AC Motor Current Estimation via Inverted Dq Correction
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Solution Overview
Problem
Existing AC motor control systems face challenges in achieving stable electric current estimation accuracy, particularly at higher rotation speeds, due to phase delays and cumulative calculation errors, which can lead to inaccurate torque control and potential system breakdowns.
Innovation Solution
A control apparatus for AC motors that includes an electric current estimation unit performing inverted dq conversion, dq conversion, and correction processes to improve estimation accuracy by removing phase delays and reducing calculation errors, using a single-phase sensor to calculate d/q axis electric current estimates based on current cycle data, and simplifying the smoothing process through gain multiplication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If single-phase electric current sensing is used to reduce sensor quantity, then cost and volume are reduced, but electric current estimation accuracy deteriorates at higher rotation speeds
Solution Approach 1:
The patent applies preliminary action by calculating and storing correction values in advance based on the relationship between rotation speed and estimation error. These correction values are pre-computed and stored in a lookup table, allowing the system to quickly compensate for estimation errors without real-time complex calculations, thus maintaining high accuracy across all rotation speeds while using only one sensor
Solution Approach 2:
The patent changes the parameter of estimation accuracy by introducing rotation speed-dependent correction values. The correction values are adjusted based on the rotation speed parameter, allowing the system to compensate for the degradation of estimation accuracy at higher speeds. This parameter-based correction transforms the fixed-accuracy estimation into a variable-accuracy estimation that is maintained across different operating conditions
2Device complexity
If conventional electric current estimation method is used, then system complexity is reduced, but phase delays and cumulative calculation errors increase
Solution Approach 1:
The patent applies feedback by continuously monitoring the actual electric current and comparing it with the estimated current to generate correction values. This feedback mechanism allows the system to detect and compensate for phase delays and cumulative calculation errors in real-time, thereby maintaining reliable torque control without significantly increasing system complexity
Solution Approach 2:
The patent applies partial action by implementing correction only for the specific phases where estimation errors occur, rather than recalculating all phase currents. The correction is applied selectively based on the detected error patterns, reducing the computational burden while improving reliability
Data Source
AI summary
A control apparatus of an AC motor improves an electric current estimation accuracy of the AC motor. The control apparatus includes an electric current estimation unit that repeatedly performs an inverted dq conversion, a dq conversion, and a correction process. Based on a d/q axis electric current estimate values of a previous cycle, the inverted dq conversion calculates an electric current estimate value of a sensor phase. The dq conversion calculates a d/q axis electric current correction values based on an electric current estimation error of the sensor phase, which is derived from the electric current estimate value and the electric current detection value detected by an electric current detector. The correction process calculates the d/q axis electric current estimate values of a current cycle by correcting the d/q axis electric current estimate values of the previous cycle by using the d/q axis electric current correction values.