Dual-Bridge Motor Current Sensing for High-Side Fault Detection
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Solution Overview
Problem
Existing dual bridge and dual current sensor designs for motor control circuits fail to accurately measure current in phases during faults, such as high-side short circuits, as the fault current bypasses the current sense resistor, preventing effective fault detection and motor performance compensation.
Innovation Solution
A motor circuit with two independent sets of phase windings and bridge drivers, utilizing a single current sensor for each set and a third sensor to measure the combined current across pairs of phases, allowing for accurate current determination in both sets even during faults, and a controller that generates compensating signals to maintain motor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two independent bridge drivers are provided for fault resilience, then motor reliability is improved, but device complexity increases
Solution Approach 1:
The patent combines two independent current sensing systems into a single integrated current sensor that measures the sum of currents from both bridge drivers. This merging approach maintains the reliability benefits of dual bridge drivers while reducing device complexity by eliminating redundant current sensing components and simplifying the control system architecture.
2Measurement precision
If two current sensors are provided for each bridge driver, then current measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent merges the current sensing function for both bridge drivers into a single current sensor that measures the combined current. This approach maintains adequate measurement precision for fault detection while significantly reducing device complexity by eliminating redundant sensors and associated circuitry.
Solution Approach 2:
The single current sensor performs multiple functions: it senses current from the first bridge driver, senses current from the second bridge driver, and enables fault detection for both drivers. This multi-functionality approach reduces the number of components needed while maintaining the necessary measurement capabilities.
3Ease of operation
If current is sensed through low-side MOSFETs, then ease of operation is improved, but measurement precision deteriorates during high-side short circuit faults
Solution Approach 1:
The patent introduces a single current sensor as an intermediary measurement point that captures the combined current from both bridge drivers. This intermediary approach allows the system to maintain the operational simplicity of low-side MOSFET switching while achieving accurate current measurement even during high-side short circuit faults, as the sensor measures the total current flowing through the system.
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 continuous operation and accurate fault detection by measuring current in all phases, even when one lane is faulty, ensuring the motor maintains performance and stability by compensating for the effects of faulted phases.
Implementation Method 1
A current sense resistor may be provided in a common output line from the motor through which the current from the motor must pass, the voltage dropped across the resistor providing the indication of the current based on the application or Ohms law.
Data Source
AI summary
A motor circuit for driving a motor having two independent sets of windings forming 3 or more phases, wherein each phase of a first set is paired with a respective phase of a second set. A first bridge driver circuit has a top side switch and a bottom side switch driving each phase of the first set, and a second bridge driver circuit has a top side switch and a bottom side switch driving each phase of the second set. First and second current determining means determine current flowing in each respective sets of windings independent of the current flowing in the other set of phase windings. A third current determining means is configured to determine the sum of the current flowing in each pair of the N pairs of phases of the motor.