Research Areas

1 - Microgrids.

(a) - Dual Voltage Source Inverter Scheme for Microgrid Systems:

In this scheme, microgrid system consists of two inverters, where one inverter acts as main inverter and another as auxiliary inverter. The main inverter supplies available microgrid real power at the point of common coupling (PCC). The auxiliary inverter supplies unbalance, reactive and harmonics components of load power. Hence, grid will exchange only balanced and sinusoidal currents at the PCC.

(b) - Parallel Operation of DC-DC Boost Converters in Microgrid:

In microgrid system, energy from various sources like solar, wind, fuel cell etc. may exist in the same site, but can be scattered depending upon the ease of energy harness. Integrating renewable energy sources by using power electronic interfaces gives flexibility in conversion and power level. Operation and control of parallel connected converters are important and some advantages are (i) expandability of output power (ii) reliability (iii) efficiency (iv) ease of maintenance.

(c) - Microgrid Interactive Voltage Source Converter (VSC):

The microgrid interactive voltage source converter is also called as multi functional voltage source converter which acts as 1) a bidirectional power sharing converter to control the power flow from the dc side to the ac side and vice versa, based on renewable power available at the dc link; 2) a power quality compensator with the features of reactive power compensation, load balancing, and mitigation of current harmonics generated by nonlinear loads at the point of common coupling, thus enabling the grid to supply only sinusoidal current at unity power factor; and 3) also damps out the oscillations in the grid-VSC currents effectively using damping filters.

(d) - Microgrid Power Management Strategies:

Sound operation of a microgrid with more than two DER units, especially in an autonomous mode, requires a power management strategy (PMS) and an energy management strategy (EMS). Fast response of the PMS/EMS is more critical for a microgrid compared with a conventional power system. Due to presence of multiple DER units with significantly different power capacities and characteristics, potentially no dominant source of energy generation during an autonomous mode, and fast response of electronically coupled DER units that can adversely affect voltage/angle stability.

(e) - Single Stage Converters for Microgrid Applications:

2 - Power Quality.

(a) - Distribution Static Compensator (DSTATCOM):

Unbalanced and nonlinear loads create current related power quality (PQ) problems such as poor power factor, increased source currents, losses in lines and transformers, unbalanced and distorted load voltages, and non-zero neutral current. A distribution static compensator (DSTATCOM) is one of the custom power devices and it is utilized for mitigation of above mentioned PQ problems with suitable control strategies. The DSTATCOM consists of a voltage source inverter (VSI), dc link capacitor, and interfacing filter. It is connected parallel to load at the PCC. To mitigate current related PQ problems, it injects harmonic and reactive component of load current to make source currents balanced, sinusoidal, and in phase with the respective load voltages.

(b) - Unified Power Quality Conditioner (UPQC).

Unified Power Quality Conditioner (UPQC) is a versatile custom power device which consists of two inverters connected to a common DC link and deals with both load current (i.e., supplies load harmonic, reactive power), supply voltage (i.e., compensates voltage sag, swell etc) imperfections. The series component of the UPQC (i.e., DVR) inserts a voltage so as to maintain the voltage at the load terminals at a desired level, balanced and free of distortion. Simultaneously, the shunt component of the UPQC (i.e., DSTATCOM) injects current into the AC system such that the utility currents are maintained as balanced sinusoids even the load currents are unbalanced and distorted.

(c) - Storage-less Dynamic Voltage Restorer (DVR):

Voltage sag is a serious power quality problem to be addressed. It refers to a momentary decrease (1/2 cycle to 1 minute) in Root Mean Square (RMS) voltage between 0.1 and 0.9 p.u. at power frequency. Conventional voltage restorers have two stage power conversions with an intermediate dc-link. Whereas a direct ac-ac converter based DVR topology eliminates the dc-link. The topology has two choppers per phase, to provide the necessary phase angle at the injected voltage. Each chopper consists of two IGBT switches (CT60AM18F), a diode bridge (made of MUR1660), input and output filters. The filters are required to filter the high frequency switching noise from propagating to the input and to the output. The topology has advantages such as reduced losses, compact size, more ride through capability and real power injection.

(d) - Dynamic Voltage Restorer (DVR):

3 - Renewable Energy & Grid Integration.

(a) - Wind Energy Conversion System (WECS):

WECS consists of wind turbine emulator connected to dc bus through a diode bridge rectifier and a dc-dc boost converter. Wind turbine emulator replaces the actual wind turbine characteristics. This setup allows research on wind power generation and evaluation of the control algorithms realizing maximum power point tracking from the available wind. It consists of a DC drive whose torque is mapped from the given wind speed is used to apply the referenced torque to the shaft of the PMSG electrical generator. The control algorithm is implemented using TMS320F28335 DSP controller with various modules such as rectifier – chopper - inverter module, analogue & digital circuits, equivalent load on system and Code Composer Studio (CCS) development environment to interface the system with real-world.

(b) - PV Based DC Grid:

4 - Energy Storage.

(a) - Hybrid Energy Storage System:

The rapid penetration of ESSs into microgrid is mainly driven by two factors i.e., increasing use of RES powered DG units and energy arbitrage. However, they are very intermittent in nature. Hence, in order to integrate RES, it is necessary to propose a suitable energy storage system. However, a single energy storage device cannot meet the variations in RES and load. Therefore a combination of energy storage devices called as composite energy storage systems (CESSs) is preferred for microgrid applications. For microgrids, where power levels are in the range of a few megawatts, battery, supercapacitor, and flywheel are the more suitable options. Battery and supercapacitor are considered as high energy density storage and high power density storage, respectively, and their combination is a very promising option to realize the CESS system, which is also called as hybrid energy storage system (HESS).