Kazi Ahsanullah

Analysis of MMF and back-EMF waveforms for fractional-slot concentrated-wound permanent magnet machines

An analytical modelling technique to calculate the generated magneto-motive force (MMF) and back-EMF of fractional slot concentrated wound (FSCW) permanent magnet synchronous machines (PMSMs) is reported. The generated MMF of a FSCW stator is analyzed and modelled using a Fourier series technique. General expressions of the harmonic winding factors for FCSW stators with different slot-pole combinations are then obtained. A general expression for the generated back-EMF of FSCW PMSMs is then derived. The obtained analytical results are validated through finite-element analysis (FEA) and experimental tests on a prototype FSCW PMSM. A comparison between the generated voltages of various FSCW stator topologies is also performed.

Fault ride-through of doubly-fed induction generators

The aim of this paper is to explore the various dynamic controllers to enhance the fault ride-through (FRT) of doubly-fed induction generators (DFIGs). A wind farm of total capacity 9 MW is considered for the study. The flexible AC transmission system (FACTS) controllers like Static Synchronous Compensators (STATCOM) and Unified Power Flow Controllers (UPFC) are modelled and analysed to study their effect on the voltage at the point of common coupling (PCC) and FRT capability. This is then compared with the FRT capability of existing crow bar controller added to the converters of DFIG. The simulation is carried out using MATLAB/Simulink. A new Simulink model is developed for DFIG, to make it versatile for any FRT control strategy. The results presented show the effectiveness of the model.

Design and simulation of quasi-Z-source grid-connected PV inverter with bidirectional power flow for battery storage management

In a small to medium scale PV inverter system, energy storage functionality such as battery is significant to ensure the obtained energy is efficiently stored, used and delivered to the load. As for the grid-connected system, having a bidirectional power flow in the system is an advantage in case the power from the PV array is insufficient to fulfill the demand from the load. The grid power can also be used to charge the battery storage in case the energy stored is at the critical level and cannot be recovered immediately due to low/zero level of sun irradiation. In relation to this, the quasi-Z-source inverter (qZSI) topology, apart from other well known advantages for DC-DC-AC conversion, offers a flexible ways on how the battery storage can be added to the system. In this paper a new way of connection and control method for battery storage is proposed which can be attach to the system easily with minimal modification. It also realizes a bidirectional charging capability from the grid where its use can be extended for example in vehicle charging station. Apart from that, the paper also study on use of PV emulator which can be an alternative to realize the PV source behavior. The system configuration and design is detailed and simulation results demonstrate the system works according to the requirement.

Distributed and concentrated winding Interior PM Synchronous Machine (IPMSM) for direct drive wind turbine

This paper compares the distributed winding and concentrated winding IPMSMs designed for direct-drive wind turbine. Apart from different stator winding configuration, the two IPMSMs have identical rotor and stator dimensions, air gap length, magnet length and stack length. The paper also discusses various techniques that were applied to minimize the cogging torque and torque ripple.

Efficiency analysis of a 42- pole/54-slot fractional-slot concentrated-wound interior permanent magnet synchronous machine

Fractional slot-concentrated wound interior permanent magnet synchronous machines (FSCW- IPMSM) display high power density and high efficiency due to the short stator end windings and absence of rotor windings. The purpose of this paper is to analyze the efficiency of a 42-pole/54-slot FSCW-IPMSM under three commonly used current reference trajectory control algorithms namely zero direct axis current control(id = 0), maximum torque per ampere (MTPA) control and loss minimization (LM) control. Analysis of the experimentally measured efficiency shows that loss minimization control is not as effective as it is in the distributed winding IPM machines. A possible reason for this is that additional rotor losses that are caused by the harmonics of the magneto motive force (MMF) of the FSCW stator are not accounted in the LM control technique. It considers stator core loss due to the fundamental flux only. LM control shows an improvement of efficiency in partial load of FSCW-IPMSM. The analysis of the paper is based on test results conducted on a 4kW prototype FSCW IPMSM.

Design of a 4KW interior permanent magnet machine suitable for low speed application

This paper presents a systematic design process for an interior permanent magnet machines (IPMM) containing distributed and concentrated windings in the stator and flat shaped and a v-shaped magnets in the rotor. The machine was designed with large pole numbers suitable for low speed application such as direct drive wind turbine. The paper also presents a comprehensive comparison of performances between distributed and concentrated windings stator in a low speed IPMM. The various steps taken to minimize the cogging torque and torque ripple in the studied IPMMs are discussed in details.

Cogging Torque and Torque Ripple in a Direct-Drive Interior Permanent Magnet Generator

This paper investigates the cogging torque and torque ripple in high pole number interior permanent magnet generators, designed for direct-drive applications. Two interior permanent magnet rotor topologies — flat-shaped and V-shaped were considered with distributed wound and fractional slot concentrated wound stators. A comparison of torque performances was made between distributed wound and fractional-slot concentrated wound generators. Cogging torque was minimized by finding an optimum magnet pole arc length and torque ripples were minimized by finding optimum slot-opening and flux barrier shape. Design analysis was carried out in finite element models. It was found that flat-shaped rotor topology in the fractional slot concentrated wound stator can provide the best torque performance regarding low cogging torque and torque ripple. This finding was verified in constructed prototype machine.