Low-voltage digital distributed terminal power quality control system and control method

Abstract

The invention discloses a low-voltage digital distributed terminal power quality control system and a control method. The system comprises n groups of converters in parallel connection with the power grid; the converters share a DC-side energy storage unit, a high-pass filter and a grid-connected filter reactor; the DC-side energy storage unit is connected with a converter main circuit, and the switch of the converter main circuit controls current output of the DC-side energy storage unit; and the high-pass filter is located on a power transmission line for a power supply line by the converter main circuit, and the grid-connected filter reactor is also located on the power transmission line for the power supply line by the converter main circuit. Multi-target power quality control such as low-voltage terminal voltage stabilization and voltage regulation, harmonic compensation, reactive power compensation and three-phase unbalanced compensation can be realized; intelligent self-recognition and two-way control on the power quality at the node can be realized; the power quality problem brought from a power supply-side power grid can be controlled, and the power quality problem generated by a load side can also be controlled; and the composite voltage stabilization function for the DC-side capacitor power supply and rectifier power supply can be realized, and the stability of DC voltage can be improved.

Description

technical field [0001] The invention relates to the technical field of power quality control, in particular to a low-voltage digital distributed terminal power quality control system and a control method. Background technique [0002] In the hospital low-voltage power transmission and distribution network system, various types of large and medium-sized nonlinear medical equipment such as nuclear magnetic resonance MRI, CT, and linear accelerators are more and more widely used, making the low-voltage power transmission and distribution system voltage drop and flicker, voltage and current harmonics Wave distortion, current three-phase imbalance, reactive power fluctuations, active power fluctuations and other power quality problems are normalized, and the quality of power quality is deteriorating day by day. [0003] The load characteristics of these harmonic sources and reactive sources: 1) The load capacity mostly fluctuates in the range of 20kw to 100kw, among which the tra...

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Problems solved by technology

[0005] Traditional SVC devices, including TCR, TSC, etc., have the main problems: slow dynamic response, poor real-time performance; easy to produce overcompensation, undercompensation, and resonance; can only compensate reactive power; large volume; in practical applications, through combination, multi-purpose Centralized compensation on the low-voltage side of power transformation and distribution

[0006] SVG is a new type of power electronic equipment, which has fast response speed, good dynamic real-time performance, and small size. If the technology is not optimized or multi-level technology, the harmonic problem generated by itself is serious, which will affect the compensation object

[0007] APF is a new type of power electronic equipment, which is mainly used to eliminate harmonics, and can also provide some reactive power. The main problems are: first, in the case of single use, if it handles multiple targets, its ability is limited, and the compensation capacity must be increased. The dynamic response speed is slowed down, the real-time performance is deteriorated, and the volume is also increased; the second is that in the case of independent use, affected by its control method, its main harmonic control efficiency is only 55% to 70% in actual measurements

[0008] UPQC is the Universal Power Quality Controller, which is a new type of power electronic equipment. It has powerful functions and can simultaneously regulate voltage, suppress harmonics, and compensate reactive power. Network application report), if it is used to control the power quality of low-voltage terminal nodes, the main problems are: first, the core of the device is composed of active filters (APF) connected in series and parallel, and the parallel active filter groups are connected in parallel to the power grid, mainly To provide reactive power compensation, the series active filter group is connected in series to the grid (load front end) through a transformer, mainly to provide voltage regulation

In general, large and medium-sized medical equipment needs to be equipped with a voltage stabilizing transformer on site according to its use requirements, so that it forms a repeated setting with the series transformer of UPQC, which increases energy consumption; second, the device is large in size and expensive, and the low-voltage terminal The economic applicability of the application is poor, and it is not suitable for low-voltage terminal power quality control

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