Virtual synchronous machine low voltage ride through comprehensive control method

Abstract

The invention relates to a virtual synchronous machine low-voltage ride-through comprehensive control method. When a voltage drop fault occurs in a power grid, a positive-sequence d-axis component of the voltage of the power grid is fed forward to a VSG reactive power excitation voltage regulation equation of a differential-free link, so that the output voltage of the VSG can quickly follow the drop of the amplitude of the voltage of the power grid; the VSG output reactive power instruction value is increased according to the voltage drop depth, and meanwhile, the VSG output active power instruction value is reduced to avoid VSG steady-state output overcurrent; when the VSG output inductive current exceeds a set threshold value, a virtual resistor is input to suppress transient overcurrent; and when three-phase voltage asymmetric drop occurs in a power grid, VSG three-phase output current balance, VSG output active power frequency doubling pulsation suppression and VSG output reactive power frequency doubling pulsation suppression are realized by setting current instruction compensation values of different positive and negative sequence d-axis and q-axis current loops. According to the method, the low voltage ride-through capability of the VSG is improved, and the output electric energy quality of the VSG during the voltage fault of the power grid is improved.

Description

technical field [0001] The invention belongs to the technical field of grid-connected inverter control, and in particular relates to a low-voltage ride-through comprehensive control method for a virtual synchronous machine. Background technique [0002] As the link between distributed energy sources and distribution grids, traditional grid-connected inverters are composed of power electronic devices with fast response and almost no inertia. With the increasing penetration of distributed power sources, more and more inverters The integration of the inverter into the large power grid will greatly reduce the equivalent total damping and equivalent total inertia provided by the traditional generator in the large power grid, which limits the development of new energy to a certain extent. For this reason, some scholars have proposed the concept of virtual synchronous generator (VSG, Virtual synchronous generator). As a control method, VSG simulates the mathematical model of synchr...

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Problems solved by technology

[0003] When a voltage drop fault occurs in the distribution network, the traditional grid-connected inverter is equivalent to a current source after being connected to the grid, so it can directly limit the current command value to ensure that the inverter will not be disconnected or damaged due to overcurrent , so the current-type VSG is easier to control low voltage ride-through, because the penetration rate of distributed energy will continue to increase, and the voltage-type VSG can provide stable voltage and frequency in the case of off-grid, so the application of the voltage-type VSG will be more Widely, the voltage-type VSG is connected to the grid because the equivalent model of the grid is two voltage sources with a small connection impedance in parallel, so the voltage-type VSG low-voltage ride-through technology cannot directly refer to the traditional inverter low-voltage ride-through technology

At present, there are two main categories of VSG low-voltage ride-through technology. The first category is the smooth switching of voltage source control and current source control: switching VSG control to current source control during grid voltage faults; the second category is grid faults. The VSG is still controlled as a voltage source during the period; the first category of control changes the properties of the VSG during the grid voltage fault; the second category of control currently mostly only discusses grid voltage symmetry or asymmetry faults, and lacks a comprehensive , complete VSG low voltage ride through control scheme

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