Projects

ElectricalMachinesandDrivesLaboratory

DepartmentofElectrical&ComputerEngineeringNationalUniversityofSingapore

ResearchProjects

DevelopmentofEnergyEfficientPropulsionSystemforUnmannedAerialVehicles

The objective of this research project is to develop an energy efficient propulsion system for Unmanned Aerial Vehicles (“UAVs”). A hybrid propulsion system is proposed, which aims to reduce the fuel consumption of the UAV thereby increasing the endurance time. The hybrid UAV propulsion system consists of internal combustion engine, generator, motor, battery, propeller and transmission mechanism. Two major issues are addressed in the hybrid propulsion system design: high power density and high efficiency of the overall system. To achieve optimal system integration and meanwhile reach the targeted efficiency of the propulsion system, research work in the following aspects are conducted: (1) development of efficient AC-DC rectifier; (2) development of efficient DC-DC bi-directional converter; (3) development of sensor-less PMSM drive.

ConditionMonitoringandPrognosticsOfElectricalEquipment

Critical systems are becoming more and more complex to ensure functionality and reliability requirements. These systems often consist of a large number of subsystems or components, which interact with each other and collectively influence the system performance and reliability. As a result, conventional reliability analysis and asset management methods have significant shortfalls and face great challenges. For example, in a large-scale power or petro-chemical plants, many components are designed to work for decades. However, as the components deteriorate, the system might not work in an optimal way, leading to significant (opportunity) cost. On the other hand, for such expensive components, any decision on maintenance or replacement has enormous financial impact. In addition, due to geographical, environmental, or usage differences, maintenance strategies and asset management policies proven to work in one place might completely fail in a different place. Consequently, there is an urgent need to develop a comprehensive set of condition monitoring and asset management methods, which take the real time operation and condition information into account, to provide quantitative and rigorous decision support for system monitoring, maintenance planning, and strategic asset managements.

Renewableenergybasedhighperformancepowerelectronicconvertersforgreendatacenters‐FundedbyA*Star

Phase 1 – AC Power Distribution : In AC powered data centers, the three-phase loads are unbalanced considering that per phase computing demand is stochastic in nature. A three phase-four-wire supply with a neutral path is needed to power the unbalanced loads. In this work, a three-phase inverter with a neutral lag is used in the AC Uninterruptible Power Supply (UPS) design, which provides a path for neutral current. The objective of this research work is to eliminate or minimize the neutral current such that the thermal losses in the neutral wire can be reduced and the power usage efficiency (PUE) in date centers can be improved. Three different methods are proposed to control the amplitudes and the mutual phase differences of the inverter output voltages. The effectiveness of the proposed strategies is validated through intensive experimental testing. The proposed AC UPS power supply architecture enables to power the server computers with the same 230V AC (optimal efficiency operation of servers) while supplying the data center with three-phase-three-wire utility power supply.

Phase 2 – DC Power Distribution :DC distribution is becoming a new voltage interface for telecommunication buildings because of the fact that almost all of the critical payloads in the data center are DC loads. With the penetration of renewable energy sources in the distribution networks, the paradigm is shifting towards DC powered Data Centers. In a typical DC power architecture the efficiency is low due to huge transmission, distribution losses and also the power conversion stages are not optimized. This will affect the Power Usage Efficiency of the Data Center. In this research work, a novel DC distribution architecture is proposed with less power conversion stages which can provide higher efficiency than the typical DC distribution system. This work proposes a new three-phase AC-DC single stage 9 switch converter to provide 380 Vdc transmission bus and 48 Vdc distribution bus.

MarineVesselsElectricPropulsionSystems

Under the Singapore Maritime Institute’s Maritime Energy Systems (SMI-MES) R&D Programme, this project aims to address the needs of maritime sector towards development of innovative and unique solutions to manage energy usage and efficiency. To accomplish this, novel electric propulsion architectures for marine vessels are investigated with design, development and analysis of integrated on board power system for optimal operation at system level under various mission profiles of the vessels. The research is conducted on development of intelligent power management system (PMS) to solve various complicated operational tasks where the control objectives differ depending on the particular kind of operation and environmental circumstances. With integration of advanced power electronics, machines, energy storage and control technologies in such PMS, it is targeted to enhance the performance of the marine vessels in terms of reduced volume, weight, operational & life cycle costs, maintenance, fuel consumption and gas emission with improved efficiency, quality and reliability of shipboard power supply. This research is in the leading edge of the current developments in marine technology and the outcome of the project is anticipated to be of significant contribution to the marine research, and can provide operators of marine vessels with powerful decision-making tools for optimum operation of the vessel.

IntelligentInformationManagementSysteminSmartBuildingsUsingMulti‐Agent‐EnabledWirelessSensor‐ActuatorNetwork

This project intends to implement real-time Energy Informatics and strategic decision making, with the Electrical Information System (EIS) as its back-bone for energy management in buildings, especially in the tropics. The Building Management and Information System (BMIS) would be developed based on Systems Thinking to achieve energy efficiency along with human comfort while maintaining good indoor air-quality. This new approach is possible through Wireless Sensor-Actuator Network (WSAN) – which enables distributed sensing, simple decision-making and actuation of local loads. The act of decision-making, facilitated by multi-agent technologies, is possible both locally and globally. The Systems Engineering approach would help electrically operated devices not only perform towards meeting their local optimality, but also optimality of the system in a holistic manner. This project also intends to develop dashboards as a part of the overall project, through which authenticated users can visualize data flow, make qualitative assessments and take necessary corrective actions if needed. It is anticipated that the proposed research work would be able to reduce the overall energy consumption of the building by at least 15-20% while maintaining user comfort and without sacrificing quality living. Moreover, the proposed research work can also be extended with the inclusion of suitable additional sensors for water conservation as well as cooking gas usage from safety point of view in residential buildings in Singapore.

Analysis of High Voltage AC/DC Power Transmission and Penetration ofRenewablesforSubseaPowerSystemDistributionNetwork

This project addresses issues in subsea electric power system equipment technology through the analyses of suitable electric power transmission schemes from onshore facilities, their efficiency comparisons, harmonic analysis with accurate medium/long transmission line models, reactive power compensations, real-time monitoring, fault identification as well as location and control along with data analytics for predictive maintenance of the subsea electrical equipment. This multifarious project focuses on the effective operation of the subsea power system (both transmission and distribution), their energy efficiency and increment in reliability. Coupled with condition monitoring of the electrical equipment, data analytics generated would help to exercise predictive estimation of the system states that could possibly be used for advanced control of the electrical equipment. This calls for incorporation of advanced information processing of continual sensor outputs and embedded intelligence in the monitoring devices. The most desired “low-maintenance-equipment” objective could be achieved through accurate understanding of the relations between transmission, distribution and terminal power consumptions and their real-time monitoring. Enhanced life-time of the equipment would be an implicit benefit.

UnderwaterVehicleTechnology‐StarFishII

Our team at Electric Machines and Drives Lab (EMDL), NUS has designed and developed 5 unmanned underwater vehicle prototypes based on biology principles that we believe is key to the future marine robotics. The research aim is to replicate in a robot, the locomotion of vertebrate animals like fish, turtle etc. by translating this biological phenomenon into locomotion design, actuation, sensing and control mechanisms. At the same time, we can also use the robot model to understand the kinematic behavior of biological vertebrate fish. To this end, we have developed an optimal model-based design and control of bio-inspired underwater vehicle propulsion for fluid environments. The robotic fish is propelled by a single oscillating n-joint caudal fin and two pectoral fins. The robot model is based on kinematic studies of actual yellow-fin tuna. To generate thrust for forward movements, we have used a bio-inspired algorithm based on Lighthill’s slender body theory and central pattern generators, to produce a body wave along the robot’s joints. A comprehensive comparative study of the different kinematic parameters of the robotic fish and the kinematic behavior of actual fish has been carried out. This study also lays the foundation for generating the robot behavior mimicking real fish. We are able to demonstrate the feasibility of a real-time flexible-bodied robotic fish underwater vehicle using the proven Lighthill framework. The team has also tested various standard control strategies to stabilize and maneuver the vehicle’s motion in fluid. The new propulsion system has been shown to be time-effective, fuel-efficient, more agile and less noisy while boasting stealth features. Other than the above work, we have developed an omnidirectional underwater robot prototype which is designed to harvest wave energy. We have also been doing experiments with different soft actuators like Electroactive polymers (EAP), Ionic polymer metal composites (IPMC) and Shape Memory Alloy (SMA) to investigate muscle like actuation for the robotic fish propulsion and other bio-inspired mechanisms.

Solar Energy Harvesting and Active Energy Management System for Nano-Satellites

Over the past few years, the growth of small satellites has fuelled the need for compact and modular power supplies. The Electrical Power System (EPS) for nanosatellite is highly specialized power supply with many sophisticated features. The primary function of EPS is to convert/condition and distribute power to different loads of nanosatellite. It also stores energy for eclipse period and peak demands. Improving the conversion efficiency with optimum size of energy storage device leads to the development of various power electronic converter topologies that could effectively improve the power-weight ratio and reliability of the converter. This project aims to design and develop space qualified EPS powered by solar power. The main focus of research lies in developing efficient electric system topology, Maximum Peak Power Tracking (MPPT) converters and load regulators. It also deals with optimization of power source and battery storage for efficient utilization of available energy.

High Power Density Converters for More Electric Aircraft (MEA)

The More Electric Aircraft (MEA) is one of the significant steps taken by aerospace industries in direction of having more efficient and reliable aircraft system. Adopting the MEA achieves numerous benefits such as improving the aircraft performance and decreasing operating and maintenance costs. However, MEA also puts challenge in terms of high power density and high power efficiency required for power electronic converters. Therefore, it becomes imperative to investigate and develop power electronic converters of reduced weight and increased efficiency without compromising the reliability and Electromagnetic Interference (EMI) standards specified by aerospace industries.

Various types of power converters have emerged in the wake of making power converters more suitable for MEA systems. Recent advances in semiconductor devices has also fuelled the use of new power conversion topology and control for improved performance. The objective of this project is to identify and develop power electronic converters for MEA system for improved power density and efficiency.

EnergyefficientandSmartlighting

In recent years, it became more apparent that light-emitting diodes (LED) is the technology of choice to achieve those savings. LEDs presently have an average source-lumen efficacy of 120-150 lm/W. One key reason for the lacking penetration of the market with LED technology for lighting applications is its higher upfront cost. Sophisticated current controlling drivers are required to operate LEDs for lighting. Commercial drivers presently available are costly, complex, relatively bulky and typically account for 50% of the total cost of a commercial LED lamp. A substantial reduction in cost while maintaining the high efficiency of LED drivers is possible by reducing the number of stages and components, providing the same functionality of the driver. Hence, we propose a driver solution containing only one single stage high frequency DC-DC converter with single controller for providing isolation and a controlled equal amount of current to “N” strings of LEDs at the output irrespective of any fault condition in one or more LED strings.

This project also demonstrates the potential energy savings by using an interactive lighting interface using a Zig-Bee based Wireless Sensor Network (WSN) while performing the monitoring and control of the lighting system. Existing lighting systems is clock-oriented and offers limited control and monitoring capabilities. The developed system automatically adjusts the illumination level of individual lamps in accordance to ambient lighting conditions and occupancy pattern of the surrounding and is adaptable to regions (or) different time-zones by itself. The inter-lamp communication over the master-slave network facilitates a pleasing and effective lighting ambience. Remote monitoring helps in condition monitoring and online energy consumption data logging while remote control enables easy user interruption. The development of such a system will result in lower operational cost, have higher energy savings and provides a faster return-on-investment of the system. In this paper, a prototype of the system is developed and demonstrated.

SolarPhoto‐voltaicMicro‐inverter

Photovoltaic AC (PVAC) module technology is a modular approach to scale up or down the size of solar power system. PVAC module is described as: “A complete, environmentally protected unit consisting of solar cells, optics, inverter, and other components, designed to generate AC power when exposed to sunlight.” The key element of a PVAC module is the ‘Micro-inverter’. It has an ability to provide maximum power independent of the faulty or shaded panels which is a significant benefit over string or central inverters. However, to capture the utmost advantages of PVAC modules, the scope of this project lies on improving the key features which include:

• A high level of reliability to operate for the lifetime of a PV module (25 years).

• A wide operation range that is required to support a variety of PV modules.

• High efficiency for effective ROI (return-on-investment).

An effective means of ripple mitigation, novel magnetics design, highly efficient power conversion and control methodology is being developed to realise the said features.

ResearchProjects–Information

Project Title : Development of Energy Efficient Propulsion System for Unmanned Aerial Vehicles – Pure Drive Total fund : SGD 816,000 Funded by : DSTA Duration : 26.02.2013 - 25.02.2015 Project Title : Renewable energy based high performance power electronic converters for green data centers - Funded by A*Star Total fund : SGD 756,492 Funded by : A*Star Duration : 01.08.2011 – 31.05.2015 Project Title : Underwater Vehicle Technology - Star Fish II Total fund : SGD 475,200 Funded by : MINDEF - DSTA Duration : 25.10.10 – 30.06.2015 Project Title : Condition monitoring and prognostics of electrical equipment Total fund : SGD 150,000 Funded by : SMI, Rolls Royce Duration : 17.09.2013 – 16.09.2016 Project Title : Intelligent Information Management System in Smart Buildings Using Multi-Agent-Enabled Wireless Sensor-Actuator Network Total fund : SGD 786,334 Funded by : NRF, SINBER BEST, University of California, Berkely, USA Duration : 10.01.2012 - 31.04.2017 Project Title : Intelligent Power Management System for Electric Propulsion based Marine Vessels for improving Reliability, Operational cost, Performance and Efficiency (ROPE) operating under different operating conditions Total fund : SGD 805,600 Funded by : SMI, ST Marine Duration : 01.08.2014 – 31.07.2017 Project Title : Analysis of High Voltage AC/DC Power Transmission and Penetration of Renewables for Subsea Power System Distribution Network Total fund : SGD 464,000 Funded by : SMI, Schlumberger Duration : 02.05.2014 – 01.05.2017 Project Title : Integrated Chemical and Electrical System Operation - ICESO Total fund : SGD 895,955 Funded by : CAMBRIDGE-CARES-NRF-CREATE Duration : 01.04.2014 – 22.04.2018 Project Title : Solar Energy Harvesting and Active Energy Management System for Nano-Satellites Total fund : SGD 173,400 Funded by : M.O.E - NUS Duration : 01.03.2013 – 28.02.2016

EMDL

AreasofResearch

GreenDataCenters,NanoSatellites,WSN‐SmartBuildings

Conditionmonitoring&Prognostics,MarineVesselsPropulsion

UnmannedAerialVehicles,BiomimeticStar‐Fish

HighEfficientPower

ElectronicConverters&Controllers

IntelligentControl,Reliability,Energy

Management&

Optimization

RenewableEnergy

Harvesting,SmartGrid,SubseaPowerDistribution

Electrical Machines and Drives Laboratory

Dr. Sanjib Kumar PandaAssociate Professor

Department of Electrical and Computer Engineering

1.ConditionMonitoringofTransformers

• Online CM techniques are necessary to enable operational reliability

• Improvements in condition monitoring techniques for transformers include

Current harmonics analysis • Spectral analysis of line currents of primary and secondary of 

the transformerFlux distribution analysis • Comparison of flux distribution of the sensor placed at 

different location on the surface of the transformerThermal image analysis• Analysis on the thermal image obtained by IR thermographyThermography of Dry type transformer with load imbalance

Transformer failure modes

2.ConditionMonitoringofInductionMachines

Current Signature Analysis is able to findincipient faults

Frequency domain analysis of motor currentsignature analysis (MCSA) was done to identify

Stator winding faultsBroken rotor barAir‐gap eccentricityBearing faultsVoltage unbalance faults

An online Fault Detection and Diagnosis system(FDD) using dSPACE1104 has been done andvalidated.

Frame work of proposed algorithm

Data acquistion

Signal pre‐processing

If transient ?

Stator/ Rotor fault detection

Fault identification and diagnosis

Fault notificationIfFault ?

Yes

No

No

Yes

IM failure modes

Bearings 41%

Windings37%

Rotor10%

Other 12%

Frame work of wireless CM of IM

Wireless condition monitoring ofinduction machine using Zigbee protocolhas been done

Frequency signatures are transmittedinstead of actual raw signal

Developed a GUI for local and remotemonitoring of machine’s health

Wirelessmodule

3.MarineElectricalPowerSystemArchitectures

Evaluation of marine vessel grid architectures (LV/MV AC/DC) having Integrated Power System 

Design of Performance Metrics based on – Reliability, Efficiency, Gas emission, Weight, Volume and Cost; and identification of Operation Profile of target vessel with DP Class‐II

Architecture assessment based on notional‐model using the vessel operation profile and performance metrics

Identify superior architecture and develop advance control technique and multi‐objective optimization algorithm for improved performance of target vessel

Image Courtesy: http://www.nexans.de/

Condition Monitoring and Predictive Maintenance

Fault detection and Fault Localization in Cables

Variable Power Extraction from Renewables & Harmonic Analysis for Variable Speed Drives

4.AnalysisofHighVoltageAC/DCPowerTransmissiontogetherwithPenetrationofRenewables,ConditionMonitoring&FaultIdentificationandLocationinSubseaPowerSystemDistributionNetwork

HVAC, HVDC & Modular Stacked DC (MSDC)

High Voltage DC and AC Transmission Studies

Power Distribution Center at sea‐bed

Long AC umbilical power cable

6

• Analytical comparison of HVDC and HVAC approaches for subsea transmission and  fault identification in long transmission lines 

• Analysis of harmonics and reactive power compensations required Integration of offshore renewable energy source into the power grid

• Development of intelligent algorithms for condition monitoring and fault location identification for cables at the distribution side

Modern subsea power technologies require in excess of100 MWs of electrical power, extensive conditionmonitoring and clean power supply for reliability andlongevity.

• Analytical study of subsea power umbilical chords can give quantitative idea regarding the choice of HVAC,  HVDC and stacked modular DC (MSDC) systems

• Rigorous condition monitoring and real‐time data analytics can keep the subsea power system alert and fast‐acting towards changes, improving robustness

• Harmonic power for variable speed drives can be locally supplied rather than drawing from onshore

Incorporation of the proposed ensemble of technologies does not require major changes in the current infrastructure of subsea power systems

7

ICEngine

(0~20%)

( )Gear Box

(95%)

Propeller

ConventionalICEBasedPropulsionSystem

ProposedHybrid

PropulsionSystem

5.HybridPropulsionSystemForUnmannedAerialVehicle‐UAV

ICEngine

Generator

AC/DCRectifier

DC/ACConverter

BatterySensorlessControl

Sensorless Control

Motor

BidirectionalDC-DC

Converter

• Selection of IC Engine, battery, motor and generator for aerospace use, under the consideration of power density and system specifications

• Design of AC‐DC Rectifier with high efficiency (92%)

• Design of DC‐DC Bi‐directional Converter with high efficiency (88%)

• Sensorless Control of Permanent Magnet Synchronous Motor (PMSM) by estimating the rotor  position and rotor speed using feedback observer & System Integration

Dual Active Bridge

SG1 SG2 SG (Auxilliary)

AC BUS: 230 V, 360-800 Hz

Battery DC BUS (270 V)

AC/AC converter

AC BUS: 3X115 V, 400 Hz

AC Loads

Isolated Bidirectional AC-DC

Isolated Bidirectional

AC-DC

HVDC load

Isolated Bidirectional AC-DC

DC load

28 VDC

LaVa

LbVb

LcVc

Ca

Cb

Cc

D1

D2

D3

D4

C0 R0

RA1 RA2

RB1

RA3

RB2 RB3

RC1 RC2 RC3

RD1 RD2 RD3

Ll T

N:1

Vxy

Ip

Vsec

6.MATRIXConverterforMoreElectricAircrafts(MEA)

Smaller Transformer • High switching Frequency

Lower THD for wider range of input/load• Active devices switched at high 

frequency 

Controllable Power factor• Controllable Active devices

Reduced common mode filter Design• Transformer isolation

• Reliability issues of power converters can be improved by providing redundancy and improves switching modulation and control scheme

7.IntegrationofRenewableEnergySources

1.Single‐phase Parallel connected inverter

• Active power flow control from the renewable energy sources along with controlling the THD of the current drawn form the common AC bus in the micro‐grid

2.Single‐phase Series connected inverter

• Active power flow from the renewable energy source along with regulating the load voltage in the presence of grid voltage disturbances

3.Three‐phase parallel connected inverter

•The proposed system can take care of thegeneralized grid voltage conditions:Unbalanced grid and harmonic contaminatedconditions

•Traditional six‐switch based topology (b‐6)or optimized switch count based four‐switchbased topology (b‐4).

High band‐width active and reactive power flow control, THD control of current drawn from common AC bus, Load voltage regulation

8.DevelopmentofSmartGrid

Power‐line communication between multiple generators to maintain stability

Development of Energy Management System for optimal scheduling & dispatch

System integration with PLC‐SCADA for control & monitoring

10

Development of ‘plug and play’ type ‘Autonomous’ Smart‐micro‐grid system

High‐performance control application for current and voltage quality control

Sudden change is loading condition while maintaining the bus stability

Arbitrary integration of renewable energy sources, Diesel generators and other generation systems with bus voltage stabilization capability

Automatic changeover to energy storage elements in case of excess active power. 

Test‐bed

9.RenewableEnergyBasedHighPerformancePowerElectronicConvertersforGreenDataCenters

Phase 1 

AC Powered Data Center

3 Phase Four Leg Inverter

Phase 2 

DC Powered Data Center

9 Switch Converter 

ResearchFocus

3 new Control Strategies are designed to eliminate the Neutral Current under unbalanced loads: Reduction in heat generation due to electrical losses ‐ less cooling requirements.

A novel topology is proposed to reduce the number of power conversion stages and number of active switches : Reduced output voltage and current ripple, Lesser filtering requirements.

10.Bio‐inspiredUnderwaterRoboticVehicleandNextgenerationUUV's

Turtle Bot and working prototype BAUV 3 design and working prototype

1. The new propulsion system has been shown to be time‐effective, fuel‐efficient, more agile and less noisy while boasting stealth features.

2. Developed an omnidirectional underwater robot prototype  which is designed to harvest wave energy. 

3. Experiments with different soft actuators like Electroactive polymers (EAP), Ionic polymer metal composites (IPMC) and Shape Memory Alloy (SMA) to investigate muscle like actuation for the robotic fish propulsion

Spherical Robot

Turtle Robot

Developed 5 unmanned underwater vehicle prototypes based on biology principles