Search

This paper proposes a comprehensive steady-state analysis for a front-end Modular Multi-Parallel Rectifiers (MMR) system with a shared DC-link. A generalised mathematical representation for n number of parallel rectifiers is proposed. The MMR is analysed for both Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM). In addition, the CCM and DCM boundary of the MMR is identified mathematically. A 60kW Simulink model for the MMR is utilised to confirm the proposed steady-state mathematical modelling equations.

A battery energy storage system (BESS) can play a critical role in regulating system frequency and voltage in an islanded microgrid. A $\mu$ -synthesis-based robust control has been proposed for dc link voltage regulation of BESS for achieving frequency regulation and voltage quality enhancement of islanded microgrid. Variation in the operating condition of ac microgrid affects the operating condition of the BESS’ converter. This controller synthesis accounts for such uncertain variations as parametric uncertainty. The stability and performance of the proposed controller can be guaranteed for bounded parametric variations. The bounds on parameters are selected based on practical limitations of BESS. In this article, the proposed controller's performance is tested on an islanded CIGRE TF C6:04:02 benchmark low voltage ac microgrid system. The importance of dc link voltage regulation is analyzed based on performance comparison with a benchmark controller. The controller performance is also validated using a real-time Typhoon HIL emulator.

The next decade is likely to witness considerable growth in the application of plug-in electric vehicles (PEVs). However, uncoordinated PEV charging in low-voltage distribution networks may cause grid issues, such as transformer overload and voltage unbalance (VU). Therefore, it is essential to consider a more suitable methodology of voltage regulation for the consumers placed at the end of the feeder when the network is predominantly resistive. With this background, this article investigates the capability of dynamic PEV load transfer within the three phases of a distribution network to propose a new hybrid PEV coordination approach. In addition to the online centralized battery charging and var discharging, this approach performs local voltage profiles improvement by switching PEV at selected single-phase residential houses such that a PEV can be switched from a heavily loaded phase to a (relatively) lightly loaded phase. This results in better voltage regulations and VU reductions. The impacts of uncoordinated and proposed genetic algorithm (GA) coordinated PEV charging on VU and node voltage profiles and losses are simulated for a real unbalanced Western Australian distribution network in the Perth solar city over 24 h.

Gate controllable electronic trap detection method has been demonstrated by regulating the gate potential of MIS devices. This method is based on shift of capacitance voltage (CV) curve as well as flatband voltage (VFB) measure in less than 10 micro-seconds due to injection or ejection of electrons through the metal gate. Using this method, an electronic trap energy distribution was measured in the HfO2 dielectric film and it confirms a maximum number of traps (Delta_NT) of 1.7x1012 cm-2 corresponding to an energy level (Delta_EIL) of 0.45 eV above silicon conduction band (Si-ECB). In comparison, ZrO2-based MIS devices showed a broader distribution of electronic traps throughout the band gap. However, HfO2 contained more than 60% traps in deep level compared to 50% in ZrO2, which establishes the effects of material variation., Comment: Electronic traps, metal insulator semiconductor (MIS), energy level (EIL), silicon conduction band (Si ECB)

The worldwide acceptance of plug-in electric vehicles (PEVs) is expected to tremendously grow in the next few years. Uncoordinated PEV charging can cause serious grid issues such as overloading of transformers and unacceptable voltage drops. Single-phase residential charging can also initiate or contribute to voltage unbalance in distribution networks. A potential solution for the PEV integration is shifting the charging activities from peak to valley periods. Therefore, this paper firstly investigates the impacts of uncoordinated single-phase PEV charging at residential houses on three-phase distribution networks. Then, it proposes a novel PEV charging coordination strategy based on heuristic genetic algorithm (GA) to perform online centralized charging considering transformer loading and bus voltage profiles. Based on this, a decentralized PEV reactive power discharging approach is presented where the reactive power is discharged at selected nodes for further reduction of voltage unbalance. The impacts of uncoordinated PEV charging as well as the performance of the proposed centralized PEV charging and decentralized var discharging strategies are tested on a real unbalanced Western Australian distribution network under the Perth Solar City project over 24 hours.

The operation of multiple microgrids (MGs) in coordination with distribution system enables high penetration of locally available distributed energy resources (DERs). This approach enhances the reliability and resiliency of the power supply significantly. Also, the overall cost of energy gets reduced because of the integration of cost-free power from photovoltaic panels and wind turbines. The most effective utilization of DERs can be achieved through networked MGs. However, the implementation of the concepts of networked MGs requires extensive research. This paper presents a comprehensive literature review of the most important research works on networked MGs. Major benefits and challenges related to this new and highly exploring area have been analyzed. Also, some of the most important research areas related to networked MGs have been highlighted and discussed as the future perspectives.

With increasing photovoltaic (PV) penetration in low-voltage (LV) distribution networks, voltage violation during the peak PV generation period is one of the main power quality concerns. To minimize the PV power curtailment caused by voltage violations, this paper proposes a new approach utilizing one dynamic voltage restorer (DVR) at the secondary of an existing urban distribution transformer as a continuous voltage compensator with an accompanying control algorithm. The voltage compensation algorithm controls the DVR in real-time to prevent over-voltage and under-voltage at all network nodes, thereby maximizing PV injection and preventing equipment damage. The controller uses the equivalent line impedance of network to estimate the average voltage of load points without the need for any communication links for measuring load voltages. In this approach, the fixed tap changer of the distribution transformer is also optimally adjusted to minimize the DVR rating using a proposed offline optimization method. Simulation results on IEEE LV test feeder prove the ability of the DVR in maintaining all network node voltages within the allowable range in peak demand and peak PV generation periods with the benefit of injecting only a small amount of active and reactive power to the system, in contrast to alternative algorithms.

Demand for converter-fed distributed energy resources are rapidly growing in microgrids and these energy sources are mainly responsible for sharing loads in islanded mode of operation. In high voltage lines, sharing real and reactive load power requirements can be achieved by conventional droop control methods, nevertheless strong coupling between active and reactive power in medium voltage lines with low X/R ratio degrades rating-based load sharing among converters. A transformation matrix which incorporates the line impedance effect in droop parameter calculation by modifying droop coefficients can be used to overcome this drawback. However, inclusion of power decoupling term in reference voltage calculation, has found to be more powerful to overcome coupling effects in load power sharing. By utilizing lesser steady state frequency deviation of angle droop in comparison with frequency droop, this paper adopts angle droop in real power loop. Angle droop concept along with power decoupling factor has an added advantage of improved reactive power sharing with surplus accuracy in real power distribution, which in turn, allows harmonic power distribution based on converter rating under different load conditions. Moreover, discrete state feedback control together with third harmonic injection-based pulse width modulation scheme provides additional robustness to individual converters.

Effect of interference correlation on wireless systems is often studied by modeling the locations of interferers as a Poisson Point Process (PPP). However, in many cases, the complicated nature of this correlation limits the analytical tractability of the PPP-based approach. For example, for an interference-aware $N$-antenna Maximum-Ratio Combining (MRC) receiver, the analytical expression for outage probability is available only for $N=2$. For $N>2$, the exact analysis using standard PPP-based approach becomes intractable because of which one has to either resort to bounds or to simulations. In this letter, we overcome this issue and derive the MRC outage probability for an arbitrary $N$ by employing the mixture-based method of modeling the correlation in the interference powers. This method offers a much simpler analytical structure to the correlated interference, thereby lending analytical tractability to such analyses. The mixture parameter ($q$) is tuned based on the matching of joint Signal-to-Interference Ratio (SIR) statistics, which results in a very accurate mixture-based result. The tightness of these approximations is verified using Monte Carlo simulations., To appear in IEEE Communications Letters

A two-level decentralized hierarchical control strategy is developed to cope with active power deficiencies in remote microgrid (MG) systems containing intermittent energy resources. The primary level consists of a multilayer droop-based scheme designed to dispatch the required loads to be shed amongst controllable loads (CLs). The dispatch is proportionally fulfilled through the appropriate assignment of each layer of the droop curves to its corresponding priority type of the CLs. If the primary level is unable to handle the shortfall, the secondary level of the scheme is invoked by coupling of the overloaded MG with a neighboring one. Appropriate criteria are accurately formulated to assure desirable interconnections and proper isolations of the MGs. By detecting an overloading condition, the primary level attempts to raise the frequency by managing the CLs, whereas the secondary level assesses the possibility of forming a system of coupled MGs (CMG). Depending on the level of support provided by the neighboring MG, the shed loads can be restored completely or partially once the system of CMG is formed. Implementation of the two levels is coordinated such that the power shortfall can be relieved with very low bandwidth communication systems. Validity of the proposed strategy is demonstrated through several PSCAD/EMTDC studies.

This paper proposes a supervisory control scheme to facilitate coupling of remote droop-regulated microgrids (MGs) during power shortfalls. In this scheme, instead of power converters, an instantaneous static switch is incorporated for the interconnection. Therefore a supervisory controller is essential to cope with the associated challenges, which are: 1) the level of supporting power provided by the neighboring MG and 2) isolation procedure of the coupled MGs (CMG) when the power deficiency condition is removed. Droop coefficients of distributed generators of the overloaded MG are dynamically updated by the controller according to the three operating modes defined to address the aforementioned challenges. The transit criteria, as well as the controlling signals, are accurately formulated based only on the local measurements to decrease the dependency on the communication systems. This enhances the reliability level of the coupled system. Effectiveness of the proposed strategy is validated through the results obtained from PSCAD/EMTDC simulations. Also, small-signal stability of the CMG operated by the proposed controller is examined using a developed model in MATLAB.

International audience; Swift variations in the cloud cover may cause significant power output fluctuations in solar power systems, jeopardizing power quality. Forecasting the power output with a very short horizon below 30 s can be seen as a cloud cover forecasting problem solved by processing images from a sky camera. After a preprocessing stage that identifies clouds with a criterion based on the red-green blue values of each pixel, a probability hypothesis density filter or a more advanced cardinalized probability hypothesis density filter can be used to an unknown and varying number of clouds. The time when cumulus clouds will shade the sun can be forecasted with an absolute precision 6 s ahead and with an acceptable accuracy 27 s ahead. It has been found that both filters are equally well suited for a real-time online nowcasting application. They also have the potential to deal with noise and the swift dynamics and high variability of clouds.

A wireless data communication system for future microgrids (MGs) is presented in this paper. It is assumed that each MG has a central controller and each distributed generation unit in the MG has a local controller. The communication system is responsible for transmitting and receiving data amongst these controllers. This communication system is based on ZigBee technology, which is a low cost and low power consumption device. However, its main limitation is the low data transfer rate. To reduce the number of data transactions, a data management scheme is presented in this paper. The required data to be transferred are defined and a suitable coding is proposed. Finally, the number of transmitted symbols and the processing time of the proposed data management scheme are numerically analyzed. In addition, the dynamic operation of an MG is evaluated considering the delays that are imposed by this communication system.

This paper suggests a supervisory control for storage units to provide load leveling in distribution networks. This approach coordinates storage units to charge during high generation and discharge during peak load times, while utilized to improve the network voltage profile indirectly. The aim of this control strategy is to establish power sharing on a pro rata basis for storage units. As a case study, a practical distribution network with 30 buses is simulated and the results are provided.

This paper proposes a distributed control approach to coordinate multiple energy storage units (ESUs) to avoid violation of voltage and thermal constraints, which are some of the main power quality challenges for future distribution networks. ESUs usually are connected to a network through voltage source converters. In this paper, both ESU converters active and reactive power are used to deal with the above mentioned power quality issues. ESUs' reactive power is proposed to be used for voltage support, while the active power is to be utilized in managing network loading. Two typical distribution networks are used to apply the proposed method, and the simulated results are illustrated in this paper to show the effectiveness of this approach.

Summary form only given. In this paper, a new comprehensive planning methodology is proposed for implementing distribution network reinforcement. The load growth, voltage profile, distribution line loss, and reliability are considered in this procedure. A time-segmentation technique is employed to reduce the computational load. Options considered range from supporting the load growth using the traditional approach of upgrading the conventional equipment in the distribution network, through to the use of Distributed Generators (DG). The objective function is composed of the construction cost, loss cost and reliability cost. As constraints, the bus voltages and the feeder currents should be maintained within the standard level. The DG output power should not be less than a ratio of its rated power because of efficiency. A hybrid optimization method, called Modified Discrete Particle Swarm Optimization, is employed to solve this nonlinear and discrete optimization problem. A comparison is performed between the optimized solution based on planning of capacitors along with tap-changing transformer and line upgrading and when DGs are included in the optimization.

To cover wide range of pulsed power applications, this paper proposes a modularity concept to improve the performance and flexibility of the pulsed power supply. The proposed scheme utilizes the advantage of parallel and series configurations of flyback modules in obtaining high-voltage levels with fast rise time (dv/dt). Prototypes were implemented using 600-V insulated-gate bipolar transistor (IGBT) switches to generate up to 4-kV output pulses with 1-kHz repetition rate for experimentation. To assess the proposed modular approach for higher number of the modules, prototypes were implemented using 1700-V IGBTs switches, based on ten-series modules, and tested up to 20 kV. Conducted experimental results verified the effectiveness of the proposed method.

Cooperative applications for VANETs will require seamless communication between vehicle to infrastructure and vehicle to vehicle. IEEE 802.11p has been developed to facilitate this effort. However, in order to have seamless communication for these applications, it is necessary to look at handover as vehicles move between roadside units. Traditional models of handover used in normal mobile environments are unable to cope with the high velocity of the vehicle and the relatively small area of coverage with regard to vehicular environments. The Y-Comm framework has yielded techniques to calculate the time before vertical handover and the network dwell time for any given network topology. Furthermore, by knowing these two parameters, it is also possible to improve channel allocation and resource management in network infrastructure such as base stations, relays, and so on. In this article we explain our overall approach by describing the VANET Testbed and show that in vehicular environments it is necessary to consider a new handover model that is based on a probabilistic rather than a fixed coverage approach. Finally, we show a new performance model for proactive handover, which is then compared with traditional approaches. Introdu

This paper presents a novel topology for the generation of high voltage pulses that uses both slow and fast solid-state power switches. This topology includes diode-capacitor units in parallel with commutation circuits connected to a positive buck-boost converter. This enables the generation of a range of high output voltages with a given number of capacitors. The advantages of this topology are the use of slow switches and a reduced number of diodes in comparison with conventional Marx generator. Simulations performed for single and repetitive pulse generation and experimental tests of a prototype hardware verify the proposed topology.

The flying capacitor multicell inverter (FCMI) possesses natural balancing property. With the phase-shifted carrier-based scheme, natural balancing can be achieved in a straightforward manner. However, to achieve natural balancing with the harmonically optimal phase-disposition (PD) carrier-based scheme, the conventional approaches require (n - 1) × (n - 1) trapezoidal carrier signals for an n-level inverter, which is ( n - 1) × (n - 2) times more than that in the standard PD scheme. This paper proposes two improved natural balancing strategies for FCMI under PD scheme, which use the same (n - 1) carrier signals as used in the standard PD scheme. In the first scheme, the on-line detections are performed of (i) the band in which the modulation signal is located, (ii) corresponding period number of the carrier, and (iii) rising or falling half cycle of the carrier waveform to generate the switching signals based on certain rules. In the second strategy, the output voltage level selection is first processed and the switching signals are then generated according to a rule based on preferential cell selection algorithm. These methods are easy to use and can be simply implemented as compared to the other available methods. Simulation and experimental results are presented for a five-level inverter to verify these proposed schemes.

The hysteresis modulation for power electronic converters is attractive in many different applications because of its unmatched dynamic response and wide command-tracking bandwidth. Its application and benefits for two-level converters are well understood, but the extension of this strategy to multilevel converters is still under development. This paper summarizes and reviews the various hysteresis modulation approaches available in the literature for multilevel converters. The pros and cons of various techniques are described and compared for tracking the reference signal in order to attain an adequate switching optimization, excellent dynamic responses and high accuracy in steady-state operation. By using the recently developed multilevel hysteresis modulation approaches, the advantages of using several accessible dc potentials in a multilevel inverter have been fully exploited. All of these hysteresis modulation approaches are tested for tracking a current reference when applied to a five-level inverter. The relevant simulation and experimental results are also presented. This study will provide a useful framework and point of reference for the future development of hysteresis modulation for multilevel converters.

In this paper, the performance of voltage-source converter-based shunt and series compensators used for load voltage control in electrical power distribution systems has been analyzed and compared, when a nonlinear load is connected across the load bus. The comparison has been made based on the closed-loop frequency resopnse characteristics of the compensated distribution system. A distribution static compensator (DSTATCOM) as a shunt device and a dynamic voltage restorer (DVR) as a series device are considered in the voltage-control mode for the comparison. The power-quality problems which these compensator address include voltage sags/swells, load voltage harmonic distortions, and unbalancing. The effect of various system parameters on the control performance of the compensator can be studied using the proposed analysis. In particular, the performance of the two compensators are compared with the strong ac supply (stiff source) and weak ac-supply (non-still source) distribution system. The experimental verification of the analytical results derived has been obtained using a laboratory model of the single-phase DSTATCOM and DVR. A generalized converter topology using a cascaded multilevel inverter has been proposed for the medium-voltage distribution system. Simulation studies have been performed in the PSCAD/EMTDC software to verify the results in the three-phase system.

An algorithm based on the concept of combining Kalman filter and Least Error Square (LES) techniques is proposed in this paper. The algorithm is intended to estimate signal attributes like amplitude, frequency and phase angle in the online mode. This technique can be used in protection relays, digital AVRs, DGs, DSTATCOMs, FACTS and other power electronics applications. The Kalman filter is modified to operate on a fictitious input signal and provides precise estimation results insensitive to noise and other disturbances. At the same time, the LES system has been arranged to operate in critical transient cases to compensate the delay and inaccuracy identified because of the response of the standard Kalman filter. Practical considerations such as the effect of noise, higher order harmonics, and computational issues of the algorithm are considered and tested in the paper. Several computer simulations and a laboratory test are presented to highlight the usefulness of the proposed method. Simulation results show that the proposed technique can simultaneously estimate the signal attributes, even if it is highly distorted due to the presence of non-linear loads and noise.

This paper proposes new droop control methods for load sharing in a rural area with distributed generation. Highly resistive lines, typical of rural low voltage networks, always create a big challenge for conventional droop control. To overcome the conflict between higher feedback gain for better power sharing and system stability in angle droop, two control methods have been proposed. The first method considers no communication among the distributed generators (DGs) and regulates the converter output voltage and angle ensuring proper sharing of load in a system having strong coupling between real and reactive power due to high line resistance. The second method, based on a smattering of communication, modifies the reference output volt-age angle of the DGs depending on the active and reactive power flow in the lines connected to point of common coupling (PCC). It is shown that with the second proposed control method, an economical and minimum communication system can achieve significant improvement in load sharing. The difference in error margin between proposed control schemes and a more costly high bandwidth communication system is small and the later may not be justified considering the increase in cost. The proposed control shows stable operation of the system for a range of operating conditions while ensuring satisfactory load sharing.

This paper discusses a new paradigm of real-time simulation of power systems in which equipment can be interfaced with a real-time digital simulator. In this scheme, one part of a power system can be simulated by using a real-time simulator; while the other part is implemeneted as a physical system. The only interface of the physical system with the computer-based simulator is through data-acquisition system. The physical system is driven by a voltage-source converter (VSC)that mimics the power system simulated in the real-time simulator. In this papar, the VSC operates in a voltage-control mode to track the point of common coupling voltage signal supplied by the digital simulator. This type of splitting a network in two parts and running a real-time simulation with a physical system in parallel is called a power network in loop here. this opens up the possibility of study of interconnection o f one or several distributed generators to a complex power network. The proposed implementation is verified through simulation studies using PSCAD/EMTDC and through hardware implementation on a TMS320G2812 DSP.

In this paper, a fixed-switching-frequency closed-loop modulation of a voltage-source inverter (VSI), upon the digital implementation of the modulation process, is analyzed and characterized. The sampling frequency of the digital processor is considered as an integer multiple of the modulation switching frequency. An expression for the determination of the modulation design parameter is developed for smooth modulation at a fixed switching frequency. The variation of the sampling frequency, switching frequency, and modulation index has been analyzed for the determination of the switching condition under closed loop. It is shown that the switching condition determined based on the continuous-time analysis of the closed-loop modulation will ensure smooth modulation upon the digital implementation of the modulation process. However, the stability properties need to be tested prior to digital implementation as they get deteriorated at smaller sampling frequencies. The closed-loop modulation index needs to be considered maximum while determining the design parameters for smooth modulation. In particular, a detailed analysis has been carried out by varying the control gain in the sliding-mode control of a two-level VSI. The proposed analysis of the closed-loop modulation of the VSI has been verified for the operation of a distribution static compensator. The theoretical results are validated experimentally on both single- and three-phase systems.

This paper presents the stability analysis for a distribution static compensator (DSTATCOM) that operates in current control mode based on bifurcation theory. Bifurcations delimit the operating zones of nonlinear circuits and, hence, the capability to compute these bifurcations is of important interest for practical design. A control design for the DSTATCOM is proposed. Along with this control, a suitable mathematical representation of the DSTATCOM is proposed to carry out the bifurcation analysis efficiently. The stability regions in the Thevenin equivalent plane are computed for different power factors at the point of common coupling. In addition, the stability regions in the control gain space, as well as the contour lines for different Floquet multipliers are computed. It is demonstrated through bifurcation analysis that the loss of stability in the DSTATCOM is due to the emergence of a Neimark bifurcation. The observations are verified through simulation studies.

This paper examines the application of a diode-clamped multilevel inverter (DCMLI)-based distribution static compensator (DSTATCOM) connected to a three-phase, four-wire (3p4w) distribution system. The DCMLI has an inherent unbalancing problem among its DC capacitor voltages. Additionally, when the load contains a DC part, the neutral point of the compensator also becomes unbalanced. In this paper, the effects of different loading conditions on the DC capacitor voltages of the inverter are studied. Two new control circuits are proposed for equalizing the capacitor voltages. Different control techniques are presented for the equalizing circuits. Equations of the proposed equalizing controllers are developed corresponding to the control of the switching devices. Comparative studies of different control techniques and the performances of the two controllers are performed. Simulation studies are performed using PSCAD/EMTDC to validate the efficacy of the proposed equalizing controller circuits.

In this paper, the method of triangular carrier switching control of two-level inverters is extended to cascaded multilevel inverters using phase-shifted multicarrier unipolar pulsewidth modulation (PWM). The condition for smooth modulation is obtained using the Bessel's function representation of the PWM output and the switching condition of the multilevel-inverter-controlled system. A method is proposed for the determination of the minimum amplitude of the triangular carrier for smooth modulation at fixed switching frequency. It is shown that the multilevel modulation based on the phase-shifted carriers significantly reduces the ripple magnitude in the switching function and allows the use of a smaller carrier amplitude under closed loop. This increases the forward gain and, hence, improves the tracking characteristics. The proposed cascaded multilevel inverter control is implemented for the operation of a distribution static compensator (DSTATCOM) in the voltage control mode. The experimental verification of the theoretical and simulation results is provided through a field-programmable gate array (FPGA) based control of a laboratory model of a single-phase DSTATCOM.

This paper proposes a new connection for a unified power quality conditioner (UPQC) to improve the power quality of two feeders in a distribution system. A UPQC consists of a series voltage-source converter (VSC) and a shunt VSC both joined together by a common dc bus. It is demonstrated how this device is connected between two independent feeders to regulate the bus voltage of one of the feeders while regulating the voltage across a sensitive load in the other feeder. Since the UPQC is connected between two different feeders (lines), this connection of the UPQC will be called an interline UPQC (IUPQC). The structure, control and capability of the IUPQC are discussed in this paper. The efficacy of the proposed configuration has been verified through simulation studies using PSCAD/EMTDC

Flying capacitor multilevel inverter (FCMLI) is a multiple voltage level inverter topology intended for high voltage and power operations with low distortion. It uses capacitors, called flying capacitors for clamping the voltage across the power semiconductor devices. In this paper, the implementation of a distribution static compensator (DSTATCOM) using an FCMLI is presented. A hysteresis current control technique for controlling the injected current by the FCMLI-based DSTATCOM is discussed. A new method for controlling the flying capacitor voltages is proposed which ensures that their voltages remain constant and at the same time maintain the desired current profile under the hysteresis current control operation. Simulation studies are performed using PSCAD/EMTDC to validate the efficacy of the control scheme and the FCMLI-based DSTATCOM

In this paper, load compensation techniques under unbalanced and distorted voltages have been discussed. Two kinds of compensation methods are considered. In the first category, synchronous detection and modified equal current strategies are used under the unbalanced but sinusoidal source voltages. In the second method, load compensation based on instantaneous symmetrical component theory with positive sequence extraction is proposed and is shown to work under unbalanced and the non-sinusoidal source voltages. To support the proposed method, a 440 V (L-L) three-phase, four-wire distribution system is considered. The compensator is realized using a three-phase voltage source inverter (VSI) operated in the current control mode. Detailed digital simulation and experimental results are presented to validate the approach. � 2006 IEEE.

In this paper, the commonly used switching schemes for sliding mode control of power converters is analyzed and designed in the frequency domain. Particular application of a distribution static compensator (DSTATCOM) in voltage control mode is investigated in a power distribution system. Tsypkin's method and describing function is used to obtain the switching conditions for the two-level and three-level voltage source inverters. Magnitude conditions of carrier signals are developed for robust switching of the inverter under carrier-based modulation scheme of sliding mode control. The existence of border collision bifurcation is identified to avoid the complex switching states of the inverter. The load bus voltage of an unbalanced three-phase nonstiff radial distribution system is controlled using the proposed carrier-based design. The results are validated using PSCAD/EMTDC simulation studies and through a scaled laboratory model of DSTATCOM that is developed for experimental verification

The flying capacitor multilevel inverter (FCMLI) is a multiple voltage level inverter topology intended for high-power and high-voltage operations at low distortion. It uses capacitors, called flying capacitors, to clamp the voltage across the power semiconductor devices. A method for controlling the FCMLI is proposed which ensures that the flying capacitor voltages remain nearly constant using the preferential charging and discharging of these capacitors. A static synchronous compensator (STATCOM) and a static synchronous series compensator (SSSC) based on five-level flying capacitor inverters are proposed. Control schemes for both the FACTS controllers are developed and verified in terms of voltage control, power flow control, and power oscillation damping when installed in a single-machine infinite bus (SMIB) system. Simulation studies are performed using PSCAD/EMTDC to validate the efficacy of the control scheme and the FCMLI-based flexible alternating current transmission system (FACTS) controllers.

The paper discusses the concept of a mini custom power park in which the voltage inside the park is tightly regulated by a distribution static compensator (DSTATCOM). It will be shown on the basis of simulations with ideal components that solid state protection devices, along with the DSTATCOM will eliminate many transients in all the loads of the park during disturbances. Moreover, the DSTATCOM, backed by a diesel generator, will supply the most sensitive loads during the total line outages, thereby nearly making them both transient and interruption free. In this paper, a configuration of the park is proposed and then various issues involved with the operation of the park are discussed. The proposed operation of the custom power park is verified through extensive digital computer simulation studies.

The paper discusses the operating principles and control characteristics of a dynamic voltage restorer (DVR) that protects sensitive but unbalanced and/or distorted loads. The main aim of the DVR is to regulate the voltage at the load terminal irrespective of sag/swell, distortion, or unbalance in the supply voltage. In this paper, the DVR is operated in such a fashion that it does not supply or absorb any active power during the steady-state operation. Hence, a DC capacitor rather than a DC source can supply the voltage source inverter realizing the DVR. The proposed DVR operation is verified through extensive digital computer simulation studies.

The paper discusses load compensation using a distribution static compensator (DSTATCOM). It is assumed that the DSTATCOM is associated with a load that is remote from the supply. It is shown that the operation of a DSTATCOM assuming that it is connected to a stiff source in such situations will result in distortions in source current and voltage at the point of common coupling. To avoid this, the DSTATCOM is connected in parallel with a filter capacitor that allows the high frequency component of the current to pass. However, this generates control issues in tracking, as standard controls such as a hysteresis control are not suitable in these circumstances. This paper proposes a new switching control scheme and demonstrates its suitability for this problem. It also proposes a scheme in which the fundamental sequence components of a three-phase signal can be computed from its samples. The overall performance of the proposed scheme is verified using digital computer simulation studies.

In this paper, a static synchronous series compensator (SSSC), along with a fixed capacitor, is used to avoid torsional mode instability in a series compensated transmission system. A 48-step harmonic neutralized inverter is used for the realization of the SSSC. The system under consideration is the IEEE first benchmark model on SSR analysis. The system stability is studied both through eigenvalue analysis and EMTDC/PSCAD simulation studies. It is shown that the combination of the SSSC and the fixed capacitor improves the synchronizing power coefficient. The presence of the fixed capacitor ensures increased damping of small signal oscillations. At higher levels of fixed capacitor compensation, a damping controller is required to stabilize the torsional modes of SSR.

This paper presents the operating principles of a distribution static compensator (DSTATCOM) that is used to maintain the voltage of a distribution bus. A three-phase, four-wire distribution system is assumed in this study. A three-phase bridge inverter circuit that is supplied by two neutral-clamped dc storage capacitors realizes the DSTATCOM. Three filter capacitors, one for each phase, are connected in parallel with the DSTATCOM to eliminate high-frequency switching components. The voltage across the filter capacitor is controlled by a dead-beat controller to maintain the ac bus voltage. The magnitude of the bus voltage is chosen as a nominal value, i.e., 1.0 per unit, while its phase angle is obtained through a feedback loop that maintains the voltage across the dc storage capacitors. Through detailed simulation and experimental results it has been shown that the DSTATCOM can maintain the voltage against any unbalance and distortion in either the load or supply side.

A dynamic voltage restorer (DVR) is a power-electronic controller that can protect sensitive loads from disturbances in the supply system. In this paper, it is demonstrated that this device can tightly regulate the voltage at the load terminal against imbalance or harmonic in the source side. The behavior of the device is studied through steady-state analysis, and limits to achievable performance are found. This analysis is extended to the study of transient operation where the generation of the reference voltage of the DVR is discussed. Once the reference signals are generated, they are tracked using a switching band scheme. A suitable structure in which the DVR is realized by voltage-source inverters (VSIs) is also discussed. Particular emphasis to the rating of this device is provided. Extensive simulation results are included to illustrate the operating principles of a DVR.

This paper presents a new approach for generating reference currents for an active filter and/or a static compensator. It is assumed that the compensator is connected to a load that may either be connected in star or in delta. The load can be unbalanced and may also draw harmonic currents. The purpose of the compensating scheme is to balance the load, as well as make the supply side power factor a desired value. The authors use the theory of instantaneous symmetrical components to obtain an algorithm to compute three phase reference currents which, when injected to the power system, produce desired results. They also propose a suitable compensator structure that will track the reference currents in a hysteresis band control scheme. Finally, the feasibility of such a scheme is demonstrated through simulation studies.

The design, modeling and control design of a 48-step inverter based static synchronous series compensator (SSSC) is presented in this paper. A magnetic circuit is chosen which contains eighteen single-phase three winding transformers and six single-phase two winding transformers to add the output voltages of eight three-phase inverters. An equivalent circuit model of the SSSC is derived and based on this model a proportional-plus-integral controller is proposed. The controller gains are chosen through eigenvalue analysis of the IEEE first benchmark model for subsynchronous resonance (SSR) analysis. The SSSC model, its control and the results of the eigenvalue analysis are then validated through PSCAD/EMTDC simulation. It is shown that for certain controller gains torque amplification of the shaft modes can occur.

This letter presents a new method for the generation of reference voltage for a dynamic voltage restorer (DVR). These volt- ages, when injected in series with a distribution feeder by a voltage source inverter, can tightly regulate the voltage at the load terminal against imbalance or harmonics in the source side. It is stipulated that the DVR does not supply any real power in the steady state. The refer- ence voltage generation scheme is validated through digital computer simulation studies.

Optimum path planning algorithms for robot manipulators are presented. It is assumed that a manipulator is working in an environment that contains a static obstacle or another manipulator. A collision avoidance strategy is developed based on a simplified representation of the robot arm. The two different path planning problems addressed are the minimum-time path planning and the minimum-energy path planning. These problems are solved using a variational approach called the method of local variations (MLV). This method finds a solution to the optimal control problem iteratively under constraints on state and control variables. To solve these problems, a collision-free path is first chosen. Then the MLV is applied based on a discrete-time state-space model of the manipulator. The collision checking strategy is incorporated in the variational structure to obtain the optimal paths. The proposed algorithms are tested through digital computer simulations. >

This letter discusses a new general algorithm for shunt active power filters using instantaneous reactive power theory. The general vector expression for desired source current has been formulated. Proper choices of source power terms give different levels and types of compensation.

A microgrid (MG) is expected to supply its local loads independently; however, due to intermittency of wind and solar-based energy resources as well as the load uncertainty, it is probable that the MG experiences power deficiency (overloading). This problem can be mitigated by coupling the overloaded MG to another neighboring MG that has surplus power. Considering a distribution network composed of several islanded MGs, defining the suitable MGs (alternative) to be coupled with the overloaded MG is a challenge. An MG overload management technique is developed in this paper, which first identifies the overloaded MG(s) and then selects the most suitable alternative. The alternative selection is based on different criteria, such as available surplus power, reliability, supply security, power loss, electricity cost, and CO2 emissions in the alternative MGs. Moreover, the frequency and voltage deviation in the system of coupled MGs are considered in the selection. A dynamic multicriteria decision-making algorithm is developed for this purpose. To contemplate the uncertainties in the considered distribution network, a cloud theory-based probabilistic analysis is deployed as the research framework and the performance of the developed technique is evaluated in MATLAB.

Micro- and nano-mechanical resonators have been proposed for a variety of applications ranging from mass sensing to signal processing. Often their actuation and/or detection involve external subsystems that are much larger than the resonator itself. We have designed a simple microcantilever resonator with integrated sensor and actuator, facilitating the integration of large arrays of resonators. This unique design can be manufactured with a low-cost fabrication process, involving just a single step of lithography. The bilayer cantilever of gold and silicon dioxide is used as piezoresistive sensor as well as thermal bimorph actuator. The ac current used for actuation and the dc current used for piezoresistive detection are separated in the frequency-domain using a bias-tee circuit configuration. The resonant response is measured by detecting the second harmonic of the actuation current using a lock-in amplifier.

The author discusses the original paper ("A new approach to load balancing and power factor correction in power distribution system", A. Ghosh et al., see ibid., vol.15, no.1, p.417-22, 2000) and presents his observations and suggestions. The original authors' response to the discussion is also included.

Voltage imbalance in capacitors is a well-known problem in compensator topologies which use two or more capacitors. This imbalance may exist even if the load does not contain any DC component, due to practical factors. However, when the load contains a DC part, the voltage imbalance problem becomes critical. In this paper, a two-quadrant chopper has been used to regulate the capacitor voltages in a two-capacitor compensator structure. Two different control strategies for the two-quadrant chopper to equalize the voltage of the capacitors have been proposed. The strategies are validated through detailed simulation studies. Experiments have also been carried out to validate the hysteresis control of chopper.