Research On Harmonic And Negative-sequence Signal Detection Algorithms In Power System

With the rapid development of the modern industry, the nonlinear loads inpower system are increasing gradually, and the harmonic problem of power systemhas become more and more complex. Now, harmonic pollution has become a seriousproblem that affects the quality of power in both transmission and distribution ofpower systems. The problems caused by harmonics include malfunctioning of relayprotection and automatic devices, harmonic losses, insulation degradation andcommunication interference. To reduce or eliminate harmonics in power system hasbecome an urgent problem because of a variety of hazards caused by harmonics.Harmonic detection is the premise and basis of harmonic suppression, so harmonicdetection has very important significance in improving power quality.For harmonic detection problem in power system, this paper studies thesecond-order generalized integrator-delayed signal cancellation (SOGI-DSC)algorithm and cascaded delayed signal cancellation (CDSC) algorithm. TheSOGI-DSC algorithm based on a combination of SOGI filter, DSC method andlow-pass notch filter phase-locked loop (LPN-PLL) is used to extract fundamentalpositive-sequence component in distorted and asymmetric three-phase systems. Thismethod is analyzed through Matlab simulation.For the SOGI-DSC algorithm, it can only obtain fundamental positive-sequencecomponent, without the ability of extracting arbitrary harmonic. This paperpresented the CDSC algorithm based on DSC method. This algorithm can detect themagnitude and phase angle of any individual harmonic from the source with variousbackground harmonics. This method is also analyzed through Matlab simulation.In this paper, in order to verify the effectiveness of the above two methods, theexperimental platform based on dSPACE real-time simulation system is designed. Itconsists of dSPACE single board system DS1104, harmonic sources and asymmetricthree-phase system. Harmonic sources and asymmetric three-phase system isdeveloped based on FPGA, and it can realize a three-phase programmable signalsource and the communication with dSPACE system. Since the faults includingvoltage sag, asymmetries and harmonic distortion will probably happen in the grid,some significant test cases are designed in this paper. Experimental results show thatboth of the two detection algorithms can quickly and accurately obtain harmonicsfrom the source.