Tushar Kanti Roy

Robust nonlinear adaptive backstepping controller design for three-phase grid-connected solar photovoltaic systems with unknown parameters

This paper presents a nonlinear control scheme to regulate the dc-link voltage for extracting the maximum power from PV system and the current to control the amount of injected power into the grid. The controller is designed using an adaptive backstepping technique by considering the parameters of the system as totally unknown. The control of power injection into the grid requires the regulation of active and reactive components of the output current of the inverter in order to control active and reactive power, respectively. The proposed controller is adaptive to unknown parameters of grid-connected solar photovoltaic (PV) systems and these parameters are estimated through the adaptation laws while guaranteeing the extraction of maximum power from the PV system and delivering appropriate active and reactive power into the grid. The overall stability of the whole system is analyzed based on the formulation of control Lyapunov functions (CLFs). Finally, the performance of the designed controller is tested on a three-phase grid-connected PV system under changeing environmental conditions and the result is also compared with an existing backstepping controller in terms of improving power quality. Simulation results indicate the robustness of the proposed scheme under changing atmospheric conditions.

Nonlinear adaptive excitation controller design for multimachine power systems

This paper presents a nonlinear adaptive excitation control scheme to enhance the dynamic stability of multimachine power systems. The proposed controller is designed based on the adaptive backstepping technique where the mechanical power input to the generators and the damping coefficient of each generator are considered as unknown. These unknown quantities are estimated through the adaption laws. The adaption laws are obtained from the formulation of Lyapunov functions which guarantee the convergence of different physical quantities of generators such as the relative speed, terminal voltage, and electrical power output. The proposed scheme is evaluated by applying a three-phase short-circuit fault at one of the key transmission lines in an 11-bus test power system and compared with an existing backstepping controller and conventional power system stabilizer (CPSS). Simulation results show that the proposed scheme is much more effective than existing controllers.

Nonlinear excitation control of synchronous generators based on adaptive backstepping method

In this paper, the design of a nonlinear excitation control of a synchronous generator is presented where the generator is connected to a single machine infinite bus (SMIB) system. An adaptive backstepping method is used to design the excitation controller with an objective of enhancing the overall dynamic stability of the SMIB system under different contingencies. In this paper, two types of contingencies are considered- i) unknown parameters and physical quantities during the controller design process and ii) controller performance evaluation under different system configurations such as three-phase short circuit faults. The adaption law, which is mainly based on the formulation of Lyapunov function, is used to estimate the unknown parameters which guarantee the convergence of different physical quantities of synchronous generators, e.g., the relative speed, terminal voltage, etc. The effectiveness of the proposed scheme is evaluated under different system configurations as mentioned in the second contingency and compared to that of an existing adaptive backstepping controller and a conventional power system stabilizer (PSS). Simulation results demonstrate the superiority of the proposed control scheme over the existing controllers.

Nonlinear backstepping controller design for sharing active and reactive power in three-phase grid-connected photovoltaic systems

In this paper, a nonlinear backstepping controller is designed for three-phase grid-connected solar photovoltaic (PV) systems to share active and reactive power. A cascaded control structure is considered for the purpose of sharing appropriate amount of power. In this cascaded control structure, the dc-link voltage controller is designed for balancing the power flow within the system and the current controller is designed to shape the grid current into a pure sinusoidal waveform. In order to balance the power flow, it is always essential to maintain a constant voltage across the dc-link capacitor for which an incremental conductance (IC) method is used in this paper. This approach also ensures the operation of solar PV arrays at the maximum power point (MPP) under rapidly changing atmospheric conditions. The proposed current controller is designed to guarantee the current injection into the grid in such a way that the system operates at a power factor other than unity which is essential for sharing active and reactive power. The performance of the proposed backstepping approach is verified on a three-phase grid-connected PV system under different atmospheric conditions. Simulation results show the effectiveness of the proposed control scheme in terms of achieving desired control objectives.

Robust adaptive backstepping excitation controller design for simple power system models with external disturbances

This paper presents a nonlinear robust adaptive excitation controller design for a simple power system model where a synchronous generator is connected to an infinite bus. The proposed controller is designed to obtain the adaption laws for estimating critical parameters of synchronous generators which are considered as unknown while providing the robustness against the bounded external disturbances. The convergence of different physical quantities of a single machine infinite bus (SMIB) system, with the proposed control scheme, is ensured through the negative definiteness of the derivative of Lyapunov functions. The effects of external disturbances are considered during formulation of Lyapunov function and thus, the proposed excitation controller can ensure the stability of the SMIB system under the variation of critical parameters as well as external disturbances including noises. Finally, the performance of the proposed scheme is investigated with the inclusion of external disturbances in the SMIB system and its superiority is demonstrated through the comparison with an existing robust adaptive excitation controller. Simulation results show that the proposed scheme provides faster responses of physical quantities than the existing controller.

Robust adaptive backstepping controller design for DC-DC buck converters with external disturbances

In modern power electronic systems, DC-DC converter is one of the main controlled power sources for driving DC systems. But the inherent nonlinear and time-varying characteristics often result in some difficulties mostly related to the control issue. This paper presents a robust nonlinear adaptive controller design with a recursive methodology based on the pulse width modulation (PWM) to drive a DC-DC buck converter. The proposed controller is designed based on the dynamical model of the buck converter where all parameters within the model are assumed as unknown. These unknown parameters are estimated through the adaptation laws and the stability of these laws are ensured by formulating suitable control Lyapunov functions (CLFs) at different stages. The proposed control scheme also provides robustness against external disturbances as these disturbances are considered within the model. One of the main features of the proposed scheme is that it overcomes the over-parameterization problems of unknown parameters which usually appear in some conventional adaptive methods. Finally, the effectiveness of the proposed control scheme is verified through the simulation results and compared to that of an existing adaptive backstepping controller. Simulation results clearly indicate the performance improvement in terms of a faster output voltage tracking response.

A nonlinear adaptive backstepping approach for coordinated excitation and steam-valving control of synchronous generators

Steam-valving and excitation systems play an important role to maintain the transient stability of power systems with synchronous generators when power systems are subjected to large disturbances and sudden load changes. This paper presents a nonlinear adaptive backstepping approach for controlling excitation and steam-valving systems of synchronous generators. In this paper, the proposed excitation and steam-valving controllers are designed in a coordinated manner so that they can work under several and most severe operating conditions. Both excitation and steam-valving controllers are designed by considering some critical parameters as unknown. The effectiveness of the proposed coordinated control scheme is evaluated on a single machine infinite bus system under different operating conditions such as load changes and three-phase short circuit faults at the generator terminal. Finally, performance of the proposed scheme is compared to that of a similar nonlinear adaptive backstepping excitation controller without any coordination and simulation results demonstrate the superiority of the proposed one.

Feedback Linearizing Model Predictive Excitation Controller Design for Multimachine Power Systems

In this paper, a nonlinear excitation controller is designed for multimachine power systems in order to enhance the transient stability under different operating conditions. The two-axis models of synchronous generators in multimachine power systems along with the dynamics of the IEEE Type-II excitation systems are considered to design the proposed controller. The partial feedback linearization scheme is used to simplify the multimachine power system as it allows decoupling a multimachine power system based on the excitation control inputs of synchronous generators. A receding horizon-based continuous-time model predictive control scheme is used for partially linearized power systems to obtain linear control inputs. Finally, the nonlinear control laws, which also include receding horizon-based control inputs, are implemented on the IEEE 10-machine, 39-bus New England power system. The superiority of the proposed scheme is evaluated by providing comparisons with a similar existing nonlinear excitation controller, where the control input for the feedback linearized model is obtained using the linear quadratic regulator (LQR) approach. The simulation results demonstrate that the proposed scheme performs better as compared to the LQR-based partial feedback linearizing excitation controller in terms of enhancing the stability margin.

Nonlinear Adaptive Excitation Controller Design for Multimachine Power Systems With Unknown Stability Sensitive Parameters

In this paper, a nonlinear control scheme is proposed for synchronous generators in a multimachine power system to damp out low-frequency oscillations and enhance the transient stability. The proposed controller is designed recursively to adapt some unknown stability sensitive parameters of synchronous generators. These unknown parameters, estimated through the adaptation laws with the inclusion of the projection operator, are incorporated into the controller to ensure the stability of whole power system with the formulation of control Lyapunov functions (CLFs). The convergence of different physical properties of synchronous generators, such as relative speed, terminal voltage, and rotor angle, is ensured from the negative definiteness or semidefiniteness of the derivative of CLFs. The performance of the proposed controller is evaluated through simulation results on a two-area multimachine power system in terms of robustness to estimate the unknown parameters and maintain the steady-state operation of power systems under different operating conditions. Simulation results are compared with an existing nonlinear adaptive backstepping controller and a conventional power system stabilizer, which illustrate the effectiveness of the proposed control scheme over the existing controllers.

Nonlinear adaptive backstepping controller design for controlling bidirectional power flow of BESSs in DC microgrids

In this paper, a nonlinear adaptive backstepping controller is designed to control the bidirectional power flow (charging/ discharging) of battery energy storage systems (BESSs) in a DC microgrid under different operating conditions. The controller is designed in such a manner that the BESSs can store the excess energy from the renewable energy sources (RESs) in a DC microgrid after satisfying the load demand and also feeding back the stored energy to the load when RESs are not sufficient. The proposed controller is also designed to maintain a constant voltage at the DC bus, where all components of DC microgrids are connected, while controlling the power flow of BESSs. This paper considers solar photovoltaic (PV) systems as the RES whereas a diesel generator equipped with a rectifier is used as a backup supply to maintain the continuity of power supply in the case of emergency situations. The controller is designed recursively based on the Lyapunov control theory where all parameters within the model of BESSs are assumed to be unknown. These unknown parameters are then estimated through the adaptation laws and whose stability is ensured by formulating suitable control Lyapunov functions (CLFs) at different stages of the design process. Moreover, a scheme is also presented to monitor the state of charge (SOC) of the BESS. Finally, the performance of the proposed controller is verified on a test DC microgrid under various operating conditions. The proposed controller ensures the DC bus voltage regulation within the acceptable limits under different operating conditions.