Application case of the hottest oscilloscope in Br

2022-07-28
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Application cases of oscillograph in DC brushless motor industry

in recent years, brushless motor has been widely used in high-precision control industries such as medical treatment, industrial control, consumer electronics and automotive electronics. The performance of brushless motor largely depends on the motor driver. In the R & D stage, how can engineers quickly, conveniently and truly analyze the driver signal with the help of oscillograph? This paper mainly introduces the typical test and case analysis of zds4054plus data mining oscilloscope for motor driver

I. Introduction to brushless DC motor

with the development of power electronics and the emergence of new permanent magnet materials, brushless DC motor has developed rapidly. Brushless DC motor realizes the commutation of motor through electronic devices, replacing the traditional mechanical brush and inverter. It is a typical mechatronic product, which is composed of motor body and driver. The stator winding of the motor is mostly made into three-phase symmetrical star connection, which is very similar to the three-phase asynchronous motor. The rotor of the motor is adhered with a magnetized permanent magnet. In order to detect the polarity of the motor rotor, a position sensor is installed in the motor. The driver is composed of power electronic devices and integrated circuits. Its function is to receive the starting, stopping and braking signals of the motor to control the starting, stopping and braking of the motor; It receives the position sensor signal and the forward and reverse signals to control the on-off of each power tube of the inverter bridge and generate continuous torque; Receive speed command and speed feedback signal to control and adjust speed; Provide protection, display, etc. Brushless motor is widely used in medical treatment, industrial control, consumer electronics, electric tools, electric vehicles and other fields because of its low noise, long service life, high speed, small size, good dynamic performance, large output torque and simple design

it can be seen from the above figure that the MCU outputs six PWM signals through the configuration register, which is only a control signal, and its maximum voltage is only 5V. It cannot directly drive the motor, but makes the motor run by controlling the switch of the power tube. The drive circuit is generally composed of a drive bridge composed of multiple MOSFETs and a power tube of the electric drive bridge. The commutation of brushless motor depends on the detection of rotor position. The inductive drive mode uses Hall sensor to detect the rotor position. The non inductive drive mode detects and calculates the changes of current, voltage and other parameters during the rotation of brushless motor, infers the rotor position, and then carries out commutation

commutation principle

a Hall sensor is installed inside the brushless motor, which can give an output signal of 1 or 0 according to the distribution of different magnetic field directions at different positions of the rotor. The three sensors are installed evenly, and there are 6 overturning levels at 360 ° electrical angle, with a difference of 60 ° electrical angle each time. The position of the rotor is measured according to the signal code of the three sensors, which is the common inductive drive mode. In addition, the non inductive drive mode detects and calculates the changes of current, voltage and other parameters during the rotation of the brushless motor, infers the rotor position, and then carries out commutation

working principle of the drive circuit

simplified diagram of the drive circuit

it can be seen from the above figure that the MCU outputs six PWM signals through the configuration register, and its maximum voltage is only 5V. It cannot directly drive the motor, but makes the motor run by controlling the switch of the power tube. The drive circuit is generally composed of a drive bridge composed of multiple MOSFETs and a motor drive bridge power tube. The commutation of brushless motor depends on the detection of rotor position. The inductive drive mode uses Hall sensor to detect the rotor position. The non inductive drive mode detects and calculates the changes of current, voltage and other parameters during the rotation of brushless motor, infers the rotor position, and then carries out commutation

commutation principle

a Hall sensor is installed inside the brushless motor, which can give an output signal of 1 or 0 according to the distribution of different magnetic field directions at different positions of the rotor. The three sensors are installed evenly, and there are 6 overturning levels at 360 ° electrical angle, with a difference of 60 ° electrical angle each time. The position of the rotor is measured according to the signal code of the three sensors, which is the common inductive drive mode. In addition, the non inductive drive mode detects and calculates the changes of current, voltage and other parameters during the rotation of the brushless motor, infers the rotor position, and then carries out commutation

working principle of driving circuit

simplified diagram of driving circuit

59 gypsum board

Q1 to Q6 in the diagram are power field effect tubes. When AB phase conduction is required, only Q1 and Q4 tubes need to be opened to keep other tubes cut off. At this time, the current flows through: positive pole → Q1 → coil a → winding B → Q4 → negative pole. MCU sends a PWM signal to Q1 grid and a normally open signal to Q4 grid, so you can control the effective voltage of the drive motor by controlling the duty cycle of the PWM signal at Q1 input. The same is true for the other five step commutation. The measured waveforms of each phase are as follows:

measured results of voltage waveforms of each phase

III. ZDS at this stage, we can apply and analyze the measured waveforms that are not called adjustment 4054plus

for the PWM signal analysis of the above brushless motor driver, what new test experience does zds4054plus oscilloscope have

512mpts large data storage

for the driving voltage of the brushless motor in the case, when the engineer observes the PWM signal, if there is an abnormality in the signal, it is difficult to trigger by triggering. It is necessary to analyze the signal in the envelope through the scaling mode on a large time basis (observe the waveform details in the scaling window). The PWM signal frequency is more than tens of K. It is necessary to ensure a high sampling rate. At the same time, the PWM signal is accompanied by current Carrier signals such as encoders need to be observed by multiple channels, and large storage is required in terms of waveform time, sampling rate and multi-channel. Figure 1 shows the PWM drive signal of the brushless motor. When the storage depth is set to 350m, the waveform of 7S is captured, and the sampling rate is still as high as 50m sa/s, ensuring that the waveform is not distorted. According to the formula: storage depth = waveform time * sampling rate, zds4000 series oscilloscope is equipped with 512mpts storage depth as standard to ensure high sampling rate while capturing long-time waveform

dual Zo speed regulation range is wide om mode + Intelligent marking

as shown in the figure above, how to analyze PWM driving signal or abnormal signal after capturing waveform for a long time? In addition, in industrial servo applications, under different working conditions, when switching different loads, the driver waveform change or abnormal signal displacement corresponding to different times is related to the movement of the object's position in the movement process. The whole load switching process takes a long time. It is also necessary to view the waveform details in a large storage depth. In view of the above situation, Zds4000 series oscillograph supports double zoom scaling mode under the condition of ensuring large storage depth. It can set coefficients for the two scaling windows respectively, and label the signals of interest at any place with the intelligent labeling function. The figure shows the PWM driving signal. The waveform in the main time base is amplified in two zoom windows respectively. Zoom1 is the PWM periodic signal, and zoom2 is the oscillation waveform of a PWM peak. Under the guarantee of large storage depth, the sampling rate is 50m sa/s, ensuring the authenticity of waveform details. At the same time, with the intelligent annotation function, such as making a annotation on the main time base, you can quickly find the annotation points on zoom1 and zoom2, you can see the annotation point in zoom1 - the third spike of PWM, and you can see the oscillation and amplitude of the spike in zoom2

IV. summary

zds4000 series data mining oscillograph, with the functions of 512M deep storage, dual zoom mode, template triggering, fir hardware filtering and intelligent calibration, can quickly and truly locate and analyze the abnormal waveform of brushless motor driver, and provide a perfect solution for waveform debugging in the brushless motor industry

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