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How motor control can be achieved "to power the motor at the right time"?

2022/09/22

Motors, regardless of their type, are matched with some type of controller, which can vary in characteristics and complexity, depending on the capabilities of the particular motor. The simplest example of a motor control mechanism is a conventional switch that connects the motor to its power source. This switch can be a manual controller or a relay connected to an automatic sensor to start and stop the motor.



Preparation of control circuit design

Before facing the "right time", there is still a pre-work of "power transmission" that needs to be prepared, that is, the drive circuit needs to be determined. Its role is how to design a controllable power supply system. It needs the following information to ensure that the circuit board design and heat dissipation design, electronic components and other hardware meet the system needs.


The power supply capacity needs to match the specifications of the motor. To receive control commands to operate, it needs to be matched with the controller. Power transmission efficiency, signals and power can be transmitted normally without interference from other signals or electromagnetic waves. Whether the system can operate normally under the operating environment. security protection capability.



With a perfect drive circuit, the "right time" can be determined. Although the use of time is a noun, its real meaning is "position", that is, the relative position of the rotation of the motor rotor, or it can be called an angle.


Τ=1/2π·I·L·D^2·N·Sin(δ)


The above equation is the motor torque formula, where Sin(δ) represents the angle between the current of the motor and the magnetic field, when Sin(90°)=1 is the maximum value, and Sin(0°)=0 is the minimum value. The angle position "transmits "current" to the motor to achieve the best output effect.


How to do the "right time"

To achieve the "right time", the first step is to obtain the correct position of the motor rotor, which requires the use of position sensors. However, position judgment will be affected by the phenomenon of sensor resolution, installation position, signal processing, data transmission, programming calculation, etc., and the possible reasons are analyzed as follows:


Insufficient resolution will cause the sensor to be unable to directly mark the position of the power transmission, which needs to be obtained indirectly through signal processing techniques. If there is a sensor with sufficient resolution, there is no need to worry about the installation problem. On the contrary, if the installation position is deviated, the correct position cannot be directly marked. The sensor provides an electronic signal, which is used to judge the position change by observing the voltage level change. However, all voltage level changes are actually achieved by current transmission. In the sensor circuit, capacitors are often added for filtering and voltage regulation to stabilize the voltage level, but it will also affect the current working time, so that the voltage level needs a long time to change, resulting in a delay. The electronic signal obtained by the sensor needs to be transmitted to the controller before it can be used. Then, there will be capacitive and inductive elements on the control circuit board, which will affect the time when the electronic signal enters the controller. After the position signal enters the controller, it may still need to be calculated or processed, or wait for other programs to run first, which makes it impossible to respond to the position signal immediately.


The most common causes are listed above as a reference. After obtaining the correct position information, the "current" must be fed into the motor. It should be noted that the "correct time" refers to the time when the current enters the motor. The motor can be regarded as Inductive components, which can cause a significant delay in the time when the current enters the motor. In fact, the inductance value in the motor will be changed by the size of the inflow current and the switching frequency (speed) of the power supply. Therefore, the current delay time will also change at different speeds.


In addition, pay attention to the time required from receiving the position signal from the controller to processing the output control command, as well as the response time and bandwidth of the switching element, which may affect the time to send the current.


How to be a good driver

Ensure the speed of the signal: the delay of the signal is an inevitable result, but if the delay rate is fixed and known, it can be compensated by hardware or software; since the calculation function in the equation is Sin(δ), Therefore, if the difference angle is not large, the calculated value is still very close to 1, and the influence is not large. To effectively ensure the speed of signal transmission, it depends on the ability of circuit design, including the selection of various electronic components, power supply energy configuration and circuit wiring planning.


Software programming ability: The motor driver does not have a large burden on the controller, but the controller needs to handle a lot of work at the same time, so the weight, sequence and the time to master the operation should be paid attention to. If you choose a high-level controller, its operation response speed is fast, and you don't need to worry about the problem of dragging each other's time. For low-level controllers, it is necessary to pay attention to the continuous program compilation, and it may be necessary to directly use the assembly language to write the code to achieve the shortest program execution time.


The overall understanding of the motor system: It is still necessary to have a deep understanding of the motor to drive the motor. At present, most electronic circuit systems are controlled and processed for the voltage signal. First, the current value is not large, and secondly, the loss caused by the current and the loss of the current are considered. effects of electromagnetic waves. In the motor system, the current is the direct source of the torque force, and the importance of observing the change of the current is far more important than the voltage. The inductance in the motor and the electromagnetic waves generated are much larger than the electronic circuit system. If it is not considered properly, it is very likely that the back-feeding will directly cause adverse effects in the driving circuit. Furthermore, the use environment of the motor is relatively harsh, and special attention should be paid when placing the circuit directly inside the motor.


Conclusion

Depending on the application of the motor, the controllers can provide different functions, they help the motor start under low voltage conditions, allow multiple speed or reverse control operations, prevent overcurrent and overload faults, and perform various other functions. Some sophisticated motor control devices also help to effectively control the speed and torque of the motor, and may also be part of a closed-loop control system responsible for precise positioning of the motor-driven machine.


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