Motor Control Device Calibrating Current Sensor for Capacitor Discharge
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing methods for discharging the smoothing capacitor in motor systems, such as those in hybrid or electric vehicles, often result in unintended torque generation due to detection errors in current sensors, leading to potential motor rotation during the discharge process.
Innovation Solution
A motor control device that includes an electric discharge control unit and a current sensor calibration unit, which calibrates the current sensor when no current is flowing to accurately control the discharge process, ensuring zero q-axis current and preventing torque generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the current sensor is used to detect motor current during capacitor discharge, then the discharge control can be implemented, but detection errors cause unintended q-axis current flow and torque generation
Solution Approach 1:
The patent applies preliminary action by performing current sensor calibration in the period between relay cutoff and discharge control start. This preliminary calibration eliminates detection errors before discharge begins, ensuring accurate current detection during the critical discharge phase and preventing unintended torque generation.
Solution Approach 2:
The patent changes the operational state of the current sensor by switching from a calibrated state (with potential errors) to a calibrated state (with errors eliminated). The calibration process adjusts sensor parameters to ensure accurate detection during discharge, directly addressing the measurement precision issue.
2Productivity
If discharge control is started immediately after relay cutoff, then the discharge process is faster, but torque may be generated due to uncalibrated current sensor errors
Solution Approach 1:
The patent implements preliminary calibration action in the time window between relay cutoff and discharge start. This ensures that the current sensor is calibrated and ready for accurate detection, allowing discharge to proceed immediately after calibration without compromising torque control accuracy.
Solution Approach 2:
The calibration process uses feedback from the current sensor to detect and correct offset errors. By measuring the actual current (which should be zero) and adjusting the sensor output accordingly, the system ensures accurate current detection during subsequent discharge operations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces motor torque during smoothing capacitor discharge, enhancing the reliability of the motor control system by accurately calibrating the current sensor to prevent unintended current flow.
Implementation Method 1
a current sensor configured to detect a current flowing through the motor
Implementation Method 2
an electric discharge control unit configured to discharge, in the motor via the inverter, an electric charge accumulated in the smoothing capacitor
Implementation Method 3
the q-axis current which comes directly to the d-axis and that imparts torque to the motor
Implementation Method 4
torque is generated in the motor
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The occurrence of torque in the motor due to an unintentional flow of the q-axis current in the motor during discharging of the smoothing capacitor is reduced. A motor control device according to the present invention controls a system including an inverter including a smoothing capacitor connected to a power source via a relay, a motor connected to the inverter, and a current sensor configured to detect a current flowing through the motor, the motor control device including: an electric discharge control unit configured to discharge, in the motor via the inverter, an electric charge accumulated in the smoothing capacitor; and a current sensor calibration unit configured to calibrate the current sensor in a state where no current in the motor flows during a time period from when the relay is cut off to when discharge control by the electric discharge control unit is started, wherein the electric discharge control unit performs discharge by controlling the current in the motor based on a value of the current sensor calibrated by the current sensor calibration unit.