Sensorless Rotor Position Detection via Symmetrical Components
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Solution Overview
Problem
Existing methods for determining the rotor position of synchronously running three-phase machines without a rotary encoder face challenges such as acoustic emissions, disrupted current control, and the need for mechanical position sensors, especially at low speeds.
Innovation Solution
The method employs the theory of symmetrical components to analyze and evaluate current rise curves, introducing a new coordinate system called the 'measuring direction fixed coordinate system', which allows for the determination of rotor position using only active voltage space vectors, eliminating the need for additional measurement pulses and mechanical sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measuring pulses or measuring sequences are impressed to determine rotor position without encoder, then rotor position can be detected, but acoustic emissions occur and current control is disrupted
Solution Approach 1:
The invention extracts only the necessary information (rotor position) from the current measurements during normal PWM operation, without requiring separate measuring pulses. By using the existing current measurements during active voltage space vectors and applying symmetrical component analysis, the method obtains rotor position information without injecting additional test signals that would cause acoustic emissions.
Solution Approach 2:
The current measurements taken for normal current control purposes are made to serve dual functions: both for current control and for rotor position detection. The symmetrical component analysis enables the extraction of position information from the same current measurements used for control, eliminating the need for separate measurement pulses.
2Measurement precision
If measuring pulses are used to determine rotor position, then position information can be obtained, but current control is disrupted
Solution Approach 1:
The invention extracts rotor position information from the existing current measurements during normal operation without requiring separate measuring pulses that would disrupt current control. The symmetrical component analysis processes the current measurements already available during active voltage space vectors.
Solution Approach 2:
The same current measurements used for current control are simultaneously used for rotor position detection, making the measurement system multi-functional and eliminating the need for separate measurement sequences that would disrupt control.
3Measurement precision
If mechanical encoders are used for rotor position detection, then high-quality control can be achieved, but device complexity and cost increase
Solution Approach 1:
The invention replaces the mechanical encoder system with an electrical measurement and analysis system. By using symmetrical component analysis on current measurements during normal PWM operation, the method achieves rotor position detection without mechanical sensors, thereby reducing device complexity and cost.
Solution Approach 2:
The system uses its own operating currents for position detection purposes. The current measurements taken during normal operation contain information about rotor position through inductance variations, and the symmetrical component analysis extracts this information without requiring external sensing hardware.
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 enables noise-free and high-quality rotor position determination up to zero speed without mechanical encoders, simplifying the machine structure and reducing costs, while maintaining accurate current control and position sensing across various speed ranges.
Implementation Method 1
the phase inductances of the machines mentioned fluctuate depending on the rotor position. This has already been used to determine the rotor position without a rotary encoder.
Implementation Method 2
The recorded current increases are transformed into a coordinate system with a fixed measuring direction and further into symmetrical components
Data Source
Figure 1
AI summary
The invention relates to a method for the sensor-free determination of the rotor position of a synchronously running three-phase machine (4), which is supplied via an inverter (3), wherein active inverter states excluding short circuit states acting in different space vector directions are used for current control and current rises (10) of the phase currents are detected during said active inverter states. The current rises (10) detected are transformed in a computing unit (7) into a fixed measuring direction coordinate system and further into symmetrical components and at least one of the symmetrical components computed from said current rises (10), which components rotate at double the electric rotational speed, single electric rotational speed and at zero speed, is evaluated, wherein at least the symmetrical components functioning down to zero speed and rotating at double electric rotational speed are evaluated and the electrical rotor position of the machine (4) is determined therefrom. The invention further comprises a circuit arrangement for the method.