Theoretical And Experimental Researches For The Sinusoidal Low-frequency Phase Perturbation Islanding Detection Method

Reviewing the100-year developmental history of industry，we can see clearly that theentire industry mainly consume fossil energy. Coal and oil energy as the carrier, greatlyliberating the productive forces, promote the industrialization all over the world. Reducingincreasingly at the same time, they have sounded an alarm to humans. Humans are facing aserious energy crisis. We have to find new alternative energy as soon as possible. Theenergy problem has become a social problem related to the national economy and nationalsecurity.This paper first introduces the research background and significance of photovoltaictechnology. Then the article explains the islanding, analyzing the causes and effects.Through analyzing the passive and active islanding detection methods, we can know thatmost islanding detection methods have none-detection zone. To solve this problem, a newactive islanding detection method is proposed, which is called sinusoidal low-frequencycurrent phase perturbation method.This paper introduces the islanding detection principle, discussing the power factorand THD. According to the theoretical analysis, the method can realize islanding detectionwithout none-detection zone for all the loads whose quality factor Q are less than or equalto2.5load, and satisfy the requirement of national standard when the parameters arechosen properly.The experimental platform of the study is a single-phase photovoltaic grid-connectedinverter. The system structure and the operating principle of the main circuit are illustrated.The generation of current instruction and the design of the close-loop current controlsystem are also introduced. In the design of close-loop current control, the typical Ⅱmodel is used, with which the PI regulator can perform stable work. The system controlsection is digitally implemented by ARM. It included software phase locking, PWM generation module, the digital realization of PI regulator and so on.Finally, some experiments are studied, including open loop experiment, short-circuitexperiment, grid-connected experiment and islanding detection experiment. The islandingdetection experiment result verified the feasibility of the newly proposed method.