Capacitive Winding Temperature Monitoring in EC Motors
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Solution Overview
Problem
Conventional circuits for monitoring the temperature and characteristics of electric motor winding leads require additional connections and components, increasing complexity and effort, and existing solutions either need extra cables or require the temperature monitor to carry the motor current, which is inefficient.
Innovation Solution
An electronic circuit using capacitive two-terminal poles with temperature-dependent impedance, connected in parallel to the winding connections, and a current detection device to analyze steep-edged voltage changes from the frequency converter, allowing temperature monitoring without additional lines or switching elements, utilizing existing current detection mechanisms in EC motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional temperature monitor switches or temperature-dependent resistors are used to monitor winding temperature, then temperature monitoring function is achieved, but additional connection elements and evaluation circuits are required, increasing device complexity
Solution Approach 1:
The existing current detection device, originally designed for overcurrent detection, is made multi-functional by enabling it to detect temperature through response function analysis. The same hardware infrastructure (current sensors, processors) serves both overcurrent protection and temperature monitoring purposes, eliminating the need for separate temperature sensing circuits and reducing overall system complexity.
Solution Approach 2:
The motor winding itself serves as the temperature sensor through its inherent electrical characteristics. The impedance of the winding changes with temperature, and this change is detected by analyzing the response function of the winding when excited by voltage steps. The system uses the motor's own properties for self-diagnosis without requiring external sensing elements.
2Measurement precision
If three temperature monitor switches are used to detect asymmetric temperature increases in each winding strand, then detection precision is improved, but the number of connections and components increases
Solution Approach 1:
The single current detection device performs the function of multiple temperature monitor switches by analyzing phase-specific current responses. Each phase winding's response function is independently analyzed to detect temperature conditions, achieving the same monitoring capability as three separate switches without requiring three separate detection circuits.
Solution Approach 2:
The temperature monitoring function is extracted from the physical temperature sensor domain and implemented in the electrical signal processing domain. Instead of using physical switches that open at threshold temperatures, the system extracts temperature information from the electrical response characteristics of the windings, eliminating the need for physical temperature-sensing components.
3Device complexity
If a digital temperature monitor is integrated directly in series with winding strands, then temperature monitoring is achieved without additional cables, but the monitor must carry all motor current during normal operation, increasing energy loss
Solution Approach 1:
The temperature monitoring function is extracted from the power path and implemented in the signal processing domain. The current detection device measures current through sensing elements with minimal impedance, separate from the main power carrying conductors. This allows temperature monitoring without placing any significant additional impedance or energy loss in the power path.
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 reliable and simple temperature monitoring of winding leads without additional connections, using existing current detection devices to analyze response functions for temperature and other characteristics, reducing circuit complexity and component count.
Implementation Method 1
capacitive two-terminal poles with a temperature-dependent impedance
Implementation Method 2
a current detection device as a detector for detecting the current responses in the phase windings due to steep-edged voltage changes of the frequency converter
Data Source
Figure 1~2d
Figure 2e~4
Figure 5~5(e)
AI summary
The invention relates to an electronic circuit (1) for detecting the current winding temperature of phase windings (10) and/or for detecting other characteristics of an electronically commutated electric motor (2) which is connected, or can be connected to a frequency converter (3). The circuit comprises one or more capacitive two-terminal networks (6) with a temperature-dependent impedance, each network being arranged parallel to two winding terminals (u, v, w) of the phase windings (10). The invention also relates to a detector (20) for detecting the current responses in the motor feeds on the basis of steep-flanked voltage changes at the output of the frequency converter.