Ryan Roderick
System Engineering Manager
Published: August 14, 2020

Electric scooters (e-scooters) are quickly emerging as a faster and more convenient mode of transportation than walking. They are also cheaper and more environmentally friendly than personal cars and are ideal for short distance travel, such as last-mile commutes from public transit stations. With the e-scooter market size estimated to grow at a CAGR of 7.7% in 2020-2030, there is huge potential for entering the e-scooter market right now.

Renesas has developed a turnkey mobility solution reference design for an e-scooter that powers a 1600W motor and has a 48V Li-ion battery pack. This e-scooter reference is a starting solution to productizing a final scooter design. The major functional components used in the design are Renesas components, making it easier to integrate the solution. The system has starting software to speed the time to market.

The scooter solution powers a maximum speed of 5000 rpm. The solution has a wireless charging option that transfers 60W of power to charge the battery. A mobile phone app is used to communicate to and from the scooter.

Li-ion batteries have a higher energy density and are lighter than lead acid batteries. They are much safer for the environment and require less frequent replacements. A 48V motor design provides greater torque and better power efficiency. This can result in better acceleration and longer run times than 24V or 36V solutions.

mobility -solution-block-diagram

Figure 1. 48V Mobility Solution

The system block diagram is illustrated in Figure 1. The system has two main boards. One board has a battery front end manager, a charger, and a central MCU. The other board monitors the motor status and conditions the signal that drives the motor. The system has two optional boards - a Bluetooth® board that can be used to expand the functionality of system and a wireless power transfer option for contact-free charging.

The system has a line-in connector that accepts a 24V power adaptor used to charge the battery pack through an ISL81601 buck-boost controller. The controller has high efficiency and a constant current feature when under load. The controller has input and output current monitors and overvoltage and over current checks for system safety and status. The ISL28214 operational amplifier with the ISL84051 multiplexer are used to condition the input and output current sense signals from the ISL81601 to the MCU. The MCU monitors these signals as a redundancy and diagnostic check to the system.

The ISL94216 monitors the battery pack health and system status. The ISL94216 is a 16-cell battery front-end (BFE) integrated circuit. The BFE scans for extreme voltage, current, temperature and open wire conditions regarding the battery pack. Upon detection of any of the prior conditions, the BFE can autonomously disconnect the power to the system via an integrated FET control driver circuitry. The system design supports up to 14-cell battery packs. An SPI communication with a CRC_CITT16 X25 error check is used to communicate with the MCU.

The RX23T MCU serves as the central controller of the system. The RX23T specializes in driving single motor solutions with synchronous 3-phase measurements and accurate pulse width modulation (PWM) timers that are used to commutate the motor. The RX23T has GPIOs and supports SPI and I2C serial communication protocols. These peripherals are used to monitor and control the remainder of the system.

The motor control and inverter board has a 3-phase inverter with individual phase current sensing (ISL28191) to monitor extreme conditions such as a stalled motor. The individual phase current measurements also enable sensor-less motor control or different types of control loops. The HIP2211 is a high frequency half-bridge NMOS FET driver that conditions the PWM signal from the MCU to drive the gates of each phase of the inverter. The driver has a 100V operating range, making it resilient to motor transients and other harsh conditions.

Besides current sensing, the motor control and inverter board can monitor each phase voltage, allowing for back EMF calculations. The board has Hall connections for motors that include sensors. The board and system supports throttle and brake connections.

The ISL80410 LDO powers the driver and conditional circuitry for the board. 

The system has a Bluetooth option that utilizes the RX23W single chip Bluetooth MCU. Within this system, the RX23W (the server) is used as a through to a mobile application (the client) by way of Bluetooth communication. The RX23T periodically sends system status to the RX23W. The RX23W then transmits the status to the mobile app using the Bluetooth 5.0 protocol. The mobile app can turn the scooter on and off by transmitting to the RX23W. The inclusion of wireless option to the system allows for functional expansion.

There is an alternate provision for wireless charging using the P9415. The P9415 is a wireless receiver that rectifies a coupled signal to 20V. Two receivers are used in parallel to boost the output powered to a maximum of 60W. The wireless power transfer option is beneficial for applications where mechanical fatigue and simplicity of connection is important.

The major benefit of this system is that it uses a modular design approach, allowing different blocks to be adapted for various other applications. The structure of the code is modular as well. This allows the user to pick and choose the functional blocks that are most beneficial to the end application. This helps improve the time to market.

The solution has a battery management system that supports Li-ion batteries with a charger, a 1600W inverter power train for motor control, wireless charger with 60W capacity, and Bluetooth connectivity for diagnosis and control. These modules can be adapted for use in applications such as lawn mowers, cleaners, power tools, e-bikes, carts, rovers, power banks, and more. Renesas customers will receive complete hardware and software reference designs to assist and accelerate their development.

Visit the winning combinations page to see more winning combination solutions that help our customers accelerate their designs to get to market faster.

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