Interleaved Forward Converter Duty Cycle Control
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Solution Overview
Problem
Conventional welding and cutting power supply systems with multiple inverters can become unbalanced, leading to thermal imbalances and reduced power output due to uncontrolled magnetic dynamics and limited PWM duty cycles.
Innovation Solution
A power supply system with two solid state switching circuits and a control circuitry that applies PWM control signals to maintain balanced loading by determining the duration of signals for one circuit and applying similar signals to the second circuit without re-determining its duty cycle, ensuring equal duty cycles and extending PWM duty cycles beyond 50% to enhance power output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If multiple inverters are used to reduce output inductor size, then the inductor size is reduced, but the system becomes unbalanced leading to thermal imbalance
Solution Approach 1:
The control circuitry monitors the output current and adjusts the PWM duty cycles of multiple inverters in real-time to maintain balanced loading. This feedback mechanism ensures that each inverter shares the load equally, preventing thermal imbalance while maintaining the benefits of reduced inductor size.
Solution Approach 2:
The system dynamically adjusts the operating parameters of each inverter based on real-time conditions. By making the duty cycles adaptive rather than fixed, the system maintains balance despite variations in load conditions, thereby resolving the contradiction between using multiple inverters and maintaining loading balance.
2Device complexity
If PWM duty cycle is limited to 50%, then transformer magnetic dynamics are simplified, but power output is reduced
Solution Approach 1:
The system uses periodic switching of the transformer with duty cycles exceeding 50% by utilizing both sides of the transformer core alternately. This periodic action allows full utilization of the transformer magnetic dynamics, enabling higher power output while maintaining controlled magnetic behavior through the structured switching pattern.
Solution Approach 2:
The invention changes the PWM duty cycle parameter from the conventional 50% limit to values greater than 50%. This parameter change, combined with appropriate dead-time insertion and complementary switching, allows the system to extract more power from the transformer without causing magnetic instability, thereby resolving the contradiction between complexity and power output.
3Power
If independently controlled inverter circuits are used, then power output is increased, but thermal imbalance occurs due to unbalanced loading
Solution Approach 1:
The control circuitry implements feedback control that monitors the output current and adjusts the PWM duty cycles of independently controlled inverters to maintain equal loading. This ensures that each inverter operates within safe thermal limits while collectively delivering high power output, thereby resolving the contradiction between increased power capability and thermal balance.
Solution Approach 2:
The system maintains equipotentiality in terms of loading distribution across all inverters by ensuring they operate at equal duty cycles and current levels. This balanced operating condition prevents thermal runaway in any single inverter while maintaining high overall power output capability.
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 solution maintains balanced loading and thermal stability, reduces ripple current, and increases the effective power output by ensuring equal duty cycles and allowing extended PWM duty cycles, thereby improving the efficiency and performance of welding and cutting operations.
Implementation Method 1
The switching is commonly performed by pulse width modulation (PWM) signals applied to the gates of power electronic switches of converter circuits within the supplies
Implementation Method 2
Conventional systems utilize a single inverter in this converter circuitry, along with an inductor to smooth the output waveform
Data Source
AI summary
A power supply for welding, cutting and similar operations includes a dual two-switch forward converter. The converter has two inverter circuits coupled in parallel but controlled to provide output power in an interleaved fashion. To avoid “walking” of the circuits (which could result in different duty cycles and imbalance of the load sharing), control signals are determined and applied to a first of the inverter circuits, and “on” times of the first circuit is monitored, such as by augmenting a counter to determine the number of clock cycles the first circuit is “on”. The same duration is then used for commanding output from the second inverter circuit. The duty cycles of both circuits is thus ensured to be the same regardless of changes in the total output power.