A. Otin

Modeling of resonant inverters with high harmonic content using the extended describing function method

This paper analyzes the extended describing function technique (EDF) for modeling a resonant power converter applied to induction heating applications. Since in this specific application operating conditions may be far from resonance, this paper is focused on extending the model to several harmonics and verifying its validity range. The main goal is to obtain accurate control-to-power transfer functions which predict the resonant inverter small-signal behaviour. A simulation test bench is proposed and evaluated for measuring the open-loop duty cycle and frequency-to-power transfer function plots from time domain simulations of the switching model. Finally, the accuracy of the model is analyzed.

A design strategy for VHF filters with digital programmability

In this paper we report 2nd and 3rd-order Gm-C filters based on fully-balanced pseudo-differential continuous-time transconductors for applications in low-voltage systems over the VHF range. By using a 0.35 mum standard CMOS process, low-pass filter approximations have been implemented with a cut-off frequency programmability over the 40-200 MHz range, which confirm the feasibility of the proposed strategy in applications such as data storage systems and IF strips. The filters consume less than 4.8 mW per pole at 45 MHz from a 2V supply. The measured dynamic range was better than 53 dB at THD of 1% for all filters. The maximum active chip area is 0.025 mm2 per pole

Half-bridge resonant inverter for domestic induction heating based on silicon carbide technology

This paper presents a half-bridge SiC resonant inverter applied to induction heating for domestic appliances. The main objective of this work is to evaluate a SiC normally-ON VJFET as this device is commercially available. Two different references of this nO-JFET have been tested. This design is focused in the extension of the usable frequency range and efficiency over the parameters typically achieved in traditional Si-IGBT domestic induction heating inverters. The paper describes the design methodology to obtain the optimal switching conditions at higher frequency limits, considering SiC technology. Fundamental aspects to be taken into account are switching losses, the choice and convenience of snubber capacitors and the driver design. Comparative results for output power delivered to an induction heating coil and load are presented, verifying the advantages of SiC technology in improved efficiency at low output power range.

Silicon carbide JFET resonant inverter for induction heating home appliances

This paper presents a one switch silicon carbide JFET normally-ON resonant inverter applied to induction heating for consumer home cookers. The promising characteristics of silicon carbide (SiC) devices need to be verified in practical applications; therefore, the objective of this work is to compare Si IGBTs and normally-ON commercially available JFET in similar operating conditions, with two similar boards. The paper describes the gate circuit implemented, the design of the basic converter in ideal operation, namely Zero Voltage Switching (ZVS) and Zero Derivative Voltage Switching (ZVDS), as well as some preliminary comparative results for 700W and 2 kW output power delivered to an induction heating coil and load.

Digitally programmable CMOS transconductor for very high frequency

Abstract This paper describes a new approach for realizing digitally programmable VHF/UHF transconductors compatible with pure digital CMOS technologies. A programmable/tunable transconductor, based on a parallel connection of unit cascode cells, is used to implement a fully balanced current-mode G m – C integrator to operate over the 30–200 MHz range with more than 70 dB of dynamic range for 1% of THD.

Inverse-Based Power Control in Domestic Induction-Heating Applications

The wide variability of the load is the main problem of domestic induction-heating technology. The considered power control strategy should guarantee stability and regulation with a suitable response time and no overshoot independently of any perturbation or load variation. In addition to this, it has to ensure the operation under safety conditions. This paper is focused on the power control applied to one heating unit by means of continuous modulations. An inverse-based power controller is proposed for dealing with load uncertainties. The proposed power control combines different variable frequency pulsewidth modulation strategies (constant duty cycle, constant on-time, and constant off-time modulations) for reaching the target power level while minimizing the switching frequency. Finally, simulation and experimental results compared with other techniques in a prototype of an induction-heating system are presented in order to validate the proposed control strategy.

Half-bridge resonant inverter with SiC cascode applied to domestic induction heating

This paper presents an evaluation of a SiC MOSFET-JFET n-ON cascode structure for induction heating home appliances. In particular, the SiC cascode is applied in a resonant half-bridge inverter (HB-SCR). The cascode under test is comprised of a high power JFET n-ON in series with a low voltage MOSFET with a reduced conduction resistance. This small signal auxiliary device controls the conduction status of the main power JFET device. Operation modes for Zero Voltage Switching (ZVS) are analyzed. The obtained results are compared with those obtained with a similar resonant HB with n-ON SiC JFETs. The cascode structure applied to induction heating yields similar results in terms of conduction and switching than the classical resonant half-bridge. The improvement consists on a direct normally-off operation avoiding the need for additional security features and simplifying the driver circuit. Experimental verification of this stage applied to induction heating is presented in this paper opening future lines for driverless and snubberless inverters.

A 0.18 μm CMOS 3rd-Order Digitally Programmable G m -C Filter for VHF Applications

In this paper we report a 3rd-order Gm-C filter based on pseudo-differential continuous-time transconductors for applications in low-voltage systems over VHF range. By using a 0.18 μm pure digital CMOS process, a prototype low pass filter with -3 dB frequency programmable from 38 MHz to 213 MHz confirms the feasibility of the proposed filter in applications such as data storage systems.

Low-Voltage Differentiator for VHF Filtering

In this paper a Gm-C resonator circuit is proposed which is based on a new current-mode differentiating concept, compatible with low voltage and very high frequency operation.A prototype 4th-order 200 MHz band pass filter has been fabricated using a 0.8 μm CMOS process and shows a side-band rejection lower than −80 dB. This response confirms the feasibility of the proposed resonator in very-high frequency applications such as IF band pass sections of RF front-end circuits. The filter consumes less than 5.5 mW from a 2.7 V supply and the measured dynamic range is 57 dB at IM3 of 0.5%, where the active area is 0.12 mm2.

Decoupling output power control of two series resonant inverters sharing resonant capacitor for domestic induction heating

Domestic induction heating applications require an accurate control of the power delivered to the vessel to be heated, ensuring power topology operation under safety conditions. Particularly, this paper is focused on applying a power control of two induction heating loads in a dual-half bridge sharing a common resonant capacitor. This topology leads to a control strategy harder than the classical arrangement which features a dedicated resonant capacitor. A Phase Shift Square Wave Modulation (PSSWM) is performed to control the output powers of the vessels to be heated. Thus, the considered plant is a two-input two-output (TITO) system. The two control inputs are (fsw, θ) and the two outputs are (P1, P2). Since the transfer function matrix is not diagonal, the Relative Gain Array (RGA) methodology is used to analyze if a multi-loop control is feasible. Due to the fact that the system is strongly coupled a centralized control must be applied. Therefore, the aim of the paper is to apply a decoupling control to handle the interactions. Simulation and experimental results in an induction heating prototype are performed in order to validate the proposed control technique.