Vinicius Bernardi Fuerback

Bio: Vinicius Bernardi Fuerback is an academic researcher from Universidade Federal de Santa Catarina. The author has contributed to research in topics: Voltage & Modular design. The author has an hindex of 2, co-authored 4 publications receiving 9 citations.

Modular ISOP Flyback converter: Analysis of auto-balancing mechanism in steady state

Abstract: DC-DC Modular converters have been proposed as a solution to reduce electrical stresses on semiconductors due to the capacity of sharing current or voltage among modules. This characteristic allows the increasing of the switching frequency, the use of low voltage/current semiconductors and the standardization and expansion of converters. This paper presents a steady-state analysis of an input-series-output-parallel (ISOP) modular Flyback converter operating in the discontinuous conduction mode (DCM). The analysis of the average input voltage and output current balance is presented, whose results depend on the magnetizing inductance and on the duty cycle of any number of modules. Once the equations are obtained, all the results are underpinned by a set of simulations undertaken for three modules. In order to evaluate the theoretical analysis, a prototype consisting of three Flyback modules in DCM operation, with a rated power of 600 W and conversion ratio from 600 V to 200 V, was built. The obtained waveforms show the independence of each module to the connection, leading to an equal division of the current and voltage stresses over the semiconductors. This characteristic, added to the modularity, high efficiency and high current gain, makes the converter an alternative to DC/DC systems where the output voltage must be lower than the input voltage.

DCM forward-flyback converter integrated with a 5-order cockcroft-walton voltage multiplier: A steady-state and resonant current analysis

Abstract: This paper presents the steady state and resonant current analysis of a Forward-Flyback Voltage Multiplier operating in discontinuous conduction mode. The operation stages are approached, taking into account the resonant current. The static gain and the conditions for the operations modes are obtained. A sinusoidal approximation is proposed to represent the resonant current with respect to the number of stages, voltage multiplier capacitors and leakage inductance. The characteristics of voltage sharing among capacitors, that allows the use of small voltage components, and the high-gain with reduced turns of the transformer are verified. Bench tests were made for a 200 V/2000 V prototype, from one to five stages, highlighting the overall circuit effects for a 200 W output power. Obtained waveforms for different number of voltage multiplier stages validate the theoretical and simulated results, making this converter an alternative to isolated DC/DC systems where the output voltage must be higher than the input voltage.

Hybrid Unidirectional MMC-Based Rectifier

Abstract: More-electric ships (MESs) and subsea oil processing electric power systems are typically fed by synchronous generators. These are primarily driven by gas turbines in the case of O&G or diesel engines in MESs. In neither of these applications the generators should experience regenerative operation, i.e., they do not operate under reversed power flow. Medium voltage dc unidirectional rectifiers are well suited and provide natural protection against power flow reversals. Thus, a hybrid rectifier concept that is based on line commutated diodes to transfer a large portion of electric power allied with the redundancy and higher operating frequency of modular multilevel converter (MMC) submodules (SMs) is proposed. The hybrid rectifier operates the MMC SMs to synthesize waveforms that are ideally composed of triplen harmonics. Therefore, the frequency of the power oscillations at the capacitors are shifted to frequencies higher than those of a conventional MMC. The overall required capacitance is consequently reduced. Furthermore, a much lower number of SMs is required when compared to a conventional three-phase MMC. These characteristics are welcome in the cited applications. This work discusses how to operate and control the proposed system.

Analysis of modular DCM Flyback converters in input parallel connections with parametric mismatches

Abstract: This paper analyzes the effects of parameter mismatches in the balance mechanism of modular DC-DC Flyback converters operating in discontinuous conduction mode. The natural current and voltage distributions among modules are evaluated when mismatches on duty cycles, transformer magnetizing inductances and transform turns ratios are present. From these results, the critical values of inductances and duty cycles that assure the discontinuous operation are equated. The smallsignal equivalent circuit for Input-Parallel-Output-Series and Input-Parallel-Output-Parallel connections are found, followed by a simple control strategy. The theoretical analysis is verified by experimental results obtained with a prototype composed of three 200 W Flyback modules, with a rated power of 600 W and maximum efficiency of 95.5%. Results corroborate the proposed equations for the steady state balance and dynamic behavior of both connections, highlighting the modular characteristic of the converter.

A Review of Voltage/Current Sharing Techniques for Series–Parallel-Connected Modular Power Conversion Systems

Abstract: Recently, more occasions with high input voltage and/or high output voltage applications are emerging. However, the existing switching devices are limited by the voltage stress, e.g., the available maximum blocking voltage of insulated-gate bipolar transistors is 6.5 kV. Therefore, several methods are provided to solve this issue, including series connection of switches, multilevel converters, and modular series–parallel structures, where the modular series–parallel systems are the most popular choice due to the advantages of low cost, simple design process, high modularity, reliability, and redundancy. The main objective of series–parallel systems is to ensure the sharing of input/output voltage/current. Based on this, a comprehensive review on the available voltage/current sharing methods for series–parallel systems, which include input-series output-parallel, input-parallel output-series, and input-series output-series structures is provided in this article. Moreover, the relationships between the input voltage/current sharing and output voltage/current sharing of series–parallel systems are explained.

A Flying Capacitor Hybrid Modular Multilevel Converter with Reduced Number of Submodules and Power Losses

Abstract: This paper presents a novel flying capacitor type hybrid modular multilevel converter (FC-HMMC) as an alternative to the traditional modular multilevel converter (MMC) for medium voltage (MV) applications. Combining the high voltage line-frequency switches with the low voltage high frequency submodule (SM) based chain-link, the proposed hybrid solution can balance the benefits from conventional multilevel converter and MMC. Compared to the HB-MMC, FC-HMMC can save 50% SMs, 25% devices, 37% capacitor and 20% conduction losses, hence improving the power density and power efficiency a lot. Besides, the dc and ac side is not coupled for this topology, which means the modulation index is not fixed. Another advantage is that the high voltage switch operates in soft-switching naturally at any modulation index or power factor, thereby reducing the power losses. Based on this characteristic, a unidirectional FC type hybrid modular multilevel rectifier (FC-HMMR) with only HV diodes is proposed as well. Finally, the feasibility of the proposed topology is validated by both simulation and experiments.

A Flying Capacitor Hybrid Modular Multilevel Converter With Reduced Number of Submodules and Power Losses

Abstract: This article presents a novel flying-capacitor-type hybrid modular multilevel converter (FC-HMMC) as an alternative to the traditional modular multilevel converter (MMC) for medium-voltage applications the high-voltage line-frequency switches with the low-voltage high-frequency submodule (SM)-based chain-link, the proposed hybrid solution can balance the benefits of the conventional multilevel converter and the MMC. Compared to the half-bridge MMC, the FC-HMMC can save 50% SMs, 25% devices, 37% capacitor, and 20% conduction losses, hence improving the power density and power efficiency a lot. Besides, the dc and ac sides are not coupled for this topology, which means the modulation index is not fixed. Another advantage is that the high-voltage switch operates in soft switching naturally at any modulation index or power factor, thereby reducing the power losses. Based on this characteristic, a unidirectional FC-type hybrid modular multilevel rectifier with only high-voltage diodes is proposed as well. Finally, the feasibility of the proposed topology is validated by both simulation and experiments.

Analysis of modular DCM Flyback converters in input parallel connections with parametric mismatches

Abstract: This paper analyzes the effects of parameter mismatches in the balance mechanism of modular DC-DC Flyback converters operating in discontinuous conduction mode. The natural current and voltage distributions among modules are evaluated when mismatches on duty cycles, transformer magnetizing inductances and transform turns ratios are present. From these results, the critical values of inductances and duty cycles that assure the discontinuous operation are equated. The smallsignal equivalent circuit for Input-Parallel-Output-Series and Input-Parallel-Output-Parallel connections are found, followed by a simple control strategy. The theoretical analysis is verified by experimental results obtained with a prototype composed of three 200 W Flyback modules, with a rated power of 600 W and maximum efficiency of 95.5%. Results corroborate the proposed equations for the steady state balance and dynamic behavior of both connections, highlighting the modular characteristic of the converter.

The Cockcroft-Walton voltage multiplier fed by an inverter in which the series resonant phenomena were used

Abstract: The article describes the phenomena occurring in the Half-Wave Cockcroft-Walton voltage multiplier when it is supplied through a transformer by an inverter with a rectangular shape of output voltage. The frequency of the inverter output voltage was selected so that a series resonant phenomena occurs in the system. They are caused by the presence of voltage multiplier capacitors and transformer leakage inductances. In the article the characteristics and waveforms of voltages and currents obtained by simulations are presented. The results of simulations were used to build two prototypes with maximum powers of about 60 W and 160 W and a 40 kV output voltage.