2021 Question B-Three-phase AC-DC conversion circuit-Primitive Animal Research Institute

1. Introduction

  My fate with e-sports began in the 2020 Beijing College Student Electronic Design Competition. In 2020, due to the COVID-19 epidemic, I could only participate in electronic competition training at home. At that time, it was based on small experiments and Proteus simulations of the Texas Instruments (TI) MSP430 series. After several months of tossing, I finally faced a notice of cancellation of the competition. It is a pity. . The 2021 National E-Sports Competition is also full of twists and turns. Preparations for the competition began in April, and in the meantime we were faced with various things such as courses, internships, and promotions. On August 3rd, the day before the competition, although I felt that I was not fully prepared, I was still ready to win the electronic competition in one go. Unexpectedly, the school's teacher Zou Jia, who was leading the team, had just finished the mobilization meeting, but in the afternoon he was notified that the event would be postponed for a week due to the epidemic, and he had no choice but to continue preparations. The next day, the notice changed to an indefinite extension. As the captain, I instantly lost motivation, and the entire team relaxed. After all, the intense preparations in the weeks before the game were really stressful. Fast forward to the end of September, and the work on pushing for exemptions has basically been completed, and the competition is scheduled for November 4th. One of the students on the team needs to take the postgraduate entrance examination, and another student is not interested in the e-sports competition, so I can only do it. One person continues to prepare for the game.
  The four days and three nights of the electronic competition made me very anxious, and I also experienced the first all-nighter in my life, but fortunately the result was not that disappointing. There were only eight teams in Beijing that chose question B. The two teams from our school, China University of Mining and Technology (Beijing), who chose question B, finally won the top two in Beijing. My team was the only team recommended to enter the national competition for question B in Beijing, and finally won the second prize in the country. Although I feel like I didn’t do better, it’s still worthy of the trip. It is also an honor to be invited by Lichuang to share my experience with everyone here. 2. Team introduction

  There are three team members, namely Zhou Jian, Yang Hansen, and Wang Xuebei. Yang Hansen majored in applied chemistry, and Wang Xuebei and I both majored in electrical engineering and automation. It is hard to imagine that Yang Hansen, a "layman", has also joined the e-sports team, and is also the main force in our team's algorithm and programming, contributing considerable strength to the entire team. I am mainly responsible for hardware, drawing board, welding and debugging. I am also responsible for the code structure and team training management. Student Wang Xuebei is mainly responsible for writing the design report.
 3. Project Analysis

1. Task:
  Design and produce the three-phase AC- as shown in Figure 1 DC conversion circuit, the DC output voltage Uo of this circuit should be stable at 36V, and the DC output current Io rating is 2A.
![Three-phase AC-DC conversion circuit principle block diagram] 2. Requirements:
1. Basic requirements
  (1) AC input line voltage Ui=28V, when Io=2A, Uo=36V±0.1V.
  (2) When Ui=28V and Io changes within the range of 0.1A~2.0A, the load regulation rate SI≤0.3%.
  (3) When Io=2A and Ui changes in the range of 23V~33V, the voltage adjustment rate SU≤0.3%.
  (4) Under the conditions of Ui=28V, Io=2A, Uo=36V, the efficiency η of the AC-DC conversion circuit is not less than 85%.
2. Performance part
  (1) Under the conditions of Ui=28V, Io=2A, Uo=36V, the power factor of the input side of the AC-DC conversion circuit is not less than 0.99.
  (2) Under the conditions of Ui=28V, Io=2A, Uo=36V, the efficiency η of the AC-DC conversion circuit is not less than 95%.
  (3) The three-phase AC-DC conversion circuit can automatically adjust the power factor according to digital settings. The power factor adjustment range is 0.90~1.00, and the absolute value of the error is not greater than 0.02.
  (4) Others.

  Since we have been using the Texas Instruments F28027 development board as the DSP during the preparation period, we did not hesitate to choose this DSP as the main control chip when we got the question. In the hardware circuit, the direct current voltage from the first-level three-phase bridge PWM rectifier circuit is higher than 36V. Therefore, a three-phase bridge PWM rectifier circuit is first used to convert the three-phase alternating current with a line voltage of 28V into a DC of about 50V, and then A synchronous PWM rectifier circuit steps down the DC voltage to 36V. In order to achieve high power factor rectification and ensure that the AC side voltage and current phases are the same, single-cycle control is adopted as the control strategy. This method is simple and convenient and requires few sensors. It only needs to sample the current on the AC side and the voltage on the DC side without sampling the AC side voltage. 4. Schematic circuit analysis:

  The three-phase rectifier bridge selects a topology of three half-bridges connected in parallel, sharing a DC bus. Compared with using three independent full-bridge rectifiers, the hardware complexity is reduced, but it is a little more troublesome to control. The latter stage synchronous rectifier bridge is also a half-bridge structure. The MOSFET is AP70N100K from All Power Semiconductor, which is packaged in TO-252 for easy soldering. The drain voltage UDS=100V, the continuous leakage current ID=70A at 25℃, the on-state resistance Ron=10mΩ when the gate-source voltage UGS=4.5V.
![AP70N100K]   The half-bridge gate driver chooses EGmicro's EG2104. Features: high-end suspended bootstrap power supply design, withstand voltage up to 600V; adaptable to 5V, 3.3V input voltage; maximum frequency supports 500kHz; low-end VCC voltage range 2.8V−20V; output current capability Io+/-2A/2.5A; built-in dead zone control circuit; SD# input channel is active at low level, turning off HO and LO outputs; few peripheral components; quiescent current is less than 1μA, Great for battery situations.
![EG2104]   DC voltage detection uses a large resistor in series to divide the voltage and add a follower to directly detect the DC voltage. The voltage dividing resistor can be combined with an appropriate capacitor to filter out high-frequency noise interference.
![Resistor voltage dividing network]   AC current detection uses Hall current sensor. Nanjing Chieful Technology's CSM005A is a current sensor that applies the Hall effect closed-loop principle. It can measure DC, AC, pulse and various irregular waveform currents under electrical isolation conditions. The rated input current of the primary side is 5A and requires ±12V~±15V dual power supply. The rated output current of the secondary side is Is=25mA. The measuring resistor RM at the output end is selected according to needs, generally in the range of 100Ω∼460Ω. The AC output requires conditioning circuitry before it can enter the ADC sampling.
![CSM025A]   The auxiliary power supply uses a 2W06G rectifier bridge to convert 28V AC power into DC power, and then uses the Jinshengyang power module URA4815YMD-6WR3 to convert the ±15V voltage to the Hall current sensor. At the same time, it uses K78L05-500R3 and K78L03-500R3 to convert the 5V and The voltage of 3.3V is supplied to the gate driver EG2104 and DSP TMSF28027 respectively.
![2W06G]
  In the PCB layout, heat dissipation holes should be drilled in areas where MOSFET heat is serious, and bare copper should be laid over a large area to guide the heat to a larger area of ​​exposed metal for effective dissipation. GND copper is generally not laid near the power tube to avoid excessive switching noise to the ground. The power ground and signal ground, signal ground and analog ground should be grounded at a single point. One way is to place a 0Ω resistor at the connection. The wiring is based on the experience of 100mil 5A, and can be appropriately increased to reduce resistance loss. Slots need to be set near the AC to prevent electricity creepage and ensure safety.
![PCB line width] ![PCB copper laying]
  The actual picture of the work is as follows:
![The actual picture]


  The test part effect diagram is as follows:
![Waveform diagram] ![Power factor] ![Efficiency]
  See attachments f28027_ac_dc.c and f28027_dc_dc.c.
![Hardware Block Diagram] ![Program Block Diagram] ![Simulation Diagram]
  This competition could not have won the second grade without the help of teachers Zou Jia and Wang Yingying from the laboratory, as well as many selfless trainings and doctoral student Yuan Wei Answer patiently. After months of hard work preparing for the e-sports competition, I have a relatively in-depth understanding of hardware selection, PCB drawing, welding, and DSP programming, and I can be considered an introduction to power electronics. It's a coincidence that if it weren't for the electric competition, I wouldn't have chosen power electronics so firmly during my graduate studies. Under my influence, Yang Hansen, a team member from the applied chemistry major, also planned to take the exam from celestial objects to power electronics, which can be regarded as a small gain in the electric competition. I also hope that every partner preparing for the competition can gain something from participating in the competition and continue to learn in practice. 10.   Please see the

attached source code, documents, reports, and demonstration videos.