| Under the background of "30·60"dual-carbon target,new energy has become a popular research object in the power industry.However,the increasing proportion of photovoltaic,fan and other intermittent energy in the power grid makes the power grid present low inertia,weak stability and other characteristics,which are not conducive to the stable operation of the power grid.At present,problems such as low inertia and weak stability of high permeability source containing power system urgently need to be solved.The new energy source adopts the new grid-connection mode of Motor-Generator Pair(MGP),which not only makes the new energy station have the excellent attributes of synchronous motor,but also improves the inertia supporting capacity of the power grid.And effectively improve the stability of the power grid,the main work of this paper and solve the problems are as follows:(1)The power transmission aspect of MGP driven by a single inverter is relatively mature.Therefore,taking MGP driven by a single inverter as an example,the frequency modulation capability of MGP grid-connected new energy station is studied.However,it is found that although MGP can provide a large moment of inertia for the power grid,which is conducive to the stable operation of the power grid,its frequency modulation capability is not as good as that of traditional thermal power units.Based on this,this paper proposes to introduce an energy storage system into the grid-connected mode of MGP for new energy.Through the combination of MGP and energy storage,the frequency modulation capability of the new energy station can achieve the effect of traditional thermal power units.In addition,the control strategy of MGP and energy storage jointly participating in the frequency modulation of the power grid is proposed.The control strategy calls the rotor kinetic energy stored by the synchronous motor in MGP and the stationary energy in the battery to suppress the frequency change of the system when the system frequency changes.(2)Considering that grid-connection of MGP driven in parallel by multiple inverters is the main trend in the future,this paper conducts theoretical and simulation research on i_d=0 vector control of MGP driven in parallel by inverters at present,and finds that when MGP output is large,The output power factor of the inverter connected to the MGP input side may be too low,which is difficult to ensure the active power transmission efficiency of new energy through the MGP grid-connected.In addition,the current multi-inverter parallel drive MGP mainly focuses on the same capacity and output of multi-inverter,which is inconsistent with the engineering practice.Based on this,this paper proposes the Unity Power Factor(UPF)control strategy of multi-inverter parallel drive MGP.This strategy ensures the active power transmission efficiency of MGP in all working conditions of the new energy station by calculating the stator d and q axis current of the synchronous motor with all active power output and the established dynamic current distribution coefficient k_i.(3)The combined frequency modulation capability of MGP and energy storage is simulated and verified by building a three-machine nine-node simulation model.The results show that the combined system of MGP and energy storage can effectively enhance the frequency support capability of the system,which is conducive to the stable operation of the power grid.The simulation verification is carried out in a simulation model of three inverters driving MGP in parallel.The results show that the proposed UPF control mode can ensure the active power transmission efficiency of MGP under all operating conditions in new energy stations. |
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