Electric Machine Torque Estimation Using Flux and Power Balance
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Solution Overview
Problem
Existing methods for estimating the torque of electric machines, particularly in electric vehicles, are inaccurate at high and low speeds, and costly due to the need for precise sensor measurements.
Innovation Solution
A method that combines two torque estimation methods—cross product of magnetic flux and actual current, and power balance with an inverter—using weighted averaging to improve accuracy and reduce susceptibility to errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensor-based torque measurement is used to achieve high accuracy, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces mechanical sensor-based torque measurement with an electrical calculation method. Torque is estimated by computing the cross product of estimated magnetic flux and phase currents, substituting physical sensors with mathematical models that process electrical signals already present in the control system.
Solution Approach 2:
The patent introduces an intermediary estimation process that uses magnetic flux as a intermediate variable. Instead of directly measuring torque with sensors, the system first estimates magnetic flux from electrical measurements, then derives torque from this intermediate quantity, allowing accurate torque estimation without direct mechanical sensing.
2Measurement precision
If high-precision sensors are used to meet torque accuracy requirements, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent uses inexpensive electrical measurements (current and voltage signals already available in the drive system) instead of expensive mechanical torque sensors. The estimation method leverages low-cost electrical sensors that are already part of the motor control system, eliminating the need for additional expensive measurement hardware.
Solution Approach 2:
The patent substitutes expensive mechanical torque measurement systems with an electrical calculation approach using magnetic flux and current vectors. This replacement eliminates costly sensors while maintaining the required measurement precision through mathematical estimation based on electrical parameters.
3Device complexity
If a single torque estimation method is used, then device complexity is reduced, but measurement precision deteriorates at certain operating conditions
Solution Approach 1:
The patent implements a dynamic estimation approach where the torque calculation adapts to operating conditions. The magnetic flux estimation and torque computation adjust based on the electrical state of the motor, allowing accurate torque estimation across varying speeds and loads without requiring multiple separate measurement systems.
Solution Approach 2:
The patent changes the parameters used in torque estimation based on operating conditions. By using estimated magnetic flux and phase currents that are continuously updated from electrical measurements, the system maintains measurement precision across different operating points without increasing device complexity.
Data Source
AI summary
The present disclosure relates to a method for estimating a torque of an electric machine, comprising the following steps: estimating a first torque using a first method by forming a cross product from an estimated magnetic flux of the electric machine and an actual current of the electric machine, estimating a second torque using a second method by determining a power balance which can be calculated with the aid of a difference between an AC output power of an inverter, which is connected to the electric machine, and a total power loss of the electric machine, and determining the final torque as a weighted average from the first torque, which is weighted with a first weighting, and the second torque, which is weighted with a second weighting. The present disclosure also relates to a control unit for carrying out this method and to an electrical traction drive having such a control unit.