Development Of Distributed Photovoltaic Grid Connected Device

With the 13th Five-year national energy planning published.The gravity center of photovoltaic power generation begins to transfer to the distributed photovoltaic power generation.The permeability of distributed PV is getting higher in the distribution network has an increasingly significant impact on the existing protection devices,feeder automation,economic dispatch,power quality and other aspects of the distribution network,which has brought New challenges to the safe and stable operation.The Current focus are how to ensure the safe and stable economic operation of distributed PV,and solve the problems of protection,management and control caused by distributed PV grid connected when distributed PV access in distribution network.In order to reduce the cost of secondary equipment for the common coupling point(PCC)of distributed photovoltaic power plant and distribution network.A distributed photovoltaic grid connected device is developed in this paper according to the relevant standards and technical regulations for distributed grid connected operation of distributed photovoltaic power stations at home and abroad.Main work of this paper includes the following issues:1)research the function requirement and design the system function of distributed photovoltaic grid connected device.2)develop he distributed photovoltaic grid connected device with dual MCU structure based on 1).And the software composition and hardware structure of the device are analyzed in detail.Besides,the function of the device is simulated and tested to verify whether the work of the device meets the requirements of the design and the requirements of the relevant national standard and technical specification.3)The device has passed the function test of the experimental verification center of Power Science Resear-ch Institute of national network.4)the device has applied to the 10KW distributed photovoltaic power station of CSG Science&Technology Co.Ltd which proved that the device can stable operation and meet the requirement of the field operation.Comparing with the traditional devices,the distributed photovoltaic grid connected device developed by this paper has enriched the function and improves the function algorithm.It embodied in five aspects:1)Enrich the protection function:including the direction and compound voltage blocking overcurrent protection,Reverse power protection.zero sequence current protection,overload protection,passive islanding protection.2)Increase the power quality monitoring function.Real-time monitoring for the power quality of distributed PV.such as harmonic,voltage imbalance,voltage deviation and so on.3)Realize communication with inverters and other equipment and distribution network based on the conversion of multiple communication modes and protocols.4)design the different-frequency grid-connection algorithm based on catching closing point based on phase-angle difference prediction of sampling point to support for the distributed PV seamless connected to the distribution network.5)All-phase discrete Fourier transform(DFT)algorithm with adaptive sampling sequence length proposed in this paper to measure the frequency,amplitude and phase angle of the voltage at the point of common coupling(PCC)of Distributed PV station.And according to the principle of double-line correcting spectrum method,the calculation formula of frequency,amplitude and phase angle of fundamental signal is deduced based on Hanning double-window all-phase DFT.