Solid-State Variable Transformer Circuit for Clean Sine Wave Output
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Solution Overview
Problem
Variable transformers are heavy, expensive, mechanically prone to wear, and impractical for quick output voltage changes, while solid-state replacements often cause output wave distortion and are limited by current delivery.
Innovation Solution
A lightweight, inexpensive solid-state circuit using IGBTs or other transistors with internal or external diodes, capable of quickly changing output voltage by switching low-frequency AC with a high-frequency carrier, allowing greater current delivery to the load than drawn from the source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If variable transformers are used to regulate AC voltage, then voltage regulation is achieved, but the device becomes heavy, expensive, mechanically prone to wear, and impractical for quick output voltage changes
Solution Approach 1:
The patent replaces the mechanical variable transformer with a solid-state electronic circuit using transistors (Q1-Q4) as electronic switches controlled by a microprocessor. This substitution eliminates mechanical moving parts, reducing weight and enabling rapid voltage changes through electronic control of the switching elements rather than mechanical adjustment.
Solution Approach 2:
The patent implements dynamic voltage regulation by using a microprocessor to dynamically adjust the duty cycle of the switching elements based on feedback from voltage sensing resistors. This allows the output voltage to change quickly in response to control signals, making the system adaptable and responsive compared to static mechanical transformers.
2Weight of moving object
If solid-state replacements are used to replace variable transformers, then weight and cost are reduced, but output wave distortion occurs
Solution Approach 1:
The patent uses periodic pulse-width modulation (PWM) switching of the transistor pairs, where the duty cycle is varied periodically to control the average output voltage. This periodic switching action, when properly synchronized and controlled, produces a clean output waveform that can be filtered to eliminate distortion, maintaining wave quality while achieving weight reduction.
Solution Approach 2:
The patent incorporates feedback through voltage sensing resistors (R5-R8) that monitor the output voltage and provide feedback to the microprocessor. This feedback loop allows the control system to adjust the switching duty cycle to maintain accurate output voltage and minimize waveform distortion, ensuring high manufacturing precision in the output wave quality.
3Ease of operation
If solid-state solutions are placed in series with the load, then voltage control is achieved, but current delivery to the load is limited by the source current
Solution Approach 1:
The patent uses a high-frequency carrier signal (19.5 kHz) generated by the microprocessor before the actual power switching occurs. This preliminary high-frequency carrier is used to modulate the switching of the power transistors, allowing the system to prepare and control power delivery in advance, enabling current multiplication effect where the load current can exceed the source current through the transformer action during the switching cycles.
Solution Approach 2:
The patent changes the operating parameters by using high-frequency switching (19.5 kHz carrier) instead of direct low-frequency power switching. This parameter change allows the transformer to operate in a mode where it can deliver multiplied current to the load during the on-periods of the switching cycle, effectively decoupling the load current from the source current limitation and enabling greater current delivery 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
The circuit provides a clean, undistorted variable voltage with increased current delivery to the load, overcoming the limitations of traditional variable transformers and solid-state solutions, with no need for synchronization and adjustable output voltage control.
Implementation Method 1
The transformer we use is a simple one-stage LC low-pass filter and will produce a clean sine wave at its output, even though the high frequency carrier is being chopped.
Data Source
AI summary
The invention is directed to a solid-state replacement for a variable transformer. The circuit arrangement presented is not placed in series with the load. It can change output voltage quickly, and is able to deliver more current to the load than is drawn from the source while stepping down because the circuit is not placed in series with a load. The output voltage from the driver circuit is a low-frequency sine wave that is “chopped” by a high frequency carrier, yet the end result after the transformer or LC filter is a very clean sine wave. The circuit arrangement is lightweight and inexpensive to fabricate.