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The new era of power semiconductor devices is exploiting the high potential of wide bandgap device-based high-frequency power converters. The advanced capabilities of Silicon carbide (SiC) semiconductors allow the power converters to switch at higher switching frequencies with lower switching and conduction losses. Operation under higher switching frequencies can drastically reduce the output filter requirements in grid-connected converters. At higher frequencies, an L-type filter can sufficiently eliminate the switching frequency harmonics. This will reduce the size and cost of the filter, which eventually results in the optimised system cost. In this paper, the filter requirements of SiC based high-frequency converters are investigated. Usage of LCL filters to remove high-frequency harmonic will shift the resonance frequency to high-frequency region, where these harmonics can create electromagnetic compatibility issues. In industries, passive damping is utilised for mitigating these oscillations. This will result in additional losses and compromise the advantages of SiC devices. Even though active damping can be utilised to eliminate resonance oscillations, the high bandwidth processors and measurement devices may increase the cost further. Simulation study is conducted on PSCAD/MATLAB and the experimental verification using Cree SiC devices verify the filter requirements, stability issues, and possible mitigating solutions for high-frequency grid converters.

This study introduces a bidirectional power sharing scheme between an ac electric utility and a dc microgrid. These two are connected together through an interlinking converter (IC) and a dual active bridge (DAB). The proposed control scheme allows predefined amount of power to be supplied from the ac to dc side or the other way around. The DAB is connected at the dc side of the IC and it controls the bidirectional power flow. The dc microgrid contains dc-dc converters, where boost converters are used with the sources and buck converters are used to supply loads. These dc-dc converters and the DAB are controlled by state feedback with integral control in a linearised discrete domain. The DAB linearisation and control law are presented in detail. The dc microgrid is controlled by conventional V-P droop where the power from/to the ac side is considered as negative/positive load. Detailed simulation results are presented to validate the proposal. Also some hardware results are included that support the findings.

This study proposes a decentralised droop control method for guaranteeing precise load sharing among distributed resources in an islanded microgrid. Distributed resources are usually fed through power electronic converters and the switching harmonics produced by them are eliminated by third-order output LCL filters. Output impedance is considered as a major factor for finding exact power-angle droop coefficient in droop design - neglecting this factor can affect the load sharing accuracy. Even though an acceptable active power sharing can be achieved with higher droop gains, increased droop gain may adversely affect the microgrid stability. Here, a modified angle droop control is proposed such that the dependence on the output inductance on the real power sharing is removed. Thus, the lower droop coefficients are sufficient for droop sharing and the system stability is not endangered. It has been assumed that the microgrid is converter-dominated, where a proportionalresonant controller has been utilised for converter switching control. This controller has an outer voltage loop and an inner current loop. A harmonic term has been added to the voltage loop to facilitate more accurate reactive power sharing. Simulation studies are conducted using PSCAD/EMTDC to validate the efficacy of the proposed controller.

Dielectric spectroscopy (DS) is a non‐invasive, label‐free, and promising technique for measuring dielectric properties of biological cells. Recent developments in microfabrication techniques made it possible to perform DS measurements with minute volume of cell suspensions. However, when the cell size approaches the size of the measurement chamber, especially, for single cell measurements, the analytical models [Maxwell–Wagner and Bruggeman–Hanai (BH) mixture models] to extract cell parameters lose their accuracy. Moreover, variations in the cell position relative to the measurement electrodes decrease the accuracy of the analytical solutions. Impedance spectrum of a typical eukaryotic mammalian cell is generated for different geometrical configurations using finite element. The generated data are fitted to the analytical models and extracted cell parameters are compared with the original values. The results show that BH model works more effectively when chamber to cell radius ratio is

This paper proposes a power exchange strategy for sustainable microgrids (MGs) of remote areas that have no access to a utility grid. This strategy manages the MG during power deficiencies under a decentralised approach (DA), which is the most probable case for remote MGs due to the lack of communication systems, or a centralised approach if a data communication system is available. Under each approach, a two-level (internal/external) control is established. The internal support is provided through power exchange with local energy storage while the external support is provided through power exchange with a neighbouring MG, after their temporary coupling. Appropriate conditions and constraints, under which the necessity and possibility of internal/external power exchange can be determined, are defined and formulated. These terms are based on local frequency measurements (for DA) and instantaneous power generation of the dispatchable distributed energy resources (for centralised approach). The dynamic performance of a remote system, composed of two MGs, operating with this strategy is evaluated by simulation studies in PSCAD/EMTDC. Furthermore, the small signal stability of such a system is investigated in MATLAB.

Low voltage feeders (LVFs) experience several voltage quality (VQ) issues such as voltage drop at network peak periods, voltage rise at middays when high number of rooftop photovoltaic cells (PVs) are existing in the feeder, rapid voltage fluctuations as the results of the clouds effects on the power generation of PVs, and voltage unbalance due to the inherent random characteristics of the single-phase loads and PVs. This study addresses these problems by proposing the concept of coupling the neighbouring LVFs. Based on this concept, two or more LVFs of the same distribution transformer or different distribution transformers are interconnected to support each other and minimise the VQ problems. First, the performance of LVFs in the existing form is discussed and three approaches of coupling the LVFs are presented. Among the presented techniques, coupling of LVFs through a distribution static compensator (DSTATCOM) at the end of the feeder is proposed and focused as an effective technique with minimal side effects such as power losses and cost. Proper dynamic control methods are also proposed for the DSTATCOM and the performance of such a system is investigated under steady-state and dynamic conditions via numerical analysis and simulation studies in MATLAB and PSCAD/EMTDC.

This study proposes a new method for stabilising disturbed power systems using wide-area measurement and controllable devices. A new control algorithm based on kinetic energy is proposed to be applied on the controllers to improve the first swing stability of power systems following large disturbances while also damping the subsequent inter-area oscillations. The wide-area controller is implemented by using the Kalman filter estimation of the area-based model of the system, to stabilise the inter-area dynamic and improve the stability margin of the system. The proposed approach is simulated on several test systems and the results show significant improvement in the first swing and damping stability of the test systems.

A hybrid NanoGrid (NG) can be considered as the power supply system, for future community houses. In this study, the operation and control of an NG are presented. The NG consists of an AC bus and a DC bus, interconnected through a tie-converter (TC). All AC loads and distributed energy resources (DERs) of the community houses are connected to the AC bus while all their DC loads and DERs are connected to the DC bus. The NG has an adequate generation capacity to supply its loads in off-grid status as well as the capability to exchange power with the grid. The TC exchanges the power between two buses and regulates the voltage in both buses, in the case of off-grid operation. The NG dynamics, with the proposed structure and developed primary and secondary control algorithms are validated through extensive computer simulations in PSCAD/EMTDC.

The authors report a detailed investigation of the flicker noise (1/f noise) in graphene films obtained from chemical vapour deposition (CVD) and chemical reduction of graphene oxide. The authors find that in the case of polycrystalline graphene films grown by CVD, the grain boundaries and other structural defects are the dominant source of noise by acting as charged trap centres resulting in huge increase in noise as compared with that of exfoliated graphene. A study of the kinetics of defects in hydrazine-reduced graphene oxide (RGO) films as a function of the extent of reduction showed that for longer hydrazine treatment time strong localised crystal defects are introduced in RGO, whereas the RGO with shorter hydrazine treatment showed the presence of large number of mobile defects leading to higher noise amplitude.

The usual practice to study a large power system is through digital computer simulation. However, the impact of large scale use of small distributed generators on a power network cannot be evaluated strictly by simulation since many of these components cannot be accurately modelled. Moreover, the network complexity makes the task of practical testing on a physical network nearly impossible. This study discusses the paradigm of interfacing a real-time simulation of a power system to real-life hardware devices. This type of splitting a network into two parts and running a real-time simulation with a physical system in parallel is usually termed as power-hardware-in-the-loop (PHIL) simulation. The hardware part is driven by a voltage source converter that amplifies the signals of the simulator. In this paper, the effects of suitable control strategy on the performance of PHIL and the associated stability aspects are analysed in detail. The analyses are validated through several experimental tests using an real-time digital simulator.

A new approach is proposed for obtaining a non-linear area-based equivalent model of power systems to express the inter-area oscillations using synchronised phasor measurements. The generators that remain coherent for inter-area disturbances over a wide range of operating conditions define the areas, and the reduced model is obtained by representing each area by an equivalent machine. The parameters of the reduced system are identified by processing the obtained measurements, and a non-linear Kalman estimator is then designed for the estimation of equivalent area angles and frequencies. The simulation of the approach on a two-area system shows substantial reduction of non-inter-area modes in the estimated angles. The proposed methods are also applied to a ten-machine system to illustrate the feasibility of the approach on larger and meshed networks. © The Institution of Engineering and Technology 2014.

To minimise the number of load sheddings in a microgrid (MG) during autonomous operation, islanded neighbour MGs can be interconnected if they are on a self-healing network and an extra generation capacity is available in the distributed energy resources (DER) of one of the MGs. In this way, the total load in the system of interconnected MGs can be shared by all the DERs within those MGs. However, for this purpose, carefully designed self-healing and supply restoration control algorithm, protection systems and communication infrastructure are required at the network and MG levels. In this study, first, a hierarchical control structure is discussed for interconnecting the neighbour autonomous MGs where the introduced primary control level is the main focus of this study. Through the developed primary control level, this study demonstrates how the parallel DERs in the system of multiple interconnected autonomous MGs can properly share the load of the system. This controller is designed such that the converter-interfaced DERs operate in a voltage-controlled mode following a decentralised power sharing algorithm based on droop control. DER converters are controlled based on a per-phase technique instead of a conventional direct-quadratic transformation technique. In addition, linear quadratic regulator-based state feedback controllers, which are more stable than conventional proportional integrator controllers, are utilised to prevent instability and weak dynamic performances of the DERs when autonomous MGs are interconnected. The efficacy of the primary control level of the DERs in the system of multiple interconnected autonomous MGs is validated through the PSCAD/EMTDC simulations considering detailed dynamic models of DERs and converters.

Common-mode voltage generated by a power converter in combination with parasitic capacitive couplings is a potential source of shaft voltage in an AC motor drive system. In this study, a three-phase motor drive system supplied with a single-phase AC-DC diode rectifier is investigated in order to reduce shaft voltage in a three-phase AC motor drive system. In this topology, the AC-DC diode rectifier influences the common-mode voltage generated by the inverter because the placement of the neutral point is changing in different rectifier circuit states. A pulse width modulation technique is presented by a proper placement of the zero vectors to reduce the common-mode voltage level, which leads to a cost-effective shaft voltage reduction technique without load current distortion, while keeping the switching frequency constant. Analysis, simulations and experimental implementation have been presented to investigate the proposed method.

Most high-power ultrasound applications are driven by two-level inverters. However, the broad spectral content of the two-level pulse results in undesired harmonics that can decrease the performance of the system significantly. On the other hand, it is crucial to excite the piezoelectric devices at their main resonant frequency in order to have maximum energy conversion. Therefore a high-quality, low-distorted power signal is needed to excite the high-power piezoelectric transducer at its resonant frequency. This study proposes an efficient approach to develop the performance of high-power ultrasonic applications using multilevel inverters along with a frequency estimation algorithm. In this method, the resonant frequencies are estimated based on relative minimums of the piezoelectric impedance frequency response. The algorithm follows the resonant frequency variation and adapts the multilevel inverter reference frequency to drive an ultrasound transducer at high power. Extensive simulation and experimental results indicate the effectiveness of the proposed approach.

This study presents a new multi-output DC/DC converter topology that has step-up and step-down conversion capabilities. In this topology, several output voltages can be generated and can be used in different applications such as multi-level converters with diode-clamped topology or power supplies with several voltage levels. Steady-state and dynamic equations of the proposed multi-output converter have been developed; these can be used for steady state and transient analysis. Two control techniques have been proposed for this topology, based on constant and dynamic hysteresis band height control, to address different applications. Simulations have been performed for different operating modes and load conditions to verify the proposed topology and its control technique. Additionally, a laboratory prototype is designed and implemented to verify the simulation results.

As the use of renewable energy sources (RESs) increases worldwide, there is a rising interest on their impacts on power system operation and control. An overview of the key issues and new challenges on frequency regulation concerning the integration of renewable energy units into the power systems is presented. Following a brief survey on the existing challenges and recent developments, the impact of power fluctuation produced by variable renewable sources (such as wind and solar units) on sysstem frequency performance is also presented. An updated LFC model is introduced, and power system frequency response in the presence of RESs and associated issues is analysed. The need for the revising of frequency performance standards is emphasised. Finally, non-linear time-domain simulations on the standard 39-bus and 24-bus test systems show that the simulated results agree with those predicted analytically.

This study presents an analysis of phasor measurement (PM) method for tracking the fundamental power frequency to show if it has the performance necessary to cope with the requirements of power system protection and control. In this regard, several computer simulations presenting the conditions of a typical power system signal especially those highly distorted by harmonics, noise and offset, are provided to evaluate the response of the PM technique. A new method, which can shorten the delay of estimation, has also been proposed for the PM method to work for signals free of even-order harmonics.

The topology and control are discussed of a distribution static compensator (DSTATCOM) that can be operated flexibly in the voltage or current control mode. In the voltage control mode, the DSTATCOM can force the voltage of a distribution bus to be balanced sinusoids. In the current control mode, it can cancel distortion caused by the load, such that current drawn by the compensated load is pure balanced sinusoid. Both these objectives are achieved, irrespective of unbalance and harmonic distortions in load currents or source voltages. The chosen DSTATCOM topology includes three single-phase voltage source inverters connected in parallel to a filter-capacitor, which allows the high-frequency component of the current to pass. A switching control scheme is proposed, and its suitability is proved for this problem. The proposed scheme is verified using computer simulation studies.

The extent and nature of control interaction between a power system stabiliser and a static synchronous series compensator (SSSC) has been studied. Countermeasures are suggested to reduce such interactions. The study system considered is IEEE first benchmark model for subsynchronous resonance. The SSSC is used as a fixed compensator and the DC-link voltage of the SSSC is regulated by a simple PI controller. Stability of the system is determined from eigenvalue analysis. Nonlinear simulations are performed to verify the results of eigenvalue analysis.

The various compensation strategies for shunt compensators using a generalised instantaneous reactive power theory are discussed. A general instantaneous vector expression for compensator current in terms of active and reactive source powers is given. The equivalent general time domain expressions for compensator reference currents are also derived. Detailed simulation results using MATLAB have been presented to validate the proposed reference current algorithm. The algorithm is implemented in real time on a PC. The experimental generation of ideal compensator currents demonstrates its suitability for practical shunt compensators. A prototype model of the compensator has been implemented in the laboratory with a voltage source inverter. Simulated and experimental results are presented and compared.

A linearised discrete-time model of a thyristor-controlled series-compensated transmission line is presented, in which a thyristor-controlled reactor (TCR) is used as the compensating device. The discretisation is performed at the peaks of the capacitor voltage of the series compensator. Since these peaks are broad, rather than sharp spikes, they are quite good indicators of variations in the fundamental component. During transients this will result in variation from uniform sampling. However, the system degenerates to a uniform sampled system in the steady state, and thus all the standard tools for the stability analysis of a standard discrete-time model can be applied. As a part of the linearised model, two different output equations are determined. They are the line current, which is in quadrature with capacitor voltage, and the real power flowing through the line. These output equations are then used for control design. The model developed is validated through digital computer simulation studies, in which the robustness of the closed-loop system is investigated through eigenvalue plots as a function of the operating points.