Control method for improving stability of grid-connected inverter under low short circuit ratio

Abstract

The invention discloses a control method for improving the stability of a grid-connected inverter under a low short circuit ratio, and the method comprises the steps: sampling a PCC point voltage, a grid-connected current, and a DC bus voltage; the grid-connected inverter obtains the voltage phase of the PCC point through the PLL; obtaining a grid-connected current reference value according to the PCC point voltage phase and current amplitude information obtained by PLL locking, and adding the grid-connected current reference value to the actively injected inter-harmonic current reference to obtain the total reference of the grid-connected current; harmonic response components in PCC point voltage and grid-connected current are extracted through a discrete Fourier transform algorithm, so that power grid line impedance is evaluated, and then a line inductance value is obtained. Feeding back the product of the virtual negative inductance and the grid-connected current to a current loop controller according to the evaluated line inductance value and the line negative inductance with the virtual inductance value larger than the current loop controller, obtaining a final modulation signal, comparing the modulation signal with a carrier signal, and generating a PWM signal to drive an inverter switching tube.

Description

technical field [0001] The invention belongs to the technical field of control strategies for grid-connected inverters for new energy power generation, and in particular relates to a control method for improving the stability of grid-connected inverters under low short-circuit ratios. Background technique [0002] In recent years, with the depletion of traditional fossil energy and the increasingly serious environmental pollution, new energy generation such as photovoltaics, wind power, and energy storage has become the focus of global attention. With the massive penetration of new energy power generation and the existence of long-distance transmission lines in distributed power generation systems, the power grid presents the characteristics of a weak power grid. Under the weak power grid, due to the unreasonable design of the inverter's own controller, the influence of the PLL (phase-locked loop) and the PCC point (common connection point) voltage feed-forward, etc., the re...

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Problems solved by technology

[0004] The control method provided by the above patent and the stability of the inverter are controlled by controlling the bandwidth, but this method will affect the dynamic performance of the power generation system

[0005] In addition, in the prior art, there is also a method of using feedforward control of the PCC point voltage and adding phase and amplitude correction to improve the stability of the grid-connected inverter, which is equivalent to shaping a parallel virtual impedance in the output impedance of the inverter. However, the impedance shaping effect of this method depends on the system and PLL parameters, and has certain application limitations; in the prior art, there is also a method of connecting an additional converter in series in the grid-connected line to control the grid-connected inverter. The method will obviously increase the cost of the system and is difficult to be widely applied

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