AC-Side Precharge Isolation Circuit for Surge-Free Relay Switching
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Solution Overview
Problem
Conventional precharge control methods using a fixed delay time for relay short circuiting the PTC resistor result in large surge currents, overheating, and inadequate charging of electrolytic capacitors, especially when dealing with varying input voltages, leading to prolonged precharge times and potential component damage.
Innovation Solution
An AC-side precharge-isolation-detection circuit comprising a step-down rectifier module, optocoupler isolation module, and voltage drop detection module, connected in parallel to the current limiting resistor, which isolates operating voltages, detects voltage drops, and transfers signals to an MCU for sampling to determine precharge completion, preventing surge currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If relay short circuits PTC at a fixed delay time, then precharge control is simple to implement, but large surge current occurs impacting relay and other components
Solution Approach 1:
The patent uses a detection circuit that monitors the voltage across the PTC resistor in real-time and feeds this information back to the MCU. The MCU adjusts the relay switching timing based on the actual voltage rise rate, rather than using a fixed delay time. This feedback mechanism prevents excessive surge current by optimizing the precharge timing to match actual circuit conditions.
Solution Approach 2:
The patent replaces the conventional mechanical timer-based fixed delay control with an electronic detection and control system. The detection circuit uses operational amplifiers and comparison circuits to electronically monitor voltage changes and generate control signals, substituting the mechanical timing approach with a more precise electronic control method that reduces surge current.
2Stability of the object's composition
If fixed delay time is used for precharge control, then control timing is consistent, but cannot adapt to different input voltages causing prolonged precharge time
Solution Approach 1:
The patent transforms the static fixed delay time control into a dynamic control system that adapts to different input voltages. The detection circuit continuously monitors the voltage across the PTC resistor and calculates the voltage rise rate, allowing the system to dynamically adjust the precharge timing based on actual circuit conditions and input voltage levels, thereby optimizing precharge time for each specific scenario.
Solution Approach 2:
The patent changes the control parameter from a fixed time delay to a variable parameter based on voltage rise rate detection. By monitoring the actual voltage change across the PTC resistor and using this information to determine when precharge is complete, the system adapts to different input voltages and circuit conditions, preventing both premature and excessive precharge timing.
3Speed
If frequent switching on and off occurs, then precharge control responds quickly, but PTC heats up causing resistance increase and prolonged precharge time
Solution Approach 1:
The detection circuit provides real-time feedback on the voltage across the PTC resistor, allowing the MCU to monitor the heating effect through resistance changes. By continuously detecting the voltage rise rate and adjusting switching timing accordingly, the system prevents excessive heating while maintaining responsive control, optimizing the balance between response speed and thermal management.
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 isolates voltages, detects voltage drops across the current limiting resistor, and samples signals to determine precharge completion, ensuring stable charging and preventing surge currents, thus improving precharge efficiency and component longevity.
Implementation Method 1
an input end of the optocoupler isolation module is connected to the step-down rectifier module, and an output end of the optocoupler isolation module is connected to the voltage drop detection module
Implementation Method 2
the step-down rectifier module is connected in parallel to both ends of a current limiting resistor of a precharge circuit
Implementation Method 3
the voltage drop detection module is configured to detect voltage drop change of the current limiting resistor of the precharge circuit
Data Source
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AI summary
The present application discloses an AC-side precharge circuit. An AC-side precharge-isolation-detection circuit (100) is connected in parallel to both ends of the current limiting resistor (PTC) of the AC-side precharge circuit. The AC-side precharge-isolation-detection circuit (100) includes a step-down rectifier module (110), an optocoupler isolation module (120), and a voltage drop detection module (130), wherein the step-down rectifier module (100) is connected in parallel to the current limiting resistor (PTC) on the AC side, the input end of the optocoupler isolation module (120) is connected to the step-down rectifier module (110), and the output end of the optocoupler isolation module (120) is connected to the voltage drop detection module (130).