Motor Control System Limiting Regenerative Current via Phase Advance
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Solution Overview
Problem
Existing motor control systems face challenges in effectively limiting regenerative current to prevent battery performance degradation in electrical power steering systems, particularly in quadrants 2 and 4, where passive elements are large and difficult to package, and phase advance methods either increase electrical stress or produce excessive regenerative current.
Innovation Solution
A motor control system that includes a control module capable of determining a target field weakening current to limit regenerative current to a threshold value by calculating a phase advance angle and motor voltage command based on motor torque, rotational velocity, and circuit parameters, allowing for efficient current management without large passive elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If passive elements such as a resistive element are used to dissipate regenerative current, then regenerative current is reduced, but the device becomes large and difficult to package
Solution Approach 1:
The patent replaces passive mechanical/resistive elements with an active control system that uses phase advance control of the inverter to limit regenerative current. The controller adjusts the phase angle of the PWM signals to control the amount of regenerative current flowing to the battery, eliminating the need for large physical resistors or other passive dissipation elements.
2Force
If phase advance is employed to meet torque versus speed requirements, then torque performance is improved, but the amount of power generation and motor current increases, creating electrical stress and noise
Solution Approach 1:
The patent dynamically adjusts the phase advance angle based on operating conditions (motor speed, torque demand, battery state of charge). The controller calculates an optimal phase advance angle that is sufficient to meet torque requirements while minimizing regenerative current. This dynamic adjustment allows the system to use minimal phase advance when possible, reducing electrical stress and noise, while still achieving required torque performance.
3Force
If phase advance is used in quadrant 2 and 4 to meet torque versus speed performance requirements, then torque performance is improved, but regenerative current increases
Solution Approach 1:
The patent changes the phase advance angle parameter dynamically based on operating conditions. In quadrants 2 and 4, the controller calculates a phase advance angle that balances torque production with regenerative current limitation. The phase advance angle is adjusted as a function of motor speed, torque demand, and battery state of charge, allowing the system to optimize between torque performance and regenerative current management in real-time.
4Device complexity
If zero phase advance value is used, then software complexity is reduced, but motor current increases to as high as 220 Amps, creating electrical stress and noise
Solution Approach 1:
The patent implements a calculated phase advance angle parameter that varies with operating conditions, replacing the fixed zero phase advance approach. The controller computes the optimal phase advance angle based on motor speed, torque demand, and circuit parameters, then applies this dynamic parameter through the PWM inverter. This approach increases software complexity slightly but dramatically reduces motor current and associated electrical stress and noise.
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 system effectively limits regenerative current to a threshold value, reducing electrical stress and noise, while meeting torque versus speed requirements, thereby enhancing the reliability and efficiency of the motor control system.
Implementation Method 1
In the event that the electric actuator is operating in either quadrant 2 or quadrant 4, the electric actuator operates as a generator. That is, in the event the motor torque and the motor velocity have opposing signs (i.e., positive or negative), a supply current may become negative. The negative supply current is also referred to as a regenerative current.
Implementation Method 2
Phase advance involves allowing the phase of an applied motor voltage to shift versus a phase of a developed motor back electromotive force (BEMF). The control module includes control logic for determining a phase advance angle to generate the target field weakening current.
Implementation Method 3
The control module includes control logic for determining a motor voltage command based on the motor torque command, the rotational velocity and the plurality of motor circuit parameters. The motor voltage command is applied at the phase advance angle.
Data Source
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AI summary
A motor control system is provided, including a motor and a control module. The motor operates at a rotational velocity, and creates a regenerative current. The motor has a target field weakening current that is configured for limiting the regenerative current to a threshold value. The control module is in communication with the motor. The control module receives a motor torque command. The control module includes control logic for identifying the target field weakening current based upon the motor torque command and the rotational velocity of the motor.