Abstract
As new energies integrated into grid, the harmonics in the grid are more serious, and the Voltage Detection Active Power Filter (VDAPF) has been used as the mitigation equipment to solve the harmonic problems in power electronic distribution network. The global optimization method generally utilizes 15 min to mitigate harmonic which is named long-time-scale, and it is impossible to mitigate harmonic timely. This paper studies a multi-time-scale harmonic mitigation method which adds 5 min prediction to the global optimization method which is named multi-time-scale. The objective is to correct the deviation of harmonic caused by the long-time-scale harmonic prediction error. This paper utilizes MPC to predict the amplitude and phase variation of the harmonics in short time scale, and utilizes distributed VDAPF to optimize harmonic in long time scale. The IEEE 33 nodes system was used as an example to conduct a comparative analysis of mitigation effects in two different harmonic injection scenarios which injected separately 10 and 20%. The results shows that the mitigating effect of the global optimization method is limited under two different harmonic injection scenarios, and it needs to combine with short time scale harmonic prediction information to ensure the effectiveness and rationality of the mitigation results. When the harmonic current fluctuates, there are unqualified voltage distortion nodes in each region, and the voltage distortion rate is larger. But the MPC can change harmonic prediction in a short time, so every harmonic of each VDAPF conductance values is set bigger, and harmonic conductance of the higher harmonics is relatively lower.
Highlights
The harmonics on the power grid reduce the life of power supply equipment; and nowadays a new situation has emerged from the power grid, that is a large number of new energies such as photovoltaics and wind power are used to distribution network (Yang et al, 2017; Xie et al, 2021), and new elements such as controllable load, distributed power generation, distributed energy storage, and electric vehicles were used (Munir et al, 2020)
The global optimization results of the equivalent conductance of each harmonic of the Voltage Detection Active Power Filter (VDAPF) at each control node in Scenario 1 and Scenario 2 were shown in Tables 2, 3
Since the equivalent harmonic conductance of VDAPF characterizes the intensity of harmonic control, the content of low-order harmonics in the network is relatively high, and the corresponding harmonic conductance value is relatively large, so greater control intensity is required for low-order harmonics
Summary
The harmonics on the power grid reduce the life of power supply equipment; and nowadays a new situation has emerged from the power grid, that is a large number of new energies such as photovoltaics and wind power are used to distribution network (Yang et al, 2017; Xie et al, 2021), and new elements such as controllable load, distributed power generation, distributed energy storage, and electric vehicles were used (Munir et al, 2020). To the diversification of equipment types and characteristics, and the complexity of disturbance distribution (Ebrahimzadeh et al, 2019; Wang et al, 2019; Artale et al, 2021) In response to this situation, a distributed global optimization for harmonics on the grid side was proposed, which used the strategy of combining global optimization and local control to achieve distributed harmonic mitigation. This method aims at the overall optimization of the voltage distortion of all nodes of the distribution network, and solves the global optimization model by establishing the objective function and constraint conditions of the power electronic distribution network, so as to obtain the optimized parameters of VDAPF at operating point in the longterm scale. The long-time scale global optimization method which combined with the short-time scale optimization is called the multi-time scale harmonic optimization method
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