Robust Renewable Energy System with Proper
PCS Based on Bidirectional DAB Converter
Topology and Uninterruptible
Energy Storage System by Muhammad Adil Khan
Dissertation for the degree of Doctor of Philosophy
August 2018
Department of Electrical and Computer Engineering
The Graduate School
Pusan National University
ABSTRACT
In the modern era, there is an increasing demand to utilize renewable energy resources
(RES) due to the depletion of conventional energy resources. This research endeavor reports
selection of an optimal RES system with the proper power conditioning system. Despite recent
advances in RES systems, these systems are still more costly than conventional energy
resources. Among them the use of solar photovoltaic (PV) electric systems is growing rapidly
in the sustainable renewable energy market and is expected to play an important role in the
future sustainable energy mix. Reducing the price of solar PV systems has been a constant
challenge. For the first time, this study examines the effectiveness of three different
structures/materials: (i) silvered glass plane mirror; (ii) convex spherical mirrors; and (iii)
aluminum (Al) foil as reflector. Comparative analysis of four different cooling techniques, i.e.,
water sprinkling system, passive heat sink method, active air fan method, and closed loop
method, for enhancement of output power was performed. A novel Bi reflector solar PV system
(BRPVS) was suggested to control the working of the reflectors. The Al foil enhanced the power output compared to the others. In addition, the effect of using a reflector on the temperature of
a solar PV system was studied. High operating temperatures resulted in a decrease in the
maximum output power under the same solar radiation conditions. The combined enhancement
of the output power by both Al foil BRPVS system and cooling system was almost 22.75–
38.55%.
The dual active bridge isolated bidirectional DC-DC converter (DAB-IBDC) is one of
the prime converters used in dual active bridge renewable energy storage system (RESS)
applications, particularly where a high-power density is required. A 2 kW, 50 kHz digital
control dual active bridge isolated bi-directional dc-dc converter (DAB-IBDC) was developed
for interfacing the supercapacitor bank in standalone solar power system. A blended SPS-ESPS
digital control algorithm was used for DAB-IBDC converter instead of using a traditional
single-phase shift (SPS) control algorithm, which is commonly used for large input to output
voltage varying applications. The proposed blended SPS-ESPS control algorithm achieved high
power conversion efficiency during a large input to output voltage variation, over a traditional
phase shift control algorithm by reducing the back-power flow and current stress in a circuit.
A novel uninterruptible and environmental friendly solar-wind hybrid energy system
(HES) for remote area having closed loop cooled-solar system (CLC-SS). The results validate
that the optimized system’s energy cost (COE) is 0.26 $/kWh and the net present cost (NPC) of
the system is $7110.53. Moreover, reducing the charging time of an electric wheelchair using
a hybrid electric system (HES) composed of a supercapacitor (SC) bank and a lithium-ion
battery with a fuzzy logic controller (FLC)-based fast charging system for Li-ion batteries and
a fuzzy logic-based intelligent energy management system (FLIEMS) for controlling the power
flow within the HES is detailed analyzed. The fast charging FLC was designed to drive the
voltage difference (Vd) among the different cells of a multi-cell battery and the cell voltage (Vc)
of an individual cell. These parameters (voltage difference and cell voltage) were used as input
voltages to reduce the charge time and activate a bypass equalization (BPE) scheme. BPE was
introduced in this research so that the battery operates within the safe voltage range. The
charging time was reduced by 13.13 %, 12.26%, 13.60%, and 19.23% for IC, 1.5C, and 2.0C,
respectively, using FLC charger discussed in this research compared with conventional CC-CV
charging.
