Research On Some Key Technologies Of Power System Harmonic And Interharmonic Control Based On Time-Delay Robust H? Control Theory

With the rapid development of power electronics technology,a lot of power electronic devices have been used in the grid.However, these power electronic devices usually are non-linear so that it brings harmonic and interharmonic pollution to the grid.Parallel Active Power Filter is an efficient, stable, flexible and improve power quality equipment and it has been widely recognized and applied.Research of Shunt APF control strategy focused on current target detection and target current tracking control.Existing APF control strategy in current target detection consider the effect of time-delay so that the phase delay of target current has been forecast and the accuracy of the APF compensation has been improved.However in target current tracking control,APF output current as a time-delay variable is used as the state quantity feedback but it is ignored in existing APF control strategy.Existing APF control strategy has considered the impact of parameter perturbation and dead zone effects,but the interaction effects of the time-delay in target current tracking control with parameter perturbation and dead zone effects is not in considered.The impact of random disturbance on the sensor and harmonic/inter-harmonic unity compensation also is not in considered in exisiting APF control strategy.Therefore,APF still exist following problems:the overall compensation is not so good,it is because the time-delay of APF output current and the parameter perturbation of APF control system severely narrow the stability range of the controller gain so the interference caused by dead zone effects is enlarged; the compensation accuracy may directly get worse when the sensor especially the one for APF output current as a state feedback is affected by random disturbances;the compensation accuracy may indirectly get worse because the load current contains harmonic and interharmonic currents could imapct current target detection.These key issueses hinder the further application of APF.For convenience of description,this paper start with APF used for harmonic compensation.So the complex interference on APF compensation accuracy of time-delay, paprameter perturbation,the dead zone effects and random effects is considered in order to propose an improve method and compare the improve method with the existing method. Then simulation and physical experiment is designed to propose the accuracy and effectiveness of the improve method.Finally,the improve method will be promoted to the APF for harmonic/interharmonic unity compensation.The main contents of this paper are as follows:Considering the inference of time-delay,parameter perturbation and dead zone effects,an error control system model of APF is derived,which is a typical delay system,and it is analyzed by Time-delay Robust H? theory.The analysis results indicates time-delay and paprameter perturbation narrow the stability range of the controller gain so the interference caused by dead zone effects is enlarged.This is the reason why the compensation accuracy of APF exisiting is not so good.Robust H? control strategy containing predictive control (ie,improved state observer) is proposed for shunt APF.First,improved state observer is used to forecast APF output current so that the time-delay in controller is eliminated and APF error control system turn to a no delay expression.On this basis,the relationship between the feedback error matrix value of the improved state obsever and status tracking capabilities is analyzed.Then, a robust H? controller for shunt APF system including predictive control is designed with better performance of interference suppression. Simulation results verify the improved state observer can accurately predict changes in the APF output current, Robust H? control strategy containing predictive control significantly improve the compensation accuracy of APF especially when the load is lighter or the harmonics frequency is higher.H? control strategy containing predicitive and repetitive control is proposed for shunt APF.The predictive control is used to eliminate the impact of time-delay and the complex control with PI control and repetitive control is used to estimate and eliminate the periodic interference caused by parameter perturbations and dead zone effects.The method do not need a high control gain, which may cause control output saturation or system instability when using a robust H? controller. Simulation results verify compared with Robust H? control strategy containing predictive control,H? control strategy containing predicitive and repetitive control has better compensation accuracy with the same controller gain.On this basis,it is analyzed the influnence on dynamic performance caused by complex control.And it is also analyzed the influence of random interference on sensors.Finally,it is verified the choice of controller gain should comprehensive conside the dead zone effects and the random interference on sensors.The shunt APF for harmonic/inter-harmonic unity compensation is studied.Since the inter-harmonic loads such as AC-DC-AC converter can be substantially equivalent to a voltage source load,it can not be directly compensated by shunt APF.Using AC-DC-AC converter as a example to get the conditions AC-DC-AC converter parallel compensation system can be realized.Then considing the frequencies of power system inter-harmonic is usually unkowned,the repetitive control is difficult to realize.So the Robust H? control strategy containing predictive control is used in the AC-DC-AC converter parallel compensation system and simulation results verify inter-harmonic achieve a good compensation accuracy.The experiment using DSP28335 as controller core is designed to verify the theoretical analysis and the improved control stategy in this paper.The experimental results show the correctness and validity of theoretical analysis and the improved control strategy.