horizon, and weighting factor design. A time-delayed model with an advanced and flexible control algorithm is developed. As a result, the system is reliable in terms of applying the optimal sequence at the right interval. In order to decrease the computational burden and consequently prediction horizon, a simplified MPC can be utilized. To achieve robustness of the MPC technique under different operating conditions, a self-tuning MPC for power flow control and power quality improvement in grid-connected power converters is proposed. The second part of this thesis, Chapter 6, employs MPC scheme for the power sharing problem of parallel DGs in a grid-connected microgrid, to attain autonomous power sharing and power quality improvement. Generally, the droop control is used as the conventional control method of parallel inverters for regulating active power and reactive power in microgrids. The proposed scheme is modeled mathematically and simulated via MATLAB SIMULINK for two case studies. Case 1 consists of two parallel 2L-3Ph VSIs, whereas in case 2, a 2L-3Ph VSI and a 3L-3Ph neutral point clamped VSI are paralleled. The MPC algorithm shows a better performance than the droop control in terms of power sharing between two parallel grid-connected inverters. The measurements show that although the active and reactive power ripples are not compensated much by the MPC approach, the rise time and settling time are reduced considerably. As a result, the MPC scheme provides a better transient dynamics than the droop control scheme.
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