Efficient motor control for e-bike applications

Since the 1990s, e-bikes have been steadily growing in popularity across the globe, with the market expecting to grow to around 7 million units by 2025. In fact, several sources predict that almost half of all bikes made in future will incorporate an electric motor. China remains the main market globally for e-bikes. Although the range concerns surrounding automobiles are not as predominant in the e-bike market, it is still essential that consumers can enjoy the advantages of their electrically supported bicycle without the need to charge it up after every journey.

Taking some cues from modern cars, today’s e-bikes are becoming very feature-rich, incorporating features such as automatic gear changing, walk assist (where the e-bike can be pushed with no effort) and increasingly sophisticated on-board computing that provides parametric information for the journey as well as GPS-based navigation. In the past, cycling to work usually meant arriving tired, hot and sweaty, often needing a shower before starting the day in the office. Modern e-bikes flatten out hills, provide extra effort to combat headwinds and allow cyclists to travel further and quicker, while arriving at work fresh and ready to start the day.

The growth in e-bikes has been made possible due to the availability of highly efficient motors, high-density batteries, and low-loss drive implementations for motor control. On the motor drive side, highly integrated microcontroller (MCU) solutions are being continuously refined. Today’s MCUs integrate a competent analog front-end and highly configurable timers, coupling them with motor control peripherals that move the complexity of field-oriented-control (FOC) from the software to the hardware domain.

Devices such as the TXZ family of Arm® Cortex® based MCUs integrate a Vector Engine (VE). The latest iteration of this peripheral not only implements the Park-Clarke transformations required for motor control but is also tightly coupled with the other on-chip peripheral needed for accurate motor control. This includes the pulse-width-modulation (PWM) timers and the analog-to-digital converter (ADC). Such tight integration simplifies configuration, ensures accuracy and efficiency in control, and leaves the processing core with much more time to execute other application functions.

In order to ensure a highly efficient drive implementation, such MCUs should be coupled with low on-resistance MOSFETs. Here the focus also broadens to cover the need for compact packaging and excellent thermal dissipation. Devices such as the UMOS IX low voltage (LV) MOSFETs from Toshiba provide the perfect partner to such motor control implementations. This latest generation of devices has reduced gate charge and recovery charge while also reducing on-resistance (RDS(ON)).

Advanced packaging for power devices also needs to be taken into consideration, allowing developers to ensure that any heat generated is dissipated appropriately. Packaging technology, such as the DSOP Advance, are surface mount solutions that provide thermally conductive metal heat spreading pads on both the top and bottom sides.

The ubiquity of smartphones opens up new options for the development of the e-bike human-machine interface (HMI). Low-power Bluetooth can potentially be used, together with a smartphone app, as the HMI displaying all the necessary statistics and data regarding remaining range and battery charge status. Alternatively, a high-end HMI with colour display and navigation capability can use the Bluetooth interface to provide information to a smartphone’s fitness app.

This area can be supported by a device such as the TC35680, a solution supporting all major Bluetooth Low Energy 5 features. One of them is the standard’s new 2Mbit/s high-speed data rate, which allows for very fast transmission speeds between the user’s smartphone and the e-bike, useful when a firmware upgrade is required. With the growth in bike sharing, it would be convenient to unlock the e-bike from an application on the smartphone instead of typing in a code. However, such convenience comes with the risk of eavesdropping and man-in-the-middle attacks. To secure the connection against these attacks the TC35680 provides dedicated hardware features such as a true random number generator (TRNG), a unique ID for every chip, and an AES-128bit hardware encryption unit.

One thing is clear – e-bike development offers a host of challenges but, equally, plenty of exciting opportunities to innovate. To support engineers tackling this application space Toshiba has created a free white paper. It covers each of the aforementioned design elements, offering insights and potential solutions based upon a wide range of Toshiba technologies. This ranges from background and implementation, to development and evaluation tools. To download this comprehensive white paper, the link provided here can be used: LINK