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 phaseaccumulator 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 phase-accumulator 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.
The equivalent load of an induction hob is strongly dependent on many parameters such as the switching frequency, the excitation level, the size, type and material of the vessel, etc. However, real-time methods with the ability to capture the variation of the load with the excitation level have not been proposed in the literature. This is an essential issue as most of the commercial induction hobs are based on an ac bus voltage arrangement. This paper proposes a method based on a phase sensitive detector that offers an online tracking of the equivalent impedance for this type of arrangements. This algorithm enables advanced control functionalities such as clustering of vessels, material recognition and premature detection of ferromagnetic saturation, among others. After simulation and experimental validation, the method is implemented into a prototype with a system-on-chip (SoC) to verify its real-time behavior. The proposed approach is applied to different real-life situations which prove its great performance and applicability.
Successive approximation register (SAR) analog-to-digital converter (ADC) manufacturers recommend the use of a driver amplifier to achieve the best performance. When a driver amplifier is not used, the conversion speed is severely penalized because of the need to meet the settling time constraint. This paper proposes a simple digital correction method to raise the performance (conversion speed and/or accuracy) when the acquisition chain lacks a driver amplifier. It is intended to reduce the cost, size and power consumption of the conditioning circuit while maintaining acceptable performance. The method is applied to the measurement of the output power delivered by a series resonant inverter for domestic induction heating.
Dual half-bridge inverter with common resonant capacitor is a cost-effective solution that is often used in induction heating appliances. In this topology, a simple and reliable calculation of the power supplied by both inverters would involve measuring the output voltages, both load currents and the resonant-capacitor voltage. This study presents a real-time implementation of two methods to calculate the output powers without measuring the voltage of the resonant capacitor. Simulations are performed to confirm the validity of the methods, which are also experimentally verified through a high-level synthesis implementation in a real prototype with a system-on-chip.
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