Lijuan Lin

An integrated harmonic optimization strategy for distribution networks typically models control devices as ideal current sources, formulating a convex optimization problem with multiple constraints. However, due to inherent nonlinearities, these devices often exhibit frequency coupling effects, leading to non-ideal harmonic control behavior. This article proposes a harmonic optimal control strategy for distribution networks that accounts for the actual operating characteristics of voltage-regulating active power filters (VRAPFs). First, a complete harmonic state-space (HSS) model of the VRAPF is developed to quantitatively analyze the internal signal exchange process between internal modules of VRAPF, thereby elucidating the mechanism behind frequency coupling effects. Second, a coupled virtual admittance model of the VRAPF is established to reshape the network impedance for improved harmonic suppression. Third, a multi-timescale harmonic control strategy based on coordinated global-local operation is proposed, enabling effective mitigation of harmonic injection uncertainties and ensuring that the harmonic voltage distortion at all distribution-network nodes remains below 4%. The proposed approach is validated through hardware-in-the-loop (HIL) experiments, demonstrating its effectiveness and practicality.

With the widespread application of cable lines in urban distribution grids, the amplification of harmonic standing waves has become increasingly prominent, leading to significant power quality deterioration. To mitigate this issue, this paper proposes an optimal planning strategy for voltage-regulating active power filters (VRAPFs) in meshed cable distribution grids, explicitly accounting for harmonic propagation paths. First, a harmonic propagation model is established to characterize typical scenarios with varying propagation characteristics. Subsequently, K-means clustering is applied to the propagation coefficients, partitioning the distribution grid into regions where nodes exhibit similar harmonic behaviors. Within each region, the node with the highest propagation coefficient is selected as the installation site of the VRAPF to ensure uniform harmonic suppression. Furthermore, the operational parameters of the VRAPF are optimized to simultaneously satisfy network performance requirements and minimize total cost. Comparative analyses with alternative site-selection strategies validate the effectiveness and superiority of the proposed approach.

The escalating integration of distributed renewable energy into the grid has precipitated a decentralized and network-wide proliferation of harmonic sources. In urban distribution networks, the pronounced capacitive and distributed-parameter characteristics of cable lines exacerbate harmonic complexity, rendering them predisposed to multipoint local resonance. This study proposes a rigorous harmonic resonance suppression strategy for cabled distribution networks, grounded in global and local collaborative optimization. The global controller employs modal analysis to discern network-wide resonance modes, formulating a global admittance optimization reshaping model for weighted harmonic voltage to quell resonance across the entire network. Addressing dynamic changes in network parameters, a network division predicated on an event-triggered mechanism determines the local control scope for each suppression device. Ultimately, a localized dual-objective dynamic optimization adjustment model reshapes the virtual conductance of voltage-regulating active power filters and multifunctional grid-connected inverters in each region. Results attest to the efficacious suppression of harmonic resonance voltages to a qualified level, coupled with the successful resolution of parameter disturbances through local conductance adjustment.

The scarcity of inertial resources in the new AC–DC hybrid grids makes the grid frequency prone to fluctuation. In this paper, the relationship between the grid-side and load-side characteristics of the power router is constructed. By adjusting the port load parameters, the load power can respond quickly to the fluctuation of the grid frequency, thereby realizing rapid support of the grid frequency. Firstly, two kinds of mathematical models for sensitivity identification of load characteristics, variable voltage and variable frequency, are established to calculate the characteristic parameters of a multi-port load. The allocation rules of port power and allocation coefficients are designed according to the parameters. A frequency modulation control method that matches the load response capability of the multi-port router is proposed. Then, taking into consideration the uncertainty of load group characteristics and power, a variable coefficient frequency modulation control strategy for a multi-port power router that can adapt to the adjustable margin of loads is proposed. The proposed model is built based on a Simulink platform for validation. The simulation results show that the proposed frequency modulation strategy can be added, and the frequency modulation performance of the power grid is further improved compared to the situation without this method. The frequency is suppressed to 49.93 HZ. It is verified that this method can make the controllable load respond sensitively and effectively to grid disturbance.

Dispersed harmonic control makes a critical guarantee for safe and stable operation of distribution networks. However, conventional point-to-point local control method has limitations. In addition, harmonic current injection has volatility and time-variability, and the residual capacity (RC) of multi-functional grid-connected inverter (MFGCI) employed for auxiliary harmonic compensation is uncertain, which challenges mitigation decision-making. In this study, a grid-side distributed mitigation strategy based on distributed model predictive control (DMPC) is proposed. Firstly, the voltage distortion observation node is selected based on node clustering, and sensitivity analysis of harmonic mitigation for observation nodes is conducted to divide the whole network into multiple control areas. Secondly, for global optimal of voltage distortion, the long time scale distributed optimization model for mitigation parameters orienting partitional coordination is established. Finally, a rolling optimization model based on DMPC for correction of conductance parameters is developed from regional autonomy perspective. The results show that: (1) Distributed mitigation scheme can improve the total harmonic distortion of voltage (THDV) of the whole network node; (2) Compared with control references, the corrected parameters can reduce the decision deviation and further lower the THDV by about 2%; (3) In multi-uncertain scenarios, multi-time-scale optimization can alleviate the uncertainty in harmonic control.