高压直流控制器交互影响可能导致后续换相失败恶化，为此，分析了故障后各时段换流器控制交互影响机理，设计了降低后续换相失败风险的策略。依据逆变侧控制器动作逻辑，将系统故障发生至恢复稳态划分为4个阶段，基于各阶段的动态轨迹分析，得到逆变侧控制器对换相失败恢复过程的影响规律，结果表明逆变侧定关断角控制与定电流控制的二次交互过程，即电流偏差控制阶段极易引发后续换相失败。提出了一种改进型电流偏差控制策略，通过补偿控制器二次交互期间电流偏差，提升关断角状态识别的准确度，从而抑制因控制器交互不当引发的后续换相失败。最后，在PSCAD/EMTDC仿真平台中以CIGRE标准算例，对不同工况下所提改进控制策略进行测试，结果表明所分析故障后动态过程准确，所提出的后续换相失败抑制策略效果显著。

 The interaction of HVDC controllers may lead to the deterioration of subsequent commutation failure. Therefore, this study analyzes the mechanism of converter control interaction at each stage after a fault and designs a strategy to reduce the risk of subsequent commutation failure. According to the action logic of the inverter-side controller, the process of system recovery from fault occurrence to a steady state is divided into four stages. Based on the dynamic trajectory analysis of each stage, the influence of the inverter-side controller on the commutation failure recovery process is determined. The results showed that the secondary interaction process between the constant extinction angle control and constant DC current control on the inverter side, namely, the current deviation control stage, could easily cause subsequent commutation failure. An improved current deviation control strategy is proposed to improve the accuracy of the extinction angle state recognition by compensating for the current deviation during the secondary interaction of the controllers to suppress the subsequent commutation failure caused by improper controller interaction. Finally, based on the CIGRE HVDC benchmark model, an improved control strategy is tested under different operating conditions using the PSCAD/EMTDC simulation platform. The results showed that the analysis of the fault recovery process was accurate, and that the proposed subsequent commutation failure suppression strategy was effective.

高比例新能源接入配电网对配电网电压控制造成了巨大挑战。传统电压控制方法在高比例可再生能源渗透的情景下无法取得满意的控制效果，同时传统电压控制依赖机械式调压设备，其频繁机械式动作显著影响了使用寿命。为解决以上问题，提出一种基于模型预测控制(model predictive control， MPC)的多层电压控制方法。在所提方法中，机械式调压设备，例如变压器和并联电容，在上层以较长控制周期进行控制；而下层，对分布式电源的有功和无功输出以较短的时间尺度进行快速调节。在所提方法中，上层控制的控制目标是降低机械式调压设备的动作次数，下层的控制目标为降低系统的网损和有功消减，保证配电网运行的经济性。所提方法考虑了配电网当前及将来的系统状态，能确保高比例新能源接入后电压在允许的范围内。仿真结果表明：所提方法能有效解决高比例风光接入配电网带来的电压越限问题，系统电压均方误差从3.9%降低至0.97%；同时，该方法能显著降低有载调压变压器和并联电容的动作次数，仅为传统电压控制方法的40%和16.4%。

The integration of high proportion of new energy into distribution networks poses significant challenges for voltage control of distribution network. Traditional voltage control methods cannot ensure satisfactory control performance in scenarios with high penetration of new energy. Additionally， traditional voltage control relies on mechanical voltage regulation equipment， and frequent operation of these equipment significantly affects their lifespan. To address these issues， this paper proposes a multilayer voltage control method based on model predictive control (MPC). In the proposed method， mechanical voltage regulation equipment， such as transformers and shunt capacitors， is controlled in the upper layer with a longer control period， while active and reactive power outputs of distributed generations are rapidly adjusted in the lower layer with a shorter timescale. The objective of the upper-layer control is to reduce the number of operation of mechanical voltage regulation equipment， while the lower-layer control aims to minimize network losses and active power curtailment， ensuring the economic operation of the distribution network. The proposed method considers both the current and future states of the distribution network， ensuring that voltage operates within allowed limits under high penetration of new energy. Simulation results show that the proposed method can effectively address the voltage violation issues introduced by the high penetration of new energy in the distribution network， decreasing the system voltage mean square error from 3.9% to 0.97%. Additionally， the proposed method significantly reduces operation number of mechanical voltage regulation equipment， which is only 40% and 16.4% of those under traditional voltage control methods， respectively.

针对大容量直流和高比例新能源集中接入的交直流送端系统中,由于故障扰动引起的暂态过电压难以快速准确计算导致系统安全稳定运行的问题,提出综合能源交直流混联外送系统暂态过电压分析与快速估算方法。首先,建立风火打捆的送端系统等效模型,考虑储能系统接入后的交直流综合能源的调节特性,对故障后的暂态过电压进行修正。分析故障扰动下风电机组的有功功率和无功功率动态变化特性,给出暂态过电压的计算流程。然后,分析暂态过电压时变参数辨识方法,提出交直流系统暂态过电压快速估计方法。最后,以某地交直流送端系统数据建立仿真模型,仿真结果验证了所提方法在交直流送端系统暂态过电压的计算精度和收敛速度方面具有优越性。

Aiming at the problem that the transient overvoltage caused by fault disturbance is difficult to calculate quickly and accurately in the AC-DC transmission terminal system with large capacity DC and high proportion of new energy centralized access, which leads to the safe and stable operation of the system, a method of transient overvoltage analysis and rapid estimation of the integrated energy AC-DC hybrid transmission system is proposed. In this regard, this paper firstly establishes an equivalent model of the sending end system of wind and fire bundling, considering the regulation characteristics of the AC and DC integrated energy after the energy storage system being connected, and corrects the transient overvoltage after the fault. The dynamic change characteristics of active power and reactive power of wind turbines under fault disturbance are analyzed, and the calculation flow of transient overvoltage is given. Then, the time-varying parameter identification method of transient overvoltage is analyzed, and a fast estimation method of transient overvoltage in AC-DC system is proposed. Finally, a simulation model is established based on the data of the AC/DC transmission side system in a certain place. The simulation results verify that the proposed method has superiority in the calculation accuracy and convergence speed of the transient overvoltage of the AC/DC transmission side system.

针对特高压混合直流系统的送端电网由于高比例风电接入带来的频率易越限的问题，提出了风电与混合直流系统协调参与的送端电网频率控制策略。首先，介绍了混合直流系统的拓扑，其中送、受端均采用电网换相换流器串联模块化多电平换流器的结构；其次，分别在风机和传统直流换流站中引入考虑一次调频特性与惯性特性的附加频率控制策略，在柔性直流换流站中引入虚拟惯性控制策略；设计了风电与混合直流系统各站协调参与送端电网调频的时序动作规则与各换流站之间的电压协调策略；同时，基于风电与直流并网系统的频率响应模型，定性分析了风电与混合直流系统参与调频的机理，提出了相关控制参数的设计方法；最后，通过PSCAD/EMTDC中建立模型进行仿真验证。仿真结果表明所提频率协调控制策略可以提高送端系统的惯量与一次调频能力，有效改善交流系统在不同运行工况下的频率稳定问题。

Aiming at the frequency out-of-limit problem caused by the high proportion of wind power in the power grid at the sending-end of hybrid ultra-high voltage direct current (UHVDC） system, the coordinated frequency control strategy of power grid at the sending-end by wind power and hybrid DC system is proposed. Firstly, the topology of hybrid DC system is introduced, in which the structure of the line commuted converter in series with modular multilevel converter is adopted at the sending and receiving ends; Secondly, the additional frequency control strategy considering primary frequency and inertia characteristics is introduced in the wind turbines and the line commuted converter station respectively, and the virtual inertia control strategy is introduced in the voltage source converter (VSC） station; The timing action rules of wind power and hybrid DC system coordinating and participating in power grid frequency control and the voltage coordination strategy between converter stations are designed; At the same time, the mechanism of wind power and hybrid DC system in frequency control is qualitatively analyzed based on the frequency response model of wind power and DC integrated system, and design method of related control parameters is put forward. Finally, a model is built in PSCAD/EMTDC for simulation verification. The simulation results show that the proposed frequency coordinated control strategy can improve the inertia and primary frequency capability of the sending-end system and effectively improve the frequency stability problem of the AC system under different operating conditions.

构网型变换器的虚拟同步环节是影响其频率动态的最主要因素，但构网型变换器内电势的频率并不仅包含虚拟同步环节的频率。对此提出了一种表征电压控制对构网型变换器频率动态影响作用的研究方式。首先类比同步机的频率分析方法，提出了构网型变换器内电势的概念，将变换器的频率通过内电势频率进行表征，进而通过运动方程建模的方法分析了机电时间尺度内交流电压控制在响应有功功率扰动时对频率动态的作用，分析了电压控制参数对构网型变换器有功功率和频率响应能力的影响趋势。研究发现，较大的电压控制比例和积分参数会使得系统频率动态恶化，但变换器的响应性能主要由虚拟同步环节决定。以3机9节点系统和实际区域电网系统的MATLAB/Simulink仿真验证了所提方法的有效性。

The virtual synchronous generator section of a grid-forming converter is the most important factor affecting its frequency dynamics, but the frequency of the internal voltage within a grid-forming converter does not only include the frequency of the virtual synchronous generator. To address this point of view, a research approach is proposed to characterize the effect of voltage control in influencing the frequency dynamics of grid-forming converter. Firstly, analogous to the frequency analysis method of the synchronous generator, the concept of the internal voltage of the grid-forming converter is proposed, and the frequency of the converter are characterized by the frequency of the internal voltage. Then the effect of the AC voltage control on the frequency dynamics in response to the active power perturbation within the electromechanical time scale is analyzed through the method of the motion equation modeling, and the influence trends of the voltage control parameter on the active power and the frequency response capability of the grid-forming converter are analyzed. It is found that larger voltage control proportional and integration parameters deteriorate the system frequency dynamics, but the response performance of the converter is mainly determined by the virtual synchronous generator. The simulations in MATLAB/Simulink with a 3-machine 9-node system and a real-world regional grid system verify the effectiveness of the method respectively.