Kalman State Estimation-Based Voltage And Reactive Power Control Method For Microgrids

Microgrid technology is an essential component for smart grid technology, which is one of the effective strategies for distributed generation application. The existing control technology commonly depends on communication system. However, side effects induced by communication system such as data loss, time delay and high cost have negative influences on microgrid development and industrial application. In order to improve operation economy, reliability and flexibility of control system, this work presents kalman state estimation-based voltage and reactive power control method. The objective of this work is to perform voltage and reactive power control without communication system. Small signal model, state estimation method, voltage control method as well as reactive power control method are studied seperately. The main aspects of this thesis are composed of four components.First of all, small signal models of distributed generators, network, and loads are built separately. And each subsystem is transferred to common frame, then small signal model of the whole microgrid is formulated. The study results show that the proposed small signal model reflects effectively DG unit dynamics and network voltages response, which is a prerequisite for system analysis and synthesize.Second, the thesis presents a kalman filter-based state estimation method for islanded microgrids, which is developed to estimate microgrid state response just by local voltage and current information of distributed generator in the absence of communication system. The study results show that the kalman estimator is able to observe accurately output voltage, active power and reactive power of distributed generators as well as network voltage response.Third, the thesis proposes a kalman state estimation-based voltage control method for islanded microgrids, which is composed of voltage estimator and voltage controller. The voltage estimator is adopted to observe system voltage response, while voltage controller is developed to perform offset-free voltage control for a specified bus. Dynamic performance of the voltage controller is analyzed, from which the relationship between controller parameters and dynamic performance is investigated. Then robustness of the proposed voltage controller is studied under a series of parameters uncertainties, including the line parameters perturbation, load parameters variation, different disturbance locations, LC filters perturbation, output impedances perturbation, and DG unit fault. The study result shows that the kalman state estimation-based voltage control strategy is able to perform offset-free voltage control without any communication links and has a good capability to reject uncertain perturbations.Finally, the thesis presents a kalman state estimation-based reactive power and voltage control method. Reactive power and voltage control is addressed as asymptotic tracking and disturbance rejection problem of multi-input and multi-output system. Furthermore, the condition for power tracking and voltage disturbance rejection is analyzed. And an improved small signal model is developed to reconstruct the system input-output relationship, where the relationship is evaluated by sensitivity analysis. A state estimator is then constructed based on the new input-output relationship in order to observe reactive power and system voltages by local measurement. A kalman state estimation-based optimal control strategy is proposed to perform both reactive power sharing and system voltage restoration. The study result shows that the kalman state estimation-based optimal control method is able to perform reactive power sharing and system voltage control simultaneously without communication links.The main aspects of this work have been analyzed and validated by theory analysis, simulation verification and experimental verification. The research results are able to improve reliability and flexibility of microgrid control system and reduce operation costs, which has theory valuable and application valuable for microgrid industrial application.