The invention discloses a method for preventing
overvoltage of the neutral point of a main
transformer in high-permeability photovoltaic access. The method is based on a traditional photovoltaic grid-connected decoupling double closed-
loop control method, and can be divided into 3 states: in a state 1, the
voltage of the neutral point of the main
transformer is over the rated
voltage but the
overvoltage is within an allowable range, and a traditional grid-connected control method is adopted; in a state 2, the
voltage of the neutral point of the main
transformer rises to the phase voltage and does not reach the breakdown condition, the voltage and current of the
grid connection point and the voltage of the neutral point of the main transformer are collected, the photovoltaic grid connectionphase angle is adjusted to limit the voltage of the neutral point of the main transformer within a safety range, and active
power output of photovoltaic
grid connection is ensured; and in a state 3,the voltage of the neutral point of the main transformer is broken down, the photovoltaic power supply operates in an off-grid mode, the voltage of the neutral point of the main transformer decreasessubstantially, and the
photovoltaic system is connected with an
energy storage device through a
DC converter. By changing the photovoltaic grid-connected control strategy and adding a supporting
energy storage device, the problem that transformer damage is caused due to too
high voltage of the neutral point of the main transformer during operation of a high-permeability photovoltaic
access grid infault can be solved.