Research On Resonance Damping For Three-phase Buck-Type Dynamic Capacitor

With the advancement and development of science and technology,the use of reactive loads,power electronic converters,and non-linear loads can cause harmonics and reactive power problems in power grid systems.In the field of power electronics,power quality problems such as reactive power and harmonics have always been the focus of research,and power quality compensation devices are one of the most effective ways to solve power quality problems.Due to the pursuit of more efficient and economical power quality regulating devices,Dynamic Capacitor(D-CAP)as a new type of power quality compensation device,is used to realize reactive power compensation and harmonic suppression.Because of its excellent performance and economic efficiency,D-CAP has a good application prospect in inhibition field.In the present research process,the functions of reactive power compensation and harmonic suppression of D-CAP have successfully achieved,and the experimental verifications of single-phase and three-phase Buck-type and Boost-type D-CAP are completed.However,few studies are done to focus on resonance problem when D-CAP is compensating reactive power.This paper is based on the three-phase Buck-type D-CAP.Firstly,it analyzes the basic structure and principle of reactive power compensation of D-CAP.Then,through impedance analysis,the reason of resonance under the influence of background harmonics of the power grid is studied.Since the distortion of the waveform cannot be fully compensated by only using the harmonic suppression function of the D-CAP,two control strategies for further suppressing the harmonics by using the active damping resonance method are proposed.By detecting D-CAP power capacitor current or voltage,two methods of constructing variable feedback to achieve active resonance damping are proposed.Then,the reactive power compensation system structure and control strategy of the three-phase Buck-type D-CAP are analyzed.Based on the even harmonic modulation strategy(EHM),D-CAP can realize compensation of the distortion of the output current waveform itself.Finally,two hybrid control strategies for harmonic suppression and active resonance damping while D-CAP is realizing reactive power compensation are proposed.The harmonic distortion caused by resonance is suppressed well.Current quality of net-side is improved and its current harmonics component meets the IEEE power quality standards.With the help of Matlab/Simulink software environment,and 33 kVA three-phase Buck-type D-CAP experimental prototype,the simulation and experimental results verify the effectiveness of the theoretical analysis successfully.