精品国产sm全部网站免费_日韩精品毛片_推荐高清免费不卡网站_亚洲无码人成电影在线观看_一本伊大人香蕉久久網手機_福利视频你懂得_亚洲欧美曰韩在线_成年男女免费网站点播_成年人播放一级片高清_亚洲视频在线视频

Service Hotline: 13823761625

Support

Contact Us

You are here：Home >> Support >> Technology

Technology

Summary of Ultra Full BLDC Motor Control

Time:2023-10-24 Views:664
BLDC motor control algorithm
    Brushless motors belong to the self commutation type (self directional conversion), so their control is more complex.
    BLDC motor control requires understanding the rotor position and mechanism of the motor for rectification and turning. For closed-loop speed control, there are two additional requirements, namely, measuring the rotor speed/or motor current and PWM signal to control the motor speed and power.
    BLDC motors can use edge or center arranged PWM signals according to application requirements. Most applications only require speed change operation and will use 6 independent edge arranged PWM signals. This provides the highest resolution. If the application requires server positioning, energy consumption braking, or power reversal, it is recommended to use a supplementary center arranged PWM signal.
    In order to sense the rotor position, the BLDC motor uses Hall effect sensors to provide absolute positioning sensing. This leads to more line usage and higher costs. Sensorless BLDC control eliminates the need for Hall sensors and instead uses the back electromotive force (electromotive force) of the motor to predict rotor position. Sensorless control is crucial for low-cost variable speed applications such as fans and pumps. When using BLDC motors, the refrigerator and air conditioning compressor also require sensorless control.
Insertion and supplementation of idle time:
    Most BLDC motors do not require complementary PWM, no-load time insertion, or no-load time compensation. BLDC applications that may require these characteristics are only high-performance BLDC servo motors, sine wave excited BLDC motors, brushless AC, or PC synchronous motors.

    Many different control algorithms are used to provide control for BLDC motors. A typical approach is to use power transistors as linear regulators to control motor voltage. This method is not practical when driving high-power motors. High power motors must adopt PWM control and require a microcontroller to provide starting and control functions. Many different control algorithms are used to provide control for BLDC motors. A typical approach is to use power transistors as linear regulators to control motor voltage. This method is not practical when driving high-power motors. High power motors must adopt PWM control and require a microcontroller to provide starting and control functions.
The control algorithm must provide the following three functions:
     PWM voltage used to control motor speed
    Mechanism for rectifying and reversing the motor
    Method for predicting rotor position using back electromotive force or Hall sensor
    Pulse width modulation is only used to apply variable voltage to the motor winding. The effective voltage is proportional to the PWM duty cycle. When appropriate commutation is obtained, the torque speed characteristics of BLDC are the same as those of the following DC motors. Variable voltage can be used to control the speed and variable torque of the motor.
Figure 1
    The commutation of power transistors enables the appropriate winding in the stator to generate the optimal torque based on the rotor position. In a BLDC motor, the MCU must know the position of the rotor and be able to perform rectification and commutation at the appropriate time.
     One of the simplest methods for DC brushless motors is to use the so-called trapezoidal rectification commutation.
Figure 2: Simplified block diagram of trapezoidal controller for BLDC motor
    In Figure 2, each time the current is controlled through a pair of motor terminals, while the third motor terminal is always electrically disconnected from the power supply.
    Three types of Hall devices embedded in large motors are used to provide digital signals, which measure rotor position within a 60 degree sector and provide this information on the motor controller. Due to the equal amount of current on both windings each time and zero current on the third winding, this method can only generate a current space vector with one of the six directions. As the motor rotates, the current at the motor terminals is switched on and off (rectified commutation) once every 60 degrees, so the current space vector is always at the position closest to 30 degrees in a 90 degree phase shift.
Figure 3: Ladder control: Drive waveform and torque at rectifier
    Therefore, the current waveform of each winding is trapezoidal, starting from zero to positive current, then to zero and then to negative current.
    This generates the current space vector, which will approach equilibrium rotation when it steps up in six different directions as the rotor rotates.
    In motor applications such as air conditioning and refrigerators, using Hall sensors is not a constant choice. The back electromotive force sensor induced in a disconnected winding can be used to achieve the same results.
    This trapezoidal drive system is very common due to the simplicity of its control circuit, but they encounter torque ripple problems during the rectification process.

    The trapezoidal rectifier commutation is not sufficient to provide balanced and accurate control of brushless DC motors. This is mainly because the torque generated in a three-phase brushless motor with a legitimate wave back electromotive force is defined by the following equation:
    Shaft torque=Kt [IRSin (o)+ISSin (o+120)+ITSin (o+240)]
Among them:
    O is the electrical angle of the shaft
    Kt is the torque constant of the motor
     IR, IS, and IT are phase currents
    If the phase current is sinusoidal: IR=I0Sino; IS=I0Sin (+120o); IT=I0Sin (+240o)
    We will obtain: shaft torque=1.5I0 * Kt (a constant independent of shaft angle)
    The sinusoidal rectifier commutation brushless motor controller strives to drive three motor windings, and the three currents of the motor smoothly undergo sinusoidal changes as it rotates. Select the relevant phases of these currents, so that they will generate a stationary rotor current space vector with a direction orthogonal to the rotor and invariant. This eliminates torque ripple and steering pulse related to steering.
    In order to generate a smooth sine wave modulation of the motor current as it rotates, an accurate measurement of the rotor position is required. The Hall device only provides a rough calculation of the rotor position, which is not enough to meet the purpose requirements. For this reason, angular feedback is required from encoders or similar devices.
Figure 4: Simplified block diagram of BLDC motor sine wave controller
    Due to the fact that the winding current must be combined to generate a stable constant rotor current space vector, and each positioning angle of the stator winding is 120 degrees apart, the current of each line group must be sinusoidal and have a phase shift of 120 degrees. The position information in the encoder is used to synthesize two sine waves, with a phase shift of 120 degrees between them. Then, multiply these signals by the torque value, so that the amplitude of the sine wave is proportional to the required torque. As a result, the two sine wave current commands are properly phased, resulting in the generation of a rotating stator current space vector in the orthogonal direction.
    The sinusoidal current command signal outputs a pair of P-I controllers that modulate the current in two appropriate motor windings. The current in the third rotor winding is the negative sum of the controlled winding currents, therefore it cannot be controlled separately. The output of each P-I controller is sent to a PWM modulator and then to the output bridge and two motor terminals. The voltage applied to the third motor terminal is derived from the negative sum of the signals applied to the first two wire groups, used for three sinusoidal voltages spaced 120 degrees apart.
    As a result, the actual output current waveform accurately tracks the sine current command signal, resulting in a smooth rotation of the current space vector, which is quantitatively stable and positioned in the desired direction.
    Generally, the sine rectification steering result cannot achieve stable control through trapezoidal rectification steering. However, due to its high efficiency at low motor speeds, it will separate at high motor speeds. This is due to the increase in speed, and the current return controller must track a sine signal with an increasing frequency. At the same time, they must overcome the back electromotive force of the motor that increases in amplitude and frequency as the speed increases.
    Due to the limited gain and frequency response of the P-I controller, the time variable interference in the current control loop will cause phase lag and gain error in the motor current. The higher the speed, the greater the error. This will interfere with the direction of the current space vector relative to the rotor, causing displacement in the orthogonal direction.
    When this situation occurs, a certain amount of current can generate a smaller torque, so more current is needed to maintain the torque and reduce efficiency.
    As the speed increases, this decrease will continue. To some extent, the phase shift of the current exceeds 90 degrees. When this situation occurs, the torque decreases to zero. By combining sine waves, the speed at this point above leads to negative torque, so it cannot be achieved.

1. Scalar control 
  Scalar control (or V/Hz control) is a simple method of controlling the speed of a command motor. The steady-state model of the instruction motor is mainly used to obtain technology, so transient performance is impossible to achieve. The system does not have a current loop. In order to control the motor, the three-phase power supply only changes in amplitude and frequency.
2. Vector control or magnetic field oriented control
     The torque in an electric motor varies with the function of the stator and rotor magnetic fields, and reaches its peak when the two magnetic fields are orthogonal to each other. In scalar based control, the angle between two magnetic fields changes significantly.
    Vector control attempts to create orthogonal relationships again in AC motors. In order to control torque, each generates current from the generated magnetic flux to achieve the responsiveness of the DC machine.
    The vector control of an AC command motor is similar to the control of a separate excitation DC motor. In a DC motor, the magnetic field energy generated by the excitation current IF Φ F and the armature flux generated by the armature current IA Φ Orthogonal A. These magnetic fields are decoupled and stable with each other. Therefore, when the armature current is controlled to control torque, the magnetic field energy remains unaffected and faster transient response is achieved.
    The field oriented control (FOC) of three-phase AC motors includes imitating the operation of DC motors. All controlled variables are converted to DC instead of AC through mathematical transformation. Its goal is to independently control torque and magnetic flux.

There are two methods for Field Oriented Control (FOC):
    Direct FOC: The direction of the rotor flux angle is directly calculated through a flux observer.
    Indirect FOC: The direction of the rotor flux angle is indirectly obtained by estimating or measuring the rotor speed and slip.
    Vector control requires understanding the position of rotor magnetic flux and the ability to use knowledge of terminal current and voltage (using the dynamic model of AC induction motors) to calculate through advanced algorithms. However, from an implementation perspective, the demand for computing resources is crucial.
    Different methods can be used to implement vector control algorithms. Feedforward technology, model estimation, and adaptive control techniques can all be used to enhance response and stability.
3. Vector control of AC motors: in-depth understanding
    The core of vector control algorithm is two important transformations: Clark transformation, Park transformation, and their inverse operations. By using Clark and Park transformations, the rotor current can be controlled to the rotor region. This allows a rotor control system to determine the voltage that should be supplied to the rotor to maximize torque under dynamically changing loads.
    Clark transformation: Clark mathematical transformation modifies a three-phase system into two coordinate systems:

    Among them, Ia and Ib are components of the orthogonal reference plane, while Io is the unimportant homoplanar part

Figure 5: Relationship between three-phase rotor current and rotational reference frame

4. Park transformation: Park mathematical transformation converts a bidirectional static system into a rotational system vector

    two-phase α，β The frame representation is calculated through Clarke transformation and then input to the vector rotation module, where it rotates the angle θ， To correspond to the d, q frames of the energy attached to the rotor. According to the above formula, the angle is achieved θ Conversion of.
The Basic Structure of Field Oriented Vector Control for AC Motors
    The Clarke transformation uses three-phase currents IA, IB, and IC, where the currents of IA and IB in the fixed coordinate stator phase are transformed into Isd and Isq, becoming elements in Park transformation d and q. The current Isd, Isq, and instantaneous flow angle calculated through the motor flux model θ Used to calculate the electric torque of AC induction motors.

Figure 6: Basic principle of vector controlled AC motor

    These exported values are compared with the reference values and updated by the PI controller.

Table 1: Comparison of Scalar Control and Vector Control for Electric Motors

    An inherent advantage of vector based motor control is that it can use the same principle to select suitable mathematical models to control various types of AC, PM-AC, or BLDC motors separately.
Vector Control of BLDC Motors
    BLDC motors are the main choice for field oriented vector control. Brushless motors using FOC can achieve higher efficiency, with a maximum efficiency of 95%, and are also very efficient for motors at high speeds.
1. Stepper motor control

Figure 7

    The stepper motor control usually adopts bidirectional driving current, and the motor stepping is achieved by sequentially switching the windings. Usually, this stepper motor has three driving sequences:
① Single phase full step drive:
    In this mode, the windings are energized in the following order, AB/CD/BA/DC (BA indicates that the energization of winding AB is in the opposite direction). This sequence is called single-phase full step mode, or wave drive mode. At any one time, only one phase is energized.
② Dual phase full step drive:
    In this mode, the two phases are energized together, so the rotor is always between the two poles. This mode is called two-phase full step. This mode is the normal driving sequence of the bipolar motor and can output the maximum torque.
③ Half step mode:
    This mode combines single-phase and two-phase stepping for power up: single-phase power up, then two-phase power up, and then single-phase power up... Therefore, the motor operates in half step increments. This mode is called half stepping mode. The effective step angle of each excitation of the motor is reduced by half, and the output torque is also low.
    The above three modes can be used for reverse rotation (counterclockwise direction), but not if the order is opposite.
    Usually, stepper motors have multiple poles to reduce step angle, but the number of windings and driving sequence remain unchanged.
2. General DC Motor Control Algorithm  
Speed control for general motors, especially motors using two types of circuits:
    Phase angle control
    PWM chopping control
① Phase angle control
    Phase angle control is the simplest method for general motor speed control. Control the speed by adjusting the arc angle of TRIAC points. Phase angle control is a very economical solution, but it is not very efficient and prone to electromagnetic interference (EMI).

Figure 8: Phase angle control of general motors

    Figure 8 shows the mechanism of phase angle control, which is a typical application of TRIAC speed control. The phase shift of the TRIAC gate pulse generates efficient voltage, resulting in different motor speeds. A zero crossing cross detection circuit is used to establish a timing reference to delay the gate pulse.
② PWM chopping control
    PWM control is a more advanced solution for general motor speed control. In this solution, the power MOSFET or IGBT is connected to the high-frequency rectified AC line voltage, thereby generating a voltage that varies over time for the motor.

Figure 9: PWM Chopping Control for General Motors

    The switching frequency range is generally 10-20KHz to eliminate noise. This universal motor control method can achieve better current control and better EMI performance, resulting in higher efficiency.

 












   
      
      
   
   


    Disclaimer: This article is transferred from other platforms and does not represent the views and positions of this site. If there is any infringement or objection, please contact us to delete it. thank you!
    矽源特科技ChipSourceTek