I. Millan

Load-Adaptive Control Algorithm of Half-Bridge Series Resonant Inverter for Domestic Induction Heating

Domestic induction cookers operation is based on a resonant inverter which supplies medium-frequency currents (20-100 kHz) to an inductor, which heats up the pan. The variable load that is inherent to this application requires the use of a reliable and load-adaptive control algorithm. In addition, a wide output power range is required to get a satisfactory user performance. In this paper, a control algorithm to cover the variety of loads and the output power range is proposed. The main design criteria are efficiency, power balance, acoustic noise, flicker emissions, and user performance. As a result of the analysis, frequency limit and power level limit algorithms are proposed based on square wave and pulse density modulations. These have been implemented in a field-programmable gate array, including output power feedback and mains-voltage zero-cross-detection circuitry. An experimental verification has been performed using a commercial induction heating inverter. This provides a convenient experimental test bench to analyze the viability of the proposed algorithm.

Efficiency-Oriented Design of ZVS Half-Bridge Series Resonant Inverter With Variable Frequency Duty Cycle Control

The efficiency of zero voltage switching half-bridge series resonant inverter can be decreased under certain load conditions due to the high switching frequencies required. The proposed variable frequency duty cycle (VFDC) control is intended to improve the efficiency in the medium and low output power levels because of the decreased switching frequencies. The study performed in this letter includes, in a first step, a theoretical analysis of power balance as a function of control parameters. In addition, restrictions due to snubber capacitors and deadtime, and variability of the loads have been considered. Afterward, an efficiency analysis has been carried out to determine the optimum operation point. Switching and conduction losses have been calculated to examine the overall efficiency improvement. VFDC strategy efficiency improvement is achieved by means of a switching-frequency reduction, mainly at low-medium power range, and with low-quality factor loads. Domestic induction heating application is suitable for the use of VFDC strategy due to its special load characteristics. For this reason, the simulation results have been validated using an induction heating inverter with a specially designed load.

Series-Resonant Multiinverter for Multiple Induction Heaters

Multiple-load and multiple-source systems are widely present in the current technology. These systems require controlling either the supplied voltage or power to several loads with different requirements simultaneously. As a consequence, the cost and size of the power stage may increase beyond the admissible limits for certain applications. Considering multiple-inductor loads, a novel series-resonant multiinverter topology is proposed to obtain a cost-effective and high-power density solution. The converter is based on a common inverter block and a resonant-load block. The performed analysis includes the description of the operation modes and the control strategy analysis. Domestic induction heating has been considered for application due to its special cost and size requirements, and the extensive inductor use. The proposed converter has been designed and validated experimentally through a prototype, which includes the power converter and the field-programmable gate array-based control architecture.

An FPGA-Based Digital Modulator for Full- or Half-Bridge Inverter Control

This letter presents a powerful tool for the study of the performance of control strategies and consists of a versatile modulator capable of synthesizing triggering signals for various fixed-frequency and pulse width modulation controls based on a digital implementation. Among many other advantages, the approach provides a straightforward, flexible, and rapid means for prototyping because of its reprogramming capability and user-friendly interface. Field programmable gate array was chosen as the hardware platform because of the additional benefits it provides, such as high operating frequency and parallel processing capabilities. Several practical examples of its application demonstrate the utility of this approach

Analysis and Modeling of Planar Concentric Windings Forming Adaptable-Diameter Burners for Induction Heating Appliances

Adaptable-diameter inductors are being implemented in domestic induction hobs in order to increase the range of suitable pot diameters and to achieve the better use of the rated power electronics. Such inductors are arranged by means of several concentric planar windings, usually up to three units, each one of them comprising several litz-wire turns. Currently, one resonant inverter is dedicated to supplying each winding. In this paper, a characterization of these inductors in terms of their impedance matrix is derived. The self-impedance of each winding and those caused by the coupling between them are analyzed. The contribution of this paper lies in the understanding and analysis of the coupling between concentric windings. Unlike transformers, where ideally the magnetic path consists of a lossless material, in domestic induction heating, the vessel is part of the flux path. Consequently, the off-diagonal terms of the impedance matrix have been generalized because they have a resistive component in addition to the classical mutual-inductance component. The analysis presented in this paper also includes the losses in the litz wires generated by the currents in each winding as well as the losses produced by the windings over their concentric neighbors.

Improved Performance of Half-Bridge Series Resonant Inverter for Induction Heating with Discontinuous Mode Control

In this paper, a study of the Discontinuous current Mode (DM) control applied to a half-bridge series resonant inverter for domestic induction heating is presented. The proposed control is interesting for this application because it exhibits reduced switching losses and the output power control is linear with the switching frequency. Considering that the load is disconnected from the source during part of the switching period, with DM control. A time-domain analysis method is proposed to obtain the analytical expression of the output power, the capacitor voltage and load current. The validity of the analytical expression is checked through simulation. Finally, an experimental comparison of efficiency between traditional controls and the DM control is performed for the induction heating application. In the low power range the efficiency of DM control is higher than traditional schemes.

Versatile High-Frequency Inverter Module for Large-Signal Inductive Loads Characterization Up to 1.5 MHz and 7 kW

This paper presents the challenges encountered and the solutions adopted during the construction of a versatile voltage-fed high-frequency series-resonant half-bridge inverter module. It is used in the large-signal power generator of an inductive load characterization test-bench operating from 1 kHz up to 1.5 MHz and up to 7-kW output power for a variety of loads. Square wave operation of the module is established slightly above resonance under zero voltage switching conditions. Output power is controlled by means of a variable dc bus while resonant conditions are fixed by means of two adjustable capacitor banks. The control of every test-bench block and the triggering waveform generation is performed digitally with a field programmable gate array. Two prototype modules have been designed, constructed and evaluated for operation in half-bridge and full-bridge configurations showing rugged and stable operation under hazardous conditions such as voltage transients as high as dv/dt = 50 kV/mus at 1 MHz during the characterization of domestic induction heating loads.

A new dynamic electrical model of domestic induction heating loads

Traditionally the domestic induction heating load has been electrically modelled by means of the series connection of an energetic equivalent resistance and inductance. Due to the nonlinear nature of the load and the excitation dependence of these equivalent parameters, which are only valid for a given waveform, there exists a strong lack of accuracy in certain situations and applications. In case precise temporal waveform is required a more complex and complete model reproducing dynamic effects must be develop. In this paper a well-known topology for the frequency dependent modelling in the linear case is modified obtaining the Foster series nonlinear network (FSNL) which is able to include both nonlinear and frequency dependent effects providing a complete dynamic behavioural load model. Results are presented for a typical induction heating load which has been characterized using a large-signal and wide frequency (12 kW- 1.5 MHz) measurement testbech. Optimization procedure is explained and performance is tested in the time domain in order to validate the modelling approach.

Multiple-output resonant inverter topology for multi-inductor loads

Multiple-inductor systems are widely present in the current technology. These systems require controlling either the supplied voltage or power to several loads with different requirements simultaneously. As a consequence, the cost and size of the power stage may increase beyond the admissible limits for certain applications. Considering multiple-inductor loads, a novel multiple-output series resonant inverter (MOSRI) topology is proposed to obtain a cost-effective and high-power-density solution. The converter is based on a common inverter block and a resonant-load block. The performed analysis includes the description of the operation modes and the control strategy analysis. Domestic induction heating has been considered for application due to its special cost and size requirements, and the extensive inductor use. The proposed converter has been designed and validated experimentally through a prototype, which includes the power converter and the FPGA-based control architecture.

Methods and procedures for accurate induction heating load measurement and characterization

Current research topics in domestic induction heating field, such as the analytical description or the grey- box modelling of the impedance behaviour of the inductor- pot coupled system, require experimental measurements to be obtained in a variety of situations covering wideband frequency operation and output power conditions due to its nonlinear nature. Frequency values up to the MHz range and current levels as high as several tenths of amperes can be needed to get the required information to describe the operation in real-working conditions. While small-signal impedance measurements are easily achieved up to 1 MHz and above with commercial LCR meters, no commercial equipment provides the complete solution for the power, frequency and load quality factor ranges required under large-signal operation so a custom- made measurement testbench must be designed. The testbench design comprises the development of a specific hardware for load excitation and the definition of the characterization procedures to obtain accurate impedance measurements which are described in this paper using a high performance digital oscilloscope and standard power electronics probes.