Power and Energy Systems

—The state-of-art in research practices across the globe emphasizes the real-time implementation of the control techniques. This paper investigates the performance of an Field Programmable Gate Array (FPGA)-based real-time implementation of a three-phase three-level Voltage Source Inverter (VSI) for grid integration of multi-string PV array. FPGA-based prototyping of control circuits enables the study of sensitivity on parameters variations, increases the safety and reduces the time and costs of implementation. The proposed system consists of a centralized multilevel inverter that aids in the conversion of DC power obtained from a multi-string PV array to AC power, which is fed to the utility grid as well as the three phase local loads connected at the Point of Common Coupling (PCC). The multilevel structure finds use in handling large amount of power, reducing voltage stress across the semiconductor devices and reducing the harmonic distortion. The system is developed in Matlab/Simulink environment and the control algorithm of the VSI is implemented in Virtex-6 ML605 Evaluation-Kit with Xilinx System Generator providing the effective grid-interfacing environment.

—Small-scale distributed energy systems possess the potential to meet local demand of power as well as feed the excess power to the grid. In such grid-tied systems, it is necessary to ensure the reliable tripping of grid-interfaced inverters whenever the grid is unintentionally disconnected. As such, anti-islanding protection schemes are crucial for grid-interfaced Distributed Generation (DG) systems which assure the safety of critical loads, devices and personnel. This paper evaluates the implementation of various FPGA based passive anti-islanding protection schemes and their comparative performance. The synchronization of the DG inverter with the grid is ensured with a Moving Average Filter based Phase Locked Loop (MAF-PLL). The filter also aids for providing an input to the Over/Under Frequency and the Rate of Change of Frequency (ROCOF) protection techniques that has been employed for protection against events of islanding in the DG system. The dc-link capacitor voltage is a reflection of the active power exchange at the Point of Common Coupling (PCC) and hence any mismatch at the PCC causes the dc-link voltage to fluctuate. An over and under voltage protection scheme at the PCC has also been used. The schemes are tested in simulation as well as hardware co-simulation environment to validate their functioning. Index Terms—Field Programmable Gate Array (FPGA),Photovotaic (PV).

—In this paper a current controller based on H∞ control strategy is proposed for grid connected photovoltaic inverters with an aim to inject clean current into the grid. It consists of an internal model, a stabilizing compensator and a current controller. The repetitive control aids in dealing with large number of harmonics at the same time. The study is conducted with three different test systems and the results obtained are compared with PI, PR and deadbeat controllers. The proposed controller is simulated in MATLAB/ Simulink environment in order to validate its performance. Keywords—voltage source inverter (VSI), current controller, total harmonic distortion (THD), H∞ control, repetitive control (RC).

Inroduction DC Microgrids are gaining popularity due to high efficiency, high reliability and ease of interconnection of renewable sources as compared to ac system. In this study the dc-dc power conversion topologies have been analyzed. In order to achieve safe and reliable MG performance, its dynamic stability needs to be ensured in all operating conditions. Averaging and linearization is a common approach for modeling, analysis and design of switching power converters in DC MGs. The resulting small signal models are valid for frequencies of upto around half of the switching frequency because the bandwidth of practical converters are typically in the range of one tenth of the switching frequency.

—The report investigates the performance of Direct and Indirect-Model Reference Adaptive Control schemes for the angular motion control of a helicopter which is achieved by tilting its main rotor and as a result altering the direction of the rotor thrust vector. This action includes a change in the angular moments acting on the vehicle and results in pitch,roll and yaw angular motion. In hover, the helicopter pitch dynamics depend primarily on the vehicle pitch rate q(t) and on the applied longitudinal control input δ(t) which is equivalent in its effect to an elevator of a fixed-wing aircraft. Extensive simulations in MATLAB/Simulink have been implemented investigate the performance of the schemes. I. SYSTEM MODEL The pitch dynamics of an aircraft assuming constant thrust while ignoring the small vertical and forward speed components can be approximated by he equation (1). ˙ q = M q q + M δ δ (1) where, M q =-0.61 rad/s represents the vehicle pitch damping and M δ =-6.65 rad/s 2 is the elevator effectiveness. The objective is for the pitch dynamics to have a desired closed-loop tracking behavior given by the reference model. ˙ q ref = M qr q ref + M δr q cmd (2) II. CONTROL OBJECTIVE To design a direct and indirect MRAC δ(t) such that the plant state q(t) in (1) tracks the reference model given by (2) as a series of step input commands of different magnitudes eg. from t=0-5 s, q cmd = +1 • ;t=5-10 s, q cmd = −1 • ;t=10-15 s, q cmd = +2 • ;t=15-20 s, q cmd = −2 • ;t>20 s, q cmd = +3 •. The reference model has parameters M qr =-4 and M δr =-4. For the purpose of control design, the plant parameters M q is unknown and only the sign of M δ (i.e.negative) is known. For the indirect scheme it is assumed that |M δ | > 2. III. CONTROLLER EXPRESSIONS This section details the mathematical expressions for both the Direct and Indirect Model Reference Adaptive Control schemes in order to provide an insight for the design of the controller. A. Direct Model Reference Adaptive Control (DMRAC) In the direct MRAC , the controller is designed keeping in view the following : (a) the error between the output of plant and reference model is identically zero for identical initial conditions. (b) an initial error will vanish with certain dynamic. Considering the plant model given by (3). ˙ q = M q q + M δ δ (3) where, M q , M δ are unknown and q is measurable. The reference model for the plant can be modeled as ˙ q ref = M qr q ref + M δr δ r (4)

—Robot manipulators have become major component of manufacturing industries due to he advantages associated with them like high speed, accuracy and repeata-bility.Two link robot manipulator is a very basic classical and simple example of robot followed in understanding of basic fundamentals of robotic manipulator. Due to uncertainties and non-linearities involved in its behavior, it is a challenging task to control their motion. This paper focuses mainly on the control of robot manipulator by employing design of various controllers like the PD controller, computed torque controller, adaptive controller and a robust adaptive controller. Their design and their performances are compared in extensive simulations carried out in MATLAB/Simulink.

—The report investigates the performance of Direct and Indirect-Model Reference Adaptive Control schemes for the angular motion control of a helicopter which is achieved by tilting its main rotor and as a result altering the direction of the rotor thrust vector. This action includes a change in the angular moments acting on the vehicle and results in pitch,roll and yaw angular motion. In hover, the helicopter pitch dynamics depend primarily on the vehicle pitch rate q(t) and on the applied longitudinal control input δ(t) which is equivalent in its effect to an elevator of a fixed-wing aircraft. Extensive simulations in MATLAB/Simulink have been implemented investigate the performance of the schemes. I. SYSTEM MODEL The pitch dynamics of an aircraft assuming constant thrust while ignoring the small vertical and forward speed components can be approximated by he equation (1). ˙ q = M q q + M δ δ (1) where, M q =-0.61 rad/s represents the vehicle pitch damping and M δ =-6.65 rad/s 2 is the elevator effectiveness. The objective is for the pitch dynamics to have a desired closed-loop tracking behavior given by the reference model. ˙ q ref = M qr q ref + M δr q cmd (2) II. CONTROL OBJECTIVE To design a direct and indirect MRAC δ(t) such that the plant state q(t) in (1) tracks the reference model given by (2) as a series of step input commands of different magnitudes eg. from t=0-5 s, q cmd = +1 • ;t=5-10 s, q cmd = −1 • ;t=10-15 s, q cmd = +2 • ;t=15-20 s, q cmd = −2 • ;t>20 s, q cmd = +3 •. The reference model has parameters M qr =-4 and M δr =-4. For the purpose of control design, the plant parameters M q is unknown and only the sign of M δ (i.e.negative) is known. For the indirect scheme it is assumed that |M δ | > 2. III. CONTROLLER EXPRESSIONS This section details the mathematical expressions for both the Direct and Indirect Model Reference Adaptive Control schemes in order to provide an insight for the design of the controller. A. Direct Model Reference Adaptive Control (DMRAC) In the direct MRAC , the controller is designed keeping in view the following : (a) the error between the output of plant and reference model is identically zero for identical initial conditions. (b) an initial error will vanish with certain dynamic. Considering the plant model given by (3). ˙ q = M q q + M δ δ (3) where, M q , M δ are unknown and q is measurable. The reference model for the plant can be modeled as ˙ q ref = M qr q ref + M δr δ r (4)

—Neural networks are simplified models of the biological nervous system and therefore have drawn their motivation from the kind of computing performed by human brain. A NN is a highly interconnected network of a large number of processing elements called neurons in an architecture inspired by the brain. A neural network can be massively parallel and therefore is said to be massively parallel distributed processing. NN have been successfully applied to problems in the fields of pattern recognition, image processing,forecasting, and optimization. This paper investigates the performance of the neural network design to robot manipulators. Their performances is evaluated in extensive simulations carried out in MATLAB/Simulink by varying the number of neurons and layers in an NN structure.

—The work proposes an adaptive control architecture for maximum power point tracking in photovoltaic systems. MPP technologies have been used in PV systems to deliver maximum available power to the load under changes in insolation and ambient temperature. To improve the performance of MPPT, the work focuses on MRAC based MPP tracking.

Balancing the rift between demand and production of energy has become one of the major growing concerns globally. This has prompted the technocrats, policy-makers, etc. to contemplate on the potency of renewable energy (RES) sources. The outcome has resulted in the world-wide adoption of RES to meet energy deficits. However various grid codes govern their integration to the grid. These monitor the functioning of the RES power converters and impose active and reactive power injection requirements. This is termed as the low voltage ride-through capability of the power converters in order to ensure unnecessary tripping of the interfacing converter resulting in sudden demand-shift on the conventional sources. Cascaded failures and blackouts could be an immediate result.
Furthermore proper, fast and dynamic tracking and synchronization of the grid angle also emerges as a necessity in order to respond to the scenario of sudden grid disconnection. But the vulnerability of the grid-interfacing converters to disconnection due to grid voltage and frequency distortions contributes to the fragile interconnection. Taking into consideration all the discussed issues the need for a control law accounting for synchronization and grid distortions emerges as a foreseeable solution.  This paper investigates the functioning of adaptive window-based MAF-PLL and the operation of an LVRT scheme for low voltage interfaced PV inverters. Extensive simulations in MATLAB/Simulink have been investigated under different scenarios to validate the proposed scheme.