Motor Drive Dead Time Estimation via Current Step Response
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Solution Overview
Problem
Conventional motor drive devices face challenges in accurately estimating dead time in output stages due to variations in gate drive circuit components, leading to inappropriate dead time correction and adverse effects on current control, with existing solutions requiring additional circuits that increase size, cost, and measurement errors.
Innovation Solution
A motor drive device incorporating a dead time estimator that calculates the actual dead time from the difference between current command and detection value using constants derived from current step response measurements, allowing for accurate dead time correction without additional circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional measurement circuits are added to accurately measure dead time, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The system uses its own existing current detection unit to measure the dead time effect by comparing current command values with actual current detection values. The dead time estimator calculates the actual dead time based on this self-generated data, eliminating the need for separate measurement circuits while maintaining measurement accuracy.
Solution Approach 2:
The current detection unit, originally designed for current control, is also utilized for dead time measurement. By making the current detection unit serve multiple functions (current control and dead time estimation), the patent avoids adding dedicated measurement circuits while achieving accurate dead time measurement.
2Device complexity
If dead time correction is applied using fixed predetermined values, then device complexity is reduced, but manufacturing precision deteriorates due to component variations
Solution Approach 1:
The dead time correction system transitions from using fixed predetermined values to dynamically calculated actual dead time values. The dead time estimator continuously calculates the actual dead time based on real-time current command and detection value comparisons, adapting to component variations and ensuring accurate correction without increasing system complexity.
Solution Approach 2:
The patent changes the dead time parameter from a fixed predetermined value to a dynamically calculated actual dead time value. By using the relationship between current command values, actual current detection values, and voltage commands, the system adjusts the dead time parameter to match actual circuit conditions, improving correction accuracy while maintaining simple control logic.
Data Source
AI summary
A motor drive device includes an inverter for generating an AC voltage from a DC voltage by switching power elements, a current detection unit for detecting a current to be inputted to a motor, a current controller for generating a voltage command from a current command and a current detection value, a gate drive command generator for generating drive commands for the power elements such that a dead time in an output stage, that is a period of time in which both of the power elements for upper and lower arms that compose the output stage of the inverter are turned off, becomes a predetermined value, a gate drive circuit unit for outputting gate drive signals for the power elements, and a dead time estimator for estimating the dead time in the output stage that is produced by the gate drive signals for the power elements.