Current Source Half-bridge Thyristor Frequency Power Supply

Rescent years, as a high-power resonant power supply with many advantages, thyristor medium frequency power supply is widely used in melting, induction through heating, heat treatment etc. But its tonnage is small and its furnace wall is thin. These two disadvantages restrict its further development. Its small tonnage can't meet the need of maximization and the thin furnace wall leads to series problems. For the thin furnace wall, furnace lining life is short, oxygen blowing and slagging are impossible.The existing high-power medium frequency power supply can usually be divided into parallel compensating inverter and series compensating inverter.Parallel compensating inverter is current source mode, with its compensating capacitor parallel to its furnace coil. Parallel inverter is current resonance, which owns the advantages such as the avoiding of the high resonant voltage and strong load adaptability. On the other hand, the forced commutated thyristor has starting problem under heavy load, and the larger the inverter power is, the more difficult to start, so its tonnage is small. Its output power decreases with the increase of the Q factor, so its lining can't be thick.Series compensating inverter is voltage source mode, with its compensating capacitor series to its furnace coil, it is voltage resonance. Series inverter is natural commutation mode and has no start-up problem, so it is suitable to the situation witch need to start up frequently. On the other hand, the disadvantage of the series inverter is the high resonant voltage loading on the equipment, witch increases when the inverter power grows and not only causes the equipment damage but also is dangerous for the operators.According to the problems mentioned above, a current source mode half-bridge thyristor inverter is designed. It is current source mode, with the zero wire of the power supply connect to the middle point of the two resonant capacitors. Compared to parallel inverter, this circuit is natural commutation mode and has no starting problem. Compared to series inverter, it has no high resonant voltage danger. Based on the circuit, a 1200kW experimental prototype is designed. The experimental prototype has stable operation performance.Analysis of the "reactive power converted to real power" operating principle is made in detail and the components of the experimental prototype are introduced. On the experimental prototype, small power experiment is done. Electrical characteristic of the circuit is measured and the experimental results are analysised in detail.The experimental results indicate that the circuit has two obvious advantages:1. The inverter has the abnormal characteristic-"the higher Q-value, the higher output power ", based on witch the double-layer-lining induction furnace body is designed.2. It is shown that the inverter breaks the law of Q factor and has "half Q-value characteristic". The voltage of the furnace is one fourth of that on series inverter, so it has no high voltage danger.In chapter 4, based on the differential equations, mathematical analysis of the full procedure of the inverter from transient to stead state is done. Theoretical waveform, output power characteristic and calculation data are compatible with the experiment. It is proved from theoretical that the inverter has the characteristic: "the higher of the resonance circuit quality factor, the higher of the output power is" . The mathematical analysis is important for theoretical analysis of the circuit and the design of the experimental prototype.With its unique advantages, the current source mode half-bridge thyristor inverter will play an important role in high-power medium frequency field.