Dynamic Control Of Transformer-less Single-phase Half-bridge Unified Power Quality Conditioner

The load components in the power distribution system are becoming more and more complex,and high-quality power distribution has become a challenge.In modern society,active power technology is an important method to solve power quality problems.Among them,the unified power quality conditioner(UPQC)has gradually become a research hotspot because it can handle a variety of power quality problems.This thesis studies the related technology of transformer-less single-phase half-bridge UPQC,the main research work is as follows:Firstly,based on the topological structure of transformer-less single-phase half-bridge UPQC,the working mode of the series converter and parallel converter are analyzed in detail,and the mathematical model of the series converter and parallel converter are established.On this basis,the power flow of UPQC is analyzed.Secondly,a detailed analysis of the sub-capacitor voltage ripple of the single-phase halfbridge structure is carried out.Starting from the single-phase half-bridge rectifier,the equivalent capacitance current is proposed,and then derive the mathematical expression of sub-capacitor voltage ripple.Extending this idea to the transformer-less single-phase halfbridge UPQC,the sub-capacitor voltage ripple expression can be obtained.Analyze the capacitor voltage under various load conditions,and simulate to verify the correctness of the theoretical analysis of the sub-capacitor voltage.Thirdly,aiming at the influence of sub-capacitor voltage ripple and nonlinear load on the output voltage of the series-side converter,based on the traditional double closed-loop voltage and current control,a voltage outer-loop characteristic subharmonic control method is proposed.In view of the large voltage ripple of the sub-capacitor in the actual circuit and the deviation of the steady-state average value,a moving average calculation method is proposed to calculate the real-time average value of the sub-capacitor voltage,thereby reducing the voltage error fluctuation in the proportional integral voltage equalization control.Finally,simulation and experiment verify the correctness of the proposed control method.Finally,Based on Si C devices,a low-power prototype of transformer-less single-phase half-bridge UPQC was designed,and the system circuit design and FPGA-based controller design were completed.For the aforementioned control method,all programs based on Verilog HDL have been completed,and UPQC compensation experiments,load change experiments,grid-side voltage mutations experiments,UPQC start-up and shutdown experiments,connecting capacitor comparison experiments and efficiency tests have been completed.The experimental results show that the low-power prototype has good dynamic and static performance of harmonic suppression and voltage compensation,which proves the effectiveness of the proposed control method.