In industry, for superior utilization of large capital equipment, a single large-current high-power converter is desired to convert electrical energy to a controlled high-intensity heat source to cater to the dynamic requirement of several welding methods (e.g., welding, hard-facing, gouging, weld overlay, etc.). The dynamic process behavior of multi-input minimally semiautomatic or single-input manual processes could follow either constant voltage (CV) or constant current (CC) arc type. Due to completely different type of arc or load characteristics, this article proposes a de-coupled control approach to guide the power source to independently take care of each arc type. It proposes feedforward control for CV arc type and robust second order sliding mode control (SOSMC) approach for dynamically uncertain CC arc type for manual welding. It further highlights that low-loss resonant or soft-switching topologies are less compatible for decoupled control of high-power loads with wide range impedance characteristics. For desired energy efficiency of a full-bridge DC-DC converter for arc welding, this article details that robustness features of SOSMC could be used for superior component engineering that incur low power loss. Finally, this article completely validates the proposed idea in a 1000A power converter for both CC and CV arc types.

Two popular application domains of low-power single-switch induction heating systems are cooking and off-line sealing of plastic/glass containers. Sealing operation could be using cap or capless, the latter is preferred because of ease of inspection of sealing quality. For near continuous-duty operation of the converter, due to the superior power loss and thermal characteristics, two SiC MOSFETs connected in parallel are preferred for the switch. The design of gate drive circuit (GDC) for these devices is complicated. The desired gate voltage is not only highly asymmetrical, due to small gate threshold voltage, it is sensitive to ringing in gate signal, the range of negative bias is also constrained. The duty-cycle of the high-frequency gate signal for the switch is small. This article proposed a novel GDC where, using a single-polarity control power supply, a pulse-transformer is used to feed desired asymmetrical gate voltage to several isolated devices. To avoid spurious turn-on, this research further proposed a novel transformer for feeding bi-polar asymmetrical gate voltage with requisite signal and power-noise isolation to effectively use of respective Kelvin source terminal. The proposed idea has been completely validated by driving two SiC MOSFETs in a power converter for high-speed off-line induction sealing applications.

Due to its simple gain selection and implementation procedures high-gain sliding mode control idea was introduced. Apart from achieving robustness features, the aim was to reduce product-design cycle time. To overcome its basic chattering issues, it was replaced by complex super twisting control (STC). Subsequently, the research in this field has been extensive, intense and persistent. The idea has been validated in several applications generating great hope in minds of industry experts. Its real success, however, would depend on its adoption and diffusion into industry domain, where an analysis of validating STC based products is due. In STC, selection of gains is based on worst-case values of disturbance and/or its derivative. Can such procedure ensure controller’s reliable functioning? This article proposes that such simplistic procedure of gain selection may not work for power electronics controllers where, particularly, the actuation or controlled power transfer to load is through magnetically-coupled system. Using practical approach, this article elaborates that optimally designed transformer, driven by high-gain super twisting controller, invites problem of core saturation leading to higher switching losses, poor operating duty cycle of the system and there could be problem of reliability. It further details an alternate high-gain controller that generates superior efficacy.

In medium to high frequency power transformers, apart from minimizing the power loss in the core and copper, the design of its thermal circuit plays an important role in containing the temperature rise in different parts. It is extremely complex because there exist multiple loss centers with different heat removal characteristics. Moreover, the power loss is concentrated around a small core volume and the rest of it is available for convection and radiation. This article proposes to use a hybrid core configuration to improve the heat removal feature of the transformer. This article establishes through practical validation on suitability i.e., the magnetic compatibility of cores in the hybrid magnetic circuit. It further explores the application prospect of the proposed concept where the thermal performances have been compared using different core types in two different application domains. In the first case, the core could always remain energized to its rated value, and in the second design, both the windings could always draw their respective rated current.

One of the most prominent application areas of induction heating principle is for sealing of caps of plastic and glass containers. It is increasingly being used to seal containers with extremely wide range industrial products. The process ambience around the controller for sealing of bottles containing different types of products could be different. Such prospects, often, could act as constraints for design of power controllers. Dust prone environment prevailing in processes such as for sealing nutraceuticals, coffee, a few pharma products, etc. recommends use of air-tight enclosure. It does not have any ventilation, even the natural air movement inside or the free convection is restricted. This article proposes that the internal convection could still be made effective by creating requisite buoyant force where both power converter topology and component engineering could play important roles. The topology should optimally reduce the power loss and surface temperature of components should be high. The proposed idea has been validated by designing a zero-ventilated 1.5 kW, 50 kHz induction heating system that includes the induction coil head.

High-power high-frequency air-cooled induction heating transformers, mostly used as current multiplier and isolation purposes, are custom designed. For their reliable performance and long life, the thermal evaluation at rated load is necessary. Creating an equivalent load as test facility for reliability testing of such type of transformer is difficult. Characteristics of such loads drastically change after Curie temperature. Moreover, prolonged heating could increase the nearby ambient temperature and, more importantly, the traditional heat run test wastes large amount of energy. Whenever the coil is energized, windings of transformer draw respective rated current; even at no load condition the copper loss is at rated value. While both windings drawing rated current at desired frequency, using the concept of localized eddy current loss as well as excess eddy current loss, this article proposes a novel method to inject requisite core loss to the magnetic circuit to emulate the characteristics of full load condition but the power drawn from the transformer would be zero. The proposed idea would be validated where only 200 W resonant inverter would be used to inject power loss equivalent to full-load condition of 30 kW transformer to emulate the heat run test.