A low-voltage ride-through control method for grid-connected inverters based on control mode switching

Abstract

The invention discloses a low-voltage ride-through control method for a grid-connected inverter based on control mode switching. The method comprises the following steps: during normal operation of the grid, a grid-connected inverter adopts a VSG control mode, the d-axis and q-axis positive and negative sequence components of the grid voltage are acquired and the phase angle of three-phase modulated wave is output in a PR current control mode, and the phase angle is used to follow the grid-connected inverter in order to output a voltage phase angle; when the grid fails, the given values of the d-axis and q-axis positive and negative sequence components of the current are calculated, the given value of current under a static coordinate system is obtained through inverse rotation transformation, a PR current controller generates a voltage signal, and the grid-connected inverter is quickly switched from the VSG control mode to a PR current control mode; and at the end of failure, the grid-connected inverter is switched back to the VSG control mode from the PR current control mode at an appropriate time. A grid-connected inverter can be smoothly switched between control modes. The grid-connection impact current can be limited, and reactive power can be provided for the grid. Thus, low-voltage ride-through of a virtual synchronous generator under grid failure is realized.

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 control method of a grid-connected inverter based on control mode switching. Background technique [0002] Most of the current research on grid-connected inverters is under the condition of normal grid voltage. Few articles mention the operation of grid-connected inverters under grid faults. Low-voltage ride-through, using the current as a state follower to achieve smooth switching of control modes, using traditional low-voltage ride-through to achieve current limiting and reactive power support during grid failures. Although this method can achieve low-voltage ride-through of VSG, but Its method is complicated. A current loop is also added to enhance the VSG inertia and low voltage ride-through ability through the power angle. The analysis of this scheme is more comprehensive, and the impact of the current during th...

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Problems solved by technology

[0002] Most of the current research on grid-connected inverters is under the condition of normal grid voltage. Few articles mention the operation of grid-connected inverters under grid faults. Low-voltage ride-through, using the current as a state follower to achieve smooth switching of control modes, using the traditional low-voltage ride-through to achieve current limiting and reactive power support during grid failures. Although this method can achieve low-voltage ride-through of VSG, but Its method is complex

A current loop is also added to enhance the VSG inertia and low-voltage ride-through capability through the power angle. The analysis of this scheme is more comprehensive, and the impact of the current during the fault period can be verified through simulation. However, this method has many parameters and is not easy in engineering. accomplish

Through virtual resistance technology and phasor current limiting technology, the fault current transient state and steady state of VSG are respectively limited, which can effectively guarantee the safe and reliable operation of the unit when VSG has a symmetrical fault. However, this method is currently Difficult to implement under asymmetric faults

[0003] To sum up, the grid-connected inverter controlled by VSG technology lacks the ability to limit current and provide reactive power support when the grid fails, that is, the low voltage ride-through capability is low due to the control characteristics of VSG technology itself.

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