Electric Machine Stator Biasing for Faster Pulsed Torque Rise
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Solution Overview
Problem
Current electric machines, particularly externally excited synchronous machines, face challenges in rapidly turning the rotor current ON and OFF during pulsed operation due to high resistance and inductance, which limits their efficiency and torque rise rate, especially in dynamic motor drive applications.
Innovation Solution
The method involves simultaneously exciting both the rotor and stator with current to rapidly build magnetic flux, using stator current biasing to improve the rate of rise of torque, allowing for faster transitions between ON and OFF states while maintaining efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If rotor current is increased to build magnetic flux quickly, then rate of rise of torque improves, but resistance and inductance effects cause energy loss and slow down the response
Solution Approach 1:
The patent applies preliminary action by providing a biasing current to the stator windings before the rotor current is applied. This pre-establishes a magnetic flux in the stator that interacts with the rotor current to produce torque more quickly. The biasing current is applied in advance during the transition from zero torque to pulsed torque, enabling faster torque rise without requiring excessive rotor current that would cause resistive losses.
2Productivity
If rotor current is turned ON and OFF rapidly for pulsed control, then productivity improves, but high inductance prevents fast switching
Solution Approach 1:
The biasing current applied to the stator windings beforehand creates a pre-existing magnetic field that facilitates faster establishment of torque when rotor current is applied. This preliminary magnetic flux reduces the time required for the rotor current to build up sufficient magnetic interaction, enabling faster ON transitions during pulsed control operations.
Solution Approach 2:
The stator biasing current acts as an intermediary that mediates the interaction between the rotor current and the magnetic field. By establishing a magnetic flux in the stator beforehand, it creates a favorable magnetic environment that accelerates the torque development process, effectively reducing the switching transition time without requiring changes to the rotor circuit's inherent inductance.
3Speed
If stator current biasing is applied to improve torque rise rate, then rate of rise of torque improves, but additional current control complexity increases
Solution Approach 1:
The stator windings serve multiple functions: they generate the rotating magnetic field for normal motor operation and simultaneously provide the biasing current for accelerated torque rise during pulsed transitions. This multi-functionality eliminates the need for separate biasing windings or additional hardware, reducing overall system complexity while achieving the desired performance improvement.
Solution Approach 2:
The control system changes the current parameters in the stator windings dynamically - applying a DC biasing current component during transition periods and switching to normal AC operation during steady state. This parameter change approach allows the same hardware to perform different functions at different times, avoiding the need for additional complex control systems while achieving fast torque rise 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
This approach significantly reduces the time required to achieve desired torque levels, enhancing the overall efficiency and reducing energy consumption by minimizing transition times, thus improving the machine's performance in pulsed control scenarios.
Implementation Method 1
Direct current can be provided to the rotor to excite the rotor and thus, produce magnetic flux of the rotor
Implementation Method 2
the multi-phase inverter can be a 3-phase inverter that generates a stator flux in the stator
Implementation Method 3
The magnetic flux of the rotor interacts in an air gap between the stator and the rotor with the stator flux to cause rotation of the rotor and produce power in the form on an electromotive force (EMF)
Data Source
AI summary
A method of controlling an electric machine having a separately excitable rotor and stator includes pulsing the electric machine and controlling the electric machine to an OFF state. Pulsing the electric machine includes exiting the rotor with direction current and the stator with a stator biasing current at the same time to generate magnetic flux in the rotor via two separate paths. Pulsing the electric machine may also include terminating the stator basing current when a desired magnetic flux is generated in the rotor. Pulsing the electric machine may include proving a stator flux to the stator such that the electric machine provides a pulse torque.