Resonance Mitigation For Low-Voltage Hybrid Reactive Power Compensation Systems

With the rapid development of new energy sources,power quality issues in distributed power generation systems have received more and more attention.In distributed systems,there are problems such as slow and inaccurate compensation,high cost,and resonance.Due to the above problem,this thesis take the hybrid compensation system composed of distributed interface converter and reactive power compensation device as the research object,and the related research is carried out on the mechanism of resonance generation and the control method of virtual impedance for resonance mitigation.The power quality control of multifunctional distributed power generation based on weighted average current and the virtual impedance resonance mitigation scheme of the hybrid compensation system based on PCC voltage feedback are proposed.Aiming at the problem that multi-functional distributed power sources are prone to LCL oscillation when compensating for local load harmonics,a weighted average current based deadbeat control method for distributed power generation microgrid enhancement is proposed.Firstly,this thesis has developed a virtual output filter system which can reduce the physical third-order LCL filter to a single virtual inductor filter.Secondly,to meet with the high bandwidth requirement for harmonic compensation,a deadbeat control with weighted average current is proposed,and with the involvement active damping for filter oscillation mitigation.Through a simply modifying of weighted current reference,this method can effectively compensate local load harmonics without using additional sensors and harmonic current extractions.Finally,the effectiveness and the practicality of the proposed method has been verified in different scenarios.For the resonance problem of the hybrid compensation system considering the parallel resonance between the reactive power compensation device and the grid impedance,the mathematical model of the hybrid compensation system is established firstly.This thesis analyzes the compensation effect of extracting different feedback points as the harmonic current reference,and draws the conclusion that the compensation performance of detection of nonlinear load and power capacitor branch current is the best.Secondly,the reasons and dominant factors of resonance in the hybrid compensation system are analyzed based on the open-loop transfer function.Through the above analysis,a resonance mitigation strategy for a hybrid compensation system based on virtual impedance is proposed finally.The PCC harmonic voltage component is adjusted by the virtual impedance controller,which is added to the reference current as a damping term to achieve resonance mitigation and improve the stability of the system.The feasibility of this method is verified through simulation and experiment,which has certain practical engineering application value.