| With the sharp increase in world energy demand and the increase in electricity load,the environmental degradation caused by primary energy generation is becoming more and more serious.In recent years,distributed photovoltaic grid-connected power generation has developed rapidly.However,the islanding effect in the grid-connected system is one of the main phenomena that mainly endangers the safe and stable operation of the power system.It will bring hidden dangers to the safe operation of power equipment and endanger the personal safety of the relevant staff.Therefore,it is a key technical problem that needs to be solved in the photovoltaic inverter grid-connected power generation system.At present,the detection methods for the island effect are mainly divided into two types: remote detection method and local detection method,and the application object of the detection method is mainly directed to a single inverter grid-connected power generation system.Therefore,most of the existing island detection methods have goo d detection effects for single inverter systems.But at the same time,with the ra pid development of the economy,the demand for electricity has risen sharply,and the single inverter grid-connected power generation system is difficult to meet the power su pply needs.As a multi-inverter grid-connected system put into use,how does the existing active island detection method improve the dilution effect and the interference of power quality and how the passive island detection method can reduce the detection dead zone and accurately and quickly multi-inverter Distributed photovoltaic grid-connected power generation system for reliable detection,at the same time,how to propose new detection methods to improve the effectiveness of detection has important pract ical significance.Taking the single-phase photovoltaic grid-connected system as an example,the research work on the islanding detection technology of multi-inverter photovoltaic grid-connected power generation system is mainly carried out from the follow ing aspects:Firstly,the structure of photovoltaic power generation system is analyzed and the mechanism of islanding effect is analyzed.The equivalent circuit model of islanding effect is established.The expression of power relationship is derived and the relationship between power,frequency and voltage when the island effect occurs is studied.At the same time,the remote and local two types of island detection methods are studied,and their detection principles and their respective advantages and disadvantages are analyzed.The four evaluation principles for evaluating the effectiveness of the island detection method are analyzed.Secondly,the active frequency offset method,the active frequency offset method with positive feedback and the sliding mode frequency offset method are combined and applied to the islanding detection in the multi-inverter system to study the dilution effect,and the above three methods are respectively the detection blind zone and shape were analyzed,and the above studies were simulated and analyzed.In addition,the dilution effect of active frequency offset method with positive feedback in multi-inverter island detection,improve initial chopping coefficient and positive feedback coefficient and algorithm optimization,the dilution phenomenon was improved and the simulation was verified on the basis of theoretical analysis.Finally,combined with the passive detection method,there is no dilution effect and interference power quality characteristics in the multi-inverter island detection.Based on the wavelet signal analysis,the passive island detection method based on Morlet complex wavelet transform on multi-inverter is studied.The problem of discontinuous phase wavelet coefficients is improved.The extracted complex wavelet transform coefficients are improved.Based on the theoretical analysis,the simulation model is established to verify,and the detection performance of Morlet wavelet is verified by comparison with real wavelet with high application rate. |
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