Electric Vehicle Motor Control Method for Smooth Acceleration
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Solution Overview
Problem
Existing electric vehicle control systems face issues with constant braking and speed regulation, leading to unreliable and load-dependent driving behavior, as torque control sets torque to zero at the 'zero' accelerator position, causing coasting and inability to maintain constant speed, and speed control results in overshoots and uneven acceleration/deceleration.
Innovation Solution
A method that combines torque and speed control, switching between states based on a speed threshold, using non-linear torque control for large speed deviations and aperiodic speed control when close to target speed, with proportional and integral components for smooth transitions, ensuring continuous acceleration and braking without overshoots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If torque control is used with accelerator pedal position mapping to target torque, then the control system implementation is simple and continuous acceleration is achieved, but permanent recuperation of braking energy is not possible and constant speed maintenance requires continuous driver correction
Solution Approach 1:
The control system dynamically adapts its behavior based on vehicle speed and accelerator pedal position. At low speeds, it provides torque control for responsive acceleration, while at higher speeds it transitions to speed control for maintaining constant speed and enabling reliable recuperation, thus combining simplicity with reliability through dynamic adaptation
Solution Approach 2:
The system changes control parameters (switching between torque control and speed control modes) based on operating conditions. The control mode transitions from torque-based at low speeds to speed-based at high speeds, allowing the system to optimize performance and reliability for different driving scenarios
2Reliability
If speed control is used to maintain constant speed, then constant speed maintenance is possible, but overshoots occur during acceleration and deceleration leading to non-uniform transition processes
Solution Approach 1:
The control system dynamically adjusts the control mode based on the magnitude of speed deviation. For small deviations near target speed, it uses speed control to maintain precision. For large deviations during acceleration/deceleration, it switches to torque control for smoother, overshoot-free transitions, thus maintaining both constant speed capability and transition smoothness
Solution Approach 2:
The system periodically monitors speed deviation and switches control modes accordingly. When deviation exceeds a threshold, it transitions from speed control to torque control to prevent overshoot, then switches back when deviation is reduced, creating a periodic adaptation that ensures smooth transitions while maintaining constant speed capability
3Loss of energy
If accelerator pedal is reset to zero position for coasting, then energy recuperation should occur, but torque is set to zero causing undefined rolling behavior especially on downhill gradients
Solution Approach 1:
Instead of setting torque to zero for coasting (which causes undefined behavior), the system inverts the approach by using speed control with a non-zero target speed even when the accelerator pedal is at zero position. This maintains predictable coasting behavior and enables reliable energy recuperation by keeping the motor in generating mode with controlled speed
Data Source
Figure 1~3
Figure 2
AI summary
The method involves performing torque control in which position of driving signal generator is associated with target torque of traction drive motor (17) in primary operating state (25), \and speed control in which position of driving signal generator is associated with target rotation speed of drive motor in secondary operating state (26). The control of drive motor is performed in primary operating state when deviation of target rotation speed to actual speed of vehicle drive motor is greater than threshold value and otherwise, drive motor is regulated in secondary operating mode.