This article presents the analysis of a converter based on an LLC resonant output inverter and its optimal design used in induction heating applications. The new optimal design method improves several operating parameters that leads to an optimization of the dimensioning of the components of the converter. Additionally, this converter achieves an output power factor that can be considered optimal since it allows to minimize the reactive power of the resonant circuit components and reduces the rms values of the output current of the inverter and the current of its switching devices in relation to that found in traditional designs. A complete study of the circuit based on classic models is carried out to introduce simple rules for the design of this type of inverter for induction heating applications and to control its output power based on a phase shift (PS) system. Since the inverter is made with silicon carbide MOSFET transistors, an efficiency greater than 99% is reached. The experimental results were obtained from the test of a 12 kW 20 kHz converter for induction heating application.

This article presents a control method for an isolated bidirectional dual active bridge DC–DC converter (IBDC) where single phase shift (SPS) and variable frequency (VF) modulations are combined simultaneously with the purpose of improving the efficiency of the converter applied to the bidirectional charging of electric vehicles batteries. A complete power characterization of the dual active bridge (DAB) converter is carried out. The combined control achieves lossless turn-on and turn-off on the primary bridge for a wide range of output powers. A comparative study of power losses between the traditional SPS control and the combined method proposed here was also carried out. A prototype with an output power of 10 kW was built based on Silicon Carbide (SiC) Metal Oxide Semiconductor Field-Effect Transistors (MOSFET), with which a peak efficiency close to 99% was obtained, thus verifying the viability of the method.

Multiple Coupled Inductors are used in power electronics to improve dynamic cross regulation and to reduce mass and volume, mainly in high performance application, like space or defense, where manufacturing cost is not the main driver. These elements can be modeled with its inductance matrix which is a symmetric and positive semidefinite matrix. The inductance matrix eases circuit analysis, many known circuital models are directly related to it and it can be used in SPICE simulation via its coupling coefficient component, which can be identified as the normalized matrix of the inductance matrix. Therefore, a precise and correct measurement technique of the inductance matrix or coupling coefficient matrix is needed. This paper analyzes different measuring techniques described in technical literature and proposes a new method to measure the coupling coefficient or inductance matrix of tight coupled or dissimilar turns' number windings, where other methods fail. A discussion follows, to know the influence of parasitic elements in the accuracy of the new proposed method called resonance (RE) method. The paper adds three experimental examples to verify the theoretical study and concludes that the RE method provides correct values of coupling coefficient k of tight coupled or dissimilar turns' number windings compared to other measurement techniques.

This paper analyses a high power (50 kW), high frequency (150 kHz) voltage fed inverter with a series resonant load circuit for industrial induction heating applications which is characterized by a full bridge inverter made with IGBT and the power control based on pulse density modulation (PDM). This power control strategy allows that the inverter works close to the resonance frequency for all output power levels. In this situation zero-voltage switching (ZVS) and zero-current switching (ZCS) conditions are performed and the switching losses are minimized. The results are verified experimentally using a prototype for induction hardening applications. A comparative study between the PDM and the classical frequency power control will be made.

This article presents a generalized analysis to explain current ripple of an m windings coupled inductor with a given coupling factor k _ij for each pair of windings and then studies more in detail its use in the continuous conduction mode and with pulsewidth modulated signals. To determine the current ripple, a generalized expression of the equivalent inductance of each winding is calculated, including the influence of voltage unbalance. In the ideal case, the equivalent inductance shows that the current ripple can only become m times smaller than that with uncoupled inductors. But in the unbalanced case, some divergences of the equivalent inductance appear that are responsible for zero ripple current. The proposed generalized expressions of the equivalent inductance also describe the current ripple of the new appearing intervals due to out-of-phase signals. An easy to design condition is proposed that achieves zero current ripple in all windings but one. Experimental results are provided that validate the presented theoretical expressions under the given conditions.

Induction surface hardening (ISH) processes are widely used in the heat treatment of numerous industrial components, especially in the automotive industry. Since this industry operates under very demanding quality standards, it is crucial for these heat treatment processes to meet rigorous specifications to ensure the safety and reliability of the produced components. This implies the precise and repeatable control of certain parameters throughout the manufacturing process of each of the parts treated, through precise and reliable instrumentation in electromagnetically harsh environments. The main objective of this work is to define the monitoring process for an industrial IHS application, determining the control needs and the methods of measurement, recording, and verification of the parameters that ensure the quality of the process. This paper describes the monitoring process of induction surface hardening, emphasizing the use of sensors and modern measurement and control systems. A comprehensive monitoring system supported by a programmable logic controller (PLC) and mixed acquisition and instrumentation systems (analog and digital) implemented with a high-performance Field Programmable Gate Array (FPGA) will be presented.