Brushless DC motor and permanent magnet synchronous motor are both permanent magnet motors, but their performance is very different. In the field of electric vehicles, as the core driving component, the performance of motor directly determines the acceleration, endurance and driving experience of the vehicle.

Basic Structure: Difference in Similarity

From the appearance, BLDC and PMSM are indeed very similar. Their basic structure consists of a permanent magnet rotor and a winding stator. This is one of the reasons why many people have difficulty distinguishing between the two.

However, details determine success or failure, and it is the difference in internal details that leads to the huge difference in performance between the two.

The stator of brushless DC motor usually adopts concentrated winding, and the rotor magnetic circuit is designed to produce trapezoidal magnetic field distribution. On the contrary, the stator of permanent magnet synchronous motor (PMSM) mostly uses distributed short-pitch windings, and the shape of rotor magnetic pole is specially optimized to produce sinusoidal magnetic field distribution.

This structural difference directly determines the back EMF waveform of the two types of motors — the BLDC presents a trapezoidal wave, while the PMSM presents a sinusoidal wave. This structural difference directly affects the installation space of the motor and the matching with the transmission system. PMSM, with its better magnetic field distribution, can often achieve higher power density, which is particularly important for space-constrained electric vehicle chassis layout.

Driving Principle: The Essential Difference Between Square Wave and Sine Wave

The driving principle is the core to distinguish between BLDC and PMSM.

The brushless DC motor is driven by a square wave (also known as the six-step commutation method), and each electrical angle cycle is divided into six steps, with each step conducting 60 degrees of electrical angle. This control method is relatively simple, which only needs to control the on-off sequence of inverter power transistors according to the rotor position signal.

Permanent magnet synchronous motor (PMSM) is driven by sine wave, which generates three-phase sinusoidal alternating current to control the operation of the motor. This drive requires continuous and precise control of the amplitude and phase of the current to ensure that the stator and rotor magnetic fields are always synchronized.

It is this difference in driving mode that leads to the difference in torque generation mechanism between the two. Because BLDC is driven by square wave, it has obvious torque ripple problem, especially in the case of low speed and light load. The PMSM, on the other hand, achieves smooth torque output with almost no pulsation.

For electric vehicle drivers, this difference translates directly into a different driving experience — the smooth acceleration and low-noise operation provided by PMSM are significantly better than slight vibration caused by the torque ripple of BLDC.

Control Strategies: Simple and Complex Tradeoffs

Control strategy is one of the areas where BLDC and PMSM differ the most.

The control of brushless DC motor is relatively simple, mainly using position sensor feedback or back EMF detection. The direction and magnitude of the current are controlled by detecting the position of the rotor to determine the commutation timing. This control strategy has a small amount of calculation and low requirements for the processor.

Permanent magnet synchronous motor (PMSM) usually uses complex algorithms such as field oriented control (FOC) or vector control. These algorithms need to estimate the rotor position and magnetic field direction in real time, and decompose the three-phase current into excitation component and torque component through coordinate transformation to realize decoupling control.

Control Characteristics	Brushless DC Motor (BLDC)	Permanent Magnet Synchronous Motor (PMSM)
Control method	Six-step commutation, square-wave driven	Field-oriented control, sine-wave driven
Algorithm complexity	Relatively simple	Complex, requiring coordinate transformation
Processor requirements	Lower	Higher performance controller
Position detection	Hall sensor or back EMF method	High precision encoder or resolver
Implementation cost	Lower	Higher

This difference in control strategy directly affects the cost and development difficulty of the electronic control system. Although PMSM has superior performance, it requires more powerful processors and more complex software algorithms, which increases the complexity and cost of the system.

Performance Features: Each Has Its Own Advantages

Application Scenario: Different Market Positioning

Based on the above differences, BLDC and PMSM have found their own application scenarios in the field of new energy vehicles.

Future Outlook: Technology Convergence and Innovation