E-Bikes and E-Scooters: A Full System Design Solution, Wall to Battery

­The rise of e-bikes and e-scooters is transforming urban mobility, offering a cleaner, more convenient alternative to traditional modes of transportation. Central to the success and efficiency of these electric vehicles are the charging, battery management, motor driver, and control systems, as shown in Figure 1. This article delves into the design considerations for the above systems, emphasizing the critical functions of power semiconductors.

Battery Management 

The Battery Management System (BMS) is a crucial component in e-bikes and e-scooters, ensuring the safe and efficient operation of the battery pack. The three primary functions of a BMS include monitoring, protection, and cell balancing. The BMS continuously monitors the status of individual cells within the battery pack for voltage, temperature, and state of charge. It also prevents conditions such as over-charging/discharging, short circuits, and thermal runaway. Finally, it ensures uniform charge distribution among cells to maximize battery life and performance. These functions can be done with discrete devices or a Battery Management Integrated Circuit (BMIC). Switches such as MOSFET transistors control the charging and discharging processes. They enable precise control over the current flow, which is essential for protecting battery cells and maintaining efficiency. Next, a method for obtaining and processing accurate data for voltage, current, and temperature measurements is done with Analog-to-Digital Converters. Finally, a stable power supply to the BMS and its components is critical to maintaining reliability and accuracy in monitoring and control.

The Renesas FGIC, RAJ240100, integrates all the aforementioned blocks, reducing size and cost. It also includes an MCU for fuel-gauging purpose. It supports 6 to 10-cell battery pack, widely used in 36V e-bikes designs. A block diagram can be found in Figure 2. For bigger battery packs supplying 48V e-mobility platforms (up to 14 cells), the Renesas BMIC, RAA48920, enables scalable and modular design through robust, proprietary, daisy-chain-able, two-wire communication. A fuel gauge can be included with the addition of a Renesas microcontroller among the RL78Gxx family.

Click image to enlarge

Figure 2: Block diagram of BMS

Motor Control

Designing and implementing a brushless DC (BLDC) motor and driver for e-bikes/scooters involves an advanced integration of hardware and software to ensure efficient and reliable motor control. The BLDC motor driver typically consists of several key components. A microcontroller unit (MCU) is selected for its processing power, capability to handle real-time control algorithms, and other ancillary functions. The motor driver circuitry includes gate drivers to control the switching of power transistors, such as MOSFETs, ensuring precise timing and commutation of the motor phases. The MCU coordinates with the motor driver to commutate the motor windings to enable smooth and efficient operation of the BLDC motor across a wide range of speeds and loads. It can also detect the rotor position based on feedback from position sensors, like a Hall effect sensor, or sensor-less algorithms through back EMF signals.

Control algorithms such as field-oriented control (FOC) or trapezoidal control ensure optimal torque generation, speed regulation, and efficiency throughout the vehicle’s operational range. Additionally, safety features such as overcurrent, overvoltage, and thermal protection are integrated into the firmware to safeguard the motor and electronics from damage during operation.

Renesas offers comprehensive motor control solutions that enable short design cycles by providing integrated hardware and firmware development platforms. Both RA6Tx (ARM-Cortex M33) and MX23x (proprietary core) guarantee suitable computation power, and the RAA227603 three-phase gate driver combined with our Low-Voltage (40V - 200V rated) MOSFETs is a winning combination for e-bike/scooter motor driving, as shown in Figure 3.

Click image to enlarge

Figure 3: Motor control block diagram

AC-DC Conversion

Charging systems for e-bikes/scooters require efficient AC-DC conversion and involve several key components. A Power Factor Correction (PFC) circuit ensures that the power drawn from the grid is used efficiently. It reduces reactive power, improving the overall power efficiency. A secondary DC-DC regulator efficiently converts the high-voltage output of the PFC (typically in the range of 360V to 400V) to a 36V or 48V level, suitable for e-bikes and e-scooter battery packs.

AC-DC solutions from Renesas, as shown in Figure 4, enable fast charging time and efficient conversion using digital control in combination with Gallium Nitride (GaN) HEMT switches. The iW9801 Flyback converter, in addition to the TP65H150G4PS, 150 mΩ ON-resistance GaN HEMT, enables the needed power to supply the secondary-side controller, iW780, producing up to 48V/5 A DC output.

Click image to enlarge

Figure 4: Block diagram of AC-DC and USB-C wall to battery solution

Using USB-C EPR for a Common Connector Configuration

USB-C 3.1 Extended Power Range (EPR) technology is revolutionizing the charging capabilities for e-bikes/scooters by pushing power delivery to new heights, now reaching up to 240W. This advancement makes USB-C EPR perfectly suited for fast and efficient charging requirements. The increased power capacity allows for rapid charging of high-capacity batteries found in e-bikes/scooters, significantly reducing downtime, enhancing user convenience. Renesas offers a range of products that are USB-C certified, ensuring they meet stringent industry standards for safety, interoperability, and performance.

By using the iW780, a secondary-side controller, the USB-C PD 3.1 EPR protocol can be implemented, making it universally suitable for both single and multiport AC-DC adapters, as shown in Figure 4. These certified solutions can be easily integrated into e-scooter and e-bike designs, providing manufacturers with reliable and efficient charging solutions that comply with the latest USB-C specifications and European standards for a common connector.

UI/Display and Control Circuits

The display of an e-bike/scooter has several functions, such as displaying the state of charge, real-time speed, distance traveled, activation, and anti-theft protocols. A Bluetooth IC with an embedded processor has adequate processing power and communication capabilities to integrate these functions into a cost-effective and compact solution. An example can be found in Figure 5.

Click image to enlarge

Figure 5: Block diagram of UI/Display/Connectivity Circuits

Driving the Display

An embedded processor is responsible for driving the scooter’s display, typically an LCD screen mounted on the handlebar. This display provides the rider with essential real-time information such as speed, battery level, and mode settings and is received from various sensors or systems such as motor controllers, battery management systems, position sensors, accelerometers, etc. To simplify the overall integration, a BLE with an embedded MCU can process the data and drive the display in real time, providing the relevant information to the user. It can also connect to a user’s mobile phone for activation and data collection on an app.

Ensuring Activation

Activation protocols are essential for ensuring that only authorized users can operate an e-scooter or e-bike. Users typically activate the device through a mobile app, the NFC and BLE ICs provide secure access and mobile switch-off support. This combination of NFC and BLE may offer two-factor authentication, enhancing security. The connectivity chip receives the unlock request and passes it to the processor, which initiates an authentication process involving verification of a PIN, password, or unique digital key stored in the mobile app. Once authenticated, the processor sends signals to unlock the scooter's electronic systems, allowing the motor to engage and the scooter to become operational, thus preventing unauthorized use.

In case of theft, users can remotely disable the scooter via a mobile app, rendering it inoperable. The processor's firmware includes secure boot mechanisms to prevent tampering and allows for Over-the-Air (OTA) updates, ensuring maintenance and security improvements. These features collectively enhance the scooter's security and provide users with peace of mind.

Renesas offers a comprehensive approach to addressing the challenges encountered when designing e-bikes/scooters. With industry-leading System-on-Chips (SoCs) and modules for Wi-Fi, Bluetooth, and NFC, Renesas ensures robust and reliable performance crucial for seamless communication amongst connected devices.

 Wide-Bandgap Semiconductors

Advancements in power semiconductor materials, particularly Silicon Carbide (SiC) and Gallium Nitride (GaN), have significantly improved the performance of electrical power systems, including e-bikes/scooters. These materials offer several benefits over traditional silicon-based semiconductors. SiC and GaN devices have lower on-resistance and faster switching capabilities, reducing energy losses during operation. This results in higher overall efficiency, smaller and lighter solutions, extending battery life and range for electric vehicles.

Conclusion

As we have seen, E-bikes and E-scooters use a wide variety of power devices in addition to many other components that need to work together seamlessly across multiple subsystems. It goes without saying that safety and reliability are critical as well.  The ideal design partner will offer comprehensive expertise in power management, embedded processing, connectivity solutions, analog circuitry, and sensor integration, along with a history of quality components and deep technical support capabilities.

Renesas Electronics