Synchronous Rectifier Power Loss Reduction in Resistance Welding
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Solution Overview
Problem
Existing resistance welding devices using diode rectifiers suffer from high power losses due to forward resistance, leading to inefficiency and increased energy consumption, which results in higher cooling requirements and material costs.
Innovation Solution
The implementation of a resistance welding device with a synchronous rectifier and a control method that utilizes a welding transformer with coupled secondary windings and a primary winding, where the synchronous rectifier is controlled to minimize power losses by blocking field effect transistors during active phases and allowing energy to flow through the low-impedance drain-source path, reducing the need to overcome body diode threshold voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If diode rectifiers are used in resistance welding devices, then the device can operate with simple structure, but high power losses occur due to forward resistance of diodes
Solution Approach 1:
The patent changes the fundamental operating parameters of the rectifier by transitioning from passive diode rectification to active synchronous rectification using IGBTs. This allows control of the rectifier's on-state resistance and switching timing, fundamentally changing how power is processed and reducing losses from the fixed forward resistance of diodes to variable low resistance of controlled switches
Solution Approach 2:
The patent replaces the passive mechanical/electrical diode rectifier system with an active electronic controlled system using IGBTs and microprocessor control. This substitution enables precise control of current flow and timing, replacing the fixed characteristics of diodes with programmable control logic that optimizes power delivery and minimizes losses
2Loss of energy
If synchronous rectifier with low on-state resistance is used, then power loss is reduced, but device complexity increases
Solution Approach 1:
The patent makes the rectifier system multi-functional by combining power conversion, current control, and protection functions into a single integrated synchronous rectifier system. The IGBTs serve both as rectification switches and as controlled current regulators, while the microprocessor provides both control and monitoring functions, reducing the need for separate components
Solution Approach 2:
The patent introduces a microprocessor-based control system as an intermediary between the power source and the synchronous rectifier. This intermediary coordinates the switching of multiple IGBTs, manages the complex timing requirements, and provides intelligence to the system, making the increased complexity manageable and beneficial
3Reliability
If high currents of several kiloamperes are required for resistance welding, then welding quality is improved, but power losses and heat generation increase
Solution Approach 1:
The patent employs periodic switching action through the full-bridge inverter and synchronous rectifier, converting DC to AC and back to DC with controlled frequency. This periodic action allows the system to deliver high peak currents for welding while maintaining lower average power loss through controlled duty cycles and timing, as the IGBTs switch on and off in synchronization with the AC waveform
Solution Approach 2:
The patent ensures continuous useful action by maintaining synchronized operation between the inverter and synchronous rectifier throughout the AC cycle. The IGBTs are controlled to conduct during the entire half-cycle when current flows, eliminating dead times and ensuring continuous power delivery to the welding electrodes, which maintains welding quality while minimizing interruptions that would increase effective power loss
4Device complexity
If diode rectifiers with high forward resistance are used, then device simplicity is maintained, but cooling requirements and material costs increase
Solution Approach 1:
The patent changes the resistance parameter of the rectifier from the fixed high forward resistance of diodes to the controllable low on-state resistance of IGBTs. By actively controlling the switching timing and duty cycle of the IGBTs, the system maintains low effective resistance during power transfer, significantly reducing I²R losses and heat generation compared to passive diode rectifiers
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
This approach significantly reduces power losses by up to 70% compared to diode rectifiers, leading to lower energy consumption, reduced cooling needs, and improved efficiency, allowing for higher frequency operation and cost savings.
Implementation Method 1
the synchronous rectifier is controlled to minimize power losses by blocking field effect transistors during active phases and allowing energy to flow through the low-impedance drain-source path
Implementation Method 2
reducing the need to overcome body diode threshold voltages
Implementation Method 3
Transformers are usually used to generate these currents, which are controlled on the primary side by means of a full bridge and on the secondary side supply the welding guns with current
Data Source
Figure 1~2
Figure 3
AI summary
The aim of the invention is to provide an improved method for operating a resistance welding device and a corresponding device such that the efficiency and rate of work can be substantially improved relative to conventional solutions. Said aim is achieved by means of a resistance welding device having a welding transformer with first and second coupled secondary windings (4b, c) and primary windings (4a), making up a synchronous converter with a first and second converter branch each operated by means of the first and second secondary winding (4b, c) and which supply a first and a second welding electrode (5a, b) with welding current. Control of the synchronous converter is carried out by means of a control device (31a, b, 32a, b, 34, 35) such that, the converter branch, controlled with regard to the direction of the corresponding windings of the primary circuit and the secondary circuit, with the welding electrode polarity opposing that of the current control, is blocked when the primary winding is controlled. The inventive advantages provide a resistance welding device with improved efficiency and the advantages of an improved rate of work.