Zubkov I. Control systems of high-frequency transistor converters with pulse density modulation for induction heating equipment.

The dissertation is devoted to increasing the energy and technical and economic indicators of induction heating equipment due to the development of new methods and means of controlling high-frequency transistor converters with phase auto-adjustment of frequency and pulse density modulation. Compared to other technologies, induction heating has many advantages, such as locality of heating, direct transfer of energy from the inductor to the detail, environmentally safe organization of the work process, speed and automation of production. Induction heating installations on transistor converters are characterized by high efficiency, small dimensions, a wide range of operating frequency (from 10 to 500 kHz and higher), long-term service life, the possibility of modernization and improvement of power equipment when the production technology or type of part is changed, the possibility of monitoring and controlling the process with the help of the appropriate software. When developing and modeling inverters for induction heating installations, the issue of reducing static and dynamic losses in power switches is important. Since static losses of high-frequency converters make up a smaller part of total losses, the main goal is to minimize dynamic losses in transistors. This is achieved by adjusting the control system, when the switching of the power switches occurs at current and voltage close to zero. To ensure such switching modes, transistor converters with pulse density modulation (Pulse density modulation or PDM) are widely used. Unlike other control methods (frequency-pulse, phase-pulse, PWM), control systems of high-frequency transistor converters with pulse density modulation allow switching the inverter keys at almost zero current.The development of algorithms for switching transistors of resonant voltage inverters with PDM is a rather important stage in the design of power converters and is a key factor in reducing dynamic power losses. Therefore, in order to create a stable phase shift between the output voltage and current of the inverter and to ensure minimal dynamic losses in transistors, it is necessary to develop new systems for phase self-adjustment of the PLL frequency, which would take into account all features of using resonant voltage inverters with pulse density modulation for induction heating installations.