Rene Barrera-Cardenas

Comparative Study of Wind Turbine Power Converters Based on Medium-Frequency AC-Link for Offshore DC-Grids

This paper considers an offshore wind turbine modular power converter (ac/dc) with permanent magnet synchronous generator based on three stages: an ac-ac converter, a medium-frequency transformer, and a full-bridge diode rectifier with LC output filter. Six converter topologies are compared; three of them are based on back-to-back (B2B) topology: the conventional B2B with three-phase sinusoidal waveform, the B2B with three-phase squared waveform, and the B2B with single-phase squared waveform. The other solutions are based on matrix topologies: the direct matrix converter, the indirect matrix converter, and the reduced matrix converter (RMC). A systematic methodology and main component models are introduced to evaluate the power loss, volume, and mass of the wind energy conversion system for all considered topologies as a function of the medium-frequency transformer operational frequency and the number of modules parallel connected. The comparison involves a tradeoff study between total power losses, size and weight of 10 MW modular converters. It was found that when Metglas alloy 2605SA1 is the transformer core material, the RMC topology leaves the best tradeoff between the considered performance indicators with an extra benefit in reducing the semiconductor devices cost of the modular converter.

Capacitor size reduction of MMC-based STATCOM for medium voltage power distribution network

This paper presents the capacitor size reduction of a MMC-based transformer-less STATCOM for medium voltage ac distribution system. The instantaneous power swinging flows into the single-phase configuration results in a high capacitance needed; however, by accepting the swinging voltage in the capacitor, the capacitance can be drastically reduced. This paper analyzes the dimensional size reduction of this method and thermal characteristics by using a meta-parameterization technique based on existing film capacitor technologies, and estimates that the dimensional size of the capacitor can be about 34% of the conventional design.

Comparative study of the converter efficiency and power density in offshore wind energy conversion system with single-phase transformer

In this paper is presented a comparison of two converter topologies based on single-phase link for offshore wind turbines with permanent magnet synchronous generator. The scheme of the converter module considered is based on four stages: an inductive filter, an 3AC-AC converter, a single-phase high-frequency transformer and a full-bridge diode rectifier. The conventional 3AC-AC converter with DC-Link and the Reduced Matrix Converter are the selected topologies. Analytical models and numerical simulations are considered in order to evaluate the converter efficiency and the power density as function of switching frequency. It was found that for range of transformer frequencies from 1[KHz] to 20[KHz], the Reduced Matrix Converter topology was the most efficient topology and had the highest power density.

Optimal control for an HVDC system with series connected offshore wind turbines

This paper studies an HVDC system based on pulse-width-modulated current source converters (PWM-CSC) which is suitable for series connection of offshore wind turbines. A high-frequency link based on reduced matrix converter is proposed as energy conversion system in each wind turbine. An optimal linear quadratic regulator is designed in order to reduce the complexity of the inner-loop and to improve its dynamic performance. Operation features of this control are tested in stationary state and transient conditions.

Optimized design of wind energy conversion systems with single-phase AC-link

Major concerns in the converter design are the efficiency and the power density. In this paper is presented a comparison of six modular power converter solutions based on single-phase link for offshore wind turbines with permanent magnet synchronous generator. The scheme of the converter module considered is based on three stages: 3AC-AC converter, a single-phase high-frequency transformer and a full-bridge diode rectifier. The conventional 3AC-AC back-to-back converter and the Reduced Matrix Converter are the compared topologies, combining with IGBT with three blocking voltage (1.7kV,3.3kV,6.5kV). Analytical models and numerical simulations are considered in order to evaluate the converter efficiency and the power density as function of AC-link frequency and the number of converter modules. It has been found that the Reduced Matrix Converter topology will lead a higher efficiency and a higher power density when it is used with lower voltage level. Also, the converter solutions based on low blocking voltage IGBTs presents higher efficiency than switch based on high blocking voltage IGBTs, leaving evidence of a deficiency in the technology for higher blocking voltage.

Comparison of wind energy conversion systems based on high frequency AC-Link: Three-phase Vs. single-phase

In this paper is presented a comparison of three converter topologies based on high-frequency link for offshore wind turbines with permanent magnet synchronous generator. The scheme of the wind energy conversion system considered is based on three stages: an AC-AC converter, a high-frequency transformer and a full-bridge diode rectifier. The incidence of the number of phases in the AC link of the power converter is investigated in terms of the efficiency and the power density. The conventional Back-to-Back converter with three-phase (sinusoidal and square wave output) and single-phase square wave output are the chosen topologies for comparative study. It has been found that AC-Link with three-phase square wave will lead the best solution with the more convenient tradeoff between efficiency and power density in the range of frequencies considered (100 Hz-50 kHz). A convenient increase in the power density can be obtained if the number of modules in the modular power converter is optimized.

Influence of CCM and DCM operation on converter efficiency and power density of a Single-Phase Grid-Tied Inverter

In this paper the Continuous Current Mode (CCM) and Discontinuous Current Mode (DCM) operations of a Single-Phase Grid-Tied Inverter are compared regarding efficiency and power density. Main design guidelines and component models are introduced for both operation modes. Optimal design is used to perform the comparative analysis. It was found that for range of switching frequencies from 10kHz to 100kHz, and nominal power of the inverter between 0.5kW and 2kW, the CCM operation was the most efficient design and had the highest power density. Also, it was pointed out that the main drawback for design based on DCM operation are the high peak inductor current and the required output filter capacitor. The higher peak current for DCM designs produced higher losses in all cases. Also, the output filter capacitor limited the reduction in volume for high switching frequency operation.

Comparative study of semiconductor devices based on a meta-parameterised approach: SiC MOSFET vs Si IGBT technologies

This paper presents a meta-parameterised approach for evaluation and comparison of Power Semiconductors Devices (PSD). General models and main PSD parameters needed for evaluation of power electronics switches are presented. Then, meta-parameterisation is performed for two PSD technologies, Si-IGBT and SiC-MOSFET. A comparative analysis based on current capability, frequency dependency and overrated factor for these PSD technologies is presented. Even more, a 50kW 2L-VSI and a 20kW DC-DC converter are considered to show how meta-parameters can be used to evaluate the impact of PSD technology on converter performance.

Optimal design of air-core inductor for medium/high power DC-DC converters

Inductors are one of the largest and heaviest components of the DC-DC converter in medium/high power applications. As volume/weight of the converter becomes more important, high frequency is considered in the design of the converter and inductors with low inductance and high currents are required. Air-core inductors can be considered as good alternative, since they are not subject to saturation problems and may provide a reduction on total weight and losses of the converter if an appropriated design is performed. This paper presents an analysis of air-core inductors for DC/DC converters. First, a simplified inductor design is proposed to optimize the power losses by using litz wire winding. Then, results from the proposed design methology are compared with commercial iron-core inductors byusing metaparameterisation approach. A comparative analysis is performed between commercial iron-core inductors and air-core inductors regarding power losses, volume and weight for a bidirectional DC-DC converter. Because the number of parameter that influence the selection of the inductance in a DC-DC converter, then the comparison is done by use desicion chart, which help to define when a type of inductor is better than the other. Air-core inductor will left more benefit for power rating higher than 1MW.

Meta-parameterisation of power semiconductor devices for studies of efficiency and power density in high power converters

This paper presents a meta-parameterised approach for evaluation of power switch modules (PSMs) in high power converters (HPCs). General models and parameters for evaluation of power losses and volume of PSMs are presented. Then, meta-parameterisation is performed for the High Power Semiconductor Devices (HPSDs) that are commonly used in HPCs, considering two types of package, press-pack and module type, and including IGBT, IGCT and IEGT chip technologies. A comparative analysis based on current capability and its dependency with the frequency in voltage source converters is introduced for the considered HPSD technologies. Press-pack IGBT technology shows the higher current capability and power dissipation performance, so it can be good choice for increase the operative frequency in HPCs.