The design goals of a DC motor drive circuit mainly consider the following points: Function: Does the motor rotate unidirectionally or bidirectionally? Is speed regulation required? For unidirectional motor drives, a high-power transistor, MOSFET, or relay can directly drive the motor. When bidirectional rotation is required, an H-bridge circuit composed of four power components or a double-pole double-throw relay can be used. If speed regulation is not required, a relay is sufficient; however, if speed regulation is required, switching components such as transistors and MOSFETs can be used to implement PWM (Pulse Width Modulation) speed regulation.
I. Overview of Brushless DC Motors (BLDC) and Their Drive Methods
Brushless DC motors (BLDC) are a highly efficient and reliable type of electric motor, widely used in numerous fields. Their unique drive mechanism, combined with electronic commutation technology, enables the motor to maintain high efficiency and smooth operation. This article will delve into the various drive methods of brushless DC motors to help readers fully understand their working principles and performance characteristics.
1.1 BLDC and its components
Brushless DC motors replace the mechanical commutation device of traditional DC motors with an electronic commutator, effectively solving many problems associated with brushes and commutators, such as noise, sparking, electromagnetic interference, and short lifespan. This type of motor not only inherits the advantages of AC motors, such as simple structure, reliable operation, and convenient maintenance, but also possesses the high operating efficiency, zero excitation loss, and excellent speed regulation performance of DC motors. As a result, brushless DC motors are increasingly widely used in industrial fields, covering multiple areas including household appliances, power tools, electric bicycles, electric motorcycles, and electric balance scooters.
A brushless DC motor consists of three main parts: the motor body, the position sensor, and the electronic switching circuitry. Structurally, the motor body is quite similar to that of a permanent magnet synchronous motor. The electronic switching circuitry comprises a power logic switching unit (such as IGBTs and MOSFETs) and a position sensor signal processing unit. The conduction sequence of this circuitry is synchronized with the rotor's rotation angle, thus realizing the commutation function of the mechanical commutator.
1.2 Working principle of BLDC
The working principle of a brushless DC motor (BLDC) can be summarized as a "three-phase, six-step" commutation process. Its electronic switching circuit, based on signals from the position sensor, sequentially controls the energization and de-energization of the three-phase windings of the motor body, thereby achieving continuous rotation. This commutation method not only ensures high motor efficiency but also significantly extends its service life.
The control principle of a brushless DC motor can be simplified into a schematic diagram, clearly illustrating the motor's operation. Through signals from the position sensor, the electronic switching circuit precisely controls the energization and de-energization of the three-phase windings of the motor body, thus achieving smooth motor rotation. This control method is not only efficient but also reliable, providing a strong guarantee for the long-term stable operation of the motor. The main circuit adopts a typical voltage-type AC-DC-AC circuit design, where the inverter is responsible for generating a 5-24kHz modulated wave of equal amplitude and frequency, which is then converted into a symmetrical alternating rectangular wave. The alternating N and S poles of the permanent magnet induce the position sensor to output square waves H3, H2, and H1 with a phase difference of 120 degrees. After processing, these square waves generate an effective six-state coded signal.
In the circuit design, the main circuit adopts a classic voltage-source AC-DC-AC architecture. The inverter is a key component, capable of generating stable 5-24kHz modulation waves in terms of amplitude and frequency. These modulation waves, after conversion, form symmetrical alternating rectangular waves. Simultaneously, the alternating N and S poles of the permanent magnet trigger the position sensor to output H3, H2, and H1 square waves with a phase difference of 120 degrees. These square waves are further processed to generate a highly efficient signal with six-state coding capabilities.
In the main circuit section of the circuit design, we adopted a time-tested voltage-source AC-DC-AC system. The core of this system is the inverter, whose function is to generate stable modulated waves with frequencies ranging from 5-24kHz. These carefully modulated waveforms undergo a series of transformations, ultimately becoming symmetrical alternating rectangular waves to provide a stable power supply to the circuit. Furthermore, the alternating N and S poles of the permanent magnet directly trigger the position sensor, thereby outputting square waves H3, H2, and H1 with a phase difference of 120 degrees. These square waves, after careful processing, generate a highly efficient signal with six-state encoding capabilities, providing strong support for the stable operation of the circuit.
At a 60° electrical angle, the rotor will rotate following the rotation of the stator magnetic field, a process equivalent to the rotor moving 60° in space. At this new position, position sensors U, V, and W will generate a new set of codes according to pre-set rules. This new set of codes will further change the conduction state of the power transistors, thereby guiding the axis of the magnetic field generated by the stator windings to continue moving forward.
The 60° electrical angle cyclic rotation enables the brushless DC motor to continuously generate torque, thereby driving the load to perform continuous rotational motion.
II. Mainstream Driving Methods for BLDC
Currently, the mainstream driving methods of BLDC can be summarized into three types: square wave control, also known as trapezoidal wave control, and two other methods.
120° control or 6-step commutation control, sine wave control, and FOC control (also known as vector frequency conversion or magnetic field vector orientation control).
2.1 Square Wave Control
Square wave control is a fundamental motor control method. In motor drive systems, square wave control generates square wave voltage or current to drive the motor, thereby enabling its operation. This control method is simple and direct, and is widely used in various motor drive applications. However, square wave control also has some drawbacks, such as torque ripple and noise, requiring selection and optimization based on specific application scenarios.
A BLDC motor drive refers to a control system that drives a brushless direct current motor (BLDC). It replaces the traditional mechanical commutation device with an electronic commutator, thus solving problems such as noise, sparking, and electromagnetic interference found in brushed motors. A BLDC motor drive system mainly consists of the motor body, position sensors, and electronic switching circuitry.
Working principle of BLDC motor drive
The working principle of a BLDC motor drive is based on a "three-phase, six-step" commutation process. The electronic switching circuit, based on signals from the position sensor, sequentially controls the energization and de-energization of the three-phase windings of the motor body, thereby achieving continuous motor rotation. This commutation method not only ensures high motor efficiency but also significantly extends its service life.<sup>1</sup>
Application scenarios of BLDC motor drives
BLDC motor drives are widely used in various fields due to their high efficiency, reliability, and ease of maintenance. Common applications include household appliances (such as air conditioners and refrigerators), power tools, electric bicycles, electric motorcycles, and electric balance scooters.<sup>1</sup> Furthermore, BLDC motors are also widely used in industrial equipment, medical devices, and automobiles, especially in applications requiring high efficiency and precise control.<sup>2</sup>
Advantages of BLDC motor drives
High efficiency: BLDC motor drives replace mechanical commutation devices with electronic commutators, reducing energy loss and improving motor efficiency.
High reliability: By eliminating mechanical contact parts, the possibility of wear and failure is reduced, improving the operational reliability of the motor.
Low noise: There are no sparks and noise from mechanical commutation, making operation quieter.
Long lifespan: Electronic commutation reduces mechanical wear and extends the service life of the motor.
