Because brushless DC motors lack excitation windings, commutators, brushes, and slip rings, their construction is simpler than that of conventional AC and DC motors. As a result, they operate more reliably and are easier to maintain. Compared with squirrel-cage induction motors, their structural simplicity and operational reliability are roughly comparable. Moreover, since there is no iron loss or copper loss associated with excitation, the power efficiency is... 300W Under the following conditions, its efficiency is higher than that of a motor with current excitation of the same specifications. 10%~20%; It has higher efficiency compared to an induction motor.

    Brushless DC motors typically use square-wave drive. , Use a Hall sensor to obtain the rotor position. , Forced commutation via this signal. . This plan control method is simple. , Low cost , Widely used in current electric vehicle projects. . However, when phase commutation is driven by a square wave, it results in current discontinuities. , Causes significant torque ripple. , Therefore, the noise performance is poor. , Difficult to implement in the home appliance application domain. . And sinusoidal drive can prevent current surges during commutation. , Of course, the maximum torque will decrease. , But it has a clear advantage in noise performance. .

    Usually, the control of permanent magnet synchronous motors employs... DSP, Moreover, the motor requires an optical encoder to accurately detect the rotor position. , Capable of achieving high-precision control , So much so that it can be used in servo systems. , But the cost will be high. , Household appliance applications are highly price-sensitive. , Moreover, some applications don't have high performance requirements. , For example, an electric fan. , Traditional DSP Vector-control sinusoidal drive, while offering high cost-performance, is also relatively difficult to implement. . Therefore, the approach proposed in this paper adopts 8 Single-chip microcontroller integration PWM The sinusoidal drive scheme for the oscillator has high market value. .

    The air-gap magnetic field of a conventional sinusoidal-driven brushless DC motor is sinusoidal. ( Also known as a permanent-magnet synchronous motor. ) Alternatively, it could be the magnetic field waveform after high-order harmonics are injected into a sinusoidal wave. The stator typically uses distributed windings, so the back electromotive force is also sinusoidal. Three Hall sensors are mounted on the rotor. , Every other 60° The electrical angle output changes once. , Use this as the synchronization signal for the sine wave. , Ensure there is no accumulated error. .

    II. Hardware Architecture

    At the heart of this plan is an integrated... PWM of the generator 8 Single-chip microcontroller SH79F168, Adopt an optimized single-machine cycle 8051 Kernel , Built-in 16kFlash Memory , Compatible with tradition 8051 All hardware resources , Adopt JTAG Simulation method , Built-in 16.6MHz Oscillator , At the same time, the following functions have been expanded: :

    Double Data Pointer Register Pointer .16 position x8 Multiplier and 16 position /8 Divisor .

    Channel 12 Dead-zone control with bit band PWM, 6 Road output , Output polarity is adjustable. , Center and edge alignment form

    Integrated fault detection function , Can be instantly shut down PWM Output .

    Built-in amplifier and comparator , Can be used for electric discharge, large-scale sampling, and overcurrent protection. .

    Provide hardware anti-interference measures. .

    Provide Flash Self-programming function , Capable of imitation and use. EEROM, Bento storage parameters .

    The main system architecture adopts a three-phase fully controlled bridge. , Self-boosting drive IC, The signal ground and power ground are shared. , Adopt IC Built-in amplifier and ADC Complete current and voltage sampling. , Voltage saving / Current transformer , Apply simultaneously IC Internally integrated comparator and PWM The fault detection function implements overcurrent protection. .

    III. Handling of the Leading Phase Angle

    The above plan achieves the voltage-driven waveform under ideal conditions. , Simply ensure that the voltage vector is fundamentally perpendicular to the direction of the rotor magnetic flux. , In practice, since the motor is a linear load, , The stator current vector of the motor lags behind the stator voltage vector. , Therefore, the stator magnetic potential also lags behind the stator voltage vector. , That is to say. , If according to the above SPWM Waveform-driven motor , The angle between the stator magnetic potential and the rotor magnetic potential will be less than. 90 degree , The induced motor torque is not at its maximum. , The stator current has a d-axis component. , Produce a demagnetizing effect , The power factor of the controller is not high. , Therefore, it is necessary to adopt advanced commutation processing. . So that the angle between the stator magnetic potential and the rotor magnetic potential is as close as possible. 90 degree .

    It’s actually quite simple to complete. , Just when creating the sine table. , Just advancing the initial angle will do. , No need to change the software architecture. . A more sensitive approach is to add an offset to the needle used for taking readings. , This allows for the flexible setting of the leading commutation angle based on the load conditions. .

    IV. How to Adjust the Speed

    As can be seen from the above text, SPWM The frequency of the modulating wave is not arbitrarily specified; rather, it is determined based on... Hall The signal adjusts in real time and is a self-regulating variable-frequency system. , If you want to adjust the motor speed, , The frequency of the modulated sine wave cannot be changed. , Instead, it adjusts the amplitude of the modulating wave. , Therefore, the sine table values extracted from the software will be multiplied by the external speed reference coefficient before being written. PWM In the duty cycle register of the oscillator. , After amplitude modulation correction , Equivalent Voltage Variation on the Motor , Then the speed changes. , Meanwhile, the frequency of the sinusoidal modulation wave is passively adjusted according to the rotor Hall signals. .

    V. Summary

    The controller made using the above plan , The practical operation yields lower noise levels compared to using square-wave control. , Smooth rotation , Stepless speed regulation can be achieved. , Particularly suitable for brushless motor control in household electric fans or air-conditioning fan control.