多馈入直流输电系统的控制策略研究
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摘要
利用直流输电系统的快速可控性，实现对交流输电系统的紧急功率支援，其本质就是研究在大扰动发生后应对直流系统采取何种控制策略。由于在不久的将来，我国华东和广东电网中将形成多馈入直流输电系统的格局，且多馈入直流输电系统的应用也将日益广泛，本文着重探讨了目前研究较少的与多馈入直流输电系统相关的控制策略问题。主要内容包括：
1．基于NETOMAC软件的混合仿真功能，建立了直流输电系统的混合仿真计算模型。该模型能够在对交流网络进行机电暂态计算的同时，对直流网络进行电磁暂态的计算，因而能较精确地考察暂态过程中直流线路的动态行为，并可对任意对称的交流系统故障、直流线路故障以及故障后直流输电系统的恢复等过程进行仿真，且仿真时间较短，为在复杂系统中研究直流输电系统与交流输电系统间的相互作用奠定了基础。
2．针对一个典型的多馈入直流输电系统，首次定义了影响多馈入直流输电系统中换相失败及其发生类型的两个重要参数，即强耦合临界导纳和弱耦合临界导纳。通过仿真研究，分析了交流系统强度、直流输电系统的控制器参数、直流功率输送水平及负荷特性等因素对上述两个参数的影响，取得了一些重要的认识。
3．提出了一种针对多馈入直流输电系统的协调恢复控制策略。该协调恢复策略的三个特点是：在常规的控制器结构中加入一个基于准稳态工作点的非线性前馈回路；在交流故障被切除后的一个短暂时间内，逆变侧采用定交流电压控制：对不同的直流输电子系统采取一种渐进的恢复策略。该方法更注重直流系统两端控制间的协调，更注重在直流系统恢复期间对其换流母线电压的维持。
4．针对大扰动情形，提出了一种用于改善多机交直流混合电力系统(有多条直流线路落点于其中)暂态稳定性的非线性调制策略。该方法基于微分几何理论，将直流输电系统等效为两个分别连接在整流侧和逆变侧的变导纳支路；在推导出直流输电系统的等效变导纳与各发电机输出电磁功率间的解析关系后，传统的发电机动态方程可被表示成仿射非线性的形式，因而可应用全局线性化方法来求得直流输电系统的调制量。该方法的主要特点在于，所求得的直流调制功率是一个交流系统状态的非线性和自适应函数。
浙江大学博士学位论文 摘 要
5．将己有的基于线性方法的有功及无功调制策略由单馈入直流输电系统推
广至多馈入直流输电系统，并提出一种非线性的有功及无功调制方法。该方法
利用最优目标策略（Optimal－Aim Strategy，简记为 OAS八 来得出有功功率的
调制量，它是系统状态的解析函数。该方法的创新之处在于，它所研究的对象
是多馈入直流输电系统，所采用的调制方法是非线性的，且适用于多机电力系
统c
6．提出了一种在大扰动下用于改善交直流系统性能的两层递阶控制策略。
该方法具有如下特点：由于己将多馈入亘流系统中的非线性和相互作用考虑进
去，加之具有反馈的本质，使得出的控制规律对系统运行点的改变和不同的扰
动类型以及系统模型的误差不十分敏感，即该策略具有对扰动的鲁棒性；此外，
由于己将直流系统的换流母线电压隐含在待优化的性能指标中，因而通过适当
修改能反映直流系统换流母线电压动态的状态变量的权值，还可实现各直流输
电子系统控制间良好的协调。
This dissertation focuses on the application of the fast controllability of HVDC systems to realize emergency power support to its connected AC system in the presence of large disturbances occurred in AC system, and more emphasis is given to the control strategies concerned with multi-infeed HVDC systems. The main works are as follows:
A new hybrid simulation model of HVDC system is established based on NETOMAC's hybrid simulation function in this paper. Using this model, simultaneous calculation of AC network in the programs stability section and calculation of DC network in the program's transient section can be made. In case of complicated DC circuit, any type of symmetrical AC system fault. DC line fault and DC line's recovery after fault can be more accurately simulated, and the DC line's dynamic response can be better represented. All the above is very important when doing the research on DC power support to AC system under emergency conditions, and has laid a solid foundation for the interaction study which will be met in a hybrid AC/DC power systems.
Two important parameters. i.e. strong coupling critical admittance and weak coupling critical admittance that affect the occurring conditions and types of commutation failures in multi-infeed HVDC system, are defined in this paper. Factors which has great influence on the above two parameters, such as AC system strength. controller parameters of HVDC system, DC power transfer capacity as well as load characteristics, are analyzed in this paper. Some valuable conclusions are drawn from the simulation results, theoretical explanations are also given to the phenomenon occurred during the simulation process.
In this paper, a coordinated recovery strategy for Multi-infeed HVDC system is proposed. A non-linear feed-forward loop is used to realize the coordinated control between the two controlled variables at the two control ends at first. Secondly, a constant AC voltage control is implemented for a short period after the AC fault removal. Finally, a staggered recovery strategy for different HVDC subsystems is also adopted, with the restart time interval of them optimized using the steepest descent gradient search method. The simulation results show that, with the proposed coordinated recovery strategy implemented, the recovery performance of the tested multi-infeed HVDC system has been improved a lot when compared with the conventional control strategy'.
Based on differential geometric theory, a novel nonlinear modulation strategy for multi-
III
infeed HVDC systems to enhance the transient stability of AC system in the presence of large disturbances is presented in this paper. Taking the HVDC systems as a variable admittance connected at the inverter or rectifier AC bus, the analytical description of the relationship between the variable admittance and active power flows of each generator can be derived. The traditional generator dynamic equations can thus be expressed with the variable admittance of HVDC systems as an additional state variable and changed to an affine form, which is suitable for the global linearization method being used to determine its control variables. An important feature of the proposed method is that, the modulated DC power is an non-linear and adaptive function of the AC system states. The design procedure is tested on a typical dual-infeed hybrid AC/DC system.
This dissertation proposes a new approach to nonlinear active and reactive power modulation control design for multi-infeed HVDC systems, which realizes the emergency power support to AC system in the presence of large disturbances occurred in AC system. The Optimal-Aim Strategy (OAS) is used to decide the controller's input variables, i.e. the modulated active and reactive power which can be determined according to the practical operating conditions of AC system and operating states of DC system. The essence of the method is that, it is basically a nonlinear method and is adaptable to multi-machine hybrid AC/DC power systems.
A two level
1．基于NETOMAC软件的混合仿真功能，建立了直流输电系统的混合仿真计算模型。该模型能够在对交流网络进行机电暂态计算的同时，对直流网络进行电磁暂态的计算，因而能较精确地考察暂态过程中直流线路的动态行为，并可对任意对称的交流系统故障、直流线路故障以及故障后直流输电系统的恢复等过程进行仿真，且仿真时间较短，为在复杂系统中研究直流输电系统与交流输电系统间的相互作用奠定了基础。
2．针对一个典型的多馈入直流输电系统，首次定义了影响多馈入直流输电系统中换相失败及其发生类型的两个重要参数，即强耦合临界导纳和弱耦合临界导纳。通过仿真研究，分析了交流系统强度、直流输电系统的控制器参数、直流功率输送水平及负荷特性等因素对上述两个参数的影响，取得了一些重要的认识。
3．提出了一种针对多馈入直流输电系统的协调恢复控制策略。该协调恢复策略的三个特点是：在常规的控制器结构中加入一个基于准稳态工作点的非线性前馈回路；在交流故障被切除后的一个短暂时间内，逆变侧采用定交流电压控制：对不同的直流输电子系统采取一种渐进的恢复策略。该方法更注重直流系统两端控制间的协调，更注重在直流系统恢复期间对其换流母线电压的维持。
4．针对大扰动情形，提出了一种用于改善多机交直流混合电力系统(有多条直流线路落点于其中)暂态稳定性的非线性调制策略。该方法基于微分几何理论，将直流输电系统等效为两个分别连接在整流侧和逆变侧的变导纳支路；在推导出直流输电系统的等效变导纳与各发电机输出电磁功率间的解析关系后，传统的发电机动态方程可被表示成仿射非线性的形式，因而可应用全局线性化方法来求得直流输电系统的调制量。该方法的主要特点在于，所求得的直流调制功率是一个交流系统状态的非线性和自适应函数。
浙江大学博士学位论文 摘 要
5．将己有的基于线性方法的有功及无功调制策略由单馈入直流输电系统推
广至多馈入直流输电系统，并提出一种非线性的有功及无功调制方法。该方法
利用最优目标策略（Optimal－Aim Strategy，简记为 OAS八 来得出有功功率的
调制量，它是系统状态的解析函数。该方法的创新之处在于，它所研究的对象
是多馈入直流输电系统，所采用的调制方法是非线性的，且适用于多机电力系
统c
6．提出了一种在大扰动下用于改善交直流系统性能的两层递阶控制策略。
该方法具有如下特点：由于己将多馈入亘流系统中的非线性和相互作用考虑进
去，加之具有反馈的本质，使得出的控制规律对系统运行点的改变和不同的扰
动类型以及系统模型的误差不十分敏感，即该策略具有对扰动的鲁棒性；此外，
由于己将直流系统的换流母线电压隐含在待优化的性能指标中，因而通过适当
修改能反映直流系统换流母线电压动态的状态变量的权值，还可实现各直流输
电子系统控制间良好的协调。
This dissertation focuses on the application of the fast controllability of HVDC systems to realize emergency power support to its connected AC system in the presence of large disturbances occurred in AC system, and more emphasis is given to the control strategies concerned with multi-infeed HVDC systems. The main works are as follows:
A new hybrid simulation model of HVDC system is established based on NETOMAC's hybrid simulation function in this paper. Using this model, simultaneous calculation of AC network in the programs stability section and calculation of DC network in the program's transient section can be made. In case of complicated DC circuit, any type of symmetrical AC system fault. DC line fault and DC line's recovery after fault can be more accurately simulated, and the DC line's dynamic response can be better represented. All the above is very important when doing the research on DC power support to AC system under emergency conditions, and has laid a solid foundation for the interaction study which will be met in a hybrid AC/DC power systems.
Two important parameters. i.e. strong coupling critical admittance and weak coupling critical admittance that affect the occurring conditions and types of commutation failures in multi-infeed HVDC system, are defined in this paper. Factors which has great influence on the above two parameters, such as AC system strength. controller parameters of HVDC system, DC power transfer capacity as well as load characteristics, are analyzed in this paper. Some valuable conclusions are drawn from the simulation results, theoretical explanations are also given to the phenomenon occurred during the simulation process.
In this paper, a coordinated recovery strategy for Multi-infeed HVDC system is proposed. A non-linear feed-forward loop is used to realize the coordinated control between the two controlled variables at the two control ends at first. Secondly, a constant AC voltage control is implemented for a short period after the AC fault removal. Finally, a staggered recovery strategy for different HVDC subsystems is also adopted, with the restart time interval of them optimized using the steepest descent gradient search method. The simulation results show that, with the proposed coordinated recovery strategy implemented, the recovery performance of the tested multi-infeed HVDC system has been improved a lot when compared with the conventional control strategy'.
Based on differential geometric theory, a novel nonlinear modulation strategy for multi-
III
infeed HVDC systems to enhance the transient stability of AC system in the presence of large disturbances is presented in this paper. Taking the HVDC systems as a variable admittance connected at the inverter or rectifier AC bus, the analytical description of the relationship between the variable admittance and active power flows of each generator can be derived. The traditional generator dynamic equations can thus be expressed with the variable admittance of HVDC systems as an additional state variable and changed to an affine form, which is suitable for the global linearization method being used to determine its control variables. An important feature of the proposed method is that, the modulated DC power is an non-linear and adaptive function of the AC system states. The design procedure is tested on a typical dual-infeed hybrid AC/DC system.
This dissertation proposes a new approach to nonlinear active and reactive power modulation control design for multi-infeed HVDC systems, which realizes the emergency power support to AC system in the presence of large disturbances occurred in AC system. The Optimal-Aim Strategy (OAS) is used to decide the controller's input variables, i.e. the modulated active and reactive power which can be determined according to the practical operating conditions of AC system and operating states of DC system. The essence of the method is that, it is basically a nonlinear method and is adaptable to multi-machine hybrid AC/DC power systems.
A two level
引文
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