Braking Resistor Value Estimation in Power Converters
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Solution Overview
Problem
Existing power converters lack a method to accurately estimate the value of the braking resistor, which is crucial for ensuring the integrity of switching devices and diodes during braking, as no protective system is provided to guarantee a minimum resistance value.
Innovation Solution
A method and system that determine the capacitance of the bus capacitor and the braking resistor's value during motor braking, using the DC bus voltage and current generated, and compare it to a minimum required value, activating freewheel braking if the resistor value is insufficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If no protective system is provided to guarantee minimum resistance value, then the power converter structure remains simple, but the switching device and diode may be damaged during braking
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring the braking resistor value through capacitance measurement and comparing it against a minimum threshold value. The control unit adjusts the braking cell operation based on this feedback, activating freewheel braking when the resistor value falls below the threshold, thereby protecting the switching device and diode without requiring a complex protective system structure
Solution Approach 2:
The system uses the existing bus capacitor and its inherent capacitance characteristics to self-diagnose the braking resistor value. By measuring the voltage decay rate of the bus capacitor during braking, the system automatically determines the resistor value and triggers protective actions without requiring external protective devices or complex additional components
2Reliability
If the braking resistor value is not monitored, then the system operation is simple, but the switching device and diode may be damaged due to insufficient resistance
Solution Approach 1:
The patent replaces physical protective mechanisms with an electrical measurement and control system. Instead of using mechanical switches or complex protective circuits, the system uses electrical capacitance measurement and digital comparison to monitor braking resistor value and control the braking cell, simplifying the overall system while ensuring reliability
Solution Approach 2:
The bus capacitor serves multiple functions: it maintains DC bus voltage during normal operation and simultaneously acts as a measurement probe for detecting braking resistor value during braking. This multi-functionality eliminates the need for separate monitoring hardware, maintaining ease of operation while enabling protective functionality
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 effectively estimates the braking resistor's value, preventing damage to switching devices and diodes by ensuring it meets the minimum required resistance, thereby maintaining system integrity and safety during braking operations.
Implementation Method 1
a bus capacitor connected to the two power supply lines and responsible for maintaining the DC voltage of the bus at a constant value
Implementation Method 2
the electrical energy generated during motor braking cannot be returned to the network and is for example dissipated in a resistor, called braking resistor
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a method for estimating the value of a braking resistor (Rf) used in a power converter connected to an electric motor (M). The power converter comprises a braking cell (CelF) connected to the first power supply line (L1) and to the second power supply line (L2) of the bus of the converter, and comprises a switching member (Sw), a diode (D) connected in series to the switching member, and the braking resistor (Rf) connected in parallel to said diode. Said method is implemented during the braking of the electric motor (M), and involves: determining the capacity value (C) of the bus capacitor when the switching member is in an open state; and determining the value (R) of the braking resistor (Rf) from the capacity value (C) of the bus capacitor, the voltage (Vbus) of the continuous power supply bus, and the current (Im) generated by the electric motor during braking when the switching member is in a closed state.