Juan B. Ejea

Improving the Efficiency of IGBT Series-Resonant Inverters Using Pulse Density Modulation

This paper analyzes a high-power (50 kW) high-frequency (150 kHz) voltage-fed inverter with a series-resonant load circuit for industrial induction heating applications, which is characterized by a full bridge inverter made of insulated-gate bipolar transistor and a power control based on pulse density modulation (PDM). This power control strategy allows the inverter to work close to the resonance frequency for all output-power levels. In this situation, zero-voltage switching and zero-current switching conditions are performed, and the switching losses are minimized. An additional improvement of inverter efficiency is achieved by choosing appropriate values of the modulation index. Results are verified experimentally using a prototype for induction hardening applications. A comparative study between the PDM and the classical power control by frequency variation will be made.

Improving the Reliability of Series Resonant Inverters for Induction Heating Applications

This paper analyzes a high-power (100-kW) high-frequency (50-kHz) voltage-fed inverter with a series resonant load circuit for industrial induction heating applications which is characterized by a full-bridge inverter composed of isolated-gate bipolar transistors and a new power control based on phase-shift (PS) control. This power control circuit incorporates a load-adaptive variable-frequency controller and automated blanking time management in order to allow the inverter to work in zero-voltage switching for all output power levels and load conditions. An important improvement of the inverter reliability is achieved by choosing an appropriate and novel switching sequence for the PS inverter. The results are verified experimentally using a prototype for induction hardening applications. A comparative study between the proposed and standard PS power control will be made.

Soft switching bidirectional converter for battery discharging-charging

This paper presents the results of a project that looked after a high efficiency bidirectional converter which could be used as a battery discharge/charge regulator when the bus voltage is above the battery voltage. High efficiency, high stability and simplicity are the main goals, no galvanic isolation is required. Taking into account all these parameters, our proposed solution has been a new topology based on a boost converter with coupled inductors. The use of a bidirectional converter reduces the mass of the overall charge/discharge subsystem and lowers cost and component count. In the project, its use is intended for space applications, but telecom, automotive or similar applications can also benefit of this new concept.

Comparative Study of a Single Inverter Bridge for Dual-Frequency Induction Heating Using Si and SiC MOSFETs

The induction surface hardening of parts with nonuniform cylindrical shape requires a multifrequency process in order to obtain a uniform surface hardened depth. This paper presents an induction heating high power supply composed by a single inverter circuit and a specially designed output resonant circuit. The whole circuit supplies simultaneously both medium- and high-frequency power signals to the heating inductor. An initial study is made to select the most appropriated topology for this application. The resonant output circuit is analyzed, and a design procedure is presented. The selected inverter operation is described and simulated. Simulations are experimentally verified on a 10-kW dual-frequency resonant inverter operating at 10 and 100 kHz using MOSFETs of silicon (Si) and silicon carbide (SiC) technology. A comparative study is presented based on the measurements of power losses and the energy efficiency of the inverter using both types of MOSFETs.

Small-signal modeling of a controlled transformer parallel regulator as a multiple output converter high efficient post-regulator

This paper presents a post-regulator based on the use of a controlled transformer, which adds or subtracts an additional voltage to the output filter of a converter in order to regulate its output voltage. So, their actuation is complementary to that of more known post-regulators, such as the magnetic amplifier (magamp) and synchronous switch post-regulator (SSPR), because the regulation is achieved by controlling the voltage across the filter inductor instead of its charge time. Besides, the post-regulator processes the power in parallel to the one flowing from input to output and only handles a percentage of it. The post-regulation by controlled transformer is suitable of being employed in any isolated PWM power converter and combines a good efficiency and the easiness of design of classical switched power supplies. The work describes the post-regulation strategy for obtaining two outputs independently regulated, and presents a model to obtain the control transfer function and the cross-impedance expressions.

Control circuit design of the L-LC resonant inverter for induction heating

In this article, the frequency variation control strategy for an induction heating L-LC resonant inverter is analyzed. The control consists of three loops, which are analyzed and reduced to their corresponding small-signal block diagrams. From these diagrams, the optimal structure of the compensation network and the design boundaries for first order closed-loop response are derived. The special case of phase limitation is analyzed because it is unstable in open-loop operation. Finally the implementation of the control circuit is described and experimental results are shown.

Influence of the Parasitic Solar Array Capacitance in the Sequential Switching Shunt Series Regulator

This work deals with the effect produced by the solar array capacitance on the sequential switching shunt regulator, S4R. In the past, silicon solar cells were widely used with practically no effect upon the solar array regulator, so that the solar array capacitance was a minor problem in the design. Nowadays, the usage of triple junction GaAs solar cells with larger parasitic capacitance has prompted new questions about power losses, steady state and dynamic responses in the S4R. In this work, the effect of the solar array capacitance is quantified by analytical models. Simulations and experimental prototyping support the models

Bidirectional High-Efficiency Nonisolated Step-Up Battery Regulator

The design and results of a high-efficiency high-power (5 kW) nonisolated bidirectional dc-dc converter is presented. High stability due to minimum phase behavior is an additional benefit of the topology. The converter is a new boost with output filter where input and output inductors are coupled. This converter is useful with any system that needs to charge and discharge backup batteries and can be applied in space, automotive, and telecom power systems.

Bidirectional Coupled Inductors Step-up Converter for Battery Discharging-Charging

The present paper shows the preliminary results of a project that looks for a high power, high efficiency bidirectional step-up converter which could be used as a battery discharge/charge regulator. High efficiency and low mass are the main goals, no galvanic isolation is required and MTBF should be as large as possible. Taking into account all these parameters our proposed solution has been a new topology based on a boost converter with output filter and that couples input and output inductor. The use of a bidirectional converter reduces the mass of the overall charge/discharge subsystem and lowers cost and component count. Stability has been studied theoretically and verified experimentally

High power passive soft switched interleaved boost converters

The present project was developed in order to find a high power (/spl ges/5 kW), high efficiency step-up converter which could be used as a battery discharge regulator. Efficiency should be higher than 97%, mass should be lower than 2.5 kg, no galvanic isolation was required and MTBF should be as large as possible. Taking into account all these parameters our proposed solution has been two interleaved boost converters with passive soft switching.