Machine Terminals Research Articles

Experimental performance verification of an intelligent detection and assessment scheme for disturbances and imbalances of three-phase synchronous machine output using coherence estimators

In this article, power quality disturbances, such as voltage and current unbalances, series and shunt faults, are monitored in three-phase synchronous machines. Because the imbalances affect machine efficiency and service life, it is essential to figure out whether the three-phase voltages/currents are balanced or unbalanced. An integrated detection algorithm is proposed to detect the unbalanced voltages/currents and various abnormal conditions precisely and quickly, which is based on the coherence estimator. Most existing detection methods require more than one cycle time to determine the contingency conditions, while the proposed technique detects these situations in a fast and discrete protection system. The suggested scheme acquires instantaneous measurements of the three-phase voltages and currents taken at the synchronous machine terminals in order to calculate fifteen coherence coefficients that are utilized to detect and assess any unbalance or trouble accurately and swiftly. A new proposal for imbalance and disturbance indicators based on the coherence estimators is developed in this study. Multiple test cases have been conducted to validate the proposed algorithm capabilities using a real power system, which includes a motor-generator set, a three-phase load and measurement transformers. The experimental results have been revealed that the relay reliability and accuracy percentages have been found to be 98.28% and 98.52%, respectively. The quantitative findings of the imbalance and disturbance assessment are recorded.

Impact of close proximity pulse width modulation switching events on electric machine terminal voltages

AbstractElectric machines form an essential part of a wide range of modern systems. When speed control is required, the use of pulse width modulation‐based inverters is generally the solution of choice. It is also usual to connect the machine to the inverter using a cable. The combination of these three elements produces the potential for voltages which exceed the dc link voltage to occur at the machine terminals. Methods for predicting the terminal voltage exist; however, these methods assume that the pulses applied to the system can be considered as isolated, discrete events. The authors highlight an issue with this assumption. When a switching event occurs, it will cause a voltage disturbance in the unswitched phases of the system due to the mutual coupling between the phases. If a second switching event occurs within a short time of this event the resultant voltage will interact with the previous switching event resulting in a higher terminal voltage than would be the case for an isolated event. This effect can be problematic for insulation design if it is not considered. This issue is demonstrated, with the worst‐case scenarios identified and potential methods of reducing terminal voltage being proposed.

Methods for Determining Losses and Parameters of Cylindrical-Rotor Medium-Power Synchronous Generators

This paper presents the analytical and numerical application of a method to determine the parameters and power losses in the core of two medium-power synchronous generators. These generators are used as emergency power sources powered by diesel engines, gas engines, and gas turbines. They cover peak electricity demand but can also be used in traction drives. This article presents a new numerical method for determining losses in the generator core based on the use of a time-stepping solution using the FEM method and calculating these losses using analytical formulas. In calculating the losses for the FEM method, approximations of the loss characteristics of the sheet were used with a wide range of induction values and frequencies. This method is specific to the solution used and was adapted from the authors’ previous work on losses in induction machines. A one-phase winding with alternating voltage was supplied to determine the basic parameters in the form of synchronous reactance. Also, an important novelty is the introduction of a new method of determining the saturation state of the magnetic circuit, which significantly affects the machine parameters. The obtained results were used in analytical calculations and implemented in a computer program that allows for the calculation of electromagnetic parameters, operating characteristics, and core losses, taking into account additional losses, total losses, and efficiency, as well as machine parameters in unsteady operating states and the current characteristics of a three-phase symmetrical short circuit at the machine terminals. The calculations obtained were verified experimentally by measurements of real machines.

Pure sine wave generation in battery-less solar system using advanced control through single machine

Due to the reduction of conventional energy sources, humanity faces a critical challenge, forcing innovative solutions to bridge the growing gap between energy demand and supply. Solar energy has emerged as a promising alternative, owing to its efficiency and renewable nature. Despite their benefits, conventional solar power systems face many challenges, including their reliance on battery banks, which introduce complexities and inefficiencies, such as voltage fluctuations and harmonic content. To overcome these challenges, researchers propose a novel solution: the Dual Winding Machine (DWM). This innovative system integrates motor and generator functionalities within a single machine, operating on a dual stator core to achieve synchronous operation. In contrast to traditional setups, the DWM eliminates the need for batteries during periods of low solar energy. A crucial component in this novel approach is the utilization of a Zeta converter, which adjusts the switching frequency to regulate the DC voltage and machine terminals. By doing so, the DWM maintains a constant voltage supply without relying on a battery, mitigating the fluctuations observed in traditional solar power systems. The proposed solution offers several benefits over existing strategies. Firstly, by eliminating the need for a battery, the DWM reduces system complexity and enhances overall efficiency. The absence of a battery backup also minimizes the risk of fluctuations in the inverter's input voltage and mitigates potential increases in output harmonic content. This not only improves the reliability of the solar power system but also extends the lifespan of connected machinery, such as motors and electrical devices. Furthermore, simulations conducted using MATLAB and MAXWELL programs validate the effectiveness of the DWM, confirming its ability to generate harmonic-free sine waves without relying on a battery, thus representing a significant advancement towards more sustainable and reliable solar energy solutions. In summary, the DWM presents a promising solution to the challenges faced by conventional solar power systems, offering improved efficiency, reliability, and longevity.

A Generalized Fault Tolerant Control Based on Back EMF Feedforward Compensation: Derivation and Application on Induction Motors Drives

In this paper, a fault-tolerant three-phase induction drive based on field-oriented control is studied, and an analytical approach is proposed to elucidate the limitations of FOC in flux-torque regulation from the controller perspective. With an open-phase fault, the disturbance terms appear in the controller reference frame and degrade the controller performance when operating in a d-q plane with DC quantities. In addition, the hardware reconfiguration, which is essential to operate faulted three-phase drives, causes substantial change in the way the control parameters vd, vq are reflected onto the machine terminals. An accurate understanding of the feedforward term, by considering the open-phase fault and the hardware modifications, is provided to re-enable the FOC in presence of an open-phase fault. Furthermore, the concept of feedforward term derivation is generically extended to cover multiphase induction drives encountering an open-phase fault whereby no hardware reconfiguration is intended. The proposed method is explained based on a symmetrical six-phase induction and can be extended to drives with a higher number of phases. The effectiveness of the proposed derivation method, which is required to form a feedforward fault-tolerant controller, is verified and compared through the simulation and experiment, ensuring smooth operation in postfault mode.

Situational Awareness for Autonomous Ships in the Arctic: mMTC Direct-to-Satellite Connectivity

The maritime autonomous surface ship (MASS) promises a revolution in naval logistics by offering sustainability, safety, and operational costs reduction. The MASS can bring to the Arctic and other hard-to-reach regions numerous social and economic benefits, thus contributing to equalizing access for human and machine terminals to connectivity, and equate the life quality of their inhabitants with that of other regions. In this article, we suggest a hybrid communication architecture that separates a ship's data traffic into awareness and emergency components. For the former traffic, we advocate the possibility of direct-to-satellite using massive machine-type communication (mMTC) and low-power wide-area network (LPWAN) technologies. To validate this hypothesis and investigate the potential performance and effect of different design and configuration parameters, we conduct simulations based on real-life positions of ships and satellites, traffic patterns, and the LoRaWAN connectivity model. Our results demonstrate the suggested approach's feasibility and clarify the different parameters' effects on the connectivity performance for the classical LoRa and novel long-range frequency hopping spread spectrum modulation coding schemes. Notably, the combination of multi-connectivity of LoRaWAN LPWAN technology and multi-satellite visibility dramatically boosts the probability of packet delivery.

Holistic Modeling of High-Frequency Behavior of Inverter-Fed Machine Winding, Considering Mutual Couplings in Time Domain

Prediction of the voltage distribution within the winding due to pulsewidth modulated voltage impinging at the machine terminals is prevalent in the literature. For this purpose, the state-of-art work employs a high-frequency model of the stator winding but fails to represent the mutual inductive and resistive couplings between the turns and the coil. Herein, this article proposes a multiconductor transmission line model for representing the high-frequency behavior of the stator winding. A distinctive feature of the proposed model is that it incorporates the mutual inductive and resistive coupling between the turns and the coils using a current-dependent voltage source with due account of frequency-dependent parameters in the form of a ladder network. It enables the modeling of the mutual coupling of both single and multilayer winding in the time domain without the explicit use of modal transformation, convolution integral, or inverse Fourier transform. The close agreement between the simulation and the experimental results validates the proposed model of an automotive-grade 60-kW permanent magnet synchronous machine adapted in the Toyota Prius vehicle. In addition, a more intuitive analytical model is proposed to explain the voltage distribution and to characterize the peak voltage stress within the winding. The analytical model can be used to predict voltage stress as an alternative to the high-frequency model.

Flux Observation of Induction Machine Based on the Enhanced Sensorless Voltage Model

This paper presents the identification of the rotor flux of the induction machine. In the field-oriented control topology, since the terminal stator voltages are a pulsating voltage, so the only way is to calculate the reference values of the voltages from the inverter states phase. At very low speed, the reconstructed voltages are nearly not real, so that, the range of speed rotation of an encoder-less field-oriented control is not quite enough to cover all the speed range. However, the design of a 3-phase inverter which is prepared by silicon carbide (SiC)-MOSFETs with inserting an output filter between the inverter and the machine may supply sinusoidal voltages and currents at the output. The high switching frequency which can be applied with the SiC MOSFETs permits the proposal and implementation of a small low pass LC filter that can be equipped with the inverter output side. With this structure, it is possible to reduce the harmonic of the output voltages in addition to reduce the content of the current harmonics causing in a practically sinusoidal voltage as confirmed in the experimental results of this work. The main goal of this outline is two points, on the first side it can be reduce the winding machine stress, therefore, it is minimizing the harmonic in the voltages at the machine terminals. And on the other hand, is to use the measured voltages as an alternative of the recalculated ones to enhance the voltage model and the performance of the control scheme. It is predictable that the range of machine speed of an encoder-less field-oriented control can be extended.

Investigation of cable influence on the interturn transient voltage distribution in rotating machine windings using a three-phase model

Turn-to-turn and turn-to-ground transient voltages due to the surges which arrive at rotating machine terminals shall be known as exactly as possible to optimize the insulation design. Normally these overvoltages are obtained by Multiconductor Transmission Line Theory using only part of one phase of the stator winding by applying a surge at the line-end coil. Moreover, many works consider the feeding cable to analyze only the voltage at machine terminals by using a simple model for the motor. This paper analyses the influence of the cable length on the transient voltage distribution inside the machine by numerical simulations using a three-phase model for the machine windings. The results are obtained by a cable-motor model using Finite Elements Method (FEM). The model couples the transient magnetic fields solved in a 2D geometry with electric circuit elements. Results show that the cable length has influence on the transient voltage distribution, especially for the line-end coils from the phase where the surge has been applied to.

Analytical Study of SiC MOSFET Based Inverter Output dv/dt Mitigation and Loss Comparison With a Passive dv/dt Filter for High Frequency Motor Drive Applications

Fast switching characteristic of wide bandgap devices enables high switching frequency of power devices and thereby, can facilitate high fundamental frequency operation of electrical machines. However, with the switching transition times in orders of tens of nanoseconds, the high dv/dt is observed across the switching device. The high dv/dt experienced by the switches, and consequently by the machine, can degrade winding insulations or bearings over a period of time. Therefore, it is imperative to maintain the dv/dt below recommended values depending on the machine insulation. The dv/dt across the devices can be adjusted by varying the gate resistance. A high value of gate resistance, however, introduces additional switching losses on the device. Using different dv/dt filtering techniques can also help to control the dv/dt on the machine terminals. These techniques do not increase the switching losses on the device. However, it introduces additional losses in the filter resistors and also increases the cost of the system. In this paper, an analysis based on the impact of gate resistance on the dv/dt across the machine, and the corresponding losses is carried out. An analytical dv/dt filter design strategy is proposed to limit the dv/dt to a particular value. With the proposed design scheme, the value of each filter component can be easily obtained, and filter losses can be estimated accurately. Lastly, a comparison is performed on the basis of efficiency between these two techniques.

Study and Active Enhancement by Converter Reconfiguration of the Performance in Terms of Stator Copper Loss, Derating Factor and Converter Rating of Multiphase Drives Under Two Open Legs With Different Stator Winding Connections

Multiphase machines offer inherent tolerance to faults such as open converter legs (OCLs), which are especially frequent. Because of this reason, they are particularly attractive for applications where fault tolerance is important, such as offshore wind energy or aerospace, naval and military vehicles. It has been previously shown that, under an OCL, certain stator winding configurations (SWCs) different from star yield smaller stator copper loss (SCL) and larger maximum achievable torque (MAT) than star SWC for the same torque command and machine. This advantage comes just at the expense of a moderate increase in converter rating. However, only the case of single OCL was studied in general. The SCL, MAT and required converter rating for two OCLs are currently unknown for different combinations of phase number, faulted legs and SWCs. Actually, under two OCLs (unlike for one OCL) it may be possible to actively modify the order of the faulted/healthy legs to enhance the performance in these terms, but this possibility has not been studied so far in spite of its potential. This paper addresses the postfault performance of multiphase drives with two OCLs, for various SWCs. The MAT (derating factor), SCL and necessary converter rating are assessed in numerous possible scenarios. The most convenient alternatives are established. Most importantly, in view of the conclusions of this analysis, a novel method is proposed to improve substantially the MAT and SCL by actively altering the connections between the converter and machine terminals. Experimental results with six-phase and twelve-phase setups are provided.

A novel block chain based cluster head authentication protocol for machine-type communication in LTE network: Statistical analysis on attack detection

“Machine-to-machine (M2M) is a kind of application and service based on intelligent interaction and networking among machine terminals, which is also called machine-type communications (MTC)”. Here, this paper intends to develop an enhanced secure MTC in LTE Network that takes place under two phases namely, (i) coarse grained attack detection system and (ii) fine grained attack detection system. Initially, the clustering of nodes takes place using LEACH approach and followed by that cluster head (CH) selection takes place by considering the constraints like distance, penalty, energy, and delay. The penalty determined may ensure the secured CH selection results from optimized Neural Network (NN) model. If penalty is assigned as one, particular node is forbidden, which cannot be selected as head node (simply dropped from network). Nodes information is transmitted in Blocks of block chain to authenticate the nodes with the support of Cluster Head (CH) and to ensure the integrity of the block chain. Further, fine grained attack detection system is carried out that authenticate the selected CH to assure attack free network. As a major contribution, the training of NN is carried out by means of a novel algorithm named as Whale with Tri-level Update (WTU). Finally, the superiority of the adopted scheme is analyzed over existing schemes in terms of correlation.

Electric drive systems with long feeder cables

Electric drive systems with long feeder cables connecting inverter and machine are used for oil exploration, mining, remote operated vehicles, industrial, and aerospace applications. Though this topology has the advantage of providing a better operating environment and easier serviceability for the inverter if the machine is located in an inhospitable and inaccessible environment, it does come with its own drawbacks. Steep-fronted switched voltages and cable-machine surge impedance mismatch can lead to high-amplitude, high-frequency (HF) voltage oscillations along the feeder cable, at the machine terminals, and throughout the machine's stator windings. These effects can cause high-electromagnetic interference, corona discharge, insulation failure in the feeder cable and machine's stator windings, common-mode, differential-mode, and bearing currents. This study discusses the HF issues relating to electric drive systems with long cable feeders. HF models for feeder cable and machine to analyse these phenomena are presented. The effects on long feeder cable loading on inverter switching characteristics are discussed. Methods to mitigate high-amplitude and HF oscillations in such systems are shown.

A Comprehensive Induction Machine Model for Multi-Phase Power Flow Studies – Application to Industrial Power Systems and Wind Farms

Abstract This paper presents the development of three comprehensive static models of a 3-phase induction machine in phase frame of reference for interfacing with multi-phase power flow programs. The models developed are based on specified slip or specified power, either at the rotor shaft or at the terminals of the induction machine. The development of these models also takes into consideration load torque characteristics. The mathematical formulation of these models is based on branch constraint approach instead of the traditional node constraint approach. This facilitates the arbitrary connections of the induction machine, namely wye, wye-grounded, wye-grounded through impedance, and delta. The models are ideally suited for application in the present trend of operating power and distribution networks with high penetration of renewable energy sources (RES). These models assist in evaluating the performance of wind generators operating under unbalanced system conditions and also in selection of proper phase wise compensation. These static models compute the correct initial operating conditions of induction machines for 3-phase transient stability studies and EMTP-type simulation studies, to evaluate the precise dynamic behaviour of the power system. The procedure for integrating these models in the multi-phase power flow program is also described. The performance of the developed multi-phase power flow program, including static induction machine models, has been evaluated for various power network sizes. The results obtained are verified against the existing literature to clearly demonstrate the efficacy of the proposed methodology.

Open geospatial infrastructure for data management and analytics in interdisciplinary research

The terms Internet of Things and Big Data are currently subject to much attention, though the specific impact of these terms in our practical lives are difficult to apprehend. Data-driven approaches do lead to new possibilities, and significant improvements within a broad range of domains can be achieved through a cloud-based infrastructure. In the agricultural sector, data-driven precision agriculture shows great potential in facilitating the increase in food production demanded by the increasing world population. However, the adoption rate of precision agriculture technology has been slow, and information and communications technology needed to promote the implementation of precision agriculture is limited by proprietary integrations and non-standardized data formats and connections. In this paper, an open geospatial data infrastructure is presented, based on standards defined by the Open Geospatial Consortium (OGC). The emphasis in the design was on improved interoperability, with the capability of using sensors, performing cloud processing, carrying out regional statistics, and provide seamless connectivity to machine terminals. The infrastructure was implemented through open source software, and was complemented by open data from governmental offices along with ESA satellite imagery. Four use cases are presented, covering analysis of nearly 50 000 crop fields and providing seamless interaction with an emulated machine terminal. They act to showcase both for how the infrastructure enables modularity and interoperability, and for the new possibilities which arise from this new approach to data within the agricultural domain.

Grounding Concept and Common-Mode Filter Design Methodology for Transformerless MV Drives to Prevent Bearing Current Issues

Recently, the transformerless design of medium-voltage drives is an emerging design concept of variable-speed drives (VSD). Here, no dedicated feed transformer is used. The VSD is directly connected to the on-site facility transformer, where multiple other loads are connected as well. The benefits of such a transformerless VSD are reduced total volume, weight, losses, and system costs. However, without a dedicated feed transformer, the converter-generated common-mode (CM) voltage may generate harmful bearing currents that could yield serious bearing failures within a short time. For this reason, the suppression of bearing currents is a fundamental design aspect of VSD systems. In this publication, a comprehensive bearing current study highlights the two dominating bearing current mechanisms in transformerless VSDs. Both mechanisms are caused by the converter-generated CM voltage applied to the machine terminals. Their physical understanding is used to define thresholds that ensure a sufficient mitigation of bearing currents. The newly introduced CM voltage limits allow the development of a generalized CM filter design for transformerless VSDs. Accordingly, a suitable filter grounding concept including a CM filter design methodology for transformerless high-power medium-voltage converters is presented for the first time. Here, both the CM voltage injection to the grid and the CM voltage applied to the machine terminals is considered. At the machine-side, the novel design reference to prevent bearing currents is applied. By this, the reliable transformerless operation of general purpose drives and retrofit applications is feasible.

Electrical behaviour of the pump working as turbine in off grid operation

The use of pumps working as turbines (PATs) connected to the electric system, in the replacement of pressure reduction valves to reduce the excessive pressure in water distribution networks, have been studied for the last years. The introduction of PATs is very important in the water-energy nexus to promote the increase of the energy savings. As consequence, the majority of the water systems does not have access to the electrical grid and, therefore, the need to study the PATs operation off-grid is necessary. In this line, the novelty of this research is the application and optimization of a PAT in water systems when the recovery solution is off-grid type. To operate correctly, the induction machine requires an external source of reactive power, which is typically provided by the electrical grid. To supply the required reactive power, a bank of capacitors is installed at the machine terminals, so-called self-excited induction generator (SEIG). The analytical model, simulation and experimental works were performed, to analyse the SEIG behaviour. The results were applied in a SEIG-PAT system obtaining the global efficiency of the system for different speeds and loads. The global efficiency decreases 47% when off-grid operation, showing the need to optimize the electrical parameters of the generator to operate as off- grid with acceptable efficiency levels. In this framework, a tuning methodology for the SEIG capacitor bank values was developed to be automatically adjusted according to the operating point of the PAT to maximize its efficiency.

Efficient interaction algorithm of multi-thread data under resource sharing platform

This paper proposes an efficient interactive algorithm for multi-threaded data under resource sharing platform. In this algorithm, an allocation condition control for multi-thread data transmission is proposed. And on this basis, through the efficient encoding combination of lost packet in the process of multi-thread data transmission, the multiple virtual machine terminals can access data packet transmitted for the multiple switches in priority in a multicast or broadcast transmission, to realize efficient interaction of multi-thread data under resource sharing platform. Experimental results show that the proposed algorithm can improve the transmission interaction efficiency and throughput, and reduce the packet loss rate, which has good interactive performance.

Post-Demagnetization Performance Assessment for Interior Permanent Magnet AC Machines

This paper assesses the post-demagnetization performance of interior permanent magnet (IPM) ac machines by employing the more accurate recoil line approach based on a 2-D transient finite-element analysis (FEA). The method predicts continuous demagnetization of each magnet element undergoing partial demagnetization and evaluates the machine behavior after an event of short-circuit faults across its terminals. Along with the short-circuit faults, a failure in a drive controller or a position sensor, which may lead to a reverse voltage across the machine terminals that can eventually be more fatal and can cause significant reduction in the performance due to high levels of demagnetization, is analyzed as the worst case scenario. The FE predicted post-demagnetization performance is validated by experimental measurements in which a six-phase IPM machine designed for electric vehicle traction is allowed to lose its synchronization with the inverter when forced to operate on a torque–speed envelope, which is way beyond the drive voltage setting.

Relative ability of UHF antenna and VHF capacitor methods to detect partial discharge in turbine generator stator windings

On-line partial discharge (PD) monitoring is widely used to detect stator winding insulation deterioration. The most common type of on-line PD sensor for turbine generators is the 80 pF capacitive coupler installed at the machine terminals which detects the PD in the very high frequency (VHF) range. More recently, ultra high frequency (UHF) antennae have also been used to detect stator winding PD in large turbine generators. Both types of sensors have been installed in 16 turbine generators. This paper discusses the results from near simultaneous measurements from both types of sensors on the same machines. It was expected that the UHF sensors would have stronger discrimination of the electrical disturbances internal to the machine compared to the VHF sensors, but the VHF sensors would be more sensitive to PD. As expected, the VHF sensors were generally more corrupted by electrical disturbances. However, in about half of the machines investigated here, the UHF sensors were significantly more sensitive than the VHF sensors. Many examples of phase-resolved PD patterns that illustrate these findings are presented.