Because the brushless DC motor has no excitation winding, no commutator, no brush, and no slip ring, its structure is simpler than ordinary traditional AC and DC motors, the operation is more reliable, and the maintenance is simpler. Compared with the squirrel-cage induction motor, the simple level of its structure and the reliability of operation are roughly equivalent. Since there is no excitation iron loss and copper loss, the power is300WWhen the following, its efficiency is higher than that of the same specification with current excitation motor10%~20%;Compared with induction motors, it is more efficient.

   Brushless DC motor is generally driven by square wave,Using Hall sensor to obtain rotor position,Forced commutation through this signal.This plan control method is simple.,Low cost,It is widely used in the current electric vehicle plan..However, due to the square wave drive commutation will present a current mutation.,incur large torque ripple,Therefore, the noise index is poor,Difficult to implement in the application of home appliances.The sinusoidal drive can prevent the current mutation during commutation.,Although the maximum torque will be reduced,But there is a clear advantage in the noise index..

   Usually the control of permanent magnet synchronous motor is used.DSP,And the motor needs to provide photoelectric coding disk to accurately detect the rotor position.,Able to complete high-precision control,It can be used in servo systems.,But the cost will be high,Home appliance applications are very price sensitive,And some applications have low performance requirements.,For example, an electric fan,traditionalDSPVector control sine drive high cost plan is also more difficult to implement.Therefore, this paper proposes the use8bit microcontroller integrationPWMThe sine drive plan of the generator has a high market value..

   The air gap magnetic field of ordinary sinusoidal drive brushless DC motor is sine wave(Also known as permanent magnet synchronous motor)Or the magnetic field waveform after the sine wave is injected into the high harmonic wave, the stator is mostly used to spread the winding, so the back electromotive force is also a sine wave. Three-way hall sensor device on the rotor,Every60°Electric angle output changes once,As a synchronous signal of the sine wave,Guaranteed no cumulative error.

   2. hardware construction

   The center of this plan is an integratedPWMof the seizure device8bit microcontrollerSH79F168,Optimized Single Machine Cycle8051Kernel,Built-in16kFlashMemory,Compatible with traditional8051All hardware resources,AdoptJTAGSimulation mode,Built-in16.6MHzOscillator,At the same time extended the following functions:

   DoubleDPTRPointer.16Bitx8multiplier and16Bit/8Divider.

   Channel12Bit band dead band controlPWM,6Road output,Output polarity can be set,Center and edge alignment forms

   Integrated fault detection function,Can be closed instantaneouslyPWMOutput.

   Built-in amplifier and comparator,Can be used as large sampling and overcurrent maintenance for electric banishment.

   Provide hardware anti-interference measures.

   ProvideFlashSelf-programming function,Able to imitate the useEEROM,Benton storage parameters.

   The main system architecture adopts three-phase full control bridge,bootstrap boost driveIC,control ground and power ground sharing,AdoptICBuilt-in amplifier andADCComplete current and voltage sampling,frugal voltage/Current transformer,simultaneous applicationICInternally integrated comparator andPWMFault detection function Complete overcurrent maintenance.

   3. Advanced Phase Change Angle Disposal

   The above plan is to complete the ideal state of the voltage drive waveform.,It is only to ensure that the voltage vector is fundamentally perpendicular to the direction of the rotor magnetic potential.,In practice, since the motor is a rational load,Motor stator current vector lags stator voltage vector,Therefore, the stator magnetic potential also lags behind the stator voltage vector.,That is to say,In accordance with the aboveSPWMwaveform drive motor,The angle between the stator magnetic potential and the rotor magnetic potential will be less90Degree,Incurring motor torque is not maximum,Stator current exists Direct axis weight,produce demagnetization effect,Incurring the power factor of the controller is not high,Therefore, the need to participate in advanced commutation disposal.So that the angle between the stator magnetic potential and the rotor magnetic potential is as close as possible.90Degree.

   Finished up is actually very simple,Just when doing sine table,It is possible to advance the initial angle.,No need to change software architecture.A more sensitive solution is to add an offset to the meter holding needle.,This allows the advanced commutation angle to be set sensitively depending on the load condition..

   How to Speed 4.

   As can be seen from the above,SPWMThe modulation wave frequency is not arbitrarily given, but based onHallThe change of the signal is adjusted at any time and belongs to the self-controlled frequency conversion.,If you want to adjust the motor speed,Modulation sine wave frequency cannot be changed,Instead, the amplitude of the modulated wave is corrected.,Therefore, the sine table value extracted from the software will be multiplied by the external speed given coefficient before writing it.PWMThe duty cycle of the generator is stored in,After modulation amplitude correction,Equivalent voltage change on the motor,Then the speed attack changes,The frequency of the sinusoidal modulation wave is passively adjusted according to the rotor Hall signal..

   5. Summary

   Controller made with the above plan,The practical operation effect is smaller than that of square wave control noise.,Rotation Smooth,Can complete stepless speed regulation,Especially suitable for household electric fan brushless motor control or air conditioning fan control.