High Power Series-parallel Thyristor Frequency Power Supply Start Method

In this paper, the starting issue for thyristor-based high-power medium-frequency series-parallel resonant current source inverters, with particular reference to induction heating applications, is studied and discussed in-depth.The load is changed with many factors such as temperature, magnetic reluctivity, etc. and its parameters are difficult to measure. So the worst working situation is difficult to know, which is a serious problem when the starting issue is studied. In order to deal with it, the concept of limit load under steady working conditions is put forward. It is a feasible alternative method. Under the result of the inverter's steady sate study, the limitation limited by two factors: the minimum time of opposing voltage and the ajustive range of power factor can be gained.A qualitative analysis method based on energy decomposing is applied to study the initialized energy. In the parling process, the viewpoint that the initialized energy can be classified into medium-frequency energy and low-frequency energy is proposed. And it is pointed out that the medium-frequency energy is useful for inverter starting but the latter is harmful.Tow novel starting methods are put forward in the paper. From the viewpoint of energy compensation, a new starting method, named as magnetizing to the load, is developed. The mathematical model of working process is built, and the theoretical analysis is accomplished, too. From the viewpoint of energy building and transform, another new method, named as additional resonant starting way, is presented. The principle of working and the structure of the circuit are described in detail. Finally, it is indicated that the two methods are available for the inverters with series-parallel resonant load and verified that the methods can dissolve the starting difficult of high power supply by a number of simulations.