Electric motors with high torque density are sought after in applications with constrained equipment footprint. In recent years, torque density enhancement is often being achieved by using magnetic gears with the motors. The gear ratio has a substantial impact on the relative size of the motor and the magnetic gear and eventually on the system volume and performance. This paper investigates the effect of gear ratio on the design and performance parameters of a magnetic gear integrated machine in two different ways. Firstly, five machines are designed for the same output torque and speed ratings but for different gear ratios. In another set of five machines, magnetic gears of different gear ratios are integrated to the same motor to determine the trend and limitation in torque density enhancement. These designs are optimised with finite element analysis for a fair comparison. A magnetic gear integrated segmented rotor switched reluctance motor has been chosen for this study. The optimised designs are compared for material mass, loss, footprint and efficiency. Guidelines are provided towards the choice of gear ratio for magnetic gear integrated electric motors.

A Two stage on-board electric vehicle charger (OBEVC) has a front-end power factor correction (PFC) converter and a dc-dc converter to charge the main battery. In addition, there is an isolated dc-dc converter, typically one-third the rating of the main battery charger, to supply various auxiliary low voltage loads. In this paper, a new on-board charger consisting of fewer circuit components and having a higher power density compared to the converters reported in the literature, is proposed. This is achieved by completely eliminating the isolated low power dc-dc converter. In grid connected mode, Totempole PFC and dual active bridge (DAB) perform either grid to vehicle (G2V) or vehicle to grid (V2G) operation with main battery. In driving mode, an interleaved buck converter is formed using the first stage circuit (Totempole) components. The second leg of Totempole PFC is integrated with ripple power compensation (RPC) circuit to eliminate the second order ripple power in the dc link. It also serves as one of the phases for interleaved buck converter in driving mode. The DAB along with interleaved buck converter supply power to the auxiliary battery and low voltage loads. The operation of this converter is explained and detailed simulation studies on a 7.2 kW on-board charger are carried out.

Medium-frequency (MF) transformer is employed in several DC-DC converters, where its leakage inductance plays a crucial role in the converter operation, such as creating resonance in soft switching converter, limiting current in dual active bridge converter, etc. Therefore, it is paramount to accurately estimate the leakage inductance during the design stage. In the literature, leakage inductance calculation at medium frequency is analyzed considering the effects of eddy currents, winding arrangement, etc., but the effect of winding material remains unexplored. This is analyzed by calculating the magnetomotive force (MMF) distribution in the winding volume for different conductor materials. This helps deduce the energy stored in the winding and thereby formulate the effective leakage inductance analytically. Moreover, conductor materials with different resistivities exhibit different temperature coefficients. Therefore, this study also investigates the effect of temperature rise in the windings on the effective leakage inductance due to the change in the wire resistivity. Finally, a comparative analysis between Al and Cu foil designs of a 16 kVA, 1.5/20 kV, 20 kHz transformer is presented to summarize the relative benefits of using Al foils for high power MF transformer designs. The analytical model is verified using 2D FEM analysis. This study shows that higher resistivity material leads to higher leakage energy stored in the conductor volume; consequently this helps achieving higher leakage inductance. As the material resistivity increases with temperature, this also leads to higher leakage inductance.

Electrical machines with high torque density are required for traction application. Availability of bonded magnets with complex shapes and magnetization pattern can significantly extend the design space of electrical machines. This paper introduces a hybrid flux barriers design to improve the torque density of permanent magnet assisted synchronous reluctance (PM -SynRel) machine using ferrite magnets. The torque density with hybrid flux barriers is found to improve along the entire range of speed compared to the conventional flux barriers. The hybrid barrier design achieves similar performance to that of curved barrier with relatively flat shaped magnets in the last flux barrier. Thus, the hybrid barrier is able to enhance the torque density at a potentially reduced cost of manufacturing. The hybrid flux barrier design is validated for both electromagnetic and mechanical performance using commercial finite element analysis (FEA) packages.

High power density and high torque density are the fundamental requirements for electric machines used in traction application. The former is obtained by potentially increasing the speed of the machine while the latter by using high energy density rare earth magnets. Ferrite magnets are explored as a viable alternative to rare earth magnets which are relatively expensive and geographically concentrated. The paper is intended to bring out the current trend of electric machines used in electric vehicles (EVs) with due focus on permanent magnet assisted synchronous reluctance (PM-SynRel) machine. High power and high speed PM-SynRel machine with rare earth and ferrite magnets are designed and compared based on the requirements for a future electric commercial vehicles. The ratio of stack length, mass of magnet, total mass and inertia of rare earth machine in comparison to ferrite PM-SynRel is found to be 0.72, 0.42, 0.72 and 0.32, respectively. Based on these, the rare earth based machine is found to have high power density, torque density and also utilizes lesser volume of magnets but PM-SynRel with ferrite is getting closer.

As the market for two-wheeled Electric Vehicle (EV) is growing, it is imperative to improve the efficiency of electric powertrain. Most of the two-wheeled EVs have either motor mounted in the wheel-hub or connected to the rear wheel through a transmission. In-wheel motor has limited torque capacity whereas in the other configuration, transmission reduces the system efficiency. This paper proposes a Dual-motor powertrain topology which aims to combine the best of both configurations. To evaluate and compare the configurations, the energy consumption of the Single-motor and the Dual-motor topologies is calculated over a driving cycle. It is shown that Dual-motor topology efficiently utilizes the available energy compared to Single-motor topology.

This paper proposes a power electronic architecture for DC level 3 fast charging station (FCS) that can charge three classes of EV batteries with different voltage and power levels. The proposed architecture based on a solid state transformer (SST) can be directly connected to a medium voltage grid hence eliminating the bulky line frequency transformer. Further, at the output side, several dual active bridges are paralleled to take care of the heavy charging current required for fast charging of the EV. In addition, battery storage and solar PV are integrated at each FC port to relieve the stress on the utility grid. The dynamic equations of the converters are derived and the controller architecture of the FCS is presented. Since the power in the three phases of the converter are different, a balancing scheme using zero sequence currents to equalize the power among the phases is described. In order to verify the effectiveness of the proposed architecture and its control, simulation studies are carried out in MATLAB/Simulink with an arbitrary real life scenario.

Over the years with increase in energy demand, efficiency of electric motors is a major concern since they contribute to majority of this demand. Many of these motors are in the low-power range (<;7.5 hp)and usually induction motors are widely being used in this power range for industrial, household, irrigation water pumping, etc. These motors are inefficient and it is difficult to achieve the new international efficiency (IE)standards using the conventional design approach. In this paper, a new toroidal winding is proposed for efficiency improvement of a 5 hp squirrel-cage induction motor (SCIM). A transient 3-D finite element (FE)analysis is carried-out for ascertaining the claims of efficiency improvement and the results are presented.

This paper proposes a multi-port solid state transformer (SST) to integrate a hybrid microgrid with 380 V dc, 48 V dc and 415 V ac sub-grids to the medium voltage distribution network. The system replaces multiple single phase transformers in the conventional SST with one multi-winding transformer thereby reducing the magnetics involved. Moreover, the individual dual active bridges (DAB) in the conventional SST is replaced by Multiple Active Bridge (MAB) configuration which reduces the number of H-bridges. The individual sub-grids are isolated, thus eliminating circulating current flow between them. The control architecture and power management for the system are discussed and verified through simulations using MATLAB Simulink.

High speed motors rotating at speeds above 10,000 rpm are gaining more attention nowadays for various high performance applications. High efficiency and reliability are demanded by the applications like centrifugal compressors, pumps, machine tools, drills, aerospace etc. This paper presents novel design and analysis of a high speed axial flux permanent magnet motor for high speed, low power applications. The major issues and challenges in the electromagnetic, mechanical and thermal design of high speed axial flux motors are discussed. The motor is designed to rotate at a speed of 30000 rpm. The proposed axial flux motor has light, yet strong, well-balanced rotor. The designed motor is optimized for obtaining superior performance. MagNet 3-D and OptiNet are used for the Finite Element Analysis (FEA) and optimization of the motor respectively and the results are presented. Finally, the fabricated motor is tested using sensorless Field Oriented Control (FOC) for experimental verification.

Modular multilevel converter (MMC) is one of the recent developed converter for high power applications. However, the major drawback of this converter in variable speed drives is that the capacitor ripple voltage increases at lower speed, when the load torque remains constant. This ripple voltage can be reduced by reducing the dc-bus voltage at lower speeds, while the capacitor voltages are maintained at their rated value. In this paper, a full-bridge submodule based MMC is proposed as front end rectifier in back-to-back MMC based drives to reduce the dc-bus voltage when the drive is operated at lower speeds. Therefore, the capacitor ripple voltage is maintained constant over the wide speed range of operation for constant load torque. This also enables the drives with regeneration capability and eliminates the requirement of complex phase-shifting transformer at the input side. The proposed configuration is simulated in MATLAB/Simulink and the simulation results are presented.

Active power decoupling (APD) topologies are well known for improving the reliability of a single-phase inverter by eliminating the need for electrolytic capacitors at the DC-link. In this paper, several APD topologies are analysed for grid connected PV application, where, the common mode leakage currents are one of the main concerns. It is found that few APD topologies can minimize these leakage currents without any modification in the original circuits. The performance of these APD topologies in minimising the leakage currents are analysed and evaluated using the simulation studies. Further, a new transformerless APD topology is derived and its performance is analysed in minimising the leakage current.

Modified topologies of a Z-Source DC Circuit breaker with bi-directional power flow capabilities are introduced in this paper. Conventional Z-Source breaker (ZSB) topologies can provide protection for unidirectional power flow. Proposed topologies of bi-directional ZSB (Bi-ZSB) and bi-directional ZSB with coupled inductor (Bi-CZSB) can clear the fault in either direction of power flow. Both topologies utilize a SCR as a switch to instantly isolate the fault from source. No sensing and detection of fault is required. For second topology, mutual inductance is used for SCR commutation. Coupled inductors help to reduce size of inductors, cost and also eliminate the need of additional Z-Source breaker capacitor. Performance of both topologies is verified in MATLAB and validated on laboratory prototype.

Bulk electrolytic capacitors are used in single phase inverters to reduce the ripple in dc link voltage which is due to the pulsating nature of the instantaneous power. The reliability of an inverter is limited by the lower lifetime of these capacitors. In addition, the switching devices also deteriorate the reliability, due to their significant failure rate. In order to improve the overall reliability of the inverter, a novel active power decoupling topology is proposed with fault tolerant ability. The proposed topology eliminates the need of bulk electrolytic capacitors by using an auxiliary circuit for active power decoupling. It ensures redundancy in achieving the active power decoupling in case of a switch failure. It is observed that the proposed topology can deliver 50% of the rated power along with ripple power compensation under fault tolerant operation. The operation and modulation strategy of the proposed topology are explained under normal and fault tolerant operations. Simulation studies validate the claims of the proposed topology.

A high resolution m-cell Symmetric Cascaded H-Bridge Multilevel Inverter (SCHB-MLI) based on cascade connection of one 5-level Transistor Clamped HB (TCHB) power cell and (m-1) 3-level HB power cells is proposed in this paper. The proposed hybrid converter features reduced number of components, reduced number of redundant switching states, and near equal power distribution among the power cells. Operation of proposed converter is explained using Staircase modulation technique and Hybrid PWM technique for 9-level converter and, Hybrid PWM technique for 13-level converter. The analysis of dc link midpoint current of TCHB power cell is also presented. Finally the operation of proposed converter system is verified by simulation results for 9-level converter with 500 hp induction motor as load.

Optimization plays a crucial role to bring out a trade-off between the cost and efficiency of permanent magnet motors. Optimization algorithm coupled with analytical magnetic circuit analysis, is one such technique to improve the performance of a motor. However, the non-linear effects like saturation, cross-magnetization, etc. are cumbersome to be modelled analytically. In addition, the interdependency between the motor design parameters adds to the complexity in the formulation of an optimization problem. Finite Element Method (FEM) based optimization with stochastic optimization algorithms overcome the said complexities. In this paper, a parametric feasibility analysis is initially carried out to obtain a design prior to optimization of a PV based bore-well submersible "Semi-Modular Dual-Stack" (SMDS) spoke type (ST) Brushless dc (BLDC) motor. Later, the motor model is "parameterized" in MagNet FE environment enabling the feasibility analysis. Further, transient 2D-FEM based multi-objective optimization is carried out using OptiNet Software and the results are presented.

DC system for solar photovoltaic (PV) application is gaining popularity due to high efficiency and reliability. This system could be interconnected to ac and dc grids. For high availability of power supply to loads, energy storage elements are interconnected using dc-dc converters. Power management control for this system is necessary to ensure high utilization of renewable sources and stable operation of system. DC bus signaling technique, suggested in literature, does not consider extreme system operation, for instance battery fully charged or battery deep discharge conditions. A modified technique based on dc bus voltage signaling considers the above mentioned conditions only for one battery storage unit. Moreover, power sharing among multiple battery units is not discussed. To address these limitations, this paper presents a distributed power management scheme based on dc bus signaling controller. The proposed scheme is capable of controlling multiple storage, solar PV and grid converters. Detailed simulation studies are carried out to verify the effectiveness of the scheme and results are included.

To improve the reliability and efficiency of grid tied inverters, it is suggested to replace some of the fully controllable devices by semi-controllable devices like thyristor. A modification for the HERIC topology is proposed, wherein the upper two switches of inverter leg and additional series connected switches for freewheeling are replaced by thyristors. The efficiency and reliability of full bridge transformerless inverter, full bridge transformer based inverter, HERIC transformer-less inverter and proposed transformer based inverter are calculated. It is shown that the proposed change not only improves reliability but also the efficiency. Calculated efficiency is around 98% and calculated failure rate of inverter stage is 4150 FIT (Failures In Time = 10-9failures per hour). These figures are better than those reported for the other popular topologies. Simulation results of the grid tied inverter feeding power at unity power factor are given.

A four switch, low power, battery integrated, photovoltaic stand-alone inverter system is proposed in this paper. The proposed topology is derived by combining a DC-DC bidirectional converter with a Ćuk based inverter. The derived topology has a simple structure consisting of four switching devices and an isolation transformer. A simple integrated control strategy for maximum power point tracking (MPPT) and battery charging is proposed. A modification in the conventional perturb and observe MPPT algorithm is proposed for efficient charging of the battery. Various modes of operation of the circuit are studied. In addition, simulation study is carried out using PSCAD and results are given.

Grid-connected photovoltaic (PV) systems with power electronic interfaces are becoming popular since they do not contribute to environmental pollution. However, one of the issues with grid feeding inverter is the requirement of high dc-link voltage. In view of this, single stage solar inverters using conventional inverters may not be suitable, since they require input dc voltage higher than the peak of line-line voltage. Therefore, two-stage topologies which typically consist of one dc-dc power stage to boost the dc voltage, in addition to a Current Source Inverter (CSI) for dc-ac conversion are reported for applications where the input voltage is lower than the peak of the output voltage. However, this increases the circuitry complexity. In addition, CSI requires bulky inductance in DC side, which increases losses. Hence, In this paper a novel single stage solar inverter using shunt active hybrid filter is presented. The inverter features a single power stage, with dc link voltage less than the peak line-line voltage, which will reduce the power losses and circuit complexity. In addition, the proposed solar inverter can also provide harmonic filtering to improve the power quality of the system. The operation and control of the novel single stage solar inverter for active power control and harmonic control is described. A detailed analysis, simulation along with the hardware results for the proposed single stage solar inverter is presented. Experiments are carried out on a 1.5kW laboratory prototype which demonstrated the performance of the inverter for active power control and harmonic compensation. The proposed inverter has an efficiency of 94%, compared to an conventional active filter based solar inverter's efficiency of 90%. Moreover, it has been shown that the switching ripple injected by the proposed solar inverter is just half of the conventional active filter based solar inverter.

Among the carrier based pulse width modulation (PWM) techniques, Phase Shifted PWM (PS-PWM) technique is preferred for Cascaded H-Bridge (CHB) multilevel inverters. This technique distributes power evenly among the modules and also ensures equal utilization of inverter switches within a module. On the other hand Carrier Disposition PWM (CD-PWM) technique has superior output voltage profile, but results in uneven power distribution and non-uniform switch utilization. Modified CD-PWM and Hybrid-PWM techniques can be used to mitigate the problem related to uneven power distribution. In this paper, the performance comparison of above mentioned modulation techniques is presented for a 7-level CHB multilevel inverter for same device switching frequency. It is found that at low modulation index, the line voltage and line current THDs are less with Hybrid-PWM technique as compared to those with PS-PWM and Modified CD-PWM techniques. But in Hybrid PWM technique, the switches within a module are not equally utilized. A Modified Hybrid-PWM technique is proposed, which retains the power distribution and uniform switch utilization features of PS-PWM technique and results in output voltage profile similar to that with Hybrid-PWM technique.

A novel full-bridge single-phase neutral point clamped (NPC) transformerless inverter for grid-connected photovoltaic system is proposed in this paper with the intent to improve the reliability and reduce the common-mode leakage current. The proposed inverter incorporates two coupled inductors along with series connected switch on ac side that operate alternately in positive and negative half period of grid. This inverter eliminates shoot through problem which is common in NPC topologies, resulting improved system reliability. Therefore, dead time at both switching frequency commutations and grid current zero crossing instants is not required. The coupled inductor along with series connected switch will not allow current to flow through antiparallel diode of switches, avoiding reverse recovery issues. Switches such as cool MOSFETSs now can be used in the proposed inverter, which increases the converter efficiency. In addition to high reliability, the proposed inverter maintains common-mode voltage at a constant level resulting low common-mode leakage current. Derivation of the full-bridge NPC inverter from existing single-phase transformerless H6 topology is presented. Other alternative full-bridge NPC inverter topology is also illustrated. The principle of operation and leakage current analysis of proposed NPC inverter are described. Finally, performance of the NPC inverter is verified by simulation studies and results are presented for peak power rating of 2.2kW.

Characterized by high efficiency and low cost, single-phase transformerless inverters are suitable for grid-connected photovoltaic (PV) generation especially at low power (<;5kW). Since galvanic isolation is omitted, leakage current can flow through stray capacitance between the PV array terminals and the ground. Therefore, the leakage current generated by transformerless inverter has to be regulated in order to meet the safety requirements. Full-bridge neutral point clamped (NPC) inverter topologies feature reduced input voltage and low leakage current. Hence, they are preferred in the applications like transformerless grid-connected PV systems. In this paper an improved full-bridge NPC transformerless inverter, which eliminates leakage current is presented. Unipolar sinusoidal pulse width modulation (SPWM) is used to achieve high efficiency and three-level output voltage. The detailed operating principle and the effect of parasitic capacitance of switches on common-mode voltage are described. Finally, the improved leakage current performance of full-bridge NPC inverter is verified by simulation studies and results are presented for peak power rating of 1kW.

The intra-campus two wheeler is a vehicle used for small daily commutes inside a campus. It is characterized by low power and small range thus making it suitable for conversion into an electric vehicle. In this paper, the electric drive-train of the vehicle is designed. Generally high torque density brushless DC hub motor is preferred for this application. But to achieve constant power output, the hub motor is severely overloaded reducing overall vehicle efficiency. To improve efficiency, the field weakening capability of the electric motor is utilized. However, such a motor has high rated torque and therefore large size. Hence, a planetary gear is used between wheel and the motor as a reduction gear to reduce the motor size. Furthermore, instead of expensive permanent magnet based motors, Switched Reluctance Motor (SRM), which has good field weakening capability, is chosen for this application. It is shown that a 4 phase SRM has better field weakening capability than a 3 phase SRM. Thus a 4 phase SRM is designed and fabricated for this purpose. The SRM is to be fitted inside the rear wheel of the vehicle along with the planetary gear.

Switched reluctance motor (SRM) has gained attention due to simple construction, ruggedness, high reliability, low cost, minimum maintenance and advancement in power electronics technology. However, SRM has some inherent disadvantages such as torque ripple, acoustic noise, requirement of rotor position information and control difficulties due to nonlinearities. It is reported in literature that smooth torque in SRM is achieved using the philosophy of direct torque control (DTC) of ac machines. In this paper, a comparative study of DTC with other torque control methods for 3-phase SRM is performed. It is observed that in case of DTC, high phase rms current is required to maintain constant flux linkage at all rotor positions of SRM thereby reducing the torque/ampere. It is also observed that in this scheme, different flux linkage references are required at different speeds to produce same torque for optimum torque/ampere. A new DTC scheme which addresses these limitations is proposed in this paper. In this scheme, the voltage vectors are selected judiciously to increase torque/ampere. The flux linkage is maintained constant only during phase commutation to avoid the need for rotor position information.

Demand for high power direct grid feeding solar photovoltaic (PV) inverters in increasing. To reduce stress on semiconductor devices and harmonic distortion of current waveform, multilevel topology based solar inverters are suggested in literature. Use of Neural Point Clamped (NPC) topology is limited due to complex layout of switches and diodes as compared to 2-level Voltage Source Converter (VSC). Moreover, both NPC and VSC offer only one MPPT tracker for each inverter. Therefore, these inverters may not be effective in extracting maximum power from large PV array under partial shading condition. To address these limitations, a 3-level solar inverter integrating two 2-Level VSCs, supplying real power to the grid is proposed in this paper. Simple layout of the switches and two MPPT trackers are the attractive features of the proposed topology over the 3-level NPC based solar inverter. Mathematical model of the system is derived based on which a controller for the scheme is designed. Effect of partially shaded PV array on current harmonic distortion is analyzed. Effectiveness of the scheme is verified through detailed simulation study.

Uninterrupted power supply for telecom base transceiver stations (BTS) is required to ensure reliable communication services. This becomes a severe challenge if the BTS is located in remote areas where access to continuous power supply from grid is not available. In this context, this paper presents a hybrid solar-wind energy telecom power supply with battery storage. An improved dual-input Cuk-SEPIC converter (IMDICS) topology is proposed and this converter is configured in parallel power transfer mode (PPT) to achieve higher efficiency. It's efficiency is compared with Dual-input Cuk-SEPIC converter (DICS) topology. A detailed component wise comparison between these topologies is presented to establish reduction in size of energy storage elements and device ratings. These topologies can extract maximum power from two renewable sources, simultaneously or individually. In order to evaluate the performance of these topologies, simulation studies are carried out and the results are presented. The efficiencies achieved by the DICS and IMDICS are 91% and 93% respectively, thus indicating an improvement in efficiency.

A ac distribution system is very common in various commercial installations. Most of the loads require front end ac-dc converter to interact with the ac system. Also, various storage systems and renewable sources connect to the ac system through dc-ac converters. These multistage conversions in the power flow path from renewable sources and storage systems to the loads reduce system efficiency. In view of this, an ac distribution system can be replaced by a dc distribution system within a commercial facility to improve overall system efficiency. This paper proposes a module integrated dc-dc converter for integration of a photovoltaic (PV) source with a dc distribution system. Current-fed topology is suggested to avoid limitations associated with large energy storage capacitor. The converter injects very low ripple, continuous current into the dc microgrid. Effect of converter switching ripple at low insolation levels is analyzed. Use of L-C filter at the converter front end is proposed, to improve power extraction at low insolation levels. This modification also enables utilization of non-dissipative snubber circuits. The converter allows large voltage step-up ratio, suitable for integration of low voltage PV module with high voltage dc micro-grid. It has compact size and high reliability. The steady state and dynamic performance of the converter are studied through computer simulations and experimental tests.