Definition and construction of the electric tricycle power system
The electric tricycle power system is broadly composed of a drive motor, a motor controller, a battery, a transmission shaft, a differential, and wheels. The motor controller receives output signals from the speed control lever (equivalent to the accelerator of a car), brakes, and different gears, controlling the rotation of the drive motor. Through a reducer, differential, transmission shaft, and half shaft and other mechanical transmission devices, it drives the drive wheels. According to the type of drive motor, the electric tricycle power system can be classified into permanent magnet synchronous motor (PMSM) power system and brushless DC motor (BLDCM) power system.
The electric tricycle power system is the link between the energy storage system and the wheels. Its function is to convert the electrical energy output by the battery into mechanical energy to drive the vehicle to overcome various rolling resistance, air resistance, acceleration resistance, and climbing resistance. When braking, it converts the kinetic energy into electrical energy and feeds it back to the energy storage system. Modern electric tricycles are different from traditional fuel tricycles. Their power system can omit the complex mechanical gear shifting structure and can provide torque and speed characteristics that meet the wide speed range and large load changes of the vehicle.
Drive Motor
The drive motor is used to provide power. There are various types, but currently in the electric tricycle industry, the mainstream drive motors are permanent magnet synchronous motors and permanent magnet brushless DC motors. Among the permanent magnet brushless DC motors, there are also square wave and sinusoidal wave permanent magnet brushless DC motors. These three types of motors have their own characteristics in performance, structure, and control methods, and are suitable for different electric tricycles and usage scenarios.
The square wave permanent magnet brushless DC motor has a stator current that is a square wave or trapezoidal wave. To maximize its output, the air gap magnetic flux is often designed to be a square wave or close to a square wave, so its rotor is often made in a tile shape.
The permanent magnet synchronous motor has a stator current that is a sinusoidal wave. To reduce ripple torque and harmonic losses, the air gap magnetic flux is usually designed to be a sinusoidal wave or close to a sinusoidal wave. Therefore, its rotor often adopts the structure shown in the figure.
The sinusoidal wave permanent magnet brushless DC motor and the permanent magnet synchronous motor have similar rotor structures. The air gap magnetic flux is usually designed to be a sinusoidal wave or close to a sinusoidal wave, but the rotor conductors can be removed.
The stator winding methods of the three single machines are also slightly different. The square wave motor tries to concentrate the winding in the full distance to improve the utilization rate of the winding; the permanent magnet synchronous motor generally uses distributed, short-rectangular winding to weaken the influence of harmonics, and the structure is simpler and more sturdy; the sinusoidal wave permanent magnet brushless DC motor generally uses distributed, short-rectangular winding, and sometimes uses fractional slots or sinusoidal winding to further reduce the ripple torque.