G. Saravana Ilango

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.

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.

Estimation of daily global solar radiation using temperature, relative humidity and seasons with ANN for Indian stations

Global solar radiation (GSR) is an important parameter in the design of photovoltaic systems. An accurate knowledge of the GSR of a location is essential for the efficient design and utilization of photovoltaic systems. The main objective of the paper is to predict the daily GSR under clear sky conditions of any location on a horizontal surface, based on meteorological variables. The various parameters such as earth skin temperature, relative humidity (simply humidity), date and month of the year are used to estimate the daily GSR. In order to consider the effect of each meteorological variable on daily GSR prediction, six combinations of the meteorological parameters are utilized in training the artificial neural network (ANN). Two cases were considered to train the ANN. In one case three years data of Hyderabad and in other case three years data of three cities (total nine years data) namely Hyderabad, Delhi and Mumbai are used. In both the cases, 90 days of Trichy data is used for testing the network. Accuracy was tested with statistical indicators like root mean square error (RMSE), mean absolute percentage error (MAPE) and mean bias error (MBE). It is found that MAPE value is minimum when date, month, temperature and humidity are considered as input variables.

Modified sliding mode observer for position and speed estimations in Brushless DC motor

This paper reports an adaptive gain sliding mode observer for Brushless DC (BLDC) motor for large variations in speed. BLDC motor based on sliding mode observer exhibits multiple zero crossing in back EMF which leads to commutation problem at low speed. In this paper a modified sliding mode observer incorporating the speed component in the estimation of back EMF is proposed. It is found that after incorporating speed component in the back EMF observer gain, multiple zero at low speeds and phase shift at higher speeds are eliminated. Detailed simulation results are carried out to verify the effectiveness of the proposed scheme.

A three phase reference current generator for power electronic converters under distorted utility conditions

This paper presents an improved three phase PLL technique to generate the reference signals for power electronic converters in a grid connected system. The synchronization scheme employed for phase information should provide a high degree of immunity to power system disturbances because its sensitivity affects the reference signal generated. The SRF PLL works well under balanced and undistorted conditions however the reference signal generated using SRF PLL is distorted under phase unbalancing and harmonics conditions. The performance of the SRF PLL can be improved by reducing the bandwidth but this increases the locking time. To overcome the above limitation an improved three phase PLL based on a linear phase finite impulse response (FIR) filter has been developed. The addition of FIR to the system eliminates the ripples due to the distortions in the utility. The improved PLL technique is simulated in MATLAB and results for abnormal grid conditions such as unbalance, harmonics, phase jump and dc offset are presented to demonstrate its phase-tracking ability.

Power control of grid connected doubly fed induction generator using Adaptive BackStepping approach

This paper presents the findings of investigation of decoupled power control of grid-connected doubly fed induction generator (DFIG) based on Adaptive Back Stepping Control (ABSC) technique. The Adaptive Back Stepping control technique offers a systematic stabilizing procedure wherein unwanted cancellation of favourable nonlinearities can be avoided. Incorporation of the proposed controller improves both transient and steady state performances due to the excellent tracking response for the given power references. Numerical simulations are carried out in MATLAB programming environment for the laboratory DFIG test set up.

Feedback Linearization control based power control of grid connected DFIG with grid synchronization

This paper presents implementation of Feedback Linearization based control (FBLC) for the smooth connection of the doubly fed induction generator to the power grid and for the power control of the grid connected doubly fed induction generator. The induced stator voltage vector of the DFIG is synchronized with the grid voltage irrespective of the accuracy of signal from position encoder. Computer simulation results for the test set up show excellent response in starting up the generator on the fly and also in achieving decoupled power control thereby validating the effectiveness of the proposed control approach.

An Improved Rotor PLL (R-PLL) for Enhanced Operation of Doubly Fed Induction Machine

A versatile method to compute the rotor position of a three-phase induction machine under balanced or unbalanced grid voltage is proposed in this paper. The rotor position of a doubly fed induction machine (DFIM) is computed in closed loop using R-PLL with the q-axis stator flux as the reference signal and the computed rotor speed as feed forward input. A PI controller is used to reduce the phase error while the updated feed forward input (rotor speed) eliminates the frequency error, thereby facilitating a quick and accurate response. Furthermore, the rotor speed is computed directly using only the measured stator voltages and currents, independent of any measurement of rotor current or position. Also, the speed computation process is free from voltage or flux integration or heuristic mathematical calculations. Starting on the fly and accurate computation near and through the synchronous speed even under unbalanced grid voltage are the attractive features. The effectiveness of the scheme is validated through PSCAD/EMTDC simulations and laboratory experiments. Excellent results demonstrate the efficacy of the proposed scheme.

Solar Power Based Intelligent Battery Charging System Compatible with Existing Home Inverters

PV modules are increasingly used in battery charging applications in home inverter systems due to the power crisis faced in developing countries. This work aims at maximizing the use of solar energy by charging the battery as well as by supplying it to the loads when in excess. This system is implemented using two subsystems namely a charge controller and a Power Flow Management System(PMS). The charge controller is used to control the power flow from the PV module to the battery by operating in two modes. The Maximum Power Point Tracking mode(MPPT) extracts maximum power from PV panels and the Voltage Control Mode prevents overcharging of the battery. A 160W prototype of the charge controller is simulated in MATLAB/Simulink environment and is implemented in hardware. The operation of the controller in the two modes is verified and the relevant results are presented. A PV system implemented in houses involves various power sources and sinks. A control strategy is formulated in the PMS to balance the power flow among these elements using State of charge (SoC) of the battery as the criterion. The SoC is determined using coulometric measurements and is periodically recalibrated using Open Circuit Voltage method. The PMS is implemented and verified using experimental results and the energy savings are presented.