DC-link control filtering options for torque ripple reduction in low power wind turbines

Small Wind Energy Conversion Systems (WECSs) are becoming an attractive option for distributed energy generation. WECSs use permanent magnet synchronous generators (PMSGs) directly coupled to the wind turbine and connected to the grid through a single-phase grid-tie converter. The loading produced on the DC-link is characterized by large ripple currents at twice the grid frequency. These ripple currents are reflected through the DC bus into the PMSG, causing increased heating and ripple torque. In this paper, the PMSG inverter is used to control the DC link voltage. In order to avoid reflecting the ripple currents into the PMSG, the feedback DC-link voltage is passed through a filter. The Butterworth filters, notch filters, antiresonant filter (ARF) and moving average filter (MAF) are considered. For a fair comparison, formulas are provided to tune the filter parameters so that DC-link voltage control will achieve the selected bandwidth. The different filtering options produce different levels of torque ripple reduction. Notch Filter, ARF and MAF obtain the best results and there is a trade-off between the filter implementation complexity, bandwidth, overshoot and the torque ripple reduction. Simulations and experiments using a 2.5 kW PMSG turbine generator validate the proposals

Fault location in DC microgrids based on a multiple capacitive earthing scheme

This paper presents a new method for locating faults along feeders in a DC microgrid using a multiple capacitive earthing scheme. During fault conditions, capacitors within the earthing scheme are charging by transient currents that correlate to the fault distance and resistance. Therefore, by assessing the response of the capacitive earthing scheme during the fault, the distance to fault is estimated. The proposed method uti- lizes instantaneous current and voltage measurements (obtained from the feeder terminals and earthing capacitors) applied to an analytical mathematical model of the faulted feeder. The proposed method has been found to accurately estimate the fault position along the faulted feeder and systematic evaluation has been carried out to further scrutinize its performance under different loading scenarios and highly-resistive faults. Addition- ally, the performance and practical feasibility of the proposed method has been experimentally validated by developing a low- voltage laboratory prototype and testing it under a series of test conditions

Robust design of LCL-filters for active damping in grid converters

Grid converters require a simple inductor or an LCL-filter to limit the current ripples. The LCL-filter is nowadays the preferred solution as it allows lower inductance values. In order to solve the stability concerns, active damping is preferred to passive damping since it does not use dissipative elements. However, large variations in the grid inductance and resonances arising from parallel converters may still compromise the system stability. This calls for a robust design of LCL-filters with active damping. This paper proposes a design flow with little iteration for two well-known methods, namely lead-lag network and current capacitor feedback. The proposed formulas for the resonance frequency, grid and converter inductance ratio, and capacitance of the LCL-filter allow calculating all the LCL-filter parameters. An estimation for the achieved Total Harmonic Distortion (THD) of the grid current is also provided. Experimental results show very robust designs to the parameter variations

Modeling and control design of a Vienna rectifier based electrolyzer

Hydrogen production is an interesting alternative of storing energy. Electrolyzers produce hydrogen through water electrolysis; the resulting hydrogen is later used to generate electricity by using fuel cells, that reverse the process. Electrolyzers use rectifiers to convert the grid ac voltage into dc voltage for supplying the electrolyzer cells. Previous research used a rectification process based on conventional rectifiers (diode-or thyristor-based) which draw non-sinusoidal current from the main grid. This requires increased filtering to prevent power quality problems and equipment malfunctioning/failure. In addition, previous literature assumed simplified models for the power electronics converters and lacked a detailed control system. The Vienna rectifier is a non-regenerative converter that produces sinusoidal currents with low losses due to the reduced number of active switches. This manuscript proposes using the Vienna rectifier as an interface to connect electrolyzers to the ac grid. The dc voltage applied to the electrolyzer is regulated by using another DC-DC converter, which is selected to be a synchronous buck converter for simplicity and maximum efficiency. In this paper, the models of the Vienna rectifier, synchronous buck converter, and the electrolyzer are developed along with their respective controls. The control system has the ability to function in two operation modes for the overall reference: hydrogen production and power demand. The first one is adequate for grid-connected operation and the later for off-grid operation. Simulation results are given to show the validity of the proposed procedures

Voltage based current compensation converter control for power electronic interfaced distribution networks in future aircraft

Superconductors have a potential application in future turboelectric distributed propulsion (TeDP) aircraft and present significant new challenges for protection system design. Electrical faults and cooling system failures can lead to temperature rises within a superconducting distribution network, which necessitates a reduction or temporary curtailment of current to loads to prevent thermal runaway occurring within the cables. This scenario is undesirable in TeDP aircraft applications where the loads may be flight-critical propulsion motors. This article proposes a power management and control method that exploits the fast-acting measurement and response capabilities of the power electronic interfaces within the distribution network to maximize current supply to critical loads, reducing the impact of a temperature rise event in the superconducting distribution network. This new algorithm uses the detection of a resistive voltage in combination with a model-based controller that estimates the operating temperature of the affected superconducting cable to adapt the output current limit of the associated power electronic converter. To demonstrate the effectiveness of this method and its impact on wider system stability, the algorithm is applied to a simulated voltage-source converter supplied aircraft dc superconducting distribution network with representative propulsion motor loads

Capacitive earthing charge-based method for locating faults within a DC microgrid

This paper presents a new fault location method using capacitive earthing charge current combined with moving average and Savitzky-Golay filters. Locating a DC fault in a DC microgrid can be challenging due to reduced fault current magnitudes, resulting either from high resistive faults, or during the transition between grid-connected and islanded modes. The capacitive earthing method is proposed for earthing DC systems to avoid the corrosion of earthed metallic surfaces. Under different fault conditions and at different locations, the capacitive earthing with the earth path, charges a transient current with a peak value that depends on the initial voltage of the capacitor and the fault loop between the capacitor and the fault point. Therefore, this paper utilises earth capacitor pre-fault voltages, transient current peak and the derivative current of the capacitive earthing to estimate the total inductance of the fault loop. This in turn can be used to determine the location of DC faults. This paper also quantifies the impact that resistive faults have on the accuracy of the method, especially when the resistance of the fault dominates the total fault loop. The ability to distinguish between downstream and upstream faults with respect to the earthing point location also adds significant value to the proposed method. The proposed fault location technique is tested against pole-to-earth fault at different locations using Matlab-Simulink

Interface compensation for more accurate power transfer and signal synchronization within power hardware-in-the-loop simulation

Power hardware-in-the-loop (PHIL) simulation leverages the real-time emulation of a large-scale complex power system, while also enabling the in-depth investigation of novel actual power components and their interactions with the emulated power grid. The dynamics and non-ideal characteristics (e.g., time delay, non-unity gain, and limited bandwidth) of the power interface result in stability and accuracy issues within the PHIL closed-loop simulations. In this paper, a compensation method is proposed to compensate for the non-ideal power interface by maximizing its bandwidth, maintaining its unity-gain characteristic, and compensating for its phase-shift over the frequencies of interest. The accuracy of power signals synchronization and the transparency of power transfer within the PHIL configuration are assessed by employing the error metrics. In conjunction with the frequency-domain stability analysis and the time-domain simulations, a case study is made to validate the proposed compensation method

Characterizing semiconductor devices for all-electric aircraft

Cryogenic propulsion with hydrogen fuel cells replacing fossil fuels is a promising solution to cut carbon emissions in the aviation sector. Hydrogen will also be used for cooling the superconducting machines and power converter circuits. This article aims to test devices suitable for power electronic converters supplying a 1.6 MW superconducting machine. SiC MOSFET and Si IGBT modules with ratings of 1200 V and more than 450 A are selected to assess their performance at different temperatures. Four tests are conducted to determine: 1) the forward voltage drop, 2) the breakdown voltage, 3) the switching behavior, and 4) their operation with two modules in parallel. A bespoke current sensing rig has been developed that avoids the need to extend conductors outside the cryogenic zone in the switching losses measurement test. This configuration introduces minimal stray inductance into the circuit, which minimizes errors in the measurement. One of the aims of this article is to assess the suitability of different module technologies for SiC MOSFET and Si IGBTs in cryogenic applications. Six power modules (SiC MOSFETs and Si IGBTs) were evaluated at both room and cryogenic temperatures. Three of the modules employed conventional bond wire technology, while the other three utilized solid cover (SLC) technology that has no internal bond wires. It was found that the modules which employed SLC technology were the only ones able to survive the extreme temperatures. Following this, a comparison was made between the energy losses of the three SLC modules (two Si IGBTs and one SiC MOSFET) that were able to withstand low temperatures. The results indicated that the performance of the SiC MOSFET module worsens at cryogenic temperatures, whereas the performance of the Si IGBT modules improves with decreasing temperatures. Finally, an inverter simulation was conducted with each of the IGBT modules to estimate the efficiency

Design automation using exclusion-based hierarchical computation for power electronics converters in harsh environments

Designing power electronics converters for harsh environments is challenging due to the absence of components’ performance under harsh conditions, the frequent transition and data-passing among various software, and the time-consuming and computationally heavy work flow. This paper promotes using design automation to address the aforementioned design challenges. The implementations include public-accessible component databases, automated co-action among circuit simulators and finite element simulations to perform electrical, electromagnetic and thermal co-design, and finally an exclusion-based work flow with hierarchical computation to reduce computational load. The theorized framework is exemplified on designing a real world 175 ◦C 1.5kW Three-level Neutral-point-clamped dc-dc converter. A database containing the high-temperature characteristics of SiC MOSFETs and ferrites is established and shared through a web application with graphical user interface. In 310 min, the program, which includes computationally heavy 3D finite element simulation, delivers design output after evaluating the converter’s electrical, electromagnetic and thermal performance under 10 million parameter sets. Finally, a 1.5kW dc-dc converter prototype is built and tested in 175 ◦C ambient temperature to verify the quality of the design output