Anti-islanding control algorithm and system employing active frequency drift with voltage frequency absolute value positive feedback

Abstract

The invention discloses an anti-islanding control algorithm and system employing an active frequency drift with voltage frequency absolute value positive feedback. The method comprises the following steps: (S1) detecting a common coupling point voltage frequency f and an amplitude I of common coupling point current and calculating inverter output current i(<omega>t); (S2) judging whether the condition that the common coupling point voltage frequency f is less than the maximal frequency f<max> or greater than the minimal frequency f<min> is established or not, if so, executing the step (S5), if not, executing the step (S3); (S3) adding disturbance to grid-connected output current of an inverter by the inverter output current i(<omega>t) calculated in the step (S1) in each cycle, and detecting the common coupling point voltage frequency f' after the disturbance is added; (S4) judging whether the f' is greater than the maximal frequency f<max> or not, if so, entering the step (S5), or else, returning to the step (S1); and (S5) adopting an anti-islanding action. According to the method, the problems of relatively large non-detection zone and total harmonic coefficient (THD) of an active frequency drift method (AFD) are overcome; and the islanding phenomenon can be quickly detected.

Description

technical field [0001] The invention belongs to the field of anti-islanding protection for distributed grid-connected power generation, and in particular relates to an active frequency offset anti-islanding control algorithm and system with positive feedback of absolute value of voltage and frequency. Background technique [0002] The island phenomenon means that when the power grid loses voltage, the photovoltaic system still maintains the state of continuing to supply power to a certain part of the power grid, thus forming an uncontrollable power supply network. Specifically, when the power supply of the power company trips due to a fault or a power outage for maintenance (such as a large power grid outage), the distributed grid-connected power generation system fails to detect the power outage in time and cuts itself off from the power supply network, forming a grid-connected system. The generation system and local loads form an island of self-sufficiency that the utility...

AI Technical Summary

Problems solved by technology

[0004] 1) Endanger the life safety of electric maintenance personnel;

[0005] 2) Affect the protection switch action program on the power distribution system;

[0006] 3) The unstable nature of the power supply voltage and frequency in the island area will cause damage to the electrical equipment;

[0007] 4) When the power supply is restored, the voltage phase out of synchronization will generate a surge current, which may cause tripping again or cause damage to the photovoltaic system, load and power supply system

The national standard requires that the total harmonic coefficient THD of the output current of the photovoltaic grid-connected inverter shall not be greater than 5%. Therefore, according to the introduction of the literature, the maximum value of the truncation coefficient is c f =0.05, too large truncation coefficient will lead to excessive THD and affect power quality, but too small truncation coefficient will make it difficult to detect the anti-islanding phenomenon, so there is a large detection blind area

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