Nested Loop Damping Control for Driveline Oscillations
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Solution Overview
Problem
Driveline systems experience undesirable oscillations at high resonant frequencies due to the interaction of rotating electric machines and the stiffness of the drive axle, which existing control methods are unable to effectively damp.
Innovation Solution
A nested loop-based active damping control methodology is employed, where a fast inner control loop modifies the effective inertia of the motor by sensing rotational acceleration and generating acceleration-based feedback torque, while a slower outer control loop calculates the commanded torque to actively damp the oscillations by shifting the resonant frequency within the control capability of the nested control loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single control loop is used to damp driveline oscillations, then the control structure is simple, but it cannot effectively damp high-frequency resonant oscillations because the sampling rate is insufficient
Solution Approach 1:
The control system is segmented into two distinct control loops: an outer control loop operating at a lower sampling rate for general torque control, and an inner control loop operating at a higher sampling rate specifically for damping high-frequency oscillations. This segmentation allows each loop to be optimized for its specific function, with the inner loop capable of responding to high-frequency resonant oscillations that the outer loop cannot address due to sampling rate limitations.
Solution Approach 2:
The control loops are nested with the inner control loop embedded within the outer control loop structure. The inner loop receives torque commands from the outer loop and adds additional damping torque based on high-frequency oscillation detection. This nested architecture allows the faster inner loop to enhance the capabilities of the slower outer loop without requiring a complete redesign of the entire control system.
2Reliability
If the sampling rate is increased to control high-frequency oscillations, then the damping capability improves, but the computational load and control system complexity increase
Solution Approach 1:
The control system segments the damping function from the general torque control function by creating a separate inner control loop dedicated to high-frequency oscillation damping. This inner loop operates at the higher sampling rate required for effective high-frequency damping, while the outer loop maintains the lower sampling rate sufficient for general torque control. This segmentation allows the system to achieve high-frequency damping capability without requiring the entire control system to operate at the higher sampling rate, thus managing computational load more efficiently.
3Measurement precision
If the inner control loop operates at high sampling rate, then it can detect and respond to high-frequency oscillations, but it increases the computational requirements
Solution Approach 1:
The control system segments the computational tasks by sampling rate requirements: the inner control loop uses high sampling rate only for detecting and responding to high-frequency oscillations, while the outer loop handles general torque control at lower sampling rate. This segmentation ensures that high computational resources are used only when necessary for oscillation damping, rather than continuously, thereby reducing overall computational energy consumption while maintaining precise oscillation detection capability when needed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The nested loop control architecture effectively reduces high-frequency driveline oscillations by modifying the motor's inertia, allowing the slower outer control loop to damp the oscillations, thereby improving the system's stability and reducing resonance frequencies within controllable limits.
Implementation Method 1
The faster inner loop modifies the effective inertia of the motor by sensing the rotational acceleration of the motor shaft and generating an acceleration-based feedback torque command
Implementation Method 2
an acceleration-based feedback torque command, which is negatively proportional to the sensed acceleration, thereby creating virtual inertia
Data Source
AI summary
A driveline system includes a drive axle coupled to a load, an electric machine, and a control system. The electric machine is responsive to a commanded torque, has a rotor shaft coupled to the axle, and produces an output torque that rotates the axle and load to produce driveline oscillation at a high resonant frequency. The control system generates the commanded torque using a nested control loop architecture in which an outer control loop operates at a sampling rate that is below a critical rate necessary for controlling the resonant frequency, and an inner control loop operates at a sampling rate that is above the critical rate. The inner loop determines a modified torque command and acceleration value in response to a commanded torque from the outer loop. The electric machine is thereafter controlled via the commanded torque.