Sensorless Back-EMF Estimation via PWM Off-Periods
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Solution Overview
Problem
Conventional methods for determining rotor position in synchronous motors are limited in high and mid-speed ranges with high torque levels, especially when using sensorless technologies that rely on measuring back EMF voltages of motor phases not powered.
Innovation Solution
The method involves controlling a permanent magnet motor using PWM current control to determine phase back EMF voltage and inductance values during powered states, allowing for the calculation of rotor position and speed, which can be adapted for motors with varying phase inductance characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sensorless methods measure back EMF voltages of motor phases not powered, then good resolution and low speed performances are achieved, but high and mid speed ranges with high torque levels are limited
Solution Approach 1:
The patent dynamically adapts the measurement method based on operating conditions. At low speeds, it uses conventional back EMF measurement of unpowered phases. At high speeds with high torque, it transitions to measuring back EMF during PWM off-periods when phases are naturally de-energized, allowing continuous accurate rotor position determination across the entire speed range without sensors
Solution Approach 2:
The patent changes the measurement parameters (which phase to measure, when to measure) based on the PWM switching state and speed range. By measuring back EMF during the off-period of powered phases at high speeds, it maintains measurement accuracy while adapting to conditions where conventional continuous measurement of unpowered phases becomes unreliable
2Power
If PWM current control is used to power motor phases, then high torque levels are achieved, but determination of back EMF voltage becomes difficult due to switching noise and transient effects
Solution Approach 1:
The patent performs back EMF measurement during the off-period of PWM switching, after the current has already been established during the on-period. This preliminary establishment of current ensures that the back EMF measured during the off-period reflects the true motor state without being corrupted by switching transients, while still maintaining high torque capability during the on-period
Solution Approach 2:
The patent extracts the back EMF measurement from the powered phase during PWM on-period (where switching noise corrupts the signal) and relocates it to the off-period measurement window. By separating the measurement function from the power delivery function in time, it achieves both high torque during on-period and accurate measurement during off-period
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
Enables accurate determination of rotor position and speed across a range of speeds and torques, improving control precision and resolution without the need for position sensors, particularly suitable for high-torque applications.
Implementation Method 1
the back EMF voltage which varies as a function of the speed and the rotor position
Data Source
AI summary
The methods and devices provided herein include methods and devices for controlling a permanent magnet motor. In one implementation, a method is provided that allows for the determination of the values of the phase back EMF voltage and of the phase inductances while the phases are powered with a PWM (Pulse Width Modulation) controlled current and/or voltage.