Research And Design Of AC/DC Converter Protection Based On Thyristor

Thyristor is an ideal device in high power conversion. It has the advantages of high capacity, high voltage-proof, high efficiency, fast response, controllability, good reliability, etc. It has become the basic of power conversion development. The thyristor power converter has been applied widely in various domains of modern industry, metallurgy, electrolysis, electroplating, HVDC and so on for instance.The thyristor AC/DC converter works in the environment of high power. The faults such as over current, short circuit, over voltage are inevitable. So the protection system which is equipped to the thyristor AC/DC converter is indispensable. The protection of thyristor AC/DC converter can be divided into two kinds. One is the protection based on device, such as RC snubber, over current relay, snap switch, current-limiting inductance, rapid fuse, voltage dependent resistor. The other is the protection using electronic circuit. At home, the selection of protection parameters in thyristor AC/DC converter mostly depends on empirical equation. That sometimes results in huge error in parameters. If the selection of protection parameter is unreasonable, it may result in spike voltage, which can decrease the insulation of the power electronic device, intermittently discharge and even damage the device. So the research on the high power thyristor AC/DC converter protection is significant practically and theoretically.First, this dissertation aims at 12 pulse thyristor AC/DC converter. It is researched from the faults of over current, over voltage, and over load. The methods of parameter design about over current protection and optimal parameter design in RC snubber about over voltage protection are proposed. And the 12 pulse thyristor AC/DC converter protection system is designed. Second, to aim at the phenomenon that is for the RC snubber resistance of Over-voltage protection often burn because of high temperature, in the Saber simulation software using the test circuit simulation and actual measurement method study the temperature of RC snubber resistance. under conditions of the same capacitance, and different resistance values to simulate. The greater of the resistance, the faster the temperature rise. When system is stable, higher temperature resistance is greater, and consistent with the measured temperature. This method for high-power RC snubber design has a certain significance. At last, a 12-pulse thyristor-based AC-DC converter protection system software and hardware are designed. The hardware design of the protection system, including DC power, phase detection, the voltage and current sampling, over-voltage protection circuit, digital I/O and serial communication design. Software includes ADC sampling, I/O and protection function.At last, the methods this thesis proposed about over-current protection and over-voltage protection in thyristor AC/DC converter are verified. The simulation model is established using the software SABER, to verify the calculated protection parameter by simulation. Meanwhile, the 12 pulse thyristor AC/DC converter protection is also verified by experiments. The actual measured waveform and the simulated waveform are consistent. And that means the simulation system can take the place of the experiment device to realize the waveform measurement of DC output voltage without RC snubber. Through the waveform comparation, it can be observed that the voltage waveform with RC snubber is much btter than the voltage waveform without RC snubber. That means the parameter of resistor and capacitor makes good effect on protection of AC/DC converter. And that also verifies the optimal method of over-voltage protection RC snubber parameter.