AC Motor Controller Current Estimation Using Single Sensor
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Solution Overview
Problem
Existing control systems for high-powered AC motors using a single current sensor face challenges in accurately estimating currents for other phases, leading to unstable control due to estimation errors and complexity in calculations, particularly when the motor constant changes with temperature and lag occurs in current estimation.
Innovation Solution
A three-phase AC motor controller that includes a current sensor detecting current in one phase, with a current estimation section calculating the current phase relative to the sensor phase using α-axis and β-axis currents in a stationary coordinate system, and estimating currents for other phases based on detected and command values, thereby improving accuracy and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a single current sensor is used to detect current in one phase, then the number of sensors is reduced and cost is lowered, but accurate current estimation for other phases becomes difficult leading to control instability
Solution Approach 1:
The patent introduces an intermediary calculation process that uses the detected current from one phase, combined with motor constants and electrical angle information, to estimate currents in the other two phases. This intermediary estimation mechanism allows the system to function with a single sensor while maintaining control stability through mathematical relationships between the phases.
Solution Approach 2:
The patent implements feedback by continuously monitoring the detected current and using it to adjust the estimation of other phase currents through calculated relationships. The control system uses feedback from the single sensor to maintain accurate current estimates for all phases, ensuring stable motor control despite using fewer sensors.
2Measurement precision
If current estimation is performed using state equations with motor constants, then current estimation is achieved, but estimation errors increase when motor constant changes with temperature
Solution Approach 1:
The patent addresses temperature variations by using parameter relationships that remain valid across different operating conditions. Instead of relying on fixed motor constants that change with temperature, the system uses fundamental electrical relationships and detected current values to estimate other phase currents, making the estimation more robust to temperature-induced parameter changes.
3Measurement precision
If complex calculations are performed for current estimation, then estimation accuracy may be improved, but calculation complexity increases making it difficult for ECU to perform real-time control
Solution Approach 1:
The patent extracts only the essential calculation elements needed for accurate current estimation, removing unnecessary complexity. By focusing on the fundamental relationships between phase currents and using readily available data (detected current, electrical angle), the system achieves accurate estimation without burdening the ECU with complex computations.
4Stability of the object's composition
If first order lag filter is used for averaging, then smoothing is achieved, but lag occurs in current estimation values causing control instability
Solution Approach 1:
The patent employs dynamic current estimation that adapts to changing motor conditions without introducing significant lag. By using real-time detected current values and electrical angle information in calculation relationships, the system maintains current estimates that closely follow actual current changes, avoiding the time delays inherent in filtering approaches while still providing smooth control signals.
Data Source
AI summary
A controller for a three-phase AC motor includes a current sensor and a current estimation section. The current sensor detects current flowing through one phase of the motor. The one phase is defined as a sensor phase. The current estimation section calculates a current phase relative to an axis of the sensor phase based on α-axis current and β-axis current in a stationary coordinate system defined by a α-axis parallel to the sensor phase axis and a β-phase perpendicular to the sensor phase axis. The current estimation section estimates current flowing through another phase of the motor based on the current phase and the detected current. The current estimation section calculates the α-axis current based on the detected current. The current estimation section calculates the β-axis current based on the detected current and a command value for the current flowing through the other phase of the motor.