Motor Current Detection Using Leveled Drive Current Signals
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Solution Overview
Problem
In air conditioning systems where the motor and driver are integrated into a motor device, existing current detection methods struggle to accurately measure motor current due to the drive current flowing through the shunt resistor, making it difficult to separate and quantify the motor current accurately.
Innovation Solution
A current detecting device with a current leveling unit that levels the drive current, allowing for accurate determination of motor current by detecting the sum of motor and drive currents on a single wire, and a correction constant calculating system that adjusts for variations in the motor and detection unit, using a filter circuit with a resistor and capacitor to level the drive current and a power meter to calculate a correction constant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shunt resistor is connected in series on the wire to detect motor current, then the motor current can be detected using both end voltages of the shunt resistor, but the drive current flowing through the motor drive unit also flows through the shunt resistor, making it difficult to obtain an accurate motor current
Solution Approach 1:
The current detection is segmented into two parts: drive current detection (using the sum of both end voltages of the shunt resistor) and motor current detection (using the difference between both end voltages). This segmentation allows separate measurement and processing of drive current and motor current components, enabling accurate motor current extraction despite drive current interference.
Solution Approach 2:
The patent introduces an intermediary calculation method where the motor current is derived as the difference between the sum of both end voltages and the drive current. This intermediary approach acts as a mediator to eliminate the drive current component from the total current measurement, leaving only the accurate motor current value.
2Volume of moving object
If the motor and motor drive unit are built into a motor device, then the configuration is more compact, but it becomes difficult to separately dispose the wire for motor current and the wire for drive current, making accurate current detection more difficult
Solution Approach 1:
The patent uses an intermediary calculation approach where the motor current is obtained by subtracting the drive current from the sum of both end voltages of the shunt resistor. This mathematical intermediary method allows current separation without requiring physical wire separation, enabling accurate detection in compact motor device configurations.
Solution Approach 2:
The shunt resistor serves multiple functions: it detects both the drive current and the combined current (drive current + motor current). This multi-functionality allows the same component to provide information for both current types, eliminating the need for separate wires and enabling accurate motor current detection in integrated motor device configurations.
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 motor current detection and control, even when the drive current fluctuates, and ensures precise motor speed control by accounting for individual motor variations, resulting in consistent air volume delivery and improved system performance.
Implementation Method 1
a capacitor (C1) is connected to the drive-use power supply wire (92) in parallel with respect to the resistor (R1)
Data Source
AI summary
A current detecting device includes a current leveling unit, a first wire and a current detecting unit. The current leveling unit is configured to level a drive current that is passed through a motor drive unit to drive a motor. The first wire is configured and arranged to carry flow of a motor current that has been passed through the motor and the drive current that has been leveled by the current leveling unit. The current detecting unit is configured to detect a sum of the motor current flowing on the first wire and the drive current that has been leveled flowing on the first wire.