| Global environmental pollution and energy crisis issues have greatly promoted the development of new energy power generation technologies in the world.Microgrid power supply mode based on distributed energy,such as photovoltaic power generation and wind power generation,has emerged as the times require,and has become a research hotspot in the academic circles.While the microgrid effectively manages and utilizes distributed power sources,saves energy and protects the environment,it also brings a series of power quality problems,and puts forward higher requirements on the grid-connected control technology and strategy of the power system.The phase synchronization technologies can obtain the phase and amplitude of the fundamental voltage of the power grid in real time,which play a vital role in the process of achieving safe and stable grid connection.Among them,the phase-locked loop is composed of a phase detector,a loop filter and a voltage-controlled oscillator.It has a simple structure and is easy to implement,and has been widely used in power systems.This article is dedicated to introducing and improving the phase synchronization technology represented by the phase-locked loop.In view of the widespread existence of DC offset and harmonic interference in power grid voltage,an in-depth study of single-phase phase-locked loop technology is focused on.Firstly,the background and significance of the research,the current research status and development trend at home and abroad are introduced in detail,including: the phase-locked requirements in the application of grid connected control of microgrid,the origin,classification and basic structure of phase-locked loop technology,the research results of three-phase phaselocked loop and single-phase phase-locked loop at home and abroad.By means of basic structure demonstration,working principle analysis,mathematical model derivation and stability analysis,the basic theories of three parts of the phase-locked loop technology based on the synchronous rotating coordinate system,the quadrature signal generator and the singlephase phase-locked loop based on the second-order generalized integrator are studied in detail.It lays a foundation for the following new and improved methods for the shortcomings of the single-phase enhanced phase-locked loop and the phase-locked loop based on the second-order generalized integrator.Secondly,aiming at the inherent shortcomings of traditional single-phase enhanced phaselocked loop,this paper designs an improved enhanced phase-locked loop technology,which is suitable for microgrid grid-connected control technology based on distributed power.The coupling relationship between the angular frequency of the output voltage and the amplitude of the input voltage is derived,then normalize the amplitude of the error signal on the input side to achieve decoupling.The cost function of error signal is built,and the DC offset estimation loop is designed by the gradient descent method.The DC offset in input signal is eliminated by a closed-loop negative feedback loop.Then,the moving average filter is introduced in all estimation loops of the phase-locked loop to enhance the anti-interference ability of highfrequency harmonics of the control system.The simulation model of single-phase phase-locked loop technologies are built in Matlab/Simulink,and the comparison and analysis are carried out.The simulation results verify the effectiveness and correctness of the proposed method.Thirdly,in view of the ubiquitous DC offset and harmonic interference problems in the power grid,this paper proposes an improved single-phase phase-locked loop technology based on the second-order generalized integrator.The phase-locked loop adds a product branch in the front-stage second-order generalized integrator and changes it to a fixed-frequency structure to suppress DC offset and simplify parameter design.In order to enhance the filtering performance and speed up the dynamic response,the moving average filter is introduced into the back-stage phase-locked loop and the integral part of the proportional integral controller is removed.Use methods such as Bode diagram analysis and small signal model derivation to guide the improvement of structural design and determine the corresponding parameters.The simulation modeling analysis is carried out by Matlab/Simulink,and the experimental verification is carried out on the hardware platform based on the rapid prototyping controller YXSPACE.The results prove the effectiveness and superiority of the proposed method. |
