The development of electric vehicles is accelerating, and the research and development of electric vehicle motors has attracted much attention. However, very few people truly understand electric vehicle motors. This article gathers information from various sources to explain the basics of electric vehicle motors. Let's explore this high-tech heart of the car!
The status of electric vehicle motors
The electronic control system is the brain of an electric vehicle, directing the operation of its electronic components. The on-board energy system is the core technology of the electronic control system, serving as a link between the battery, battery pack, and the entire vehicle system. It includes battery management technology, on-board charging technology, DC-DC converter technology, and energy system bus technology. Therefore, on-board energy system technology is increasingly becoming an important direction for industrial application technology research and a significant indicator of industrial development. Currently, this technology has become a major bottleneck restricting the connection and development of the electric vehicle industry chain.
Industrialization transformation of electric vehicle motors
Electric vehicles are showing signs of transitioning from research and development to industrialization. Leading automotive companies and manufacturers of core components such as power batteries, drive motors, and controllers have grown and expanded through years of promotion and demonstration efforts, launching a series of products that meet performance requirements. However, the reliability, cost, and durability of key components such as drive motors and batteries—common key technologies—still cannot meet the needs of electric vehicle development, becoming a major constraint on its progress.
Difficulties in developing electric vehicle motors
From the perspective of the electric vehicle industry chain, the beneficiaries are likely to be concentrated in core components, and companies with strong control over resources in the upstream sector will also benefit.
The main reasons for the difficulties in research and development are as follows:
First: Batteries are currently the biggest bottleneck in electric vehicle technology and cost.
Second: Due to the scarcity of mineral resources, upstream resource companies such as lithium and nickel will also reap significant profits.
Third: The current vehicle manufacturers are quite fragmented and lack a clear monopoly advantage. We should first focus on manufacturers that have core technologies or have technologically mature and commercially viable models.
Electric vehicle motor requirements for drive system
High voltage, small mass, large starting torque and wide speed range, good starting and acceleration performance, high efficiency, low loss, and high reliability. Several key issues need to be considered when selecting an electric vehicle motor drive system: cost, reliability, efficiency, maintenance, durability, weight and size, and noise. Selecting a motor for a pure electric vehicle includes choosing the motor type, power, torque, and speed.
Electric vehicle motor classification
The motors currently used in electric vehicles mainly include DC motors, AC induction motors, permanent magnet motors, and switched reluctance motors.
1. DC motor for electric vehicles
Advantages: It has a huge starting acceleration, good electromagnetic torque control characteristics, convenient speed adjustment, simple control device, and low cost.
Disadvantages: It has a mechanical commutator, which produces sparks on its surface when operating at high speeds and heavy loads, thus limiting its suitability for high motor speeds. Compared to other drive systems, it is at a disadvantage and has been gradually phased out.
2. AC induction motor for electric vehicles
The stator of an AC induction motor generates a magnetic field and consists of a stator core, stator windings, a housing outside the core, and bearings supporting the rotor shaft. AC motors offer advantages such as low cost, ease of maintenance, and small size; however, their control is more complex. They have become the preferred choice for AC-driven electric vehicles.
3. AC induction motor for electric vehicles
Permanent magnet motors use permanent magnets to generate air gap magnetic flux, replacing the magnetic field coils in DC motors and the exciter in the stator of induction motors. Permanent magnet synchronous motors possess high efficiency, high torque-to-inertia ratio, and high energy density. Their high torque at low speeds, in particular, allows them to meet the demands of vehicles operating on complex and varied road conditions. They are high-performance, low-carbon, and environmentally friendly motors. With the emergence of rare-earth permanent magnet materials, they are expected to compete with AC induction motors in the market. They are particularly widely used in the small to medium power range.
4. Switched reluctance motor for electric vehicles
The stator and rotor of the switched reluctance motor are both double salient pole structures made of ordinary silicon steel sheets stacked together.
Advantages: Simple and reliable, wide adjustable speed range, high efficiency, flexible control, and low cost.
Disadvantages include large torque ripple, high noise, the need for a position detector, and nonlinear characteristics. This limits its applications.
The performance of an electric vehicle is directly related to its power output. The greater the power, the better the acceleration and maximum climbing ability, as well as the better the quality. However, the size of the motor will also increase. But the motor cannot operate at high efficiency for a long time, as this will reduce the utilization rate of the electric vehicle's capacity and reduce its driving range.
Generally speaking, the rated power of the motor should meet the requirements of the car's maximum speed, and the peak power of the motor should meet the requirements of the car's maximum gradeability and acceleration performance. The required power of the motor can be calculated using the following formula.
The vehicle's driving force comes entirely from its onboard motor. The driving force required by the car varies under different operating conditions. The motor can only output torque; the force required by the vehicle under each condition is generated by the torque output by the motor, which passes through the transmission system and propels the vehicle forward in the form of torque at the drive wheels. The torque required by the drive motor can be calculated from the driving force required by the car.
The choice of motor speed is directly related to the speed of the race car. Its maximum speed should meet the requirements of the car's maximum speed.
How to test an electric vehicle motor
Testing the motors of new energy vehicles is particularly important, as it directly affects the vehicle's operating status. Only motors that meet the relevant functional test requirements can handle such a demanding task. This article will tell you how to test them.
1. Testing of the motor drive system
The electric motor drive system is the core component of a pure electric vehicle, which converts the DC bus voltage output from the battery into AC power and uses the AC power to drive the motor.
2. Testing of the battery charging system
The battery charging system converts the alternating current (AC) from external charging piles and stations into direct current (DC) to charge the battery in a pure electric vehicle, storing the electrical energy in the battery. The main function of the DC load power supply system is to convert the stable high-voltage electricity output from the DC bus of the electric vehicle's battery into a low-voltage output to power the low-voltage DC loads in the vehicle.
3. Testing of DC regulated systems
Because of frequent charging and discharging, the voltage across a battery fluctuates within a certain range. It is necessary to stabilize this voltage within a certain range to a stable DC bus voltage for direct application or other voltage conversion.
Electric vehicle usage precautions
Although electric vehicles are not as delicate as you might think, careful maintenance can allow you to better experience the joy of green travel.
1. Avoid high current discharge.
When starting an electric vehicle, carrying passengers, or going uphill, avoid sudden acceleration to prevent a large instantaneous current discharge. Large current discharge can easily lead to lead sulfate crystal formation, which damages the physical properties of the battery plates.
2. Avoid overheating of the plug during charging.
Loose 220V power plugs or charger output plugs, oxidation of contact surfaces, etc., can all cause the plug to overheat. Prolonged overheating can lead to short circuits or poor contact, damaging the charger and battery and causing unnecessary losses. Therefore, if you find any of these issues, you should promptly remove the oxides or replace the connector.
3. Regular inspections
If, during use, the electric vehicle's range suddenly drops significantly by more than ten kilometers in a short period, it is very likely that at least one battery in the battery pack is faulty. In this case, you should promptly take it to the sales center or the dealer's service department for inspection, repair, or replacement.
This can extend the battery pack's lifespan and save you money to the greatest extent possible.
4. Do not store in a state of electrical failure.
Batteries must never be stored in a discharged state. A discharged state refers to a battery that has not been charged promptly after use.
Storing batteries in a discharged state can easily lead to sulfation, where lead sulfate crystals adhere to the plates, blocking ion channels, causing insufficient charging, and reducing battery capacity. The longer a battery is left idle in a discharged state, the more severe the damage. Therefore, when batteries are not in use, they should be recharged once a month to better maintain their health.
