Arash Kiyoumarsi

Voltage sag is one of the most common power quality disturbances that significantly impacts consumers. Since short‐circuits are the main source of voltage sags, detecting the disturbance and determining the fault location are essential for evaluating responsibility. In this paper, a new method is proposed for the voltage sag monitors (VSMs) allocation to detect fault locations. First, the vulnerability area of system buses is determined and the optimisation problem is solved separately for various short‐circuit types. Then, monitor failure scenarios are considered to obtain a unique placement scheme for each fault type. The fault location detection (FLD) index is calculated for each monitor failure scenario the solution with the highest weighted FLD and load coverage is selected as the final VSMs solution for each short‐circuit type. Finally, the optimal VSMs allocation scheme for the system is determined from the unique obtained solutions. The proposed method is implemented on the IEEE 9‐, 30‐ and 57‐bus systems under different fault impedance conditions. The results demonstrate that the proposed method achieves approximately 95% fault location detection compared to 78% obtained by existing methods with the similar number of monitors, improving the fault locating while maintaining an acceptable number of monitors in the system.

PM‐assisted synchronous reluctance machines are becoming so attractive for electrical machine designers because of their lower cost due to minor usage of PMs in comparison to IPM and SMPM machines. Besides, they can effectively utilise both the magnetic and reluctance torques, thus, they can play an important role in many industrial applications including electric transportation systems. Up to now, more or less, the conventional distributed‐windings are employed in design of the synchronous reluctance machines. However, recent advancements have seen the adoption of fractional‐slot concentrated windings (FSCWs) due to their shorter end‐winding length, simpler structure, and higher slot fill factor. Although FSCWs offer these advantages, they also suffer from higher magnetomotive force (MMF) space harmonics, which can lead to undesirable effects such as localised iron saturation and increased core losses. The main target of the present research was introducing the winding layouts, which have the benefits of both FSCWs and distributed windings to use in PM‐assisted synchronous reluctance machine. To solve the problems related to FSCWs, in this research, the stator slot‐shifting has been developed and new types of fractional‐slot winding topologies, comprising significantly low MMF harmonics and short‐end windings length have been proposed. Based on these proposed winding configurations, a prototype machine was built as case study; and analytical results, finite element analysis, and experimental tests were conducted to validate the machine’s characteristics. Although in the proposed machine the winding is converted to overlapped type and is not concentrated anymore, but the obtained results show significant advantages over the conventional design in terms of air‐gap flux density, back electromotive force, torque profile, power factor, power losses, efficiency and flux weakening capability.

The vibration and acoustic noise of a permanent‐magnet synchronous motor are analysed and evaluated. Acoustic noise sound levels, their prominent frequencies, and the noisiest motor speed range are predicted. According to many resources, the radial vibration of the stator system due to the magnetic attraction between rotor permanent magnets and stator iron teeth is the main reason for the acoustic noise propagation of the PMSMs. The dominant orders of the spatial circumferential harmonics of the radial magnetic forces (RMFs) have been investigated and compared. The complete and complicated mechanical components, materials, and harmonics of the magnetic forces of the motor and their interaction are simplified and equalised to a vibration model, which consists of the interaction between the stator system and the dominant harmonic orders of the RMFs. Based on this approach, the simplest and most adequate semi‐analytical‐FEM model for noise prediction in PMSMs is proposed. This model, in addition to simplification, clarifies the role of the main mechanical and electromagnetic origins of noise generation. The acoustic noise prediction, using the proposed method has been compared with the experimental results. There is a proper agreement between the analytical, the FEM, and measurement results.

An innovative control method for reducing the torque ripple of non-sinusoidal brushless DC motors in field weakening region based on direct power control is proposed here. Torque ripple, due to the disproportionate stator current and its non-sinusoidal back-EMF voltage, is one of the known drawbacks of brushless DC motor drives. Upon motor speed acceleration, the waveform of the stator current becomes distorted, which in turn intensifies the torque ripple. This proposed method is able to control the motor speed from zero to values higher than the base speed range. The realization of the proposed method in the stationary reference-frame makes the method implementation simple and robust. In addition to controlling motor speed, by applying a three-phase conducting method instead of the conventional two-phase conducting method and control of instantaneous input power into the rotor in the proposed method, the torque ripple is also reduced, simultaneously. The torque ripple reduction and robustness of the proposed method are compared with the phase advance angle (PAA) method through simulation and experimental. The results indicate the superiority of the proposed method in both the steady- and transient-states. Moreover, the implementation of the proposed method on a prototype BLDC drive is successfully evaluated.

With the growing use of sensitive loads and distributed generations (DGs), power quality is of great importance in distribution networks (DNs). Voltage sag is a significant power quality disturbance. Hence, monitoring of the voltages and currents of the network is necessary to identify the voltage sag occurrence and its location. However, installing measuring units at every busbar in very expensive. In this article, an optimal method for locating the voltage sag monitors (VSMs) in DNs is proposed, considering the DGs. The proposed method is based on the DN zoning algorithm that utilizes the matrix of voltage sag transfer coefficients. The optimal number of zones is determined based on the proposed threshold value or the financial limits. Then, in each zone, the electrical center busbar is determined by solving an optimization problem. The electrical center busbar in each zone is chosen as the optimal location of the VSMs. The location, size, type, and control strategy of DGs, and the network structure affect the optimal location of the VSMs. The proposed method is implemented in different simulation scenarios at the IEEE 33 bus test system and the simulation results show the efficiency of the proposed algorithm.

Finding efficient and satisfactory energy storage systems (ESSs) is one of the main concerns in the industry. Flywheel energy storage system (FESS) is one of the most satisfactory energy storage which has lots of advantages such as high efficiency, long lifetime, scalability, high power density, fast dynamic, deep charging, and discharging capability. The above features are necessary for electric vehicles (EVs), railways, renewable energy systems, and microgrids. Also, electrical machines, power electronics converters, and control systems are the cores of energy transfer in FESS. Therefore, they have a critical role in determining efficiency, power rating, power factor, cost, angular velocity, and volume of FESS. So, in this study, the FESS configuration, including the flywheel (rotor), electrical machine, power electronics converter, control system, and bearing are reviewed, individually and comprehensively. Additionally, the mentioned components have been categorized to be a guide for future research. The investigated electrical machines are compared by Finite Element Analysis (FEA). Subsequently, our laboratory’s measurement results are reviewed experimentally showing the progress in the field of FESS, such as designing robust control algorithms and an Interior Permanent Magnet-Synchronous Reluctance Machine (IPM-SynRM) to use in FESS.

In this paper, a second-order sliding mode control, based on super-twisting algorithm, is proposed for direct power control of the brushless DC (BLDC) motor. The proposed controller uses a super-twisting scheme that requires only sliding surface information and can handle system uncertainties and external disturbances, well. This scheme can improve the BLDC motor torque ripple by solving the disadvantages of the conventional sliding mode control method, such as the chattering effect and high frequency switching control. This method is simple and robust for the BLDC motor’s biggest challenge, torque ripple, which does not require any voltage and current control loops or complex reference frame transformations. The simulation results of the proposed method are compared with the direct power control (DPC) and model predictive control (MPC) methods, which indicate the superiority of the proposed method in both the steady- and transient-states. Moreover, the motor parameters variation in the tracking of active and reactive power are discussed. In addition, the practical results of the proposed method in both cases of speed and load variation show the effectiveness of this method in reducing power (torque) ripple and current total harmonic distortion (THD) and increasing the system’s efficiency compared to other methods.

Power quality disturbances can cause damages to the electrical network’s customers. Therefore, nowadays power quality is considered an essential issue in distribution networks. In this regard, voltage sag is of a lot of significance among power quality disturbances. The first step in the reduction of damages caused by voltage sag is to determine the location of the disturbance source. Furthermore, recent attention to distributed generation (DG) particularly in distribution networks led to the inefficiency of the previous voltage sag source location approaches. In this paper, a new method based on voltage and current measurement data is proposed, in which cosine similarity is used to locate a voltage sag source. In the proposed method, the cosine similarity sign between two data sets is used to identify the relative location of the voltage sag source. Simulation results are presented for different scenarios in the IEEE 33 bus test network. In doing so, various issues including voltage sag source location, voltage sag original type (symmetric/asymmetric short-circuits or motor starting), the fault resistance, the x/r ratio of the grid lines, DG size, DG location, measurements error, and current transformer saturation are studied in simulations. The simulation results confirm the performance of the proposed method for the voltage sag source locating. Moreover, the comparison with some previous methods shows that the proposed method gives a better response in determination of location of the voltage sags.

Fractional‐slot concentrated‐windings are appreciated for their simple construction, short end‐winding length, high copper fill factor, low cogging torque, good field‐weakening capability and fault‐tolerant ability. However, in comparison to the conventional distributed windings, the fractional‐slot concentrated‐windings are characterised with high space magnetomotive force (MMF) harmonics, which results in undesirable effects on the machine performance, such as localised core saturation, eddy current loss in the rotor and noise and vibration. In order to improve winding characteristics, several techniques have been developed recently. This manuscript introduces the 5 new winding topologies by using the general concept of stator slot shifting. It means that, in order to cancel undesirable MMF harmonics, by doubling (or tripling or even multiplying) the slot number and dividing the winding and then relatively shifting the winding by one (or more) slots, the undesirable harmonics have been eliminated effectively. The best choice is chosen according to the lowest amount of the MMF harmonic, highest value of winding factor and torque desirable characteristics. At the end, comprehensive comparisons for the designed synchronous reluctance motor (SynRel) equipped with proposed windings and also distributed winding are presented. The analytical study and 2D FEM analysis results show that it is possible to get an ideal low space‐harmonic winding topology, and consequently, a low torque ripple for these motors.

The present paper devises a second‐order system frequency response (SFR) model for power systems integrating virtual synchronous variable speed wind turbines (VSWTs). The inertial response model of full converter VSWTs, in which grid‐side converters are controlled using a virtual synchronous generator concept, is developed. The derived model is incorporated into the traditional SFR model deployed to estimate the frequency behaviour of the synchronous generators following infeed loss contingencies. The proposed SFR model formulates interaction between the VSWTs rotor speed reduction and the system frequency drop. The system loads inertia is also included in the SFR model. Additionally, an analytical approach to derive the suggested SFR model for the large power system including VSWTs with different capacities and operating points is presented. Solving the proposed model gives the analytical functions for estimating deviations in the system frequency as well as VSWTs rotor speed variations. Finally, the accuracy of the devised SFR model is verified through the time‐domain simulations of a modified IEEE 39‐bus system. Particularly, impact of the VSWTs virtual inertia on the efficiency of the proposed SFR model is studied.