Off-network inverter control method based on frequency division virtual impedance

Abstract

The invention discloses an off-network inverter control method based on frequency division virtual impedance. The off-network inverter control method comprises the steps of measuring a voltage u<c> of an inverter capacitor, an output current i<L> of an inverter and an output current i<o> of an LC filter; extracting a fundamental wave from the voltage of the capacitor C to obtain u<cf>, and extracting an angular frequency Omega<f> of the u<cf>; giving a reference voltage amplitude /U<ref>/, wherein the reference voltage amplitude /U<ref>/ and the angular frequency Omega<f> form a reference capacitance voltage u<creff>; employing a fundamental wave field P regulator by a current regulation ring; setting frequency division virtual resistances z<vir5>, z<vir7> until z<virh>; obtaining harmonic virtual impedance voltages u<vir5>, u<vir7> until u<virh>; employing harmonic fields PR5, PR7 until PRh regulators by a voltage outer ring, and generating an inductive current reference value; employing harmonic fields P5, P7 until Ph regulators by the current regulation ring to obtain a harmonic field modulation signal; and subtracting the harmonic field modulation signal from the fundamental field modulation signal, and outputting a switch pulse to control switch-on and switch-off of an inverter power device after pulse width modulation (PWM). By the off-network inverter control method, a harmonic current is suppressed, balanced running without circulation current of a parallel inverter is achieved, and the system reliability is improved.

Description

technical field [0001] The invention relates to the technical field of distributed power generation and power electronics, in particular to an off-grid inverter control method based on frequency division virtual impedance. Background technique [0002] At present, distributed power generation technology has increasingly become a research hotspot in the field of new energy power generation due to its advantages of high flexibility, low cost and loss, energy saving and environmental protection. In order to utilize distributed energy resources on a large scale, various distributed power generation can be accepted in the form of micro-grid, which can flexibly realize grid-connected operation with large power grid or autonomous operation off-grid. In the micro-grid, most distributed micro-sources are connected to the large power grid through the inverter interface, thus forming a multi-inverter parallel operation environment. Therefore, the stable operation of the multi-inverter...

AI Technical Summary

Problems solved by technology

When the inverters are connected in parallel with non-linear loads, harmonic currents will be generated in the circuit. At this time, the harmonic currents will generate harmonic voltage drops on the larger virtual resistance, which will lead to distortion of the output voltage of the inverters. Increased harmonic circulation among devices and unbalanced power distribution

[0004] The line impedance between the distributed power source and the load will not be completely equal, and the parameters and output impedance of the inverter itself will also be different, resulting in different voltage drops on the line, making it difficult to achieve equal sharing of reactive power, and it is very difficult to A small voltage drop difference will cause a large reactive power error, resulting in inverter overcurrent; when there is a nonlinear load in the microgrid, it will cause harmonic current and voltage generation

These will have an impact on the stability of the microgrid system

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