In recent years, there is an increased use of passive filters in both transmission and distribution systems due to the proliferation of power electronic devices. However, the problem of filter design has not been well addressed in the past and one example is the application of high-pass filters in a filter package. Three types of HP filters are widely used to mitigate multiple harmonics, i.e., 2 ^nd HP filter, 3 ^rd HP filter and C-type filter. There is still a lack of research to clearly reveal the characteristics of each filter, which makes it difficult for the designer to select the optimal filter topology under different circumstances. The main goal of this paper is to solve the problem of how to select a proper configuration among three HP filter candidates for a given harmonic problem. Unlike the conventional optimization-based filter studies, this paper investigates three HP filters in an analytical way. As a result, the paper provides a deep insight into the inherent characteristics of the filter and the conclusions drawn in the paper are universal; thus can be used in different applications, ranging from low voltage levels to high voltage levels. The research results lead to a recommended application scope of each HP filter, which is very useful to guide the design of filter packages and help designers to evaluate the design results.

Configuring a shunt capacitor as a detuned C-type filter is an effective way to mitigate the capacitor caused harmonic resonance. A design method has been developed recently that can guarantee the damping performance of the filter even if the system imped-ance data is not available. This paper further improves the design method by considering the case where the system impedance data is available. It also answers the question if cost can be reduced by utilizing known system impedance data. For this purpose, the cost and power loss characteristics of the filter are investigated and included in the design. The performance of various design methods is compared from the perspectives of reso-nance-mitigation, power loss, cost and robustness. The results have shown that the system independent design leads to superior performance except for the power loss. A guide on how to design detuned C-type filter is recommended.

Utility harmonic impedance is an important parameter for harmonic mitigation. In this paper, a method for utility harmonic impedance estimation method based on constrained independent component analysis is proposed. The conventional impedance estimation method based on ComplexICA has two major problems: the algorithm is not suitable for separating weak and strong source mixed signals, and lots of sample data should be provided to avoid converging on a local optimum. To solve the two problems, the prior information of the utility harmonic source is added to the objective function of ComplexICA; in this paper, the measurement data at PCC when the load is shutdown are chosen as the prior information. Then the utility harmonic source signal can be recovered and the separated matrix can be obtained effectively. The connection between the utility harmonic source, utility harmonic impedance and the data at PCC are established using Norton equivalent circuit, and then the separation matrix is used to calculate utility harmonic impedance. The performance and feasibility of the proposed method are verified by the computer simulation and field test. Compared with the current ComplexICA method, the proposed method is more adaptive to changes in the background harmonic and the calculation result is more stable.

Adding a damping unit to a shunt capacitor is an effective way to mitigate capacitor-caused resonance. However, damping units suffer from power loss issues. This shortcoming is amplified further in cases where resonance has a low possibility of occurring. In view of this, an adaptive damping method is proposed to improve the existing scheme. The damping unit is capable of mitigating resonance and eliminating the power loss under the non-resonance condition. The core idea of the proposed approach is to add a breaker so that the damping unit can be switched on or off depending on whether resonance occurs. The design of and control mechanism for the proposed switchable damping unit are presented. The performances of the new resonance mitigation scheme in terms of harmonic mitigation, loading, switching transient and cost are verified for an actual capacitor application case.

Distributed photovoltaic storage charging piles in remote rural areas can solve the problem of charging difficulties for new energy vehicles in the countryside, but these storage charging piles contain a large number of power electronic devices, and there is a risk of resonance in the system under weak grid conditions. Firstly, the topology of a photovoltaic storage charging pile is introduced, including a bidirectional DC/DC converter, unidirectional DC/DC converter, and single-phase grid-connected inverter. Then, the maximum power tracking control strategy based on improved conductance micro-increment is derived for a photovoltaic power generation system, and a constant voltage and constant current charge–discharge control strategy is derived for energy storage equipment. Additionally, a segmented reflective charging control strategy is introduced for charging piles, and the quasi-PR controller is introduced for single-phase grid-connected inverters. In addition, an improved second-order general integrator phase-locked loop (SOGI-PLL) based on feed-forward of the grid current is derived. Finally, a simulation model is built to verify the performance of the solar–storage charging pile and lay the technical groundwork for future integrated control strategies.

Addressing uneven accuracy across multiple measurement sources and the insufficient adaptability of traditional data-driven models to topological changes, a data-driven state estimation method for distribution networks based on power-flow constraints is proposed. Firstly, historical prior information is used to supplement missing data, thereby constructing a complete measurement dataset and establishing a reliability index to assess the credibility of measurements from different sources. Secondly, according to the physical topological map structure of the distribution network, an improved graph neural network algorithm is proposed to realize state estimation. The bus power balance relationship is embedded as a soft constraint in the loss function to enhance the consistency between the estimation results and physical laws. Then, an adaptive method of topology change based on transfer learning is proposed to improve the adaptability of the model to the dynamic changes of distribution network topology. Finally, the proposed method is evaluated using various metrics on the IEEE 33 and IEEE 118 systems. The analysis results show that the method can maintain high estimation accuracy under multi-source measurements and exhibits good robustness to noise disturbances.