Method for suppressing and controlling current harmonics of three-phase LCL (Lower Control Limit) type grid-connected inverter

Abstract

The invention discloses a method for controlling a three-phase LCL (Lower Control Limit) type grid-connected inverter, comprising the steps of: (1) detecting a capacitor current iCx and a grid-connected current iL2x by respectively utilizing a current sensor Hi1 of the capacitor current and a current sensor Hi2 of filter inductance, carrying out collection and coordinate transformation to obtain a capacitor current feedback signal iC-of-m and a grid-connected current feedback signal iL2-of-m, detecting a grid voltage vgx by utilizing a voltage sensor Hv2 of the grid voltage, carrying out collection and coordinate transformation, and computing to obtain a grid voltage feed-forward signal vg-fd-m via a grid voltage feed-forward function Gg-fd; (2) computing to obtain an error signal e1m according to the iL2-of-m and iref-m; (3) carrying out closed-loop processing on the e1m by a controller to obtain a reference signal iC-ref-m of the capacitor current feedback signal iC-of-m, wherein the error signal e2m is equal to (iC-ref-m)+(vg-fd-m)-(iC-of-m); and (4) generating a PWM (Pulse Width Modulation) control signal for controlling a switching tube of an inverter bridge by utilizing the e2m. Through the method, the influence of the grid voltage on the grid-connected current waveform quality can be effectively suppressed, the network-access power factors are improved, the grid-connected current waveform quality is good and balanced current can be still injected into the grid by the inverter when the voltage of the three-phase grid is imbalanced.

Description

technical field [0001] The invention relates to a control method of a three-phase LCL type grid-connected inverter, in particular to a control method for suppressing the influence of the grid voltage on the quality of the grid-connected current waveform. Background technique [0002] figure 1 It is the structural diagram of the three-phase LCL grid-connected inverter. The LCL grid-connected inverter includes a DC power source 1 , an inverter bridge 2 , an LCL filter 3 , a public grid 4 , and a controller 5 . Among them, the inverter bridge 2 is composed of the switch tube S 1 ~S 6 and freewheeling diode D 1 ~D 6 Composition; LCL filter 3 is composed of filter inductor L 1 , L 2 And filter capacitor C composition. h i1 and H i2 Respectively, the detection capacitor current and the filter inductance L 2 The grid-connected current sensor, H v2 It is a grid voltage detection sensor. [0003] exist figure 1 In the structure, the grid-connected current command is inp...

AI Technical Summary

Problems solved by technology

The fundamental wave of the grid voltage will affect the phase of the grid-connected current, the harmonics of the grid voltage will cause distortion of the grid-connected current, and the unbalanced component of the grid voltage will cause the unbalance of the three-phase grid-connected current

If effective measures are not taken to suppress the influence of the grid voltage on the grid-connected current, the grid-connected current output by the grid-connected inverter will inevitably fail to meet the grid-connected standard

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