| With the distributed photovoltaic power supply a large number of access to the large increase in low voltage distribution network and photovoltaic permeability of various random disturbance is introduced into the traditional distribution network and the active power distribution network,serious damage to the power quality of the system,the harmonic pollution,power supply voltage instability,three-phase voltage and reactive power imbalance,such as serious problems.In cost volume efficiency consideration,distributed photovoltaic with LCL filter,it has better high frequency current ripple suppression effect,but with the increasing of the grid number,the distribution network into a higher order of LC network,easy to induce resonance distribution network,and the resonant frequency distribution is complex,difficult to detect accurately and in time,to the safe and stable operation of power distribution network.This article first to the single photovoltaic grid inverter resonant process analysis in detail,based on the equivalent model of many sets of photovoltaic inverter parallel system between many sets of parallel inverter was studied between complex resonant inverter and power grid as a coupling relationship,analyzes the power grid impedance and filtering capacitance parameter,parallel inverter stations as well as the system network frame structure change of photovoltaic resonant characteristics,resonant frequency and the influence of the distribution range and so on.Timely and accurate detection and positioning of resonance is of great importance to the development of resonant protection of distribution network,the optimization of network structure and the formulation of resonant suppression strategy.This paper developed a high permeability oriented distributed photovoltaic power quality online monitoring device,distribution network using STM32 MCU as the core,equipped with network communication module,the resonant test PC platform development at the same time,will be part of the complex algorithm of judgment and transferred to PC,through the combination of terminal and the upper machine,complete power harmonic detection analysis.The device cost is significantly lower than the current common DSP core power monitoring device,which ensures the detection performance while taking into account the low cost requirements,and is suitable for large-scale use of distributed photovoltaic power distribution network with high permeability.Due to dispersion of photovoltaic resonance frequency arbitrary and decomposition basis function is difficult to determine,based on measured data monitoring device accurately extract the photovoltaic oscillation mode is a difficult problem,this paper proposes a distributed photovoltaic based on empirical mode decomposition(EMD)resonant rapid detection extraction algorithm,can be completely according to the data itself adaptive decomposition time scale characteristics,effectively overcome the traditional Fourier change,artificial set the basis function of the impact of wavelet decomposition,finally,its validity is verified by the simulation. |
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