隨著化石燃料的日益枯竭和全球能源需求的持續(xù)增加,環(huán)境問題變得日益嚴(yán)峻。由于光伏組件及其系統(tǒng)的技術(shù)進(jìn)步和政府對清潔能源的激勵,光伏發(fā)電系統(tǒng)的成本逐年下降。在過去幾十年中,光伏的累計裝機(jī)容量在全球范圍內(nèi)以極高的速度增長。光伏發(fā)電系統(tǒng)的大規(guī)模并網(wǎng)給電力系統(tǒng)的穩(wěn)定和安全運(yùn)行帶來了重大沖擊。因此,光伏發(fā)電系統(tǒng)接入電網(wǎng)需要一種有效的控制策略,該策略應(yīng)能確保系統(tǒng)在電網(wǎng)正常和故障條件下均能良好運(yùn)行,并滿足可再生能源可靠和安全并網(wǎng)規(guī)范要求。本文針對電網(wǎng)正常和故障運(yùn)行兩種情況,研究和提出了兩級光伏發(fā)電系統(tǒng)的建模與控制方法。針對電網(wǎng)正常運(yùn)行情況,設(shè)計了用于調(diào)節(jié)兩級并網(wǎng)光伏發(fā)電系統(tǒng)的多層控制結(jié)構(gòu),以滿足電網(wǎng)規(guī)范要求并能有效地促進(jìn)光伏發(fā)電系統(tǒng)的集成。設(shè)計的控制方案具有最大功率跟蹤功能,該功能由升壓DC-DC變換器對電流進(jìn)行調(diào)節(jié)來實(shí)現(xiàn),能根據(jù)電能質(zhì)量需求調(diào)節(jié)注入電網(wǎng)的電流。通過控制并網(wǎng)逆變器實(shí)現(xiàn)所需的電能質(zhì)量,其中電流控制通過dq坐標(biāo)系下的PI控制器來完成。針對網(wǎng)側(cè)對稱故障情況,建立了完整的雙級光伏發(fā)電系統(tǒng)低電壓穿越模型,滿足電壓跌落期間提供無功電流的電網(wǎng)規(guī)范要求。提出的模型通過更新電流發(fā)生器的參考值及相應(yīng)的控制器,有效地實(shí)現(xiàn)低電壓穿越和改善電能質(zhì)量及并網(wǎng)穩(wěn)定性。提出的控制方案有助于滿足電網(wǎng)規(guī)范要求,并確保光伏發(fā)電系統(tǒng)在電網(wǎng)發(fā)生對稱故障時能夠平穩(wěn)運(yùn)行。針對網(wǎng)側(cè)不對稱故障情況,提出了兩級光伏發(fā)電系統(tǒng)的低電壓穿越控制策略。提出的策略包括適應(yīng)電網(wǎng)規(guī)范要求的功率參考值計算、有功和無功功率控制,以及實(shí)現(xiàn)低電壓穿越的靈活電能質(zhì)量控制和峰值電流限幅控制。該控制策略通過dq坐標(biāo)系下的電流參考值發(fā)生器,實(shí)現(xiàn)低電壓穿越過程中電能質(zhì)量的靈活控制,并具有峰值電流限制能力,以避免逆變器過電流。所設(shè)計的電流參考值發(fā)生器,能夠?qū)崿F(xiàn)光伏發(fā)電系統(tǒng)在各種電網(wǎng)故障下均能可靠運(yùn)行。而且,提出了用于有效降低PV功率的故障穿越方案,采用光伏陣列功率削減策略來避免DC電壓增加,以防止故障期間出現(xiàn)直流過電壓。首先,將減少的光伏陣列功率注入電網(wǎng),如果由于網(wǎng)側(cè)電壓跌落過大或持續(xù)時間過長而使直流電壓持續(xù)增加的話,則直流斬波器將被激活,以防止直流母線電壓超過其允許極限。此外,所提出的控制策略還包括:用于電網(wǎng)電壓幅值計算和故障檢測的混合電網(wǎng)同步和序列分離方法。通過現(xiàn)場測試和模擬仿真驗(yàn)證了提出的建模和控制策略的有效性。最后,研究了光伏發(fā)電系統(tǒng)接入對弱電網(wǎng)電壓穩(wěn)定性的影響,主要包括光伏電站不同控制策略對光伏系統(tǒng)輸出特性及并網(wǎng)點(diǎn)電壓的影響。建立了簡化的光伏電站動態(tài)模型,在不同的負(fù)荷模型和電網(wǎng)強(qiáng)度下,對比分析了各種控制策略對并網(wǎng)點(diǎn)電壓恢復(fù)特性的影響。提出了一種改進(jìn)的有功電流恢復(fù)方法,實(shí)現(xiàn)光伏發(fā)電功率和并網(wǎng)點(diǎn)電壓的有效恢復(fù)。采用MATLAB/SIMULINK仿真驗(yàn)證了提出的光伏系統(tǒng)控制策略的有效性。
【學(xué)位單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位年份】：2019
【中圖分類】：TM615
【文章目錄】：
摘要
Abstract
Chapter 1 Introduction
    1.1 Background and significance of study
    1.2 Objective of the thesis and main contributions
    1.3 Review of related research
    1.4 Outlines of the thesis
Chapter 2 Fundamentals of Grid-Connected PV Systems and TheirControls
    2.1 Introduction
    2.2 Structure and topologies
        2.2.1 Connection topologies of PV systems
        2.2.2 Power conditioning unit
    2.3 Description of grid-connected PV System and component modeling
        2.3.1 Description of PV system structure
        2.3.2 Modelling of PV system components
    2.4 Mathematical model of a grid-connected PV system in dq frame
        2.4.1 Park’s transformation (or dq transformation)
        2.4.2 Mathematical model of a PV system in dq frame
        2.4.3 Grid synchronization
    2.5 PV system control under normal operation
        2.5.1 DC-DC converter control and MPPT
        2.5.2 Three-layer control scheme
    2.6 Simulation results
    2.7 Summary
Chapter 3 Control of PV Systems under Balanced Grid Faults
    3.1 Introduction
    3.2 Standards and requirements for PV grid integration
        3.2.1 Grid codes
        3.2.2 Stationary grid support
        3.2.3 Voltage support during grid disturbance
    3.3 Control strategies under balanced grid faults
        3.3.1 Boost DC‐DC converter control
        3.3.2 Two-layer inverter control scheme
    3.4 Simulation results
    3.5 Summary
Chapter 4 Control of PV Systems under Unbalanced Grid Faults
    4.1 Introduction
    4.2 Control strategy under unbalanced grid faults
        4.2.1 Framework of the proposed control strategy
        4.2.2 Fault detection and grid voltage synchronization
        4.2.3 Power references calculation
        4.2.4 Power reduction strategy for DC-link voltage control
        4.2.5 Proposed current reference generators
    4.3 Inverter controller implementations
        4.3.1 Inner control loop: current controller design
        4.3.2 Outer control loops
        4.3.3 Inverter current limitation
    4.4 Simulation results
    4.5 Summary
Chapter 5 Impacts of PV Integration on Voltage Stability of Weak Grids
    5.1 Introduction
    5.2 Definition and measure of grid strength
        5.2.1 Definition of grid strength
        5.2.2 Measurement of grid strength
    5.3 Overview of voltage stability analysis
        5.3.1 Definition of voltage stability
        5.3.2 Classification of voltage stability
    5.4 Test system and its modeling
        5.4.1 Test system
        5.4.2 Simplified PV system model
        5.4.3 Load modeling
    5.5 Impacts of FRT strategies of PV systems on voltage stability of weak grids
        5.5.1 Existing FRT control strategies
        5.5.2 Proposed FRT control strategy
        5.5.3 Case studies for analysis of voltage stability
    5.6 Summary
Conclusions and Future Work
    Conclusions
    Future work
References
Publication During the Doctoral Study
Acknowledgement
Cirriculum Vitae (CV)


本文編號：2846842