混合双馈入直流输电系统中电压源和电流源换流器相互作用规律研究

发布时间：2017-12-26 19:41

本文关键词：混合双馈入直流输电系统中电压源和电流源换流器相互作用规律研究　出处：《华北电力大学(北京)》2017年博士论文　论文类型：学位论文

【摘要】：随着基于电网换相换流器型高压直流输电(Line comuutated coverter based high voltage direct current,LCC-HVDC)在输电领域的广泛应用和基于电压源换流器的高压直流输电技术(Voltage Source Converter based HVDC,VSC-HVDC)的快速发展,含有LCC和VSC的混合多馈入直流输电系统近年来受到了广泛的关注。研究混合多馈入直流输电系统中LCC-HVDC和VSC-HVDC的相互作用规律,具有重要的理论和工程意义。混合双馈入直流输电系统作为混合多馈入直流系统的基础,其基本特性和运行规律对混合多馈入系统的研究具有重要的借鉴意义。论文围绕混合双馈入直流输电系统中VSC-HVDC和LCC-HVDC的相互影响关系,通过研究系统的稳态和暂态运行特性,从混合双馈入直流输电系统的小信号建模和稳定性分析、等值有效短路比的定量评估方法、换相失败抵御能力和故障后功率恢复特性等三方面对混合双馈入系统中LCC-HVDC和VSC-HVDC的相互作用规律开展了相关研究,并得到了一系列具有工程指导意义的结论。(1)混合双馈入直流输电系统的数学模型和控制策略为了研究混合双馈入系统中LCC-HVDC和VSC-HVDC的相互作用规律,首先分别研究了LCC-HVDC和VSC-HVDC的基本结构,推导了包括换流器交直流电压转换关系、功率传输特性等在内的数学模型,分析了两种不同类型直流输电系统的常用控制方式。然后研究了混合多馈入直流输电系统的典型拓扑结构和控制策略,基于混合双馈入直流输电系统,研究了LCC-HVDC不同的控制方式组合、VSC-HVDC不同的有功控制方式对LCC-HVDC换相失败和故障后功率恢复特性的影响规律。分析结果表明,LCC-HVDC的控制方式会在一定程度上影响其换相失败和故障后功率恢复特性,而VSC-HVDC的有功控制方式对LCC-HVDC的换相失败和故障恢复特性影响很小。最后选取了LCC-HVDC整流侧定直流电流、逆变侧定关断角,VSC-HVDC整流侧定直流电压、逆变侧定直流功率作为后续研究的基本控制策略。(2)混合双馈入直流输电系统的小信号稳定性分析小信号稳定性分析是揭示混合双馈入系统中VSC-HVDC和LCC-HVDC相互作用规律的重要研究手段。首先基于交直流侧功率守恒原理,推导了LCC和VSC换流器在dq坐标系下的线性化模型,结合换流站中PLL、控制系统、滤波器等主要基本单元的数学模型,分别推导了LCC换流站和VSC换流站的小信号模型。然后以各个换流站为子系统,研究了直流输电系统直流侧和交流侧接口模型以及不同坐标系下变量的转换模型,提出了混合双馈入直流输电系统的小信号模型建立方法。基于混合双馈入直流输电系统,将建立的小信号模型和PSCAD/EMTDC中的仿真模型进行了对比,验证了建立的小信号模型的正确性。在此基础上,基于建立的小信号模型,重点针对交流系统强度、VSC-HVDC传输功率、LCC-HVDC传输功率等条件变化时系统的小信号稳定性问题,通过特征根分析和参与因子分析方法,研究了混合双馈入系统在交流系统强度变化时的主导振荡模态及其主要参与状态变量。研究结果表明上述变化条件下LCC和VSC的状态变量在主导振荡模态中的参与度相似,说明在系统因交流系统强度减弱而失去稳定的过程中VSC-HVDC和LCC-HVDC存在显著的相互作用关系。最后,计算了上述变化条件下混合双馈入系统的有效短路比,结果表明传统有效短路比评价指标对混合双馈入直流输电系统的强度仅具有定性的指导作用,在定量评价方面,该评价指标有待进一步改进和完善。(3)基于运行阻抗的混合双馈入系统等值有效短路比定量评估方法为了将传统有效短路比指标扩展应用到混合双馈入系统的交流系统强度定量评估中,揭示LCC-HVDC和VSC-HVDC交流系统强度的相互作用规律,提出了换流器运行阻抗和基于运行阻抗的混合双馈入系统等值有效短路比(impedance based effective short circurt ratio,IESCR)的概念。首先基于建立的小信号模型,通过在系统稳态运行点施加特定小扰动的方法,获得换流器交流侧的端口特性,通过分析端口电压电流偏移量的数学关系,得到了换流器的基频等效阻抗计算方法。该等效阻抗与系统的运行点相关,故在论文中称之为换流器的运行阻抗。在既定运行状态下,将目标换流器(LCC或VSC)以外的其他换流器等效为运行阻抗,然后通过与交流网络的等值,提出了基于运行阻抗的混合双馈入直流输电系统等值有效短路比的定量评估方法,并通过仿真研究验证了该评估方法的有效性。基于IESCR,研究了混合双馈入系统中LCC-HVDC和VSC-HVDC交流系统强度的相互作用规律,研究发现,LCC-HVDC的交流系统强度受到VSC控制方式、功率等级以及VSC与LCC的电气距离等因素的影响,LCC-HVDC对VSC-HVDC的交流系统强度也有类似的作用规律。最后,结合建立的小信号模型,研究了控制器参数对直流系统能稳定传输额定功率所需的最小IESCR的影响规律,研究发现混合双馈入系统中定关断角控制器及换流器锁相环的控制参数对该最小IESCR有显著的影响,在控制参数相对较小的条件下,系统更容易在接近临近短路比的条件下传输额定有功功率。(4)混合双馈入直流输电系统中LCC-HVDC的换相失败和故障恢复特性为了研究混合双馈入系统中VSC-HVDC对LCC-HVDC换相失败和故障恢复特性的作用规律,首先研究了VSC控制方式、VSC控制器参数以及VSC和LCC间电气距离不同对LCC-HVDC的换相失败抵御能力和故障后有功功率恢复速度的影响。研究结果表明,当VSC-HVDC采用定交流电压控制方式时,相比定无功功率控制,能更好地改善LCC-HVDC的换相特性,尤其在LCC和VSC间电气距离较小、VSC定交流电压控制器响应速度较快的条件下,改善效果更加明显。然后通过研究换相过程中VSC的无功功率变化规律以及LCC的换相电压、换相电流等的变化过程,得到了VSC-HVDC改善LCC-HVDC换相特性的基本原理。同时研究发现,通过这种利用VSC在交流侧和LCC并联的方式改变LCC换相电压的方式受到VSC和LCC间电气距离、VSC控制器响应速度等因素的限制。为了充分发挥VSC电压源的特性,提出了一种LCC的新型拓扑,该拓扑采用子模块与LCC阀臂串联的方式直接改变LCC的换相电压。通过仿真研究发现,所提出的LCC新型拓扑能够进一步增强混合双馈入直流输电系统的换相失败抵御能力,同时加快其故障后功率恢复速度。
[Abstract]:Based on the power grid with commutation Converter Based HVDC (Line comuutated coverter based high voltage direct current, LCC-HVDC) is widely used in the field of power transmission and voltage source converter based HVDC (Voltage Source Converter based HVDC, VSC-HVDC) the rapid development of hybrid multi infeed HVDC system with LCC and VSC has received extensive attention in recent years. It is of great theoretical and engineering significance to study the interaction between LCC-HVDC and VSC-HVDC in hybrid multi infeed HVDC transmission system. Hybrid dual infeed HVDC transmission system is the foundation of hybrid multi infeed DC system. Its basic characteristics and operation rules are of great significance for the study of hybrid multi infeed system. The interaction of the mixture of VSC-HVDC and LCC-HVDC in dual infeed HVDC systems, through the study of the system steady-state and transient operation characteristics, from analysis, small signal modeling and stability of hybrid dual infeed HVDC system equivalent effective short circuit ratio, quantitative evaluation method of commutation failure resilience and fault recovery characteristics after power three to carry out the research on interaction of mixed LCC-HVDC and VSC-HVDC double feed system, and get a series of useful conclusions. (1) the mathematical model and control strategy of hybrid dual infeed HVDC systems in order to study on the interactions between LCC-HVDC and VSC-HVDC hybrid dual infeed system, we study the basic structure of LCC-HVDC and VSC-HVDC, the mathematical model including the converter DC voltage conversion relationship, power transmission characteristics, the analysis is deduced. The common control mode of two different types of HVDC system. And then study the typical topology structure and control strategy of hybrid multi infeed HVDC systems, hybrid dual infeed HVDC system based on the effects of different combinations of control modes of LCC-HVDC and VSC-HVDC with different active control mode of LCC-HVDC commutation failure and fault recovery characteristics of power. The analysis results show that the control mode of LCC-HVDC will affect the power recovery characteristics of commutation failure and fault after a certain extent, while the active power control mode of VSC-HVDC has little effect on the commutation failure and fault recovery characteristics of LCC-HVDC. Finally, LCC-HVDC rectifier side fixed DC current, inverter side turn off angle, VSC-HVDC rectifier side fixed DC voltage and inverter side DC power are selected as the basic control strategy for subsequent research. (2) small signal stability analysis of hybrid dual infeed HVDC transmission system. Small signal stability analysis is an important research method to reveal the interaction rule between VSC-HVDC and LCC-HVDC in hybrid dual infeed system. Based on the principle of AC and DC power conservation, the linear model of LCC and VSC converter in the DQ coordinates is deduced according to the mathematical model of PLL control system in converter station, and filters the main basic unit, the small signal model of LCC converter and VSC converter are derived respectively. Then, taking the converter stations as subsystems, the DC side and AC side interface models of HVDC transmission system and the transformation models of variables under different coordinate systems are studied, and a small signal modeling method for the hybrid dual infeed HVDC transmission system is proposed. Based on the hybrid dual infeed HVDC transmission system, the small signal model established in this paper is compared with the simulation model in PSCAD/EMTDC, and the correctness of the established small signal model is verified. On this basis, the small signal model is established based on the small signal stability problems and changes in the strength of AC system and VSC-HVDC power transmission, LCC-HVDC transmission power condition is the focus of the system, through the analysis of the characteristic roots and participation factor analysis method of the mixed double fed into the dominant oscillation mode changes in the strength of AC system when the system and its main in the state variable. The results show that the participation of LCC and VSC in the dominant oscillation modes is similar under the above changing conditions, indicating that there is a significant interaction between VSC-HVDC and LCC-HVDC in the process of instability due to the weakening of the strength of the AC system. Finally, the effective short mixed double feed system under the condition of the change ratio was calculated, the results show that the traditional effective short circuit ratio guidance has only qualitative evaluation index of the mixed double infeed HVDC system strength, in the quantitative evaluation, the evaluation index should be further improved and perfected. (3) based on the equivalent effective short-circuit impedance of double infeed system than to the traditional quantitative evaluation method is effective short circuit ratio applied to AC system strength index of quantitative assessment of hybrid dual infeed system, LCC-HVDC and VSC-HVDC reveal the strength of AC system interaction rules, put forward converter operation impedance and equivalent effective short mixed double infeed system operation based on the impedance ratio (impedance based effective short circurt ratio, IESCR) concept. First, based on the small signal model established, the port characteristic of the converter's AC side is obtained by applying a small perturbation method to the steady-state operation point of the system. By analyzing the mathematical relationship between the voltage and current offset of the port, the fundamental frequency equivalent impedance calculation method of the converter is obtained. The equivalent impedance is related to the operating point of the system, so it is called the running impedance of the converter in this paper. In the given operating conditions, the target converter (LCC or VSC) other than the converter equivalent to running resistance, and then with the communication network equivalent, put forward the operating impedance of the hybrid dual infeed HVDC system equivalent effective short-circuit ratio method based on quantitative assessment, and effectiveness of the evaluation method. The simulation results show. Based on IESCR, the interaction law of the intensity of LCC-HVDC and VSC-HVDC AC system in a hybrid double feed system is studied. It is found that the communication system of LCC-HVDC is strong.
【学位授予单位】：华北电力大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM721.1

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