Traditional drive motors are complex in structure, inefficient, and noisy. Brushless DC motors, on the other hand, are a new type of DC motor that uses electronic commutation instead of mechanical commutation. They have no excitation losses, low thermal resistance, and easy heat dissipation, offering advantages such as high efficiency, strong overload capacity, and no commutation sparks, making them an important development direction for high-speed motors. Typically, brushless DC motors use electronic or electromechanical position sensors to obtain rotor position information. However, some sensors have low resolution or poor operating characteristics, and some are very sensitive to environmental conditions such as vibration, humidity, and temperature changes, leading to performance degradation and reduced system reliability and accuracy. Sensors also significantly increase the number of electrical connections, increase interference, and increase size and cost. Therefore, under small, light-load conditions, sensorless brushless DC motors are an ideal choice and have broad development prospects. Electric motorcycles using sensorless brushless DC motors offer advantages such as simple operation, comfortable riding, convenient maintenance, low pollution, and low noise as green and environmentally friendly transportation tools. This article introduces a sensorless brushless DC motor control system based on the ST7FMC1K2. Electric Motorcycle Controller Structure, Working Principle, and Motor Control Hardware Design Electric Motorcycle Controller Structure and Working Principle The electric motorcycle controller has basic functions such as motor drive control, parameter display, and battery management. The controller collects parameters under various conditions to control motor operation, adjust vehicle speed, improve motor and battery efficiency, and ensure the safety of riders and others. The energy management system effectively manages the battery, monitors and controls the charging and discharging process, keeps the battery in good working condition, and ensures its effective lifespan. Its overall structure is shown in Figure 1. [align=center] Figure 1 Electric Motorcycle Controller Structure[/align] The main control chip ST7FMC1K2 serves as the control core, transmitting PWM signals to the drive circuit to drive the motor; and transmitting clock, reset, and data signals to the panel display circuit through I/O ports. The microcontroller obtains and processes the back EMF detection signal from the drive circuit to commutate the motor in a timely manner; simultaneously, it obtains current sampling signals from the drive circuit for overcurrent protection; and obtains voltage signals from the battery power detection circuit for undervoltage protection. The throttle signal is used to change the voltage to change the duty cycle of the PWM to adjust the speed of the motor, and the brake signal is used to stop the motor in time in an emergency. Introduction to ST7FMC1K2 chip [1] There are many brushless motor dedicated control chips on the market. Most manufacturers use Motorola's MC33035 for control, which has the basic functions required for brushless motor control systems. This design takes into account factors such as cost performance and adopts STMicroelectronics' ST7FMC1K2 as the main control chip, which can realize all functions and meet the required control accuracy. Specific features include: 8KB of flash memory and 384 bytes of RAM, equipped with LVD, watchdog timer, high noise immunity EMC circuitry, a 10-bit multi-channel A/D converter, SCI, SPI, I2C, USB, and a timer with PWM functionality. Its most significant feature is the built-in enhanced dedicated MTC (see Figure 2), containing a PWM management unit. Different PWM modes can be set via software. The built-in operational amplifier and comparator amplify the motor winding current sampling signal, enabling two different drive modes: voltage mode and current mode. In current mode, the current in the stator winding is directly controlled. By changing the current setting reference value through the microcontroller's internal PWM duty cycle and external RC circuitry, the current in the stator winding can be accurately tracked, achieving direct control of the output torque. This reduces processor cost, the number of peripheral components, the PCB size, optimizes the system, and shortens the development cycle. [align=center] Figure 2 MTC block diagram of st7fmc1k2[/align] Hardware design of brushless DC motor control part[2] [align=center] Figure 3 Hardware diagram of brushless DC motor control part[/align] The brushless DC motor control part is the core of the whole controller. Its design will affect the whole system. The main circuit diagram of this design is shown in Figure 3. In order to obtain an adjustable square wave voltage, the PWM pulse width modulation technology is used to directly modulate the constant DC voltage into an AC voltage of variable magnitude and polarity as the armature terminal voltage of the motor, so as to realize the smooth speed regulation of the system. The inverter circuit and the drive circuit are the link between the main control chip and the controlled motor. The quality of their transmission performance directly affects the operating quality of the whole system. MOSFET has the significant characteristics of fast switching speed, good high frequency characteristics, high input impedance, low drive power, excellent thermal stability, no secondary breakdown problem, wide safe working area and high cross-conductivity. This control system adopts a full-bridge inverter conversion circuit composed of MOSFETs driven by three sets of independent control signals. The driver chip uses an eight-pin IR2103, and the MOSFET uses an STP75NF75, which has a built-in freewheeling diode, thus reducing the size of the PCB. The back EMF is detected by the zero-crossing detection method [3][4]. Each zero-crossing point is 30° electrical angle ahead of the next commutation point. As long as the zero-crossing time of the unconducted phase is measured and then a 30° electrical angle delay is performed, commutation can be achieved. The back EMF signal is sent to MCIA, MCIB, and MCIC for processing to perform commutation on the brushless DC motor. Software design of brushless DC motor system [5] The software of the brushless DC motor control system is designed in C language. It adopts modular programming and structured programming, that is, the program is decomposed into several small modules. Each module maintains relative independence and is connected by only a small number of input and output parameters, which makes the debugging, modification, and maintenance of the program more convenient. Each module uses strict transfer and call statements to form a tight whole. It mainly realizes the functions of position detection, speed adjustment, and PWM signal generation of the sensorless brushless DC motor. It consists of a main program, subroutines, and interrupt service routines. Main Program Design The main program primarily implements: system initialization of timers, I/O ports, and related peripheral devices; watchdog initialization; setting the interrupt priority of the ST7MC1K2; and the transitions between the five states (idle, start, run, brake, and stop) and their corresponding processing routines. After system initialization and corresponding interrupt handling, it enters the main loop, which includes key scanning, I/O port processing, motor start-up, transitions between the five states, and voltage/current mode switching, etc. The flowchart is shown in Figure 4: [align=center] Figure 4 Main Program Flowchart[/align] Subroutine Design The subroutine modules include I/O port initialization subroutines, Timer A subroutines, peripheral device initialization subroutines, watchdog initialization and refresh subroutines, A/D conversion subroutines, motor pre-positioning subroutines, operational amplifier setting subroutines, closed-loop adjustment subroutines, and period-to-frequency conversion subroutines, etc. Each module is relatively independent yet connected through certain parameter inputs and outputs. Interrupt Procedures The interrupt procedures include the interrupt handler for Timer A, the commutation and demagnetization interrupt handlers, the rate update interrupt handler, and the zero-crossing detection interrupt handler. This brushless DC motor uses a typical six-step control method. This part of the program is embedded in the commutation and interrupt handlers. The relevant register settings for the six-step control are shown in Figure 5. [align=center] Figure 5: Register bit settings related to the six steps[/align] Experimental Results and Analysis Using the above theory, an Austere 48V brushless DC motor with a maximum starting current of 18A and a normal operating current of 10-15A was used. Combined with relevant hardware and software design, the control of a sensorless brushless DC motor on an electric motorcycle has been successfully implemented. Experimental results show that, under a constant power supply voltage, as the duty cycle of the control signal PWM wave continuously increases, the average voltage on the motor increases accordingly, and the speed also increases. Figure 6 shows the phase current waveform of the entire process, and Figure 7 shows the phase voltage waveform during normal operation. The process in Figure 6 can be analyzed as follows: The motor adopts a three-step starting method. First, the rotor is pre-positioned, then it accelerates synchronously. After accelerating to a certain stage, back EMF can be detected. When two back EMFs are detected, it enters the automatic switching mode. At this time, the current mode is used first, and then it switches to the voltage mode. The duty cycle is controlled by the throttle to control the motor speed. [align=center] Figure 6 Phase current waveform of the whole process Figure 7 Phase voltage waveform[/align] Conclusion As a new type of green transportation tool with broad market prospects and huge social benefits, electric motorcycles are increasingly favored by manufacturers, research institutions and consumers. This paper introduces a sensorless brushless DC motor control system designed using the ST7FMC1K2 dedicated motor control chip produced by STMicroelectronics. Experimental results show that this design achieves a good control effect. At the same time, it simplifies the system circuit, reduces the size of the controller, improves the system operating efficiency, extends the life, and enhances the flexibility and reliability, and has good market promotion value.