Study Of Islanding Detection Technology Of High Frequency Isolated Grid-Connected PV Inverter

Solar energy is one of the cleanest sources of energy in the world, and inexhaustible,which received wide attention with its unique advantages. However, as grid-connected PVinstallations widely used in power gerneration systems, the incidence rate of the islandingeffect is increasing and the dangers caused is not ignored. Therefore, resolving island issue isespecially important. Currently, for some anti-landing schemes at home and aboard, there aresome problems, for example, a large non-detection zone, a long time to detection islangdingand so on. Under this background, with grid-connected photovoltaic inverter as a researchobject, the anti-islanding, a key technology, was deeply studied and researched in this paper.Based on detailed analysis of islanding detection methods, passive detection methodwhich combines the active frequency shift method and the active phase shift method wasapplied to abtain the minimum blind zone.According to anti-islanding schemes used, thehardware and software control system of the grid-connected inverter based on DSP controlwere designed systematically.The NDZ is regarded as performance index to evaluate anti-islanding methods’effectiveness in this paper. Power non-match coordinate system△P×△Q was to describethe non-detection zone of passive islanding; load parameters coordinate systemL×C_normand load characteristic parameters coordinate systemQ_f×f₀was to describe thenon-detection zone of the active frequency shift method and the active phase shift method,and through a comparative analysis, the latter could more clearly reflect the effect of loadresistance on non-detection zone.By analyzing the control strategies of grid-connected, the grid-connected control ofvoltage source input and current source output with double closed-loop control method wasselected as the system control strategy, in order to ensure getting the output sine wave ofstable and high quality, and own the same grid voltage and frequency.A grid-connected experiment platform was established. The experiment results showedthat the control strategies of grid-connected inverter could effectively control output current waveform. And the experiment results showed that non-detection zone area description theoryanalysis method was reasonable and feasibility. Meanwhile, the anti-Islanding scheme’seffectiveness and rapidity used in this paper are verified.