| China is the world’s largest manufacturer,and its industrial sector consumes a significant portion of the grid power supply.High-end industrial users such as those engaged in precision machining,chip electronics manufacturing,data storage,etc.,demand sufficient power supply with higher quality.The most immediate consequence of power quality problems is equipment damage,which disrupts industrial production and causes substantial economic losses.Therefore,ensuring high power quality has become the most pressing concern for advancing industrial development.Currently,power quality management in distribution networks is primarily implemented at the public power network,factory power network,and sensitive equipment level.The approach employs hierarchical,separate or coordinated measures,utilizing treatment equipment such as a solid-state transfer switch,active power filter,static synchronous compensator,and dynamic voltage restorer.However,these power quality management devices face single functionality,redundant investment,decentralized operation and maintenance,and difficulty achieving global optimization when multiple power quality issues coexist.Therefore,researching key technologies for comprehensive power quality control devices in distribution networks holds immense theoretical and practical significance.This dissertation adopts the technical routes of topology optimization,key parameter design,control strategy development,and field application verification to construct a comprehensive power-quality control device for distribution networks.The proposed solution utilizes a novel power unit composed of an H-bridge cascaded converter and energy storage battery pack as the fundamental building block,offering an innovative perspective for power quality integration solutions in medium-voltage and large-capacity scenarios.The research findings can provide substantial backing for the rapid development of the integrated circuit industry and chip electronic manufacturing.This dissertation’s primary research and contributions are as follows:1.To address the difficulties in medium-voltage power quality management,such as variable spatio-temporal characteristics,diverse load types,and multiple-scene demands,the topology structure optimization of power quality control devices is carried out.The research compares and analyzes the pros and cons of various topological structures and their applicable scenarios,and a cascade power unit of a novel topology structure is proposed to construct a power quality control device for medium-voltage distribution networks.The working principle is thoroughly analyzed,and the critical parameters of the comprehensive control device are designed in detail based on the corresponding functions and performance requirements.The influence of characteristic parameters such as energy storage configuration,power component,and filter on device performance is analyzed,and the main circuit parameters for a 10 k V/1MVA experimental prototype of the comprehensive power quality control device for the distribution network are given.The field applications and experimental results demonstrate that the proposed power quality control device can meet or exceed the national standard requirements of power quality control.2.To ensure the power quality control device meets the high precision requirements of a medium-voltage distribution network on output voltage amplitude,frequency,unbalanced degree,dynamic and steady-state characteristics,and waveform quality,this research applied comparative analysis on a variety of waveform control technologies.A voltage-current double closed-loop control strategy based on carrier phase shift is adopted to guarantee the waveform stability under load sudden change and ensure the output voltage waveform quality under steady-state.The effects of capacitor current feedback and inductor current feedback on the dynamic performance of output voltage waveform are analyzed.Considering the characteristics of this new control device,the charging and discharging control strategy of the energy storage unit is studied.A control method of energy storage unit charge state equalization based on negative sequence voltage injection is proposed under the passive discharge operation mode,and the related control steps are explained in detail.The control strategy does not increase hardware costs,and the algorithm is simple and easy to implement.3.When the comprehensive power quality control device has a nonlinear load,the traditional double closed-loop control strategy may result in a high output voltage harmonic distortion rate and slow harmonic suppression response speed,failing to meet high-end manufacturing users’ high-quality power supply requirements.In this dissertation,a compound control strategy,based on the voltage-current double closed-loop control strategy,is proposed upon the harmonic current feedforward and harmonic voltage feedback,and the harmonic suppression mechanism is deduced and analyzed.The simulation and experimental results demonstrate that,compared with the traditional single control strategy,the proposed method can improve the harmonic suppression effect by 2.2% and reduce the response time to 100 ms.4.To enhance the reliability of the power quality control device,an analysis was conducted on the factors impacting its reliability,highlighting that their junction temperature directly influences the lifespan of these core power devices.Based on this analysis,a control strategy for power unit rotation work using real-time temperature feedback control was proposed.This control strategy combines sequential rotation control and optimal temperature rotation control to reduce the operating temperature of the core devices,thereby improving their reliability.Furthermore,a classification of fault categories for power units was performed,followed by research on the fault diagnosis system of the device.A fault diagnosis method based on recognizing output voltage waveform characteristics was proposed to achieve fast and accurate diagnosis of open-circuit faults in power units.Lastly,a fault-tolerant strategy combining hardware and software design was adopted to enable the device to continue operating even in faulty conditions.5.A 10 k V/1MVA experimental prototype of the comprehensive power quality control engineering in distribution networks is created to authenticate the theoretical analysis and the practicality of the proposed control strategy.In response to the application requirements of medium-voltage and large capacity distribution networks for power quality management,a system scheme for connecting the prototype to the distribution network is proposed,and the design of the prototype control system is expounded in detail.Finally,the prototype is experimentally verified in terms of functionality,performance,response time,and efficiency,thereby building a relatively complete experimental system.The above experimental results are analyzed in-depth and are consistent with the theoretical analysis. |
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