AC Motor Controller Current Estimation for Noise Reduction
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Solution Overview
Problem
Existing controllers for AC rotating machines and electric power steering systems face challenges in maintaining low noise levels without increasing the control cycle, as longer control cycles lead to decreased PWM frequency, causing noise generation due to the AC rotating machine's current components.
Innovation Solution
A controller with a first and second winding, current detectors, and a control section that computes voltage commands to assist steering torque, using an estimated sum current when the first winding's current cannot be detected, allowing for improved output without changing the control cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the control cycle Tsw is increased to improve current detection accuracy, then the detectability of winding current is improved, but the PWM frequency decreases causing noise generation
Solution Approach 1:
The patent introduces an intermediary calculation method using the relationship between windings to estimate undetectable currents. When current detection is unreliable, the system uses the detectable current from one winding and the known phase relationship to compute the current in another winding, thereby maintaining control accuracy without extending the control cycle and avoiding noise generation.
Solution Approach 2:
The patent changes the parameter used for control from directly measured current to estimated current derived from winding relationships. By switching between direct detection and estimation based on system state, the patent maintains both detection accuracy and PWM frequency, preventing noise while achieving reliable current information.
2Reliability
If the control cycle Tsw is increased to ensure adequate holding time for current detection, then the detection reliability is improved, but the PWM frequency drops below 20 kHz generating audible noise
Solution Approach 1:
The patent performs preliminary determination of detection reliability based on voltage command values and phase information before actual current detection. When reliability is predicted to be insufficient, the system pre-switches to estimation mode using winding relationships, ensuring continuous reliable control without extending the control cycle and maintaining PWM frequency above 20 kHz.
Solution Approach 2:
The patent dynamically switches between direct current detection mode and estimation mode based on real-time assessment of detection reliability. This dynamic adaptation allows the system to maintain high detection reliability when conditions permit while keeping the control cycle short to prevent noise, achieving both reliability and low noise operation.
3Measurement precision
If multiple current detectors are used to detect currents from different windings, then the current detection coverage is improved, but the device complexity increases
Solution Approach 1:
The patent makes the current detectors multi-functional by using them not only for direct current measurement but also as the basis for estimating currents in other windings through phase relationships. This universal usage allows the system to achieve complete current information with fewer detectors, reducing device complexity while maintaining detection precision.
Solution Approach 2:
The patent merges the function of multiple detectors into a unified estimation system. By combining the output from one or more detectors with the known phase relationships between windings, the system computes currents for all windings, effectively merging detection and estimation functions to reduce the total number of required detectors.
Data Source
AI summary
This invention is concerning a controller for an AC rotating machine, this controller having an estimated sum current computing unit configured to output, as estimated sum current, a sum of current of a first winding and current of a second winding when it is determined that the current of the first winding can be detected, and maintain the estimated sum current which has been outputted as a previous value when it is determined that the current of the first winding cannot be detected. When it is determined that the current of the first winding cannot be detected, a first voltage command for the first winding is computed based on an estimated current value of the first winding, which has been calculated by subtracting the current of the second winding detected by the second current detector, from the estimated sum current output from the estimated sum current computing unit.