Motor Control Unit Dead Time Compensation
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Solution Overview
Problem
Conventional electric power steering apparatuses face issues with current waveform distortion and torque ripple due to dead time in inverter switching devices, leading to poor steering control and increased noise and vibration, which existing compensation methods fail to adequately address without tuning operations or accurate compensation for temperature and motor rotational angle.
Innovation Solution
A vector control type motor control unit that calculates dead time compensation values based on motor rotational angle and temperature, adding these values to voltage command signals after space vector modulation to compensate for inverter dead time, thereby improving current waveform accuracy and reducing noise and torque ripple without the need for tuning operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dead time compensation is performed using conventional methods, then current waveform distortion and torque ripple are reduced, but tuning operations are required and compensation accuracy deteriorates with temperature and rotational angle variations
Solution Approach 1:
The patent pre-calculates and stores dead time compensation values in a lookup table for various motor rotational angles before operation. During actual control, the controller simply retrieves the appropriate compensation value from the table based on the current rotational angle, eliminating the need for real-time calculation and tuning operations while maintaining high accuracy across different temperatures and speeds
Solution Approach 2:
The patent divides the motor rotational angle range into multiple regions and applies different compensation values for each region. By changing the compensation parameter based on the rotational angle region, the system achieves accurate compensation across the entire operating range without requiring complex real-time adjustments or tuning operations
2Device complexity
If simple dead time compensation is applied, then device complexity is reduced, but compensation accuracy deteriorates under varying temperature and rotational speed conditions
Solution Approach 1:
The system pre-computes compensation values covering the full range of operating conditions (temperature and rotational angle) and stores them in a lookup table. This preliminary preparation allows the controller to achieve high compensation accuracy under all conditions by simply retrieving pre-calculated values, without requiring complex real-time computation or frequent tuning operations
Solution Approach 2:
The patent implements dynamic compensation by selecting different compensation values from the lookup table based on the current motor rotational angle and temperature conditions. The compensation parameter dynamically adapts to operating conditions while maintaining a relatively simple control structure, achieving high reliability without excessive complexity
3Device complexity
If no dead time compensation is applied, then control system simplicity is maintained, but current waveform distortion and noise increase significantly
Solution Approach 1:
The patent pre-calculates dead time compensation values for all possible motor rotational angles and stores them in a lookup table during system initialization or manufacturing. During operation, the controller retrieves the appropriate compensation value based on the current rotational angle, effectively eliminating current waveform distortion and torque ripple without adding complex real-time computation or tuning mechanisms to the control system
Data Source
AI summary
[Problem]An object of the present invention is to provide a vector control type motor control unit that compensates a dead time of an inverter without a tuning operation, improves a distortion of a current waveform and responsibility of the current control, and suppresses sound, vibration and a torque ripple.[Means for Solving the Problem]The present invention is the vector control type motor control unit that calculates a q-axis control assist command value, calculates dq-axes current command values from the control assist command value, converts the dq-axes current command values into 3-phase duty command values, and drives and controls a 3-phase brushless motor by a PWM-controlled inverter, wherein dead time compensation of the inverter is performed by calculating 3-phase dead time reference compensation values based on a motor rotational angle, calculating 3-phase dead time compensation values by temperature-correcting the 3-phase dead time reference compensation values, and adding the 3-phase dead time compensation values to 3-phase voltage command values after performing dq-axes space vector modulation.