交流系统对直流输电系统运行的影响相关问题研究

发布时间：2019-05-10 03:46

【摘要】：随着电网的不断发展，我国逐渐形成了一个十分复杂的交直流混联系统，交直流系统的相互影响成为电网安全稳定运行关注的重点之一，其中，交流系统故障引起换流母线电压跌落及换相电压过零点移动，则可能导致换流器关断角过小而换相失败，连续换相失败会导致直流闭锁，严重影响系统稳定运行，需要研究有效准确的换相失败判别方法；另一方面，直流系统移相触发脉冲需与系统保持同步，因此触发环节中都会包含脉冲修正环节，可以根据系统状态的变化来调整触发脉冲。但若系统频率变化，在调整过程中触发脉冲的异常是否会引起直流系统运行状态的变化，也需要开展研究。本论文研究交流系统电压和频率变化对直流系统换相过程和移相触发环节的影响，主要完成如下方面的工作：（1）阐述了直流系统换相过程和触发环节的基本原理，着重介绍了换相失败的影响因素及触发环节中两种触发控制环节对频率的敏感度，，建立了直流双极输电系统详细电磁暂态仿真模型；（2）研究判断直流换相失败的最小电压降判断法，对传统对称情况下的最小电压降计算方法加以改进，提出了一种计及直流电流变化和故障时刻影响的最小电压降计算方法；该方法也可以用于计算换相失败的概率曲线；（3）在此基础上提出了不对称情况下的最小电压降计算方法，算例仿真结果表明本文提出的最小电压降计算方法较传统方法有更高的精度，验证了其有效性。（4）研究了直流输电系统MACH2的触发原理，分析了频率对换相电压过零点的影响。研究表明，由于频率变化引起锁相环对换相电压过零点的判断失误，直流系统触发脉冲将出现短时异常；直流系统的波动幅度主要受触发延迟角幅值限制环节的影响，在整流侧频率升高或逆变侧频率降低时直流系统运行状态的变化较大。
[Abstract]:With the continuous development of power grid, a very complex AC / DC hybrid system has been gradually formed in our country. The interaction of AC and DC system has become one of the key points of attention in the safe and stable operation of power grid. The voltage drop of converter bus and zero-crossing shift of commutation voltage caused by AC system fault may lead to converter turn-off angle too small and commutation failure, and continuous commutation failure will lead to DC locking, which will seriously affect the stable operation of the system. It is necessary to study an effective and accurate method for judging the failure of commutation. On the other hand, the phase-shifting trigger pulse of DC system needs to be synchronized with the system, so the trigger pulse can be adjusted according to the change of system state. However, if the frequency of the system changes, whether the abnormal trigger pulse in the process of adjustment will cause the change of the running state of the DC system, it is also necessary to carry out research. In this paper, the influence of voltage and frequency change of AC system on phase change process and phase shift trigger link of DC system is studied. The main work is as follows: (1) the basic principle of phase change process and trigger link of DC system is expounded. The influencing factors of commutation failure and the sensitivity of two trigger control links to frequency are introduced in detail, and the detailed electromagnetic transient simulation model of HVDC transmission system is established. (2) the minimum voltage drop judgment method for judging DC commutation failure is studied, and the traditional minimum voltage drop calculation method under symmetrical condition is improved. A method for calculating the minimum voltage drop considering the change of DC current and the influence of fault time is proposed. This method can also be used to calculate the probability curve of commutation failure. (3) on this basis, a minimum voltage drop calculation method under asymmetric condition is proposed. The simulation results show that the minimum voltage drop calculation method proposed in this paper has higher accuracy than the traditional method, and its effectiveness is verified. (4) the trigger principle of MACH2 in HVDC system is studied, and the influence of frequency on zero crossing point of commutation voltage is analyzed. The results show that the trigger pulse of DC system will be abnormal for a short time because of the error of judging the zero crossing point of phase-locked loop to phase-locked voltage due to the change of frequency. The fluctuation amplitude of DC system is mainly affected by the limiting link of trigger delay angle amplitude. When the rectifier side frequency increases or the inverter side frequency decreases, the operation state of DC system changes greatly.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM721.1

【相似文献】