Grid Power Inverter Start-Up Control for Relay Welding Prevention
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Solution Overview
Problem
Existing grid connection power conversion devices face challenges in reducing inrush currents to capacitors during start-up, leading to potential relay welding and increased manufacturing costs due to the need for additional circuitry, while also failing to effectively detect disconnection or welding of relays.
Innovation Solution
A grid connection power conversion device with an inverter, capacitor, commercial voltage amplitude detection circuitry, amplitude adjustment circuitry, and start-up control circuitry that gradually adjusts the output voltage to match the commercial system voltage, along with phase angle adjustment and detection circuitry to manage phase differences, allowing for reduced inrush currents and reliable relay state detection without additional inrush current prevention circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an inrush current prevention circuitry is added to reduce inrush current to the capacitor, then the inrush current is reduced, but the manufacturing cost increases due to additional components
Solution Approach 1:
The system uses its own existing components (inverter, capacitor, control circuitry) to detect and respond to inrush current conditions. The control circuitry monitors the capacitor voltage and automatically adjusts the inverter output to prevent excessive inrush current, eliminating the need for external prevention circuitry while maintaining reliability
Solution Approach 2:
The control circuitry continuously monitors the capacitor voltage and uses this feedback to regulate the inverter output. When the capacitor is uncharged, the control circuitry detects the low voltage condition and limits the inverter output to prevent inrush current, then gradually increases output as the capacitor charges, achieving reliable inrush current protection through feedback control
2Measurement precision
If conventional detection methods are used to detect relay welding, then relay welding can be detected, but disconnection of relays cannot be detected
Solution Approach 1:
The control circuitry uses the same voltage monitoring mechanism to detect multiple relay states (both welding and disconnection). By monitoring capacitor voltage under different relay conditions, the system can distinguish between normal operation, relay welding, and relay disconnection, achieving multi-functional detection with a single system
Solution Approach 2:
The system detects relay abnormalities by monitoring changes in capacitor voltage parameters. Different relay states (welding vs. disconnection) produce distinct voltage patterns that the control circuitry can distinguish, enabling detection of multiple fault types through parameter analysis
3Productivity
If the voltage to the capacitor is applied abruptly at start-up, then the system starts quickly, but inrush current flows causing relay welding and potential circuit damage
Solution Approach 1:
Before fully applying voltage to the capacitor, the control circuitry performs preliminary monitoring of capacitor voltage and gradually increases the inverter output. This preliminary action prevents sudden inrush current while still achieving relatively quick start-up by being ready to apply full voltage as soon as the capacitor is charged
Solution Approach 2:
The system dynamically adjusts the inverter output voltage based on real-time capacitor voltage conditions. The control circuitry continuously modifies the output level, transitioning from limited output during charging to full output after charging, achieving both fast start-up and inrush current prevention through dynamic control
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 solution effectively reduces inrush currents to capacitors and reliably detects disconnection or welding of relays, preventing operational issues and reducing manufacturing costs by eliminating the need for additional circuitry.
Implementation Method 1
a capacitor connected between the inverter and the commercial power system
Data Source
AI summary
A grid connection power conversion device is provided in which an amplitude of an output voltage from an inverter is increased stepwise from 0, after start-up of the power conversion device, to adjust the amplitude of the output voltage from the inverter to match an amplitude of a commercial system voltage as detected, and thereafter the inverter is connected to the commercial power system to start grid-connected operation. This makes it possible to prevent the voltage applied to a capacitor provided between the inverter and the commercial power system from abruptly increasing from 0V to the commercial system voltage at the start-up of the power conversion device, thereby making it possible to reduce an inrush current to the capacitor at the start-up without using an inrush current prevention circuitry.