Studying the effect of over-modulation on the output voltage of three-phase single-stage grid-connected boost inverter

AbstractVoltage boosting is very essential issue in renewable-energy fed applications. The classical two-stage power conversion process is typically used to interface the renewable energy sources to the grid. For better efficiency, single-stage inverters are recommended. In this paper, the performance of single-stage three-phase grid-connected boost inverter is investigated when its gain is extended by employing over-modulation technique. Using of over-modulation is compared with the employment of third order harmonic injection. The latter method can increase the inverter gain by 15% without distorting the inverter output voltage. The performance of extended gain grid-connected boost inverter is also tested during normal operation as well as in the presence of grid side disturbances. Simulation and experimental results are satisfactory

Multi-terminal Hvdc system with offshore wind farms under anomalous conditions: Stability assessment

Droop control is widely adopted to control Multi-Terminal high-voltage Direct Current (MTDC) systems with offshore wind farms. During permanent faults, the faulty line should be isolated promptly to preserve a high reliability of the MTDC system. This paper examines the MTDC system performance following a faulty line outage. This study aims to identify the outage types that may lead to a complete loss of system voltage stability and the outages that may have a secondary effect on the system. Moreover, strategies for dealing with outages that may lead to a complete shutdown of the system are also presented. Furthermore, the ranges of droop gains' values that can be employed following fault occurrence to preserve system transient stability are studied. Different scenarios are explored during faulty conditions such as surplus and sparsity of wind power, line overcurrent, outage of lines connected to wind farms, and outage of lines connected to AC grids to validate this study.MATLAB/Simulink platform has been employed to elucidate the presented concept.Qatar National Research FundScopu

Interplane cross-saturation in multiphase machines

The use of electrical machines in electric vehicles and high-power drives frequently requires multiphase machines and multiphase inverters. While appropriate mathematical models under the linear magnetic conditions are readily available for multiphase machines, the same cannot be said for the models of the saturated multiphase machines. This paper examines the saturation in an asymmetrical six-phase induction machine under different supply conditions and addresses the applicability of the existing saturated three-phase machine models for representation of saturated multiphase machines. Specifically, the mutual coupling between different sequence planes in the vector space decomposed model under saturated conditions is analyzed. The paper relies on analytical considerations, finite element analysis and experimental results. It is shown that the saturation of the main flux path is influenced by the current components in the orthogonal (non-fundamental) sequence plane. This implies the need to develop new multiphase machine models which take this effect into account

Performance evaluation of a five-phase modular external rotor PM machine with different rotor poles

The performance of fault-tolerant modular permanent magnet (PM) machines depends on the proper selection of the pole and slot numbers which result in negligible coupling between phases. The preferred slot and pole number combinations eliminate the effect of low order harmonics in the stator magneto motive force and thereby the vibration and stray loss are reduced. In this paper, three external rotor machines with identical machine dimensions are designed with different slots per phase per pole (SPP) ratios. A simulation study is carried out using finite element analysis to compare the performance of the three machines in terms of machine torque density, ripple torque, core loss, and machine efficiency. A mathematical model based on the conventional phase model approach is also used for the comparative study. The simulation study is extended to depict machine performance under fault conditions

A five-phase linear induction machine with planar modular winding

Linear induction motors (LIMs) have become a competitive alternative in electric traction. Three-phase LIM commonly uses double layer overlapping distributed windings. Although this winding configuration results in more sinusoidal magneto-motive force (MMF), hence good machine performance, it has relatively bulky end windings and uses either half-filled slots or overhanging coil sides at the machine end sides. On the other hand, planar concentrated or modular winding will be the simplest and most cost effective alternative for such systems, where the coils are butted closely together and do not overlap. In the available literature, little interest has been given to employ modular windings in induction machines. This is because the MMF produced by a conventional three-phase modular winding contains of two main space harmonics with close magnitude but travel in opposite directions. These two components induce rotor currents with different frequencies yielding additional rotor bar losses and with a resultant limited net torque due to the resulting opposite torque components. In this paper, a five-phase LIM with a planar modular winding is investigated and compared with a three-phase linear machine with a conventional double layer winding and rated at same output thrust. The comparative study is carried out using finite element analysis.Qatar National Research FundScopu

Sensorless field oriented control of five-phase induction machine under open-circuit phase faults

Recently, multiphase machine is promoted to replace three-phase drives in high power safety-critical applications. Among the numerous advantages of multiphase induction machine drives, operation and self-starting under some phases open stand as the most important feature of such drives. With some phases open, optimal current control is proved viable to provide disturbance-free operation with some objective functions and under some operational constraints. Although hysteresis current control was simply employed in the literature with conventional field orientation to control the currents of healthy phases, it is not suitable for high power applications as it usually corresponds to high switching frequency and is susceptible to noise. Alternatively, synchronous reference frame (dq) control is much suitable; however, it requires back and forth transformations with several trigonometric calculations and additional sophistication to the controller with a corresponding intricate tuning process. In this paper, a simple controller using only two PR controllers for each sequence plane, with a total of four PR controllers for five-phase system, is presented. Moreover, a sensorless operation is also provided by estimating machine speed using rotor flux based MRAS speed estimator. The proposed controller is experimentally verified using a prototype 1.5Hp five-phase induction machine.Scopu

Sensorless V/f control with MRAS speed estimator for a five-phase induction machine under open-circuit phase faults

This paper introduces a sensorless scalar controller with MRAS speed estimator based on simple Proportional Resonant PR controllers to provide a disturbance-free operation to a five-phase induction machine under phase open and based on optimal current control. The machine speed is estimated using MRAS observer based on rotor flux (RF-MRAS). Under open phase, the torque-producing fundamental sequence current is used to estimate the required third sequence current components to ensure equal remaining healthy currents. Two PR controllers are then used to determine the corresponding third sequence voltage components. The used optimization criterion ensures maximum fundamental torque, minimum torque ripples, and equal line currents. The proposed controller is verified using a 1.5hp prototype machine for both dynamic and steady-state cases.Scopu

Interior permanent magnet motor-based isolated on-board integrated battery charger for electric vehicles

This study proposes an isolated on-board integrated battery charger using an interior permanent magnet (IPM) machine with a nine-slot/eight-pole combination or its multiples, and equipped with a non-overlapped fractional slot concentrated winding. The proposed winding layout comprises three three-phase winding sets that are connected in such a way as to provide six motor terminals. Hence, a six-phase or two three-phase converters will be required for propulsion. Under motoring mode, the machine can be effectively regarded as a six-phase machine, which provides a high fault-tolerant capability, and allows for a 'limp home' mode of operation. Additionally, all magneto motive force subharmonics are eliminated, which significantly reduces the induced rotor eddy current losses, when compared with a conventional three-phase motor having the same slot/pole combination. In battery charging mode, the winding is reconfigured, so that the machine is considered as a three-phase to six-phase rotating transformer. A 40 kW IPM machine is designed and simulated under different modes of operation using two-dimensional finite element analysis to validate the proposed concept. A small-scale prototype machine is also used for experimental validation.Scopu

A bearingless coaxial magnetic gearbox

Recently, magnetic gearboxes (MGBs) are serious contenders to their conventional mechanical counterparts in terms of reduced maintenance requirements, improved reliability, tolerance to mechanical inaccuracies, and inherent overload protection. MGBs are preferably employed in high speed applications and compact harsh environments subjected to severe shock and vibration. A high gear ratio MGB is also a suitable candidate for single stage high-speed transmission applications such as helicopter power transmissions. In this paper, the conventional planetary magnetic gearbox is equipped with a three-phase winding to provide additional magnetic levitation capabilities besides torque transmission, thus creating a bearingless MGB configuration. This was achieved by adding a three-phase winding in the space between the ferromagnetic pieces. The current in this additional winding is controlled to provide decoupled axial forces irrespective of the transmitted mechanical power. This feature is important to reduce the mechanical losses especially for high-speed rotors and can be a viable method for vibration suppression

Nine-phase six-terminal pole-amplitude modulated induction motor for electric vehicle applications

In electric drive applications that are based on high-speed induction motors (IMs) with an extended speed range, stator winding pole-changing is a possible technique to avoid oversizing the driving motor. The electronic pole changing employed in multiphase IMs has gained recent interest because it avoids physical winding reconfiguration. The effective number of poles of the air gap flux distribution can be electronically altered by simply changing the applied current sequence to a multiphase stator. The main problem associated with this technique is the significant increase in machine magnetising current with the increase in effective pole number when conventional multiphase distributed windings are employed. This study proposes a new fractional-slot concentrated winding layout with a special stator connection suitable for pole-amplitude modulated IMs that offers a 2:1 pole ratio while maintaining equal magnetising current for both winding pole pairs. Moreover, constant power operation can be achieved for a speed range of over 4 pu. The main concept is discussed and verified through simulations and experimentally. The machine mathematical model and the required vector space decomposition-based controller are also presented. - The Institution of Engineering and Technology 2019.Scopu