Capacitor Temperature Estimation for Electric Power Steering
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Solution Overview
Problem
Conventional rotary electric machine controllers that estimate temperature to prevent overheating often fail to accurately protect capacitors, leading to excessive current limitation and reduced motor performance due to overestimation of temperature changes.
Innovation Solution
A rotary electric machine controller with a capacitor current estimating unit, capacitor temperature estimating unit, and current limiting unit that accurately estimates capacitor temperature and limits current based on this estimation, avoiding excessive current limitation and ensuring motor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the capacitor temperature is over-estimated to ensure safety, then the capacitor is protected, but the current is excessively limited and motor performance cannot be exhibited
Solution Approach 1:
The system dynamically changes the temperature estimation parameters based on operating conditions. By calculating capacitor temperature using equivalent series resistance and actual current measurements rather than conservative fixed values, the system achieves accurate real-time temperature assessment, preventing both over-protection and under-protection scenarios.
Solution Approach 2:
The patent implements feedback control where the estimated capacitor temperature is continuously monitored and used to adjust current limiting decisions. The temperature estimation feedback loop allows the system to maintain safe operating temperatures while maximizing current output within actual thermal constraints, avoiding unnecessary performance limitations.
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 solution improves temperature estimation accuracy for capacitors, preventing excessive current limitation and maintaining motor performance by accurately assessing capacitor temperature and adjusting current accordingly.
Implementation Method 1
The capacitor is connected to the power supply and smooths the voltage of the power supply
Implementation Method 2
The capacitor current estimating unit estimates the current flowing in the capacitor based on the current flowing through the rotary electric machine
Implementation Method 3
The capacitor temperature estimating unit estimates the temperature of the capacitor based on the current flowing through the capacitor
Data Source
AI summary
A capacitor current estimating unit estimates a capacitor current based on phase currents. A capacitor temperature estimating unit estimates a capacitor temperature based on the capacitor current. A motor controller can accurately estimate not only a temperature of a switching element but also the capacitor temperature based on the phase currents. As a result, the capacitor does not need to have excessive heat characteristics. Further, a current limiting unit limits a current flowing from a battery to an inverter based on the capacitor temperature. Therefore, an amount of temperature change is not over-estimated due to overheating of the capacitor. As a result, excessive current limitation can be avoided and the performance of the motor can be demonstrated.