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1. From the above schematic diagram of the main circuit of the intermediate frequency furnace in series, it can be seen that the power supply part of the series intermediate frequency furnace is composed of the power supply contactor and the three-phase AC absorption; the rectification part is composed of three-phase full-controlled rectifier bridge composed of multiple thyristors. It enables the output power of the series intermediate frequency furnace to be continuously adjusted from 0.1Pn (Pn for rated power) to Pn. When it is shut down or fails, the rectifier can be converted from the rectified working state to the inverter working state, so that it is mainly stored in DC. The energy in the intermediate circuit is fed back to the power supply network. In order to protect the rectifier thyristor, a fast fuse and DC reverse overvoltage protection are also provided in the circuit.
The DC intermediate circuit is essentially composed of a water-cooled choke with a core. Its function is to filter the pulsating DC of the rectified output to suppress the influence of the intermediate frequency voltage on the grid. When the load is short-circuited, it also acts to prevent the current from rising too fast.
The inverter is composed of a single-phase full-control inverter bridge composed of a plurality of fast thyristors. By alternately triggering the thyristors, the current is output to the input terminals u and v of the parallel resonant load in a continuously changing direction at an intermediate frequency.
In addition, the main circuit of the series intermediate frequency furnace also includes an AC and DC starting circuit.
2. Control loop
The circuit in the schematic diagram of the main circuit is the control loop of the series intermediate frequency furnace. A more detailed control and adjustment block diagram is given for this section. It can be seen from the figure that the rectifier of the series intermediate frequency furnace is controlled by two units: a rectifier regulator and a rectifier trigger. The inverter is mainly composed of an inverter regulator (constant counter voltage controller), an inverter regulator II and a counter. Variable pulse amplifier to control.
The fault monitoring and protection of the entire series intermediate frequency furnace is controlled by electronic protection and inverter monitoring. The signals for current and voltage are exclusively performed by the signal feedback board.
The starting of the entire series intermediate frequency furnace is accomplished by the start-up control.
The coordination of all the above units is controlled by a programmable controller (PLC).
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