A low-voltage three-phase load balance control method based on on-load commutation technology

Abstract

The invention discloses a low-voltage three-item load balance control method based on on-load reversing technology. Phase load unbalance is detected and calculated in real time. If the three-phase unbalance exceeds a given value, the load that needs to be adjusted is calculated through the mean value iterative method, and then the reversing switch number and reversing switch that need to be operated are obtained based on the principle of multi-objective optimization. Adjust the phase sequence to achieve three-phase load balance. This algorithm fully considers factors such as the number of switching actions and the degree of unbalance of the three phases. Within the scope of ensuring that the three load unbalanced degrees reach the standard value, the number of switching actions is minimized and the cost of reversing is the lowest. At the same time, the load transfer user is uninterrupted. Power supply requirements, that is, on-load commutation technology.

Description

technical field [0001] The invention mainly relates to the three-phase load balance control of the low-voltage line of the distribution network. Based on the theory of the three-phase load balance algorithm, the load-on-load commutation is realized, and belongs to the field of control technology. Background technique [0002] In the three-phase four-wire system of urban residents and rural low-voltage distribution networks, most users use single-phase loads or single-phase and three-phase loads. Due to unbalanced loads and asymmetrical system component parameters, the unbalanced current between the three phases is objective ubiquitous. At the same time, the irregularity and unpredictability of user load imbalance lead to long-term imbalance of three-phase load in low-voltage distribution network. GB / T 15543-2008 "Power Quality Three-phase Voltage Permissible Unbalance" clearly stipulates that under normal circumstances, the three-phase unbalance of the negative sequence vol...

AI Technical Summary

Problems solved by technology

Three-phase unbalance will lead to additional heating and vibration of rotating motors, increased magnetic flux leakage and local overheating of transformers, increased power grid line losses, and misoperation of various protection and automatic devices, etc.

[0005] However, the reactive power adjustment and compensation devices developed by related manufacturers, due to the complex and changeable operating conditions of inductive loads in the low-voltage distribution network, make it difficult to achieve the desired effect with relatively fixed capacitor compensation, and often cause problems in the reactive power transfer system. The effect of energy saving and loss reduction is not obvious

On the other hand, the TCR branch in the traditional SVC adopts the 6-pulse connection form, and its line current contains 6k±1 order harmonics (k is a positive integer), which requires additional filtering devices, which increases the cost

If the current advanced STATCOM technology is adopted, the cost is too high, and it is unreasonable to adopt it in the low-voltage system

In the third aspect, the adjustment and compensation device only produces effects on the power supply side of the installation location, and this product is generally installed at the outlet of the distribution transformer. Big limitations, not the development trend of the research direction of three-phase imbalance control

[0007] 2. The load on the low-voltage side is random and dynamic, and the load has obvious asymmetry, which is difficult to predict accurately;

[0008] 3. The switching capacitor method compensates for the imbalance of the three loads, the capacitor switching is frequent, and the service life is short;

[0009] 4. SVC has constant impedance, generates harmonic current, and has limited compensation ability; advanced SVG has complex structure, high cost, and inconvenient maintenance, but both have limited ability to improve imbalance, and are mainly used for reactive power compensation;

[0010] In summary, it is difficult to achieve three-phase load balance through reactive power compensation, and the economy is not high

The traditional method of adjusting load balance can no longer meet the needs of current users for safe and reliable electricity consumption.

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