Volume 19, Issue 5 - Special Issue on Power Electronics Applications in Smart Distribution Grids with Renewable Energy Sources; Guest Editors: B.Chitti Babu, Sabha Raj Arya, Ahmed F. Zobaa

Abstract: In this paper, a modified flyback snubber circuit for isolated bidirectional DC-DC converter has been introduced. The soft switching isolated snubber circuit provides an alternative path for the current difference created due to source inductance and leakage inductance. The auxiliary snubber circuit operates during the step-up conversion, and it only persists of the two semiconductor switch, two inductors one diode and two capacitors. Both semiconductor devices (G 1 , G 2 ) of flyback snubber circuit achieve soft switching during turn ON and turn OFF condition. The PWM technique has been used to control the semiconductor devices. The different mode of operation has been discussed in detail. The effective performance of proposed converter system has been validated with the PSIM simulation tool. The proposed converter is compared with the active clamp converter based on efficiency. The loss comparison proves that flyback snubber circuit has high efficiency compared to active clamp converter.

This paper proposes a new DC-DC converter for performance optimization of a solar PV(Photovoltaic) system without electrolytic capacitor for water pumping system driven by a switched reluctance motor (SRM). The proposed converter is able to replace the input electrolytic capacitor to polypropylene capacitor with small rating and size. The snubber circuit formed by storage capacitor across switch of converter is operated to minimize the voltage spikes especially during turn-on and turn-off time. The proposed DC-DC converter delivers a continuous supply to SRM drive with low ripple content and capable to step-up and step-down the input PV voltage. The PV power optimization and to limit the high initial winding currents of SRM, are two major functions of proposed converter. An improved perturb and observation (P&O) based maximum power point tracking (MPPT) control is also proposed in present system, which overcomes the deviation problem present in conventional P&O MPPT controls. Simulated and experimental results on a 500 W four-phase 8/6 SRM, are accomplished to authenticate the feasibility of proposed system under all environmental conditions.

High switching frequency and high voltage gain DC-DC boost converters are required for electric vehicles. In this paper, a new high step-up boost converter (HSBC) is designed for fuel cell electric vehicles (FCEV) applications. The designed converter provides the better high voltage gain compared to conventional boost converter and also reduces the input current ripples and voltage stress on power semiconductor switches. In addition to this, a neural network based maximum power point tracking (MPPT) controller is designed for the 1.26 kW proton exchange membrane fuel cell (PEMFC). Radial basis function network (RBFN) algorithm is used in the neural network controller to extract the maximum power from PEMFC at different temperature conditions. The performance analysis of the designed MPPT controller is analyzed and compared with a fuzzy logic controller (FLC) in MATLAB/Simulink environment.

Cascaded H-Bridge multilevel inverter (CHB-MLI) based shunt active power filter (SAPF) provides a cost-worthy and realistic solution for mitigating current related power quality problems in case of medium-voltage and high-power grid. Mitigation of current harmonic component, reactive power minimization and power factor correction depend on accuracy of control technique applied to the CHB-MLI based SAPF unit. Switching technique dynamics is not considered by most of the researchers while designing control techniques applied to SAPF unit and hence it is assumed linear in order to make system simpler. A limited amount of literature is available which considers the non-linearity of CHB-MLI switching pattern while designing control theory for MLI based SAPF. Therefore, a novel non-linear control is proposed in this paper to enhance system steady-state and dynamic performance. This non-linear control is based on dynamic mathematical modeling of five-level CHB-MLI tied SAPF. Stability of proposed control strategy applied to CHB-MLI based SAPF is rigorously checked by using Lyapunov’s direct method. Proportional-Integral controller is used for stabilizing DC-link voltages to its proper reference value. This proposed control exhibits excellent dynamic performance and compensation criteria in comparison to conventional control techniques available in the literature. The effectiveness of the proposed control theory is tested rigorously in MATLAB/Simulink and verified through hardware prototype under steady-state and transient operating conditions. Rigorous analysis from hardware and simulation results confirms that source current waveform is in compliance with IEEE-519 standard defined THD limit.

This paper introduces the direct power control (DPC) scheme controlled by a new version of the 1 st order sliding mode control to operate a distributed generator. This distributed generator is a core of the distributed generation system (DGS), which injects active and reactive power to the distribution system in a grid-connected mode. The presented 1 st order sliding mode control based direct power scheme is very efficient in terms of chattering at steady-state and its dynamic performance. The superior performance of the presented control scheme results from a novel combination of an integral form for the sliding surface along with an innovative power-rate reaching law. The feedback power of the direct power scheme is estimated using an accurate developed formulation of the sliding mode observer. The distributed generator is based on the 5-level diode clamped inverter to minimize the injected harmonics. To prove the accurate performance of this new combination of the sliding mode control with sliding mode observer, the developed sliding mode observer is compared to Luenberger observer and the traditional virtual-flux based power estimation. Also, the whole control scheme is compared to other schemes for the same application such as conventional direct power control and conventional sliding mode control based direct power control.

Voltage and frequency fluctuation under variable load or variable wind speed is the key issue to solve in distributed generation based on wind power. Further, harmonic and zero sequence current flow through the generator windings due to connection of nonlinear load deteriorate the power quality of the supply. In this paper a control algorithm known as adaptive vectorial filter (AVF) is developed for the solution of the aforesaid problems. This method lies in the category of frequency lock loop (FLL) rather than phase locked loop (PLL) and having no PI coefficient in the loop filter. Therefore it is easy to tune for that frequency component which is desired at output. The frequency locked loop extracts the frequency of the source voltage which is less affected by sudden changes in the system. Hence it is more suitable than the PLL based techniques in wind based distributed power generation system. The entire system is tested under different operating conditions using field-programmable gate array based controller with MATLAB interface in real time. The dynamic response and steady state response shown by it is found satisfactory.

This paper focuses on comparison of fault position schemes for a long transmission line joint with underground cable. To carry out fault location, two hybrid schemes were implemented. One is the impedance method based on modal transformation (MT) and the other one is the intelligent technique based on artificial neural network (ANN). In this paper one cycle of post fault current and voltage signals were collected initially from the transmission line ends for fault analysis purpose. The first method to analyze the fault position comprises of MT technique in which initially pre-processing of the data is done by Clarke’s Transformation (CT) and Discrete Fourier Transform (DFT). CT decouples the signal and DFT extracts the phasors. Thereafter the fault location is calculated by Power System distributed line modal and MT concept. The second method focuses on estimation of fault distance by ANN with Wavelet Transform (WT) in which WT is used to extract six statistical features in order to pre-process the raw faulted data. These features are then given to ANN for finding fault position. The enactment of the suggested scheme is verified by testing it under different type of fault position, such as variation of fault resistance, inception angle and type. After extensive simulation, it was found that intelligent scheme i.e ANN-WT schemes are capable of locating the fault more accurately and less sensitive to parameter variation than the impedance method i.e MT-CT-DFT.

Due to the presence of Distribution Generation (DG), power system becomes more complicated and stability of power is the main challenging task. Saturation of Current Transformer (CT) imposes great dilemma on differential relaying scheme. This manuscript presents a new differential algorithm for distribution transformer protection which adaptively set its characteristic in the event of CT saturation. The proposed scheme is capable to detect magnetizing inrush condition, high resistance internal fault and discriminate external fault with CT saturation. The validation of the proposed scheme is done by simulating a part of the power system in PSCAD TM software and programming in MATLAB software. A Full Cycle Discrete Fourier Transform (FCDFT) is implemented to validate the differential protective scheme for 15 MVA, 66/11 kV distribution transformer. An adaptive concept of the differential characteristic is employed in the algorithm to maintain the stability of relay during external fault with CT saturation. Validation and authenticity of the proposed technique are carried out with various test condition generated under wide variation in system parameters. The result on 2 kVA, 230/110 V, single phase transformer shows that the proposed scheme is capable to discriminate inrush, internal and external fault also with CT saturation conditions.

This paper presents an output and state feedback robust LQR (OSRLQR ) optimal controller for the control of active (P) and reactive power (Q) in grid-connected mode, and voltage (V) and active power in islanded mode of photovoltaic (PV) distributed generation (DG) system. The OSRLQR scheme is comprising of an output and state feedback controllers, which are designed based on LMI-LQR optimization approach. The DG inverter along with proposed controller is configured to work as a current source in grid-connected mode and a voltage source in island mode using P-Q and P-V control scheme respectively. A seamless transition between the grid connected and island modes under the presence of the proposed controller is achieved using a passive island detection and synchronization algorithm along with load shedding. The entire control scheme of the DG system is modelled and analyzed using MATLAB/SIMULINK/Robust Tool-Box, and the practical feasibility of the proposed control scheme is verified using dSPACE. A superior trade-off robustness among the stability and performance is the final outcome of the DG system with proposed control scheme. Performance of the proposed control scheme is compared with conventional PI controller and the comparative results indicate the superior performance of proposed control scheme over the conventional control scheme.

In modern electricity market, high penetration of Plug-In Electric Vehicle (PEV) creates a huge burden on distribution system operator (DSO). This high penetration creates a gap between demand-supply which further leads to the congestion in distribution lines. Power flow in a grid connected PEV is bidirectional i. e. it can work either in Grid to Vehicle (G2V) or Vehicle to grid (V2G) mode depending upon the grid constraints and owners demand. This paper proposes a charging coordination strategy of PEVs to alleviate congestion in distribution lines. Firstly, Active Power Flow Sensitivity Factors (PFSFs) are calculated to predict the branch flows or congestion status due to the uncoordinated charging of PEVs. Secondly, a coordination strategy of PEVs charging-discharging is made using different heuristic based algorithms in order to mitigate congestion in radial distribution system. The result of proposed work also shows the reduction in total active power loss while maintaining the electricity grid constraints. The present work is simulated and analyzed on IEEE 10 bus radial distribution system integrated with residential systems. Several case studies are analyzed to demonstrate the heftiness of the proposed work.

T his paper presents dynamic performance analysis of a PV-biogas-biodiesel-grid based hybrid power system designed for rural electrification. The linear small signal model of the system using power balance equations is developed and small step change in solar incident power and active and reactive load demand of the system are applied. The objective of this work is to control the system voltage (magnitude and angle), frequency and to operate the grid for controlled supply. The voltage source inverter (VSI) used for photovoltaic (PV) system provides active and reactive support and controlled to maintain system voltage and frequency constant. The biogas and bio-diesel engine are equipped with electronic governor control, uses synchronous generator (SG) with automatic voltage regulator (AVR). The variation in load demand is balanced by the biogas, bio-diesel generator and by PV system keeping grid supply constant. The system is simulated in MATLAB and the performance is analyzed for variable loads and input solar power. The PI controllers are applied and their gains are optimized using ISE method. The state variables are plotted and their oscillations are stabilized within few seconds. The system voltage, frequency and grid are controlled effectively.

This paper presents an optimum day-ahead scheduling of thermal and renewable (wind and solar photovoltaic) power generation as a multi-objective optimization (MOO) problem considering the uncertainty. System operating cost (i.e. cost of thermal, wind, solar PV and battery), reliability and emission cost are considered to be optimized simultaneously. The uncertainties due to the generator outages, wind, solar PV power and load forecast errors are incorporated in the proposed optimization problem using the Loss Of Load Probability (LOLP) and Expected Unserved Energy (EUE) reliability indices. In the proposed approach, the amount of spinning reserves (SRs) required are scheduled based on the desired level of system reliability. The proposed multi-objective optimization problem is solved using NSGA-II algorithm. Different case studies are performed considering different objective functions that may be selected by system operator (SO) based on the preference.

This paper presents a univariate equation-based selective harmonic elimination-pulse-width modulation (USHE-PWM) method for cascaded H-bridge (CHB) multilevel inverters (MLIs). Using equal-area criteria, the selection of voltage rating of dc-links have been done. The output voltage is controlled by inserting switching notch at the centre of each level of output voltage. Instead of conventional transcendental SHE-PWM equations, all these calculations are accomplished using univariate equations. This simplifies the real-time implementation of the proposed method greatly, even for the MLI with a large number of levels. The USHE-PWM method can eliminate more harmonics compared with the conventional SHE-PWM methods. While controlling the output voltage, the harmonic pattern remains unaffected. The validity of the proposed method is confirmed by the simulation and experimental studies.

This paper proposes a new version of swam optimization based algorithm for maximum power harvesting from the multilevel inverter (MLI) based photovoltaic (PV) generation systems. The ability of modified particle swarm optimization (MPSO) based maximum power point tracking (MPPT) approach is investigated for varying environmental conditions and partial shading condition. Moreover, the tracking performance is compared with perturb and observe (P&O) MPPT and standard PSO-MPPT techniques. MLIs are chosen over conventional two-level inverters due to many advantages such as; power quality improvement in PV generation system, reduce the filter size requirement etc. With the increase in number of levels; the conventional MLI circuit leads to bulky & costly due to the requirement of more number of power electronics switches. Therefore, in this work a novel MLI with reduced number of switches has been developed for off-grid PV system. Harmonic reduction is principally depended on the modulation strategy used to control the MLI. In this regard, a logical switching state selection PWM control technique is presented for the proposed MLI. The overall system is simulated in MATLAB/SIMULINK and new solution to attain MPPT from standalone PV generation system has also been validated experimentally in the laboratory.

This paper describes reduced number of switches technique for Solar Photo Voltaic (SPV) voltage source based 31-level Multi Level Inverter (MLI) for Power Quality (PQ) improvement. The proposed topology reduces number of IGBT switches to ten, which is very less compared to diode clamped, capacitor and cascaded multilevel inverter. The desired multistep AC output voltage with minimum number of switches is obtained using this topology which reduces cost of system. The proposed MLI reduces number of harmonics at the AC output voltage which improves the PQ. The square wave switching used in this topology reduces the switching losses compared to pulse width modulation technique. The performance of four solar PV voltage sources with Buck/Boost converter has been discussed in this paper. The proposed MLI is mainly used in this paper for off grid system. The results of the Solar PV System based 31-level MLI have been simulated in MATLAB R2013a environment and hardware results have been validated using Opal-RT real time simulator OP-5142.

This article describes the comparison of different phase locked loops (PLLs) based control algorithms for removal of voltage based power quality problems such as voltage sag/swell, distortions and unbalances etc. For this purpose, Dynamic Voltage Restorer (DVR) is designed with heuristic optimization technique called Multi-objective Grey wolf Optimizer (MOGWO) for PI gains calculation. Three PLLs namely adaptive transfer delay phase locked loop (ATD-PLL), multi complex coefficient filter phase locked loop (MCCF-PLL), and multi synchronous reference frame phase locked loop (MSRF-PLL) are implemented for the control of DVR in a three-phase system. These PLLs are employed for compensation of distortions and imbalances in supply along with voltage sag/swell. Basically, estimation of fundamental and positive sequence components are the basic function of these PLLs that is used for further extraction of reference load voltage. The optimization approach has been implemented for estimation of proportional integral (PI) gains of dc bus as well as ac bus in the system. This approach of tuning PI controller-gains reduces the time by integrating the fixed sized external archive to the GWO for saving and retrieving optimal solutions. Three wires DVR with developed control algorithms are implemented using MATLAB/Simulink and tested in a laboratory environment. The recorded results show satisfactory performance of DVR for compensation of voltage based power quality problems.

This paper deals with the performance analysis of different PWM techniques for three-phase and dual three-phase induction motors. In this paper, the dual three-phase induction motor is reconnected as a three-phase and six-phase winding configurations and its performances are investigated. The comparative evaluation for the aforesaid machine configurations are carried out in terms of quality of stator current waveform with different PWM techniques. Total harmonic distortion are obtained in terms of harmonic distortion factor for stator current. The theoretical findings are further verified through simulation and experimental results.