Improved regulator applied to grid-connected inverter under weak grid

Abstract

The invention discloses an improved regulator applied to a grid-connected inverter under a weak grid. The structure of the improved regulator is PI+MSFRR+OPC, wherein the MSFRR is a plurality of specific frequency resonance regulators, the OPC is an online phase compensator, Gc(s) a regulator with the parallel connection of the PI and the MSFRR, Gp(s) is a transfer function of the OPC, the Gc(s) is connected in series with the Gp(s), grid impedance is obtained by the grid impedance on-line measurement technology to update a phase compensation factor in real time, and thus the online phase compensation control is achieved. Through the improved regulator, the phase margin of a system is improved, at the same time, the system has a high open-loop shear frequency, while the stability of the system is ensured, the dynamic response speed of the system is accelerated, and the adaptability of the system to the grid impedance is improved. While the shear frequency is improved, an open-loop gainis increased, which means that the open-loop gain of specific sub-harmonic is increased synchronously, thus a steady-state error is reduced, the suppression of grid background harmonics is enhanced,the THD of grid-connected current is effectively reduced, and the quality of the grid-connected current is improved.

Description

technical field [0001] The invention relates to an improved regulator applied to a grid-connected inverter under a weak grid, and belongs to the technical field of regulator application. Background technique [0002] Distributed power generation systems are mostly located in remote areas. Due to the influence of factors such as long-distance transmission lines, leakage inductance of step-up transformers and changing power system operation modes, the previous rigid power grid presents a weak power grid, and power electronic equipment is constantly switched on and off. As well as the existence of nonlinear loads, there are serious background harmonics in the power grid, and the weak power grid presents two characteristics: a wide range of grid impedance changes and rich grid background harmonics. The existence of grid impedance will change the loop gain of the inverter, reduce the phase angle margin of the system, and threaten the stability of the system; the rich background h...

AI Technical Summary

Problems solved by technology

[0003] In order to improve the adaptability of the grid-connected inverter to the background harmonics of the grid, many patented grid current regulators use PI in parallel with multiple specific frequency resonant regulators (Multiple and Specfic Frequency Resonance Regulator, referred to as MSFRR). SFRR is used to reduce the impact of grid background harmonics on the system, but the number of SFRR is limited by the system shear frequency

As the grid impedance increases, the open-loop shear frequency of the current loop decreases. When the shear frequency is less than the maximum harmonic frequency of SFRR, the system will be unstable.

The stability of the system can be ensured by reducing the number of SFRRs, but at the same time it will reduce the suppression effect of the system on the background harmonics of the power grid, resulting in an increase in the current THD

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