Braking Resistor Resistance Estimation for Power Switch Protection
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Solution Overview
Problem
In electrical machine control systems, improper resistance values of braking resistors can lead to excessive braking current, reducing the lifespan of power switches and potentially causing them to burn out, disrupting normal system operation.
Innovation Solution
An estimating method is developed to determine the resistance value of the braking resistor based on operating parameters, specifically by monitoring bus voltage and current variations across a bus capacitor and switch, allowing for the calculation of resistance values during different switch states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the resistance value of the braking resistor is improper, then the braking current becomes too large, but the lifespan of the power switch is reduced and the system reliability deteriorates
Solution Approach 1:
The patent applies preliminary action by estimating the resistance value of the braking resistor before the power switch is activated. The system calculates the expected braking current based on the measured resistance value and compares it with the maximum allowable current. This pre-assessment prevents excessive current from damaging the power switch, thereby extending its lifespan and improving system reliability.
2Loss of energy
If the resistance value of the braking resistor is too low, then the braking current becomes excessive, but the braking resistor cannot effectively dissipate energy
Solution Approach 1:
The patent implements feedback by continuously monitoring the resistance value of the braking resistor and using this information to control the power switch. The system estimates the resistance value, calculates the corresponding braking current, and compares it with the maximum allowable current. Based on this feedback, the power switch is controlled to turn on or off, ensuring that the braking resistor operates within safe current limits while effectively dissipating energy.
3Ease of operation
If the resistance value of the braking resistor is improper, then the braking current becomes too large, but the system cannot operate normally
Solution Approach 1:
The patent applies preliminary action by performing resistance value estimation and current calculation before the power switch is activated. The system measures the resistance value of the braking resistor, estimates the expected braking current, and compares it with the maximum allowable current. This pre-assessment ensures that the system can operate normally by preventing excessive current from damaging the power switch, thereby maintaining both ease of operation and reliability.
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 method enables users to verify the proper resistance value of the braking resistor, reducing the risk of power switch failure and extending its lifespan by ensuring appropriate resistance values are used.
Implementation Method 1
a bus voltage across both terminals of the bus capacitor is monitored continuously
Implementation Method 2
the electric energy that is recharged to the electrical machine control system is consumed in the form of heat
Data Source
AI summary
An estimating method includes the following steps. Firstly, if the electrical machine control system is in the generator mode, a bus voltage of the bus capacitor is monitored continuously. Then, if the switch is turned to an on state, a first current value of a current flowing through the bus capacitor during an off state of the switch is calculated. Then, the switch is turned to the on state. Then, if the switch is turned to the off state, a second current value of a current flowing through the bus capacitor during the on state of the switch is calculated, and a resistance value of the braking resistor is estimated according to the first current value and the second current value.