Low-voltage microgrid inverter control system based on virtual impedance and virtual power

Abstract

The invention discloses a low-voltage micro-grid inverter control system based on virtual impedance and virtual power supply. The control system is divided into a droop controller, a virtual controller, and a voltage / current double-loop controller; by improving the droop parameters, a virtual inverter capable of simulating The droop controller with power supply function uses fractional order PID to track and control the droop controller voltage; by analyzing the relationship between virtual negative inductance and micro-source reactive power sharing, determine the value of virtual negative inductance required for accurate reactive power sharing , realize the virtual impedance in the virtual controller, feed back the voltage drop of the virtual controller to the droop controller, and participate in the fractional-order PID tracking control of the virtual power supply voltage; use the fractional-order PID to track the inverter voltage in the voltage / current dual-loop controller Control, according to the transfer function of the filter to determine the filter parameters in the controller, using the differential genetic algorithm to optimize the parameters of the fractional order PID controller. The invention can ensure the power decoupling of the low-voltage micro-grid and improve the effect of equal sharing of reactive power.

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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