Abstract : This paper introduces a three-phase sinusoidal frequency converter system based on the DSP TMS320F2812. The software and hardware components of the main circuit and control circuit are analyzed and designed in detail. The control strategy and three operating modes of the power system are discussed. The programming strategy and algorithm for generating SPWM waves with adjustable frequency and amplitude using the TMS320F2812 are discussed. The random access memory of the TMS320F2812 is expanded, and the effective values of line voltage and line current, as well as the frequency of the sine wave, are displayed in real time using an SPLC501 LCD. Experimental results are satisfactory, meeting all the requirements of the frequency converter system design. Keywords : DSP, TMS320F2812, SPWM, frequency conversion, modulation degree, power protection, phase loss protection Abstract : It introduced the Frequency Converter Power System of the three-phase sine wave Based on DSP TMS320F2812, detailedly analyzed and designed load software and the hardware part of the main circuit, controlling circuit, discussed the variable frequency and amplitude algorithms SPWM, that used TMS320F2812, expanded RAM based on TMS320F2812, displayed line voltage, line current RMS, as well as sinusoidal wave frequencies using SPLC501 LCD. The test was correct, the designing satisfied all the request the Frequency Converter Power System.. Key Words : DSP TMS320F2812 SPWM Frequency Conversion Modulation Power Protection the Protection of Lack Phase 1. Introduction With the rapid development of power electronics technology, sinusoidal output frequency converters have been widely used in various fields. Simultaneously, increasingly higher demands are being placed on the output voltage waveform quality of these power supplies. In laboratories and industrial sectors, three-phase sinusoidal frequency converters are commonly used in various measurement and control circuits to generate single-phase or three-phase sinusoidal signals as reference signals. The waveform quality of the reference sine wave directly affects the accuracy of measurement and control. A good sinusoidal signal source requires highly stable amplitude and frequency, low distortion, strong load-carrying capacity, and adjustable amplitude for its output reference sine wave signal. For three-phase sinusoidal signals, good three-phase symmetry is also required. Meeting these requirements often complicates the circuit. Therefore, researching and developing inverter control strategies that are both simple and possess excellent dynamic and static performance has become one of the research hotspots in the field of power electronics. II. Working Principle The overall circuit structure of the system consists of a main circuit, a control circuit, a sampling circuit, a feedback circuit, and various protection circuits. The overall schematic diagram is shown in Figure 2-1: [align=center] Figure 2-1 System Schematic Diagram[/align] 2.1 Main Circuit and Working Principle The main circuit consists of three main parts: a rectifier and filter circuit, a three-phase full-bridge inverter circuit, and a three-phase passive filter circuit. The rectifier and filter circuit converts single-phase AC power into DC power, and the three-phase full-bridge inverter circuit converts DC power into three-phase AC power. After the three-phase AC power passes through the three-phase filter circuit, a standard three-phase sine wave power supply is obtained. The main circuit is shown in Figure 2-2. [align=center] Figure 2-2 Main Circuit Schematic[/align] 2.2 Control Circuit Working Principle The control circuit uses SPWM wave modulation. The SPWM modulation method and digital control strategy of the sine wave output frequency converter power supply were analyzed. The TMS320F2812 digital signal processor is used as the main control chip to achieve optimal power supply control. The working principle of the control circuit is shown in Figure 2-3. [align=center] Figure 2-3 Control Circuit Schematic[/align] 2.3 Control Strategy The power supply uses the event manager in TMS320F2812 and adopts SPWM modulation. The inverter output signal is obtained as a standard sine wave after passing through the three-phase passive filter. The control principle diagram is shown in Figure 2-4: [align=center] Figure 2-4 Control Principle Diagram[/align] 2.4 Soft Start Function and Fault Handling The power supply system is equipped with soft start function, open circuit protection, short circuit protection, MOSFET overcurrent protection, phase loss protection, and load asymmetry protection. The power control system has three operating modes: normal operating mode, startup mode, and protection mode. When the power supply starts working or starts after a fault, in order to prevent the load-side voltage from rising too quickly and causing circuit failure, we use the soft start method. At this time, the control system is in startup mode. Soft start includes two parts. First, by slowly increasing the three-phase input voltage on the input side, we can ensure that the inverter circuit will not fail due to the direct application of the bus voltage. In addition, in the control process of the inverter circuit, we need to use a closed-loop control method. By sampling and recording the data, we adjust the drive signal frequency. When the load-side voltage rises to a certain value, we switch the circuit to normal operating mode. Therefore, under soft start conditions, the load side will not fail due to the instantaneous high voltage. During power supply operation, a short circuit fault can cause a sharp increase in operating current. Without intervention, this overcurrent can damage many components in the circuit. When an overcurrent occurs, the overcurrent protection device in the circuit will activate. At this time, the drive signal of the control circuit will be blocked, the drive signal will stop, and the circuit will switch from normal operation mode to protection control mode. In protection mode, after blocking the drive signal, the control system will automatically restart after a timing period. If an overcurrent occurs again, the power supply will stop working. III. Software Design 3.1 Overall Software Design The software mainly includes SPWM generation, A/D conversion, PID regulation, frequency capture, soft start, and protection. Its main function is to control the three-phase bridge inverter using sinusoidal pulse width modulation technology, enabling it to output a three-phase sinusoidal voltage with adjustable frequency and stable amplitude. A/D conversion samples the output voltage and current, monitoring them in real time. When the current exceeds 3.6A, the output of the three-phase inverter bridge is cut off to protect the circuit. PID regulation ensures timely response to output voltage changes, stabilizing the output voltage at 36V. Soft start is used during system startup to reduce the impact of voltage and current on the system circuit. The main program flowchart is shown in Figure 3-1: [align=center] Figure 3-1 Main Program Flowchart[/align] 3.2 SPWM Generation Principle Using these registers, the waveform shown in Figure XXX can be easily implemented in the TMS320F2812. A sine table is established in the initialization part of the program. The desired data can be obtained by looking up the table during system operation. Assuming that the number of samples in one sine wave cycle is NX, the sample value at the i-th point is where PR is the count period value in the period register. Rounding yi, from i=1 to i=NX, we get a table of NX sine sample values. The counting mode of the general timer is set to continuous increment and decrement counting mode. The corresponding square wave signal that changes according to the sine law can be generated by calling the value in the table in the interrupt program. Here, NX is 180, and the carrier ratio is an integer multiple of 3 (carrier ratio = modulation wave frequency / carrier frequency). This can make the three-phase output waveform strictly symmetrical and reduce the influence of harmonics on the output voltage waveform. [align=center]Figure 3-2 SPWM Flowchart[/align] 3.3 Display Circuit To improve the human-computer interaction of the product, a display circuit was added to the system. After comparison, we used an SPLC501A LCD screen to complete the display work. The connection diagram between the display circuit and DSP2812 is shown in Figure 3-3: [align=center]Figure 3-3 Connection Diagram between LCD and DSP[/align] The TMS320F2812 can divide the read/write access of any external device mapped in the XINTF area into three stages: setup stage, activation stage, and tracking stage. In this design, the LCD is mapped to XINTF0. By default, the cycles of the three stages are 6 XTIMCLK cycles, 14 XTIMCLK cycles, and 6 XTIMCLK cycles, respectively. If the frequency of XTIMCLK is set to 1/2 of SYSCLKOUT, the maximum value of the read/write cycle is 180ns. The read/write timing diagram for the three stages is shown in Figure 3-4: [align=center] Figure 3-4 TMS320F2812 Read/Write Timing Diagram[/align] The minimum period of the enable signal CS of the Sunplus SPLC501 LCD module is 166ns, and the timing diagram is shown in Figure 3-5. From the previous analysis, we can see that the maximum read/write period of the DSP is 180ns, and the minimum read/write period of the LCD module is 166ns. The DSP's read/write timing can meet the requirements of this LCD module. [align=center]Figure 3-5 SPLC501 Read/Write Timing[/align] IV. Innovative Design Features This system design adopts an AC-DC-AC frequency conversion method. The overall system structure uses a modular design, which integrates the various parts of the frequency converter power supply to achieve frequency conversion output. It displays voltage, current, frequency, and active power with high precision. The measured signal values are true RMS values, the voltage output accuracy is high, the error is guaranteed to be less than 5%, the three-phase sine wave output has low distortion, and it has overvoltage, overcurrent protection, and phase loss protection functions. The performance is stable. The innovative features of this system design are: 1. Combining the AD unit of the TMS320LF2812 chip, the output line voltage and line current of the three-phase frequency converter power supply are sampled. An external random access memory is added, and the voltage, current, and frequency values are displayed through the SPLC501 LCD display. It can realize autonomous sampling and data transmission, greatly improving data acquisition efficiency, and displaying the RMS values of voltage and current of the frequency converter power supply in real time with high display accuracy and good real-time performance. 2. Combining the TMS320F2812 event manager EV unit and employing sinusoidal pulse width modulation (SPWM) technology, through the design and improvement of the SPWM program algorithm, the frequency and effective value of the three-phase frequency converter output can be effectively adjusted, exhibiting good real-time performance and high accuracy. 3. The control section of the frequency converter system is fully digitalized, resulting in higher control precision and stronger anti-interference capabilities. V. Test Results 5.1 Measured Waveforms
5.2 Results Analysis According to the design requirements, we have produced a sample. The phase voltage and line voltage waveforms observed by the oscilloscope show that the waveforms are basically undistorted. The output voltage can be changed by adjusting the modulation and the frequency of the sine wave, which meets the design requirements. VI. Conclusion The digital three-phase frequency converter developed has been tested twice and improved in terms of control principle, circuit structure, etc. It has been gradually perfected and tested, proving the effectiveness and reliability of the power supply. References [1] (US) Muhammad H. Rashid Power Electronics Technology Handbook Machinery Industry Press 2005.6. [2] Zhang Weining. TMS320C28: Series DSP CPU and Peripherals (Volume 1 and Volume 2). Tsinghua University Press. [3] Luo Wen, Wang Junfeng, Shi Tielin. Design of High-Speed Serial Data Acquisition System Based on McBSP [J] Microcomputer Information 2006-8-2-176-178. [4] Zhang Pengcheng, A high-speed data acquisition and processing system based on DSP [J] Applied Technology 2006, 15-16. [5] Liu Heping, TMS320LF240Xdsp C language development and application, Beijing University of Aeronautics and Astronautics Press. [6] Su Kuifeng, TMS320F2812 Principles and Development, Electronic Industry Press 2005.4 [7] Zhao Tonghe, Chief Editor, Switching Power Supply Design Technology and Application Examples. Beijing, People's Posts and Telecommunications Press, 2007.6. [8] Chen Jian. Power Electronics, Higher Mathematics Education Press, 2002.1. [9] Wang Zhaoan, Huang Jun. Power Electronics Technology, Fourth Edition, Machinery Industry Press. [10] Keith Billings, Translated by Zhang Zhansong, Wang Renhuang, and Xie Liping, Switching Power Supply Handbook, People's Posts and Telecommunications Press, 2006.12. Name: Mei Jianwei Tel: 13972458242 Mailing Address: Department of Electrical Engineering, Hubei University of Automotive Technology, Shiyan City, Hubei Province
