A Novel Induction Heating System Using Multilevel Neutral Point Clamped Inverter

Contribution to Knowledge: The main knowledge contribution of the dissertation can be summarized as follows: 1-A new design of induction heating power supply configuration with two categories of LLC topologies: A Novel induction heating power supply topology using multilevel neutral point clamped inverter (MNPCI) is investigated and verified. The proposed converter topology decreases the switching losses by decreasing the DC link voltage to half its DC rail voltage value with the aid of operation under soft switching mode condition. Depending on the modified LLC optimum design being introduced, it shares the advantage features of both voltage fed and current fed inverters with the capability to absorb the undesired parasitic components in the design. The new design involves adding new circuit parameter that helps in controlling the power transfer from the MNPCI to the resonant load tank. All the analytical analysis made and the corresponding experimental work verifies the prototype configuration. This contribution was presented by the author and published in: {B.M. Flayyih; M.Z. Ahmed; M. Ambroze, ''A Novel Hybrid Voltage-Current Fed Induction Heating Power Supply System Using Multilevel Neutral Point Clamped Inverter '', Energycon 2014 IEEE International Energy Conference, Dubrovnik-Croatia. From 13th - 16th May 2014}. 2-An optimum power control of induction heating system by reducing harmonic distortion content: The development of IH system has become a pressing need to improve the power transfer from power supply to the IH load of the application required, and due to variable characteristic of IH load workpiece during the heating cycle, it is necessary to develop an IH system that operates using resonant inverters with switching frequency that changes according to changing load conditions during the IH application process, in order to keep tuning with natural resonant frequency of the system and keep working under optimal operational point. A novel super frequency induction heating power supply using MNPCI with optimum control algorithm is introduced. The control strategy is to keep phase shift angle between voltage and current approximately zero at all load conditions to ensure maximum power transfer whatever the load parameters changes, that is necessary to reduce the switching losses and increase the efficiency. The load topology being used consists of variable LLC resonant tank with values chosen carefully to coincide with the design. Afterword, an Optimum Harmonic Control of a proposed induction heating power supply with MNPCI is also introduced in this research. The proposed system achieves the soft switching mode for both current and voltage with low harmonic distortion and the capability to maximize the heating power by controlling the harmonics. The modulation strategy depends on changing the ON switching time of the prototype to an optimized value that achieves natural switching with lowest possible harmonic distortion and thus, gaining highest heating power efficiency. This contribution was also presented by the author and published in {B.M. Flayyih; M.Z. Ahmed; S. MacVeigh, ''A Comprehensive Power Analysis of Induction Heating Power Supply System Using Multilevel Neutral Point Clamped Inverter With Optimum Control Algorithm '', 2015 IEEE 11th International Conference on Power Electronics and Drive Systems (PEDS), From 9th - 12th June 2015, Sydney, Australia}. This contribution is also presented by the author in: {B.M. Flayyih; M.Z. Ahmed; M. Ambroze, ''An Optimum Harmonic Control of Induction Heating Power Supply System Using Multilevel Neutral Point Clamped Inverter'', The IEEE Transportation Electrification Conference and Expo Asia-Pacific (ITEC2016), Busan, Korea on 1st - 4th June, 2016}.This thesis investigates a novel DC/AC resonant inverter of Induction Heating (IH) system presenting a Multilevel Neutral Point Clamped (MNPCI) topology, as a new part of power supply design. The main function of the prototype is to provide a maximum and steady state power transfer from converter to the resonant load tank, by achieving zero current switching (ZCS) with selecting the best design of load tank topology, and utilizing the advantage aspects of both the Voltage Fed Inverter (VFI) and Current Fed Inverter (CFI) kinds, therefore it can considered as a hybrid-inverter (HVCFI) category . The new design benefits from series resonant inverter design through using two bulk voltage source capacitors to feed a constant voltage delivery to the MNPCI inverter with half the DC rail voltage to decrease the switching losses and mitigate the over voltage surge occurred in inverter switches during operation which may cause damage when dealing with high power systems. Besides, the design profits from the resonant load topology of parallel resonant inverter, through using the LLC resonant load tank. The design gives the advantage of having an output current gain value of about Quality Factor (Q) times the inverter current and absorbs the parasitic components. On the contrary, decreasing inverter current means decreasing the switching frequency and thus, decreasing the switching losses of the system. This aspect increases the output power, which increases the heating efficiency. In order for the proposed system to be more reliable and matches the characteristics of IH process , the prototype is modelled with a variable LLC topology instead of fixed load parameters with achieving soft switching mode of ZCS and zero voltage switching (ZVS) at all load conditions and a tiny phase shift angle between output current and voltage, which might be neglected. To achieve the goal of reducing harmonic distortion, a new harmonic control modulation is introduced, by controlling the ON switching time to obtain minimum Total Harmonic Distortion (THD) content accompanied with optimum power for heating energy.Iraqi Ministry of Higher Education and Scientific Research.Al Shuhadaa Establishment of Iraq

Frequency-modulation control of a DC/DC current-source parallel-resonant converter

This paper proposes a frequency-modulation control scheme for a dc/dc current-source parallel-resonant converter with two possible configurations. The basic configuration comprises an external voltage loop, an internal current loop, and a frequency modulator: the voltage loop is responsible for regulating the output voltage, the current loop makes the system controllable and limits the input current, and the modulator provides robustness against variations in resonant component values. The enhanced configuration introduces the output inductor current as a feed-forward term and clearly improves the transient response to fast load changes. The theoretical design of these control schemes is performed systematically by first deriving their small-signal models and second using Bode diagram analysis. The actual performance of the proposed control schemes is experimentally validated by testing on a laboratory prototype.Peer ReviewedPostprint (author's final draft

Resonant Power Converters

Recently, DC/DC resonant converters have received much research interest as a result of the advancements in their applications. This increase in their industrial application has given rise to more efforts in enhancing the soft-switching, smooth waveforms, high-power density, and high efficiency features of the resonant converters. Their suitability to high frequency usage and capacity to minimize switching losses have endeared them to industrial applications compared to the hard-switching conventional converters. However, studies have continued to suggest improvements in certain areas of these converters, including high-power density, wide load variations, reliability, high efficiency, minimal number of components, and low cost. In this chapter, the resonant power converters (RPCs), their principles, and their classifications based on the DC-DC family of converters are presented. The recent advancements in the constructions, operational principles, advantages, and disadvantages were also reviewed. From the review of different topologies of the resonant DC-DC converters, it has been suggested that more studies are necessary to produce power circuits, which can address the drawbacks of the existing one

Simple Lossless Inductive Snubbers-Assisted Series Load Resonant Inverter Operating under ZCS-PDM Scheme for High-Frequency Induction Heating Fixed Roller

This paper presents a high-frequency pulse-density-modulated (PDM) soft-switching series load resonant inverter for use in induction heating (IH) fixed roller applications, which is used in copy and printing machines. The proposed simple high-frequency resonant inverter uses an asymmetrical pulse pattern PDM control scheme to achieve complete zero-current soft-switching commutations over a wide output range of input power regulation. Additionally, when the printer toner requires operation in very light load conditions, this causes difficulty in achieving zero-voltage or zero-current soft-switching operations in the IH high-frequency resonant inverters with pulse frequency modulation or pulse width modulation control schemes. The proposed resonant inverter demonstrates the capability to accomplish highly efficient power conversions. In this work, a fixed roller for printing machines is developed for doing experiments to verify the efficiency of the proposed circuit topology and its PDM control schemes. The inverter’s steady-state and transient operating principles are analyzed based on the proposed control strategy at a high-frequency PDM. Operating conditions such as power loss analysis, power conversion efficiency and temperature rise characteristics of the proposed inverter are presented and analyzed through experimental results. Finally, from a practical viewpoint, a comparative study of a conventional halogen lamp heater and the proposed IH fixed roller is deliberated.publishedVersio

Load Adaptive Modulation to Heat Non-Ferromagnetic Material

Department of Electrical EngineeringInduction heating (IH) cooktops are popular to heat various vessels fast and safely in the kitchen. Conventional IH cooktop system have been developed to heat the vessel of ferromagnetic materials. Because the vessel of non-ferromagnetic materials has low-resistance which induces large resonant current to power switches in series resonant IH inverters. Hence, the rated power cannot be transferred to the vessel due to overcurrent which is higher the rated switch current. In this thesis, a load adaptive modulation (LAM) method is proposed to heat the vessel of non-ferromagnetic and ferromagnetic materials in a single IH burner. The LAM can change the magnitude of the input voltage of the IH working coil and the operating frequency induced to the IH working coil according to the resistance of the vessel. The operational principle and the design method are analyzed to implement the proposed LAM and its power control. The validity of the design method and the control algorithm is experimentally verified using a 2 kW prototype series resonant full-bridge inverter with the IH working coil.ope

A Comprehensive Study of Capacitive Loaded Resonant Converter Topologies for Charging Applications

Resonant converters (RCs) are perceiving global interests of the research community for its eminent contribution in design of many industrial and commercial applications. Rich literature and well-established technology is available to define the role of RCs in such applications where the load is predominantly passive and resistive. However in applications like charging, the nature of load is often interpreted as capacitive and the knowledge on how a RC reciprocates to such variable, non linear load is limited. Motivated by this, the paper investigates about 25 capacitive loaded resonant structures and each of them is thoroughly analyzed to evaluate various key parameters like the output current, peak input current,  and current gain. A comparative study is done to categorize and organize these topologies in regard to each of the said parameters.  This provides a quick overview of various resonant converter topologies and helps designers to choose a structure that may fit their application. To this base knowledge, the study is further narrowed down to find suitable topology for charging application and accordingly proposed a novel fourth-order RC topology called LA7. A hardware prototype was built to compare and validate the simulated and measured performances

Induction heating converter's design, control and modeling applied to continuous wire heating

Induction heating is a heating method for electrically conductive materials that takes advantage of the heat generated by the Eddy currents originated by means of a varying magnetic field. Since Michael Faraday discovered electromagnetic induction in 1831, this phenomena has been widely studied in many applications like transformers, motors or generators' design. At the turn of the 20th century, induction started to be studied as a heating method, leading to the construction of the first industrial induction melting equipment by the Electric Furnace Company in 1927. At first, the varying magnetic fields were obtained with spark-gap generators, vacuum-tube generators and low frequency motor-generator sets. With the emergence of reliable semiconductors in the late 1960's, motor-generators were replaced by solid-state converters for low frequency applications. With regard to the characterization of the inductor-workpiece system, the first models used to understand the load's behavior were based on analytical methods. These methods were useful to analyze the overall behavior of the load, but they were not accurate enough for a precise analysis and were limited to simple geometries. With the emergence of computers, numerical methods experienced a tremendous growth in the 1990's and started to be applied in the induction heating field. Nowadays, the development of commercial softwares that allow this type of analysis have started to make the use of numerical methods popular among research centers and enterprises. This type of softwares allow a great variety of complex analysis with high precision, consequently diminishing the trial and error process. The research realized in last decades, the increase in the utilization of numerical modeling and the appearance and improvement of semiconductor devices, with their corresponding cost reduction, have caused the spread of induction heating in many fields. Induction heating equipments can be found in many applications, since domestic cookers to high-power aluminum melting furnaces or automotive sealing equipments, and are becoming more and more popular thanks to their easy control, quick heating and the energy savings obtained. The present thesis focuses on the application of induction heating to wire heating. The wire heating is a continuous heating method in which the wire is continuously feeding the heating inductor. This heating method allows high production rates with reduced space requirements and is usually found in medium to high power industrial processes working 24 hours per day. The first chapters of this study introduce the induction heating phenomena, its modeling and the converters and tanks used. Afterwards, a multichannel converter for high-power and high-frequency applications is designed and implemented with the aim of providing modularity to the converter and reduce the designing time, the production cost and its maintenance. Moreover, this type of structure provides reliability to the system and enables low repairing times, which is an extremely interesting feature for 24 hours processes. Additionally, a software phase-locked loop for induction heating applications is designed and implemented to prove its flexibility and reliability. This type of control allows the use of the same hardware for different applications, which is attractive for the case of industrial applications. This phase-locked loop is afterwards used to design and implement a load-adaptative control that varies the references to have soft-switching according to load's variation, improving converter's performance. Finally, the modeling of a continuous induction wire hardening system is realized, solving the difficulty of considering the mutual influence between the thermal, electromagnetic and electric parameters. In this thesis, a continuous process is modeled and tested using numerical methods and considering converter's operation and influence in the process.Postprint (published version