AC Motor Control Device Non-Orthogonalization Current Estimation
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Solution Overview
Problem
The existing control devices for AC motors in hybrid and electric vehicles face instability when the motor is stopped, as the current sensed value in the sensor phase becomes zero, leading to inaccurate current estimation and unstable drive control due to the orthogonality of the current command vector with the sensor phase axis.
Innovation Solution
A control device that includes an inverter, a current sensor, and a controller which performs non-orthogonalization processing by adjusting the electric angle or current command phase to ensure a non-zero current sensed value, even when the motor is stopped, thereby improving estimation accuracy and stability during low rotation states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If one phase control is used to reduce the number of current sensors, then device complexity and cost are reduced, but measurement precision deteriorates when the motor is stopped at certain positions
Solution Approach 1:
The control device performs preliminary detection to determine whether the motor is in a stop state before executing the one-phase control algorithm. This preliminary action allows the system to prepare appropriate control strategies in advance, preventing the measurement precision deterioration that would occur if the motor is stopped at positions where the sensor phase current is zero.
Solution Approach 2:
The control algorithm dynamically switches between different control modes based on the motor's operational state. When the motor is detected to be in a stop state, the system transitions from standard one-phase control to a specialized control routine that uses the two non-sensor phases for current estimation, thereby maintaining measurement precision across all operational conditions.
2Ease of manufacture
If one phase control is used to simplify the control system, then ease of manufacture is improved, but reliability deteriorates due to unstable drive control when current sensed value is zero
Solution Approach 1:
The control system dynamically adapts its behavior based on the motor's operational state. When the motor is detected to be stopped, the system automatically switches to an alternative control algorithm that uses the two non-sensor phases for current estimation, ensuring reliable drive control regardless of the motor's stop position and maintaining system reliability throughout.
Solution Approach 2:
The control device continuously monitors the motor's operational state and uses this feedback to determine when to switch control modes. By detecting the stop state and responding accordingly, the system ensures that the appropriate control algorithm is always active, preventing instability and maintaining reliable drive control.
3Device complexity
If standard one-phase control is used, then device complexity is reduced, but measurement precision worsens because dq axis current deviations become zero when sensor phase current is zero
Solution Approach 1:
The control device performs preliminary detection to identify when the motor is in a stop state before executing the one-phase control algorithm. This preliminary action allows the system to switch to an alternative estimation method that uses the two non-sensor phases, preventing the dq axis current deviations from becoming zero and maintaining measurement precision.
Solution Approach 2:
The control algorithm dynamically switches between different current estimation methods based on the motor's operational state. During stop conditions, the system transitions to using the two non-sensor phases for current estimation, ensuring that dq axis current deviations remain non-zero and measurement precision is maintained.
Data Source
AI summary
A control device of a three phase AC motor includes: an inverter for driving the motor; a current sensor for sensing current flowing in a sensor phase of the motor; and a controller for switching multiple switching elements in the inverter to control the current of the motor. An electric angle is defined as θe based on one phase. A phase is defined as φ based on a dq axis. A phase angle of a current command vector is defined as (θe+φ+C). When the motor is stopped, the controller determines whether the current command vector is orthogonal to an axis of the sensor phase. When the current command vector is orthogonal to the axis of the sensor phase, the controller operates the phase or the electric angle to set the current command vector not to be orthogonal to the axis of the sensor phase.