Research On Resonance Detecting And Damping For Dynamic Capacitor

With the continuous development of industrial production and life,people not only need a lot of electric energy,but also need high-quality electric energy to meet the stable operation of various precision instruments and equipment.Due to long-distance transmission,various types of non-linear loads are connected to the system in a large amount,so that the impedance of the power grid can not be neglected,and it is easy to resonate with the shunt capacitor used to compensate for reactive power,which jeopardizes the safe and stable operation of the equipment and the power system.Dynamic Capacitor(D-CAP),as a new type of power quality control device,can solve reactive power,harmonic and harmonic vibration problems in power grid.Because of its reliability and economy,it has potential application value for its related research.The related research on D-CAP mainly focuses on the principle analysis and verification of reactive power compensation,harmonic suppression and resonance suppression functions on different circuit topologies.However,D-CAP can not only achieve the above functions,but also detect the system resonance frequency.This paper is based on the three-phase Buck-type D-CAP.Firstly,its model is analyzed,and the basic principle of reactive power compensation and harmonic suppression is given.To overcome the shortcomings of traditional control strategy,an optimal control strategy is proposed.This control strategy can greatly reduce the coupling between harmonic loops and achieve the effect of selective harmonic elimination.Then,the equivalent impedance model of the power grid is given,the main factors affecting the parallel resonance of the system are studied.The resonance detection method based on Fourier transform is analyzed.The resonance frequency of the system is detected by using D-CAP through changing the current instruction on the basis of optimization control strategy.The active resonance damping method is studied.By detecting the PCC point voltage,a “virtual resistance” is connected in parallel with the PCC point to suppress the resonance.A comprehensive control strategy of D-CAP for reactive power compensation,harmonic suppression and resonant damping is given.Based on resonance detection and resonance damping,it is pointed out that D-CAP can work in two modes to achieve better resonance damping effect.Finally,with the help of Matlab/Simulink software and the three-phase Buck-type D-AP experimental prototype,the simulation and experimental verify the feasibility and effectiveness of the theoretical analysis.