多端柔性直流系统运行及控制参数优化研究

发布时间：2018-10-16 13:16

【摘要】：柔性直流输电(Voltage Source Converter based High Voltage Direct Current,VSC-HVDC)是一种以电压源换流器和脉宽调制等技术为基础的新型直流输电技术。与传统高压直流输电相比,VSC-HVDC采用了全控型器件,实现了有功功率和无功功率的解耦,能够向弱交流系统甚至无源网络供电,不会发生换相失败,很适合应用于海上风电并网、分布式能源接入、交流系统互联、构造多端柔性直流(Voltage Source Converter based Multi-terminal Direct Current,VSC-MTDC)系统等领域,在国内外引起了广泛的关注。本文对多端柔性直流系统的电压协同控制策略、控制参数优化和优化运行进行了如下研究:在dq0旋转坐标系下建立了电压源换流器的数学模型,推导了VSC-HVDC的双闭环控制结构:外环根据所连接网络的不同选用不同的控制策略,内环采用前馈补偿的结构实现有功功率和无功功率的解耦。在VSC-HVDC控制策略的基础上,研究了VSC-MTDC适用的直流电压主从控制、直流电压偏差控制和直流电压斜率控制这三种多端系统的控制策略,对三种控制策略进行了对比,并设计了三种策略的控制器结构。提出了一种确定VSC-MTDC系统控制参数的方法,可以保证控制器对系统稳态和过渡过程进行准确、稳定的控制。首先以控制器外环控制量的稳态偏差最小为目标,确定各控制器控制参数的初始值,保证对系统稳态运行情况的控制能力;再根据系统过渡过程中控制特性区域的不同划分时间区间,构造了VSC-MTDC控制特性的评价指标,并以此为目标函数采用单纯型算法对控制参数的初始值进行了进一步的优化,最终得到控制参数的最优值。仿真验证表明本文提出的控制参数整定方法可以改善系统的控制精度和动态响应。提出了一种适用于VSC-MTDC的分层优化控制体系,可以在保证系统稳定运行的同时对系统运行的网损进行优化。其中控制体系的下层采用直流电压斜率控制策略,是控制体系的基础;上层通过采集各换流站的出力数据,以优化系统运行时的网损为目标,考虑系统功率平衡等约束条件,计算出系统的最优潮流,进而给下层的斜率控制器下发新的参考值,实现系统的最优网损运行。
[Abstract]:Flexible DC transmission (Voltage Source Converter based High Voltage Direct Current,VSC-HVDC) is a new type of HVDC transmission technology based on voltage source converter and pulse width modulation. Compared with traditional HVDC transmission, VSC-HVDC adopts full control device, realizes decoupling of active power and reactive power, and can supply power to weak AC system or even passive network without commutation failure, so it is suitable for offshore wind power grid connection. Distributed energy access, interconnection of AC systems and construction of multi-terminal flexible DC (Voltage Source Converter based Multi-terminal Direct Current,VSC-MTDC systems have attracted wide attention at home and abroad. In this paper, the voltage cooperative control strategy, control parameter optimization and optimal operation of multi-terminal flexible DC system are studied as follows: the mathematical model of voltage source converter is established in dq0 rotating coordinate system. The double closed loop control structure of VSC-HVDC is deduced. The outer loop adopts feedforward compensation structure to decouple the active and reactive power according to the different control strategies of the connected networks. On the basis of VSC-HVDC control strategy, this paper studies the three control strategies of DC voltage master-slave control, DC voltage deviation control and DC voltage slope control, which are suitable for VSC-MTDC, and compares the three control strategies. The controller structure of three strategies is designed. This paper presents a method to determine the control parameters of VSC-MTDC system, which can ensure the accurate and stable control of the steady and transient process of the system by the controller. Firstly, taking the minimum steady-state deviation of the controller's outer loop control quantity as the goal, the initial value of the controller's control parameters is determined to ensure the control ability of the system's steady-state operation. Then according to the different time interval of the control characteristic region in the transition process of the system, the evaluation index of the VSC-MTDC control characteristic is constructed, and the initial value of the control parameter is further optimized by using the simplex algorithm as the objective function. Finally, the optimal value of the control parameters is obtained. Simulation results show that the proposed method can improve the control accuracy and dynamic response of the system. In this paper, a hierarchical optimal control system for VSC-MTDC is proposed, which can optimize the network loss of the system while ensuring the stable operation of the system. The lower layer of the control system adopts the DC voltage slope control strategy, which is the basis of the control system, and the upper layer takes the power balance of the system into account by collecting the output data of each converter station, aiming at optimizing the network loss while the system is running. The optimal power flow of the system is calculated, and a new reference value is given to the lower slope controller to realize the optimal network loss operation of the system.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1

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