Braking Transistor Fault Detection to Protect DC Bus Resistors
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Solution Overview
Problem
Frequency converters with braking transistors and resistors connected in series face the risk of short circuits due to aging or overload, leading to permanent current flow through the resistor, which can cause destruction, flames, and safety hazards.
Innovation Solution
An electronic protection circuit that measures the collector-emitter voltage of the braking transistor to determine its state and compares it with a predetermined value, using a shutdown device to immediately interrupt current flow if a defect is detected, preventing further damage to the resistor and ensuring safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the braking transistor switches on the braking resistor during braking operation, then the intermediate circuit voltage is reduced, but permanent current flow through the resistor can cause destruction and safety hazards
Solution Approach 1:
The patent applies preliminary action by continuously monitoring the braking transistor's state before permanent damage can occur. The detection means constantly checks the collector-emitter voltage, and the comparison means compares it with the control signal state in advance, triggering the shutdown device to open the circuit breaker before the braking resistor can be permanently damaged by excessive current flow.
Solution Approach 2:
The patent converts the potentially harmful permanent current flow through the braking resistor into a beneficial protective action. By detecting the abnormal current flow condition and automatically triggering the circuit breaker to open, the system transforms the harmful situation into an opportunity to prevent damage, effectively using the fault condition as a trigger for protective shutdown.
2Reliability
If a protection circuit is added to monitor the braking transistor, then safety is improved, but the device complexity increases
Solution Approach 1:
The patent applies universality by designing the protection circuit components to serve multiple functions. The voltage detection means not only monitors the braking transistor state but also provides signals for the comparison means. The comparison means both compares control signal with actual state and triggers the shutdown sequence. The circuit breaker serves both as a protective device and as a circuit control element, reducing the need for separate dedicated components.
Solution Approach 2:
The patent merges multiple protection functions into a integrated control system. The detection means, comparison means, and shutdown device are combined into a unified protection circuit that works together as a cohesive system. The control signal line is utilized for both normal braking control and fault detection, eliminating the need for completely separate monitoring circuits and reducing overall system complexity.
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
The protection circuit effectively prevents the destruction of the braking resistor by interrupting current flow in case of a transistor defect, thereby safeguarding both people and property from potential harm.
Implementation Method 1
The braking resistor converts part of the stored energy in the intermediate circuit into heat, which reduces the voltage applied to the intermediate circuit
Data Source
Figure 1~2
AI summary
The invention relates to an electronic protection circuit for a braking resistor (12) of an intermediate circuit (4) connected in series with a braking transistor (13), wherein the braking transistor (13) can be switched by means of a control signal (27) depending on a voltage applied to the intermediate circuit (4), with a measuring device that measures the collector-emitter voltage applied to the braking transistor (13) and outputs a corresponding measurement signal (23), with a first comparator device (24) that compares the measurement signal (23) with a predefinable reference value (25) and outputs a corresponding reference signal (26), with a second comparator device (33) that compares the reference signal (26) with the control signal (27) for the braking transistor (13) and outputs a control signal (28) if there is an inequality.and with a shut-off device (14) which, upon detection of a control signal (28) emitted by the second comparator device (33), interrupts the current flow in the intermediate circuit (4),