Research On Interharmonic Suppression Technology Based On APF

With the continuous growth of China's economy and the increasing level of technology,the wide range of electrical equipment and variability loads are widely used in the power grid,resulting in a large number of harmonics and frequency dispersion interharmonics in the power grid.Interharmonic:its frequency is defined as a non-integer multiple of the power frequency.As a special kind of harmonic,the interharmonics will not only cause fluctuations and flicker of the system voltage,but also seriously endanger the human health.It may even lead to the failure of the measuring instrumentation device to work properly and the malfunction of the relay protection device,which will bring great economic losses to the country.Therefore,a thorough understanding of the mechanism of interharmonic generation and the development of effective filtering devices are issues that need to be solved today.Active Power Filter(APF)is a filtering device that can track and compensate harmonics and interharmonics whose amplitude or frequency changes in real time.It is very effective in overcoming the drawbacks of passive filters,so it has received extensive attention.In this paper,the parallel active power filter is taken as the research object,and the main research is how to improve the detection performance of current and the tracking performance of current.Aiming at the contradiction between the convergence speed and steady-state precision of the traditional low-pass filter(LPF)in current detection,this paper adopts the variable step size least mean square(LMS)adaptive algorithm and applies it to LPF.The algorithm uses the hyperbolic sine function relationship to relate the error signal to the step factor.As the error signal changes,the step factor can also automatically adjust the size.When the step factor is large enough it can ensure that the LPF has an excellent convergence speed,and when the step factor is small,the LPF has a high steady state accuracy.In order to improve the tracking performance of compensation current,this paper adopts a double hysteresis current control method based on voltage space vector.The current input to the hysteresis comparator is not the traditional three-phase error current,but the error current vector after abc-a?transformation,and then outputs the corresponding state value according to the established criterion table.As for the selection of the optimal output voltage,it is necessary to refer to the two values of the state value of the hysteresis comparator output and the spatial distribution of the reference voltage vector,so as to achieve a good control of the range of the error current within the hysteresis width.For the phase-to-phase influence between voltages,the voltage space vector method can be effectively eliminated,the implementation process is simple,and the transformation is not too complicated,and the current response speed is good,and the current error can be effectively limitedFinally,this paper takes the common interharmonic source-frequency converter as the research object and builds the simulation model on matlab/simulink.By analyzing the mechanism of the inter-harmonic generated by the frequency converter,the active power filter device is rationally designed and installed on the DC side of the frequency converter to filter out the interharmonics.The final simulation results verify the effectiveness of the filtering device.