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Islanding Detection Method of Photovoltaic Grid-connected Inverter

A technology of island detection and inverter, which is applied in the direction of frequency measurement device, single network parallel feeding arrangement, AC network to reduce harmonic/ripple, etc., and can solve problems such as detection method failure

Active Publication Date: 2011-11-30
ALTENERGY POWER SYST
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0011] This method is suitable for most RLC loads, but when the phase difference caused by the active frequency shift is exactly equal to the phase difference of the load RLC circuit during islanding, this detection method fails

Method used

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  • Islanding Detection Method of Photovoltaic Grid-connected Inverter
  • Islanding Detection Method of Photovoltaic Grid-connected Inverter
  • Islanding Detection Method of Photovoltaic Grid-connected Inverter

Examples

Experimental program
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Effect test

Embodiment 1

[0051] Embodiment 1, by sampling the point of common coupling (PCC) voltage, it is judged whether the voltage of the coupling point is at the zero-crossing point. The specific method is to judge whether the following relationship is established. If it is established, it means the zero-crossing point, otherwise it is not.

[0052] V s0 ≥0 and V s2 ≤0(1-1)

[0053] If it is judged by the program that it is not a zero-crossing point, continue to accumulate and calculate the voltage amplitude and period of the coupling point. The specific method is:

[0054] T grid _ c = T s · n V grid ...

example 1

[0076] Example 1. A photovoltaic grid-connected inverter island detection method, using a three-phase AC voltage source and three-phase load to simulate the power grid, the effective value of the phase voltage of the voltage source is 220V, and the frequency is 50Hz, and the photovoltaic inverter is connected to the simulated power grid ( Figure 8 is the grid-connected schematic diagram of the inverter), and the fluctuation of the grid frequency is simulated by adjusting the frequency of the voltage source. When the grid frequency is at f 11 and f 12 When fluctuating within the range, the phase angle between the inverter output current and the grid voltage is 0; when the grid frequency fluctuates beyond this range but is still at f 21 and f 22 When within the range, the phase angle between the inverter output current and the grid voltage is θ, but since the three-phase AC source still exists, the frequency of the coupling point voltage will not be due to the phase angle bet...

example 2

[0077] Example 2. Obtain a load data Z through calculation load , so that it satisfies u grid = i inv × Z load out positive, where u grid is the grid phase voltage, Z load is the phase load i inv , is the output current of the inverter. Other experimental conditions are the same as in Example 1, and at this time, the frequency of the three-phase voltage source is adjusted to exceed f 11 and f 12 range between, but still within f 21 and f 22 within the range, and then disconnect the three-phase voltage source (simulating the island effect), the voltage frequency at the coupling point will not jump at the moment of disconnection, so the island protection cannot be triggered, but at this time the three-phase voltage source has been disconnected, so the The coupling point voltage cannot have an impact, because there is a phase angle θ between the inverter output current and the coupling point voltage, the inverter output current will force the coupling point voltage frequ...

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Abstract

The invention discloses a method for detecting an island of a photovoltaic grid-connected inverter. The method comprises the following steps of: 1), detecting a voltage frequency at a common coupling point of the inverter and a power grid, wherein when the voltage frequency is between f11 and f12, a phase position of output current of the inverter is the same to that of voltage at the coupling point; and, by modifying the phase position between the output current of the inverter and the voltage at the coupling point, compared with the voltage at the coupling point, the output current is ahead of time in theta degrees (when fgrid is more than f12 and less than f22) or lags in theta degrees (when fgrid is more than f21 and less than f11); and 2), to compensate a dead zone appeared in frequency detection, judging whether an island effect exists by modifying an amplitude value of the output current of the inverter within one power frequency period after every four power frequency periods and recovering the amplitude value of the output current into an original value after the period. According to the method, harmonic waves output by the inverter to the power grid can be effectively reduced; the detection time is short; the calculation method is simple; and the computing resource of a control chip can be saved.

Description

technical field [0001] The invention relates to a photovoltaic grid-connected inverter, in particular to an active island detection method, which can improve the speed of island detection and has the advantage of little impact on the power grid. Background technique [0002] In the 21st century, energy issues have become the top ten issues of common concern in the world. As an important renewable energy source, solar energy has attracted more and more attention, and solar photovoltaic grid-connected power generation has also become one of the important power generation methods. With the continuous development of photovoltaic power generation, the grid-connected power generation mode shows its important value even more. However, the island effect of this power generation mode poses a great threat to the power grid, inverter and human safety. The so-called island effect means that the load of the inverter and the local power grid it supplies is separated from the main power g...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01R23/02H02J3/38H02J3/01
CPCY02E40/40
Inventor 陈敏任政高明智钱照明
Owner ALTENERGY POWER SYST
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