Multi-objective optimal control method based on virtual synchronous generator when grid voltage is unbalanced

Abstract

The invention relates to a multi-target optimization control method based on a virtual synchronous generator during power grid voltage imbalance. According to the method, a balance current VSG method is firstly utilized to acquire a reference current instruction value in a dq coordinate system; a current instruction value in the grid connected inverter dq coordinate system is acquired through the reference current instruction value in combination with an imbalance power grid voltage parameter when three targets including current three-phase balance, and active or reactive power no fluctuation are realized; a correction value of the three targets is acquired according to relationships between the current instruction value and the reference current instruction value; an optimization coefficient is introduced, and unification of an output current instruction correction value parameter of each target is carried out to acquire an output current instruction correction value of multi-target optimization; the current instruction value is corrected according to the correction value; the current after correction in the dp coordinate system is tracked, through adjusting the optimization coefficient, output current three-phase balance is realized, multi-target control on constant output active or reactive power is realized, and optimum grid connected inverter output performance is realized.

Description

technical field [0001] The invention belongs to the technical field of distributed power generation, and relates to a multi-objective optimal control method for grid voltage. Background technique [0002] With the increase of the installed capacity of distributed inverters in the power system, the proportion of installed capacity of synchronous generators has relatively decreased, resulting in a corresponding decrease in the rotating reserve capacity and moment of inertia in the power system, which poses a serious challenge to the safe and stable operation of the power grid. Therefore, it is required that the grid-connected distributed inverter power supply can not only provide energy to the grid, but also have a certain supporting capacity of the grid voltage amplitude and frequency to enhance the stability of the grid operation. VSG control technology, by simulating the working principle of synchronous generators, active power frequency regulation and reactive power voltag...

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Problems solved by technology

Among them, the current-type VSG control cannot provide voltage and frequency support for the power system, and is only suitable for grid-connected operation in a grid environment with a low penetration rate of distributed power; the voltage-type VSG is suitable for grid-connected operation in a weak grid environment with a high penetration rate Runtime and applications in island mode

The above research on VSG is based on ideal grid conditions, but transient and steady-state faults such as voltage drop, three-phase unbalance, and harmonic distortion often occur in the actual grid. Based on traditional VSG control, the output current of the inverter will be three If the phase is unbalanced, the output active and reactive power will fluctuate twice the fundamental frequency of the power grid at the same time; after improving the traditional VSG control technology, it is still impossible to achieve multi-objective optimization such as output current balance and no fluctuation of active or reactive power. purpose of control

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