Load Adaptive Modulation to Heat Non-Ferromagnetic Material

Department of Electrical EngineeringInduction heating (IH) cooktops are popular to heat various vessels fast and safely in the kitchen. Conventional IH cooktop system have been developed to heat the vessel of ferromagnetic materials. Because the vessel of non-ferromagnetic materials has low-resistance which induces large resonant current to power switches in series resonant IH inverters. Hence, the rated power cannot be transferred to the vessel due to overcurrent which is higher the rated switch current. In this thesis, a load adaptive modulation (LAM) method is proposed to heat the vessel of non-ferromagnetic and ferromagnetic materials in a single IH burner. The LAM can change the magnitude of the input voltage of the IH working coil and the operating frequency induced to the IH working coil according to the resistance of the vessel. The operational principle and the design method are analyzed to implement the proposed LAM and its power control. The validity of the design method and the control algorithm is experimentally verified using a 2 kW prototype series resonant full-bridge inverter with the IH working coil.ope

A describing function for resonantly commutated H-bridge inverters

Abstract—The paper presents the derivation of a describing function to model the dynamic behavior of a metal oxide semiconductor field effect transistor-based, capacitively commutated H-bridge, including a comprehensive explanation of the various stages in the switching cycle. Expressions to model the resulting input current, are also given. The derived model allows the inverter to be accurately modeled within a control system simulation over a number of utility input voltage cycles, without resorting to computationally intensive switching-cycle level, time-domain SPICE simulations. Experimental measurements from a prototype H-bridge inverter employed in an induction heating application, are used to demonstrate a high degree of prediction accuracy over a large variation of load conditions is possible using the simplified model

Analysis and mitigation of dead time harmonics in the single-phase full-bridge PWM converters with repetitive controllers

In order to prevent the power switching devices (e.g., the Insulated-Gate-Bipolar-Transistor, IGBT) from shoot through in voltage source converters during a switching period, the dead time is added either in the hardware driver circuits of the IGBTs or implemented in software in Pulse-Width Modulation (PWM) schemes. Both solutions will contribute to a degradation of the injected current quality. As a consequence, the harmonics induced by the dead time (referred to as "dead time harmonics" hereafter) have to be compensated in order to achieve a satisfactory current quality as required by standards. In this paper, the emission mechanism of dead time harmonics in single-phase PWM inverters is thus presented considering the modulation schemes in details. More importantly, a repetitive controller has been adopted to eliminate the dead time effect in single-phase grid-connected PWM converters. The repetitive controller has been plugged into a proportional resonant-based fundamental current controller so as to mitigate the dead time harmonics and also maintain the control of the fundamental frequency grid current in terms of dynamics. Simulations and experiments are provided, which confirm that the repetitive controller can effectively compensate the dead time harmonics and other low-order distortions, and also it is a simple method without hardware modifications

Robust H8 design for resonant control in a CVCF inverter application over load uncertainties

CVCF (constant voltage, constant frequency) inverters are electronic devices used to supply AC loads from DC storage elements such as batteries or photovoltaic cells. These devices are used to feed different kinds of loads; this uncertainty requires that the controller fulfills robust stability conditions while keeping required performance. To address this, a robust H8 design is proposed based on resonant control to track a pure sinusoidal voltage signal and to reject the most common harmonic signals in a wide range of loads. The design is based on the definition of performance bounds in error signal and weighting functions for covering most uncertainty ranges in loads. Experimentally, the H8 controller achieves high-quality output voltage signal with a total harmonic distortion less than 2%Peer ReviewedPostprint (published version

A practical approach to switching-loss reduction in a large-capacity static VAr compensator based on voltage-source inverters

This paper presents a simple method for reduction of switching and snubbing losses in a large-capacity static VAr compensator (SVC) consisting of multiple three-phase voltage-source square-wave inverters. The proposed method is characterized by a “commutation capacitor” connected in parallel with each switching device. The commutation capacitor allows the SVC to perform zero-voltage switching, and to reduce switching losses. The electric charge stored in the commutation capacitor is not dissipated, but regenerated to the DC-link capacitor. Moreover, a soft-starting method for the SVC is also presented to avoid forming a short circuit across the commutation capacitor during startup. Experimental results obtained from a 10 kVAr laboratory setup are shown to verify the viability of the operating principle of the commutation capacitor </p

A comparative study of electric power distribution systems for spacecraft

The electric power distribution systems for spacecraft are compared concentrating on two interrelated issues: the choice between dc and high frequency ac, and the converter/inverter topology to be used at the power source. The relative merits of dc and ac distribution are discussed. Specific converter and inverter topologies are identified and analyzed in detail for the purpose of detailed comparison. Finally, specific topologies are recommended for use in dc and ac systems

Reducing switching losses through MOSFET-IGBT combination

This paper introduces a configuration aimed at switching losses reduction trough a power leg constructed by combining a MOSFET and an IGBT. The combined use of these different switches leads to the turn-on losses reduction trough the use of the faster freewheeling diode of the IGBT, and the turn-off losses reduction trough use of the MOSFET’s lower losses because of the lack of tailing current, typical for IGBT’s. The introduced leg structure can be used to build single phase – full bridge invertors or three phase inverters. The proposed leg is realized, experimented and validated

A 2-MHz 2-kW voltage-source inverter for low-temperature plasma generators: implementation of fast switching with a third-order resonant circuit

This paper presents a specially designed third-order resonant circuit intended to achieve fast switching operation for a voltage-source series-resonant inverter using four MOSFETs. The third-order resonant current superimposed on a sinusoidal load current helps to quickly charge or discharge the output capacitance of each MOSFET. This results not only in a reduction of the commutation period which is required to turn the MOSFET on and off, but also in an improvement of the displacement factor at the output of the inverter. Moreover, the third-order resonant circuit acts as a low-pass filter to suppress the parasitic oscillation between line inductance and stray capacitance. The viability and effectiveness of the third-order resonant circuit is verified by a 2 MHz 2 kW prototype inverter developed for a low-temperature plasma generator </p