Full-Bridge Current Measurement Circuit for Inductive Loads
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Solution Overview
Problem
Existing methods for current measurement in inductive loads using full-bridge circuits face challenges such as discontinuous signal availability, polarity issues, and complexity, leading to inadequate signal filtering and increased costs due to high circuit complexity, which violate the Nyquist criterion and result in poor control accuracy and stability.
Innovation Solution
A method and circuit arrangement utilizing two identical half-bridges with measurement resistors between switching elements and ground or supply voltage, connected to a differential amplifier, where a switching device selectively connects the amplifier inputs to ground, supply voltage, or measurement devices, allowing continuous current measurement and overcoming discontinuities and recirculation phase limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If current measurement is performed in the feed line to the bridge circuit, then cost is reduced, but signal availability becomes discontinuous and measurement is possible only at specific times
Solution Approach 1:
The measurement function is segmented and distributed to both half-bridges, with each half-bridge having its own measurement resistor. This allows continuous measurement by combining signals from multiple segments (half-bridges) rather than relying on a single measurement point that is available only intermittently.
Solution Approach 2:
The measurement signals from both half-bridges are merged through the differential amplifier to produce a continuous measurement output. By combining the measurement capabilities of both half-bridges, the system achieves continuous signal availability while keeping measurement resistors in the cost-effective feed lines.
2Measurement precision
If current measurement is performed at discrete times when current passes through mean value, then continuous monitoring is achieved, but disturbances from switching operations affect measurement and filtering becomes problematic
Solution Approach 1:
The measurement system provides continuous monitoring by maintaining measurement capability throughout the entire switching cycle, not just at discrete moments. The differential amplifier continuously processes signals from both half-bridges, ensuring uninterrupted current measurement even during switching transitions.
Solution Approach 2:
The differential amplifier acts as an intermediary that processes and combines the measurement signals from both half-bridges. It filters and conditions the signals continuously, reducing the impact of switching disturbances while maintaining accurate current measurement throughout the entire cycle.
3Reliability
If measurement signal is spectrally limited to satisfy Nyquist criterion, then sampling theorem is not infringed, but control bandwidth and signal quality are reduced
Solution Approach 1:
The measurement system dynamically adapts to the switching frequency by continuously providing measurement signals at all frequencies. The differential amplifier and subsequent filtering stages can be configured to pass the necessary bandwidth for high-performance control while still satisfying the Nyquist criterion for the specific sampling rate used.
Solution Approach 2:
The system allows flexible adjustment of filtering parameters to optimize the trade-off between bandwidth and Nyquist compliance. By changing the cutoff frequency and filter order parameters, the system can achieve both high control bandwidth and proper sampling theorem compliance depending on the specific application requirements.
4Measurement precision
If complex circuit arrangements with multiple operational amplifiers are used per full-bridge, then measurement accuracy is improved, but device complexity and cost increase significantly
Solution Approach 1:
Each half-bridge measurement circuit is designed to be universal and self-contained, with its own measurement resistor and signal conditioning capability. The differential amplifier serves multiple functions by processing signals from both half-bridges simultaneously, reducing the need for additional operational amplifiers while maintaining measurement accuracy.
Solution Approach 2:
Instead of using a single complex measurement circuit for the entire full-bridge, the patent uses a simplified measurement circuit replicated in each half-bridge. This copying approach reduces the complexity of individual measurement circuits while achieving accurate full-bridge current measurement through the differential combination of the replicated circuits.
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 provides continuous and accurate current measurement, overcoming Nyquist criterion violations and reducing circuit complexity, resulting in improved control accuracy, wider bandwidth, and reduced position errors in motor control systems.
Implementation Method 1
A voltage is tapped off from each of two measurement devices, and this voltage is a measure of the current through the respective measurement device
Data Source
AI summary
The invention provides a method and a circuit arrangement for measurement of the current through an inductive load L wherein the current is fed into the inductive load L with the aid of a full-bridge circuit. By way of example, full-bridge circuits such as these are used to feed a current in a pulse-width-modulated form into a winding of a direct-current, stepping or plunger coil motor. A respective measurement device (Ra, Rb) is provided for each half-bridge. In this case, a respective measurement device (Ra, Rb) is arranged between in each case one series circuit of switching elements and ground (VSS) or the supply voltage (VDD), respectively, at which a respective voltage is tapped off, which is a measure of the current through the respective measurement device. The device for measurement of the current has at least one switching device (S), by means of which one of the two inputs (e1, e2) of differential amplifier (D) can be selectively connected to ground (VSS) or to the supply voltage (VDD), or to one of the two measurement devices.