LLCL filter with LRC (Longitudinal Redundancy Check) parallel passive damping circuit

Abstract

The invention discloses an LLCL filter with an LRC (Longitudinal Redundancy Check) parallel passive damping circuit. A parallel damping circuit (7) is in tandem connection between a connection joint (3) of a bridge arm inductance (L1) and a grid-side inductance (L2) and a parallel resonance branch circuit; the parallel damping circuit (7) is formed by a damping resistor (Rd), a damped inductance (Ld) and a damping capacitor (Cd) which are in parallel connection; the LC resonance frequency of the parallel damping circuit is identical to that of the LLCL filter; two ends of the LLCL filter are provided with an inverter (1) bridge arm lateral output terminal (2) and a grid (3) terminal (4) after the bridge arm inductance (L1) and the grid-side inductance (L2) are in tandem connection; a series resonance branch circuit which is formed by an additional inductance (Lf) and a filter capacitor (Cf) is in bridge joint between the connection joint (3) and a common terminal (6) of the inverter (1) and the power grid (5). The LLCL filter with the LRC parallel passive damping circuit in a large-power grid-connected inverter can meanwhile satisfy the high-frequency filter effect, the damping loss and the system stability.

Description

Technical field [0001] The invention relates to a PWM inverter output filter, in particular to an LLCL filter with an LRC parallel passive damping circuit. Background technique [0002] In high-power grid-connected inverters, LCL filters have been widely used due to their small size, low cost, and high harmonic attenuation rate of high-frequency currents. However, when the switching frequency is low, in order to filter out the harmonics of the switching frequency and its integer multiples generated by the inverter to meet the harmonic requirements of the grid standard on the inverter output current, the cut-off frequency of the LCL filter needs to be more Low, which not only needs to increase the filter parameters, which increases the cost of the inverter, but also limits the bandwidth of the system control and reduces the dynamic performance and stability of the system. [0003] In order to solve this problem, people have made some efforts, such as a "filter with specific frequen...

AI Technical Summary

Problems solved by technology

However, although the LLCL filter with this structure can also increase the system damping and ensure the stability of the system, it will significantly weaken the attenuation performance of the LLCL filter at a specific frequency, and the series resistance will flow through the large fundamental frequency and low frequency current, resulting in excessive loss of series resistors and severe heat generation, which not only reduces system efficiency, but also increases difficulties in the process design of high-power converter systems; at the same time, it is also difficult to take into account high-frequency filtering effects, damping losses and Three requirements for stability

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