Synchronous Machine Control for Sensorless Rotor Angle Accuracy
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Solution Overview
Problem
Existing sensorless methods for determining the rotor angle of synchronous machines face reliability and accuracy issues, particularly at low speeds and high torque conditions due to decreased anisotropy in synchronous machines, leading to unreliable rotor position information.
Innovation Solution
The method involves determining the differential value between rotor inductance in the direction of the pole axis and pole gap for various current values, creating a characteristic diagram to specify a torque-dependent operating point trajectory that maximizes the difference between d and q inductance, thereby improving rotor angle determination accuracy and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensorless rotor angle determination methods are used in synchronous machines, then the system complexity is reduced and cost is lowered, but the reliability and accuracy of rotor angle determination deteriorates at low speeds and high torque conditions due to decreased anisotropy
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal operating point trajectories in lookup tables before actual operation. The control device determines the current operating point based on torque demand and speed, then retrieves the corresponding optimal trajectory that maximizes anisotropy. This pre-computed guidance enables the sensorless method to maintain reliability across different operating conditions without real-time complex calculations.
Solution Approach 2:
The patent changes the operating parameters of the synchronous machine by adjusting the operating point trajectory to maximize the difference between d-axis and q-axis inductance (anisotropy). By modifying the current trajectory parameters rather than the physical structure, the method maintains sufficient anisotropy even at high torque conditions, thereby preserving the reliability of sensorless rotor angle determination while keeping the system simple.
2Measurement precision
If the operating point trajectory is optimized to maximize the difference between d and q inductance, then the accuracy of rotor angle determination is improved, but the efficiency of the synchronous machine may be compromised
Solution Approach 1:
The patent pre-calculates optimal operating point trajectories that balance anisotropy maximization with machine efficiency before operation. These trajectories are stored in lookup tables and selected based on current operating conditions (torque demand and speed). This approach enables real-time retrieval of pre-optimized trajectories without compromising efficiency, as the trade-off between accuracy and efficiency has already been resolved in the pre-computation stage.
Solution Approach 2:
The patent implements dynamic adaptation by selecting different operating point trajectories based on the current operating state (torque demand and speed). Rather than using a fixed trajectory, the system dynamically switches between pre-calculated trajectories to maintain optimal balance between anisotropy (for accurate rotor angle determination) and efficiency (for productivity). This dynamic selection ensures both measurement precision and machine efficiency are maintained across varying operating conditions.
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 expands the operational range of sensorless rotor angle determination methods, reducing saturation and enhancing the significance of rotor position information, especially at high torque conditions, by optimizing the operating point trajectory for efficient and accurate rotor angle estimation.
Implementation Method 1
Many of these sensorless methods are based on feeding in phase-shifted voltage pulses that exploit the anisotropy of a synchronous machine in order to obtain rotor position information from the different system responses
Implementation Method 2
In order to provide a required torque with a synchronous machine, a rotating electric field is generated in the stator of the machine, which rotates synchronously with the rotor
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a method for operating a synchronous machine, comprising the following steps: determining a difference value between the rotor inductance of the synchronous machine in the polar axis direction and the rotor inductance of the synchronous machine in the pole-gap direction for each of a plurality of different 2-tuples from values of useful current adjusted in the rotor-fixed coordinate system of the synchronous machine; preparing a characteristic diagram for the determined difference values in dependence on the 2-tuples of the values of useful current; determining a torque-dependent operating-point trajectory for the 2-tuples of the values of useful current taking into account the magnitude of the determined difference values along the operating-point trajectory to be determined; and operating the synchronous machine according to the determined operating-point trajectory.