Induction motor temperature measurement using phase controlled alternating current
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Solution Overview
Problem
Existing methods for monitoring motor temperature in line-fed induction motors, particularly in laundry appliances, are inadequate as they require additional components like DC power supplies and static motor operation, which are not feasible in all systems, leading to potential motor tripping and prolonged reset times.
Innovation Solution
A method using phase-controlled AC excitation and current measurement to monitor the temperature of line-fed induction motors, allowing for temperature fold-back procedures to prevent overheating, by applying a phase-limited AC voltage that is insufficient for starting torque, enabling current flow measurement without the need for additional power supplies or static motor operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a DC injection method is used to measure motor winding resistance for temperature monitoring, then temperature measurement capability is improved, but device complexity increases due to requirement of additional DC power supply and control circuitry
Solution Approach 1:
The motor's own AC power supply and control circuitry are utilized to perform temperature measurement, eliminating the need for separate DC power supply and measurement circuitry. The existing AC drive system serves dual purposes: motor control and temperature monitoring.
Solution Approach 2:
The AC power supply and control circuitry are designed to perform multiple functions: both motor control and temperature measurement. The same circuit components used for driving the motor are also used to inject measurement currents and sense resistance changes for temperature monitoring.
2Device complexity
If AC excitation is used to measure motor temperature, then device complexity is reduced, but the motor must be kept static which reduces productivity
Solution Approach 1:
Temperature measurement is performed periodically by briefly interrupting motor operation at predetermined intervals during the wash cycle. The motor is energized with AC voltage, current flow is measured, and this periodic measurement process continues throughout the operational cycle without requiring the motor to remain completely static.
Solution Approach 2:
The control system is pre-programmed with a measurement schedule that determines when temperature measurements should be taken during the wash cycle. This allows the system to proactively monitor temperature at optimal intervals without waiting for fault conditions or manual intervention.
3Reliability
If a motor temperature sensor with trip function is used, then temperature protection is improved, but loss of time increases due to lengthy reset time after tripping
Solution Approach 1:
The control system continuously monitors motor temperature through periodic AC excitation measurements and uses this feedback to dynamically adjust operation. When elevated temperature is detected, the system responds by reducing motor load or extending measurement intervals to allow cooling, preventing the need for complete shutdown and reset.
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 effective temperature monitoring and management during operational cycles, reducing the risk of motor overheating and associated delays, thereby improving appliance performance and customer satisfaction.
Implementation Method 1
injection of a direct current (DC) into the motor windings to measure motor winding resistance as it varies with temperature
Data Source
AI summary
Methods and systems are provided for monitoring current flow in an induction motor, particularly an induction motor associated with a washing machine and for controlling operation of the motor to limit thermals during operation of the motor. The subject matter provides for periodically stopping the motor and applying a phase limited alternating (AC) voltage to the motor that is of insufficient magnitude to start the motor rotating. A current reading is taken and converted using a look up table to a corresponding temperature. If the temperature exceeds a predetermined amount, temperature fold back procedures are initiated the may include shortening and/or pausing certain washer operations.