【CW32】Brushless DC motor driver based on CW32F030

 

Analysis of the problem of brushless motor driver based on MP6534 front-end driver
. The overall design plan is divided into CW32 minimum system, MP6534 peripheral circuit design, three half-bridge inverters composed of MOS tubes, Bluetooth serial port module, and OLED display module. The design drive current is 8A.
Schematic design description
Power input
1.
After the power input DC12V enters, it first passes through a disposable fuse and is connected in parallel with a 14V transient diode. When the input voltage is higher than 14V, the diode is broken down, and the voltage across the diode is always maintained at 14v, so that the subsequent load is not burned by the overvoltage. When there is a large current or the D1 diode is broken down and conducts, the fuse operates. Protect the subsequent chip. The 470uF electrolytic capacitor is used to provide sudden changes in current to the motor. In the actual board, two 470uF electrolytic capacitors are welded, which can be welded as needed according to the actual situation.
2.12V to 3.3V 12V-3.3V Buck circuit The
MOS pre-driver selected here comes with a BUCK module, and the built-in BUCK is directly used to save a DCDC. The built-in BUCK has a maximum output current of 500mA and a maximum input voltage of 60V. It is very fragrant.
BUCK parameter calculation:
Input capacitor: The manual recommends a 4.7uF X5R or X7R ceramic capacitor with a rated voltage higher than the input voltage. A 25V, 10uF, 0805 ceramic capacitor is used here.
Filter inductor calculation formula: The inductance calculation formula
is known to be VIN = 12V; VOUT = 3.3V; derta IL = 30%; fSW = 500KHz; Finally, a 22uH inductor with an inductor saturation current of 500mA is installed on the board.
Feedback resistor: Just calculate according to the manual. The calculation formula is as follows. The reference resistance combination is also given in the manual, but I don’t refer to it, hahaha. Note that the accuracy of the feedback resistor is preferably 1%. At the same time, in order to improve the accuracy, I chose two resistors in series to obtain a more accurate resistance value. I usually calculate the feedback resistor by fixing R2 to 10 kiloohms, and calculate the other resistor according to the formula given in the manual, accurate to 10 ohms.
Buck feedback resistor calculation formula and reference resistance value
output capacitor: the manual recommends 22uF X5R/X7R ceramic capacitor. Just follow the manual.
Note that I installed a light-emitting diode behind the 3.3V output to detect the power supply working status.
 
3. CW32 microcontroller minimum system and interface: The peripheral circuit of the
CW32F030 minimum system
chip is designed according to the official case and small blue board. OLED and SWDIO download interfaces are reserved, and a user button is added.
4. Motor drive chip MP6534
The MP6534 chip and its peripheral circuits
can be designed according to the chip manual. The parameters that need to be designed by yourself include the setting of dead time and short-circuit current. Select the resistance values ​​corresponding to the DT and OREF pins respectively. Note that the nSLEEP pin needs to be connected to an external pull-up resistor to 3.3V before the chip can start. I have stepped on a trap here.
Dead time configuration resistor calculation formula: short circuit current I did not use this function, follow the manual to connect a 100K resistor from the VREG pin to the OCREF pin.
 
 
5. Three-phase inverter circuit The MOS
of the three-phase inverter circuit
 
is SM66406D1RL, 40V@30A, and the on-resistance is less than 12 milliohms. After the board was finalized, a better MOS was discovered, but it was too late. Here we recommend two brands: Wuxi New Clean Energy and Weishuo.
The G pole of the MOS is connected in series with a 10-ohm resistor to suppress oscillation caused by the wiring inductance. The diode connected in parallel with this resistor is used to speed up the turn-off time. (The chip manual has detailed instructions and experimental diagrams, the following is excerpted from the chip manual)
G pole has no series resistance (100nS/div.)
 
G pole has a 100 ohm resistor in series (200nS/div)
 
G pole has a 100 ohm resistor in series and a 1N4148 diode in parallel (200nS/div. )
 
Through comparison, it can be concluded that the turn-on time of MOS with and without series resistance will be prolonged, but there is almost no oscillation during the turn-on process of MOS. After connecting the diode in parallel, the turn-off time is greatly shortened (yellow line). Reducing the switching time is conducive to reducing the switching time. losses and improve efficiency.
 
The lower end of the ABC three-phase bridge arm is connected in series with a 10 milliohm resistor for current sampling.
Constructing a virtual neutral point
6. Terminal voltage and phase current acquisition
 
Here a universal operational amplifier is used to construct the acquisition operator. The principle is shown in Figure 7.24 below: The hardware implementation of terminal voltage acquisition
U5 is a 4-way universal operational amplifier, model: LM324QT, package Size: VQFN-16_L3.0-W3.0-P0.50-TL-EP is the smallest 4-way op amp I can find in Lichuang Mall. According to the knowledge of analog electricity, the addition and subtraction circuit is connected according to Equation 7.2.
Similarly, there is current sampling: the current and voltage values ​​calculated by the current sampling op amp through the operational amplifier are sent to the CW32 ADC for sampling. 7.LED indicator light and Bluetooth serial port module. The Bluetooth serial port module and LED indicator Bluetooth serial port were purchased from Taobao and are very cheap. Overview of the schematic diagram This completes the explanation of the schematic diagram. PCB Design Instructions PCB TOP Overview PCB BOTTOM Overview PCB 3D Preview I have only been studying PCB design for 4 months. There are definitely many shortcomings. Please criticize and correct me. The software description originally wanted to control FOC, but as of June 14, it has not yet been implemented. Currently, it can realize non-sensory open-loop rotation and button speed adjustment, and other functions are to be developed. Physical display description The attached content of the PCB physical diagram is a document for study and reference of this work. Acknowledgments Thanks to Piggy. Thanks to Jialichuang and Wuhan Xinyuan Company for organizing the training camp, which allows novices who are new to hardware to have projects to do, materials to learn, and coupons to receive. Thanks to Jialichuang SMT, it feels so good not to have to manually apply the patch. Thanks to Chuangxin Workshop for sponsoring PWLink. Thanks Orange.