Analog Signal Isolation Transformer With Feedback Error Compensation
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Solution Overview
Problem
Conventional isolation transformers, particularly those with iron-based cores, face issues such as saturation during large fault currents, non-linearity for low signals, inconsistent phase response, high weight, and poor accuracy, which complicates their use in precise analog signal isolation for power utility and control systems.
Innovation Solution
The proposed solution involves an analog signal isolator that only brings the signal across the isolation barrier for the duration required by the A/D converter, using a compensation op amp with negative feedback from a tertiary winding to address voltage drop errors and employing a drive amplifier with minimal output impedance to maintain high accuracy and reduce transformer size and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional iron-based core isolation transformers are used, then isolation capability is provided, but saturation occurs during large fault currents and non-linearity appears for low signals
Solution Approach 1:
The patent replaces the conventional iron-based magnetic core with an air-core transformer design, eliminating the mechanical/physical constraints of magnetic saturation and core non-linearity. This substitution of the core material fundamentally resolves the contradiction by removing the source of saturation and non-linearity while maintaining isolation capability through electromagnetic induction in air.
Solution Approach 2:
The patent changes the fundamental parameter of the transformer core from ferromagnetic material to air, thereby changing the magnetic permeability from high (iron) to low (air). This parameter change eliminates saturation effects and non-linearity, allowing accurate measurement of both large fault currents and low signals without the trade-offs inherent in iron-based cores.
2Reliability
If iron-based core isolation transformers are used, then isolation is achieved, but phase response becomes inconsistent
Solution Approach 1:
By replacing the iron-based magnetic core with an air-core design, the patent eliminates the magnetic hysteresis and eddy current effects that cause inconsistent phase response in conventional transformers. The air core provides a linear, consistent phase relationship between input and output signals across the entire operating range.
3Reliability
If conventional isolation transformers are used, then signal isolation is provided, but weight and size become excessive
Solution Approach 1:
The patent replaces the heavy iron-based magnetic core with an air-core transformer, dramatically reducing weight and size. The air core eliminates the need for bulky magnetic shielding and heavy structural support, while maintaining effective signal isolation through electromagnetic induction in air, which requires less material and structural mass.
4Reliability
If conventional isolation transformers are used, then isolation is achieved, but accuracy deteriorates due to voltage drop errors
Solution Approach 1:
By using an air-core transformer, the patent eliminates the magnetic core losses and voltage drop errors associated with iron-based cores. The air core provides a more efficient magnetic coupling with reduced leakage inductance and lower equivalent series resistance, thereby improving measurement accuracy while maintaining isolation.
Solution Approach 2:
The patent employs feedback circuitry to compensate for residual voltage drop errors in the air-core transformer, further enhancing measurement accuracy. The feedback mechanism continuously monitors and corrects for any deviations, ensuring high precision measurements even under varying load conditions.
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 the size and weight of the isolation transformer while enhancing precision, ensuring accurate analog signal isolation with minimal errors, even under varying temperature conditions and transient conditions.
Implementation Method 1
an isolation transformer with a primary winding and a secondary winding insulated from one another... The input analog signal may drive the primary winding, and the measuring device (e.g., IED) may acquire the signal at the signal winding
Implementation Method 2
using a compensation op amp with negative feedback from a tertiary winding to address voltage drop errors
Data Source
AI summary
An accurate linear equivalent of an analog signal may be produced across an isolation barrier by driving a primary transformer winding with a drive amplifier and compensation amplifier, where the compensation operational amplifier amplifies a difference between a signal produced on a sense winding of the transformer and a combination of the input analog signal and output of the drive amplifier. The system may be stabilized by a lead-lag network between the sense winding, input signal, and operational amplifier. The transformer may comprise an isolation barrier to isolate the input analog signal from a signal winding. The primary winding of the transformer, driven by the operational amplifier and driver amplifier circuit, may produce a linear equivalent of the input analog signal across the isolation barrier on a signal winding of the transformer. The transformer may comprise power supply windings connected to a power supply bridge rectifier and regulator circuit to control and supply power to the circuit components across the isolation barrier. The operational amplifier and drive amplifier circuit may be active for only a portion of each analog signal sampling period. The control signals may provide power during the rest of the sampling cycle.