基于虚拟同步发电机的VSC变换器控制策略研究

发布时间：2018-03-05 12:58

本文选题：分布式发电　切入点：微网　出处：《东北电力大学》2016年硕士论文　论文类型：学位论文

【摘要】：为了解决日益严重的环境污染问题和能源危机,基于清洁可再生能源的分布式发电技术正迅猛发展。微电网作为分布式电源并网的重要形式之一,是电网和可再生能源之间的桥梁,可有效降低分布式电源的功率波动对大电网的冲击,提高系统稳定性。然而,与传统的同步发电机相比,采取传统控制策略的微网逆变器几乎没有惯性,更无法为电网提供必要的电压和频率支撑。因此,通过采取适当的控制策略来改善分布式电源的调频调压特性,对未来大规模新能源微电网具有重大的意义。如果能使并网逆变器具有与类似与同步发电机的外特性,就能改善分布电源并网特性,提高系统稳定性。为了使逆变器模拟传统同步发电机的动态特性,本文研究了一种基于synchronverters的改进型虚拟同步发电机控制策略,在原有基础上增加了底层电压电流控制,用来保证波形质量以及限制短路电流,同时增加了二次调频功能,使得频率能恢复到额定值。与传统的微网逆变器控制方法相比,虚拟同步发电机控制可以实现并网/孤岛模式无缝切换,提供必要的电压与频率支持,增加系统转动惯量,自动与电网保持同步,且不需要锁相环。虚拟同步发电机控制策略可以分成上层的功率控制与底层的电压电流双环控制两部分。其中底层电压电流环采用的是电压矢量定向控制,文中首先建立VSC在d-q旋转坐标系下的数学模型,在此基础上完成电压电流控制器参数设计。根据同步发电机的电磁暂态模型设计了功率外环,控制有功功率与无功功率。通过改变有功功率的设定值实现二次调频功能,从而消除一次调频产生的频率偏差。重点研究了基于小信号分析的系统数学模型建立方法以及利用频率响应法设计控制器参数,深入讨论了线路阻抗对系统稳定性的影响,并利用虚拟阻抗模拟同步阻抗,使该控制策略适用与不同电压等级电网。虚拟同步发电机在并网前有一个预同步过程。文中给出了两种预同步方法,一种是虚拟电枢电流法,另一种是三相锁相环法,可避免在并网时由于逆变器电压与电网电压在幅值及相位上的偏差而产生的过电流。最后,通过不同微网运行状态仿真实验验证了上述虚拟同步发电机控制策略及其控制器参数设计方法的有效性。
[Abstract]:In order to solve the increasingly serious environmental pollution and energy crisis, distributed generation technology based on clean and renewable energy is developing rapidly. It is a bridge between power grid and renewable energy, which can effectively reduce the impact of power fluctuation of distributed generation on large power grid and improve system stability. However, compared with the traditional synchronous generator, The microgrid inverter with traditional control strategy has almost no inertia, and can not provide the necessary voltage and frequency support for the power network. Therefore, by adopting appropriate control strategy, the frequency modulation and voltage regulation characteristics of distributed power generation can be improved. It is of great significance for the future large-scale new energy microgrid. If the grid-connected inverter has the external characteristics of similar and synchronous generators, it can improve the grid-connected characteristics of the distributed power supply. In order to make the inverter simulate the dynamic characteristics of traditional synchronous generator, an improved control strategy of virtual synchronous generator based on synchronverters is studied in this paper. It is used to guarantee the waveform quality and limit the short-circuit current, at the same time, the secondary frequency modulation function is added, so that the frequency can be restored to the rated value. Compared with the traditional control method of micro-grid inverter, Virtual synchronous generator control can realize seamless switching of grid-connected / islanding mode, provide necessary voltage and frequency support, increase the moment of inertia of the system, and automatically keep synchronization with the power grid. The control strategy of virtual synchronous generator can be divided into two parts: upper layer power control and bottom voltage current double loop control. In this paper, the mathematical model of VSC in d-q rotating coordinate system is established firstly, and the parameters of voltage and current controller are designed on this basis. The power outer loop is designed according to the electromagnetic transient model of synchronous generator. Control active power and reactive power. By changing the set value of active power to achieve the secondary frequency modulation function, In order to eliminate the frequency deviation caused by primary frequency modulation, the mathematical model building method based on small signal analysis and the design of controller parameters based on frequency response method are studied, and the influence of line impedance on the stability of the system is discussed. Using the virtual impedance to simulate the synchronous impedance, the control strategy is suitable for different voltage level power networks. There is a pre-synchronization process before the virtual synchronous generator is connected to the grid. In this paper, two presynchronization methods, one is the virtual armature current method, are presented. The other is the three-phase phase-locked loop method, which can avoid the overcurrent caused by the deviation between the inverter voltage and the grid voltage in amplitude and phase when connected to the grid. Finally, The control strategy of the virtual synchronous generator and the design method of the controller parameters are verified by the simulation experiments of different microgrid operation states.
【学位授予单位】：东北电力大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TM31;TM464

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