Grid power quality control system and method based on unified power quality conditioner

Abstract

The invention provides a grid power quality control system and method based on a unified power quality conditioner. The system comprises a series MMC, a parallel MMC and a control circuit. The series MMC and the parallel MMC form a unified power quality conditioner (UPQC) topological structure based on MMC, and are connected to a grid side and a load side through a transformer respectively. The method comprises the following steps: carrying out transformation on an MMC module under an abc stationary coordinate system to obtain a differential equation matrix model under a dq rotating coordinate system; obtaining small-signal models of the series MMC and the parallel MMC under the dq rotating coordinate system; utilizing the parallel MMC to output an offset current and stabilize DC side voltage; and utilizing the series MMC to output an offset voltage. A fundamental wave positive sequence voltage component and a fundamental wave positive sequence current component adopt a PI regulator, and other components adopt a PR regulator to realize non-static-error control, so that compensation is carried out not only for the cases of distortion, harmonic wave and reactive power and the like, but also for the cases of unbalance power source voltage and unbalance load, and the load is allowed to obtain reliable power supply.

Description

Technical field [0001] The invention relates to the technical field of flexible AC power transmission and distribution and power electronics, and in particular to a power quality control system and method for power grids based on a unified power quality regulator. Background technique [0002] In modern industrial power grids, various disturbances such as the start-up of motors, the start and stop of large loads, and the nonlinearity of the load lead to industrial power grid voltage distortion, unbalanced voltage rise and fall, voltage flicker, load current imbalance, etc., causing industrial power grids The power quality has dropped significantly. With the widespread application of a large number of new technologies, various detection and control equipment and other sensitive loads account for an increasing proportion, and the requirements for power quality of the power grid are correspondingly higher. Then, in order to provide users with pure power, the research on power quali...

AI Technical Summary

Problems solved by technology

The document "Multilevel voltage-source-converter topologies for industrial medium-voltage drives" proposes that the application of this topology will have great limitations in medium and high voltage applications, such as the need for a large number of capacitors, and the acquisition of capacitor signals is complicated. To maintain capacitor voltage balance, it is necessary Complex modulation strategies, etc., so UPQC implemented with diode-clamped type is limited to three or four levels

[0004] Literature "Based on Modular Multilevel Converter MMC (Modular Multilevel Converter ) topology of a new medium-voltage unified power quality controller" and the literature "Research on the control strategy of a unified power quality controller based on MMC" have studied the compensation function of MMC-UPQC, but they all focus on the distortion of the grid voltage and the harmonic of the load current. Involving reactive power and other aspects, there is no discussion on the situation of unbalanced power supply voltage and unbalanced load

In the actual operation of the power grid, various imbalances may occur, which will affect the normal operation of some important loads, and even cause some equipment to fail to protect, resulting in large economic losses.

Images