In the field of electric vehicles, although both permanent magnet synchronous motors (PMSM) and brushless DC motors (BLDC) are based on permanent magnet technology, there are essential differences in design concepts and control methods. The following analyzes the applicability of the two from the perspective of technical characteristics and vehicle requirements.
Core Differences
Back Electromotive Force and Current Waveform
Permanent Magnet Synchronous Motor (PMSM): The back electromotive force is a sine wave, and the stator current also needs to generate a sine wave through vector control (FOC). This design makes the motor run smoothly with minimal torque ripple, making it suitable for scenarios with extremely high requirements for smoothness.
Brushless DC Motor (BLDC): The back electromotive force is a trapezoidal wave, and the stator current is controlled by a rectangular wave (six-step commutation). Although the control is simple, the torque pulsation during commutation can cause jitter during acceleration or deceleration of the vehicle, affecting the driving experience.
Efficiency and Energy Consumption
For PMSM, since the sine wave magnetic field rotates synchronously with the rotor magnetic field, the iron loss and copper loss are lower. Especially in low-speed and frequent start-stop conditions, the efficiency is higher (the typical efficiency can reach over 95%), directly improving the driving range of electric vehicles.
The rectangular wave control of BLDC leads to more harmonic losses, and the commutation frequency limitation during high-speed operation also reduces its efficiency. It is more suitable for light vehicles with short trips and low speeds.
Power Density and Volume
The permanent magnets of PMSM are embedded inside the rotor, with high magnetic field utilization rate and a smaller volume under the same power. For example, the power density of the drive motor of Tesla Model 3 exceeds 3kW/kg, meeting the vehicle lightweight requirements. Due to structural limitations and heat dissipation requirements, the power density of BLDC is usually lower than that of PMSM, occupying more space.
Control Complexity and Cost
PMSM relies on complex vector control algorithms (such as FOC) and high-speed processors, resulting in a higher cost of the controller. However, its high-precision characteristics gradually reduce the cost during large-scale production.
BLDC adopts a simple six-step commutation control, with a low hardware cost, but it is difficult to meet the requirements of high-end electric vehicles for precise speed regulation and dynamic response.
Matching Key Requirements of Electric Vehicles
Long Driving Range Requirements
The high-efficiency range of PMSM is wider, especially showing obvious energy consumption advantages under commonly used medium and low-speed conditions. For example, the permanent magnet motor of BYD can increase the NEDC driving range by 8%-12%, while BLDC is difficult to support long-distance driving due to its efficiency shortcoming.
Driving Smoothness
The smooth torque output of PMSM avoids the “stepped feeling” during acceleration, and it can achieve linear acceleration comparable to that of fuel vehicles in conjunction with the vehicle’s electronic control system; the torque pulsation of BLDC may cause passengers to feel carsick, especially in urban road conditions with frequent start-stops.
High-speed Performance and Reliability
PMSM expands the high-speed operation range through field weakening control and can still maintain high efficiency even above 120 km/h. Moreover, the rotor has no mechanical commutator, resulting in a longer service life; the high-speed performance of BLDC is limited by the commutation frequency, and it is prone to demagnetization due to heat generation during long-term high-load operation.
Cost and Supply Chain
PMSM relies on rare earth permanent magnet materials (such as neodymium-iron-boron), posing a risk of resource bottlenecks. However, vehicle manufacturers gradually alleviate this through recycling technology and low-rare earth formulations (such as Toyota’s “asymmetric magnetic circuit”); BLDC does not require rare earths, has a lower cost, and is suitable for low-end models or scenarios with low performance requirements.
Practical Applications and Trends
Mainstream vehicle models choose PMSM: Brands such as Tesla, BYD, and NIO all use permanent magnet synchronous motors as the core drive units, taking into account both efficiency and performance.
Niche market of BLDC: Some micro electric vehicles (such as the early version of Wuling Hongguang MINI EV) use BLDC to reduce costs, but the driving range and driving experience are limited, and the subsequent upgraded versions have switched to PMSM.
Technical Integration Directions:
Hybrid architecture: High-end models adopt a combination of “front PMSM + rear induction motor” (such as Tesla Model S) to balance low-speed efficiency and high-speed power.
Rare earth-free: Develop ferrite permanent magnet or reluctance motors to reduce dependence on rare earths.
Intelligent control: AI algorithms optimize the FOC parameters of PMSM to further improve the response speed and energy efficiency.
Permanent magnet synchronous motors (PMSM), with their high efficiency, low vibration, and high power density, are the mainstream choice for current electric vehicles; while BLDC is only suitable for low-end vehicles for short trips due to its cost advantage. In the future, with the maturity of rare earth substitution technology and the decrease in controller costs, the dominant position of PMSM will be further consolidated, but BLDC can still play a cost-effective advantage in specific scenarios (such as low-speed logistics vehicles).