Improved range, performance, and usability are helping modern eBikes enjoy growing popularity as commuter, commercial, and recreational vehicles.
Next-generation eBikes use
BLDC motors and advanced controls
Since their emergence in the early 1990s, eBikes have undergone a steady series of improvements in range, reliability, and performance that have won them a growing number of loyal users worldwide. Yet despite nearly 30 years of technical evolution, there’s still room for innovation. Some innovations in next-generation eBikes relate to better frame designs and mechanical systems. Others include advances in electronics for the motor drive and energy-storage systems. But the most dramatic changes are in eBike controls and user interfaces for maximally enjoyable user experience (UX). Most modern eBikes use permanent magnet motor (PMM) propulsion, with brushless dc motors being especially common. BLDC motors are one of the simplest forms of synchronous motor: These have a permanent-magnet rotor assembly surrounded by a wound stator having several (usually three) winding sets. BLDCs are lighter and more efficient that equivalent brushed motors — plus need little maintenance. The catch is they need a motor controller to provide a drive waveform (commutation). The controller does this by monitoring the rotor position and supplying power to the stator windings in the correct sequence to start and maintain rotor motion. BLDC motor drive technology for eBikes is relatively mature but there are still a few places where designers can differentiate products through lower cost or better performance and efficiency. For example, a growing number of eBike designers are using motor controllers capable of supporting vector control-based commutation — also known a field-oriented control (FOC). The FOC algorithm can decouple control of torque and flux by transforming the stator current values (phase currents) from a stationary reference frame to a rotating reference frame.
32
DESIGN WORLD — MOTION
Controllers - MC 11-19 V3.indd 32
11 • 2019
This speed and torque-sensing crank shaft, manufactured by THUN-X, provides two digital outputs for the digital sin/cos speed signal and an analog output for the torque signal. With this arrangement, the eBike’s motor controller requires only two digital inputs and one analog input. | courtesy Enviado
motioncontroltips.com | designworldonline.com
11/19/19 11:05 AM
