PWM Deadtime Back-EMF Sensing for Low-Noise Motor Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing motor control methods face challenges with torque ripple, noise susceptibility, complex algorithms, high BOM costs, and resource limitations, especially when using 8-bit microcontrollers for sinusoidal PWM modulation without FOC or hall sensors.
Innovation Solution
Implementing a deadtime interval in PWM switching to measure back electromotive force (BEMF) using asymmetric deadtimes, allowing BEMF acquisition without disturbing motor operation, suitable for microcontrollers with limited resources, and enabling accurate zero-cross detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sinusoidal PWM modulation drive with FOC is used, then motor control precision and torque quality are improved, but device complexity and computational requirements increase significantly
Solution Approach 1:
The patent extracts the BEMF measurement function from the continuous control loop and performs it during the deadtime intervals of PWM switching. This separates the measurement function from the main control algorithm, allowing simpler control logic while maintaining precise BEMF detection for position and speed control.
Solution Approach 2:
The patent performs BEMF measurement during deadtime intervals before the next PWM switching cycle begins. This preliminary measurement during idle time provides advance information about rotor position and speed, enabling smooth transitions and reducing computational burden during active control periods.
2Device complexity
If block commutation drive with trapezoidal BEMF measurement is used, then control algorithm simplicity is improved, but torque ripple and acoustic noise increase
Solution Approach 1:
The patent implements periodic BEMF measurement during each PWM deadtime interval, creating a continuous stream of position information. This periodic sampling during natural idle periods enables smooth commutation transitions and reduces torque ripple compared to traditional block commutation, while maintaining algorithm simplicity.
3Measurement precision
If deadtime interval is used for BEMF acquisition, then measurement timing precision is improved, but switching losses may increase
Solution Approach 1:
The patent utilizes the existing deadtime intervals required for PWM switching, which are necessary to prevent shoot-through conditions. By performing BEMF measurement during these mandatory idle periods, the system converts previously wasted time into useful measurement opportunities without adding extra switching events or increasing energy losses.
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
Facilitates high-torque, low-noise motor control with simplified algorithms, reducing mechanical, acoustic, and electrical disturbances, while preserving the advantages of both trapezoidal and sinusoidal control methods.
Implementation Method 1
A counter force in the form of eddy currents may be generated by the armature rotating in the magnetic field. This counter force may be referred to as BEMF.
Data Source
AI summary
An apparatus and method for determining electrical characteristics has an acquisition circuit and a control circuit. The control circuit causes a first modulation circuit to issue a first set of modulated signals to a first source of alternating current energy, wherein the first set of modulated signals has a first deadtime and wherein a high side switch and a low side switch of the first modulation circuit are turned off. The control circuit further causes the acquisition circuit to acquire a first electrical characteristic of the first source of alternating current energy from the first source of alternating current energy during the first deadtime.