Wayne Chin

Forced air cooled quasi-planar 60A, 600μH inductor for a plasma cutting power supply

This paper presents the design and experimental results of a forced air cooled 60A, 600 μH quasi-planar buck converter inductor for a plasma cutting application. The inductor consists of PCBs (Printed Circuit Boards) with air ducts between the adjacent boards and conventional powder iron E cores. The winding assembly is simple and enables direct cooling of the PCB layers. A multi-physics based approach that considers factors like winding loss, air flow and heat transfer is used for the component design. Results from a 3-D FEA (Finite Element Analysis) based model that analyzes these physics are compared with experimental data from a proof-of-concept inductor prototype. A reasonable correlation is observed with average temperature errors in the 10-20% range. Factors affecting the performance of the model are also discussed. A comparison with an equivalent conventional inductor shows a four-fold increase in cooling efficiency and a three-fold reduction in copper usage. Thus, this approach is seen to be cost competitive and feasible for this application.

Planar Tesla coil arc ignition transformer for a plasma cutting power supply

The arc igniter in a plasma cutting system is a High Voltage High Frequency (HVHF) Pulse Generator typically realized using a Tesla coil resonant circuit. The ignition voltage pulse is a 5-15kV pk., 2-3 MHz sinusoid lasting for not more than 5-10 cycles. It is used to ionize the gas inside the torch thereby producing plasma [1]. The Tesla coil resonant circuit is the preferred method since it is composed of rugged components like the Tesla coil transformer, spark gaps and capacitors. However, the conventional Tesla coil transformer is expensive since it requires a special custom bobbin and the windings are manually wound. This also leads to variations in unit to unit performance. In view of this, a planar technology based Tesla coil transformer as a cost effective alternative is proposed. With this approach, there is no need for a custom bobbin or manual winding. This simplifies the build, reduces cost and ensures consistency in unit performance. The design procedure consists of obtaining characteristics of the current transformer and designing the planar version to match those characteristics. Details of the design procedure are covered in the paper. FEA (Finite Element Analysis) based models of the current and planar Tesla coil versions are used for the electromagnetic analysis and validated with experimental data. Reasonable correlation is obtained with experimental data over a 1 kHz-3 MHz frequency range. This confirms the efficacy of the analysis and the feasibility of planar technology for this application.