Switched Reluctance Motor PWM Control for Torque and Current Limits
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Solution Overview
Problem
Switched reluctance motors face inefficiencies due to leakage flux, which reduces torque production and causes braking torque, and existing control methods can damage electrical components during rapid cycling.
Innovation Solution
A method of controlling pulse-width modulation (PWM) in switched reluctance motors by applying fixed-width PWM pulses below a threshold speed and phase-advanced PWM pulses above it, with a control circuit that determines rotational speed and adjusts power to prevent excessive current through electronic switching mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If phase-advanced PWM pulses are applied above threshold speed, then torque production is enhanced, but electrical components may be damaged during rapid cycling
Solution Approach 1:
The control system changes PWM parameters (phase advance angle and pulse width) based on rotational speed thresholds. Below threshold speed, fixed-width PWM pulses are used; above threshold speed, phase-advanced PWM pulses with adjusted widths are applied to optimize torque while preventing component damage during rapid cycling.
Solution Approach 2:
The control circuit continuously monitors rotational speed and automatically adjusts PWM control mode accordingly. When speed exceeds the threshold, the system switches to phase-advanced PWM; when speed drops below threshold, it returns to fixed-width PWM, creating a feedback-based adaptive control system.
2Reliability
If fixed-width PWM pulses are applied below threshold speed, then component damage is prevented, but torque production efficiency decreases
Solution Approach 1:
The PWM control system transitions from static fixed-width pulses to dynamic phase-advanced pulses based on operational conditions. The control circuit dynamically adjusts pulse timing and width according to real-time speed feedback, optimizing both protection and efficiency across different operating ranges.
3Power
If PWM control is optimized for high speed operation, then torque production increases, but leakage flux effects worsen
Solution Approach 1:
The control system applies phase-advanced PWM pulses that anticipate the optimal timing for current application relative to rotor position. This preliminary action ensures current is applied at the most effective moment, maximizing torque production while minimizing the duration and impact of leakage flux effects.
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 enhances torque production by minimizing leakage flux and prevents damage to motor components during rapid cycling by optimizing PWM control based on rotational speed.
Implementation Method 1
Magnetic flux generated across the air gap between the rotor poles and the stator poles produces a magnetic field in the air gap that causes the rotor poles to move into alignment with the energized stator poles associated with a particular phase, thereby producing torque
Implementation Method 2
The magnetic flux generated can be divided into a main torque-producing flux and leakage flux. Leakage flux is undesirable in switched reluctance motors because it directly reduces torque production. More specifically, leakage flux causes the motor to produce a torque in a direction that is opposite to the direction of rotation of the rotor, also known as a braking torque
Data Source
AI summary
In a method of controlling current in a control circuit of an electric motor, pulse-width modulation (PWM) pulses are applied to a stator of the electric motor, via a plurality of transistors of the control circuit, using a first control mode when a rotational speed of a rotor of the electric motor is within a first range. At least one PWM pulse is applied to the stator, via a subset of the plurality of transistors, using a second control mode when the rotational speed of the rotor is within a second range. When it is determined that the rotational speed of the rotor has changed from being within the second range to being within the first range, additional PWM pulses are applied to the stator such that, for each of the plurality of transistors, a current through the transistor does not exceed a maximum current capacity of the transistor.