Contactor Backup Circuit for Low-Voltage Ride-Through
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Solution Overview
Problem
Existing backup boxes in photovoltaic or photovoltaic energy storage power supply scenarios fail to maintain grid-connected operation during low voltage ride-through conditions, leading to unreliable power converter operation.
Innovation Solution
A backup apparatus with a contactor, rectifier circuit, auxiliary power supply circuit, and controller that converts alternating current into direct current to maintain contactor activation, using stored energy during low voltage ride-through, ensuring the power converter remains connected to the grid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the contactor is driven by the power grid voltage, then the contactor can be controlled to disconnect during low voltage conditions, but the contactor cannot remain closed during low voltage ride-through scenarios
Solution Approach 1:
The power supply path is segmented into two independent circuits: a main power circuit for normal operation and an auxiliary power circuit specifically for maintaining the contactor during low voltage ride-through events. This segmentation allows the auxiliary circuit to independently control contactor closure regardless of main circuit voltage conditions.
Solution Approach 2:
An auxiliary power supply circuit is introduced as an intermediary system that provides dedicated power to the contactor coil during low voltage ride-through scenarios. This intermediary circuit decouples the contactor control from the main power grid voltage, enabling reliable grid-connected operation during voltage fluctuations.
2Reliability
If the first rectifier circuit continuously supplies power to the coil, then the main contact switch remains on, but energy is wasted during normal operation when power grid connection is already established
Solution Approach 1:
The system dynamically switches between different power supply modes: the first rectifier circuit operates during startup or grid disconnection to establish contactor closure, then the controller transitions to the second rectifier circuit for continuous operation. This dynamic switching optimizes energy consumption while maintaining contactor stability.
Solution Approach 2:
The controller discards the first rectifier circuit's power supply function after successful contactor closure is achieved, transferring the load to the more efficient second rectifier circuit. This prevents continuous energy waste from the first circuit while maintaining the contactor's on-state.
3Reliability
If the contactor opens during low voltage conditions, then the power converter disconnects from the grid, but the power converter cannot maintain grid-connected operation during low voltage ride-through
Solution Approach 1:
The controller continuously monitors grid voltage conditions and automatically activates the auxiliary power supply circuit when low voltage ride-through is detected. This feedback mechanism enables automatic maintenance of grid-connected operation without manual intervention, improving both reliability and operational ease.
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
Enhances the operating reliability of the power converter by keeping it grid-connected during low voltage ride-through, utilizing stored energy to sustain contactor activation and reduce heat generation.
Implementation Method 1
The first rectifier circuit is configured to: when the first switch is turned on, convert an alternating current from the power grid into a direct current to supply power to the coil, to turn on the main contact switch
Implementation Method 2
The controller is configured to: after the main contact switch is turned on, control the second switch to be turned on and the first switch to be turned off, so that the auxiliary power supply circuit converts an alternating current from the power grid or the power converter into a direct current to supply power to the coil
Implementation Method 3
The auxiliary power supply circuit includes an input capacitor, and when the second switch is turned on, the input capacitor supplies power to the coil when a voltage of the power grid is lower than a voltage threshold
Data Source
AI summary
A backup apparatus includes a contactor, a first rectifier circuit, an auxiliary power supply circuit, a first switch, a second switch, and a controller. The contactor includes a coil connected to the auxiliary power supply circuit through the second switch and a main contact switch connected to a power grid. The first rectifier circuit is connected to the power grid through the first switch, and the first rectifier circuit is connected to the coil. When the first switch is turned on, the first rectifier circuit supplies power to the coil. After the main contact switch is turned on, the controller controls the second switch to be turned on and the first switch to be turned off. When the second switch is turned on and a voltage of the power grid is lower than a voltage threshold, an input capacitor in the auxiliary power supply circuit supplies power to the coil.