Resonant Power Supply for Inductive Loads
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing power supplies for electrode furnaces face challenges in delivering high currents efficiently due to stray and residual inductance, leading to increased impedance at higher frequencies, which results in bulky transformers and poor power factor, causing voltage disturbances and inefficient power transfer.
Innovation Solution
A resonant alternating current (AC) power supply is implemented, using a capacitor connected in series with the transformer primary to resonate the secondary circuit inductance at the switching frequency, reducing transformer size and enhancing power transfer efficiency by minimizing peak currents and transformer winding stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If higher frequency switching supplies are used to reduce transformer size, then transformer size is reduced, but impedance increases due to stray inductance
Solution Approach 1:
The patent converts the harmful effect of stray inductance into a beneficial resonant circuit. By adding a capacitor in series with the transformer primary, the stray inductance (which normally causes impedance increase) becomes part of a resonant system that actually improves power transfer. The resonant frequency is designed to match the switching frequency, causing the inductive reactance to be canceled by capacitive reactance, thereby eliminating the harmful impedance effect while maintaining high frequency operation.
Solution Approach 2:
The patent changes the operating parameters by introducing resonance into the system. The capacitor value is specifically selected to create a resonant circuit at the switching frequency, transforming the system from a simple inductive load to a resonant load. This parameter change allows the system to operate at high frequencies with reduced impedance, as the resonant condition causes the total reactance to approach zero at the operating frequency.
2Ease of operation
If phase controlled chopper is used to regulate output current, then output current regulation is achieved, but power factor deteriorates and voltage disturbances occur
Solution Approach 1:
The patent employs periodic switching action at the resonant frequency to regulate power delivery. Instead of using phase-controlled chopping that creates non-sinusoidal current, the system uses periodic switching synchronized with the resonant oscillation. This periodic action at resonance allows for smooth current waveforms that maintain good power factor while still achieving output regulation through duty cycle control of the switching elements.
Solution Approach 2:
The patent implements feedback control to regulate output current while maintaining power factor. The control system monitors the resonant circuit conditions and adjusts the switching duty cycle accordingly. This feedback mechanism ensures that the resonant oscillation is maintained while regulating the average power delivered to the load, thereby achieving both current regulation and good power factor without the disturbances associated with phase-controlled choppers.
3Reliability
If stray inductance is present in series with crucible resistance, then impedance increases with frequency, but at 50 Hz-60 Hz the inductive reactance is insignificant
Solution Approach 1:
The patent makes the system dynamically adaptive to frequency changes by introducing a resonant circuit. At low frequencies (50-60 Hz), the system operates in a resistive mode where stray inductance is negligible. At high switching frequencies, the resonant circuit becomes active, dynamically adjusting the impedance characteristics to compensate for the increased inductive reactance. This dynamic behavior allows the system to maintain optimal performance across different operating frequencies.
Solution Approach 2:
The patent uses electrical resonance (analogous to mechanical vibration) to counteract the frequency-dependent impedance increase. The resonant circuit oscillates at the switching frequency, creating a counteracting capacitive current that cancels the inductive current. This vibrational approach at the electrical level allows the system to deliver high power at high frequencies despite the presence of stray inductance, while maintaining stable operation at lower frequencies where resonance is not required.
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 achieves efficient power delivery to the crucible, reducing peak currents by over a factor of 4 and RMS currents by more than a factor of 60, while maintaining high power output, thus addressing the inefficiencies and size constraints of prior art systems.
Implementation Method 1
a capacitor connected in series with the primary of the transformer for resonating the transformer secondary circuit inductance at the switching frequency
Implementation Method 2
a step-down power transformer. The capacitor is connected in series with the primary winding of the transformer
Implementation Method 3
The current heats the crucible and any sample material therein in excess of three thousand degrees Celsius (3000° C.)
Data Source
AI summary
A resonant power supply (900) for use with high inductive loads includes an input rectifier (903) and a switching inverter formed using a plurality of parallel connected half bridge networks for switching the voltage provided from the input rectifier (903). A transformer (927) is used whose primary is connected to the switching inverter and whose secondary is connected to load such as a crucible (931). A capacitor (929) is used in series with the primary of the transformer (927) for resonating the inductance in the secondary circuit at the frequency of the switching inverter to provide maximum power transfer to the crucible (931).