Active Disturbance Rejection Control And Its Application To Inverter Systems

Disturbances and uncertainties widely exist in controlled systems,and all the unexpected changes and their influence factors that affects the system output should be removed or suppressed.During the past thirty years,the disturbance rejection control has been deeply studied in different fields,resulting in different forms of techniques and results.More and more attention has been paid to the disturbance rejection paradigm based on the disturbances and uncertainties in both academia and industry.However,the theoretical integrity and the ease of industrial application need to be further studied.As core components of the renewable energy filed,the inverters are the most commonly used topology in industrial facilities.However,due to the nonideality,such as dead-time of switching devices,nonlinear loads and the background harmonics from the grid voltages,the output of inverters is often deteriorated and results in high total harmonic distortion(THD)and high tracking error.Active disturbance rejection control(ADRC)is regarded as a promising branch of disturbance rejection control theory.In this thesis,in-depth analysis and research of ADRC and its application to inverters is conducted through theoretical analysis,simulations,and experiments.1)The core idea,the fundamental principles,the basic design procedure and the parameters tuning of ADRC is systematically presented.The relationship between the ADRC-based control and the state-space-based control is analyzed and the discrete implementation of ADRC is studied.2)The model compensation based ADRC is adopted to suppress the unmodeled dynamics and disturbance of the stand-alone inverter,in which the known model is regarded as a part of the generalized disturbance,and the unmodeled dynamics and external disturbance is lumped as the unknow generalized disturbance.The model compensation based ADRC can achieve low THD,but the steady-state error is high.The differential feedforward based ADRC is proposed to achieve better tracking performance and the characteristics of the extended state observer(ESO)is studied.By establishing the equivalent of internal model control(IMC)structure,the performance of ADRC is studied.The effectiveness of the proposed scheme is verified by the simulations and experiments.3)As for grid-tied LCCL filter,the parameter uncertainties will influence the reduction of control order,and the external disturbance of the grid-tied inverter will deteriorate the performance.In this thesis,an ADRC-based current control strategy for LCCL-type grid-tied inverter is proposed,in which the unknown dynamics and external disturbance is lumped as total disturbance.In the digitally controlled system,there will be computation delay and pulse width modulation(PWM)delay.The input synchronization method is adopted in ADRC structure to deal with the time delay,and the ADRC-based current control strategy is efficiently applied in the LCCL-type grid-tied inverter.With parameter variations considered,the robustness of the proposed current control strategy is studied.Moreover,a series of comparative experiments have been conducted to demonstrate the effectiveness of the proposed scheme.