Diego Puyal

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.

Frequency-dependent resistance in Litz-wire planar windings for domestic induction heating appliances

In this paper, the frequency-dependent resistance in Litz-wire planar windings for domestic induction heating appliances is analyzed. For these inductors, in which the size is not an essential constraint, an analytical model is developed based on the superposition of different loss effects in the wire. Eddy current losses, including conduction losses and proximity-effect losses, both internal and external, were considered and modeled. The magnetic field necessary to evaluate the external proximity losses is as well analytically calculated considering the complete winding and load properties. To verify this model and its limitations, several inductors with different wires and numbers of turns were constructed and results with both non-loaded and loaded inductors are compared with theoretical predictions.

Efficiency optimization in ZVS series resonant inverters with asymmetrical voltage-cancellation control

This paper presents a time-domain analysis and a computerized search algorithm for optimizing the efficiency in zero-voltage switching (ZVS) full-bridge series resonant inverters with asymmetrical voltage-cancellation (AVC) control for different load quality factors. The optimum AVC control found allows all the switches to be turned on with zero voltage with the minimum switching frequency. In order to minimize losses, the switching frequency is kept as close as possible to resonance. The optimum AVC control is compared with previous fixed or narrow frequency range control strategies to show that it improves performance over all the output power range for different loads. The detailed steady-state analysis carried out here increases the precision of the first-harmonic analysis of a previous work, which is especially important with distorted output currents due to low load quality factors or highly asymmetrical modulation strategies. The theoretical results are verified experimentally.

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

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.

Frequency-dependent resistance in Litz-wire planar windings for all-metal domestic induction heating appliances

In this paper the frequency-dependent resistance in Litz-wires planar windings for all-metal domestic induction heating appliances is analyzed. For planar inductors, where size is not an essential constraint, an analytical model is developed based on the superposition of different loss effects in the wire, several inductors were constructed and results with both nonloaded and loaded inductors are compared with theoretical predictions

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.

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.

Domestic induction cooking with a new loads multiplexing topology using mechanical switches

In this paper, a novel loads multiplexing topology is proposed in order to obtain a cost effective solution, presenting high efficiency, high utilization factor of electronics, and a reduction in the system components. The topology based on two half bridge inverters and they are multiplexed for feeding four loads using six SPDT (single pole double throw electromechanical relay), also the same topology is configured for feeding three coils using four SPDT relays. The operation modes and the control strategies are explained; also the main benefits of the proposed system are discussed in details. The proposed topology is designed and tested experimentally with a prototype for induction cooking system.