Carlos Bernal

Design of Class E Amplifier With Nonlinear and Linear Shunt Capacitances for Any Duty Cycle

One of the main advantages of class E amplifiers for RF and microwave applications relies on the inclusion of a shunt capacitance in the tuned output network. At high frequencies, this capacitance is mainly provided by the output parasitic capacitance of the device with perhaps a linear external one for fine adjustments. The devices output capacitance is nonlinear and this influences the design parameters, frequency limit of operation, and performance of the class E amplifier. This paper presents a design method for the class E amplifier with shunt capacitance combining a nonlinear and linear one for any duty cycle, any capacitances nonlinear dependence parameters, and any loaded quality factor of the tuned network. Nonlinear design with possibly different duty cycles is of relevance to maximize power or, alternatively, frequency utilization of a given device. Experimental, simulated, and compared results are presented to prove this design procedure

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.

Induction cooking systems with single switch inverter using new driving techniques

In this paper, some novel and modified driving techniques for a single switch zero voltage switching (ZVS) topology are introduced. These medium/high frequency and digitally synthesized driving techniques can be applied to decrease the dangers of peak currents that may damage the switching circuit when switching in out of nominal conditions. The technique is fully described and evaluated experimentally in a 2500W prototype intended for a domestic induction cooking application.

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.

Exact analysis of a simple class E circuit version for device characterization purposes

The mathematical exact analysis of a simple class E high-efficiency switching mode tuned power amplifier is performed. The simple network only contains one capacitor and one inductor. Switch duty-cycle and Q cannot be chosen independently, and thus this circuit is only of interest for applications in which a high harmonic content in the load is permitted. In this paper, this circuit is used as a test bench for extracting, with no need for optimization, the parameters of a simple FET output port model in high frequency switching conditions. This method is a quick way to predict if a transistor will be useful in a class E application. Experimental measurements showing good agreement with theoretical results are presented.

Dynamic Model of Class-E Inverter With Multifrequency Averaged Analysis

This paper presents a novel dynamic model of a single-switch class-E inverter. Both the transient and steady-state behaviors of main variables are derived using a multifrequency averaged (MFA) modeling method. The analysis of the boundary conditions reveals that, under some approximations, the performance of the generalized averaged model is close to that of the “exact” or topological one. A detailed analysis of the errors and limitations of the model has been derived. Contrary to other class-E inverter models, based on the input-output behavioral black-box approach, the MFA modeling technique leads to a large-signal knowledge-based model. The advantage of this type of model is that it is applicable to a wide set of analysis and control design tools. The proposed model is verified by comparing the MFA, state-space, and experimental results, showing good agreement for the dynamic behavior of the inverter under supply voltage modulation and also for the frequency and phase modulation of the input control signal.

Output power capability of class-E amplifiers with nonlinear shunt capacitance

The nonlinearity of the shunt capacitance in a HF class-E power amplifier produces a switch peak voltage higher than expected, in particular at frequencies where the shunt capacitance is solely provided by the device parasitic. Peak values have to be accurately estimated in order to avoid device breakdown and to be able to choose a convenient and not too overestimated transistor for the application. Furthermore, the nonlinear behavior modifies the output power capability of a device in class-E operation. When dealing with a lossy nonlinear device, reducing the ON duty cycle of a design bellow 0.5 might help achieving higher frequencies in ideal class-E conditions, whereas increasing it results in higher output power and efficiency. For the first time, an analysis of peak voltage values and output power capability of a class-E amplifier is presented for several duty-cycles and nonlinearity parameters. Experimental results show good agreement with numerical analysis.

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.

Ultracapacitor-based plug & play energy-recovery system for elevator retrofit

Vertical transportation is a promising field in terms of efficiency improvement opportunities. Several manufacturers are working on the development of new and efficient elevator lifts based on energy-recovery schemes. This paper is focused on the retrofit of already existing inverter-based non-efficient elevator actuators. This purpose is achieved through a) the connection of only two wires to the DC bus of the existing inverter, and b) a very simple but robust control based on several voltage hysteresis-bands. Simulation and experimental results show the validity of the approach.

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.