Research On Collaborative Mitigation Of Distribution Network Background Harmonics Based On Distributed Control Architecture

With the high-density penetration of power electronic devices on each side of the source,network and load in the distribution network,a large number of power electronic harmonic sources overlap and propagate with each other,as well as with traditional harmonic sources,resulting in serious background harmonics.Meanwhile,for urban distribution networks with high cabling rates,the background harmonic amplification caused by harmonic resonance and standing waves makes the harmonic destructive power stronger.For the scattered background harmonics in the distribution network,and the calculation and communication pressure issues of centralized control in harmonic control,this dissertation constructs a distributed control structure and proposes a distribution network background harmonic collaborative mitigation scheme based on distributed model predictive control.The specific research works are as follows:Aiming at the problem of low order background harmonics mitigation caused by power electronics in distribution networks,a background harmonic collaborative mitigation scheme based on distributed model predictive control is proposed.Firstly,a harmonic observation node selection method based on node voltage data similarity clustering is proposed.By defining the background harmonic mitigation sensitivity index,a harmonic mitigation partition method based on sensitivity analysis is established.Under the distributed control structure,the entire network is divided into several control regions,on a long-term scale adjacent area controllers interact with each other through a small amount of communication,and distributed collaborative mitigation of background harmonics across the entire network is conducted.On a short time scale,based on the update prediction of harmonic source injection and the available capacity of mitigation resources,the regional controller scrolls and optimizes the amount of regional mitigation,achieving effective mitigation under the dual uncertainty of harmonic source and mitigation resources.Regarding the issue of background harmonic resonance amplification caused by high cabling rate in urban distribution networks,a background harmonic resonance amplification suppression strategy based on global and local collaborative optimization is proposed.A distributed resonance mode analysis is first conducted on the entire network,which obtains the dominant resonance frequencies and peak positions of the network.An optimization model is established on a long-term scale with the goal of minimizing the weighted harmonic voltage distortion rate of the entire network nodes,and a node voltage distortion rate optimization weight set method based on the proportion of modal impedance values is set,and distributed solutions were achieved through information exchange between regional controllers.On a short time scale,based on the predicted update values of network parameters,each regional controller constructs a global and local collaborative dynamic mitigation model for regional harmonic resonance voltage,taking global mitigation instructions as reference,achieving regional autonomy for regional background harmonic resonance voltage.For the decentralized and grid wide distribution of micro harmonic sources,background harmonics have been distributed almost at each node,while for distribution lines,there is a dual terminal harmonic voltage source excitation.A distribution parameter model of the distribution network line was established,and the standing wave form was used to express the distribution law of harmonic voltage amplification along the line.Based on the superposition theorem of voltage source phasor,the distribution of background harmonics along the line under the excitation of two terminal harmonic voltage source is derived.A robust optimization mitigation scheme for harmonic standing wave amplification in distribution networks is proposed to address network parameters and harmonic fluctuations.A line standing wave voltage distribution law characterized by affine numbers has been established.Based on a distributed control structure,each regional controller conducts robustly optimization mitigation for the peak standing wave belly voltage of the entire network through information exchange,and enables the optimization solution to effectively mitigate background harmonics within the set disturbance range.Aiming at the real-time online dynamic mitigation of background harmonics,a multiagent distributed consistency algorithm is proposed to allocate operating parameters for local harmonic autonomy of equipment.Each regional controller is regarded as an agent,and its own variables are iterated through the information interaction with the neighbor agents,which ultimately makes unified variable consistent.Considering the differences in the content of background harmonics with different frequencies,based on the actual values of each harmonic voltage at the nodes where the regional mitigation equipment is located,and using the limit value of the total harmonic voltage distortion rate as the boundary condition,the maximum allowable increment of total harmonic voltage distortion is calculated,and this increment is proportionally distributed to each harmonic voltage to obtain the allowable increment of each harmonic voltage.The ratio of the virtual conductance of the mitigation device to the slope of the conductance adjustment characteristic is defined as a consistency variable,so that the adjustment amount of the virtual conductance matches the background harmonic content.