Micro-grid Power Load Starter with Active Harmonic Filtering
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Solution Overview
Problem
Low-capacity micro-grids face instability due to high surge and harmonic currents when starting large-scale power loads, particularly with variable frequency starters, which exacerbate harmonic current issues and affect system stability.
Innovation Solution
A system comprising a PCC grid-connection switch, active power filter, battery storage inverter, current-limiting resistor, contactors, time relay, and power relay board, which bi-directionally connects the micro-grid AC bus with the bulk grid and energy storage battery, effectively reducing harmonic currents by controlling the power relay board and contactors to manage the startup process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a variable frequency starter is used to start a large-scale power load, then the output torque is improved and starting current is reduced, but harmonic current increases severely
Solution Approach 1:
The patent introduces an active power filter (APF) as an intermediary device between the variable frequency starter and the micro-grid. The APF detects and compensates for harmonic currents generated by the variable frequency starter in real-time, effectively filtering out the harmful harmonic components while allowing the variable frequency starter to continue providing improved torque and reduced starting current benefits.
Solution Approach 2:
The patent extracts the harmful harmonic current component from the total current using the active power filter. By separating and independently compensating the harmonic current, the system removes the adverse effects of harmonics while preserving the useful components (fundamental current) that provide torque and power delivery.
2Use of energy by moving object
If a voltage soft starter is used to start a large-scale power load, then the starting current is reduced, but harmonic current remains severe and output torque is insufficient
Solution Approach 1:
The patent merges the voltage soft starter with a variable frequency starter to create a combined starting system. This hybrid approach utilizes the voltage soft starter's ability to limit starting current and the variable frequency starter's capability to provide high output torque, achieving both current reduction and torque improvement simultaneously.
3Productivity
If a large-scale power load is started in a low-capacity micro-grid, then the economic efficiency is improved, but system stability deteriorates due to surge current and harmonic current
Solution Approach 1:
The patent implements a feedback control mechanism where the active power filter continuously monitors the harmonic current content in the micro-grid system and dynamically adjusts its compensation output. This closed-loop feedback ensures that harmonic currents are actively suppressed in real-time, maintaining system stability even when starting large-scale power loads in low-capacity micro-grids.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system reduces harmonic currents and improves the output torque of power loads, enhancing the stability and economic efficiency of the micro-grid by minimizing simultaneous power supply from multiple sources and dynamically compensating harmonic content.
Implementation Method 1
the active power filter (APF) is bi-directionally connected with the micro-grid AC bus
Implementation Method 2
the energy storage battery comprises two branches, wherein one branch is bi-directionally connected with the micro-grid AC bus through the battery storage inverter
Implementation Method 3
the micro-grid AC bus is connected to the large-scale power load through the rectifier circuit of converter
Implementation Method 4
the inverter circuit of converter
Data Source
AI summary
A system for staring a large-scale power load in a micro grid comprises a PCC grid connection switch, a micro grid alternating-current bus, an active power filter (APF), an energy storage inverter, an energy storage battery, a current-limiting resistor R, contactors K1-K3, a time relay KT, a power supply relay board, a micro grid maser control system, a frequency converter rectifying circuit, a frequency converter filter circuit, and a frequency converter inverter circuit. There are the advantages: an output torque of a power load can be effectively improved by using a variable frequency starting apparatus, and a starting current is also small; the provided method can effectively reduce a harmonic current when a variable frequency starting apparatus starts a power load, the phenomenon that two power sources supply power on a direct-current side of the variable frequency starting apparatus at the same time is avoided, thereby improving the stability and the economy of a micro grid.