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Three instruments have been evaluated for their ability to estimate the load conditions and efficiency of operating motors based solely on measurements of terminal voltage and current. Laboratory tests, compared to a high-accuracy dynamometer system were used to assess the instruments' accuracy. Field tests were conducted in a paper mill to determine the ease of use and lack of intrusion. In both laboratory and field tests the instruments were applied to 50-hp, 100-hp, and 200-hp 460-V induction motors. Data of the relative accuracies of the three instruments, as functions of motor load and supply voltage, are presented together with observations of ease and lack of intrusion in use. [ABSTRACT FROM AUTHOR]

This paper presents a literature review on magnetically-controlled devices, variable inductors (VI), and variable transformers (VT), and their applications to lighting gears for discharge lamps and/or LED lamps. These current-controlled devices are mainly characterized by nonlinear and non-uniform saturation of the magnetic core. The paper describes the fundamentals and basic operating principle of such devices and provides an overview of existing patents. These patents refer the devices, VIs or VTs, as useful or industrially applicable. Some present one or more claims regarding the construction of the device and behavioral characteristic; others refer to specific applications, such as voltage regulation or universal ballast operation. Afterwards, the paper focuses on the review of specific techniques and circuits taking advantage of the presence of a controlled inductance value, by covering recent applications regarding discharge and solid-state lamp drivers. These applications will show how these multi-winding devices, typically not considered due to their low efficiency, may fulfill an important role and add features to state-of-the-art lamp drivers. [ABSTRACT FROM AUTHOR]

This paper presents the flexible dc capacitor voltages balancing control method for star-connected cascaded H-bridge converters. In this paper, the power flows are analyzed by investigating all the converter's control freedoms. Based on the analyses, users can accomplish the dc capacitor voltage balancing with both negative-sequence current and zero-sequence voltage. These two kinds of control options are further integrated together with the defined weighting factor $K$. The low-voltage ride-through operation of a proposed control method is also discussed in this paper. The control method is verified with a 220-V 1-kVA static synchronous compensators based on the star-connected cascaded H-bridge converters, and the experimental test results show that all the dc voltages are well regulated at the commanded value with different weighting factor $K$. [ABSTRACT FROM AUTHOR]

The ever growing penetration of distributed generation (DG) in a distribution network has a profound impact on network protection and stability. Traditional protection schemes and algorithms need to be extensively investigated as more and more DGs get introduced into the network. The current version of IEEE Standard 1547 does not present a comprehensive solution for fault current detection in the presence of various kinds of DGs. Power electronic inverter-based DGs (IBDGs) are of special concern in distribution network protection as they are often incapable of providing sufficient fault current and their controllers play a principal role in the DG behavior. In this paper, the effects of voltage and current controllers for IBDGs on industrial and commercial power system protection schemes are investigated. It is shown that the inverter control mode has a direct impact on its fault current levels and duration. A simplified distribution network model with IBDG operating under voltage and current control modes was tested to verify the effects of these controllers. This paper also proposes an adaptive relaying algorithm to detect the faults in the presence of IBDGs with various types of controllers. [ABSTRACT FROM AUTHOR]

The next big change in various industry applications is associated with power dense motors, such as permanent magnet synchronous motors (PMSMs). Utilization of multiphase PMSM can offer an additional fault-tolerant capability to their applications. Combining both advantages, this paper proposes a simple yet robust current control strategy for a five-phase PMSM under normal operation and in a case of a loss of one phase. Traditional linear current controllers successfully applied to reference tracking of a healthy motor may become less efficient during postfault operation due to additional unmodeled dynamics. This paper proposes a modified angular transformation to a special rotating frame in which the postfault permanent magnet flux linkage remains unchanged and the motor model remains decoupled. Following this, a nonlinear current control scheme based on sliding mode control is proposed, which successfully treats model inaccuracies and provides good dynamic performance and tracking accuracy. Feasibility of the proposed control strategy is experimentally validated on a laboratory scale PMSM motor with a digital signal processor/field programmable gate array based drive. [ABSTRACT FROM AUTHOR]

To prevent the high voltage direct current ground electrode from eroding, it is usually wrapped by a coke bed, which may affect the electrical performance of the electrode, such as current distribution and step voltage. In this paper, the effect is analyzed by a numerical method, which couples moment method with circuit theory by regarding the coke bed as several resistors connecting the ground electrode with soil. The method is simple and efficient. The calculated results are in good agreement with the measured ones. The current distribution, ground resistance. and step voltage of several typical electrodes with and without coke beds are calculated. The effect of the coke bed on the above parameters is summed up. [ABSTRACT FROM AUTHOR]

This paper uses formal mathematical optimization techniques based on parametric finite-element-based computationally efficient models and differential evolution algorithms. For constant-power applications, in the novel approach described, three concurrent objective functions are minimized: material cost, losses, in order to ensure high efficiency, and the difference between the rated and the characteristic current, aiming to achieve very high constant-power flux-weakening range. Only the first two objectives are considered for constant-torque applications. Two types of interior permanent magnet rotors in a single- and double-layer V-shaped configuration are considered, respectively. The stator has the typical two slots per pole and phase distributed winding configuration. The results for the constant-torque design show that, in line with expectations, high efficiency and high power factor machines are more costly, and that the low-cost machines have poorer efficiency and power factor and most importantly, and despite a common misconception, the saliency ratio may also be lower in this case. For constant-power designs, the saliency ratio can be beneficial. Nevertheless, despite a common misconception, when cost is considered alongside performance as an objective, a higher saliency ratio does not necessarily improve the power factors of motors suitable for ideal infinite flux weakening. [ABSTRACT FROM AUTHOR]

Renewable power plants must comply with certain codes and requirements to be connected to the grid, being the ramp-rate compliance one of the most challenging requirements, especially for photovoltaic or wind energy generation plants. Battery-based energy storage systems represent a promising solution due to the fast dynamics of electrochemical storage systems, besides their scalability and flexibility. However, large-scale battery energy storage systems are still too expensive to be a mass market solution for the renewable energy resources integration. Thus, in order to make battery investment economically viable, the use of second life batteries is investigated in the paper. This paper proposes a method to determine the optimal sizing of a second life battery energy storage system (SLBESS). SLBESS performance is also validated and, as an ultimate step, the power exchanged with the batteries is calculated during one-year operation. The power profile obtained is further used to define the cycling patterns for laboratory testing of second life batteries and to study their ageing evolution when used for the power smoothing renewable integration application. Real photovoltaic energy generation data from a Spanish plant were used for the study. [ABSTRACT FROM AUTHOR]

Many research works report the use of LCL filters for grid-interfaced PV systems. Indiscreet selection of passive LCL filter parameters may result in poor filtering and increased power losses. LCL filter parameter selection is critical to get a good performance and at the same time ensure that losses and costs stay low. This paper proposes a novel approach to design the LCL filter for a grid-interfaced PV system. A cost-based minimization approach on a cost per joule basis for each of the filter elements is explored to obtain the optimal filter design. Simulation results for a 10-kVA grid-connected inverter with an LCL filter are presented in order to verify the efficacy of the proposed design. The impact of designed filter parameters on the ripple current is also discussed in this paper. The total inductance of the LCL filter is varied and filter parameter values which give lowest cost is identified while meeting harmonic standard requirements and the fundamental voltage drop across the filter. Finally, the proposed design is also experimentally validated via a hardware prototype. Results validate the design method in terms of the harmonic attenuation and total harmonic distortion. [ABSTRACT FROM AUTHOR]

This paper presents theoretical and experimental discussions on a practical speed-sensorless start-up method for an induction motor driven by a modular multilevel cascade inverter based on double-star chopper cells (MMCI-DSCC) from standstill to middle speed. This motor drive is suitable, particularly for a large-capacity fan- or blower-like load. The load torque is proportional to a square of the motor mechanical speed. The start-up method is characterized by combining capacitor-voltage control with motor-speed control. The motor-speed control with the minimal stator current plays a crucial role in eliminating a speed sensor from the drive system and in reducing an ac-voltage fluctuation occurring across each dc capacitor. Experimental results obtained from the 400-V 15-kW downscaled system with no speed sensor verify that the motor-speed control proposed for the DSCC-based drive system can enhance the start-up torque by a factor of three under the same ac-voltage fluctuation. Several start-up waveforms show stable performance from standstill to middle speed with different load torques. [ABSTRACT FROM AUTHOR]

This paper proposes a novel multifunctional controller for a dimmable high-power-factor single-switch electronic ballast that can be used with standard phase-cut dimmers. Conventional dimmable electronic ballasts lack the ability to 1) provide smooth dimming and maintain high power factor when phase-cut dimmers are used and 2) regulate the lamp power when the input line voltage varies. A digital controller with multiple control functions is proposed in this paper. The proposed controller allows high power factor to be achieved by controlling the duty cycle during dimming with standard phase-cut dimmers. On the other hand, when dimming is not required, the lamp power is regulated through the regulation of the dc-link voltage. Additional control functions, such as lamp low-power cutoff operation, and protection function are also implemented inside the digital controller. The descriptions of the controller operating principles and its logic flow diagrams are provided in this paper. PSIM simulation and experimental results are provided on a 13-W compact fluorescent lamp to highlight the merits of the proposed work. [ABSTRACT FROM AUTHOR]

This paper presents an experimental efficiency comparison study between two different direct ac–ac converter topologies; a direct matrix converter and an indirect matrix converter. The evaluation is performed under variable load conditions using both discrete silicon isolated gate bipolar transistor and silicon carbide MOSFETs working at power levels up to 9 kW. Each loss measurement is carried out using two power analyzers; one placed at the input and one at the output of the converter under study. To facilitate this measurement, an output filter was necessary in addition to the normal input filter. Both converters are modulated using the same traditional symmetrical space vector approach and feature an identical input/output filter design. [ABSTRACT FROM PUBLISHER]

This paper was written to share the experience acquired in the specification of surge suppressors (snubbers) for protection against switching transients’ overvoltage resulting primarily in dry-type transformers failures in some plants in Brazil and North America. This paper will also explain about the snubber ratings (damping resistor, surge capacitor, and surge arrester), the assembly special cares, system modeling, and simulations using the software Alternative Transient Program. [ABSTRACT FROM PUBLISHER]

In this paper, a new technique to equalize light-emitting diode (LED) currents in multiarray LED lamps is proposed. The current through the LEDs is controlled by changing the inductance of a variable inductor. The proposed technique can be employed to control the current through each LED branch independently. The operation principle of this technique and a design example of the proposed system are presented in detail in this paper. As an example, a forward converter has been selected to supply the LED branches, which can be designed to operate with one or several outputs. The component values of the converter as well as the LED current control circuit are also calculated as a design example. A prototype of the circuit has been implemented. The experimental results obtained at the laboratory are satisfactory and in accordance to the proposed design methodology. The proposed technique can prove to be very cost-effective for LED drivers in the range of 100 W and beyond with multiple independent LED arrays. [ABSTRACT FROM AUTHOR]

Where transformers are used to step down from medium voltage to low voltage, a widely used low-cost solution for primary protection is a fused load break switch. While this device provides good short-circuit protection, it provides limited protection for arcing faults on the transformer secondary and the incoming terminals of the downstream equipment connected to it. Consequently, the arc flash (AF) energy levels in this region can be very high ( > 40\ \mboxcal/cm^2) when compared with the rest of the electrical distribution system and may result in dangerous operating conditions. This paper examines a range of options for primary and secondary protection, identifying those that may result in higher levels of AF energy, and presents guidelines for the selection and application of solutions that have been implemented in existing and new installations, achieving a significant reduction in incident energy levels ( < 8\ \mboxcal/cm^2), while addressing concerns for reliability and selective coordination. Piecewise, linear modeling of transformer energization transient response is presented and compared with conventional engineering practice for selecting primary protection. Common assumptions made in modeling instantaneous overcurrent elements will be analyzed, modified, and exploited to achieve reliable application of blocking signals between devices in a protective scheme. Finally, the physical layout of electrical equipment will be discussed as a criteria for optimizing protection schemes to achieve safety by design. [ABSTRACT FROM AUTHOR]

The net drag result of the ionic current in a conductive fluid, such as electrohydrodynamic (EHD) effect and electrospray (Taylor cone effect), has been investigated as a space and energy saving technology for enforced heat and mass management. Electrostatically enforced evaporation, convection, and phase-change thermal transfer are briefly discussed and experimentally evaluated. The emphasis of the investigation was on the maximal efficiency of the consumed power. The significance of EHD phenomena for energy saving is demonstrated with examples of temperature stabilization for solid-state lighting and the dewatering of pulp in the paper industry. [ABSTRACT FROM PUBLISHER]

This paper proposes an online condition monitoring system for aluminum electrolytic capacitors used as dc-link capacitors in industrial power converters. Electrolytic capacitors are one of the most fragile components of a power converter system because of their wear-out failures and short lifespan. Therefore, the use of condition monitoring systems for aluminum electrolytic capacitors allow preventive maintenance to be performed, thereby avoiding unexpected shutdown and downtime. The dominant wear-out mechanisms in aluminum electrolytic capacitors are characterized by the increase in equivalent series resistance. Hence, the condition monitoring system proposed in this paper is based on the online estimation of the capacitor's equivalent series resistance using the switching frequency components of the dc-link capacitor voltage and current. The equivalent series resistance estimation method is tested using the PSpice circuit simulator and is validated experimentally using a custom-made inverter. Finally, the equivalent series resistance estimation method is adapted for the condition monitoring of capacitors in industrial power converters and the proposed condition monitoring system is implemented in a commercial ac drive system to prove the applicability of the proposed method to industrial power converters. [ABSTRACT FROM AUTHOR]

This paper presents a system that enables the passive reduction of noise and vibrations in a three-phase induction machine with a stator damper winding connected to capacitors. This is a simple and effective system for reducing the flux density harmonics in an electrical machine. The theoretical study is based on the modeling of a machine equipped with the damper winding obtained from Kron's theory about equivalent circuits of electrical machinery. The analysis of the equivalent circuit allows one to identify possibilities to reduce the flux density harmonics responsible of unwanted noise and vibration components. Finally, an experimental validation is performed. [ABSTRACT FROM AUTHOR]

A breaker-less shipboard medium-voltage dc (MVDC) system is gaining more attention recently due to its advantage in dealing with a dc fault by using switched-mode power modules and disconnectors. The specific power module investigated in this paper is the power conversion module (PCM) that transforms power from a MVDC to a low-voltage dc (LVDC) bus. The PCM plays an important role in a system-level fault management. The recently emerging isolated modular multilevel dc/dc converter and the widely used dual active bridge converter are promising solutions for PCM applications. The control algorithms including fault protection strategy for both topologies have been developed and presented in this paper. The MVDC side fault and LVDC side fault of each topology has been analyzed and evaluated. The simulation and experimental results are provided to demonstrate the fault protection features of two topologies in a breaker-less dc system. [ABSTRACT FROM AUTHOR]

Paralleled inverters are not only a suitable approach to increase the power capacity, but also have the capability of common mode voltage (CMV) reduction, or even elimination. The original zero CMV modulation scheme for paralleled inverters suffers from the current jump problem in phase-leg currents. This current jump phenomenon amplifies the peak values of differential-mode circulating current (DMCC) and zero-sequence circulating current (ZSCC), which is adverse for the design of coupled inductor and common-mode inductor. This paper introduces the modified modulation scheme, which can keep volt-seconds balance in whole fundamental period and mitigate the current jump in phase-leg currents. In addition, the reduction effect of the DMCC and ZSCC can be achieved. To verify the analysis, both the simulation and experimental results are presented, which validates the proposed methods and show that they are beneficial for DMCC and ZSCC reduction. [ABSTRACT FROM AUTHOR]

The conservative power theory (CPT) is a time-domain theory applicable to any periodic signal single- or polyphase system with or without a neutral conductor. The principle operation is the orthogonal decomposition of electrical variables, resulting in electrical quantities with physical meaning. An important feature of the CPT is the current decomposition. It consists of decomposing any current into five parts. The label of these parts is active current, reactive current, scattered active current, scattered reactive current, and generated current. This paper proposes the application of the current decomposition of the CPT in distributed energy resources (DERs). A supervisory controller (SC) uses the current decomposition in a load power-sharing strategy. The combination of these two issues is the main contribution of this paper. Moreover, the proposal of this paper is more attractive than the conventional droop strategy since the DERs follow their current reference in a current-controlled mode, making the load sharing faster, more reliable, and more accurate. A clear understanding of how the CPT decomposes load currents into its parts is presented, as well as the drawback found in droop strategy when dealing with load power sharing. Later, the SC load power-sharing strategy is described, indicating that the proposal of this paper makes an SC to have a broad option when managing a smart grid with dispatchable DERs. A case study with experimental results shows the efficacy of applying current decomposition of the CPT in load power-sharing strategies. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the behavior of electromagnetic forces during the occurrence of faults inside transformers as result of transients in the electrical systems. The methodology is based on the modeling of a single-phase 50-MVA transformer subjected to inrush currents through finite-element method. In this perspective, the values of inrush currents, obtained by the alternative transient program software, are used to estimate the magnetic field density dispersion in the transformer, and to find the values of forces in axial and radial directions. These forces components are distributed along the energized windings for observing the loads behavior in high-voltage windings. This paper will thus present investigations of electromagnetic forces, structural deformation, stresses, and safety factor on transformer's winding when subjected to inrush current. [ABSTRACT FROM PUBLISHER]

The benefits of variable-frequency drives (VFDs) have not been fully realized in many applications because they compete in the power density of legacy equipment, such as electromechanical motor controllers. This is particularly the case in Navy shipboard systems where sensitive equipment is in close proximity to VFDs. This paper compares the power densities, efficiency, and costs of both voltage-source- and current-source-based VFDs. A meaningful comparison is made based on actual hardware implementations that meet stringent power quality and electromagnetic compatibility requirements. The hardware results of a current-source-rectifier (CSR)-fed voltage-source inverter (VSI), or a CSR–VSI-based VFD, are provided in order to support the findings of this paper. Special consideration is given to operation at light loads. [ABSTRACT FROM AUTHOR]

In high-power converter design, insulated gate bipolar transistor (IGBT) modules are often operated in parallel to reach high output currents. Evaluating the electrical and thermal behavior of the parallel IGBTs is crucial for the design and reliable operation of converter systems. This paper investigates the static and dynamic characterization of parallel IGBTs and the influence of the electrical parameters on the IGBT behavior. Si-based IGBT power modules with voltage rating of 4.5 kV and current rating of 1 kA are used for the experimental evaluation of module parallel connections. Parallel-connected modules have been driven by several commercial IGBT gate units at various dc-link voltages and current levels and with different temperatures. The tested IGBT gate units show good current sharing performance between the two parallel modules. Other important influencing factors such as busbar design layout, stray inductance variation, and gate driving are also investigated for parallel connections of IGBT modules. Finally, the switching energy of the parallel modules is extracted for IGBTs and diodes under different conditions. [ABSTRACT FROM AUTHOR]

The load-commutated inverter (LCI)-based synchronous motor (SM) drive that is fed by a 12-pulse ac–dc converter results in harmonics mitigation. These drives have a further improved power quality at the ac mains if an appropriate passive filter is used at the ac mains for power factor (PF) correction and harmonics reduction. This paper deals with a simplified optimization algorithm based on a particle swarm optimization method for the selection of passive filter components. This algorithm is used to design passive filters for three types of loads on an LCI–SM drive, i.e., constant-torque–variable-speed loads, constant-speed–variable-torque loads, and variable-speed–variable-torque loads, to meet the requirements of a wide range of applications. The obtained results show reduction in the total harmonic distortion in the current and voltage at ac mains, reduced supply current, and improved PF. [ABSTRACT FROM AUTHOR]

The integration of distributed generation (DG) or distributed resources in the distribution system poses technical constraints for the electrical power system owner or manager. The addition of relatively large amounts of generation to the distribution system can potentially challenge the historical setting principles and design assumptions made in developing protection and control strategies based on overcurrent protection. The necessity and complexity of additional protection and control measures increase as the aggregate DG capacity within a potential island approaches or offsets the load within that island. In addition, the varying nature of DG availability and fault current capability must also be considered. The key issues discussed and associated with DG on the distribution feeder include anti-islanding, temporary overvoltages during fault conditions, and loss of sensitivity of feeder overcurrent protection for long feeders. As the distribution system evolves to accommodate more DG, the design and implementation of the feeder protection must also evolve. This paper presents the use of distance relays for distribution protection to solve some of the DG integration problems. This paper provides real-world event report data to further demonstrate the performance of distance protection on the distribution system. A relative cost comparison between various feeder protection solutions is presented along with a discussion on options for education of distribution companies challenged with implementing distance protection for the first time. [ABSTRACT FROM PUBLISHER]

Magnetic bearing has been developed for high-speed rotational machinery and its power electronics drive is its key technology. In this paper, a novel converter with reduced switches for magnetic bearing drive is described. The principle of the magnetic bearing and its test rig were introduced and graphically illustrated at first. Then, based on the current unidirectional and phase-leg sharing principles, the novel converter topology for magnetic bearing drive together with the current control functions is introduced, including the steady state and dynamic performance. Less power electronics devices are required for this converter in comparison with conventional magnetic bearing drives. Simulation and experimental results have successfully validated the current control capability of magnetic bearing with the proposed converter. With the novel converter and the controller, magnetic bearing can deliver superior levitation and dynamic control performance. In the rotational test, the magnetic bearing has been controlled with position error less than 20% of the air gap up to 24 000 r/min on the test rig. [ABSTRACT FROM PUBLISHER]

This paper presents the stability analysis of dc distributed power systems with multiple converter-controlled loads. The load converters are tightly controlled, behaving as constant power loads with low-damped $LC\;$ filters. The dynamic behavior of the system in high frequency range is often not studied with the classical tools based on conventional averaging techniques. However, dc power systems with the reduced size filter, and consequently, the high resonant frequency, are widely used in transportation applications. In this paper, the stability analysis of the system is established based on a discrete-time model of the system, taking into account the switching frequency and intrinsic nonlinearities of the system model. The impacts of the filter parameters and interactions among the constant power loads are investigated with the proposed discrete-time method. Moreover, an active stabilizer is developed and included in the dynamic model of the system, in order to extend the stability margin. The theoretical observations are then validated experimentally on a laboratory hardware prototype. [ABSTRACT FROM AUTHOR]

In this paper, a new generic composite load model structure for industrial facilities is proposed, which consists of four main loads, an induction motor, a synchronous motor, a motor drive system, and a static load. This structure can be applied to existing or future industry facilities. Major factors to be considered when developing this new composite load model are demonstrated. To achieve the final composite load model for an industrial facility of interest, a two-step procedure is recommended in this paper. Step 1 is to create a power system full model for existing or future industrial facilities. In this step, the full model for existing facilities can be created with the known system configurations and electrical single-line diagrams; while the full model for future industrial facilities with unknown system configurations can be created using the template-based load modeling technique. Step 2 is to perform effective load aggregation in order to obtain a simplified equivalent load model in the format of the proposed composite load model structure for industrial facilities. [ABSTRACT FROM AUTHOR]

In this paper, comparison between simulation and experimental testing of an electric hybrid telehandler vehicle is presented. A new hybridization factor for working vehicles is introduced, taking into account driving and loading power, to classify the hybrid architecture choices. The research is inserted in the frame of a cooperation project between Politecnico di Italy, and Merlo SPA, Italy, main Italian telehandler producer. The numerical model built in MATLAB/SIMULINK is used to simulate the performance level of the vehicle in different working conditions in order to study a typical telehandler cycle. The comparison between experimental and simulated results shows a very good agreement in different operating conditions. Performance level of the electric hybrid vehicle satisfies the requirements and reaches the same level of a conventional telescopic machine, but with a remarkable reduction of energy and consequently fuel consumption. [ABSTRACT FROM AUTHOR]

As industry pursues safer workplaces with arc flash mitigation programs, they face major challenges in effectively reducing incident energies on the secondary of medium-voltage to low-voltage (MV-LV) transformers. When an arc fault occurs on the transformer secondary, primary currents can be below the short-circuit range of the primary protection. Typical E-rated fuses can take over 2 s to clear, while high-side device 51 relays will have a waiting period before initiating a breaker trip. Solutions that adjust the LV main breaker's (if applied) protective functions for faster response do not address arc fault issues on the bus connecting this main breaker to the transformer secondary. This paper presents a method of applying a high-speed grounding switch at a location between the MV E-rated fuse load terminal and the transformer's primary connection. Since the transformer's primary voltage is reduced to zero in milliseconds, the low-voltage arc flash event collapses quickly to limit incident energies to less than 1.2 cal/cm2. Applications can include MV-LV transformers up to 5000 kVA. [ABSTRACT FROM AUTHOR]

This paper proposes a control method suitable for limited armature voltage and current in a permanent-magnet synchronous motor drive system based on direct torque control (DTC). First, this paper proposes torque-limiting and flux-weakening controls that are suitable for a DTC-based motor drive system. The proposed method utilizes a mathematical model in a rotating reference frame synchronized to the stator flux linkage. Second, this paper proposes an antiwindup scheme for the torque controller of the DTC system. Windup of the controller degrades the performances of torque-limiting (current-limiting) control and of torque control. Applying the antiwindup results improves the performance of the proposed torque-limiting method in the transient state. This paper presents a DTC-based drive system combined with a speed controller. The proposed system can achieve stable control, and its effectiveness is confirmed experimentally. [ABSTRACT FROM PUBLISHER]

In this paper, a new zero-sequence current suppression control strategy for the five-phase open-winding fault-tolerant fractional-slot concentrated-winding interior-permanent-magnet (FTFSCW-IPM) motor drive system with a common dc bus is proposed. By unequal distribution of the zero voltage vector, the proposed method can well suppress the zero-sequence current caused by the dead-time effect that the conventional eliminating method cannot be achieved. First, the dead-time effect to the zero-sequence current is discussed. Then the zero-axis controller is designed to obtain the reference common-mode voltage. Last, according to the principle of the unequal zero voltage vector distribution, the switching sequence of the two inverters can be calculated, and the maximum modulation index is also first deduced in detail. The proposed method is proved by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

One of the benefits of double-circuit transmission lines is that line maintenance work can be performed on a de-energized circuit while the other circuit remains energized. However, induced voltages and currents can be generated on the de-energized line due to electrostatic and/or electromagnetic coupling effects and the close proximity to energized conductors. In order to mitigate the safety concern related to high induced voltages or currents, line discharging grounding switches (LDGS) may be installed. Since this can be an expensive solution, the magnitude of induced voltage and current is the key for defining safety criteria to judge whether or not a costly mitigation plan is needed. This paper presents the theory of induced voltage and current and a sensitivity analysis of influential parameters that impact each. In addition, a safety criterion using arc reach calculation is proposed to determine when LDGS are required. A case study is included. [ABSTRACT FROM AUTHOR]

A synchronous reluctance motor drive exhibits an inherent unlimited speed range capability; in fact, the maximum speed of this kind of machine is bounded only by mechanical limits. In order to exploit this peculiar characteristic of the drive while assuring the lowest power losses, a proper control algorithm has to be used. In particular, while the working speed is increasing, the control must be able to command the reluctance motor under the maximum torque per ampere condition at first, into the flux-weakening region, and then on the maximum torque per voltage trajectory. To this purpose, a novel voltage control loop is presented in this paper. It is combined with a field-oriented current control and profitably exploits a polar coordinate representation of the current reference to operate the reluctance machine in compliance with current and voltage rating constraints in all the different operating conditions. Additional merits of the proposed scheme are the ease of implementation and the simple design. The stability of the proposed control algorithm is proved through a small signal analysis and simulations and experimental tests confirm its effectiveness. [ABSTRACT FROM AUTHOR]

With the increase of the train speed, the pantograph-catenary (PC) detachment becomes more frequent, which results in more serious PC detachment arc. In order to analyze the influence of PC detachment arc on the train system, several arc models are established. However, these models do not consider the actual PC detachment process. In this paper, an extended black-box model of PC arc is proposed, which considers the dynamic detachment process of PC based on the PC dynamics. First, the Habedank arc model is presented and the relationship of the PC detachment distance with the arc voltage and arc dissipated power is established. Next, the dynamic detachment trajectory is obtained from the dynamic simulation of the PC structure model. Then, by introducing the dynamic PC detachment trajectory model into the arc model, the dynamic arc model is built. Finally, the performance of the arc current and arc voltage is analyzed and the effectiveness of the dynamic arc model is verified. [ABSTRACT FROM AUTHOR]

The use of energy harvesting for supplying wireless sensors becomes a new market opportunity. During last years, new low power transmitters, and also power conversion ICs specifically designed for energy harvesting, have become commercially available. However, as any other power supply circuit, the specific load behavior affects to the power converter, doing that just joining the two parts takes to a nonfunctional device. In this paper, we will measure experimentally the transmitter current of some technologies, for the several sensor states. Some practical issues that affect directly the sensor design will be shown. With this information, some required modifications in the power stage will be proposed. A complete temperature sensor design and assembly is showed. The sensor has been tested in a tandem cold mill, and several experimental results are included. [ABSTRACT FROM AUTHOR]

In this paper, the dimming and frequency effects on stability, current crest factor (CCF), and power factor (PF) of high-intensity discharge lamps fed with square waveforms are experimentally evaluated. For this evaluation, the lamp was stabilized using resistances. The resistances were varied in function of the impedance of the lamp. The effects of dimming and frequency variation were observed for two types of lamps of different nominal powers. The results indicate the ranges in which the lamp is stable and the frontier values in which the lamp becomes unstable. The CCF and PF remain close to unity, and no acoustic resonances were observed during the applied tests. [ABSTRACT FROM AUTHOR]

This paper analyzes the effects of magnetic saturation, including cross-saturation and secondary saliencies, on the saliency-based sensorless control of interior permanent magnet synchronous machines. These effects are mitigated by adaptively decoupling saturation-induced saliencies via a structured neural network. This paper includes the identification of the dominant saturation-induced components of the carrier-signal current interfering with the rotor-position-dependent component being tracked, characterization of these components, and implementation of a nonlinear adaptive saturation-induced-component structured neural network model to perform their decoupling. [ABSTRACT FROM AUTHOR]

Inverters adopted in distributed power generation, active filter, and uninterruptible power supply are often connected to the grid through an inductance-capacitor-inductance (LCL) filter. The impedance of the LCL filter has a typical frequency characteristic with a resonance peak. Hence, the LCL filter has to be damped in order to avoid instability. However, the resonance of the LCL filter can be also excited in a controlled way in order to individuate the resonance frequency in the spectrum (using for example the fast Fourier transform). This paper proposes to use a controlled excitation in measuring the grid impedance, since this one influences also the resonance frequency. This paper will address some possible limits, some solutions, and some implementation issues (e.g., how to obtain a controlled resonance in the filter without damaging the system) in order to use the resonant peak for grid impedance detection. The analysis is validated both by simulations and experimental results. [ABSTRACT FROM AUTHOR]

This paper deals with the dynamic behavior of a 21-level (line-to-line) back-to-back (BTB) system based on series connection of 16 converter cells under a single-line-to-ground (SLG) fault condition. The BTB system is an ac-dc-ac power conversion system intended for achieving asynchronous power-flow control between transmission networks. When the SLG fault happens, an imbalance in the supply voltage brings an amount of negative-sequence current to the BTB system. The negative-sequence current should be mitigated because it would result in an increased supply current and a dc-capacitor voltage fluctuation. This paper intends for reducing both the negative-sequence current and the dc-voltage fluctuation to acceptable levels. A laboratory system rated at 200 V and 20 kW confirms the validity of the reduction scheme. In addition, this paper addresses the issue of magnetic saturation in the 16 three-phase converter-transformers. [ABSTRACT FROM AUTHOR]

This paper proposes a control method to null the magnet flux in an interior permanent-magnet (IPM) motor following short-circuit-type faults in either the inverter drive or motor stator windings. Phase-based control is employed to implement the flux-nulling-control method so that it is possible to take advantage of a zero-sequence current in order to minimize the current in the shorted phase. It is shown that phase-based control results in a smaller induced current than when employing a synchronous-frame dqO current regulator. The induced torque is also less than that when employing a purposely commanded symmetrical short circuit in response to a short-circuit-type fault. In the paper, the complete magnet-flux-nulling-control algorithm is derived with reference to the proposed phase-current-control method. The impact of controlling the zero-sequence current on the resulting phase currents is presented. Both simulation and experimental results are presented, verifying the operation of the proposed methods. [ABSTRACT FROM AUTHOR]

This paper presents probabilistic models developed based on the Poisson probability distribution for determining the optimal number of transformer spares for distribution transformer systems. The outage of a transformer is a random event and the probability mathematics can best describe this type of failure process. The developed models have been illustrated using illustrative 72-kV distribution transformer systems. Industry-average catastrophic transformer failure rate and a 1-year transformer repair or procurement time have been utilized in the examples considered in the paper. Among the models developed for determining the optimum number of transformer spares, the statistical economics model provides the best result as it attempts to minimize the total system cost including the cost of spares carried in the system. [ABSTRACT FROM AUTHOR]

This paper discusses incipient end-winding interturn faults in the stator winding of a permanent magnet synchronous motor caused by the mechanical vibrations of the concerned turns. With aging, the end-winding blocking system becomes weaker and turns insulation degrades until its breakdown. The fault is modeled by an intermittent interturn short circuit between the turns of the stator end winding. Intermittent fault occurrence disturbs the stator currents as well as the reference voltages leaving a specific fault signature. The detection method uses a pattern-adapted wavelet to detect fault occurrence. In this paper, it is applied to the quadrature reference voltage. Simulation and experimental results confirm the effectiveness of the proposed approach. [ABSTRACT FROM PUBLISHER]

This paper demonstrates practical considerations when studying overcurrent protection coordination in industrial systems and applying related IEEE Standards. This paper is divided into two parts. Part one focuses on protection coordination for high-voltage and medium-voltage industrial systems. Part two covers balance of distribution system topics. The main discussed subjects are time/chronologic, current/amperometric, as well as zone selective interlocking coordination. Other factors that affect coordination are also addressed. Suitable selections of the relay time–current characteristic are presented. This paper also includes practical details for accepted coordination time interval in coordinated systems. [ABSTRACT FROM PUBLISHER]

Due to the overhead ground wires of transmission lines or the transformer's neutral point connected to a substation grounding grid, it looks like that there are many currents injected into or drawn out of the grounding grid from different grounding points when fault occurs. As the grounding grid is becoming larger and larger in area, the potential difference within the grounding grid may become obvious, and the assumption that the grounding points can be regarded as one point may not be suitable. This paper proposes a method to analyze the non-equipotential grounding grids with the fault current injected from multiple grounding points due to the overhead ground wires of transmission lines or the transformer's grounded neutral point. With the method, the influences of the grid area, soil resistivity, material of the grid conductor, and relative position of the grounding points on the performance of the grounding grid are thoroughly analyzed. [ABSTRACT FROM AUTHOR]

Corrosion is an electrochemical process involving electrical currents. It consists of the destruction of a metal through its interaction with the environment. The phenomenon is observed in underground and buried structures, where aging can be strongly influenced by electrical currents flowing in the Earth. Methods of protection (i.e., “cathodic protection”) are related to the use of sacrificial anodes or more sophisticated systems, which impose a negative voltage to the metal structures to be protected. The corrosion phenomenon can be relevant also in electric power system applications. Underground or undersea electrical cables need to be protected as a consequence of stray currents flowing in the soil. This paper studies the problem of cathodic protection design for high-voltage transmission cables in undersea applications. The aim is to propose a design procedure which can be implemented by nonexpert electrical designers. A practical approach, which characterizes the distribution of the voltage on the outer layer of power cables, is formalized on the basis of common simplified assumptions. Numerical simulations give evidence to the formulation according to the features of environmental conditions. [ABSTRACT FROM PUBLISHER]

This paper presents a novel grid current control of a grid-connected voltage source converter with an LCL filter. The proposed control method uses an $\mathcal {H}_\infty$ synthesis method to shape the input admittance of the converter, to track a given current reference, and/or to limit the controller actuation at different frequency ranges. The converter admittance is shaped, both in magnitude and phase, following a model reference defined by the designer in the frequency domain. By specifying a low admittance magnitude reference, the optimization algorithm will obtain a controller that actively damp the filter resonance and attenuate/reject the grid voltage oscillations, either in a wide frequency range or concentrated at the main harmonic frequencies. Additionally, the proposed controller design methodology takes advantage of its admittance phase shaping capability to improve the system robustness in front of grid uncertainties and minimizing converter impact over grid stability due to its positive-real nature. The synthesized controller only measures the grid current and voltage to achieve the aforementioned results, reducing the number of sensors (and their associated cost) required for its implementation. Experimental results illustrate the correct behavior of the closed-loop system with the designed controller in time and frequency domain. [ABSTRACT FROM AUTHOR]

This paper discusses the energization and start-up process of modular three-stage solid-state transformers (SSTs) based on a cascaded H-bridge topology. A key element of the SST is the auxiliary power supply (APS) feeding the auxiliary circuitry. Redundancy and simpler implementation can be achieved by powering the APSs from the dc-link capacitors of cells, but at the expense of a more challenging start-up process of the SST. The first step of this process must be performed before APSs are operative. This can result in undesired transient events (inrush currents, voltage sags in the capacitors voltages, etc.), which could prevent a proper start-up of the SST or even jeopardize the power devices or other elements. A simple strategy for the energization and start-up of SSTs using this APS structure is proposed. The method is valid for both grid-forming and grid-feeding operations of the SST, regardless of the energization port and without the addition of any extra circuitry. Simulation and experimental results are provided. [ABSTRACT FROM AUTHOR]

Series-dc collection and transmission is suggested to be competitive for remote offshore wind farms. However, severe overcurrent, overvoltage, and other impacts that arise from faults cause challenges on system protection, which have not been fully studied yet. In this paper, simplified equivalent circuits are developed for fault analysis, based on which analytical models for fault transients are derived. The expressions can be used for stress estimation, as well as provide insight in understanding the mechanism of fault propagation. A cost-effective protection scheme characterized by a breakerless design is proposed. Parameter selection for stress mitigation is also discussed. Simulation results verify that the proposed fault protection and stress mitigation design is effective for such a series-dc system. [ABSTRACT FROM AUTHOR]