Low-voltage micro-grid inverter control system based on virtual impedance and virtual power source

Abstract

The invention discloses a low-voltage micro-grid inverter control system based on virtual impedance and a virtual power source. The control system comprises a droop controller, a virtual controller and a voltage / current dual-loop controller, and is characterized by establishing the droop controller capable of simulating the function of the virtual power supply through improvement of droop parameters, and carrying out tracking control on the voltage of the droop controller through fractional-order PID; by analyzing relation between virtual negative inductance and micro-source reactive power sharing, determining the value of virtual negative inductance required for accurate reactive power sharing, realizing virtual impedance in the virtual controller, and feeding back voltage drop of the virtual controller to the droop controller to participate in fractional-order PID tracking control of voltage of the virtual power source; and carrying out tracking control on inverter voltage through fractional-order PID in the voltage / current dual-loop controller, determining filtering parameters in the controller according to a transfer function of a filter, and carrying out optimization on fractional-order PID controller parameters through a difference genetic algorithm. The control system can ensure low-voltage micro-grid power decoupling and improve a reactive power sharing effect.

Description

technical field [0001] The invention relates to the field of smart grid control, in particular to the design of an improved droop control method for a low-voltage micro-grid based on virtual impedance and virtual power supply and a complete control system thereof. Background technique [0002] With the continuous penetration of new energy and renewable energy power generation, in order to effectively solve many problems caused by the large-scale grid-connected state of distributed power generation and give full play to its potential, a micro-grid has been produced in the field of distributed power generation technology. The microgrid integrates various types of renewable energy such as photovoltaic power generation and wind power generation in the form of micro-sources, which improves the efficiency of resource use and better coordinates various micro-sources through cogeneration. As one of the control methods widely applicable to inverters in microgrids, the droop control m...

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Problems solved by technology

The former can decouple the power to a certain extent by transforming the virtual coordinates of the power, but the stability of the microgrid is reduced

The latter makes the line impedance inductive by controlling the output impedance of the inverter, and then achieves the purpose of power decoupling. Generally, it can be divided into two categories. One is to take a virtual inductance with a larger value than the line impedance, so that the entire line Impedance is roughly inductive, but it increases the harmonic inductance of the system. At the same time, the existence of resistive line impedance will make the degree of power decoupling incomplete. The second is to take the virtual negative resistance whose value is equal to the line impedance to offset the line impedance. The effect of power decoupling is better, but the inductive line impedance after cancellation may increase the deviation of reactive power sharing

In addition to the power coupling problem, the problem of reactive power sharing also affects the stable operation of the microgrid. Because the impedance voltage drop of each micro-source line is different, the output voltage of each micro-source is different, so there will be a certain degree of reactive power sharing between micro-sources. There may be some abnormalities in the output of some micro-sources

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