Volume 13, Issue 4

The main objective of this paper is to design and implement a ZVS-PWM Cuk converter to extract maximum power from solar PV module which uses Adaptive Perturb and Observer (APAO) algorithm. ZVS-PWM cuk converter is the interface between the solar PV panel and load. In order to improve electromagnetic compatibility and to reduce the switching losses across the switches, the soft switching (ZVS) has been implemented for Cuk converter, resulting in high converter conversion efficiency with less EMI at high-frequency operation. The harmonic content that each of the converter circuit produces is examined using FFT analysis. The implemented adaptive PAO algorithm improves the steady state stability and dynamic response when compared to the conventional PAO method. This algorithm is simulated using MATLAB/Simulink and implemented using ATMEGA16 micro controller. Hardware validation is carried out for the converter with the solar PV panel with rating of 37W, and operating at 25 kHz.

This paper proposes a new method for assessing static voltage stability based on the local loadability boundary or P- Q curve in two dimensional power parameter space. The proposed method includes three main steps. The first step is to determine the critical buses and the second step is building the local loadability boundary or the saddle node bifurcation set for those critical buses. The final step is assessing the static voltage stability through the distance from current operating point to the boundary. The critical buses are defined through the right eigenvector by direct method. The boundary obtained by the proposed method that is combining a variation of standard direct method and Thevenin equivalent model of electric power system is a quadratic curve. And finally the distance is computed through the Euclid norm of normal vector of the boundary at the closest saddle node bifurcation point. The advantage of the proposed method is that it keeps the advantages of both efficient methods, the accuracy of the direct method and simple of Thevenin Equivalent based method. Thus, the proposed method holds some promise in terms of performing the real time voltage stability assessment of power system. Test results of New England 39 bus system are presented to show the effectiveness of the proposed method.

This paper deals with controlling the output power smoothing of a wind energy conversion systems (WECS) by using permanent magnet synchronous generator (PMSG). It uses the inertia control of the wind turbine and DC-link voltage control. The PMSG is connected to the grid through a generator-side converter and a grid-side inverter based on AC-DC-AC methods. The generator-side converter is used to control the torque of the PMSG while the grid-side inverter is used to control DC-Link voltage and grid voltage. Fuzzy logic is implemented to determine the torque command by using inertia of wind turbine. The inputs of the fuzzy logic are given by the operating point of the rotational speed of the PMSG and the difference between the wind turbine torque and the generator torque. From the proposed method, the generator torque is smoothed and kinetic energy generated by the inertia of the wind turbine is used to smooth the power fluctuations of PMSG. Also, a stable operation of WECS is achieved during the system fault by using the chopper circuit in the DC-link circuit. The output power smoothing is achieved with stability and low cost. The effectiveness of the proposed method is verified by the numerical simulations.

Dynamic voltage restorer (DVR) is a custom power device used for voltage compensation of sensitive loads against voltage disturbances in power distribution lines. However the DVR spend most of its time in standby mode, since voltage sags occur very infrequently, and hence their utilization is low. In principle, it would be advantageous if the series connected converter based DVR could also be used to compensate for any steady state load voltage harmonics and power flow control in the line. This paper proposes a phase angle regulator which compensates the load voltage during sag with minimum distortions and also controls the flow of power in line when there is no disturbance in the feeder, through a phase adjustment technique. The compensation process is accompanied by an exchange of power between the DVR supported from wind energy conversion system and the grid. Controller works according to progressive phase advance strategy to correct voltage sag as well as power sharing between the DVR and the network as per available power from the wind. In this paper, different control strategies of dynamic voltage restorer are analyzed with emphasis put on the compensation of voltage sag and power flow control. The proposed control performance of the multi-functional DVR is verified through the PSCAD/EMTDC simulation studies.

In this paper a comparative evaluation study is carried out for a 3-level, 5-level, 7-level thyristor based multi-level current reinjection (MLCR)current source converters (CSC) in terms of line current total harmonic distortion (THD) obtained, reinjection transformer requirements, reinjection switch ratings, reinjection control circuitry complexities. MLCR concept adds self commutation capability to thyristors, produces high quality line current waveforms and provides reactive power compensation in CSCs. Multi-level conversion is applied to generate the required optimum injection current which, when reinjected to the ac side reduces the line current THD. Extensive PSCAD/EMTDC simulations are presented for the comparing the different m-level reinjection schemes.

This paper presents the modelling and control of grid interfaced fuel cell distributed generation system with embedded active filter function. The features of active power filter have been incorporated in the control circuit of the current controlled-voltage source inverter interfacing the fuel cell to the grid. Thus the same inverter is utilised to inject power generated from fuel cell source to the grid and to act as shunt active power filter to compensate for load current harmonics, load reactive power demand and load current imbalance. Thus, after compensation, the grid current is sinusoidal and in-phase with grid voltage. Simulation in MATAB and experimentation using DSP is carried out to verify the operation and the control principle. The results are obtained for different operating conditions with varying load demands to prove the effectiveness of the entire system.

The insulation of transformer oil comprise of two practices: paper and dielectric fluid (such as mineral transformer oil). Ageing of these oils occur mainly by thermal, electrical and oxidative stresses. This paper describes the determination of kinetic parameters of a naphthenic based transformer oil and its blends based on the Ozawa, Flynn and Wall (OFW) and Kissinger models using data obtained from thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC), plots. Virgin oil and its blends were analysed from an initial temperature range of 20-25 ºC to 300 ºC at temperature ramps of 1, 2, 4, 6, 8 and 10 ºC min-1. The OFW method in conjunction with TGA data was used to calculate the apparent decomposition activation energies at each of the selected weight loss (% conversion or α) values. The activation energies at 10% weight loss were found to be 57.0, 63.7 and 69.3 kJ mol-1 for BHT-B (virgin oil-2,6-di-tert-butyl-4-methylphenol blends), DBP-B (virgin oil-2,6-di-tert-butylphenol blends) and VO (virgin transformer oil), respectively. However using this method the activation energy (Ea) of the oils showed no significant difference between virgin oil and its blends. DSC curves revealed that the decomposition reaction was exothermic in nature. From DSC data the activation energy was determined using two separate models: OFW and Kissinger models. Decomposition activation energy obtained from DSC data showed no significant difference when applied to these two models. Dissipation factor tests showed superior results for the blends when compared to those of virgin transformer oil. However, the blends showed substantial reductions in their dielectric breakdown voltage. The implication of the reduced breakdown voltage is that the blends show poorer dielectric strength in comparison to virgin transformer oil.