Electric Machine Flux Vector Control via Switch Timing
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Solution Overview
Problem
Conventional methods for controlling electric motors, such as induction motors, face challenges in efficiently managing torque production and current usage due to large differences in angular speeds between supplied voltage and rotor speed, leading to low rotor flux and high current consumption, without adequate control over torque direction.
Innovation Solution
A method and device utilizing semiconductor switches per phase to control AC power, where voltage and current measurements are used to estimate and calculate flux vectors, defining time instants for switch state changes to achieve a desired flux vector, thereby controlling torque, speed, and flux, with the option to divide the average voltage vector into sectors for precise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If voltage is reduced by varying off time in conventional soft starters, then current is limited to desired level, but torque production ability decreases due to low rotor flux
Solution Approach 1:
The invention changes the control parameter from simple voltage off-time to a more sophisticated flux-based control system that monitors and adjusts switching instants based on actual rotor flux conditions, enabling better torque control at reduced voltage
Solution Approach 2:
The system introduces feedback by measuring voltage and current to estimate present flux vector, then using this information to calculate reference flux vector and adjust switch timing, creating a closed-loop control system that adapts to actual motor conditions
2Device complexity
If large difference in angular speed between supplied voltage and rotor speed occurs, then voltage control is simplified, but rotor flux becomes low and current use increases
Solution Approach 1:
The control system uses feedback from voltage and current measurements to estimate flux vector and adjust switching instants dynamically, creating a responsive control system that adapts to varying speed differences without excessive current draw
3Ease of manufacture
If conventional voltage control method is used, then implementation is simple, but ability to control torque direction is insufficient without flux knowledge
Solution Approach 1:
The system implements feedback control by measuring voltage and current to estimate flux vector, then using this information to calculate reference flux vector and adjust switching instants, enabling torque direction control
Solution Approach 2:
The invention replaces direct mechanical torque control with an electrical control system that uses flux vector estimation and switching instant adjustment to achieve torque control, substituting electrical intelligence for mechanical directness
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 reduces starting current while increasing torque, suitable for applications with high initial load torque or fast braking needs, and results in a more compact device with reduced cooling requirements.
Implementation Method 1
estimating a present flux vector based on the measured voltage and current to the electric machine
Data Source
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AI summary
The present invention relates to a method of controlling power to an electric machine (10) and a controller device for performing such method. At least one semiconductor switch (41) is provided per phase (31, 32, 33) of a machine AC power (30), the semiconductor switches (40) supplying the machine AC power to the electric machine. The method comprises the steps of supplying an incoming AC power (20) comprising an incoming voltage (24) and an incoming current, to the semiconductor switches, measuring a voltage and current in the machine AC power (30) supplied by the semiconductor switches to the electric machine (10), estimating a present flux vector (51, 52) based on the measured voltage and current to the electric machine, calculating a reference flux vector (71) based on the estimated present flux vector (51, 52) and a desired operating state (61) of the electric machine, and defining time instants (101) for changing the state of the semiconductor switches (40) based on the reference flux vector (71) and the incoming voltage (24). The time instants (101) correspond to a behavior of the semiconductor switches such that a new measured voltage with a resulting current to the electric machine is predicted to achieve a new estimated flux vector corresponding to the reference flux vector.