A Method for Improving the Voltage Quality of the Parallel AC Bus of Megawatt Converters

Abstract

The invention discloses a megawatt current transformer parallel connection alternating current bus voltage quality improving method, which comprises a small harmonic wave impedance type voltage current control method, a fractional frequency virtual impedance technology and a fast robust droop control method. By aiming at a sea island multi-high-power current transformer parallel connection system, the method is used for solving the problems of the sharp drop of alternating current bus voltage caused by sudden load change and the serious distortion of the alternating current bus voltage caused by high-permeability non-linear load; the effects that on the premise of meeting the precise distribution of load power, the current transformer can fast and actively support the alternating current bus voltage, and the distortion of the alternating current bus voltage caused by the network side inductance of an LCL filter is counteracted are achieved, so that the high-precision and high-quality control of the alternating current bus of the parallel connection system is ensured; high use requirements of local loads are met.

Description

technical field [0001] The invention relates to the field of sea-island power supply, in particular to a method for improving the voltage quality of parallel-connected AC busbars of megawatt-level converters. Background technique [0002] my country has a long coastline and a large number of islands. Safe and reliable power supply is the basic guarantee for the development and construction of islands and the military's protection of maritime rights and interests. For relatively remote small islands, because the laying of submarine cables requires huge technical and economic costs, the local load on the island is often a multi-megawatt-level transformer composed of micro-sources such as wind / light / firewood / storage. The converters are connected in parallel to the system to realize the power supply. The constant-voltage DC source supported by multiple micro-sources and energy storage devices is converted into a stable power-frequency AC voltage source through the interface of ...

AI Technical Summary

Problems solved by technology

However, the traditional parallel system control of converters has not fundamentally solved the voltage quality problem of the AC bus, which is mainly reflected in three aspects: 1) The nonlinear load with high penetration rate will bring power quality problems to the converter system, Especially when the converter chooses the LCL filter to be connected to the common bus, the harmonic current will cause a large voltage drop in the filter inductor on the grid side, so that the AC bus voltage contains a large number of harmonic voltage components in the main sub-harmonic, which It will seriously affect the voltage quality of the AC busbar; 2) The sudden drop of the AC busbar voltage caused by the sudden change of the island load, the traditional R-type, L-type and RL-type converters have a large fundamental frequency output impedance, making When the local load increases sharply, the converter has a large fundamental wave voltage drop, which is not conducive to power transmission, and even causes the instability of the AC bus voltage; 3) The traditional robust droop control makes the converter put into parallel operation. , there is a large inrush current and a long transition time, which is not conducive to the high-quality control of the bus voltage

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