Switched Reluctance Motor PWM Torque Control Beyond Dead-Band
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Solution Overview
Problem
Switched reluctance motors face challenges in sensor-less operation at low torque loads due to insufficient current, resulting in a dead-band where the controller cannot determine the rotor position, affecting motor performance and efficiency.
Innovation Solution
Implementing pulse width modulation (PWM) in the controller to produce a PWM adjusted torque command that cycles between upper and lower thresholds, enabling the motor to produce desired torque even at low loads by effectively managing current outside the dead-band limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sensor-less operation is used to minimize package size and cost, then reliability and simplicity are improved, but position determination accuracy deteriorates at low torque loads due to insufficient current
Solution Approach 1:
The system changes the operating parameters by injecting a known current waveform (triangular or sinusoidal) at a specific frequency into the unenergized phase winding. This parameter change enables the estimation of rotor position through current measurement even at low torque loads, resolving the contradiction between sensor-less operation reliability and position estimation accuracy.
Solution Approach 2:
The patent introduces an intermediary measurement approach by using the current in the unenergized phase winding as a mediator to infer rotor position. Instead of directly measuring position, the system measures the current response which indirectly provides position information, thereby maintaining sensor-less operation while improving low-torque position determination.
2Measurement precision
If minimum current is required for position estimation, then a minimum torque threshold is created, but this creates a dead-band where the controller cannot determine rotor position at low loads
Solution Approach 1:
The system performs a preliminary action by injecting a known current waveform into the unenergized phase winding before attempting to determine rotor position. This preliminary current injection creates a measurable response that enables position estimation even at very low torque loads, eliminating the dead-band and expanding the operational range down to zero torque.
Solution Approach 2:
The patent employs periodic action by injecting current waveforms at specific frequencies (e.g., 100 Hz, 200 Hz, or 400 Hz) into the unenergized phase winding. This periodic current injection creates a consistent, measurable response that allows the controller to continuously estimate rotor position across the entire torque range, including low-torque conditions where continuous operation is needed.
Data Source
AI summary
A work machine includes a frame, a traction system supporting the frame, a power source mounted on the frame, a switched reluctance motor, an inverter configured to control power to the motor from a power source, and a controller. The controller is configured to receive a signal indicating a desired torque and determine if the desired torque is between an upper threshold and a lower threshold. If the desired torque is between the upper threshold and the lower threshold, pulse width modulation is used to produce a PWM adjusted torque command, and the motor is commanded based on the PWM adjusted torque command. The PWM adjusted torque command is configured to cycle between the upper threshold and the lower threshold to produce the desired torque.