David Dorrell - Academia.edu (original) (raw)

Papers by David Dorrell

The three-phase direct matrix converter has been researched exclusively as a direct AC/AC convert... more The three-phase direct matrix converter has been researched exclusively as a direct AC/AC converter, being a competitive alternative to the conventional AC/DC/AC converter. Other possibilities of the matrix converter such as AC/DC, DC/AC and DC/DC conversion still remain unexplored. This paper firstly explores these possibilities and puts forward a concept of the versatile converter. With one matrix converter, different conversion purposes can be accomplished as required. The matrix converter based conversion has some advantages compared with other converters. Model predictive control (MPC) is applied in this work to control the matrix converter to perform the required conversion goals. A generalized model is obtained for all types of conversion in this work. With MPC, different objectives and constraints can be easily included in the control scheme. In addition, the observers are used to reduce the number of voltage and current sensors. Simulation results verify the effectiveness and feasibility of AC/DC, DC/AC and DC/DC conversion with the matrix converter.

Commonwealth Scientific and Industrial Research Organisation (CSIRO) for his kind support and enc... more Commonwealth Scientific and Industrial Research Organisation (CSIRO) for his kind support and encouragement. His rich industrial experience and advices broadened my mind of microgrids, which had a very positive impact on this work.

Iet Power Electronics, May 3, 2018

The hysteresis band controller offers excellent dynamic performance. It has been widely researche... more The hysteresis band controller offers excellent dynamic performance. It has been widely researched and applied for the voltage source inverter and inverter fed drives, however it has not been investigated within the context of a matrix converter or a matrix converter based motor drive. In this paper, both fixed-band and sinusoidal-band hysteresis current controllers are proposed and developed for a direct matrix converter. A comprehensive comparative evaluation of the two methods is then carried out. Both methods have fast dynamic performance and they inherently integrate the line modulation technique of the virtual rectifier stage into the overall modulation. Surge currents are prevented with the proposed scheme. The sinusoidal-band hysteresis controller demonstrates lower total harmonic distortion at the expense of higher average switching frequency, which is only significantly observable at very high sampling frequencies. The proposed controller is integrated with the field-oriented control to drive a matrix converter fed permanent magnet synchronous machine. The proposed methods are simple and incur a light computational burden, which advances the practical applications of matrix converters in AC motor drives. The simulation and experiment results demonstrate the effectiveness and feasibility of the proposed scheme.

This paper examines several techniques for determining the parameters of the Brushless Doubly Fed... more This paper examines several techniques for determining the parameters of the Brushless Doubly Fed Reluctance Machine (BDFRM). Even though the mathematical model for this machine is like that of a double-fed induction machine, the very high leakage inductances prevent the use of the normal locked rotor/unloaded rotor tests. The accuracy of the parameters found is validated by machine testing and comparison with the FEA machine design.

IECON 2017 - 43rd Annual Conference of the IEEE Industrial Electronics Society, 2017

2017 IEEE Energy Conversion Congress and Exposition (ECCE), 2017

In this paper a prototype brushless doubly-fed reluctance machine is investigated which is aimed ... more In this paper a prototype brushless doubly-fed reluctance machine is investigated which is aimed a meeting commercial machine performance figures. The machine has 4 and 8 pole 3-phase stator windings and a 6 pole radially-laminated ducted rotor. The machine is investigated using finite element analysis (FEA), static torque tests with DC current excitation, a MATLAB/Simulink model, and experimentally using direct torque control (DTC). The investigations show that the machine can perform and match performance found in commercial industrial drives and is controllable. This is a step forward from the work that has been published because the machine is shown to be of a design that is commercially viable, and controllable using known control techniques adapted for the machine. Most previous reports use proof-of-concept machines or machines that are not suitable for commercial operation. This machine is designed to be more commercial in its design.

2018 IEEE Energy Conversion Congress and Exposition (ECCE), 2018

The direct matrix converter has been proposed for many potential applications. However, it remain... more The direct matrix converter has been proposed for many potential applications. However, it remains unexplored within the context of microgrids and distributed generation. This paper investigates the application of the direct matrix converter to these areas. Both the grid-connected and islanded operation modes are explored. Model predictive control is employed to achieve flexible active and reactive power regulation in the gridconnected mode, and stable sinusoidal voltage control in the islanded mode. It is also used to achieve grid voltage synchronization prior to grid connection. Simulation and experimental results verify the feasibility and effectiveness of the direct matrix converter when used in grid-connected and islanded microgrids. When used in the matrix converterconnected microgrid, model predictive control is effective in regulating the voltage and the power exchange with the grid.

8th IET International Conference on Power Electronics, Machines and Drives (PEMD 2016), 2016

This paper investigates the matrix converter when working as the unified power flow controller wh... more This paper investigates the matrix converter when working as the unified power flow controller which can regulate the active reactive power flowing in a transmission line. A conventional unified power flow controller usually has a DC capacitor; this is removed in the proposed controller. This reduces the volume, improves the efficiency and lifetime, and eliminates the DC voltage control. The detailed direct space vector modulation method for the matrix converter is described. Based on this modulation scheme, a PID controller is designed in order to control the power flow. Coupling effects are suppressed by feedback of the coupling components to the controller. The proposed strategy can control the active and reactive power efficiently and effectively. Simulations based on MATLAB/Simulink help verify the feasibility and effectiveness of the scheme.

2017 12th IEEE Conference on Industrial Electronics and Applications (ICIEA), 2017

The number of commercial electric vehicles has increased significantly in recent years. However, ... more The number of commercial electric vehicles has increased significantly in recent years. However, there are still limited recharging facilities for EVs. Wireless charging offers an alternative way to recharge with more flexibility and convenience. The wireless transformer/coupler is the key component in electric vehicle wireless charging. The maximum power transfer capability is limited by the coupler. In order to reach desired power transfer level, the parameters of the wireless transformer should be analyzed. The wireless power transfer system design also requires accurate coupler parameters. In this paper, rectangular pads with different size of ferrite bars were analyzed in finite element analysis software. The prototype was built to valid the simulation result.

IEEE Journal of Emerging and Selected Topics in Power Electronics, 2019

microgrid, a DG can operate in a grid-connected mode or an islanded mode. When operated in the gr... more microgrid, a DG can operate in a grid-connected mode or an islanded mode. When operated in the grid-connected mode, the main control objective is the current or power exchange with the utility grid (or microgrid bus). The main control objective during islanded operation is to maintain stable sinusoidal voltages for various loads [5]- . These operating modes depend on system operating conditions, users demand, availability of energy, and utility grid requirement. For both operating modes, a DG should be able to supply electricity in a reliable, secure and economical manner [9]- . To this end, power electronic converters play a critical role . Various power electronic converters, including multilevel converters [13], together with their corresponding control techniques, have been researched for controlling power flow, current and voltage for DG and microgrid applications . This paper mainly focuses on the islanded mode of a renewable DG. At present, a DG or microgrid is an inverterdominated system [7] [15]. However, it is difficult to maintain feed to connected loads, particularly nonlinear loads, at the required voltage and frequency with an inverter . In the literature, research projects on voltage source inverters (VSI) and neutral point clamped (NPC) inverters, with many control methods, have been carried out on uninterrupted power system (UPS) based DGs in order to regulate the output voltage [16] [17]. The LC filters are commonly used in these topics. However, these strategies are only suitable for DC DGs and microgrids. For AC DGs and microgrids, the rectifier stage and DC-link capacitor are required together with an inverter for indirect AC/AC conversion. These will make the system bulky, reduce the lifetime and increase maintenance. In addition, there exists the necessity of the DC link voltage control. Other significant drawbacks of this structure include unidirectional power flow, difficulty in controlling the input power factor, and handling of the input unbalance and intermittent disturbance of the renewable energy sources. Recent demand for the AC/AC conversion has emerged in the field of DGs and microgrids [18] [19]. A solution for direct AC/AC conversion is the matrix converter ; this is an alternative to the established indirect AC/AC conversion method with a DC link. A direct three-phase matrix converter, as shown in Fig. , features compact structure, bidirectional power flow, controllable input power factor (which can be set to unity), regeneration capability, and no energy-storage elements [20]- . In addition, it was reported in [23] that the matrix converter can be used for other conversions (i.e. AC/DC, DC/AC, and DC/DC) to feed various loads such as inductive, capacitive, nonlinear, AC and even DC systems, as

IEEE Transactions on Magnetics, 2018

Switched reluctance (SR) machines are attractive because they present relatively high efficiency ... more Switched reluctance (SR) machines are attractive because they present relatively high efficiency and torque density in spite of lacking permanent magnets. This paper focuses on a two-objective optimization of an external rotor switched reluctance motor with a stator that has concentrated coils and a rotor with magnetically isolated modules. The objectives are minimum loss and mass, and eleven independent dimensionless geometric variables are considered as inputs that affect them. A combined design of experiments (DOE) and differential evolution (DE) approach is proposed. The DOE methodology is used to reduce the search space by eliminating from consideration input variable values leading to poor-performing designs. Following this initial DOE study, an optimization study based on DE is run over the reduced search space, which leads to significant savings in computation time. Furthermore, a directed graph based method for comparing different designs on the Pareto front to rank the best compromise designs is proposed.

2009 35th Annual Conference of IEEE Industrial Electronics, 2009

With the rapid increase of population and economy, lots of cities are suffering from heavy consum... more With the rapid increase of population and economy, lots of cities are suffering from heavy consumption of fossil fuels and air pollution caused by the conventional internal combustion engine (ICE) powered vehicles. With great breakthrough in battery technology, plug-in hybrid electric vehicles (PHEVs) jointly powered by electric machines and an ICE are a good choice to reduce the vehicle pollution. In a PHEV, the battery is charged by the grid and the electric machine plays the major role in vehicle drive whereas the ICE is only required to provide extra torque when accelerating and drive the generator when the battery electricity level is low. This paper discusses one novel PHEV drive system with only one electric machine which functions as either a motor or generator at a time and a supercapacitor bank for fast charging and discharging during the regenerative braking and fast acceleration. The propulsive resistance powers in the PHEV have been investigated so as to decide major system parameters according to project requirements. The drive system has been modeled by PSAT software. Many indexes in the PHEV, such as fuel economy, engine efficiency, distance, and acceleration, have been compared with those of traditional car. Furthermore, the PHEV propulsive performance in three typical driving cycles, UDDS, EUDC, and HWFET, have been evaluated in detail. of traditional car. Moreover, the PHEV characterizations in three typical driving cycles, UDDS, EUDC, and HWFET, have been stuided comprehensively.

IET Renewable Power Generation, 2014

Unbalanced grid voltage conditions in wind farms degrade the performance of the wind turbines and... more Unbalanced grid voltage conditions in wind farms degrade the performance of the wind turbines and inject severely distorted current into the power system. This study proposes a new model-predictive direct power control strategy for a doubly-fed induction generator (DFIG) under unbalanced grid voltage conditions. An optimised cost function is derived in order to select an appropriate voltage vector. This directly regulates the instantaneous active and reactive powers in the stationary stator reference frame without the requirement for coordinate transformation, proportional-integral regulators, switching table or pulse-width modulation modulators. After that, the behaviour of the DFIGs under unbalanced grid voltage is investigated. A power compensation scheme is developed, which does not require the extraction of the negative stator current sequence. This can achieve several different control objectives; that is, obtaining sinusoidal and symmetrical stator currents, and the cancellation of electromagnetic torque oscillations. The effectiveness of the proposed control strategy is validated experimentally on a 20 kW laboratory DFIG prototype.

IEEE Transactions on Industry Applications, 2015

This paper presents a model predictive direct power control strategy for a grid-connected inverte... more This paper presents a model predictive direct power control strategy for a grid-connected inverter used in a photovoltaic system as found in many distributed generating installations. The controller uses a system model to predict the system behavior at each sampling instant. The voltage vector that generates the least power ripple is selected using a cost function and applied during the next sampling period; thus, flexible power regulation can be achieved. In addition, the influence of a one-step delay in the digital implementation is investigated and compensated for using a model-based prediction scheme. Furthermore, a two-step horizon prediction algorithm is developed to reduce the switching frequency, which is a significant advantage in higher power applications. The effectiveness of the proposed model predictive control strategy was verified numerically by using MATLAB/Simulink and validated experimentally using a laboratory prototype.

IEEE Transactions on Power Electronics, 2014

The parallel operation of inverters in microgrids is mainly based on the droop method. Convention... more The parallel operation of inverters in microgrids is mainly based on the droop method. Conventional voltage droop method consists of adjusting the output voltage frequency and amplitude to achieve autonomous power sharing without control wire interconnections. Nevertheless, the conventional voltage droop method shows several drawbacks, such as complicated inner multiloop feedback control, and most importantly, frequency and voltage deviations. This paper proposes a new control strategy in microgrid applications by drooping the virtual flux instead of the inverter output voltage. First, the relationship between the inverter virtual flux and the active and reactive powers is mathematically obtained. This is used to develop a new flux droop method. In addition, a small-signal model is developed in order to design the main control parameters and study the system dynamics and stability. Furthermore, a direct flux control (DFC) algorithm is employed to regulate the virtual flux according to the droop controller, which avoids the use of PI controllers and PWM modulators. Both the simulation and experimental results shows that the proposed flux droop strategy can achieve active and reactive power sharing with much lower frequency deviation than the conventional voltage droop method, thus highlighting the potential use in microgrid applications.

Standard double fed induction machines (DFIM) have symmetric stator – rotor side parameters when ... more Standard double fed induction machines (DFIM) have symmetric stator – rotor side parameters when they have the same turns per phase. Additionally, the magnetising inductance looking from either the stator or rotor perspective is identical. This is not so for the Brushless Doubly Fed Reluctance Machine (BDFRM). Coupling of flux between equivalent stator and rotor windings occurs at sideband frequencies due to an air-gap flux modulation process, a consequence of differing stator winding, rotor winding and reluctance rotor pole numbers [1]. This paper examines the modulation to explain the mutual inductance asymmetry found in experimental results.

Brushless Doubly Fed Reluctance Machines (BDFRM) are a class of machine that may be controlled us... more Brushless Doubly Fed Reluctance Machines (BDFRM) are a class of machine that may be controlled using a power converter that has a rating lower than the total power rating of the machine. The attractive properties of these machines have, in the past, been offset by low power density and efficiency when compared to other types of machine. Recent advances have shown that when well designed, these machines are in fact capable of operation at high torque density and efficiency. However, little guidance on how to design these machines is available in the literature. This paper presents analytical approaches to design a BDFRM with desirable qualities and the use of time stepped FEA to validate the results of the design process.

2015 IEEE Energy Conversion Congress and Exposition (ECCE), 2015

This paper puts forward a concept for measuring rotor eccentricity in a wound rotor induction mac... more This paper puts forward a concept for measuring rotor eccentricity in a wound rotor induction machine. The analysis is fully developed in the theory section then an experimental rig is described and measurements are taken. These are compared to the calculated values. Pole-specific search windings are necessary in a wound rotor machine because standard sideband current measurement techniques are only valid for cage induction machines. The search coils can also be used to suppress unbalanced magnetic pull.

Energies

Large induction motors can have a high inrush and run-up current during starting, often up to ten... more Large induction motors can have a high inrush and run-up current during starting, often up to ten times the rated current. In weak supplies, this could be a problem, causing system stability issues and the voltage to dip below acceptable levels. In islanded systems, the capacity could be pulled below its maximum. There are several different starting methods possible, but they are often only suitable for smaller machines. One method not investigated is the use of parallel capacitor compensation during the starting because large induction motors are very inductive during the starting sequence, so that supplying reactive power may be more effective than supplying energy. This paper first investigates several different induction motors with increasing size and assesses their compensation requirements in terms of the reactive power requirement during starting. It is shown that they do generally become more inductive as they increase in size. It is illustrated, using simulations, that usi...

2017 IEEE AFRICON, 2017

The round rotor induction machine (WRIM) can be described as a doubly red induction generator (DF... more The round rotor induction machine (WRIM) can be described as a doubly red induction generator (DFIG) when driven above the synchronous speed, and the stator and rotor windings are connected to the whole system. The work in this paper develops a relatively simple powerful model that can accurately analysis the behavior of DFIG with rotor-wound faults. The model is based upon the calculation of the stator current components, which are needed to the build impedance matrix. This method is used here to detect the rotor asymmetry fault on a four-pole wound rotor. Measured torque, current, and power loss results are compared with computer predictions for the machine with a rotor connected to symmetrical or asymmetrical external resistance. An equivalent circuit for a wound rotor induction machine, which includes external resistances, is derived. This is essential for building a better understanding of the fault components computed from the matrix. Simulation and experimental results evidence the validity of the suggested method, leading to an improved condition monitoring system for diagnosing faults in WRIMs.