| With the crisis of non-renewable energy shortage and increasing carbon dioxide emissions,the construction of a new power system with new energy as the main body has become one of the important measures for energy saving and emission reduction.The grid-connected converter is an important conversion interface in the power system.It is significant to improve the output of the quality of power for improving the stability of the power system.The repetitive control technique based on internal model principle can track periodic signals without error or eliminate disturbance in the grid-connected converter.The conventional repetitive controller(CRC)still has some room for improvement in storage space,fast performance,and so on.In addition,the stability of the power grid is affected by the widespread access for various new energy sources,such as fluctuations or sudden changes in the frequency of the power grid,which presents a non-ideal state of the power grid.Therefore,the gridconnected converter for the output of power quality put forward higher requirements.In this paper,in order to improve the output power quality of grid-connected converters under ideal/non-ideal power grids,the harmonic control technology of grid-connected converter is studied for an ideal power grid with constant-voltage constant-frequency and a non-ideal power grid with frequency fluctuation.Firstly,the relative control strategies of the grid-connected converter are compared and analyzed,and the research status of repetitive control technology is introduced.To illustrate the application of harmonic repetitive control technology,the mathematical modeling of a threephase grid-connected converter and repetitive control system is analyzed,and the basic principle,disadvantages,and general design method of CRC are explained.Then,the type-3 of selective harmonic RC(T3-SHRC)based on CRC and T1/2-SHRC is proposed.Compared with CRC,T3-SHRC can track and suppress specific-order harmonics without error in a steady state and has more significant advantages in fast response and memory space.Compared with T1/2-SHRC,T3-SHRC has more streamlined and RC-compliant form of controller structure and a further reduced number of internal models.T3-SHRC has further optimized in terms of storage space and computational burden,that is,the ability to differentiate between CRC and T1/2-SHRC,which can get a good compromise between storage performance,fast performance,and design complexity.The simulation results verify the feasibility and validity of the NS-SHRC.Secondly,based on the above content,the type-3 of frequency self-adaptive and SHRC(FSA-T3-SHRC)is proposed,by combining the internal model from RC with the infinite impulse response(IIR)filter.The proposed scheme can accurately approximate and compensate for the parameter variation of fundamental frequency fluctuation in the non-ideal power grid.The specific-order harmonic is suppressed and eliminated to improve the robustness of the system for the frequency variation.In this paper,the difference in computational burden and harmonic suppression ability between the IIR filter and finite impulse response(FIR)filter in FSA-T3-SHRC is discussed.Compared with FIR filters,FSA-T3-SHRC based on IIR filters can reduce the design complexity of the controller under the same conditions,while also having advantages in harmonic suppression ability.FSA-T3-SHRC can adjust the coefficient of IIR online when the fundamental frequency fluctuates,which has a certain frequency adaptive performance.The simulation results further verify the superiority of the proposed FSA-NSSHRC.Finally,the proposed T3-SHRC and FSA-T3-SHRC schemes are verified by building the experimental platform of a three-phase PWM grid-connected converter based on dSPACE 1103,the experimental results comprehensively evaluate the performance of the proposed scheme in the aspects of dynamic convergence speed and steady-state tracking accuracy and verify the effectiveness and superiority of the proposed scheme. |
PDF Full Text Request