Analytical Comparison of Power Balance Methods for Airgap Torque Accuracy Determination in Automotive Applications

Information about torque value is critical for today's hybrid electric vehicles and electric vehicles. This information can be used for improving comfort and overall safety of the vehicle. Based on the final torque accuracy of the estimator it is possible to optimize the cost of the whole system. It is unclear how much each component affects the accuracy of the torque estimation. This paper presents the sensitivity analysis of torque calculation utilizing both AC and DC input power and speed of the motor for the calculation. Based on this analysis it is possible to determine which element in the system has the highest impact on the final inaccuracy of the estimator and then modify the subsystems (individual elements) to reach the desired torque accuracy in the most cost-efficient way. The results show that it is possible to use both methods, but the accuracy of the DC power calculation method is better, because of the absence of the position sensor. However, this method requires more computational power because it is necessary to determine the power electronics' losses. Additionally, this method is unsuitable for use in an electric drive system with multiple drive units. Therefore, it is possible to use both methods, because both can be used under different conditions.