Inductive DC Bus Voltage Measurement Circuit
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Solution Overview
Problem
Direct detection of unregulated DC bus voltage is problematic due to the need for additional components for galvanic isolation, which can result in inaccurate measurements, especially for short transients or sudden changes, as existing detection circuitry may have time constants that are too long to react to rapid changes.
Innovation Solution
A voltage measuring device with a switch and sampling capacitor configuration that forms a discharge path when the input voltage exceeds a threshold, independent of the output voltage, and includes a rectifier in series with the sampling capacitor to conduct based on the voltage difference, allowing for indirect sampling of the unregulated DC bus voltage through an inductive coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct detection of unregulated DC bus voltage is used, then measurement accuracy is improved, but additional components for galvanic isolation are required
Solution Approach 1:
The patent uses the transformer's secondary winding as an intermediary to indirectly sense the primary DC bus voltage. The winding couples magnetically to the primary side through the transformer core, providing galvanic isolation while enabling voltage measurement through the reflected voltage during switch operation, thus avoiding direct electrical connection and additional isolation components.
Solution Approach 2:
The circuit creates a scaled copy of the primary DC bus voltage waveform on the secondary side through magnetic coupling. The voltage across the secondary winding during switch conduction is proportional to the primary bus voltage, allowing accurate measurement of the original voltage signal without direct contact, thereby maintaining measurement precision while reducing device complexity.
2Stability of the object's composition
If RC circuit with long time constant is used for sampling, then measurement stability is improved, but response to rapid voltage changes deteriorates
Solution Approach 1:
The circuit performs periodic sampling of the voltage during each switch conduction cycle. By capturing the voltage at specific moments in each switching period and using this sampled value for regulation, the system achieves both stability through consistent periodic measurement and fast response by updating with each cycle, avoiding the need for long RC time constants that would blur transient changes.
Solution Approach 2:
The circuit proactively samples and holds the voltage value at the beginning of each switching cycle before any potential transient occurs. This preliminary sampling ensures that the control system has the current voltage information ready for regulation, enabling rapid response to changes while maintaining stable operation throughout the cycle.
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
Enables accurate measurement of unregulated DC bus voltage by effectively sampling the voltage across the secondary winding of a DC to DC converter, even during rapid changes, without requiring synchronization circuitry and maintaining measurement accuracy through the use of a rectifier and switch configuration.
Implementation Method 1
an inductive coupling of a DC to DC voltage converter
Implementation Method 2
A switch coupled to the input forms a discharge path parallel to a sampling capacitor
Implementation Method 3
A rectifier in series with the sampling capacitor is biased to conduct upon the input voltage, minus the output voltage, equaling or exceeding a second voltage
Data Source
AI summary
A voltage measuring device includes an input configured to be coupled to a secondary of an inductive coupling of a DC to DC voltage converter. A switch coupled to the input forms a discharge path parallel to a sampling capacitor dependent on the voltage at the input equaling or exceeding a first voltage threshold and independent of an output voltage at the output of the device. The sampling capacitor is coupled to the output. A rectifier in series with the sampling capacitor is biased to conduct upon the input voltage, minus the output voltage, equaling or exceeding a second voltage.