Electric Motor Torque Control Fault Detection
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Solution Overview
Problem
Current fault detection methods for three-phase electric motors in power-assisted steering systems of automobiles are inadequate, as they cannot reliably detect phase shifts or gains, leading to incorrect torque control and potential safety hazards, and require the system to enter a diagnostic mode, which is inconvenient.
Innovation Solution
A method that generates PWM voltage signals for each phase, estimates sinusoidal currents, transforms them into direct and quadrature currents, determines residual voltages, and detects faults by comparing these values to thresholds, allowing for continuous operation without entering diagnostic mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional ADC saturation detection method is used, then short-circuit faults can be detected, but phase shifts and gain errors cannot be detected leading to incorrect torque control
Solution Approach 1:
The patent introduces an intermediary observation approach by measuring terminal voltages and calculating currents through voltage equations rather than directly measuring currents with ADCs. This intermediary method allows detection of phase shifts and gain errors that direct current measurement cannot detect, while maintaining torque control reliability through the relationship: i_s = C_inv * (u_s - R_s * i_s - L_s * di_s/dt)
Solution Approach 2:
The patent replaces the mechanical/electrical direct current measurement system with a computational approach using voltage measurements and mathematical models. Instead of relying on ADC saturation detection, the system uses terminal voltage measurements combined with motor equations to calculate currents and detect faults, enabling detection of phase shifts and gain errors without additional hardware
2Measurement precision
If diagnostic mode is entered for fault detection, then faults can be detected, but the power-assisted steering system must stop operating which is inconvenient
Solution Approach 1:
The patent enables continuous fault detection during normal steering operation by using terminal voltage measurements and current calculations that can be performed in real-time without stopping the system. The method calculates currents and detects faults through the relationship between measured voltages and calculated currents, allowing the power-assisted steering to continue operating while monitoring for faults in all three phases simultaneously
3Device complexity
If only two currents are measured using two ADCs, then system complexity is reduced, but the third current must be estimated which may reduce detection accuracy
Solution Approach 1:
The patent uses feedback from the motor's electrical equations to calculate the third current based on the two measured currents and the known relationship that the sum of three-phase currents equals zero. The system continuously monitors the calculated currents against the motor model, providing feedback that enables accurate detection of phase shifts and gain errors in all three phases while maintaining simple hardware with only two ADCs
Data Source
AI summary
Disclosed is a method for detecting a fault in an electric motor of a power-assisted steering system of an automobile vehicle. The method notably includes a step for: determination of a residual direct sinusoidal voltage and of a residual quadrature sinusoidal voltage based on the measured direct sinusoidal current, on the estimated direct sinusoidal current, on the measured quadrature sinusoidal current and on the estimated quadrature sinusoidal current; and detection of a fault when the difference between the value of the residual direct sinusoidal voltage and its moving average is greater than a first threshold and/or when the difference between the value of the quadrature sinusoidal voltage and its moving average is greater than a second threshold.