Research On Strategy Of Photovoltaic Power Reserve Control Participating In Grid Frequency Response

In recent years,a large number of photovoltaic power generation has been integrated into the power grid,replacing some conventional synchronous generator sets.Photovoltaic power generation usually runs in the maximum power point tracking mode and is integrated into the grid through a power electronic converter,and cannot provide inertia and participate in grid frequency regulation.The increase in the penetration of photovoltaic power generation reduces the frequency regulation ability and the inertial response capability of the power system.The participation of photovoltaic power generation in the frequency control of the grid is one of the ways to alleviate this problem.This paper mainly studies the strategy of photovoltaic power reserve control participating in grid frequency regulation.Main works are as follows:A photovoltaic power reserve control method based on maximum power estimation with a single sampling point is designed.The ratio of the photovoltaic current at the target power reserve point to the short-circuit current is defined as a new variable.The relationship between this variable and the target power reserve ratio is almost unaffected by irradiance and temperature.Based on this,the short-circuit current can be estimated according to the current at the current sampling point and the target power reserve ratio,and then the maximum power can be roughly estimated.With the progress of the power reserve control,the photovoltaic output current will automatically approach the current at the given target power reserve point,and the maximum power estimation value will gradually converge to an accurate value.Based on the maximum power estimation method,a variable step voltage tracking strategy is designed to track the target power reserve ratio and alleviate the power fluctuation problem at the target operating point.A two-stage photovoltaic power generation system model is built,and various target power reserve ratio and irradiance conditions are set up to verify the tracking effectiveness of the proposed photovoltaic power reserve control.A DC virtual synchronous generator control strategy applied to the two-stage photovoltaic power generation system is designed.The proposed DC virtual synchronous generator includes a virtual governor block,a maximum power estimation block,a virtual rotor motion equation block,an electromagnetic power calculation block and a photovoltaic voltage tracking block.The virtual governor block adjusts the target power reserve ratio according to the frequency deviation,and then adjusts the size of the mechanical power;According to the virtual rotor motion equation block,the angular frequency of the virtual electromotive force changes,which causes the power angle to change,and the electromagnetic power reference value generated by electromagnetic power calculation block will change;The photovoltaic voltage tracking block adjusts the output power of the photovoltaic array to make it track the electromagnetic power reference value.Therefore,when the proposed control strategy is adopted,the photovoltaic system can provide spontaneous inertia and frequency modulation response similar to a synchronous generator without the need for a phase-locked loop to measure frequency.An independent microgrid simulation model composed of a photovoltaic array and a diesel generator is built to verify the effectiveness of the proposed control strategy,and the influence of the virtual moment of inertia on the inertial response is analyzed.An IEEE14 bus high photovoltaic penetration independent microgrid simulation model is built.Various irradiance and load change scenarios are set,and the proposed DC virtual synchronous generator control is compared with the conventional photovoltaic power reserve control participating in frequency regulation control strategy.The effectiveness and superiority of the proposed control strategy to participate in system frequency adjustment under the high photovoltaic penetration are verified by simulation,and the frequency response performance of the system under different photovoltaic penetration scenarios is analyzed.