Sensorless Rotor Position Determination for Wound Field Synchronous Machines
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Solution Overview
Problem
Existing rotor position determination methods for dynamoelectric machines, such as back EMF based and signal injection methods, face reliability issues and complexity, especially at low rotor velocities or standstill, and require mechanical sensors or significant electrical stress on rotating rectifiers.
Innovation Solution
A double injection sensorless (DIS) logic system that injects both voltage or current stimuli into the main and exciter stators to determine the true rotor position using exciter stator harmonics and calibrates the system to eliminate position ambiguity, reducing reliance on mechanical sensors and electrical stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a mechanical rotor position sensor is used, then rotor position can be determined, but cost increases and reliability decreases
Solution Approach 1:
The patent replaces mechanical rotor position sensors with an electronic signal injection method. The system injects carrier signals into the stator windings and measures the resulting current harmonics to determine rotor position, eliminating mechanical sensors entirely and improving both reliability and cost-effectiveness
2Ease of manufacture
If back EMF based method is used, then implementation is simple, but reliability is poor at low rotor velocity or standstill
Solution Approach 1:
The patent changes the operating parameters by injecting carrier signals at specific frequencies and amplitudes that are independent of rotor speed. This allows the system to operate reliably at low speeds and standstill where back EMF methods fail, while maintaining implementation simplicity through standardized signal processing
3Reliability
If signal injection method is used below threshold velocity, then rotor position can be determined, but position error of up to 180 degrees occurs due to inability to recognize correct rotor position
Solution Approach 1:
The patent introduces an intermediary calibration process using exciter stator current harmonics. The exciter system acts as a mediator to provide absolute position reference, allowing the main machine to resolve the 180-degree ambiguity and achieve accurate rotor position determination at low speeds
4Measurement precision
If double CIS logic blocks are used to determine true rotor position, then absolute rotor position is achieved, but logic complexity increases significantly
Solution Approach 1:
The patent merges the position determination functions into a unified control system where the exciter and main machine work together. By combining the exciter's absolute position capability with the main machine's carrier injection method, the system achieves absolute rotor position with reduced logic complexity compared to separate dual CIS blocks
5Measurement precision
If rectification is used to determine main machine poles, then pole identification is achieved, but electrical stress on rotating rectifier diodes increases reducing reliability
Solution Approach 1:
The patent uses the exciter system as an intermediary to determine main machine pole positions. By analyzing exciter stator current harmonics during exciter operation, the system identifies pole positions without requiring high-current rectification operations, thereby protecting rectifier diode reliability
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
The DIS logic system provides accurate and reliable rotor position determination and tracking across various speeds, including standstill, with reduced electrical stress on the rotating rectifier and simplified logic complexity, enhancing the dynamoelectric machine's operational efficiency.
Implementation Method 1
The exciter stator stimulus generates a field that induces a frequency component in the exciter stator current that is five times the exciter electrical frequency, allowing rotor position determination
Implementation Method 2
The main stator stimulus is used to induce saturation in the main machine rotor to determine main machine pole positions
Data Source
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AI summary
A rotor position determination and tracking system for a dynamoelectric machine (10) includes a first AC power supply (36) to inject a carrier wave into a main stator (16) of the dynamoelectric machine and a second AC power supply (32) to inject an excitation voltage or current into an exciter stator (20) of the dynamoelectric machine. A plurality of current sensors and voltage sensors located at the exciter input lines sense current and voltage thereat. A first control logic (46) receives the sensed current and voltage and outputs an estimated rotor position (θr). A second control logic (78) receives an estimated exciter field voltage or current rotating wave form angle (θc) and filtered sensed current or voltage signals from the first control logic and utilizes a known main stator carrier frequency to determine the rotor position (θels). The rotor position is input into the first control logic to calibrate the first control logic for tracking of the true rotor position (θreal).