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To meet the new international efficiency (IE) standards, line-start (LS) synchronous reluctance motors (SyRMs) are now being considered. Conventional star and delta windings are usually employed in LS SyRMs. However, combined star-delta winding has higher winding factor and lower magneto-motive force (mmf) harmonics compared to conventional star and delta windings. Hence, in this paper, LS SyRM and LS ferrite assisted SyRM with star and star-delta winding are analyzed and their performance indices are compared. A winding function analysis is used for the design of star and star-delta windings. Further, the effect of zero sequence current on the performance of the motors under comparison is presented in detail. Star and star-delta winding prototype LS SyRMs with and without ferrite magnets in the rotor are fabricated. Experimental studies are carried-out on these prototypes and the results are presented which are in close agreement with the simulation results. [ABSTRACT FROM AUTHOR]

A modular multiport converter (MMPC), which is capable of interfacing multiple solar Photo-Voltaic (PV) modules, a battery bank, and a dc microgrid, is proposed in this article. The number of solar PV modules that can be interfaced with the proposed MMPC is equal to the number of converter modules present in the system. Furthermore, all these solar PV modules can operate at their respective maximum power point, thus increasing the power extraction capability. A high-frequency transformer facilitates the interfacing of low-voltage solar PV modules and the battery bank with a 380-V microgrid. However, the power from the solar PV modules to the battery bank does not flow through this transformer. The variation in the transformer utilization with changes in operating voltages of the solar PV modules is analyzed. Detailed simulation studies are carried out on a system having five solar PV modules to verify the performance of the proposed MMPC. A laboratory prototype of the proposed MMPC consisting of four numbers of 400-W converter modules is fabricated. The performance of the MMPC is analyzed and the experimental results are presented. [ABSTRACT FROM AUTHOR]

This article proposes a solid-state transformer (SST) based power electronic architecture for fast charging three categories of plug-in electric vehicle with batteries of vastly different voltage and power ratings. The SST accomplishes integration to a medium-voltage grid and isolation to the charging ports without the use of an LFT. Delta connected cascaded H-bridge (CHB) is used as the active front-end rectifier and quad active bridges (QABs) are utilized for the isolated dc–dc conversion stage. In the proposed architecture, an additional winding called balancing winding is provided in each of the medium-frequency transformers of the QAB. The balancing winding of the transformers are paralleled such that a circulating current flows among the transformers of the three phases, which eventually reduces the unbalance in the delta-connected clusters. Hence, the magnitude of zero-sequence current required to balance the cluster powers for a certain level of unbalance is also reduced. As a result, the total current in the devices of the CHB decreases and devices with a lesser current rating can be used. The control philosophy and detailed analysis of the system are given in the article. Experimental results with a scaled-down prototype are presented to verify the claims. [ABSTRACT FROM AUTHOR]

Electric motors used for irrigation applications contribute to a major part of worldwide energy demand. Efficiency improvement of motors used in these applications is the need of the hour. Usually, line-start (LS) induction motors are used in these applications. However, they are relatively inefficient compared to permanent magnet (PM) motors. On the other hand, PM motors have high initial cost compared to induction motors. In view of this, magnet-less machines like synchronous reluctance motors (SyRM) and PM assisted SyRM are being preferred. SyRM has poor power factor compared to induction motor and hence PM assisted SyRMs are becoming popular. In this article, a 2-pole multi-barrier LS ferrite assisted SyRM is proposed for a bore-well submersible water pump. Two-pole rotor geometry is not extensively studied for LS SyRMs. Further, the issues of ferrite magnet demagnetization for 2-pole LS applications are not explored. A separate cage is avoided by utilizing the rotor flux barriers as a cage, thereby reducing the number of ribs while housing the magnets. This improves the power factor and efficiency of proposed motor. Analytical and finite element analysis (FEA) are used for design of the proposed motor. Further, a prototype is fabricated and experimental results are presented. [ABSTRACT FROM AUTHOR]

In this article, a trust-region method based optimization approach is proposed for optimization of electromagnetic devices using a reduced number of finite-element method (FEM) simulations. This approach relies on a computationally efficient approximation of the objective function using a response surface model. A second-order polynomial model is used because of its simplicity. The design of experiments technique is used to build this model. Moreover, this approach allows the use of coarser mesh in the FEM model because of its smoothing capabilities under noisy objective function. The algorithm is tested on two benchmark problems: Loney’s solenoid design optimization and TEAM workshop problem 22. The proposed method has shown clear advantage of reduced number of FEM simulations compared to the existing algorithms tested on these problems. Later, this methodology is used for optimization of a Halbach array-based magnetic levitation device where the objective is to maximize permanent magnet utilization. This device is considered for various numbers of Halbach segments per pole. Improvement in the range of 5%–10% is observed over the past optimized results from the literature. Furthermore, this improvement is verified using a commercial optimization software, and the proposed method is found competitive to this software. [ABSTRACT FROM AUTHOR]

In this paper, a simple controller configuration for the decentralized parallel operation of single-phase inverters in stand-alone ac supply systems is proposed. The configuration is designed considering the unavailability of the filter capacitor voltage and grid current information to the controller. Due to the unavailability of voltage information, internally estimated voltage references and the measured value of the converter-side inductor current are used for the calculation of the active and reactive power. Frequency and voltage droop characteristics are used, and hence, communication is not required. The operation of the inverter at the reference voltage magnitude and frequency is achieved by the direct control of the modulating wave. Therefore, inability to implement closed loops caused by the absence of certain voltage and current information is mitigated. The proposed controller has the provision for protection of switching devices during overcurrent situation. The accuracy and feasibility of the proposed controller are validated using the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Cascaded multicell converter (CMC) is proved to be an effective solution for medium voltage drives. Three-phase diode bridge rectifiers are normally used in this converter, which do not have regeneration capability. Pulsewidth-modulated (PWM) rectifier-based power cells enable the drives with regeneration capability. However, due to their two-level voltage operation at the input side, an inductor is required for each cell to filter out the switching frequency components from the input current. In this paper, a new configuration with single-phase PWM rectifier-based power cell is proposed to achieve multilevel voltage operation at both the input and output sides of the converter. Therefore, the devices at the rectifier side are also operated at reduced switching frequency without using any filter inductor for each cell. In the proposed converter, simple modular transformers are used instead of a single large and complex transformer that is used in the conventional CMC. Further, input phase currents of the converter are controlled in the synchronously rotating d–q frame, which requires only two current sensors at the input side instead of individual current sensors for each cell. Experimental validation of the proposed converter configuration is carried out on a 4.5-kVA prototype, and the results are presented. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel automatic mode transition control strategy for multiple inverters to operate in grid-connected and standalone modes. When grid is available, these inverters feed power the grid by operating in current control mode. Upon grid failure, all inverters automatically shift to droop control mode for achieving proportional power sharing and shift back to current control mode when the grid becomes available. The synthesis of dual structure control algorithms of various inverters is achieved using novel state machines. These state machines are designed to facilitate smooth mode transition of the inverters. In this way, the control signals for mode transition are generated by state machines specific to each inverter. Unlike existing control methods, the proposed method neither requires communication-based supervisory control of inverters nor it requires dedicated storage facility for achieving smooth mode transition. The proposed control strategy is tested on a simulation model as well as an experimental prototype multi-inverter system. [ABSTRACT FROM PUBLISHER]

Cross magnetization (CM) is an inevitable phenomenon in electrical machines. It is more prominent in interior permanent magnet (IPM) brushless dc (BLDC) machines. This is because PMs demagnetize in overloaded and saturated conditions. It leads to cross coupling between the direct and quadrature-axes quantities, and a decrease in the resultant air-gap flux-density distribution under saturated conditions. In this paper, it is shown that CM leads to braking torque even in unsaturated IPM BLDC machines. Furthermore, the effect of CM on flux linkage, electromotive force, and dynamic torque is presented. Its mitigation using suitable selection of slot–pole combination is presented. It is observed that odd slot–pole combinations are least affected, and even slot–pole combinations are severely affected by CM. Furthermore, it is found that the overlap area of rotor pole arc with the stator pole arc influences the severity of CM, more particularly in fractional slot–pole combination machines. To verify these claims, finite-element method is used for modeling and analyzing various slot–pole combinations of a spoke-type IPM BLDC motor. The results obtained from these simulations are validated with a fabricated reference prototype, which support the claims. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) powered submersible electric water pumps are becoming popular in remote rural areas, due to the nonavailability of grid connectivity. However, the initial cost of a PV system is high. Permanent magnet (PM) brushless dc (BLDC) motors are efficient compared to existing induction motors, which reduce the cost of PV array. However, steep increase in the cost of rare-earth magnets like NdFeB and SmCo makes the use of PM motor uneconomical for PV systems. Thus, the design of PM motors with ferrite magnets is gaining interest. These magnets have low remanence flux density and are brittle. Thus, flux concentration rotor topologies are desirable. The conventional spoke-type (ST) rotor is one such topology. However, flux leakage is one of its prime concerns. To negotiate this, a novel “semi-modular dual-stack” ST BLDC motor along with its parametric aided three-dimensional finite element method analysis is proposed for a PV-based 100 mm deep bore-well submersible water pump. The motor features minimum flux leakage irrespective of rotor bridge width. In addition, a lumped parameter thermal network is modeled for quick estimation of the winding temperature rise. A prototype motor is fabricated to ascertain the results obtained from simulations, and the experimental results are presented. [ABSTRACT FROM PUBLISHER]

Switched reluctance motors (SRM) are becoming attractive due to the increasing cost of permanent magnets. It was reported that segmented rotor construction improves the torque output and efficiency of SRM. This paper investigates the effect of stator slot/rotor segment combination and number of phases on the performance of segmented rotor SRM (SSRM). It is found that SSRMs having higher number of rotor segments than stator slots have high efficiency and torque output, but they also have limitations of narrow speed range and low overload capability. On the other hand, it is found that SSRMs with higher number of both stator slots and rotor poles have high overload capability. The effect of increasing number of phases of SSRM is also evaluated. It is found that a polyphase SSRM improves the torque output, but does not have the limitations of low overload capability and narrow speed range. Thus, the choice of stator slot/rotor segment combination and number of phases depends largely on application. Procedure to select stator slot/rotor pole combination and number of phases of SSRM is presented here. Experimental results supporting conclusions from analysis are also given. [ABSTRACT FROM AUTHOR]

High efficiency and operating life of grid feeding solar photovoltaic (PV) inverters are demanded. Due to reduced dc-link capacitor requirement, current source inverter (CSI) offers higher reliability than the voltage source based solar inverter. However, conventional three-phase pulse width modulated (PWM) current source based solar inverter injects high earth leakage current into the grid. In order to suppress this current, an isolation transformer can be used. Use of this transformer increases the cost and size, and decreases overall efficiency. In order to address the aforementioned limitations, a modified CSI is proposed in this paper. The proposed inverter suppresses the earth leakage current without using an isolation transformer, thereby increasing the efficiency and reducing cost as compared to conventional current source based solar inverters. A mathematical model of the system is derived based on which controller for the operation of the inverter is designed. The effectiveness of the scheme is verified through detailed simulation study. To confirm the viability of the scheme, experimental studies are carried out on a scaled-down laboratory prototype. [ABSTRACT FROM PUBLISHER]