Closed-loop Torque Control for Variable Flux Electric Machines
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Solution Overview
Problem
Rotary electric machines, particularly variable flux and permanent magnet machines, experience slow and large torque transients that lead to noise, vibration, and harshness (NVH) issues, degrading drive quality due to inadequate control of transient torque responses.
Innovation Solution
Implementing closed-loop feedback control strategies that use a torque estimation block to calculate delta d-axis and q-axis current commands based on actual shunt angle or temperature, adjusting current commands to optimize torque transient response, and incorporating proportional-integral regulators and lookup tables to manage flux and back-EMF, with optional thermal adaptation for PM machines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If field weakening techniques are used to control back-EMF at higher speeds, then energy efficiency is improved, but torque transient response becomes slower and larger
Solution Approach 1:
The patent implements a closed-loop feedback control system that continuously monitors the actual torque output and compares it with the commanded torque. The torque estimation block uses feedback from current sensors and machine parameters to calculate actual torque, and the controller adjusts d-axis and q-axis current commands based on the torque error to achieve faster transient response while maintaining energy efficiency through optimized field weakening control.
Solution Approach 2:
The patent dynamically changes control parameters including d-axis and q-axis current commands, flux reference values, and back-EMF compensation factors during transient operation. By adjusting these parameters in real-time based on operating conditions and torque demands, the system optimizes both energy efficiency and torque transient response characteristics across different speed and load ranges.
2Power
If shunt angle is changed to vary magnetic flux, then back-EMF control is achieved, but torque transient accuracy deteriorates
Solution Approach 1:
The patent introduces a torque estimation block as an intermediary that calculates actual torque based on measured currents, machine parameters, and flux values. This intermediary computation allows the system to monitor and control torque transients accurately even while the shunt angle is being adjusted for back-EMF control, thereby maintaining torque transient accuracy during flux variation.
Solution Approach 2:
The patent replaces direct mechanical measurement of torque with an electrical estimation system that computes torque from current and flux measurements. This substitution allows for high-precision torque monitoring and control without mechanical sensors, maintaining accuracy during shunt angle changes while enabling sophisticated control algorithms.
3Speed
If closed-loop feedback control is implemented to improve torque transient response, then system complexity increases
Solution Approach 1:
The patent implements a universal control framework that handles multiple functions within a unified structure: torque estimation, current control, flux control, and back-EMF compensation all operate through integrated control blocks. This multi-functional approach reduces overall system complexity compared to separate independent control systems while achieving fast torque transient response through coordinated control of multiple variables.
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 solution significantly improves the speed and accuracy of torque transient responses, reducing NVH effects and maintaining torque stability during shunt angle or temperature changes, thereby enhancing drive quality and operational efficiency.
Implementation Method 1
An energized PM machine generates a back-electromotive force (back-EMF) as a voltage opposing that of the energized stator windings
Implementation Method 2
The rotating stator field interacts with strong magnetic fields of the permanent magnets to rotate the rotor shaft
Data Source
AI summary
A method for controlling transient operation of a rotary electric machine in an electric powertrain or other electrical system includes, during a shunt angle transition occurring during a maximum torque per ampere (MTPA) control region, determining an estimated output torque of the electric machine via a torque estimation block using d-axis and q-axis current commands and an additional value, i.e., an actual shunt angle or a machine temperature. The method includes subtracting the estimated output torque from a commanded output torque to derive an adjusted commanded torque value or torque error, and calculating, from the torque error, a delta d-axis current command and a delta q-axis current command. The method includes adjusting d-axis and q-axis current commands using the delta commands to produce adjusted d-axis and q-axis current commands, which are then used as closed-loop feedback control terms by the torque estimation block.