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In this paper, we address the design of an autopilot for autonomous landing of a helicopter on a rocking ship, due to rough sea. A tether is used for landing and securing a helicopter to the deck of the ship in rough weather. A detailed nonlinear dynamic model for the helicopter is used. This model is underactuated, where the rotational motion couples into the translation. This property is used to design controllers which separate the time scales of rotation and translation. It is shown that the tether tension can be used to couple the translation of the helicopter to the rotation. Two controllers are proposed in this paper. In the first, the rotation time scale is chosen much shorter than the translation, and the rotation reference signals are created to achieve a desired controlled behavior of the translation. In the second, due to coupling of the translation of the helicopter to the rotation through the tether, the translation reference rates are created to achieve a desired controlled behavior of the attitude and altitude. Controller A is proposed for use when the helicopter is far away from the goal, while Controller B is for the case when the helicopter is close to the ship. The proposed control schemes are proved to be robust to the tracking error of its internal loop and results in local exponential stability. The performance of the control system is demonstrated by computer simulations. Currently, work is in progress to implement the algorithm using an instrumented model of a helicopter with a tether. Index Terms--Attitude control, position control, robustness, tethered helicopter.

Abstract - A new Lyapunov function is constructed for a general n-machine power system with nonzero transfer conductance. The theory of dissipative dynamic systems and its modifications are used and the Lyapunov function construction procedure calls for checking positive definiteness of a sparse matrix Q. In this note, we report the results only for the case of nonuniform damping which is more complex than the uniformly damped system. The procedure is iterative and is guaranteed to converge for uniform damping but may fail to converge for a very lightly nonuniformly damped system with strong interconnections. The Lyapunov function is a quadratic term plus a weighted sum of integrals, a form not reported before. This is an extension of the previously reported quadratic Lyapunov function.

Nowadays, transformer-less Photovoltaic-based grid-connected inverters aremore popular in renewable energy application due to their reduced size, cost, and high efficiency. However, the absence of galvanic isolation leads to the flow of leakage current in such system hindering personal safety, and deteriorating power quality. Therefore, this paper presents a five-level transformer-less inverter topology for PV applications with less component count and reduced complexity. The proposed inverter topology completely eliminates the common mode leakage current. Besides, the proposed topology has an inherent capability to boost the voltage without using any magnetic component or boosting circuit, and is based on the principle of switched/auxiliary capacitor. The proposed topology do not have any limitation of modulation index since the auxiliary capacitors are naturally balanced, hence less complex or no dedicated control scheme is required for balancing/regulating the auxiliary capacitor voltages. In order to verify the performance of the proposed inverter topology, a laboratory prototype is developed which confirms the operation, and feasibility of the proposed inverter. Results depicting the output voltage, load current, and voltage across the auxiliary capacitor are presented for various operating conditions. Further, simulation results depicting the leakage current in the proposed, H5, and H6 topologies are included. Finally, a quantitative comparison study is done, highlighting the benefits of the proposed inverter topology regarding boosted voltage, elimination of leakage current, and reduced component count. [ABSTRACT FROM AUTHOR]

In this paper, the author presents students with a new and simple derivation of the law of the junctions. The law of the junctions is crucial to the correct understanding of the operation of the bipolar junction transistor. The integral of the product of the density of energy states and Fermi-Dirac distribution function is used to derive the density of free electrons and holes crossing from one side to another at a pn-junction under an external applied voltage. Index Terms--Bipolar junction transistor (BJT), diode current, electrons crossing over, pn-junction built-in potential, the law of the junctions.

This paper examines a multilevel transformer‐less grid‐tied inverter topology is proposed for PV applications. Nowadays, transformer‐less inverters are more desirous due to their small filter size, cheaper and higher efficiency. However, the removal of transformer results in the existence of leakage current due to absence of galvanic isolation. The flow of leakage current is the cause of personal safety and deteriorating power quality. A transformer‐less inverter topology is proposed which is able to solve the leakage current issue. Besides, it has the ability to generate the boosted voltage without the need of magnetic component or boosting circuit. It works on the principle of flying/switched capacitor which are able to naturally balance the voltage. Hence, it does not have the limitation of modulation index and no need of complex control scheme to balance or regulate the voltage across an auxiliary capacitor. The performance of the proposed topology is verified by implementing a laboratory prototype which validates the operation and performance of the proposed topology. Results depicting the output voltage, load current and voltage across the auxiliary capacitor are presented for various operating conditions. Moreover, a comprehensive comparison is done, in terms of component count, level and boosting ability of output voltage with leakage current condition. [ABSTRACT FROM AUTHOR]

Transformerless inverters (TIs) are widespread in photovoltaic (PV) applications due to their low cost and high efficiency. However, TIs suffer due to leakage current as a consequence of PV parasitic capacitance, and high-frequency common-mode voltage, which has resulted in the emergence of several topological and control scheme modifications. In this article, a switched-capacitor (SC) based inverter capable of synthesizing a five-level voltage is proposed. In the devised structure, the negative pole of the dc bus is directly connected to the grid neutral, thereby resulting in zero leakage current. In addition, industrial standard half-bridge modules can be employed directly for implementing the proposed inverter without modifications, making it more practically feasible. The proposed topology has the capability of self-voltage balancing of SC, reactive power processing, and full dc-bus utilization as opposed to half-bridge topologies. The principle of operation and a simple logic-gate-based pulse generation scheme is presented in detail. Simulation and experimental results confirming the practical viability of the proposed topology are presented. Finally, the superior features and the merits of the proposed topology are shown through a detailed comparison against state-of-the-art topologies. [ABSTRACT FROM AUTHOR]

In this short note we present a very simple method, useful for classroom teaching, to get a minimal state-space representation (with the exception of systems where there is a pole-zero cancellation) from a transfer function matrix. The method is direct and does not involve the intermediate step of obtaining nonminimal realization - which further requires system reduction routines - and hence is suitable as a compact self-contained topic which has been hitherto neglected in undergraduate linear control theory curriculum.

Distributed generation (DG) is one of the key components of the emerging microgrid concept that enables renewable energy integration in a distribution network. In DG unit operation, inverters play a vital role in interfacing energy sources with the grid utility. An effective interfacing can successfully be accomplished by operating inverters with effective control techniques. This paper reviews and categorises different control methods (voltage and primary) for improving microgrid power quality, stability and power sharing approaches. In addition, the specific characteristics of microgrids are summarised to distinguish from distribution network control. Moreover, various control approaches including inner-loop controls and primary controls are compared according to their relative advantages and disadvantages. Finally, future research trends for microgrid control are discussed pointing out the research opportunities. This review paper will be a good basis for researchers working in microgrids and for industry to implement the ongoing research improvement in real systems. [ABSTRACT FROM AUTHOR]

In this paper, we address the design of an autopilot for autonomous landing of a helicopter on a rocking ship, due to rough sea. A tether is used for landing and securing a helicopter to the deck of the ship in rough weather. A detailed nonlinear dynamic model for the helicopter is used. This model is underactuated, where the rotational motion couples into the translation. This property is used to design controllers which separate the time scales of rotation and translation. It is shown that the tether tension can be used to couple the translation of the helicopter to the rotation. Two controllers are proposed in this paper. In the first, the rotation time scale is chosen much shorter than the translation, and the rotation reference signals are created to achieve a desired controlled behavior of the translation. In the second, due to coupling of the translation of the helicopter to the rotation through the tether, the translation reference rates are created to achieve a desired controlled behavior of the attitude and altitude. Controller A is proposed for use when the helicopter is far away from the goal, while Controller B is for the case when the helicopter is close to the ship. The proposed control schemes are proved to be robust to the tracking error of its internal loop and results in local exponential stability. The performance of the control system is demonstrated by computer simulations. Currently, work is in progress to implement the algorithm using an instrumented model of a helicopter with a tether. [ABSTRACT FROM AUTHOR]