并网逆变器已在储能、新能源发电、电网无功补偿等众多领域得到广泛应用。采用下垂控制的并网逆变器具有功率分配均衡、无通信线路、模块化即插即用等众多优势。但采用下垂控制的并网逆变器存在线路阻抗失配、并网过程中电压难以同步等问题。为此，本文以单相并网逆变器为研究对象，对下垂控制技术以及并网预同步控制策略进行深入研究，对下垂控制在并网电源领域的应用具有重要意义。

       首先分析下垂控制原理，将电压频率和电压幅值的下垂调节分别引入单相并网逆变器输出的有功功率和无功功率中，得出并网逆变器的下垂控制方程。然后，对单相并网逆变器的功率电路和控制电路建立数学模型，引入下垂控制功率环、电压电流环并推导逆变器电压传递函数，以便分析其动态特性与稳态特性。其次，为确保单相并网逆变器在并网后可以输出较高的电能质量，对下垂控制方法进行改进，引入虚拟阻抗、电压积分环节以及二次调节算法，补偿逆变器输出电压的频率和幅值，保证系统的稳定运行。最后，离网运行状态下的逆变器输出电压与电网电压在幅值、相位和频率等参数上的不同，将导致并网瞬间产生较大的冲击电流，因此本文对传统并网预同步控制策略进行改进，引入级联式延时信号法对采集到的电网信号中的低次谐波干扰进行滤除，提出一种无锁相环跟踪电网电压相位和幅值的预同步控制策略，该方法无需对电网电压使用单独的锁相环，在下垂控制的基础上即可达到逆变器输出电压稳定跟踪电网电压的效果，简化了控制环节，提高系统的稳定性。

       根据样机参数研制了一款并网逆变器实验样机，对其关键电气性能进行测试验证，实验结果表明，逆变器在并网状态下能够稳定运行，改进的并网预同步控制策略可以精确跟踪电网相位、幅值以及频率。同时，样机其他电气性能均符合预先设定的指标，验证了理论分析的正确性和设计方法的可行性。

         Grid-connected has been widely used in many fields such as energy storage, new energy generation, and grid reactive power compensation. The grid-connected inverter with droop control has many advantages such as balanced power distribution, no communication line, modular plug-and-play and so on. However, there are problems such as line impedance mismatch and voltage synchronization difficulty in the grid-connected process in the grid-connected inverter with droop control. For this reason, this thesis takes the single-phase grid-connected inverter as the research object, and carries out an in-depth study on the droop control technology and the grid-connected pre-synchronization control strategy, which is of great significance for the application of droop control in the field of grid-connected power supply.

         Firstly, the droop control principle is analyzed, and the droop adjustment of voltage frequency and voltage magnitude is introduced into the active power and reactive power output from single-phase grid-connected inverter respectively, which leads to the droop control equation of grid-connected inverter. Then, mathematical models are established for the power and control circuits of the single-phase grid-connected inverter to introduce the droop control power loop, voltage-current loop and derive the inverter voltage transfer function in order to analyze the dynamic and steady state characteristics. Secondly, in order to ensure that the single-phase grid-connected inverter can output high power quality after grid connection, the droop control method is improved by introducing virtual impedance, voltage integration link and quadratic regulation algorithm, which compensates for the frequency and amplitude of the output voltage of the inverter to ensure the stable operation of the system. Finally, the difference between the inverter output voltage and the grid voltage in parameters such as amplitude, phase and frequency in the off-grid operation state will lead to a large inrush current in the grid-connected instant, so this paper improves the traditional grid-connected pre-synchronization control strategy, introduces the cascaded delay signal method to filter out the low harmonics interference in the collected grid signal, and proposes a phase-locked loop-free tracking of the phase and amplitude of the grid voltage in the A pre-synchronization control strategy is proposed to track the phase and amplitude of the grid voltage without phase-locked loop. This method does not require the use of a separate phase-locked loop for the grid voltage, and can achieve the effect of stable tracking of the grid voltage by the inverter output voltage on the basis of the droop control, which simplifies the control link and improves the stability of the system.

        Based on the prototype parameters, a grid-connected inverter experimental prototype is developed to test and verify its key electrical performances, and the experimental results show that the inverter can operate stably under the grid-connected condition, and the improved grid-connected pre-synchronization control strategy can accurately track the grid phase, amplitude and frequency. Meanwhile, other electrical performances of the prototype are in line with the pre-set indexes, which verifies the correctness of the theoretical analysis and the feasibility of the design method.

[1]廖华, 向福洲. 中国“十四五”能源需求预测与展望[J]. 北京理工大学学报(社会科学版), 2021, 23(02): 1-8.

[2]王卫权, 李丹, 于洋. 我国可再生能源融合发展之路[J]. 可持续发展经济导刊, 2023, (07): 12-14.

[3]韦惠肖, 任伟楠. 《中国可再生能源发展报告2022》《抽水蓄能产业发展报告2022》发布[J]. 水力发电, 2023, 49(08): 128.

[4]张涛. 《2030年前碳达峰行动方案》解读[J]. 生态经济, 2022, 38(01): 9-12.

[5]伍赛特. 分布式发电系统技术特点及应用前景展望[J]. 通信电源技术, 2019, 36 (05): 123-125.

[6]贺红军. 新能源发电和分布式发电对电力系统的影响分析[J]. 光源与照明, 2022, (08): 159-161.

[7]王成山, 杨占刚, 王守相, 等. 微网实验系统结构特征及控制模式分析[J]. 电力系统自动化, 2010, 34(01): 99-105.

[8]Xu Y, Nian H, Hu B, et al. Impedance modeling and stability analysis of VSG controlled type-IV wind turbine system[J]. IEEE Transactions on Energy Conversion, 2021, 36(4): 3438-3448.

[9]史苏苏. 低压微电网中下垂控制的研究[D]. 秦皇岛: 燕山大学, 2013.

[10]赵炳洋, 赵波, 张芳, 陈杰. 构网型逆变器技术综述[J]. 北京信息科技大学学报(自然科学版), 2022, 37(04): 57-67.

[11]葛家宁, 董学育, 周磊, 等. 微电网并联逆变器改进下垂控制[J]. 电工技术, 2020, 40(3): 25-27.

[12]别朝红, 林雁翎, 张建华. 微网技术及其标准体系的研究[J]. 高电压技术, 2015, 41(10): 3177-3184.

[13]刘靖宇. 微电网并联逆变器功率均分控制关键问题研究[D]. 长沙: 湖南工业大学, 2022.

[14]Rasheduzzaman M, Kimball J W. Modeling and tuning of an improved delayed-signal-cancellation PLL for microgrid application[J]. IEEE Transactions on Energy Conversion, 2018, 34(2): 712-721.

[15]Beheshtaein S, Savaghebi M, Guerrero J M. A fuzzy-based hybrid PLL scheme for abnormal grid conditions[C]//IECON 2015-41st Annual Conference of the IEEE Industrial Electronics Society. IEEE, 2015: 005095-005100.

[16]徐晓宁, 周雪松. 微网脱/并网运行模式平滑切换控制策略[J]. 高电压技术, 2018, 44(8): 2754-2760.

[17]梁明玉, 蔡新红, 龚立娇, 等. 基于下垂控制的微电网并网预同步控制研究[J]. 计算机仿真, 2022, 39(04): 80-86+109.

[18]Kim H J, Shin E S, Lee Y S, et al. Smooth operation transition scheme for stand-alone power system with EG and BESS-PV panels[J]. IEEE Transactions on Smart Grid, 2017, 8(4): 2042-2044.

[19]Zheng X, Cao H, Li H, et al. Multi-inverters pre-synchronization VSG control strategy for the microgrid system[C]//2019 IEEE 4th International Future Energy Electronics Conference (IFEEC). IEEE, 2019: 1-5.

[20]陈杰, 闫震宇, 赵冰, 等. 下垂控制三相逆变器阻抗建模与并网特性分析[J]. 中国电机工程学报, 2019, 39(16): 4846-4856+4986.

[21]宦昱晨. 单相并联逆变电源控制技术研究[D]. 秦皇岛: 燕山大学, 2023.

[22]王静怡, 王盼, 袁雷, 等. 单极倍频与单极性调制策略对比及特性分析[J]. 电子器件, 2023, 46(05): 1364-1371.

[23]陈衍. 电力系统稳态分析[M]: 第四版. 北京: 中国电力出版社, 2015.

[24]许吉强. 微电网接口变换器下垂控制策略研究[D]. 无锡: 江南大学, 2017.

[25]张中锋. 微网逆变器的下垂控制策略研究[D]. 南京: 南京航空航天大学, 2013.

[26]盛鹍, 孔力, 齐智平, 等. 新型电网-微电网(Microgrid)研究综述[J]. 继电器, 2007, (12): 75-81.

[27]Guerrero J M, De Vicuna L G, Matas J, et al. Output impedance design of parallel-connected UPS inverters with wireless load-sharing control[J]. IEEE Transactions on industrial electronics, 2005, 52(4): 1126-1135.

[28]Trivedi A, Jain D K, Singh M. A modified droop control method for parallel operation of VSI's in microgrid[C]//2013 IEEE Innovative Smart Grid Technologies-Asia (ISGT Asia). IEEE, 2013: 1-5.

[29]Xu S, Wang J, Xu J. A current decoupling parallel control strategy of single-phase inverter with voltage and current dual closed-loop feedback[J]. IEEE Transactions on Industrial Electronics, 2011, 60(4): 1306-1313.

[30]Liu Z, Liu J, Hou X, et al. Output impedance modeling and stability prediction of three-phase paralleled inverters with master-slave sharing scheme based on terminal characteristics of individual inverters[J]. IEEE Transactions on Power Electronics, 2015, 31(7): 5306-5320.

[31]郭小强. 光伏并网逆变器通用比例复数积分控制策略[J]. 中国电机工程学报, 2015, 35(13): 3393-3399.

[32]周晨. 基于虚拟阻抗的微电网下垂控制策略及谐波抑制方法研究[D]. 成都: 西南交通大学, 2014.

[33]Rodríguez P, Luna A, Candela I, et al. Multiresonant frequency-locked loop for grid synchronization of power converters under distorted grid conditions[J]. IEEE Transactions on Industrial Electronics, 2010, 58(1): 127-138.

[34]Zhao R, Wu S, Wang C, et al. A novel discretization method for multiple second-order generalized integrators[J]. IEEE Transactions on Power Electronics, 2021, 36(10): 10998-11002.

[35]龚星宇. 微电网并联逆变器功率均分控制策略研究[D]. 株洲: 湖南工业大学, 2021.

[36]Keyvani-Boroujeni B, Fani B, Shahgholian G, et al. Virtual impedance-based droop control scheme to avoid power quality and stability problems in VSI-dominated microgrids[J]. IEEE Access, 2021, 9: 144999-145011.

[37]Ahmadi S, Shokoohi S, Bevrani H. A fuzzy logic-based droop control for simultaneous voltage and frequency regulation in an AC microgrid[J]. International journal of electrical power & energy systems, 2015, 64: 148-155.

[38]GB/T 34129-2017, 微电网接入配电网测试规范[S].

[39]GB/T 41995-2022, 并网型微电网运行特性评价技术规范[S].

[40]吕志鹏, 罗安. 不同容量微源逆变器并联功率鲁棒控制[J]. 中国电机工程学报, 2012, 32(12): 35-42.

[41]刘云. 基于下垂控制的微电网逆变器控制策略研究[D]. 青岛: 山东科技大学, 2020.

[42]黄杏, 金新民. 微网用分布式电源变流器下垂特性控制策略[J]. 电工技术学报, 2012, 27(8): 93-100.

[43]韩运泽. 微电网分层控制及其平滑切换研究[D]. 秦皇岛: 燕山大学, 2021.

[44]朱作滨, 黄绍平, 李振兴. 微网储能变流器平滑切换控制方法的研究[J]. 电力系统及其自动化学报, 2019, 31(12): 137-143.

[45]Zhong Q C, Konstantopoulos G C, Ren B, et al. Improved synchronverters with bounded frequency and voltage for smart grid integration[J]. IEEE Transactions on Smart Grid, 2016, 9(2): 786-796.

[46]Lee C T, Jiang R P, Cheng P T. A grid synchronization method for droop-controlled distributed energy resource converters[J]. IEEE Transactions on Industry Applications, 2013, 49(2): 954-962.

[47]张治俊, 李辉, 张煦, 等. 基于单/双同步坐标系的软件锁相环建模和仿真[J]. 电力系统保护与控制, 2011, 39(11): 138-144.

[48]温华生. 基于CDSC的APF锁相环设计[J]. 电子世界, 2016, (06): 147-149.

[49]杨雅菲. 弱电网下考虑SOGI-PLL影响的并网逆变器控制策略研究[D]. 保定: 华北电力大学, 2021.

[50]Wang S, Etemadi A, Doroslovački M. Adaptive cascaded delayed signal cancellation PLL for three-phase grid under unbalanced and distorted condition[J]. Electric Power Systems Research, 2020, 180: 106165.

[51]王庭康, 龚杰. 一种基于二阶广义积分器和延时信号消除算子的改进型锁相环研究[J]. 分布式能源, 2020, 5(5): 22-29.

[52]Chakoury H K, Suan F T K, Lukose J. Single-phase phase locked loop with DC offset and noise rejection capability for photovoltaic inverters in distributed generation[C]//AIP Conference Proceedings. AIP Publishing, 2019, 2157(1).

[53]陈德志, 白保东, 王鑫博, 等. 逆变器母线电容及直流电抗器参数计算[J]. 电工技术学报, 2013, 28(S2): 285-291.

[54]Ye T, Dai N Y, Lam C S, et al. Analysis, design, and implementation of a quasi-proportional-resonant controller for a multifunctional capacitive-coupling grid-connected inverter[J]. IEEE Transactions on Industry Applications, 2016, 52(5): 4269-4280.