A Composite Filter for Megawatt Parallel/Off-Grid Converters

Abstract

The invention discloses a megawatt on / off-network converter composite filter which comprises a filter inductor, a plurality of electronic switches, an isolation boosting transformer, and controllers used for controlling turning on and turning off of the electronic switches, wherein the filter inductor is connected with the isolation boosting transformer; the electronic switches are connected in parallel between the filter inductor and the isolation boosting transformer; each electronic switch is connected with a filter capacitor; and each filter capacitor is connected in parallel with a resistor. The filter can be widely applied to the fields of a new energy converter, ship shore supply, fire-fighting emergency power supply, uninterruptible power supply and the like, can meet requirements of on-network and off-network applications, reduces the reactive loss, effectively eliminates a high-frequency harmonic wave, better adapts to a poorer power grid environment, and avoids a system shock.

Description

technical field [0001] The invention relates to the technical field of power electronics, in particular to a composite filter for megawatt-level parallel / off-grid converters. Background technique [0002] In a high-power grid-connected inverter system, the main functions of the grid-side filter include: (1) filtering and suppressing high-order harmonics in the grid-side current, so that the grid-side current maintains a sinusoidal waveform with little distortion; (2) Make the rectifier have Boost conversion performance and DC side controlled current source characteristics; (3) The output filter inductance is equivalent to the lever connecting the power grid and the rectifier bridge, through which the control of the grid side current can be realized, thereby achieving high power factor rectification; (4) Make the grid-side rectifier obtain certain damping characteristics, which is beneficial to the design of the control system. [0003] The commonly used structures of grid-s...

AI Technical Summary

Problems solved by technology

[0003] The commonly used structures of grid-side filters are L-type filter, LC-type filter and LCL-type filter. Compared with other filters, the design of L-type filter is simple. To adapt to the poor quality of the power grid, LC filter is a better and commonly used choice. The LC filter has a simple structure and is a low-pass filter. The filter sets the LC resonance frequency at the carrier frequency of the converter and the modulation frequency of the converter, so as to retain the required fundamental wave and eliminate high-frequency harmonics as much as possible, which can better adapt to the poor grid environment, but the improper value of LC will easily cause system oscillation

The design of the LCL filter is relatively complicated, but compared with the single-L filter, under the same inductance value, the effect of the LCL filter on filtering higher harmonics is significantly better than that of the single-L filter, so that it can adapt to more Poor grid environment, but the LCL filter cannot be applied to the off-grid operation of the converter, and cannot be directly connected to the load

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