Motor Current Detection Using Shared Wire for Drive and Motor Currents
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Solution Overview
Problem
In air conditioning apparatuses where the motor and driver are integrated, existing methods for detecting motor current become complicated due to the drive current flowing through the same wire as the motor current, making it difficult to accurately measure the motor current.
Innovation Solution
A motor current calculation device comprising a first wire for both motor and drive currents, a current detecting unit, a decision unit, and a calculation unit that subtracts the drive current from the total current when the motor is not rotating to isolate the motor current, and an optional current leveling unit to stabilize the detection results.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shunt resistor is connected in series to detect motor current, then the motor current can be detected, but the drive current flowing through the same wire makes it difficult to obtain the motor current only
Solution Approach 1:
The patent segments the current detection process into two distinct phases: first detecting the drive current when the motor is stationary, then detecting the combined current when the motor operates. By separating these measurement phases in time, the system can isolate and subtract the drive current component from the total current to obtain the motor current accurately.
Solution Approach 2:
The patent performs preliminary detection of the drive current before the motor starts rotating. This preliminary measurement establishes a baseline value that is stored and later subtracted from the operational current measurement, enabling accurate motor current detection without requiring separate wiring for drive and motor currents.
2Measurement precision
If separate wiring is used for motor current and drive current detection, then accurate motor current measurement is achieved, but the configuration becomes complicated when motor and driver are integrated
Solution Approach 1:
The patent merges the detection of drive current and motor current into a single detection path using one shunt resistor. By combining these measurements temporally rather than spatially, the system achieves accurate motor current measurement while maintaining a simple, integrated configuration suitable for motor-driver integrated designs.
Solution Approach 2:
The system uses the existing common wire that carries both drive and motor currents for detection purposes, rather than requiring additional dedicated wiring. The single shunt resistor leverages the natural current flow path to extract both measurement components through sequential detection, eliminating the need for separate measurement infrastructure.
3Adaptability or versatility
If the motor and driver are built into a motor device, then integration is achieved, but detecting motor current becomes difficult due to drive current interference
Solution Approach 1:
The patent employs periodic measurement cycles: first measuring drive current during a stationary phase, then measuring total current during operation. This periodic sampling approach, synchronized with motor state transitions, enables the system to distinguish and separate drive current from motor current even in an integrated configuration.
Solution Approach 2:
The patent uses the microcomputer as an intermediary that processes the raw current measurements. By subtracting the stored drive current value from the operational current measurement, the microcomputer extracts the motor current component, effectively mediating between the combined current signal and the desired motor current information.
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 simple and accurate determination of motor current even when both motor and drive currents flow through the same wire, reducing microcomputer capacity requirements and ensuring stable detection results, allowing for precise control of air volume in air conditioning systems.
Implementation Method 1
there is known a technology where shunt resistor used as current-detecting elements are serially connected to the wiring through which the motor current flows, and the motor current is detected based on the voltages at either end of the shunt resistor
Data Source
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AI summary
A motor current calculation device (9) comprises a GND wire (94), a current detecting unit (95), a decision unit (96a), and a calculation unit (96b). A motor current (Im) that has been passed through a second fan motor (81) and a drive current (Id) that has been passed through a second motor driver (82) for driving the second fan motor (81) both flow through the GND wire (94). The current detecting unit (95) detects the sum of the motor current (Im) and the drive current (Id) flowing through the GND wire (94). The decision unit (96a) determines a detection result of the current detecting unit (95) when the second fan motor (81) is not rotating as the drive current (Id). The calculation unit (96b) calculates the motor current (Im) by subtracting the drive current (Id) determined by the decision unit (96a) from a detection result of the current detecting unit (95) when the second fan motor (81) is rotating.