A double closed-loop control strategy for LCL-type grid-connected inverter based on combination state feedback

The inverter based on LCL-type filter is a main technical approach used to improve the technical index of grid-connected current, but it is likely to trigger a problem of system stability due to the existence of resonance peak. In terms of the grid-connected inverter with LCL filter, a double closed-loop control strategy based on the combination state feedback is proposed in this paper. This double closed-loop refers to the internal loop made up of grid-connected current and capacitor current and the external loop made up of grid-connected current. The control formula of this combination state feedback strategy is derived and proved by the control theory. Then the setting method of the combination state feedback coefficients and proportional integrator (PI) regulator parameters are addressed. The proposed control strategy is able to improve control system order, increase control system damping and decrease resonance peak effectively. Finally, the influence of the control strategy on the stability of the system has been analyzed by simulation experiment. The results of simulation manifest that the grid-connected current has a high power factor and the phase difference is smaller between the grid-connected current and voltage.

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