Soft Starting System for Electrical Motor Using Rogowski Sensor
Solution Overview
Problem
Existing soft-start systems for electric motors, particularly those powered by high voltage networks, face challenges in minimizing voltage transients during motor starting, which can lead to thyristor damage and increased system complexity due to electromagnetic interference (EMI) from high-frequency harmonics and magnetic fields.
Innovation Solution
The implementation of Rogowski torus sensors to measure the derivative of current flowing through electronic switches, coupled with a detection card that processes the signal to generate a binary representation of zero crossings, allowing for precise thyristor control without the need for analog-to-digital conversion and optical transmission, and using optical fiber for fast, isolated signal transmission to minimize EMI effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage measurement is used to determine thyristor closing timing, then thyristor reliability is improved, but measurement precision requirements and system complexity increase due to need for high-frequency sampling and sophisticated signal processing
Solution Approach 1:
The invention changes the measured parameter from voltage to current derivative. Instead of measuring voltage directly to determine when it reaches minimum values for thyristor closing, the system measures the derivative of current flowing through the snubber circuit. This parameter change simplifies the measurement requirements while maintaining the ability to determine optimal thyristor closing timing, thereby improving reliability without increasing system complexity.
2Measurement precision
If Rogowski torus sensor is used to measure current derivative, then measurement speed and precision are improved, but electromagnetic interference from high voltage environments increases
Solution Approach 1:
The invention introduces an intermediary approach by using a Rogowski torus sensor that measures current derivative in a non-contact manner. The sensor acts as an intermediary between the high voltage environment and the measurement system, providing galvanic isolation. This allows precise measurement of the current derivative through the snubber circuit while protecting the measurement electronics from electromagnetic interference and high voltage conditions.
3Productivity
If high voltage motor starting is controlled with electronic switches, then motor starting performance is improved, but thyristor durability decreases due to transient voltage and current stress
Solution Approach 1:
The invention implements feedback control by continuously monitoring the derivative of current through the snubber circuit and using this information to determine the optimal closing timing of thyristors. The system closes thyristors at moments when the current derivative indicates minimum voltage stress conditions. This feedback mechanism ensures that thyristors are switched at the most favorable moments, reducing transient voltage and current stress while maintaining effective motor starting control, thereby improving both productivity and thyristor durability.
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
This solution enables precise and reliable triggering of thyristors, reducing electrical stress and system complexity, while maintaining high precision and speed, thus enhancing the durability and performance of the soft-start system in high voltage environments.
Implementation Method 1
a sensor such as for example a Rogowski torus is used, which has the advantage of delivering a signal with a negligible delay of the order of a microsecond
Implementation Method 2
using optical fiber for fast, isolated signal transmission to minimize EMI effects
Data Source
Figure 1~2
Figure 3~4
AI summary
A starting system for an electric motor (M) powered by an electrical network (1), the starting system comprising an electronic control circuit (7) and an electronic switching switch (10) for controlling one phase of the motor (M), the electronic switching switch (10) being controlled by the control circuit (7). The starting system includes a sensor (3) for providing an analog signal (4) representing the derivative of a current flowing in the phase of the motor (M), a detection board (5) comprising means for transforming said analog signal (4) into a binary signal (6) representing the sign changes of said analog signal, and comprising means for transmitting said binary signal to the control circuit (7), so as to optimize the control of the electronic switching switch (10).