| In the traditional power system,the synchronous generator set has the characteristics of damping and inertia,which can guarantee the stability of the power system.With the increasing penetration of photovoltaic and other renewable energy generation,the proportion of installed synchronous generators has decreased correspondingly.Due to the lack of inertia,damping and voltage regulation and frequency modulation capabilities of photovoltaic and other renewable energy sources with inverter and other power electronic conversion devices as interfaces,the stability of photovoltaic grid-connected system is difficult to sustain.The control mode of PV virtual synchronous generator under the application scenario of high PV permeability should be changed as soon as possible so that it can participate in the dispatching,operation and control of power grid more effectively.Firstly,the structure and characteristics of the photovoltaic power generation system are introduced,and the control structure of each part of the two-stage common-direct current bus-type photovoltaic virtual synchronous generator applied in this paper is introduced in detail.Secondly,photovoltaic units in the MPPT tracking mode are difficult to respond to the fluctuation of power grid frequency,and there is no spare capacity to support the power grid frequency control.Although active standby control can enable the photovoltaic system to participate in primary frequency modulation,it needs to abandon PV under normal operation,which reduces the power generation benefit and has the problem of power regulation depth,and reduces the frequency regulation ability under the disturbance of frequency increase.Considering the fluctuation characteristics of the source and load of the photovoltaic system and taking frequency regulation as the comprehensive objective,a photovoltaic prima ry frequency modulation strategy of variable power tracking and energy storage coordinated control was proposed to realize the complementarity of the maximum power tracking control and active standby control.The proposed control strategy realizes the up unilateral control by the variable power tracking control photovoltaic Boost circuit under the disturbance of increasing frequency,and the down unilateral control by the bidirectional DC/DC converter of the energy storage device under the disturbance of decreasing frequency.Thus,the capacity configuration of the energy storage capacity under the disturbance of frequency rise is eliminated and the cost of additional energy storage operation is reduced.The effectiveness of the proposed control strategy under source and charge fluctuations is verified by MATLAB/Simulink simulation platform under multiple working conditions.The results show that the generation efficiency is close to the MPPT mode and significantly higher than the active standby mode under the random fluctuation of photovoltaic and load.Finally,for the problem of energy storage configuration in a photovoltaic grid with high permeability,the influence of photovoltaic power fluctuation curve on the capacity allocation of the energy storage device in a short time scale was studied.According to the constraint of the photovoltaic system on the climbing rate,the capacity of the energy storage device needed to smooth the photovoltaic fluctuation was determined and optimized.At the same time,considering the influence of the system frequency change on the capacity of the system energy storage device,the capacity of the energy storage unit is optimized in the corresponding adjustment time of the first frequency modulation 30 s,so as to reduce the cost of additional energy storage operation.At the same time,the capacity of the energy storage unit is optimized within the corresponding regulation time,and the coordination mechanism of optical storage is improved.Through MATLAB/Simulink simulation pl atform,the rationality of energy storage configuration under the fluctuation of source and charge is verified. |
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