Resolver Offset Correction via Steady-State Current Calculation
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Solution Overview
Problem
Conventional methods for measuring and correcting resolver offsets in eco-friendly vehicles, such as hybrid vehicles, are inefficient and prone to human error, requiring complex processes and lengthy execution times, especially when the motor or MCU is replaced, leading to inaccurate offset measurements due to time-varying current dynamics and engine speed changes.
Innovation Solution
A method involving forced rotation of the motor using a rotation device, where d-axis and q-axis currents are controlled to determine a steady state, allowing for the calculation of the resolver offset using tan−1(d-axis current/q-axis current, and averaging current values to minimize noise, enabling quick and accurate offset measurement and correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods are used to measure resolver offset, then the process can be performed without specialized equipment, but the measurement time is excessive and accuracy is compromised due to time-varying current dynamics
Solution Approach 1:
The patent applies preliminary action by forcing the motor to rotate at a predetermined speed before measuring the resolver offset. This pre-rotation establishes stable operating conditions (steady-state currents) that eliminate time-varying dynamics during measurement. The motor is rotated by a rotation device to achieve a controlled steady state, ensuring accurate offset measurement without requiring extended measurement periods.
Solution Approach 2:
The patent changes the operational parameters by controlling the motor to rotate at a predetermined speed and maintaining steady-state d-axis and q-axis currents. By fixing the rotation speed and current parameters before measurement, the system transforms a time-varying measurement problem into a stable, time-invariant measurement, thereby improving accuracy while reducing measurement time.
2Ease of manufacture
If conventional PI control methods are used to control current to 0, then the control system can operate with standard controllers, but the time-varying nature of current dynamics prevents accurate offset measurement
Solution Approach 1:
Instead of relying on PI control to gradually bring current to zero during operation, the patent applies preliminary action by forcibly rotating the motor at a predetermined speed before measurement begins. This pre-establishes the operating point and eliminates the time-varying transient behavior that plagues PI control methods, enabling accurate offset measurement from the start.
Solution Approach 2:
The patent replaces the electrical control approach (PI control of current) with a mechanical approach (forced rotation at predetermined speed). By using a rotation device to mechanically drive the motor at a controlled speed, the system eliminates the complexity and time-varying behavior of electrical current control, achieving stable measurement conditions more directly.
3Reliability
If resolver offset measurement is performed in service centers after motor replacement, then the offset can be corrected for accurate motor control, but human error and re-measurement delays occur
Solution Approach 1:
The patent enables self-service by making the offset measurement process simple enough to be performed by technicians during routine maintenance or replacement procedures. The forced rotation method requires only basic equipment and follows a straightforward procedure, eliminating the need for specialized service centers and reducing human error associated with complex measurement protocols.
Solution Approach 2:
The patent allows the measurement process to be rushed through quickly by using forced rotation to achieve steady state rapidly. Instead of waiting for natural decay of currents or gradual stabilization, the mechanical forcing method accelerates the process, enabling fast offset measurement that can be completed during brief service intervals without delaying vehicle operation.
Data Source
AI summary
Disclosed is a technique of correcting a resolver offset by measuring and correcting an offset of a resolver assembled to a motor of an eco-friendly vehicle in an accurate and simple way. The offset measurement process includes, after completing the assembly of a resolver a resolver to a motor, rotating the motor by using a rotation device able to transfer a rotation force to the motor, setting a voltage instruction and current-controlling the motor according to the voltage instruction, and obtaining a d-axis current and a q-axis current, which are feedback currents, during the current-control of the motor. Then when the system is in a steady state, a resolver offset ({tilde over (θ)}) is calculated from the d-axis current and the q-axis current by using {tilde over (θ)}=tan−1(d-axis current/q-axis current).