Medium frequency furnace series resonance control board



Medium frequency furnaces are divided into two types based on compensation: parallel resonance (current type) and series resonance (voltage type). So what is medium frequency furnace series resonance? And what does the medium frequency furnace series resonance control board look like?



 Medium frequency furnace series resonance control board



The inverter used in the series resonance medium frequency furnace is a series resonance inverter, whose load is a series resonant load. It usually requires a voltage source supply. In a medium frequency furnace, the voltage source is typically composed of a rectifier plus a large capacitor. Due to the large capacitance, the input voltage of the inverter can be approximately considered constant. By alternately turning on and off the controllable devices on the inverter, an alternating square wave voltage can be obtained at the output of the inverter. Its voltage amplitude depends on the input voltage of the inverter, and the frequency depends on the switching frequency of the devices.



The power control process is as follows: the product of the inverter input voltage Ud and current Id is compared with the set value, the difference is input to the power regulator, and its output is compared with the current Id. After the current regulator operation, it controls the output pulse frequency of the voltage-controlled oscillator, changing the counter overflow pulse time, thereby changing the trigger pulse frequency of the thyristor, achieving the desired control effect. This control effect of the medium frequency furnace series resonance control board is reflected in maintaining constant input power under heavy load conditions above the furnace rated value; within the light load range below the rated value, it controls the output current within the limit value.



Characteristics of series resonant circuit:


    (1) Constant output power control is adopted. Even when there are charging and temperature changes during the melting process, the load rate can still be close to 100%, which can shorten the melting time.

    (2) The power supply capacity can be reduced. Since it is a voltage-type inverter, when it works normally, the rectifier thyristors are fully turned on and have a high power factor, thereby reducing the power supply capacity.

    (3) Higher efficiency. The inverter adopts a half-controlled bridge, requiring fewer main circuit components, and uses direct output without a matching transformer, improving both efficiency and reliability.

    (4) Good starting characteristics. It can be started at any time even under full load.

    (5) Minimized interference to the power supply network. The rectifier circuit uses thyristors to achieve soft start and soft stop. During normal operation, the thyristors are fully turned on. Therefore, during normal operation, high-order harmonics are small, and there is no large current surge during start and stop.

    (6) Integrated structure saves space. Except for the heating coil on the furnace, other components, including matching capacitors, are installed in the cabinet, forming an integrated power supply, thus requiring small installation area and easy installation.

    (7) It has comprehensive protection and monitoring systems.

The difference between the medium frequency furnace series resonance inverter and the parallel resonance inverter stems from the different oscillation circuits they use: the former uses L, R, and C in series, while the latter uses L, R, and C in parallel.