交直流混合微电网接口变换器控制研究

发布时间：2018-07-25 17:04

【摘要】：为了更加高效可靠地将交直流混合微电网的交直流母线互联,并且协调分配功率,接口变换器(Interface Converter,IC)常可采用并联运行的方式。其中,并联下垂特性控制策略的优点包括:即插即用,为微网提供频率和电压支撑功能,可实现无通信时并联运行的各IC输出功率自动分配,并且在并离网模式下通用。基于这些优点,下垂控制广泛应用于无互联线的IC并联系统中。此外,基于虚拟同步发电机(Virtual Synchronous Generator,VSG)技术的IC控制策略在实现下垂特性控制的同时,能够模拟同步发电机的运行方式且为系统提供阻尼和惯性,成为一个研究热点。本文对交直流混合微电网接口变换器的倒下垂控制策略和虚拟同步机控制策略分别进行了深入研究。首先,根据交直流混合微电网中接口变换器的运行特点,模拟电力系统中同步发电机三次调频的运行方式,本文提出了一种改进的倒下垂控制策略。文中仔细分析了改进的倒下垂控制原理和相应的微电网三次调节方法。通过在倒下垂控制环中加入积分环节进行二次调节,实现交流母线电压和频率的无差自动调节;通过改变倒下垂控制环中有功和无功功率基准值来响应上层控制系统的功率调度,也即进行三次调节,实现微电网的功率优化分配。本文通过在DigSILENT/PowerFactory中搭建的微网模型进行仿真分析,验证了所提控制策略的准确性和有效性。其次,相比于倒下垂控制策略,虚拟同步机技术的应用使得IC不仅能够模拟三次调频的运行方式,而且能够模拟同步机的内部机制。本文针对VSG技术及其在交直流混合微电网IC并联系统中的应用进行研究,提出了一种VSG等效模型与控制策略。首先根据低压交直流混合微电网的结构特点,建立了直流子网与阻感性馈线组合等效同步发电机的VSG模型,并据此在VSG控制中加入虚拟电阻补偿和虚拟坐标变换。然后,通过在VSG功率环中加入电压和功率基准修正量来响应微电网上层控制系统的调度,使得VSG能够模拟同步发电机三次调频的运行方式;通过虚拟阻抗法解决了复杂供电网络下VSG控制策略难以适用的问题。最后,通过仿真分析验证了所提VSG控制策略的准确性和有效性,并在10kVA的储能接口变换器实验平台上进行了 VSG基本功能的实验验证。最后,关于VSG的预同步并网方式,基于锁相环(Phase Locked Loop,PLL)的方法由于所采用的PI调节器会引起多VSG系统的动态环流和功率振荡,难以满足预同步过程的快速性和稳定性要求。本文提出一种基于虚拟功率环和虚拟功率阶跃给定的开环相位预同步方法,该方法无需锁相环且VSG在预同步过程中具有良好的惯性和阻尼性能。首先对增加的VSG虚拟功率环的功能和虚拟功率阶跃给定的开环并网方式进行分析,指出预同步过程中的相角差值计算公式、预同步时间计算方法。其次,采用小信号模型对多VSG预同步过程中的有功环流问题进行理论分析,通过双功率环参数的分别整定来减小动态环流。最后,通过仿真和实验对比了不同预同步方法的预同步过程,结果表明本文所提方法在保持调整精度的同时调节过程平滑稳定,适用于多VSG的预同步控制。
[Abstract]:In order to connect the AC and DC bus of AC and DC hybrid microgrids more efficiently and reliably, and to coordinate the power distribution, the Interface Converter (IC) can often be operated in parallel. The advantages of the parallel droop characteristic control strategy include: plug and play, provide the frequency and voltage support for the micronetwork. The IC output power of the parallel operation is automatically allocated and used in the network mode. Based on these advantages, the droop control is widely used in the IC parallel system without interconnected lines. In addition, the IC control strategy based on the Virtual Synchronous Generator (VSG) technology is able to control the droop characteristics and can be used to control the droop characteristics. It is a research hotspot to simulate the operation mode of synchronous generator and provide damping and inertia for the system. In this paper, the inverted droop control strategy of AC DC hybrid microgrid interface converter and the control strategy of virtual synchronizer are studied. First, according to the operation characteristics of the interface converter in the AC and DC hybrid microgrid, In this paper, an improved inverted droop control strategy is proposed in this paper. In this paper, an improved inverted droop control strategy is proposed. In this paper, the improved inverted droop control principle and the corresponding three adjustment methods of the microgrid are carefully analyzed. The AC bus voltage is realized by adding the integral loop joint in the inverted droop control loop to achieve the AC bus voltage two times. In response to the power scheduling of the upper control system by changing the active and reactive power datum in the inverted droop control loop, the power dispatch of the upper control system can be adjusted to achieve the optimal power distribution of the microgrid. In this paper, the simulation analysis of the microgrid model built in DigSILENT/PowerFactory has been carried out to verify the control of the proposed control. The accuracy and effectiveness of the strategy. Secondly, compared to the inverted droop control strategy, the application of the virtual synchronizer technology makes IC not only can simulate the operation mode of three frequency modulation, but also can simulate the internal mechanism of the synchronous machine. This paper studies the VSG technology and its application in the IC parallel system of AC and DC hybrid microgrid. A VSG equivalent model and control strategy. First, based on the structure characteristics of the low voltage AC / DC hybrid microgrid, the VSG model of the combined equivalent synchronous generator of the DC subnet and the resistive feeder is established, and the virtual resistance compensation and the virtual coordinate transformation are added to the VSG control. Then, the voltage and power are added to the VSG power loop. In response to the scheduling of the microelectric network layer control system, the VSG can simulate the operation mode of the three frequency modulation of the synchronous generator. Through the virtual impedance method, the problem that the VSG control strategy is difficult to apply under the complex power supply network is solved. Finally, the accuracy and effectiveness of the proposed VSG control strategy are verified by the simulation analysis. The experimental verification of the basic functions of VSG is carried out on the experimental platform of 10kVA's energy storage interface converter. Finally, the method of pre synchronization and grid connection of VSG, based on the Phase Locked Loop (PLL) method, will cause the dynamic circulation and the power rate oscillation of the multiple VSG system because of the PI regulator adopted, so it is difficult to meet the speed and stability of the pre synchronization process. In this paper, an open loop phase pre synchronization method based on a virtual power loop and a virtual power step is proposed. This method does not require a phase-locked loop and the VSG has good inertia and damping performance during the pre synchronization process. First, the function of the added VSG virtual power loop and the given open loop parallel connection mode of the virtual power step are given. The calculation formula of the difference of phase angle in the pre synchronization process and the method of calculating the pre synchronization time are pointed out. Secondly, a small signal model is used to analyze the active circulation problem in the process of multi VSG pre synchronization, and the dynamic circulation is reduced by the separation of the parameters of the double power ring. The results show that the proposed method can maintain the adjustment accuracy while adjusting the process smoothly and stably, and is suitable for multi VSG presynchronous control.
【学位授予单位】：北方工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM727;TM46

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