M. Z. I. Sarkar

Nonlinear backstepping controller design for a three-phase grid-connected photovoltaic system using DPC approach

A new direct power control (DPC) approach for a voltage source inverter (VSI) based three-phase grid-connected solar photovoltaic (PV) system is proposed in this paper. The proposed DPC is designed using the nonlinear backstepping control scheme based on the power dynamics rather than the conventional dp current dynamics. As a result, the inner current control loop is eradicated in this paper which simplifies the system modeling and controller design and enhances the transient performance. Conversely, the outer voltage loop is used to generate the active power reference from the closed loop control of the dc-link voltage dynamics. The proposed controller is designed recursively based on the Lyapunov function theory and overall stability of the whole system is confirmed with the formulation of control Lyapunov functions (CLFs) at every design stage of the controller. Finally, the performance of the designed controller is tested on a three-VSI based three-phase grid-connected PV system under different operating conditions. The performance is also compared with an existing controller and it is clear that designed controller can better performance than the existing controller in terms of the total harmonic distortion (THD) of the injected current and quality of power.

Security in cooperative spatial multiplexing system with zero-forcing filtering

This paper is concerned with the analysis of secrecy capacity and secure outage performance of cooperative spatial multiplexing system with the effect of linear equalization. A confidential communication scenario is considered through Rayleigh fading channel in which a number of users communicate with a destination via multiple relays. An eavesdropper observes their communication and tries to decode the confidential information. At first, we derive the exact closed-form expression for the ergodic secrecy capacity with linear equalization in cooperative spatial multiplexing system. Then, we derive the exact closed-form expressions for the secure outage probability and the complementary cumulative distribution function (CCDF) of secrecy capacity to investigate the secure outage performance of the proposed model. Finally, we justify the validity of analytical results comparing with the Monte-Carlo simulation results.

Wireless multicasting in cooperative multiplexing system with zero-forcing filtering

In this paper, we consider a multicasting scenario in cooperative spatial multiplexing system over Rayleigh fading channel in which a source S transmits a common stream of information to a group of client receivers via K relays. We assume that there is no direct path between S and the client receivers and communication occurs only through the relays. Considering a linear equalization, e.g. zero-forcing (ZF) in cooperative spatial multiplexing system, at first, we derive the exact closed-form expression for the ergodic multicast capacity. Then, we derive the closed-form expressions for the outage probability and the complementary cumulative distribution function (CCDF) of multicast capacity to analyze the outage performance of proposed model.

Nonlinear adaptive backstepping controller design for grid currents regulation of a CSI based PV system with external disturbances

In this paper, a nonlinear adaptive controller for regulating the grid of a current source inverter (CSI) based three-phase grid-connected photovoltaic (PV) system is proposed. The proposed control structure is composed with an outer control loop-responsible for controlling the DC-side inductor current and the inner current control loop-responsible for controlling injected current into the utility grid. The proposed adaptive controller is designed recursively by considering external disturbances within the system and these unknown external disturbances are estimated through the adaption laws. The overall stability of the whole CSI based three-phase grid-connected PV system is verified by formulating the control Lyapunov functions (CLFs) at different stages throughout the design process of the proposed controller. Finally, the performance of the designed controller is tested on a similar CSI based three-phase grid-connected PV system under different atmospheric conditions. Simulation results demonstrate that the proposed control scheme can effectively meet the desired control objectives as compared to the existing controller in terms of settling time and power quality.

Robust adaptive backstepping controller design for PWM based DC-DC buck converter based on projection method

DC-DC power converter is a most important power source for driving a DC system in contemporary power electronic systems. However, owing to the time-varying and nonlinear characteristics of load resistance, it is often very challenging issue to ensure the stability of such converters. This paper is concerned about the regulation of the output voltage of a DC-DC buck converter using a nonlinear robust adaptive technique. The proposed controller is designed recursively based on the Lyapunov theory where the load resistance is considered as an unknown parameter. This unknown load resistance is estimated through the parameter adaptation law based on the projection method. Note that the projection method is a robustness augmentation technique that bounds the unknown parameter variations in a convex set which confirm through the formulation of control Lyapunov functions (CLFs) at different stages. The advantages of the proposed controller are that it can provide robust performance against external turbulence and also conquer the over-parameterization difficulty. At last the usefulness of the designed controller is verified through simulation results and compared with an existing controller. From the simulation results, it is obvious that the designed controller provides a significant performance improvement than the existing controller in terms of settling time and fast tracking desired output voltage.

Nonlinear adaptive backstepping controller design for trajectory flight control of UAHs

Considering the external disturbances, this paper proposes a new control approach, with the intention of improving the trajectory flight control in the longitudinal-lateral trajectory plane with constant altitude, to design a nonlinear adaptive controller for an unmanned autonomous helicopter (UAH). The unknown external disturbances are considered within the system model and estimated through adaption laws and incorporated with the control law to attest the robustness property of the intended control scheme. The designed controller is able to provide the robustness property against external turbulences as well as can overcome the over-parameterization problem which generally emerges in some conventional adaptive methods. To prove the convergence of longitudinal and lateral dynamics to a desired equilibrium point, in every stage of the design procedure a control Lyapunov function (CLF) is formulated and stability of the whole system is proved through the negative definiteness of the derivative of CLF. Finally, the performance of the proposed controller is verified in a MATLAB/SIMULINK model in the presence of external turbulence into the system. The robustness of the proposed controller, in terms of rejecting external disturbances, is illustrated through the simulation results.

Nonlinear robust controller design for a grid-connected PV system using DPC approach

A nonlinear robust controller based on the direct power control (DPC) approach for a voltage source inverter (VSI) based three-phase grid-connected solar photovoltaic (PV) system is proposed in this paper. The proposed robust controller is designed using the nonlinear backstepping theory based on the power dynamics rather than the usual current dynamics. One of the foremost advantages of this procedure is that the inner current control loop is eradicated here which consequently simplifies the modeling and controller design process. On the other hand, to generate the reference active power from the closed loop control of the dc-link voltage dynamics an outer voltage loop is used. To show the robustness of the designed controller, external disturbances are also considered within the system. The overall stability of the whole system is confirmed with the formulation of control Lyapunov functions (CLFs) at every design stage during the design of the controller. Finally, the performance of the designed controller is tested on a VSI based three-phase grid-connected PV system under different operating conditions. The performance is also compared with an existing controller and it is clear that designed controller can provide better performance than the existing controller in terms of the total harmonic distortion (THD) of the injected current.

Adaptive controller design for speed control of DC motors driven by a DC-DC buck converter

A nonlinear adaptive controller for controlling the desired velocity of DC motors driven by DC-DC buck converters is proposed in this paper. The proposed controller is designed recursively based on the control Lyapunov function (CLF) to assure the desired control performance under varying the load torque of the DC motor as well as by considering the system parameters as unknown. These unknown parameters along with unknown load torque are estimated using the adaptation laws and incorporated in the control law to enhance the robustness of the proposed controller. To prove the speculative stability of the whole system, the CLFs are formulated at different stages during the design process of the controller. Another key attribute of the proposed adaptive control scheme is that it can overwhelm the over-parameterization problems of unknown parameters which generally come out in some conformist adaptive backstepping methods. Finally, the helpfulness of the proposed control scheme is demonstrated through the computer simulation results and performance of the designed controller is also compared with an existing adaptive backstepping controller.

Security enhancement in the receive diversity with co-operative relay for wireless networks

In this paper, a dual hop diversity communication system which is highly confidential for wireless applications is proposed to transmit the secret information from the source to receiver in the presence of interferences. In this proposed wireless communication system, the receiver is equipped with multiple antennas whereas the relays and interference are equipped with single antenna. The output signal is combined with a maximum ratio combiner (MRC) and then process it by the weighting vector and finally amplifying the receive signal by the relays. To do that the amplify-and-forward (AF) as well as decode-and forward (DF) strategies of the relays are used to increase the signal strength of the receive diversity and relay gain. Moreover, moment generating function (MGF) is used to maximize the diversity order for increasing the capacity of the receive signal and symbol error probability (SEP). Finally, the Monte Carlo simulation model is used to show the effectiveness of the proposed technique. From the simulation results, it is clear that the receive signal capacity can be significantly optimized in terms of SEP by using the AF, and DF strategies.

Robust nonlinear adaptive backstepping controller design for unmanned autonomous vehicles

A robust nonlinear adaptive controller design for unmanned autonomous vehicles (UAVs) for controlling the hovering flight is presented. The controller is premeditated recursively based on the control Lyapunov theory where the mass of the UAV in the model is considered as anonymous parameter. To illustrate the forcefulness property of the designed controller, the effects of external disturbances are also considered in the UAV dynamical model throughout the devise of the controller. The unknown parameter (mass) is estimated using the adaptation law and incorporated in the final control law and then the overall immovability of the UAV system is confirmed by forming the negative semi-definiteness of Lyapunov functions. Note that the designed controller is adaptive to the mysterious parameter of the UAV and robust to external disturbances. Finally, the designed controller performance is experienced using a MATLAB simulation model under hovering flight condition and the performance is also compared with an existing nonlinear robust adaptive backstepping controller. The simulation results illustrate the sturdiness of the designed controller as compared to the existing nonlinear robust controller in terms of declining exterior wind gusts.