Rotor Angle Estimation via High-Frequency Current Injection
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Solution Overview
Problem
Existing methods for determining rotor position in permanent magnet AC motors, particularly at low and zero speeds, face challenges in sustaining full torque control due to the inability to accurately extract rotor magnetic axis polarity from negative sequence components without complex synchronously rotating frame filters.
Innovation Solution
A simplified signal conditioning technique that extracts rotor angle information from motor current feedback using high-frequency current injection, employing a PLL to process signals (u-v) and ((u+v-2w)/sqrt(3)) for rotor angle estimation, and d-axis DC current injection to determine magnetic axis polarity by comparing time averages of ripple currents at different levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex synchronously rotating frame filters are used to extract rotor magnetic axis information from negative sequence current component, then measurement precision of rotor position is improved, but device complexity increases
Solution Approach 1:
The patent extracts only the essential rotor position information from the negative sequence current component using a simplified signal processing approach. Instead of using complex synchronously rotating frame filters, the invention extracts the necessary magnetic axis information through a more direct method that isolates the required parameters without unnecessary computational complexity.
Solution Approach 2:
The patent changes the processing parameters by working with the negative sequence current component directly and applying a simplified extraction method. The invention transforms the approach from using complex time-domain filtering to a method that processes the signal in a more efficient manner, changing how the rotor position parameters are derived from the injected high-frequency signals.
2Adaptability or versatility
If signal injection techniques are used to enable continuous low speed operation, then adaptability to low speed applications is improved, but device complexity increases due to additional signal processing requirements
Solution Approach 1:
The patent implements a control system that can operate across a wide speed range including zero speed using the same basic signal injection technique. The simplified extraction method allows the system to maintain adaptability for low-speed applications such as electric vehicles and power steering without requiring separate control strategies or additional hardware complexity.
Solution Approach 2:
The patent enables low-speed operation by injecting high-frequency signals into the motor and extracting rotor position information from the negative sequence current component. This parameter-based approach allows continuous operation from zero speed upward by changing how position information is derived rather than requiring different control modes for different speed ranges.
3Measurement precision
If magnetic axis polarity is computed by extra means before drive torque application, then measurement precision of rotor position is improved, but loss of time occurs during startup
Solution Approach 1:
The patent performs magnetic axis polarity identification during the startup phase using the same signal injection technique. By determining the polarity information upfront through a quick measurement process that uses high-frequency signal injection and negative sequence component analysis, the system prepares the necessary position information before torque application without requiring additional time-consuming steps during normal operation.
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 fast rotor angle tracking and magnetic axis polarity identification at drive startup, eliminating the need for complex filters and ensuring continuous low-speed operation with accurate torque control.
Implementation Method 1
The increase of ripple current or time average of ripple current is due to induced magnetic saturation. This induced saturation occurs when the d-axis dc current (IdStart) is applied (during magnetic polarity determination) such that the flux introduced by this d-axis current tends to increase the resultant flux (rotor magnet flux and d-axis current induced flux).
Implementation Method 2
The rotor angle information is advantageously extracted from said pair of calculated signals by a PLL.
Data Source
AI summary
An apparatus and method for estimating rotor angle information for the control of permanent magnet AC motors having sinusoidal current excitation. The disclosed motor drive can provide full load operation at very low speeds including zero speed without the use of a shaft position sensing device. The rotor angle is estimated through injection of high frequency current, and rotor angle is extracted by a signal-conditioning algorithm, which utilizes current amplitude differential to discriminate the rotor angle. Rotor angle magnetic axis orientation (North or South pole) at startup is detected by comparing time average current ripple (at signal injection frequency) content between two different levels of d-axis current injection.