Overall layout and structural design of medium frequency induction heating equipment

When designing the structure of medium-frequency induction heating equipment, in addition to the design of general low-voltage electrical equipment, factors such as the beautiful appearance of the entire machine, ease of installation, maintenance and operation, appropriate center of gravity, and necessary ventilation and heat dissipation conditions and insulation distance must be considered. In addition, special attention should be paid to the following six aspects.

1) Medium frequency induction heating equipment mainly consists of three parts, namely power frequency rectifier and filter, inverter and load circuit, as well as necessary instruments, display signals and control systems. In order to avoid interference with each other, in addition to placing each part separately, it is best to install metal partitions. When placing components, place heavy components at the bottom and light components at the top. The configuration of each component is best to be installed in the order of the electrical schematic diagram, and try to avoid the intersection of wiring. For example, install instruments and display signal components and necessary operating switches and buttons on the panel, place heavier components such as filter reactors and electric heating capacitors on the base, and install the controllable rectifier on the left and right upper parts of the machine. components and their control boards, and the other half is installed with inverter components and their control boards. During installation, attention should be paid to keeping the control board away from the controllable rectifier components and inverter components, but the drive board of the thyristor trigger pulse transformer or inverter switching device should be as close as possible to the thyristor or switching device. The signal lines between the trigger pulse transformer and the drive board and control board should use twisted pairs or shielded wires to avoid electromagnetic interference.

2) It is best to make separate printed circuit boards for the controllable rectifier control unit and the inverter control unit. Even if they are placed on the same board, they should have clear boundaries and separate wiring to avoid mutual interference.

3) When using transistors as inverter switching devices, it is often necessary to use multiple devices in parallel to obtain the required power. At this time, in addition to taking necessary current sharing measures and selecting devices with consistent performance in circuit design, the principles of balance, symmetry, and compactness must also be followed in structure and configuration design. Components connected in parallel should be configured as close as possible to shorten the connection length between each other and make the operating temperature of the devices consistent. In addition, try to make the wiring length from the busbar to each component the same. The positive and negative busbars of the DC input line and the two lines on the output side of the inverter should be as close as possible and laid in parallel to reduce the stray inductance of the wiring to the minimum.

4) In order to prevent interference with medium-frequency induction heating equipment, the main circuit high-current transmission lines should not be laid parallel to the control lines in the same trunking, or close to each other. The operating lines of the relay contact loop must be laid separately from the input signal lines, pulse output lines and other small current lines of the control unit. Signal lines and pulse transmission lines should be connected using twisted pairs or shielded lines.

5) Due to the high frequency and large current of the output loop current, the transmission conductor should be away from the casing or other components to generate local heat. In order to reduce losses, the output reciprocating busbars or cables should be laid as close as possible.

6) Many components in medium-frequency induction heating equipment are water-cooled. The problem of condensation on water-cooled components and pipelines in humid seasons must be considered. If necessary, consider installing a water tray to drain the dew to avoid short circuit accidents caused by leakage or insulation breakdown. Using a sealed chassis, condensation can be completely avoided through a combination of internal air self-circulation cooling and water cooling, which is an ideal cooling method.