PMSM Initial Rotor Position Detection Using Current Rise Time
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Solution Overview
Problem
Existing methods for initial rotor position detection in permanent magnet synchronous motors (PMSMs) face challenges such as increased size and cost due to the use of sensors, and suffer from decreased starting torque and potential reversed rotation issues, especially at standstill, which are exacerbated by the need for accurate peak current measurement and high-resolution analog-to-digital converters.
Innovation Solution
An apparatus and method that utilize a current sensor, internal digital initial angle detector, and internal analog current processing circuit to detect both rise and fall times of motor currents under different voltage vectors, eliminating the need for ADCs and allowing for precise initial rotor position determination without sensor ambiguity, enabling faster detection and smoother startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensors (resolvers, encoders, Hall sensors) are used for rotor position sensing, then rotor position information is obtained, but machine size increases and system reliability decreases
Solution Approach 1:
The patent extracts and eliminates the position sensor component from the motor system by implementing sensorless control. The rotor position is determined indirectly through current measurement and processing rather than direct sensing, removing the physical sensor hardware that increases machine size and reduces reliability.
Solution Approach 2:
The patent replaces the mechanical/electrical sensor system with an electronic control system that uses current measurements and mathematical processing to determine rotor position. The initial angle detector and current processing circuit substitute for physical sensors, achieving position detection through electrical signal analysis rather than mechanical sensing.
2Measurement precision
If peak current measurement methods are used for initial rotor position detection, then rotor position can be detected, but high-resolution ADCs are required increasing device complexity
Solution Approach 1:
Instead of measuring peak current values that require high-resolution ADCs, the patent uses current rise time measurement which only requires detecting when current reaches certain thresholds. This partial measurement approach (measuring time to reach threshold rather than peak value) reduces ADC resolution requirements while maintaining detection accuracy.
Solution Approach 2:
The patent substitutes the ADC-based peak current measurement system with a timer-based rise time measurement system. The initial angle detector uses timing circuits to measure how long it takes for current to rise to threshold levels, replacing the need for high-resolution analog-to-digital conversion with simpler timing electronics.
3Device complexity
If conventional starting methods are used without accurate initial position detection, then system simplicity is maintained, but starting torque decreases and reversed rotation occurs
Solution Approach 1:
The patent applies preliminary action by detecting the initial rotor position (or initial angle) before the motor starts rotating. The initial angle detector determines the rotor position at standstill, and this information is used to pre-position the stator magnetic field correctly, ensuring proper starting torque and preventing reversed rotation before the motor begins operation.
Solution Approach 2:
The patent implements feedback by using the measured current rise time information to continuously refine the estimated initial rotor position. The current processing circuit and initial angle detector create a closed-loop system where current measurements feed back to determine and correct the position estimate, ensuring reliable starting performance.
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 reduces detection time, enhances noise sensitivity, and achieves thirty-degree resolution for initial angle detection, allowing for precise and efficient initial rotor position determination without the need for high-resolution ADCs, thereby improving motor startup performance.
Implementation Method 1
a current sensor to sense a motor current to thereby generate a sensing signal
Implementation Method 2
an internal analog current processing circuit to detect the sensing signal to thereby generate an over-current signal and a zero-current signal
Data Source
AI summary
An apparatus and method for use with a PMSM detect the fall time or the rise time and the fall time of a motor current in the PMSM under different voltage vectors when the PMSM is in start-up to determine an initial rotor position for the PMSM at standstill.