AC Motor Current Estimation for Steep Torque Transients
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Solution Overview
Problem
Existing AC motor control systems with single-phase current sensing face responsiveness issues due to insufficient electric current estimation during steep torque changes, leading to delayed torque response and instability.
Innovation Solution
The control apparatus includes an electric current estimation unit that calculates d/q axis electric current estimates in a rotation coordinate system, correcting these values in the sensor phase orthogonal direction based on previous and current cycle errors to improve convergence speed and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If single-phase current sensing is used to reduce sensor quantity, then cost and volume are reduced, but electric current estimation responsiveness deteriorates during steep torque changes
Solution Approach 1:
The patent changes the parameter of smoothing strength dynamically. When torque change is detected (indicating steep current change), the smoothing strength is reduced to improve responsiveness. When torque change is small, normal smoothing is applied to maintain estimation accuracy. This allows the system to adapt between accuracy and responsiveness based on operating conditions.
Solution Approach 2:
The patent introduces dynamic adjustment of the smoothing coefficient based on detected torque changes. The smoothing coefficient is not fixed but varies over time according to the operational state of the motor, transitioning between strong smoothing (stable operation) and weak smoothing (transient operation) to optimize both accuracy and responsiveness.
2Measurement precision
If strong smoothing is applied to electric current estimate values, then estimation accuracy is improved, but responsiveness to torque changes deteriorates
Solution Approach 1:
The patent dynamically changes the smoothing coefficient parameter based on torque change detection. During steady-state operation, a larger smoothing coefficient is used for accurate estimation. During transient torque changes, the smoothing coefficient is reduced to improve tracking responsiveness, resolving the contradiction between accuracy and speed.
Solution Approach 2:
The system transitions from static smoothing to dynamic smoothing where the smoothing coefficient adapts to operational conditions. This dynamic approach allows the system to maintain high accuracy during normal operation while achieving fast responsiveness during torque transients by adjusting the smoothing strength in real-time.
3Stability of the object's composition
If smoothing is applied to electric current estimates, then estimation stability is improved, but convergence speed during torque changes deteriorates
Solution Approach 1:
The patent changes the smoothing coefficient parameter dynamically based on torque change detection. During transient states when convergence is needed, the smoothing coefficient is reduced to accelerate convergence. During stable operation, the coefficient is increased to maintain estimation stability, thus resolving the contradiction between stability and convergence speed.
Solution Approach 2:
The system employs dynamic smoothing where the smoothing coefficient is adjusted according to the operational phase. During torque transients, weak smoothing enables fast convergence. During steady-state, strong smoothing maintains stability. This time-varying approach optimizes both convergence speed and estimation stability throughout the operational cycle.
Data Source
AI summary
A control apparatus includes an electric current estimation unit to improve a responsiveness of an AC motor. The electric current estimation unit performs, at predetermined intervals, a dq conversion, a correction process, and an inverted dq conversion. The dq conversion calculates d/q axis electric current estimate values based on a detection value of a sensor phase from a sensor, and on an electric current estimate values of two phases of the AC motor other than the sensor phase from a previous cycle. The correction process corrects, during the dq conversion, the d/q axis electric current estimate values in an orthogonal direction that is orthogonal to a sensor phase axis. The inverted dq conversion calculates the electric current estimate values of the two phases other than the sensor phase based on the d/q axis electric current estimate values corrected by the correction process and smoothed by a low-pass filter process.