Motor Input Current Estimation from ECU Duty Cycle Signals
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Solution Overview
Problem
Current systems for estimating input currents in electric motors, particularly in electric vehicles, face inaccuracies due to neglecting switching non-idealities and duty cycle changes, leading to significant torque estimation errors, especially in non-linear six-step operating conditions.
Innovation Solution
The proposed solution involves obtaining duty cycle parameters from an Electric Control Unit (ECU) to estimate input currents for each phase of the electric motor, accounting for switching non-idealities such as deadtime, current direction, and Fundamental frequency to Switching frequency ratios, and employing a trapezoidal estimation technique to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional current estimation methods are used, then the system complexity is low, but the measurement precision of input current is poor due to neglecting switching non-idealities
Solution Approach 1:
The patent transforms the current estimation approach by changing the parameters used for estimation. Instead of using simple voltage and resistance calculations, the system uses duty cycle parameters from the ECU and applies compensation factors for switching non-idealities (deadtime, turn-on/turn-off delays). This parameter transformation enables accurate current estimation without adding physical sensors, resolving the contradiction between measurement precision and device complexity.
2Measurement precision
If switching non-idealities are neglected, then the calculation process is simple, but the torque estimation accuracy deteriorates significantly
Solution Approach 1:
The patent introduces duty cycle parameters as an intermediary element that bridges the control system and the estimation process. By obtaining duty cycle values from the ECU and using them as the basis for current and torque estimation, the system accurately captures the effect of switching non-idealities without directly measuring currents. This intermediary approach improves torque estimation accuracy while keeping the calculation process manageable through software-based compensation.
3Use of energy by moving object
If six-step operation is used, then the motor efficiency is improved, but the current estimation accuracy worsens due to non-linear switching behavior
Solution Approach 1:
The patent applies dynamic compensation to account for the non-linear switching behavior inherent in six-step operation. By incorporating time-varying compensation factors for deadtime and turn-on/turn-off delays that change with switching frequency and load conditions, the system maintains accurate current estimation throughout the dynamic six-step operating range. This dynamic approach preserves motor efficiency while correcting the estimation accuracy that would otherwise deteriorate under non-linear switching conditions.
Data Source
AI summary
Systems and methods for estimating input current are provided, particularly when input currents are applied to an electric motor of a motor system. An Electric Control Unit (ECU), according to one implementation, is configured to control the motor system. The ECU is configured to store computer logic having instructions that, when executed, cause one or more processing devices to obtain a duty cycle parameter at an output of the ECU. The duty cycle parameter, for example, relates to control actions enforced on one or more switches of a power electronics circuit of the motor system. Based on the duty cycle parameter, the instructions further cause the one or more processing devices to estimate an input current provided to the electric motor of the motor system. A more accurate input current estimation may thereby be used to better estimate torque.