Virtual synchronous generator low-voltage ride-through method and system based on virtual voltage drop

Abstract

The invention discloses a virtual synchronous generator low-voltage ride-through method and system based on virtual voltage drop. The method comprises the steps of: enabling a power control loop to be converted into a freezing mode from a conventional virtual synchronous mode when a power grid voltage drops, guaranteeing the stability of a system, through adding virtual fault voltage drop, enabling modulation waves to be equal to a difference value between the internal potential and the virtual fault voltage drop, suppressing an overcurrent when the fault occurs, and outputting reactive power meeting the national standard requirement by an inverter, thereby facilitating the recovery of the power grid voltage; and when the voltage returns to normal, converting the power control loop into a recovery mode from the freezing mode, and in order to suppress transient current during fault recovery, adding virtual recovery voltage drop, so that the modulation waves are equal to a difference value between the internal potential and the virtual recovery voltage drop. The strategy is suitable for a control structure with or without a current inner loop, and low voltage ride through of a virtual synchronous generator can be realized without mode switching.

Description

technical field [0001] The invention belongs to the technical field of grid-connected inverter control, and in particular relates to a virtual synchronous machine low-voltage ride-through method and system based on a virtual voltage drop. Background technique [0002] With the extensive use of new energy sources such as wind energy and solar energy, power electronic devices are used more and more widely in power systems as the interface connecting the grid and distributed power sources. Virtual synchronous generator (virtual synchronous generator, VSG) is a control algorithm for grid-connected inverters. By introducing the rotor motion equation and increasing the inertia and damping of the system, it can provide voltage and frequency support for the grid and avoid rapid fluctuations in loads. The frequency is unstable, and it participates in the voltage and frequency regulation of the power grid at the same time, so that the power grid has high stability. Since the VSG cont...

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Problems solved by technology

[0003] One way for VSG to realize LVRT is to switch from the normal VSG control mode to the traditional inverter control mode during a fault, but this method depends on the stability of the grid voltage, which is not conducive to the operation in a weak grid

Some literature proposes that by changing the current command value of the current loop, the introduction of the current loop in the VSG control algorithm may cause low-frequency oscillation and affect the stability of the system

There are also literatures that use virtual resistance and phasor current limiting methods to limit the transient impact current and steady-state current of faults, and VSG provides certain reactive power support to the grid. However, the active power and reactive power of this strategy are If the adjustment time is too long, there will be vibration when the fault is cleared

The above literature is only considered from a single aspect of current limitation, system stability, etc., or the LVRT process has not been fully analyzed

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