Microgrid power electronic converters: state of the art and future challenges

This paper presents a review of the state of the art of power electric converters used in microgrids. The paper focuses primarily on grid connected converters. Different topologies and control and modulation strategies for these specific converters are critically reviewed. Moreover, future challenges in respect of these converters are identified along with their potential solutions

Robust repetitive feedback control of a three-phase grid connected inverter

This paper discusses the design of a repetitive feedback controller for a grid-connected two-level three-phase voltagesource inverter connected between a DC source and the grid through an LCL filter. The controller incorporates a classical two loop feedback of the output current and the capacitor current in addition to a repetitive feedback loop. The results show that the proposed technique improves the steady state error and the total harmonic distortion of output current in presence of utility harmonics

Particle separation with ultrasonic standing waves

Ultrasonic standing wave fields are able to trap and manipulate biological cells and other micron scale particles. The ability to levitate and move cells is of fundamental importance in a wide variety of life sciences applications. The gradients of pressure and velocity within a standing wave interact with small scatterers, such as cells, to generate time-averaged forces, in addition to the oscillatory acoustic forces. These steady-state radiation forces comprise: i) a component that acts towards the acoustic velocity maximum for a dense scatterer (relative to the surrounding fluid) and ii) a component that acts towards the acoustic pressure minimum for a relatively stiff particle. The resultant of these components will move the majority of scatterers, such as cells in aqueous suspension, towards the pressure nodes of a plane standing wave.This presentation discusses the second order terms that lead to the radiation forces and describes different approaches to modelling the forces, both numerical and analytical. The magnitude and scale of the potential wells that can be created within the standing waves complement other approaches to cell manipulation such as optical traps and dielectrophoresis. In addition, ultrasonic excitation is particularly suitable for integration into lab-on-a-chip devices and at low intensities cell damage has been shown to be negligible, making the approach ideal for handling biological cells in microfluidic devices.A number of potential applications of the technology will be described, including filtration and concentration, biosensor enhancement, and fractionation of particles on the basis of size, material properties and geometr

HeLa cell transfection using a novel sonoporation system

Sonoporation has been shown to have an important role in biotechnology for gene therapy and drug delivery. This paper presents a novel microfluidic sonoporation system that achieves high rates of cell transfection and cell viability by operating the sonoporation chamber at resonance. The paper presents a theoretical analysis of the resonant sonoporation chamber design, which achieves sonoporation by forming an ultrasonic standing wave across the chamber. A piezoelectric transducer (PZT 26) is used to generate the ultrasound and the different material thicknesses have been identified to give a chamber resonance at 980 kHz. The efficiency of the sonoporation system was determined experimentally under a range of sonoporation conditions and different exposures time (5, 10, 15, and 20 s, respectively) using HeLa cells and plasmid (peGFP-N1). The experimental results achieve a cell transfection efficiency of 68.9% (analysis of variance, ANOVA, p < 0.05) at the resonant frequency of 980 kHz at 100 Vp-p (19.5 MPa) with a cell viability of 77% after 10 s of insonication

Multi-modal particle manipulator to enhance bead-based bioassays

By sequentially pushing micro-beads towards and away from a sensing surface, we show that ultrasonic radiation forces can be used to enhance the interaction between a functionalized glass surface and polystyrene micro-beads, and distinguish those that bind to the surface, ultimately by using an integrated optical waveguide implanted in the reflector to facilitate optical detection. The movement towards and immobilization of streptavidin coated beads onto a biotin functionalized waveguide surface is achieved by using a quarter-wavelength mode pushing beads onto the surface, while the removal of non-specifically bound beads uses a second quarter-wavelength mode which exhibits a kinetic energy maxima at the boundary between the carrier layer and fluid, drawing beads towards this surface. This has been achieved using a multi-modal acoustic device which exhibits both these quarter-wavelength resonances. Both 1-D acoustic modelling and finite element analysis has been used to design this device and investigate the spatial uniformity of the field. We demonstrate experimentally that 90% of specifically bound beads remain attached after applying ultrasound, with 80% of non-specifically bound control beads being successfully removed acoustically. This approach overcomes problems associated with lengthy sedimentation processes used for bead-based bioassays and surface (electrostatic) forces, which delay or prevent immobilisation. We explain the potential of this technique in the development of DNA and protein assays in terms of detection speed and multiplexing