Control system and method for low-voltage and zero-voltage ride through of photovoltaic grid-connected inverter

Abstract

The invention discloses a control system and method for low-voltage and zero-voltage ride through of a photovoltaic grid-connected inverter. A bi-synchronous rotating coordinate system is adopted to independently control positive sequence current and negative sequence current under a steady state; positive sequence voltage and negative sequence voltage dq components of power network voltage are taken as feedforward for a regulator; when low-voltage and zero-voltage ride through occurs, the control for the negative sequence current is switched into an open loop control mode; a direct feedforward control policy is adopted for the power network voltage; a feedforward control signal of the power network voltage is switched to adopt un-decomposed power network voltage dq components to replace the positive sequence voltage and negative sequence voltage dq components to be used as the voltage given feedforward; the feedforward signal is combined with the output of dq current controllers separately; and after the feedforward signal is subjected to dq / abc inverse conversion, the feedforward signal passes through a (pulse width modulation) PWM control module to be output to the inverter for controlling the inverter. According to the control system and method, the problem that the inverter is out of the power network caused by an overcurrent protection action frequently appeared in a voltage drop process when a conventional control policy is adopted is solved; and high balance of three-phase grid-connected current output by the inverter under the steady state can be ensured.

Description

technical field [0001] The invention belongs to the technical field of photovoltaic power generation, and in particular relates to a control method for low voltage and zero voltage ride-through of a three-phase photovoltaic grid-connected inverter. Background technique [0002] In the photovoltaic power generation system, when the penetration rate of the photovoltaic power station is high or the output is increased, when the power grid failure or disturbance causes the grid voltage to drop sharply, the failure of the photovoltaic power station will deteriorate the operation status of the entire power grid and affect the safety and stability of the power grid. Operation, the current standard requires photovoltaic power plants to have low voltage and zero voltage ride through functions (LVRT / ZVRT). [0003] When the grid voltage drops asymmetrically, a large negative sequence component will appear in the grid voltage. In view of the situation that the power grid voltage drop ...

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Problems solved by technology

[0005] The purpose of the present invention is to provide a low-voltage and zero-voltage ride-through control system and method for photovoltaic grid-connected inverters, which can solve the problems caused by conventional control strategies used in existing three-phase photovoltaic grid-connected inverters during voltage drops. The problem of making the inverter over-current protection action and disconnecting from the grid can ensure a good balance of the three-phase grid-connected current output by the inverter during steady-state operation

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