Research On Active Harmonic Compensation Under Complex Load Conditions

With the development and progress of society,electric energy plays an important role in daily life and industrial production.The APF has been widely used due to its advantages of good harmonic control effect.Due to the mismatch between APF and load impedance after it is connected to the power grid,not only the system stability is poor,but also the harmonic compensation effect is affected.Therefore,it is of great theoretical and engineering value to study the impedance characteristics of the system and the failure mechanism of harmonic compensation,so as to improve the compensation performance and ensure the stability of power grid.This paper focuses on the modeling of active harmonic compensation impedance,the analysis and design of control system passivity,and the improvement of compensation adaptability.The main work is as follows:Firstly,the power grid,compensation device and load in active harmonic compensation system are introduced.Next,based on the impedance characteristics of the system and the active harmonic compensation control,an equivalent impedance model is proposed,and the equivalent output admittance expression of active power filter is derived,which provides the basis for the stability analysis and controller design.Then,based on the equivalent impedance model of the active harmonic compensation system,the current controller and the dc side voltage controller are designed to realize the accurate tracking of the fundamental wave while ensuring the dc side voltage stability.Through the analysis of the stability of the current control system,the current control output admittance passive resistance is weak.Next,put forward a design method of passive sexual enhancement,the feedforward controller with double filter,makes the equivalent output admittance of active power filter under the Nyquist frequency full frequency passive,to improve the stability of the current control system.In the part of simulation and experiment,the function of compensating resistive nonlinear load of shunt active power filter is verified.Finally,the equivalent harmonic compensation model is established to analyze the harmonic compensation characteristics of shunt active power filter.Due to the small equivalent impedance on the load side,the harmonic current of the load is amplified obviously,and the improvement of power quality is not obvious.On the contrary,due to the large equivalent impedance on the load side,the degree of amplification is weak and the compensation effect is better.Next,two optimization methods which from the control angle and the system topology respectively are proposed to suppress the harmonic current amplification effect on the ac side of the load,so as to improve the compensation performance of active power filter.The simulation and experimental results show that the shunt active power filter can compensate the nonlinear load of voltage source well,the related harmonic amplification index is basically consistent with the theoretical analysis,and it can also compensate the nonlinear load of current source and resonant type well.