The Dual-DSP Control System In Power Factor Correction Of Arc Welding Inverter Power Source

With the development of power electronics, arc welding inverter power source has been also developed rapidly. But in the arc welding inverter power source, the rectifier is composed by diodes and inductor (or capacitor), which are non-linear loads, these non-linear loads will cause the input current waveform distortion, thus will produce large amounts of harmonic currents. These harmonic currents will not only reduce the arc welding inverter power factor, but also cause harmonic pollution to grid and other adjacent electrical equipment, In order to reduce or even eliminate harmonic pollution and improve power factor, power factor correction technology is particularly important.In order to correct the power factor of arc welding inverter, corresponding control to the arc welding inverter main circuit is needed. The traditional control systems are generally based on a single chip, a single DSP or MCU+DSP composition. And because MCU has stronger control, DSP has a strong data processing capability and operation speed, their combination has been widely used. As rectifier and inverter of the arc welding inverter power factor correction are both needing to control, and data collection and necessary processing operations of each part are also needed, while the control system should also ensures real-time and accuracy of the data collection and transmission, clearly a DSP can't meet the design needs. With the DSP prices declining, which is almost the same as MCU, using two DSP to control will be able to significantly improve the arc welding inverter power factor, and have a better real-time, operating easily.In this paper, two TMS320LF2407A produced by TI will compose master-slave control system, in which the main DSP controls the main rectifier and calculates the data necessarily transmitted from the slave DSP to complete controlling the back; from major to complete the DSP Inverter control device, and the feedback collected welding current, voltage, and load status of transmission to the main DSP. TMS320LF2407A has many advantages, such as: modified Harvard architecture which enables a data bus, address bus separation of data simultaneously, the address of the call and write; has a wealth of on-chip peripheral interfaces, such as analog-digital conversion (ADC) module, Watchdog (WD) timer module, these modules are ideal for arc welding inverter power control; an independent software development environment CCS, which makes the program easy to understand control process; high speed calculation, under the clock in 40MHzCPU computational speed 40MIPS (40 million instructions per second), but the instruction cycle is 25ns.In this article, the rectifier controlling is done by the main DSP. In the controlling process, the rectifier circuit has been simplified:the rectifier circuit is composed by six IGBT and its driving circuit is EXB841 which is designed for the integrated driving module. EXB841 module fully functional with a rectifier power supply+20 V,+15 V output to the open gate voltage and gate voltage of-5V relations; built TLP550 High-speed Coupler signal isolation circuit with over current detection, cut off the circuit and so on. It is not only achieved the main circuit and control circuit high and low pressure isolation, provide the required drive current, but also both of the IGBT short-circuit over current protection.The inverter controlling is completed by the slave DSP, and the inverter circuit is composed by four IGBT, which model is GT60M102. Its driving circuit is the same with the rectifier circuit which is also composed by the EXB841. Through the current,voltage sensors collecting current, the voltage and current signals are first transmitted into the DSP for A/D conversion, and then made the appropriate PID operation, at last the output PWM signal controls the IGBT of the inverter circuit through the drive circuit EXB841, even controls the entire welding process.To ensure the two DSP can complete their work effectively, exchange data between them is necessary. In this paper, the IDT Corporation of the United States has developed a high-speed 16k×16bits dual-port static RAM (IDT7026) as its data exchange and transmission channels. It is a dual-port device that allows two processors simultaneously access and two ports to read and write data, and each port has its own control signal lines, address lines and data lines; its access data is very fast, about 15ns; pin allows two dual-port RAM on the DSP to read and write data operation; IDT7026 provide identification circuit, it will be a port to use dual-port RAM of the state transfer to another port through the identification circuit to transmit data, enabling high-speed data transfer without waiting for the state. These features can ensure real-time data and accuracy, so the main, from the DSP to complete a good inverter and rectifier control.A control system is not only including a complete hardware system, the necessary software program but also is needed to make the control process more convenient and faster. In this paper, the CCS3.1 software development environment is owned by the DSP that can design software programming to control all parts of the process. CCS (Code Composer studio) is a software development tool which was developed specifically for TI DSP software programming, its code generation tools and code debugging tools is being a overall to design software development of all aspects of the DSP system, and can significantly shorten the DSP programming time. DSP programming environment required for the source file editing, program debugging and follow-up of the simulation working, it can help the programmer in a specific software environment to complete the editing, debugging and data analysis work; it can also use assembly language and C language for software development, making programming more simple and easier to learn. In the end, through the integration of the various parts of the above, the dual-DSP controlling system is completed. Finally, collecting the necessary voltage current waveforms and other data to verify the dual-DSP controlling system for arc welding inverter power factor correction technology is feasible.