Abstract: The method includes: determining required virtual inertia based on a frequency change rate monitored at a grid connection point of a photovoltaic grid-connected system; obtaining values of indexes that affect virtual inertia provided by each virtual synchronous generator (VSG) control unit in a photovoltaic cluster of the photovoltaic grid-connected system; determining, by using a predetermined function equation, a function value corresponding to each index; and determining an allocation proportion of the required virtual inertia in each VSG control unit based on the function value corresponding to each index. A problem of difficult conversion between a plurality of kinds of performance during operation of a power system is resolved, the frequency change rate is suppressed to a certain extent, and a stable state is recovered quickly.

Abstract: The method includes: determining required virtual inertia based on a frequency change rate monitored at a grid connection point of a photovoltaic grid-connected system; obtaining values of indexes that affect virtual inertia provided by each virtual synchronous generator (VSG) control unit in a photovoltaic cluster of the photovoltaic grid-connected system; determining, by using a predetermined function equation, a function value corresponding to each index; and determining an allocation proportion of the required virtual inertia in each VSG control unit based on the function value corresponding to each index. A problem of difficult conversion between a plurality of kinds of performance during operation of a power system is resolved, the frequency change rate is suppressed to a certain extent, and a stable state is recovered quickly.

Abstract: A magnetic resonance angiography method includes: in a plurality of first repeated collecting periods, a first echo signal set is formed by flow-compensated first echo signals and a second echo signal set is formed by flow-compensated second echo signals; in a plurality of second repeated collecting periods, a third echo signal set is formed by flow-compensated third echo signals and a fourth echo signal set is formed by flow-dephased fourth echo signals; a venous blood vessel image is reconstructed according to the second echo signal set; an arteriovenous blood vessel image is obtained according to the first echo signal set, the third echo signal set and the fourth echo signal set; and an arterial blood vessel image is obtained according to the venous blood vessel image and the arteriovenous blood vessel image.