Motor Current Control with Feedforward Filtering for EPS Rumble
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Solution Overview
Problem
Closed loop current control systems in electric power assisted steering systems are vulnerable to noise in demand signals and motor phase current measurements, leading to unwanted acoustic noise and steering wheel vibrations known as 'rumble'.
Innovation Solution
A motor control circuit with a feedforward path and bandwidth filters is implemented, incorporating a voltage controller with a steady state model and bandwidth filters to estimate voltage demands, filtering out noise and mitigating rumble while maintaining responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a closed loop current control system is used to minimise error signal, then motor current accuracy is improved, but noise in demand signal and current measurements is amplified causing rumble and acoustic noise
Solution Approach 1:
The control system is divided into separate functional blocks: a feedback loop for current control and a feedforward path for voltage control. The feedforward path processes the torque demand signal separately from the feedback loop, allowing noise filtering to be applied selectively without affecting the overall control accuracy.
Solution Approach 2:
A feedforward voltage control path is introduced as an intermediary between the torque demand and the motor. This path calculates the required voltage directly from the torque demand and operational values, bypassing the noisy feedback loop while still contributing to the overall control signal.
2Object-affected harmful factors
If the bandwidth of the current response is reduced to filter noise, then rumble and acoustic noise are reduced, but the system becomes less reactive to torque demand changes
Solution Approach 1:
The control bandwidth is segmented into two paths: the feedback loop uses a lower bandwidth to filter noise and reduce rumble, while the feedforward path maintains a higher bandwidth to preserve fast response to torque demand changes. This segmentation allows both requirements to be satisfied simultaneously.
Solution Approach 2:
The feedforward path performs preliminary voltage calculation based on torque demand before the feedback loop processes the error signal. This preliminary action provides the necessary voltage headroom for fast response while the feedback loop operates at lower bandwidth to ensure stability and reduce noise.
3Object-affected harmful factors
If a feedforward voltage control path is added to the system, then noise filtering and rumble reduction are improved, but device complexity increases
Solution Approach 1:
The feedforward voltage controller performs multiple functions: it calculates the required voltage from torque demand, provides noise-free voltage reference, and contributes to the overall control signal. This multi-functionality justifies the additional complexity by delivering multiple benefits from a single added component.
Solution Approach 2:
The system maintains the feedback loop for current measurement and error calculation while adding the feedforward path. The feedback loop continues to provide accurate current control, and the feedforward path supplements it with noise-free voltage control, creating a combined control strategy that leverages both approaches.
Data Source
AI summary
A motor circuit incorporated into a control system for a motor, in which the motor circuit comprises: a current determination stage arranged to generate a current demand signal in response to a torque demanded of the motor; a feedback loop comprising: a detector stage including a means for determining one or more operational values from the motor; and a current controller configured to calculate an error signal using one or more operational values from the detector stage and the current demand signal from the current determination stage; and a feedforward path comprising: a voltage controller configured to calculate a voltage demand signal from the current demand signal and one or more operational values from the motor, wherein the voltage controller comprises a first bandwidth filter, and wherein the current controller is configured to combine the error signal and the voltage demand signal to produce a signal for the motor.