Motor Control Device Abnormality Detection Shunt Resistor
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Solution Overview
Problem
Existing motor controlling devices for three-phase brushless motors face challenges in detecting abnormalities in switching elements without increasing costs, as they either use expensive hall-effect sensors or shunt resistors that deteriorate in measurement accuracy with high duty ratios.
Innovation Solution
A motor controlling device with an inverter circuit that includes high-side and low-side switching elements and shunt resistors, where the power control unit acquires current values from shunt resistors and decides abnormality based on these values, allowing for simultaneous current value acquisition across phases without impairing the advantages of using shunt resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If hall-effect sensors are used to detect current in each phase, then measurement precision is improved, but device cost increases
Solution Approach 1:
The patent replaces expensive hall-effect sensors with inexpensive shunt resistors for current measurement. The shunt resistors provide adequate measurement precision for the application while dramatically reducing device cost, embodying the principle of using cheap components to achieve the required performance without unnecessary expense.
Solution Approach 2:
The patent substitutes the electromagnetic sensing mechanism (hall-effect sensors) with a simpler resistive voltage division mechanism (shunt resistors). This replacement eliminates the need for complex electromagnetic components while achieving the same current measurement function through basic electrical principles.
2Ease of manufacture
If shunt resistors are used to detect current from low-side switching element, then device cost is reduced, but measurement precision deteriorates when duty ratio of high-side switching element is high
Solution Approach 1:
The patent performs preliminary action by temporarily turning on the low-side switching element and turning off the high-side switching element at a predetermined timing before the main operation. This creates a dedicated measurement window where the shunt resistor can accurately measure current without being affected by high duty ratio conditions during normal operation.
Solution Approach 2:
The patent implements periodic measurement cycles where the switching elements are temporarily reconfigured to enable shunt resistor measurement. This periodic action occurs at specific intervals (when high-side element is turning off or has turned off) to capture current information without disrupting the overall motor control operation.
3Measurement precision
If current sensor is provided in each phase, then measurement precision is improved, but device cost increases
Solution Approach 1:
The patent makes the shunt resistor serve multiple functions: it acts as a current sensing element during motor operation and also serves as a test signal generation element when temporarily activated. This multi-functionality eliminates the need for separate current sensors in each phase, reducing device cost while maintaining measurement precision through the same component.
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 and cost-effective abnormality detection in switching elements and the motor, maintaining high measurement accuracy and preventing torque reduction, while reducing costs compared to hall-effect sensor arrangements.
Implementation Method 1
a shunt resistor is incorporated in a current line through which a current from the low-side switching element flows. The technique disclosed in this Patent Document 2 is arranged such that a current flowing through the low-side switching element is converted into a voltage signal via the shunt resistor
Data Source
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AI summary
Provided is a controlling device that allows decision of abnormality in a switching element without impairing the advantage of using a shunt resistor. This motor controlling device includes a high-side first switching element corresponding to each phase of a three-phase brushless motor, a low-side second switching element corresponding to each phase, a shunt resistor disposed between and connected to the second switching element and a grounding line, and a power controlling section for controlling the first switching element and the second switching element. The device further includes a decision section configured to effect an abnormality decision based on a sum of values of currents flowing in the shunt resistors of all the phases acquired by using the power controlling section to switch OFF the first switching element of any one phase whose duty ratio is found equal to or greater than a threshold value for a predetermined period and also to switch ON the second switching element of the same one phase for the predetermined period.