Three-ring controller of LCL type grid-connected inverter and parameter design method thereof

Abstract

The invention provides a three-ring controller of an LCL type grid-connected inverter and a parameter design method of the three-ring controller. The controller comprises an inverter, an inverter side current detection module, an LCL filter, a filter capacitor voltage detection module, a grid-connected side current detection module, a grid-connected point voltage detection module, a coordinate conversion module, a phase-locked loop module, an SVPWM module, an inner loop inverter side current control module, a middle loop capacitor voltage control module and an outer loop power grid current control module. According to the method, firstly, a mathematical model of an LCL grid-connected inverter is established, the three-ring controller is constructed, an equivalent admittance model of the inverter is calculated, and the stability of the system is improved by taking the fact that admittance has no non-passive area in a switching frequency as a general target. According to the method, the grid impedance factor containing capacitance is considered in the grid-connected control of the photovoltaic power station, a theoretical basis can be provided for the dense access stability analysis of the inverter under the new energy station, and meanwhile, important guidance is provided for the design of the grid-connected inverter under the weak grid.

Description

technical field [0001] The invention relates to the field of current control of grid-connected inverters, in particular to a parameter design method for a three-loop controller of an LCL type grid-connected inverter. Background technique [0002] With the increase of power demand and the concern of environmental issues, voltage-type grid-connected inverter (VSI) system has been widely adopted in recent years. This voltage source inverter system transmits renewable energy to the grid through an output filter. The role of the VSI is to convert the DC voltage obtained from renewable energy sources into an AC voltage, at its output there is a filter connection to process this AC voltage and inject a high-quality sinusoidal current into the grid. Generally, there are two types of filters (L and LCL) used to reduce the switching harmonics of the current injected into the grid. The third-order LCL filter is the most widely used topology because of its advantages: the ability to o...

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Problems solved by technology

However, due to the need for detailed system parameters, it is insufficient and inconvenient for inverter systems with parameter drift. On the contrary, by studying the terminal characteristics of the system, that is, whether the ratio of inverter output impedance to grid impedance meets the requirements , using an impedance-based approach to evaluate system stability describes the Nyquist stability criterion

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