The Basic Problem of Islanding Effect

From a physical point of view, solar power batteries have a characteristic, so the surface of the material and the recovery of the internal minority of its output characteristics of a certain impact. The single-diode model given here ignores the recovery motion of the minority carrier in the depletion layer, but only the recovery current due to the motion of the minority carrier in the region. In fact, the double-diode model is derived from a single-diode model, which differs from the single-diode model in that the double-diode model introduces the leakage current. Divided into 'and' two parts, respectively, by the equivalent of two diodes. The first diode in the dual-diode model is used to equalize the recovery current due to minority sub-motion between the zones determined by the large forward bias voltage, which is the same as the equivalent effect of the diodes in the single-diode model ; And the second diode added in the dual-diode model is used to restore the motion of minority carriers in the equivalent depletion layer due to energy excitations, so that the solar power batteriesmodel can more accurately describe the leakage current characteristics of photovoltaic cells ^ 8 ^ 1. Obviously, when the photovoltaic array is partially blocked, the relative leakage current characteristics of the solar power batteries will directly affect the output characteristics of the photovoltaic array, at this time, the advantages of the dual-diode model of photovoltaic cells will be reflected.

When the PV arrays are connected in series, the local maximum power point will appear in the curve of the PV array. In this case, if the PV array curve based on the single peak pattern is used, Therefore, it is necessary to study the method for the local maximum power point. Here are two basic methods.

Assuming that the system is running at a certain voltage point, the system should increase the disturbance voltage according to the previous judgment. If the irradiance decreases, the output power of the operating point corresponding to the voltage may be smaller than the output of the original operating point Power, that is, at this time the system will misjudge the direction of the voltage disturbance error, so that the operating point in the work away from the maximum power point. If the irradiance continues to drop, there may be continuous misjudgment of the control system, so that the operating voltage constantly moving to the left, for the grid system, this misjudgment on the one hand will increase the power loss, on the other hand Due to the DC side voltage drop and make the grid current out of control,

However, the efficiency of the grid-connected inverter itself is only the static conversion efficiency of the PV system energy. With the application of grid-connected photovoltaic power generation, it has been found that a single static conversion efficiency index is difficult to fully describe the conversion efficiency of grid-connected inverter. This is because the grid-connected inverter not only completes the DC-to-AC conversion and grid-connected control, but also controls whether or not the PV cell is running and whether the PV cell is running will directly affect the conversion efficiency of the solar power generator system. The tracking efficiency, and how to measure the efficiency of fair and accurate is an important issue in the research of solar power generator.

Test Steps for Simulated Intermittent Cloud Closures> A fast ramp is designed to simulate the effect of accumulated clouds moving from the sun. The purpose of this test is to determine how quickly the device under test reacts to changes in the output power of the array It is important to note that since the temperature does not change and the irradiance-voltage variations for the three array types are nearly identical, there is little change in the shape of the curve.

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