Rotor Position Estimation via Voltage Injection Under Sensor Fault
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Solution Overview
Problem
Existing propulsion systems with electric motors face challenges in accurately estimating rotor position, especially when position sensors fail, leading to potential loss of torque control and propulsion, particularly at low motor speeds.
Innovation Solution
A propulsion system that injects a voltage signal with an alternating periodic shape into the direct magnetic axis in a synchronous reference frame, allowing for rotor position estimation based on motor current response, even in the absence of a functional position sensor, using a controller with a processor and memory to manage the injection and processing of this signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a position sensor is used to determine rotor position, then rotor position can be accurately obtained for torque control, but the system becomes vulnerable to sensor faults causing loss of torque control
Solution Approach 1:
The patent introduces an intermediary method (voltage signal injection and current response analysis) that acts as a mediator between the position sensor and the control system. When the position sensor fails, this intermediary method provides alternative rotor position information through motor current response characteristics, ensuring continuous torque control capability without direct dependence on the faulty sensor
Solution Approach 2:
The system uses the motor's own current response to injected voltage signals as a self-service mechanism for rotor position estimation. Instead of relying entirely on external position sensors, the system leverages the motor's inherent electrical characteristics and current behavior to generate its own position information, making the system self-sufficient and resilient to sensor failures
2Speed
If traditional rotor position estimation methods are used, then the system can operate at high speeds, but torque control is lost at low speeds when position sensors fail
Solution Approach 1:
The patent changes the operational parameters by injecting voltage signals at specific frequencies and analyzing current responses differently based on speed conditions. At low speeds where traditional methods fail, the system uses specific voltage signal injection patterns and processes the current response with appropriate filtering and transformation techniques to extract rotor position information, enabling torque control across the entire speed range including zero speed
3Ease of operation
If voltage signal injection is used for rotor position estimation, then torque control can be maintained at zero speed, but additional signal processing complexity is introduced
Solution Approach 1:
The system employs periodic voltage signal injection at specific frequencies and uses periodic analysis of the current response. By injecting voltage signals in a periodic manner and analyzing the corresponding periodic current responses through synchronous reference frame transformations and filtering, the system extracts rotor position information in a systematic way that manages the complexity through structured periodic operations rather than continuous complex processing
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
Enables accurate rotor position estimation and maintains torque control capability even at zero speed, enhancing the system's ability to operate without position sensors and improving torque control dynamics and maximum torque capability.
Implementation Method 1
The rotor position is estimated based in part on a motor current response to the voltage signal
Data Source
AI summary
A propulsion system for a device includes an electric motor configured to generate torque to propel the device. A position sensor is adapted to determine a rotor position of the electric motor. The system includes a controller having instructions recorded for determining the rotor position when a sensor fault condition is detected. The controller is adapted to selectively command injection of a voltage signal in a direct magnetic axis in a synchronous reference frame when a motor speed of the electric motor is below a predefined motor speed threshold and the sensor fault condition is detected. The rotor position is estimated based in part on a motor current response to the voltage signal. The voltage signal is defined by an alternating periodic shape having respective constant segments in each of a plurality of control periods, the respective constant segments being discontinuous between the control periods.