1. Classification and technical comparison of motors
At present, electric vehicle motors mainly include: brushed DC motors, AC asynchronous motors, switched reluctance motors and brushless DC motors.
1. Brushed DC motor: divided series motor and separately excited motor
Advantages: large starting torque and strong overload capacity.
Disadvantages: carbon brushes need to be replaced regularly, low efficiency, large size, poor protection ability, and poor energy feedback; due to the influence of mechanical commutation, the motor can only run at medium and low speeds.
The mechanical characteristics of the series-excited motor are soft: the torque increases, and the speed decreases a lot, that is, when the load is increased or when climbing, the speed is automatically reduced, which is more suitable for the use characteristics of electric vehicles; but when the series-excited motor goes downhill, step on the accelerator Acceleration will burn out the motor due to the excessively high speed; if the controller drive tube breaks down, the voltage is all applied to the motor, the motor speed rises sharply, and the phenomenon of "speeding" occurs.
The mechanical characteristics of the separately excited motor are hard, the torque increases, and the speed drop is small; the separately excited motor has speed protection and can also use the brake energy to generate electricity. To
2. AC asynchronous motor:
Advantages: simple structure, high reliability of the motor itself. To
Disadvantages: The starting torque is small, the starting current is large, and the motor needs to increase the starting current to generate large torque; the control is complicated (requires an inverter), and the energy feedback performance is poor. To
3. Switched reluctance motor:
Advantages: a larger torque at low speeds. To
Disadvantages: low-speed vibration, large noise, low efficiency, and poor energy feedback.
4. Brushless DC motor:
①The motor has good external characteristics, which is very in line with the load characteristics of electric vehicles. The motor has low-speed and large-torque characteristics, which can provide large starting torque and meet the acceleration requirements of the vehicle.
②Wide speed range, the motor can run in low, medium and high speed range.
③The motor has high efficiency, especially in light-load conditions, the motor can still maintain a high efficiency, which is very important for the precious battery energy.
④ Strong overload capacity, meeting the needs of the vehicle's protruding blocking.
⑤The regenerative braking effect is good. When the car is going downhill or braking, the motor can fully enter the generator state to charge the battery, and at the same time play the role of electric braking, reducing the burden of mechanical braking.
⑥The motor is small in size, light in weight, and large in specific power, which can effectively reduce weight and save space.
⑦The motor has no mechanical commutator and adopts a fully enclosed structure to prevent dust from entering the motor and has high reliability.
⑧The motor control system is simpler than the asynchronous motor.
⑨The drive tube of the controller breaks down, the motor stops, and it will not "speed off". To
Disadvantages: The motor itself is more complex than an AC motor, and the controller is more complex than a brushed DC motor controller. To
Two, motor selection precautions
1. Leave a margin: select a motor with a margin of 20% to prevent damage to the motor. Generally, by providing the following information, the motor manufacturer can assist in calculating the motor's power, number of revolutions, torque and other parameters.
Design speed? Wheel radius? To
Self-respect? Total weight after manned?
Maximum climbing ability ≥**%?
2. Supporting use: The motor and the reducer, the motor and the controller must match; the motor factory generally provides the parameters of the reducer at the same time, or the reducer is matched.
3. Protection level: The motor must be waterproof and dustproof, otherwise it is easy to damage; some low-end electric cars on the market cannot be opened after rain or after washing the car, most of which are due to the poor waterproof performance of the motor. The protection level of brushed motors must be ≥IP44, and the protection level of brushless motors is higher, generally reaching IP65 or higher. In addition to the waterproof of the motor itself, it is also necessary to pay attention to the waterproof of the lead terminal. It should be directly led out or equipped with waterproof connectors. The method of connecting nuts is not advisable; if you choose the method of connecting nuts to save costs, you should touch the terminals after wiring. Butter to prevent corrosion by moisture and salt spray. To
4. Working voltage: On the premise of ensuring safety, the working voltage should be as high as possible to reduce the working current and prolong the battery life.
Third, the economic comparison of different motors
Under the same conditions of use, if the AC asynchronous motor is selected, the power needs to be increased, and the control system cost is very high, which is not suitable for low-speed electric vehicles. Switched reluctance motors need to be improved and should not be used temporarily. In-wheel motors face the problem of electronic differential speed, and are not suitable for use in low-speed electric vehicles.