This paper presents a comprehensive assessment for the small‐signal voltage stability of voltage source converter (VSC)‐HVDC systems supplying industrial loads represented by the induction motors (IMs) and provides a stability enhancement control for the VSCs. First, the steady‐state voltage stability is analysed to seek the factors that affect the existence of the stable equilibrium point. Then, the small‐signal voltage stability analysis is performed based on the developed linear model. Eigenvalue analysis is carried out to capture the critical factors that induce instability phenomena correlative to the system voltage. It demonstrates that decreasing either the proportional gain K of the VSC's PI controller or the electrical distance between the VSC and IM is detrimental to voltage stability. Next, the enhancement control strategy is elaborated. It adopts virtual reactance and virtual admittance control for the VSC to improve the voltage control capability. Finally, the effectiveness and robustness of the proposed enhancement control are validated via time‐domain simulations in a multi‐IM system supplied by VSC‐HVDC.

This paper presents a comprehensive assessment of the small‐signal voltage stability of voltage source converter (VSC)‐HVDC systems supplying industrial loads. Based on the stability mechanism, an enhancement control strategy is proposed to improve the voltage control capability of the VSC.image

In the context of extremely uneven sources and loads in China, several large‐scale power transmission systems have been established. Affected by the small equivalent impedance of the system, the increase of negative sequence currents during open‐phase operation has seriously threatened the stable operation of synchronous generators. The necessity of negative sequence current suppression is particularly prominent. To address the above issues, this paper analyzes the feasible negative sequence suppression capacity of the grid‐connected inverter under the principle of positive sequence priority. Using the geometric analysis method to determine the optimal suppression capacity. The none‐phase‐locked loop (PLL) control method is used to improve the response speed and form the negative sequence current suppression strategy adapted to the open‐phase operation period. A simulation model was built in PSCAD to verify the effectiveness of the proposed strategy. The result shows that the suppression strategy has a faster response than the conventional PLL control. In scenarios with large negative sequence currents to be suppressed, a maximum suppression effect of approximately 63% can be achieved. Compared with the traditional suppression capacity selection, the strategy in this paper can reduce the residual of negative sequence current by about 10% at most. The negative sequence currents intruding into the generator can be effectively suppressed without additional devices.

An optimal negative sequence suppression strategy without phase‐locked loop (PLL) based on the control of clustered new energy power station is proposed. This strategy achieves effective suppression of negative sequence current during open‐phase operation without additional devices. image

DC short‐circuit fault has become one of the major concerns in bipolar DC system operation under complicated conditions. Compared with conventional two‐port DC‐DC converter, fault‐tolerant DC‐DC converter with multiple external ports is evaluated as a preferential choice for high reliability, availability and flexibility required bipolar DC system due to its capability of fault reconfiguration. This article focuses on a type of fault‐tolerant DC‐DC converter interconnected with DC bus and integrated energy storage devices applied in bipolar DC system and theoretical analyses on transmitted power characteristics under bipolar mode and monopolar mode are also carried out in this article. For bipolar mode, the minimized‐peak‐current control strategy is proposed to reduce current stress on switching devices. As for monopolar mode and source‐port fault mode, the fault reconfiguration method and constant‐transmitted‐power control strategy are designed to eliminate fault impaction and achieve the constant transmitted power of output port connected with critical load, by means of power sharing between input port and normal output port or between the normal output ports. Furthermore, intersection of zero‐voltage‐switching (ZVS) operation area under different working modes is depicted with consideration of two optimizing control. Finally, the performance of the proposed fault reconfiguration method and optimizing control have been tested in PLECS environment and experimental prototype to verify the reliability and flexibility.

This article focuses on a type of fault‐tolerant DC‐DC converter interconnected with DC bus and integrated energy storage devices applied in bipolar DC distribution. For bipolar mode, the minimized‐peak‐current control strategy is proposed to reduce current stress on switching devices. As for monopolar mode and source‐port fault mode, the fault reconfiguration method and constant‐transmitted‐power control strategy are designed to eliminate fault impaction and achieve the constant transmitted power of output terminal connected with critical loads. It is considered as a preferable choice to enhance power supply reliability, stability and flexibility in bipolar DC power system.image

Overhead transmission line detection based on deep learning of aerial images taken by UAVs has been widely investigated. Despite its success, it is limited by several factors, including inappropriate evaluation criteria and dramatic scaling of components in the images. To mitigate these issues, a relative mean Average Precision evaluation index is proposed to accurately measure the model's detection performance for smaller objects. A data enhancement strategy including multi‐scale transformation is adopted to alleviate the problem of drastic scaling. The existing Cascade RCNN target detection technology is enhanced by incorporating Swin‐v2 and a balanced feature pyramid to improve feature characterization capabilities, while side‐aware boundary localization is utilized to improve the positioning accuracy of the model. Experimental results demonstrate that the proposed method outperforms state‐of‐the‐art methods on CPLID and achieves 7.8%, 11.8%, and 5.5% higher detection accuracy than the baseline for mAP50, relative small and medium mAP, respectively. Additionally, the paper discusses the influence of adopted data enhancement on the robustness of the model.

The network architecture of our designed model, Cascade RCNN‐improved. It is based on Cascade R‐CNN, and has a series of improvements to make it more suitable for the detection of transmission line critical components and their defects.image

The voltage endurance coefficient n of cross‐linked polyethylene (XLPE) insulation is an important indicator for the analysis of insulation failure mechanism. Accurately obtaining the value of n can provide technical support for the reliability evaluation of cable operation. The constant stress method and the step stress method are used to obtain the values of n, but the test parameters can influence the accuracy of the obtained n values. Two methods for selecting test parameters are proposed. The equivalence between the two methods is established, providing theoretical support for the accurate evaluation of the n value of solid insulation materials by using the step stress method. The accuracy of the evaluation results is verified by analyzing the test data. The test results show that the n_step  = 13.04 evaluated by the step stress test with the proposed parameter selection method is consistent with the test result of constant stress n_constant  = 12.83.