电网不平衡条件下同步逆变器的并网控制

发布时间：2018-11-03 07:08

【摘要】：可再生能源在逐年的发展,其渗透率不断攀升,多数分布式可再生能源的利用是借助DC/AC变换器(逆变器)向电网输能,在电网正常工况下保证其良好的动态响应及稳定性。同步逆变器模拟了同步发电机的基本原理,设计了虚拟的转动惯量,在不改变电网运行方式下,使分布式能源能友好并网,保证了以逆变器为并网接口的分布式能源系统的可靠性和稳定性。当电网电压不平衡时,同步逆变器并网输出负序电流导致线路三相电流严重不平衡,从而制约了其在分布式电源中的实际应用。因此,在保证逆变器并网输出功率的同时,减少系统负序电流是同步逆变器亟待解决的问题。研究的具体工作如下:(1)虚拟同步电机在分布式能源领域的发展状况以及同步逆变器控制研究现状概述。对同步逆变器与电网同步原理和过程、并网后功率的调节进行了本质分析,从而基于Simulink仿真平台,根据同步逆变器的基本参数对其在线电压380V电网电压以及不同频率的并网条件下的可行性做了验证。提出本文的研究重点:电网不平衡条件下同步逆变器的并网控制。(2)基于二阶广义积分器分量提取的控制改进。针对分量提取控制时出现的频率波动问题,采用改进的DSOGI-PLL方案对不平衡电压提取平衡分量。基于Simulink仿真平台,进行了在电压幅值、相位、电压幅值/相位分别不平衡条件下仿真验证,确定正负序分离方案的可行性。(3)同步逆变器的正/负序控制器设计。由于传统的同步逆变器数学模型在电网不平衡条件下存在的不足,而正负序控制算法具有解耦性,且独立性和适应性较好。当电网不平衡时,在不改变逆变器正常运行机制的基础上,阐述了逆变器在正负序控制器的联合控制下的同步并网过程、功率的传递以及对系统负序电流的抑制策略。并在两个控制器的联合作用下,首先保证逆变器的友好并网,然后分别用正序控制器和负序控制器来保持逆变器向电网传送功率和对系统产生负序电流的抑制。基于Simulink仿真平台,在不同情况的不平衡条件下进行仿真实验。(4)150W样机的实验平台搭建以及实验验证。利用MATLAB软件对文中提出的控制算法进行了仿真验证,同时以DSP控制实物逆变器,设计了150W的小功率同步逆变器并网系统,完成同步逆变器在电网不平衡条件下的并网。利用该样机对本文所提的控制策略进行了实验验证。
[Abstract]:With the development of renewable energy year by year, the permeability of renewable energy is increasing. Most of the distributed renewable energy sources are used to transmit energy to the power grid by means of DC/AC converters (inverters) to ensure its good dynamic response and stability under normal conditions. The synchronous inverter simulates the basic principle of synchronous generator and designs the virtual moment of inertia. The reliability and stability of distributed energy system with inverter as grid-connected interface are guaranteed. When the voltage of the power network is unbalanced, the negative sequence current output from the synchronous inverter leads to the serious imbalance of the three-phase current of the line, which restricts its practical application in the distributed generation. Therefore, while ensuring the output power of the inverter, reducing the negative sequence current of the system is an urgent problem for synchronous inverter. The research work is as follows: (1) the development of virtual synchronous motor in the field of distributed energy and the research status of synchronous inverter control are summarized. In this paper, the principle and process of synchronous inverter and power grid synchronization, and the power regulation after grid connection are analyzed in essence, which is based on Simulink simulation platform. According to the basic parameters of the synchronous inverter, the feasibility of the synchronous inverter is verified under the condition of the line voltage of 380 V grid voltage and the connection of different frequencies. The emphasis of this paper is the grid-connected control of synchronous inverter under unbalanced power system. (2) the control improvement based on the second order generalized integrator component extraction. In order to solve the problem of frequency fluctuation in component extraction control, an improved DSOGI-PLL scheme is used to extract equilibrium components from unbalanced voltages. Based on the Simulink simulation platform, the simulation is carried out under the condition of voltage amplitude, phase, voltage amplitude / phase unbalance, to determine the feasibility of the scheme of positive and negative sequence separation. (3) the design of positive / negative sequence controller for synchronous inverter. Due to the shortcomings of the traditional mathematical model of synchronous inverter under the condition of unbalanced power network, the positive and negative sequence control algorithm is decoupled and has good independence and adaptability. When the power network is unbalanced, on the basis of not changing the normal operation mechanism of the inverter, the synchronous grid-connected process of the inverter under the combined control of the positive and negative sequence controller, the transmission of power and the strategy of restraining the negative sequence current of the system are described. Under the combined action of the two controllers, the inverter can be connected in a friendly way, and then the positive sequence controller and the negative sequence controller are used to maintain the transmission power and restrain the negative sequence current of the inverter to the power grid. Based on the Simulink simulation platform, the simulation experiments are carried out under different unbalanced conditions. (4) the experimental platform of the 150W prototype and the experimental verification. The proposed control algorithm is simulated by using MATLAB software. At the same time, a 150W low power synchronous inverter grid-connected system is designed by using DSP to control the physical inverter. The synchronous inverter is grid-connected under the condition of unbalanced power grid. The proposed control strategy is verified by the prototype.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM464

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