Analysis of acoustic noise spectrum of domestic induction heating systems controlled by phase-accumulator modulators

In domestic induction heating (IH) applications, the modulation technique applied to the inverter has a high influence on the acoustic noise emissions. These noise emissions must be avoided since they may be audible and annoying to the final user. This paper analyzes the acoustic noise emissions that appear when a series half-bridge resonant inverter is operated with a phase-accumulator based modulator. This modulation technique has the advantage of operating in the frequency domain, and it is compared with the classical PWM modulator regarding the audible noise generated. The frequencies of the tones in the acoustic noise spectrum are theoretically calculated from the parameters of the phaseaccumulator based modulator. The SFM (Spectral Flatness Measure) is used to quantify the number of cases in which tones are generated by the modulation. Two techniques are applied to the phase-accumulator based modulator and their effect is tested. Theoretical results are experimentally verified

Series-Resonant Matrix Inverter with Asymmetrical Modulation for Improved Power Factor Correction in Flexible Induction Heating Appliances

Induction heating appliance operation is constrained by the nonlinear pot material behavior under the generated magnetic field. The equivalent load seen by the inverter varies with the intensity of the field, meaning that this variation is dependent on the mains voltage. In flexible-surface induction cooktops, this fact is combined with a high coil number and different pots to be powered simultaneously, increasing the complexity to control the transmitted power while maintaining proper mains current consumption. In this article, two noncomplementary asymmetrical modulations with in-cycle parameter variation are proposed for improved power factor correction while avoiding the need for switching frequency variation and intermodulation noise in multiload systems. The proposed strategies are analyzed and experimentally tested using a 3.6 kW multi-inverter prototype featuring five induction coils

A new switching frequency modulation scheme for EMI reduction in multiconverter topology

This paper presents a modulation scheme in order to reduce conducted Electromagnetic Interference (EMI) generated by modular power converters with parallel topology. The proposed scheme is based on a combination of interleaving and Switching Frequency Modulation (SFM) techniques. The objective of this modulation scheme is to cancel certain harmonics of EMI and to reduce the amplitude of the remaining harmonics. The proposed scheme has been implemented in a field programmable gate array and a four channel parallel buck converter has been used in order to verify it. A significant EMI reduction has been obtained in comparison to use the interleaving and Switching Frequency Modulation separately.Peer ReviewedPostprint (published version

Output voltage estimation of a half-bridge inverter for domestic induction heating applications

The power supplied to a vessel by a domestic induction-heating appliance is strongly dependent on several parameters the designer of the system has no control over: the type and the size of the vessel, misalignments between the pot and the inductor, temperatures, etc. A reliable estimation of the power is essential to ensure that the home appliance works under the expected conditions and the user experience is suitable. Furthermore, any reduction of hardware is totally welcome by consumer-electronics manufacturers. In this work, two methods to estimate the output voltage of a half-bridge inverter without digitizing it with an analog-to-digital converter are proposed and the effects that this estimation has on the power calculation are evaluated. Both methods are implemented and experimentally verified in a real prototype with an FPGA (Field-Programmable Gate Array)

Contribution to conducted EMI reduction in multiconverter topology

This paper contributes to the conducted EMI reduction generated by switched power converters operating in multiconverter arrangement. The EMI reduction is achieved by means of the combination of two techniques: interleaving and switching frequency modulation. The effectiveness of such methods in terms of EMI reduction is experimentally validated in a four channel parallel buck converter. The technique that provides the best attenuation results is identified. Finally, special attention has been paid to possible undesired side-effects produced by these techniques. For this reason the converter efficiency and output voltage ripple are evaluated.Peer ReviewedPreprin

Conductance control for electromagnetic-compatible induction heating appliances

The design requirements of induction hobs are strongly restricted by efficiency, heating performance, cost, the generation of acoustic noise, and electromagnetic compatibility (EMC). These two latter topics, cost and EMC, motivated the research presented in this article. The different levels at which the equivalent load of the induction hob is excited generate a variation of the equivalent impedance throughout the grid period even if all the other parameters are kept constant. This can cause a nonsinusoidal consumption of the grid current which goes against the compliance with EMC standards. This article proposes an online controller which controls the conductance seen by the inverter by only modifying the switching frequency throughout the bus period. This greatly reduces the harmonic distortion of the grid current, no matter what is the type of the vessel used. Moreover, it requires neither power-factor correction rectifiers nor any additional circuitry and it has a faster dynamic response with respect to the traditional solutions used in induction hobs due to its higher bandwidth

Interleaving and switching pattern modulation to conducted EMI reduction

This paper explores new techniques to reduce the conducted EMI generated by switched power converters operating in multiconverter arrangement. These techniques are based in the combined application of interleaving and the modulation of some characteristics of the switching patterns. The effectiveness of such methods in terms of EMI reduction is theoreticaly developed and experimentally validated in a four channel parallel buck converter operating in closed loop. The technique that provides the best attenuation results is identified. Finally, undesired sideeffects produced by these techniques, such as an increase in the output voltage ripple, are evaluated.Peer ReviewedPostprint (published version

Industrial and Technological Applications of Power Electronics Systems

The Special Issue "Industrial and Technological Applications of Power Electronics Systems" focuses on: - new strategies of control for electric machines, including sensorless control and fault diagnosis; - existing and emerging industrial applications of GaN and SiC-based converters; - modern methods for electromagnetic compatibility. The book covers topics such as control systems, fault diagnosis, converters, inverters, and electromagnetic interference in power electronics systems. The Special Issue includes 19 scientific papers by industry experts and worldwide professors in the area of electrical engineering

Multi-Frequency Modulation and Control for DC/AC and AC/DC Resonant Converters

Harmonic content is inherent in switched-mode power supplies. Since the undesired harmonics interfere with the operation of other sensitive electronics, the reduction of harmonic content is essential for power electronics design. Conventional approaches to attenuate the harmonic content include passive/active filter and wave-shaping in modulation. However, those approaches are not suitable for resonant converters due to bulky passive volumes and excessive switching losses. This dissertation focuses on eliminating the undesired harmonics from generation by intelligently manipulating the spectrum of switching waveforms, considering practical needs for functionality.To generate multiple ac outputs while eliminating the low-order harmonics from a single inverter, a multi-frequency programmed pulse width modulation is investigated. The proposed modulation schemes enable multi-frequency generation and independent output regulation. In this method, the fundamental and certain harmonics are independently controlled for each of the outputs, allowing individual power regulations. Also, undesired harmonics in between output frequencies are easily eliminated from generation, which prevents potential hazards caused by the harmonic content and bulky filters. Finally, the proposed modulation schemes are applicable to a variety of DC/AC topologies.Two applications of dc/ac resonant inverters, i.e. an electrosurgical generator and a dual-mode WPT transmitter, are demonstrated using the proposed MFPWM schemes. From the experimental results of two hardware prototypes, the MFPWM alleviates the challenges of designing a complicated passive filter for the low-order harmonics. In addition, the MFPWM facilitates combines functionalities using less hardware compared to the state-of-the-art. The prototypes demonstrate a comparable efficiency while achieving multiple ac outputs using a single inverter.To overcome the low-efficiency, low power-density problems in conventional wireless fast charging, a multi-level switched-capacitor ac/dc rectifier is investigated. This new WPT receiver takes advantage of a high power-density switched-capacitor circuit, the low harmonic content of the multilevel MFPWMs, and output regulation ability to improve the system efficiency. A detailed topology evaluation regarding the regulation scheme, system efficiency, current THD and volume estimation is demonstrated, and experimental results from a 20 W prototype prove that the multi-level switched-capacitor rectifier is an excellent candidate for high-efficiency, high power density design of wireless fast charging receiver