Electric Motor Torque Control via Adaptive Ramp Shaping
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Solution Overview
Problem
Existing electric motor control systems face challenges in rapidly increasing torque without exceeding current gradient limits, which can deplete the battery or damage the dc/dc converter, especially when battery voltage is low, leading to suboptimal ramp-up times.
Innovation Solution
A torque demand signal modifier adjusts the ramp shape based on battery voltage to ensure the current gradient does not exceed predefined limits, applying a positive scaling factor to boost the ramp when battery voltage is lower, and incorporates a motor model to estimate current and current gradient, with feedback monitoring to adjust the ramp and limit current draw.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the torque demand is increased rapidly to meet high assistance requirements, then the motor torque response is improved, but the current gradient limit is exceeded causing battery depletion or converter damage
Solution Approach 1:
The system dynamically adjusts the ramp shape parameters based on real-time battery voltage and current gradient conditions. The torque demand signal is modified using a time-varying ramp function that adapts its slope and curvature according to the electrical system's instantaneous capabilities, allowing maximum torque rise rate when conditions permit and reduced rates when safety limits are approached
Solution Approach 2:
The invention changes the parameters of the ramp function (slope, curvature, duration) based on battery voltage levels and current gradient measurements. By modifying these temporal parameters dynamically, the system optimizes the trade-off between fast torque response and safe current draw, preventing both battery depletion and converter overload while achieving the quickest possible torque buildup under prevailing conditions
2Reliability
If a fixed ramp shape is used to limit current gradient, then battery and converter safety is maintained, but the time to reach target torque demand increases
Solution Approach 1:
The system transitions from a static fixed ramp approach to a dynamic adaptive ramp that continuously adjusts its characteristics based on real-time feedback from battery voltage and current gradient sensors. This allows the ramp profile to be aggressive when electrical capacity is available and conservative when limits are approached, minimizing overall ramp-up time while maintaining safety
Solution Approach 2:
The invention implements a feedback control mechanism where actual battery voltage and current gradient measurements are fed back to the torque demand modifier. This feedback loop enables real-time adjustment of the ramp parameters, allowing the system to exploit available electrical capacity fully and reduce ramp-up time while preventing safety violations through continuous monitoring and adaptation
3Reliability
If the current gradient limit is set conservatively low, then battery depletion and converter overload are prevented, but the motor cannot meet high torque demand requirements
Solution Approach 1:
The system dynamically determines the appropriate current gradient limit based on real-time battery voltage and system conditions rather than using a fixed conservative value. The torque demand modifier adjusts the effective current gradient threshold adaptively, allowing higher torque buildup rates when battery voltage indicates sufficient capacity and lower rates when approaching depletion risks, thus maximizing torque capability while maintaining electrical system stability
Solution Approach 2:
The invention changes the effective current gradient parameter based on battery voltage levels and system state. By modifying this critical parameter dynamically, the system enables high torque output when electrical capacity permits while preventing overload and depletion conditions, resolving the contradiction between torque capability and electrical system stability through adaptive parameter adjustment
Data Source
AI summary
An electric motor apparatus having a controller and a torque demand signal modifier. The controller may produce a set signals to a drive stage of the motor where the drive stage applies a voltage to each phase of the motor to cause currents to flow in each phase of the motor corresponding to a current demand signal fed into the controller. The torque demand signal modifier may receive a target torque demand signal representative of a target torque demanded from the motor and outputs an actual torque demand signal which is converted into the current demand signal that is fed to the controller. The actual torque demand increases in value as a function of time towards the target torque demand value following a predefined ramp selected to ensure that the maximum current gradient of the current demand does not exceed a predetermined limit.