Ganesan Saravana Ilango

Enhanced Power Generation From PV Array Under Partial Shading Conditions by Shade Dispersion Using Su Do Ku Configuration

Partial shading of PV arrays reduces the energy yield of PV systems and the arrays exhibit multiple peaks in the P-V characteristics. The losses due to partial shading are not proportional to the shaded area but depend on the shading pattern, array configuration and the physical location of shaded modules in the array. This paper presents a technique to configure the modules in the array so as to enhance the generated power from the array under partial shading conditions. In this approach, the physical location of the modules in a Total Cross Tied (TCT) connected PV array are arranged based on the Su Do Ku puzzle pattern so as to distribute the shading effect over the entire array. Further, this arrangement of modules is done without altering the electrical connection of the modules in the array. The Su Do Ku arrangement reduces the effect of shading of modules in any row thereby enhancing the generated PV power. The performance of the system is investigated for different shading patterns and the results show that positioning the modules of the array according to “Su Do Ku” puzzle pattern yields improved performance under partially shaded conditions.

Control Strategy for Power Flow Management in a PV System Supplying DC Loads

The growing concern for energy saving has increased the usage of LED-based street lights, electronic chokes, compact fluorescent lamps, and inverter-fed drives. Hence, the load profile seen by the electrical grid is undergoing a notable change as these devices have to operate from a dc source. Photovoltaics (PV) being a major energy source, the aforementioned loads can be connected directly to the dc bus. A grid-connected PV system involves a power source (PV array), a power sink (load), and two power sources/sink (utility and battery), and hence, a power flow management system is required to balance the power flow among these sources. One such system is developed for selecting the operating mode of the bidirectional converter by sensing the battery voltage. The viability of the scheme has been ascertained by performing experimental studies on a laboratory prototype. The control strategy is digitally implemented on an Altera Cyclone II Field Programmable Gate Array (FPGA) board, and the algorithm is verified for different modes of operation by varying the load. Experimental results are presented to bring out the usefulness of the control strategy.

A Versatile Rotor Position Computation Algorithm for the Power Control of a Grid-Connected Doubly Fed Induction Generator

This paper proposes a simple yet versatile rotor position computation algorithm (RPCA) for the rotor position and speed of a doubly fed induction machine. The rotor position is computed in a straightforward manner obviating the need for estimation. The resolved components of stator flux vector are computed using measurable stator and rotor quantities. Although it is an open-loop technique, it does not involve integration, recursive techniques, recomputations or programmable low-pass filters, etc. Starting on the fly, accurate computation near and through the synchronous speed, immunity against fluctuations in the grid voltage, and frequency are the other advantages of the algorithm. Reduced complexity and the computational burden facilitate the easy implementation of the algorithm on a low-cost fixed-point processor. Furthermore, unlike most techniques reported so far, there is no need to assume a constant stator flux since the algorithm is versatile to allow for variations in the grid or stator flux. For the purpose of verification, the proposed RPCA, employed in decoupled power control, is implemented for the laboratory test bench with a 3-hp doubly fed induction generator (grid-connected) system and a TMS320LF2407A DSP controller. The efficacy of the algorithm is demonstrated through the extensive experimental results. Overall, the very encouraging results endorse the proposed algorithm.

Renewable Power Generation Indian Scenario: A Review

Abstract—India is faced with the major challenges of (a) providing energy access to all its citizens, (b) heavy dependence on fuel imports for energy security, and (c) complying with international protocols on climate change mitigation, although the economic and social development is the foremost priority. The increase in energy demand due to growing population and industrialization in the face of depleting fossil fuel resources has stimulated the countrys efforts in adopting power generation from renewable energy sources. Starting with 0.34 GW (2%) out of 17 GW of the countrys total installed capacity in the year 2002, the share of renewable power generation has reached 31.7 GW (12.5%) of 250 GW as of 2014. In the aspect of total installed renewable power generation, India occupies the fifth position in the world today. While the governmental policies have steadily encouraged the adoption of renewable power generation, there is need and potential for more vigorous engagement in pursuit of achieving power for all citizens along with economic development. This article presents a brief review of emergence and growth of renewable power generation in India, wind and solar sectors in particular.

Performance of UPFC on System Behavior Under Fault Conditions

This paper presents a detailed report of the performance and impact of UPFC on the power system behavior during fault conditions. A two machine — double line power system with UPFC installed in one of the lines is considered for the study. The idea is to observe the capability of the UPFC to maintain the active and reactive power flows in the compensated line (which includes UPFC) and to diminish the fall-off of the bus voltage when there is a grounding fault in the transmission line. Simulink based power system block set is used for numerical simulations. Simulation results indicate notable improvement in the behavior of the overall system with UPFC in upholding the voltage and power flows even under typical line faults by appropriate injection of series voltage into the transmission line at the point of connection. The extent of UPFC capability in maintaining the power flows in the line (Line 1), even under fault condition in an adjacent parallel line (Line 2) is provided. Minimizing the disturbances in voltages, currents and power flows in the fault-affected line (Line 2) are also discussed. Further the results illustrate how the UPFC contributes dynamically to a faster recovery of the system to the pre-fault conditions.

Independent control of real and reactive power flows using UPFC based on adaptive back stepping

This paper reports the investigations on the implementation of adaptive back stepping control technique in a power transmission system incorporating UPFC. The use of adaptive back stepping controller for controlling the operation of UPFC has not been reported earlier in the literature. The objective is to achieve effective control of the real and reactive power flows in the line, with minimum or zero dynamic interaction between them. A two bus power system with a UPFC is considered for the study. The system response to the power flow commands is investigated and the effectiveness of adaptive back stepping control is examined. Reference frame theory based mathematical models are used for analyzing the performance of the system in closed loop. The effectiveness of the proposed adaptive controller is demonstrated through digital simulations using MATLAB\SIMULINK and the results are compared using a PI based controller. It is found that the overall performance of the proposed controller is far superior especially with respect to dynamic interactions between real and reactive power.

A Control Strategy for Hybrid Autonomous Power System with a Battery Management Scheme

Abstract This article presents a coordinated control strategy for a hybrid autonomous power system to obtain a smooth power transfer between diesel generator and battery energy storage system under transient conditions. In addition, a battery management scheme is also developed to maintain the battery state of charge around 70 to 80% to absorb/inject power under transient conditions and maintains the diesel generator power above 40% of its nominal value. Simulation studies are carried out in MATLAB/Simulink and the performance of the controller is validated experimentally on a laboratory test setup. A TMS320LF2407A DSP controller is used to digitally implement the control strategy and the overall scheme is verified with step changes in load. Moreover, the dynamic behavior of the system is also investigated by directly connecting an induction motor.

A Simple Copper Loss Minimization Control Algorithm for a Grid Connected Squirrel-Cage Induction Generator Through Indirect Flux Optimization

Abstract This article proposes a simple copper loss minimization control algorithm to minimize copper losses of a squirrel-cage induction generator based wind energy conversion system to improve efficiency at low wind speeds. The proposed scheme does not necessitate rotor position information and an encoder. The proposed algorithm is used to find the optimum slip and stator voltage such that efficiency of the squirrel-cage induction generator is increased by minimizing the copper loss. This is particularly useful in extracting the power at low speeds, where losses form a higher percentage of input power when flux is maintained at the rated value. Especially at low wind speeds, the total copper loss can be minimized by decreasing the flux. The proposed algorithm is a simple scalar control that has the potential to reduce losses, and this has been attempted considering voltage and flux saturation limits. To validate the performance of the scheme, a comparison is made with an indirect field-oriented control scheme, in which rotor flux is maintained constant. Simulations are carried out on a typical 2-MW squirrel-cage induction generator in a MATLAB/Simulink environment (The MathWorks, Natick, Massachusetts, USA). Experimentations on 2.3-kW laboratory test setup further validate the efficacy of the proposed scheme.

An Energy-efficient Switching Scheme with Reduced Switching Transients for a Wind-driven Induction Generator

Abstract This article presents a scheme for improving the power output of grid-connected induction generator commonly used in wind energy conversion systems. Generally, the stator of the induction generator is connected in a star with a line voltage of √3 times the rated winding voltage to reduce the line current and, hence, conductor size. To extend the generating operation over a wider speed range, delta-star switchable stator windings are also in vogue. In such cases, the stator is star connected in the lower speed range and switched to a delta connection above a threshold speed. In this study, a new switching scheme is proposed wherein the stator coils are always connected in a star, while the stator is connected to different voltages in low- and high-speed conditions. At low wind speeds, nominal winding voltage is applied to the stator, whereas at higher speeds, the stator applied voltage is √3 times higher than the rated winding voltage. The efficacy of the scheme is demonstrated experimentally with a suitable microcontroller-based switching arrangement. Typical results indicate an increase in output with reduced switching transients. A case study on a 3-Φ, 50-kW induction generator is presented to emphasize the performance improvement with the proposed scheme.