Peak Current Control and Feed-Forward Compensation for the DAB Converter

This paper presents a double band peak current control for the DAB converter that permits to avoid the risk of transformer saturation. Additionally, feed-forward compensation is employed to achieve a fast transient response under load variations. The proposal is described, analyzed, and numerically simulated

Solid State Transformer with Integrated Input Stage

In this paper, a solid state transformer (SST) with integrated stages is addressed. The SST has been originally proposed for traction applications, after as an option to face the new requirements of the distributed generation but also suggested in many applications. There are different topologies, from one to three stages; certainly each one with their advantages and limitations. Some challenges for this type of systems are reducing the cost and increasing the efficiency.The components reduction is discussed in this paper, by integrating two stages of the SST; the ac/dc converter and the DAB converter share one leg. The proposed scheme is described and numerically simulated

Volume Optimization in Si IGBT based Dual-Active-Bridge Converters

Dual-Active-Bridge (DAB) converters are able to step up/down DC voltage in a wide range by adopting medium frequency transformer (MFT) for isolating and converting voltage level. Increase in switching frequency of Si IGBTs reduces the MFT size instead it intensifies the semiconductor switching losses which leads to increase in the heatsink size. In this paper variation of heatsink volume versus frequency is compared versus MFT. MFT and heatsink volume of a 5 kW 600 to 400 V DAB converter are optimized. Obtained results show that variation of switching frequency in range 1-10 kHz increases the size of optimal heatsink by 3 times, i.e V HS,opt ∞ √(fs [kHz])

dv/dt filter design incorporating machine impedance and voltage slew rate for WBG-based electric drives

The trend towards high power density and high reliability of electric drive systems in mobility applications pushes the use of high-speed machine in combination with Wide Band Gap (WBG) power semiconductor technology. Replacement of Si power technology with WBG without mitigating high voltage slew rates dv/dt degrades machine winding insulation. Of the different mitigation techniques employed, especially the passive LCR filter at the output of the inverter cannot be optimally designed without consideration of the inherent low impedance of the high speed machines. This paper presents the analytical techniques used for LCR filter design for motor drives and introduces the technique to incorporate machine impedance Z dm for optimal design of the parameters to achieve high efficiency. An analytical technique based optimization algorithm is introduced for the reduction of filter inductor volume to achieve high power density in these applications. The proposed design methodology is evaluated in simulations and experiments with Gallium Nitride (GaN) based inverter technology

Double Active Bridge Operated in Quasi Discontinuous Conduction Mode

The quasi discontinuous conduction mode (QDCM) of the double active bridge (DAB) is addressed in this paper. The DAB converter usually is operated turning on always two semiconductors per bridge, and this leads to a continuous inductor current: However, a similar operation to dc/dc converters can be implemented, for this, less than two switches are turned on, at certain time, in one of the bridges; this leads to the quasi-DCM. With this mode of operation, a natural soft-switching is performed during the whole range of operation, but also low current stress is performed compared to the square modulation, not only at low power range. The modulation is relatively simple compared to other techniques. The proposed technique is described, analyzed, numerically simulated, and experimentally tested

Robust Stability Analysis of Synchronverters Operating in Parallel

Recent studies have shown how synchronization units of converters operating nearby may interact with each other, affecting the stability of the system. Synchronverters are able to self-synchronize to the grid without the need of a dedicated unit because they can reproduce the power synchronization mechanism of synchronous machines. Recently, the robust stability of a synchronverter has been investigated by means of structured singular values (commonly called μ-analysis). In this paper, μanalysis is performed to investigate how the robust stability of a synchronverter is affected by the presence of another converter of the same type operating in parallel. It is demonstrated that the parallel operation of synchronverters reduces their robust stability and a possible solution is proposed, based on the implementation of virtual impedances in the control algorithm. An accurate state-space model of the system under study is developed by adopting the component connection method and the robust stability analysis is validated against time-domain simulations in MATLAB/Simulink/PLECS and experimental results with a power-hardware-in-the-loop test bench

Robust Stability Investigation of the Interactions Among Grid-Forming and Grid-Following Converters

State-of-the-art grid-connected converters can be classified as “grid-following,” meaning that they require a dedicated synchronization unit in order to inject active and reactive currents into the grid. Recently, other converter control concepts have been proposed in the literature, such as the synchronverter, which can instead achieve synchronization without a dedicated unit and, within its physical limitations, make the converter behave as an ideal voltage source. Since it should be expected that the grid-connected converters having different control philosophies will coexist for many years, in this article, the interaction among the converters operating nearby are addressed. First, the component connection method (CCM) technique is introduced, as a means for obtaining the state-space representation of a complex system with several units operating nearby. Due to the complexity of the grid and the difficulty in obtaining its exact representation, μ-analysis is adopted in this article for assessing the robust stability of the converter under different operating conditions, according to a defined set of plant uncertainties. Simulation results and experimental tests in a laboratory environment by means of a power hardware-in-the-loop (PHIL) test bench are performed to demonstrate the validity of the presented analysis