Stator Winding Temperature Monitoring via DC Injection
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Solution Overview
Problem
Existing methods for thermal protection of AC motors are inaccurate and inefficient, particularly in de-energized conditions, due to reliance on thermal models and large voltage/current inputs, which can lead to premature damage from overheating or condensation.
Innovation Solution
A system and method using a motor control device with switching devices to generate a DC signal and estimate stator winding resistance, allowing for accurate temperature monitoring and controlled heating of AC motors in idle or shutdown conditions without adding resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal model-based methods are used to estimate stator winding temperature, then temperature estimation is possible without direct measurement, but accuracy falls outside acceptable ranges due to thermal parameter variation and identification difficulty
Solution Approach 1:
The patent replaces complex thermal model-based temperature estimation with a simpler electrical resistance measurement approach. By measuring stator winding resistance and using its known temperature dependence, the system directly determines temperature without requiring thermal parameter identification or complex thermal models, thus improving accuracy while reducing complexity
Solution Approach 2:
The patent utilizes the temperature-dependent electrical resistance parameter of the stator winding as a direct temperature indicator. By monitoring resistance changes and correlating them to temperature through the known temperature coefficient of copper, the system achieves accurate temperature measurement without complex thermal modeling
2Temperature
If two phases of stator windings are used for heating with a single current flow path, then heating function is achieved, but one phase remains unheated or relies on inductive heat
Solution Approach 1:
The patent divides the heating function across all three phases by implementing separate current paths for each phase. By independently controlling heating current in each phase through individual switching devices, the system ensures uniform heating distribution across all stator windings, eliminating the unheated phase problem
Solution Approach 2:
The patent implements dynamic control of heating currents in each phase through independently controlled switching devices. The controller can adjust the magnitude and duration of heating currents applied to each phase based on real-time temperature measurements, ensuring balanced and uniform heating across all phases
3Power
If large voltage and current input is applied to heat the motor, then sufficient heating power is achieved, but stator winding life is reduced
Solution Approach 1:
The patent applies partial heating action by using controlled, limited-duration heating current pulses rather than continuous high-power input. The switching devices enable precise control of heating current magnitude and duration, applying just enough power to achieve the desired temperature increase without excessive stress on the windings
Solution Approach 2:
The patent implements periodic heating cycles with controlled duration and intensity. The switching devices can apply heating currents in periodic pulses, allowing the windings to heat gradually to the target temperature without sustained exposure to high current levels that would degrade insulation and reduce winding life
4Reliability
If motor is tripped by overload relays for thermal protection, then motor overheating is prevented, but production time is lost due to required recovery time
Solution Approach 1:
The patent implements continuous temperature monitoring through resistance measurement and active feedback control. When temperature approaches the trip threshold, the system automatically reduces or stops heating current application, preventing the need for protective tripping and enabling continuous operation without production loss
Solution Approach 2:
The patent applies preliminary thermal management by actively monitoring temperature and controlling heating before overheating conditions develop. The system preemptively adjusts heating power based on real-time temperature feedback, preventing the thermal stress that would trigger overload relay tripping and subsequent production interruptions
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 efficient and non-intrusive remote monitoring and heating of stator windings, preventing overheating and condensation damage by accurately determining and maintaining optimal temperatures.
Implementation Method 1
The triggering of a series of switches in a motor control device can generate a DC signal in an output of the motor control device
Implementation Method 2
This DC signal is analyzed to determine a stator winding resistance
Implementation Method 3
The switches can be controlled to heat the stator windings to a desired temperature
Data Source
AI summary
A system and method for measuring and controlling stator winding temperature in an AC motor while idling is disclosed. The system includes a circuit having an input connectable to an AC source and an output connectable to an input terminal of a multi-phase AC motor. The circuit further includes a plurality of switching devices to control current flow and terminal voltages in the multi-phase AC motor and a controller connected to the circuit. The controller is configured to activate the plurality of switching devices to create a DC signal in an output of the motor control device corresponding to an input to the multi-phase AC motor, determine or estimate a stator winding resistance of the multi-phase AC motor based on the DC signal, and estimate a stator temperature from the stator winding resistance. Temperature can then be controlled and regulated by DC injection into the stator windings.