Research Experiences

2005-2006: Bachelor’s thesis: “Improving Cau Giay district's aging power grid by reducing power losses”. This research re-design the distribution grid to meet new load installation to optimize the power flows.

2006: Research project “Applying DSM (demand-side management) to National Political Institute”. It was about all technical, economic, and social methods of reducing power loss and increasing power consumption efficiency. In Vietnam, recently, it is so popular to apply DSM by replacing low effective light bulbs with less power-consuming ones.

2006-2007: During working for the Northern Region Load Dispatch Center, participated in a one-year training course with many fact-finding tasks at main power plants and important sub-stations of Vietnam’s electrical power system.

2007-2008: During lecturer position at Hanoi University of Science and Technology, I have been involved in research projects regarding power system design, power system stability, power quality, lightening protection, relay protection, etc.

2008-2009: Master’s thesis “Dynamic Model Simulation of Solid Oxide Fuel Cells”

Title: Dynamic model simulation of solid oxide fuel cells

Among different types of fuel cells, solid oxide fuel cells (SOFCs) show great potential applications due to many advantages such as low emission, high efficiency, and high power rating. On the other hand, SOFC systems are beneficial because they can convert fuel such as natural gas (CH4) which is supplied by widespread systems in many countries into electricity efficiently using internal reforming. In fact, the load demand changes flexibly and fuel cell lifetime decreases by rapid thermal change. Its lifetime maybe extended by keeping an inappropriate temperature. Therefore, it is important to acquire the load following performance as well as control of operation temperature. This thesis addresses components of the simple SOFC power unit model with heat exchanger (HX) included. Typical dynamical sub-models are used for following the variation of load demand at a local location that considers temperature characteristics using the Matlab-Simulink. This thesis achieves some goals:

Calculating the heat balance inside SOFC power unit that affects the operating temperature and therefore the output voltage. The CH4 gas is also taken into consideration.
Applying in internal reforming that uses natural gas (CH4) as a direct fuel.
Adding the heat exchangers into SOFC power system and calculating the gas flow temperature attached to heat balance to compact SOFC model. Evaluating the different heat characteristic of two popular configurations of HX, and therefore increasing system energy efficiency.
Evaluating the load following ability of SOFC power unit by using feedback control the fuel and air flow which responds to the load change.
Controlling the operating temperature by the excess air.

Fig. 1. Outline of SOFC stacks model

2011: Waseda University-TEPCO joint research project “Equivalent Simulated Model of Several Induction Motors”. The aim is to find out an equivalent model for a cluster of motors in similar characteristics and in different characteristics as well. Then, characteristics of that equivalent model are investigated. Test model is carried out on MidFielder and PSCAD simulation.

2009-2012: Ph.D. research “Islanding Detection and Subsequent Actions to Remain Continuous Power Supply”

Title: Islanding Detection and Subsequent Actions to Remain Continuous Power Supply

Fig. 2. Scenario of islanded operation

The main parts of this thesis are about islanding phenomenon of Dispersed Generation (DG) system.

This thesis at first investigates an islanding detection (ID) method using Negative-sequence-(Ns-) components. The large Ns-impedance difference between grid-connected mode and islanded mode is then used to establish an islanding signal. However, in case of high induction motor penetration, this method might malfunction. Using the two-round impedance measurement, this section could solve the problem just well.
Secondly, when there is no Ns-component available at the point of measurement, an active ID by injecting an amount of Ns-component into the Point of Common Coupling (PCC) is presented. The first simple method uses no other parallel dq-coordinate, and then it injects a small Ns-voltage into networks. In this section, Adaptive Notch Filter is simultaneously introduced as a synchronous part instead of Phase-Locked Loop and as a signal processing unit as well. The proposed control strategy allows DGs to detect properly an islanding occurring in a balance distribution system.
More complicatedly, a method where another Ns-coordinate is used besides the normal positive-sequence coordinate can adjust a larger amount Ns-currents. A Power Electronic Interface (PEI) not only performs as power generation and the ID function but also implements other important duties in limiting the unbalanced currents being generated from a DG while faults happen upstream. Using Adaptive Notch Filter as a signal processing unit for the three-phase system, Ns-components could be observed.
Finally, the thesis proposes two subsequent actions after an islanding to remain power supply. When there are only uncontrollable DGs, the islanded entity is connected to a backup system by a Solid State Transfer Switch (SSTS) smoothly and quickly. On the other hand, a droop current controller for PEI of DG is projected to keep PCC’s voltages within a required range and to make islanded frequency arbitrarily at the normal value.

The performance of entire detection and control systems is evaluated by Simpowersystem, PSCAD and partially carried out by experiments. Islanding detection and islanded operation are steps of DG-smart grid as prerequisites for research approaches in the coming years.

2012-2015: Postdoctor at Shibaura Institute of Technology

Funding Research project of the Ministry of Environment - F-1201
Four topics on renewable energy, power quality and energy management form which learned much more on power electronic applied in power system.

PV-Active Power Filter (APF) combination: the proposed 3-phase 3-wire system including Photovoltaic (PV) generation, DC/DC boost converter extracts maximum radiation power by using Maximum Power Point Tracking (MPPT) and DC/AC converter acts as an APF.
Using Adaptive Notch Filter, 3-phase 3-wire and 3-phase 4-wire APF works well under non-ideal voltages at point of common coupling. Both simulation and experiment are conducted.
Optimization solution to determine location and size of DGs.
Utilize the most potential energy of one remote area, trying to use as less power from bulk utility supplying as possible. “Motase" concept is applied for stabilizing system frequency by exchanging power among electrical cells.

2015-2017: Research Fellow at Tokyo University of Science, Japan

Funding New Energy and Industrial Technology Development Organization (NEDO)-P13010
Standardization of parts for small wind turbines (SWT):

Investigate the performances of power conditioning systems (PCS) for SWT.
Measure operational conditions of some SWTs practically used by residential customers.
Field test and measurement, data logger, anemometer, data acquisition. (HIOKO 2300, GL220, GP10, etc.)
Use 10kW test system in laboratory to conduct the Fault Ride Through test for PCS

2017-2018: Researcher at AIST, Japan

An experiment system, 20 kW solar cell is connected directly to the water electrolyzer. The water electrolyzer is capable of switching its number of electrolysis cells and following the maximum power point of the solar cell. Furthermore, the system attempts to smooth out the fluctuating current due to varied solar irradiance by connecting lithium-ion capacitors (LiC)