Disturbance Rejection Control And Its Application To Inverter Systems

Inverters,as core components,are widely employed in the renewable energy field.High performance control schemes are extremely important for inverters to improve output performance and ensure the system stability,which attract much attention from both the academia and industry.However,due to the unmodeled dynamics of inverters,such as on-voltage of switching devices,dead-time,and nonlinear loads,the output of inverters is often deteriorated and results in high total harmonic distortion,as well as high tracking error.Thus,the lumped disturbance must be suppressed to improve the performance.Based on previous research results,a novel disturbance rejection control scheme,internal model based disturbance observer(IM-DOB),is proposed in this thesis for a single-phase stand-alone inverter.A comprehensive investigation of the IM-DOB scheme is conducted through theoretical analysis,simulation,and experiments,and some innovative results are also presented in this thesis.1)Two conventional disturbance rejection schemes: disturbance observer(DOB)and repetitive control(RC)are systematically presented,including the core idea introduction and performance analysis.Based on rigorous stability analysis,this thesis has pointed out that both of them cannot keep the stability of the system when the magnitude of unmodeled dynamics is large.Thus,two simple compensation schemes are proposed to enhance the robustness of those schemes,and both the theoretical analysis and numerical simulation have demonstrated the effectiveness of the proposed compensation schemes.2)Disadvantages of conventional disturbance rejection schemes are also presented,i.e.,the conventional DOB(CDOB)scheme,which is often designed based on the assumption that disturbances mainly concentrate in the low frequency region,cannot eliminate periodical disturbance,and the dynamic performance in conventional RC(CRC)scheme is also far from satisfied.Based on those conventional schemes,a novel disturbance rejection scheme-IM-DOB-is proposed in this thesis.The IMDOB scheme fuses merits of CDOB and CRC,which can notably attenuate the disturbance both in the low frequency and at harmonic frequencies.Moreover,compensation filters are also introduced into IM-DOB to deal with the parameter uncertainties,which can significantly improve the robustness of the proposed scheme.Besides,the zero phase error tracking control(ZPETC)scheme is also introduced into IM-DOB to deal with some systems that contain unstable zeros.Finally,IM-DOB is successfully adopted in the inverter systems,which serves as a voltage controller.A design case is also provided.Similar to the CDOB scheme,IM-DOB has clear physical implications and satisfied dynamic performance,and it also can effectively attenuate periodic disturbance.Moreover,a series of comparative experiments have been conducted to demonstrate the effectiveness of the proposed scheme,and the results suggest that IM-DOB can provide much better robustness and tracking performance than those of conventional schemes.