【作者】 陈诚；

【导师】 孙宇新；

【作者基本信息】 江苏大学 ， 电气工程， 2020， 硕士

【摘要】 随着电力电子技术与可再生能源发电的飞速发展,以分布式结构为主的微电网技术改变了传统电力系统的终端用电模式,促进了源-网-荷系统间的友好互动与相互协调。由于微网逆变器数量的不断增加与其自身容量的限制,加之新能源发电的发展需求,对无互连线控制的逆变器并联技术的智能化建设提出了更高要求。作为一种用逆变器模拟同步发电机(Synchronous Generator,SG)外特性的分布式无互连线微电网控制算法,虚拟同步发电机(Virtual Synchronous Generator,VSG)技术有助于提供微电网足够的惯性和阻尼支撑,激励各并联逆变器主动参与电网的暂态与动态调节。但逆变器并联单元的运行容易受到来自离网期间预同步、负载突变和并网时的电压跟随等方面影响,基于此控制要求,本文主要针对孤岛下VSG并联算法的二次调频问题、转动惯量自适应控制问题和并联单元离并网切换问题展开深入研究,主要内容如下:首先,根据传统VSG算法的基本原理,建立VSG并联系统的小信号模型。借鉴电力系统的二次调频过程,提出VSG并联运行的二次调频控制新方案。所提方案解决了微网逆变器并联瞬间的电压跌落和电流冲击问题。其次,根据并联系统小信号模型解出系统特征根,并由特征根轨迹分析推导出转动惯量自适应控制策略,对涉及参数进行优化整定。结合等效SG的基本原理,提出VSG并联运行的惯量匹配原则。所提方案在确保功率均分的同时,还能有效抑制并联系统的功频振荡问题。然后,根据准同期控制的基本原理与条件、详细推导出基于级联积分的锁相环和对双闭环控制参数的优化,提出VSG并联系统的离并网柔性切换技术。该技术解决了切换过程中并联系统内部的功率耦合现象,并有效解决了并网瞬间的暂态不稳定因素,实现了电网故障期间对终端用户的不间断供电。最后,搭建基于VSG算法的微网逆变器并联系统的实验平台,并对有关VSG算法进行了实验检测评估,初步验证了VSG算法的有效性。更多还原

【Abstract】 With the rapid development of power electronics technology and renewable energy generation,micro-grid technology based on distributed structure has changed the terminal power consumption mode in traditional power system,and promoted the friendly interaction and coordination among source-grid-load system.Due to the increasing quantity of micro-grid inverters and its own capacity limit,along with the developing needs of new energy generation,higher requirements have been placed on the intelligent construction of parallel inverter technology without interconnected control.As a distributed non-interconnected micro-grid control algorithm using inverters to simulate the external characteristics of synchronous generators(SG),Virtual Synchronous Generator(VSG)technology provides sufficient inertia and damping support for micro-grid,and encourages each parallel inverter to participate in the transient and dynamic grid regulation spontaneously.However,the stability of parallel inverter unit is easily affected by pre-synchronization and sudden load changes during off-grid,and voltage following during grid connection.Based on this control requirement,this paper mainly focuses on several problem of parallel VSG algorithm,such as the secondary frequency modulation,rotor inertia adaptive control under the island,and the parallel unit mode switching.The main contents are as follows:Firstly,according to the basic principle of traditional VSG algorithm,a small signal model of parallel VSG system was established.Based on the secondary frequency adjusting process of the power system,a new secondary frequency modulation control scheme for parallel VSG operation was proposed.The proposed scheme solves the problem of voltage drop and current oscillation when micro-grid inverters connected in parallel.Secondly,the parallel system characteristic root was solved according to the small signal model,and rotor inertia adaptive control strategy was derived from the root locus analysis,and the related parameters were optimized and set.Combined with the basic principle of equivalent synchronous generators,the inertia matching principle of parallel VSG system was proposed.The proposed method can not only suppress the power oscillation in the transient connection of the VSGs to the AC bus,but also improve the frequency support.In turn,it ensures that the load power is proportionally distributed among the VSGs.Then,the flexible mode switching technology for parallel VSG system was proposed according to the basic principle and conditions of quasi-synchronous control,the phase-locked loop based on cascading integral and the optimization of the double closed-loop control parameters.The proposed scheme can effectively suppress the power frequency oscillation of the parallel system while ensuring the power is evenly divided.Finally,an experimental platform for a parallel micro-grid inverter system based on VSG algorithm was built,and the experimental detection and evaluation of the VSG algorithm were performed to verify its feasibility.更多还原