【作者】 程改红；

【导师】 徐政；

【作者基本信息】 浙江大学 ， 电力系统及其自动化， 2006， 博士

【摘要】 近年来，随着电网互联和远距离交直流输电技术的发展，电力系统的规模日益扩大，网络结构更趋复杂，电力市场的发展和经济调度的日趋广泛又使电力系统的运行越来越接近于稳定运行的极限，从而导致大电网的安全运行存在更大的隐患，不可能绝对避免因各种原因造成的事故扩大和大面积停电事故等。为确保系统在停电事故后能快速、安全地恢复供电，本文着重对系统恢复过程中的电压和频率控制问题进行了研究。主要内容包括：(1)对电力系统恢复过程的仿真问题进行了分析，建立了发电机、负荷等元件在恢复过程中的仿真模型，对输电线路和变压器的恢复、厂用负荷的起动以及发电机的带负荷过程等的仿真方法进行了研究，以对系统恢复过程中的稳态、暂态和动态行为等进行全面的分析，为制订系统恢复计划和实际的恢复控制操作提供指导。(2)针对系统恢复初期由于空载和轻载线路的恢复所引起的工频过电压问题，提出了基于灵敏度分析的方法快速确定有效控制变量及其调节量，并通过引入有效因子的概念，综合考虑设备本身和系统运行条件的约束及其当前状态的调节裕度，确保了以最少的控制操作对过电压进行校正的同时，不会产生新的电压越限。(3)对系统恢复初期由变压器等非线性设备的恢复引起的谐波谐振过电压问题进行了分析，通过控制变压器励磁涌流和改善系统频率响应特性等实现对谐波谐振过电压的控制。通过灵敏度分析确定能最有效改善系统频率响应特性的负荷位置，实现以最少的负荷投入量和系统操作数目对谐波谐振过电压进行有效控制，并在灵敏度中引入权值反映变压器励磁涌流各次谐波分量的影响，以更精确地反映谐波谐振过电压对系统负荷的灵敏度。同时，采用信号能量的概念对电压波形的变化趋势进行判断，实现以最短时间的时域仿真对谐波谐振过电压的大小进行快速估计和有效控制。(4)建立了考虑冷负荷特性的最优负荷恢复模型，其中考虑了系统的频率、电压和发电机有功出力等动态约束条件，以确保在恢复尽可能多负荷的同时，使系统的运行频率和网络电压等维持在合理的允许范围内。利用PSS／E软件提供的二次开发语言IPLAN，引入适用于工程优化问题的粒子群优化算法对所建的最优负荷恢复问题进行求解，并采用罚函数法对动态约束条件进行处理，以快速求得在满足系统安全稳定约束条件下可恢复的最大负荷量及负荷位置。(5)对基于电压源换流器(VSC)的直流输电系统在电力系统恢复中的应用进行了研究，提出通过新型直流输电技术(VSC-HVDC)实现相邻系统或黑起动机组对停电系统中被起动电厂的厂用负荷进行恢复供电。在对dq0坐标系下VSC的暂态数学模型进行分析的基础上，建立了用于系统恢复过程中厂用电动机负荷起动的VSC-HVDC仿真模型，对VSC-HVDC两端系统的控制器分别进行了设计，并对给水泵等大型异步电动机负荷的起动过程进行了仿真验证，结果表明VSC-HVDC能够为异步电动机的起动提供有效的无功功率支持，并确保了电动机起动过程中的厂用母线电压能维持在合理的水平，以实现厂用电动机负荷的顺利起动。(6)对南方电网因直流故障切机后的恢复策略进行了研究，提出通过降低其它运行机组出力的控制策略，使被切机组能在短时间内投入，达到在保持系统稳定的前提下使被切机组快速恢复的目标。利用PSS／E软件的用户自定义计算功能对发电机的出力调节过程进行建模，对南方电网发生贵广直流双极闭锁故障后被切机组并网后的带负荷过程进行仿真，结果表明，在被切机组的带负荷过程中，适当降低其它运行机组的出力，可以保持送端系统输出功率基本不变，不会对系统的稳定性造成影响，从而证明了该方法的可行性和有效性。更多还原

【Abstract】 In recent years, power systems have increased in both size and complexity due to the rapid growth of interconnections and widespread application of long distance HVDC transmission. Meanwhile, with development of power market and extensive operation of economic dispatch, power systems tend to be operated closer and closer to their stability limits. These factors have issued big challenges to system secure operation so that bulk power systems are more vulnerable to potential disturbances and even blackouts. In order to minimize adverse impact on the public, the system needs to be restored to normal operation as quickly and reliably as possible in case of a complete or partial blackout. This dissertation mainly deals with the voltage and frequency control problems during power system restoration process. The main work is organized as follows:Modeling and simulation issues pertaining to system restoration process are addressed, which covers various stages of restoration including the static, transient and dynamic behavior of power system during restoration. Models for cold load pickup and generation ramping process of generators are developed. Simulation studies are carried out for energization of transmission lines and transformers, start-up of auxiliary motors and generation ramping process, which are indispensable for development of power system restoration plan and real system restoration.A sensitivity analysis based method is presented for control of power frequency overvoltages caused by energization of lightly loaded transmissions lines during early restoration stages. The efficient control variables are identified by means of sensitivity analysis to ensure that the minimum shifts are needed for control of overvoltages. Efficiency Coefficient (EC) is defined to take into account both voltage sensitivity to control variables and other factors including equipment limitations, system operation constraints and current adjusting margins as well. The control variables selected according to their ECs guarantee that no new voltage violations will be generated during the control process.The harmonic overvoltages originating from switching of the nonlinear devices such as transformers are of great concern during early stages of power system restoration. Based on detailed analysis on the cause of harmonic overvoltages, control of harmonic overvoltages is accomplished through control of the transformer inrush current and improvement of the system frequency response characteristics. Sensitivity analysis is performed to find the most efficient loads for improvement of the system frequency response characteristics so that the harmonic overvoltages can be controlled with the minimum loads and operations. Weighting factors are introduced to take into consideration the harmonic characteristics of the transformer inrush current so as to get sensitivity of the harmonic overvoltages to system load with enough accuracy. In order to reduce the large amount of simulation time, the energy of the signal is applied to predict the tendency of the voltage waveform and an algorithm is developed to terminate the electromagnetic transient simulation in a minimum amount of time, which enables fast assessment and efficient control of the harmonic overvoltages.The optimal load restoration model considering cold load pickup is formulated as an optimization problem subjected to system operation constraints including frequency, voltage and generation output, so that the maximum load may be picked up while maintaining reasonable frequency and voltage profiles. With IPLAN programming language provided by PSS/E, particle swarm optimization algorithm is applied to solve the proposed optimization problem. In addition, penalty is introduced to handle system operation constraints. The proposed method is able to determine the load positions and amounts that can be picked up without disturbing system security and stability.Application of voltage source converter (VSC) based HVDC transmission during power system restoration is investigated. VSC based HVDC (VSC-HVDC) technology is proposed to supply the auxiliary motors of the steam plant that is to be hot restarted by the adjacent system or black-start generator. Based on the transient model of VSC in dq0 reference frame, a simulation model of VSC-HVDC system for start-up of the auxiliary motors is developed and different control strategies are adopted for controllers at rectifier and inverter sides respectively. Simulation is performed to verify the effectiveness of the proposed VSC-HVDC scheme for start-up of large induction motors such as boiler feed pump and induced draft fan motors. The results show that VSC-HVDC is able to provide effective reactive power support for start-up of induction motors and voltage drop at the auxiliary bus can maintain reasonable profiles during start-up process of induction motors as well, which are indispensable for successful start-up of the auxiliary motors.A restoration strategy is proposed for China Southern Power Grid (CSPG) when some generating units have to be tripped following severe DC system contingencies. In case the tripped units go through a shutdown and cold start cycle for long duration, this dissertation presents a control strategy that power generation of some running units should be reduced during this process to permit the tripped units to be resynchronized to the system without changing the power level at the sending end, which enables the tripped units to be restored to load rapidly without disturbing system stability. With user models developed in PSS/E, simulations are performed on CSPG to investigate the system behavior during reloading process of those thermal units which have been tripped following DC block fault. The results show that power generation at the sending end can be maintained at a reasonable steady level when output of some running units are appropriately reduced during the reloading process of the thermal units, thus having little impact on the system stability, which demonstrates the feasibility and effectiveness of the proposed scheme.更多还原