Switching Loss Reduction for an MMC-Fed AC/DC Converter

Medium-voltage connected ultra-fast chargers are getting more popular for charging electric vehicles with large battery capacities. Here, the solution based on a modular multilevel converter is more promising, since the isolation stage can be realized as a single medium-frequency transformer interconnecting the modular multilevel converter to a single-phase ac/dc converter. A new operating scheme is proposed for this converter, enabling zero-voltage switching and nearly zero-current switching across the entire load range. In contrast to the conventional phase-shift control method, the proposed scheme effectively reduces the reactive power through the ac/dc converter, leading to decreased turn-off switching losses in the ac/dc converter and a lower RMS current stress in the power path. A control scheme, integrating the operating principle, is developed for the modular multilevel converter. The method is verified through simulation and measurements on a scaled-down prototype. The results validate the theoretical analysis and practical feasibility of the proposed operating principle and the developed control scheme

Switching Loss Reduction for an MMC-Fed AC/DC Converter

Medium-voltage connected ultra-fast chargers are getting more popular for charging electric vehicles with large battery capacities. Here, the solution based on a modular multilevel converter is more promising, since the isolation stage can be realized as a single medium-frequency transformer interconnecting the modular multilevel converter to a single-phase ac/dc converter. A new operating scheme is proposed for this converter, enabling zero-voltage switching and nearly zero-current switching across the entire load range. In contrast to the conventional phase-shift control method, the proposed scheme effectively reduces the reactive power through the ac/dc converter, leading to decreased turn-off switching losses in the ac/dc converter and a lower RMS current stress in the power path. A control scheme, integrating the operating principle, is developed for the modular multilevel converter. The method is verified through simulation and measurements on a scaled-down prototype. The results validate the theoretical analysis and practical feasibility of the proposed operating principle and the developed control scheme

Extended operating region of modular multilevel converters using full-bridge sub-modules

This paper presents an application of modular multilevel converters to remove line-frequency transformers from ultrafast charging stations, reducing cost and volume. The converter analysis with full-bridge sub-modules enables an operating region, that converts a medium-voltage grid into a lower voltage DC-bus, ideal for charging batteries rapidly

Exploring the Boundaries and Effects of the Discontinuous Conduction Mode in H-Bridge Inverter with Dead-time

Dead-time of an H-bridge inverter can cause nonlinear error on the inverter output. In different switching cycles during a fundamental period, the effect of dead-time might be different. The H-bridge inverter in different switching cycles can operate in three kinds of modes, including soft-switching continuous conduction mode, discontinuous conduction mode and hard-switching continuous conduction mode. In addition, the discontinuous conduction mode can be further classified into four different types, which have not been fully studied in previous research. In this paper, four different kinds of switching cycle in the discontinuous conduction mode are investigated. The effect of the dead-time on the voltage error is elaborated and the boundaries of each kind of switching cycle are determined by a series of constraint functions. Based on the analysis, a complete mathematical expression of the voltage error in a fundamental period is given and it yields a better accuracy compared to previous publications

A Switched-Mode Power Amplifier for Ion Energy Control In Plasma Etching

Plasma etching is an important process in the semiconductor manufacturing process. In order to precisely control the ion energy for better process quality, a tailored pulse-shape voltage waveform is applied to the plasma reactor table. Traditionally, a linear amplifier is used to generate this waveform, which results in poor efficiency. This paper proposes a switched-mode power amplifier as a substitute to the traditional linear amplifier. The electric equivalent circuit of the plasma reactor is introduced and a basic topology for the switched-mode power amplifier is derived. The basic topology is able to generate the required waveform but it has a low efficiency of charging the capacitive load in practice. Therefore, an efficiencyimproved topology is proposed by adopting resonant charging. A prototype is built in order to validate the research. The experiments show that the presented solution yields a significantly reduced input power compared to the normally used linear amplifier in this application

Output Spectrum Modeling of an H-Bridge Inverter with Dead-Time Based on Switching Mode Analysis

The distortion of an H-bridge inverter can originate from many nonlinear factors, of which the most dominant one is typically the dead-time. In previous research, analytical models have been proposed to calculate the output spectrum of the H-bridge inverter. However, the existing models have not fully explored the effects of soft-switching and discontinuous conduction mode, which might severely degrade their accuracy. In this paper, the characteristics and the corresponding effects of these switching modes are analysed. Constraint functions are proposed in order to determine the time position of each switching mode. Based on this analysis, a numerical model of the output spectrum of the H-bridge inverter is then introduced. The model is shown to have a significantly improved accuracy compared to the previous analytical models especially for large inductor current ripples. The accuracy improvement is confirmed by simulation and measurements on an experimental prototype

Model and Verification of a Plasma Etching Reactor with a Switched-Mode Power Converter

For reaching a high selectivity in plasma etching, it is required to precisely control the plasma ion energy. This can be realized by applying a tailored pulse-shape voltage waveform to the reactor table. Recent research has shown that switched-mode power converters can be used to generate this kind of waveform, with the benefit of increased efficiency compared to the traditional linear amplifier. However, the equivalent electric circuit model of the plasma etching reactor is required in order to do circuit simulation and make an optimized electronic design of such switched-mode power converters. Although several circuit models of the reactor have been presented in previous research, they can not be directly adopted in tailored pulse-shape biasing. In this paper, a modified equivalent electric circuit model of the reactor is proposed. The plasma behaviour is modelled using the equivalent electric circuit and it is suitable for electric circuit simulation together with the power converter. Both the electrical waveforms and the normalized ion energy distribution can be obtained from the simulation, which are in line with the experimental results

Improved current estimation in paralleled half-bridge converters

When paralleling half bridges, their individual currents should be balanced to prevent large circulating currents. This paper improves an existing perturbation-based current estimation method by modifying the perturbation signal allowing a faster estimation of the currents, resulting in a reduction of current stress on components

Active DC-Bias Mitigation Method for a Single-Phase Transformer-Connected Converter through DC-Link Measurement

DC-bias in the magnetic flux is a common challenge for transformer-connected converters. Typically, in isolated switched-mode converters, it is induced by a DC current flowing through one or more windings of the transformer. This bias can increase the core losses of the transformer and drive the transformer core into saturation, which deteriorates the performance of the transformer and can even result in the malfunctioning of the converter. Conventional methods for DC-bias mitigation involve expensive sensing circuitry and/or impair the performance of the converter. The proposed method utilizes the fact the DC-bias current through the transformer will result in a switching-frequency current component in the DC-link current of the converter. A band-pass filter can for example used to indirectly measure the switching-frequency current component and then mitigate that in a closed-loop manner. Both simulation results and experimental measurements are provided to verify the theoretical analysis and effectiveness of the proposed method.</p

High Power GaN Module Using 3D-Printed Liquid Coolers for Hard-Switching at Megahertz

This work presents a power module for high frequency operation, designed to get the maximum performance out of Gallium-Nitride (GaN) devices. The use of metal 3D-printed liquid coolers, ceramic insulation and advanced Indium interface material leads to extremely low thermal resistance and low parasitic impact on switching performance. The presented module consists of four half-bridges, rated for 400 V and output currents of 15 A. The thermal interface achieves a resistance of 1.38 K/W from junction to coolant at a chip cooling area of 19 mm(exp2), while the ceramic insulation contributes 3 pF to the switch-node. The low parasitic design enables a peak switching speed of 186 V/ns during a hard switched turn-on and 30 V overshoot after soft commutation at full load current