C. Nagamani

Studies on the use of conventional induction motors as self-excited induction generators

The suitability of using a normal three-phase induction motor as a capacitor self-excited induction generator (SEIG) is illustrated. The thermal limit of the stator windings being the limiting factor, the capacity of the SEIG is determined. The steady-state performance of such induction generators, maintaining a constant terminal voltage, is analyzed under resistive and reaction loads. Typical experimental results are also presented. It was found that, for low power motors, the maximum power that can be extracted as generators is 148% to 160% of the motor rating for resistive loads and 118% to 128% of the motor rating for 0.8 lagging power factor loads. Capacitive reactive volt-ampere (VAR) required to maintain constant voltage at 1.0 p.u. speed is in the range 85% to 140% of the power rating of the motor with resistive loads and 100% to 140% with lagging reactive loads. >

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.

Maximum Power from PV Arrays Using a Fixed Configuration Under Different Shading Conditions

A major challenge in photovoltaic (PV) systems is making them energy efficient. One of the major factors that contribute to the reduction of PV power is partial shading. The reduction in power depends on module interconnection scheme and shading pattern. Different interconnection schemes are used to reduce the losses caused by partial shading. This paper presents a fixed interconnection scheme for PV arrays that enhances the PV power under different shading conditions. The proposed scheme facilitates distribution of the effect of shading over the entire array thereby reducing the mismatch losses caused by partial shading. The performance of the system is investigated for different shading conditions and the MATLAB/SIMULINK results are presented to show that the power extracted from the PV arrays under partial shading conditions is improved. Experimental results are provided to validate the proposed approach using a laboratory experimental setup. A comparison is also made between the electrical array reconfiguration scheme and the proposed scheme for a 5 × 5 PV array.

A Hybrid Algorithm for Tracking of GMPP Based on P&O and PSO With Reduced Power Oscillation in String Inverters

Maximum power point tracking (MPPT) is essential for photovoltaic (PV) string inverter systems. Partially shaded PV strings with bypass diodes exhibit multiple peaks in the power-voltage characteristic. Under partial shading conditions, conventional algorithms get trapped in a local maximum power point, and fail to track the global MPP (GMPP). To overcome this problem, global search algorithms such as particle swarm optimization (PSO) have been proposed. However, these can cause excessive oscillations in the output power before converging onto the GMPP. In this paper, a new GMPPT technique combining the PSO and Perturb and Observe (P&O) algorithms has been presented. The P&O technique is used to track the MPP under uniform irradiance, and the same is used to detect the occurrence of partial shading. Only on the onset of partial shading conditions, PSO is employed. Furthermore, the search space of PSO is reduced by using a window-based search in order to reduce the power oscillations and convergence time. The effectiveness of the proposed algorithm in tracking the GMPP, both under uniform and nonuniform irradiance conditions, is demonstrated experimentally.

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.

An Effective Reference Generation Scheme for DFIG With Unbalanced Grid Voltage

This paper presents a reference current generation scheme for improved dynamic performance of a doubly fed induction generator (DFIG) subjected to unbalanced grid voltage. The power and torque oscillations induced due to the unbalance in grid voltage are minimized using additional compensatory terms in the reference currents. The focus is on estimating the reference currents and control implementation without the need for dual vector control. Real and reactive power control is implemented in the positive d-q reference frame using stator flux-oriented vector control. The rotor-side converter (RSC) is controlled to enable effective reduction of oscillations in torque and active and reactive power. The dc-link voltage oscillation is minimized and the grid-side power factor is maintained unity using the grid-side converter (GSC). Unlike the previously reported techniques, the proposed scheme enables effective reduction of oscillations in torque, active, and reactive power, and the dc-link voltage, all in a single target. The performance of DFIG is investigated in consideration with the Indian Electricity Grid Code (IEGC). Numerical simulations are carried out in power system computer aided design/electromagnetic transients including direct current (PSCAD/EMTDC) for the laboratory 3-hp DFIG test setup. The results establish that the performance of DFIG is notably enhanced with the proposed scheme.

A Method to Detect Photovoltaic Array Faults and Partial Shading in PV Systems

Abnormal conditions such as faults and partial shading lead to a reduction in the maximum available power from a photovoltaic (PV) array. Thus, it is necessary to detect partial shading and faults in a PV array for improved system efficiency and reliability. Conventional protection devices fail to detect faults under cloudy and low irradiance conditions, leading to safety issues and fire hazards in the PV field. This paper proposes a method to detect faults and partial shading under all irradiation conditions using the measured values of array voltage, array current, and irradiance. The proposed method enables classification of the status of the PV array into three possible scenarios, viz., normal operating condition, partial shading, and fault. The proposed method is tested experimentally to verify its effectiveness under different irradiation conditions.

Control Scheme for a Bidirectional Converter in a Self-Sustaining Low-Voltage DC Nanogrid

Local dc distribution systems or dc nanogrids for residential and commercial buildings are growing popular due to the increased focus on energy savings. Using low-voltage dc for the nanogrid provides various advantages such as easier integration with renewable sources and battery banks, increased savings, etc. Future systems would use renewable sources and storage devices to become self-sufficient in generation with bare minimum consumption from the grid. The objective of this paper is to develop an energy management system (EMS) to provide uninterrupted power supply to the dc loads and achieve self-sufficiency by minimizing grid power consumption. This is achieved by developing a control scheme for a cascaded two-stage bidirectional converter interface between the nanogrid and the ac distribution network. In addition, an empirical relation for power flow through the converter is obtained, and an optimal capacitor link voltage range is derived to achieve power transfer between rated limits. The efficacy of the proposed control algorithm for the EMS is analyzed and proved to be well suited for the self-sustained dc nanogrid. A 5-kVA prototype of the converter is designed and developed in hardware, and the system operation is verified with experimental results.

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.