Linear Kalman Filter for Sensorless Motor Rotor Estimation
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Solution Overview
Problem
Conventional sensorless vector control methods for permanent magnet synchronous motors require high processing capacity due to complex arithmetic operations, leading to increased costs and inefficiencies, especially when estimating rotor position at low speeds or in motors without saliencies.
Innovation Solution
A motor drive control device employing a linear Kalman filter with a stationary prediction step, expressed linearly and time-invariantly, to estimate rotor angle and speed based on q-axis current values and voltage command values, reducing arithmetic load and processing requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional extended Kalman filter is used for sensorless vector control, then accurate rotor position estimation is achieved, but complex arithmetic operations are required increasing processing load and cost
Solution Approach 1:
The patent changes the mathematical parameters of the Kalman filter by assuming constant rotor acceleration, which transforms the prediction equations into a linear form with constant coefficients. This allows the use of simpler linear Kalman filter arithmetic while maintaining estimation accuracy, directly resolving the contradiction between precision and complexity
Solution Approach 2:
The patent segments the rotor motion into distinct phases: acceleration phase (where constant acceleration assumption applies) and constant speed phase (where different estimation methods can be used). This segmentation allows optimization of arithmetic operations for each phase, reducing overall processing load while maintaining accuracy
2Productivity
If high processing capacity is provided to execute complex arithmetic operations at high speed, then sensorless vector control is achieved, but costs increase
Solution Approach 1:
By changing the mathematical model parameters to assume constant acceleration during transient phases, the patent reduces the computational complexity from nonlinear matrix operations to linear operations with constant coefficients. This enables execution on lower-cost microcontrollers while maintaining high-speed control performance
Solution Approach 2:
The patent employs a simpler, less expensive microcontroller that can execute the reduced-complexity arithmetic operations. The simplified algorithm allows use of lower-specification hardware, directly reducing device cost while maintaining adequate processing speed for motor control applications
3Measurement precision
If induced voltage method is used for rotor position estimation, then estimation is possible during rotation, but estimation fails when rotor is stopped or rotates at low speed
Solution Approach 1:
The patent implements a dynamic estimation approach that adapts to different operating conditions: using induced voltage method during constant-speed operation and using acceleration-based prediction during acceleration and low-speed phases. This dynamic adaptation extends the usable operating range from only constant-speed to include stopped, accelerating, and low-speed conditions
Solution Approach 2:
The patent introduces rotor acceleration as an intermediary parameter to bridge the gap between different estimation methods. By calculating acceleration from current position and speed data, the system can predict future position even when induced voltage is insufficient, enabling estimation across the full operating range
Data Source
AI summary
A motor drive control device includes a drive circuit configured to drive a motor with a drive control signal for driving the motor, and a control circuit configured to perform a vector control arithmetic operation based on a detection result of drive currents of coils of the motor, to generate the drive control signal and supply the drive control signal to the drive circuit. When generating the drive control signal, the control circuit estimates a rotation angle of a rotor of the motor and a rotation speed of the rotor with a q-axis current value of a two-phase rotating coordinate system calculated with a detection result of the drive current, and a q-axis voltage command value of the two-phase rotating coordinate system, by using a linear Kalman filter including a prediction step and an update step, using a stationary Kalman filter with the prediction step expressed linearly and time-invariantly.