Rojan Bhattarai

Reduced order model based state feedback control of Doubly Fed Induction Generators

A state feedback control strategy for Doubly Fed Induction Generator (DFIGs) is investigated. Both the rotor side converter and grid side converter control of DFIG has been designed using the proposed state feedback control technique. A comparison between the traditional PI based vector control (VC) of DFIG with the proposed form of control has also been presented. It has been shown that this methodology helps in easier controller design for DFIG, exhibits competitive performance in terms of low interaction between power and voltage control and provides better system damping. The simulation results for a system connected to a grid through a transmission line have been presented and the capabilities of the proposed controller are discussed.

Minimum variance adaptive speed estimation technique for vector control of Doubly Fed Induction Generator

This paper presents a novel sensor-less speed estimation technique applicable for vector control of the Doubly Fed Induction Generator (DFIG). The proposed technique can substitute the use of speed sensors and rotor position measurements. The proposed method is based on online identification of system parameters that minimizes the speed estimation error using minimum variance controller based on the machine rotor currents. The paper explains about the design of the controller and small signal model of the DFIG for the controller design. The technique is validated both in MATLAB Simulink and Opal RTs Real Time simulation platform for a 2kW Doubly Fed Induction Machine setup.

Minimum variance controller based adaptive control for Doubly fed induction generator

This paper presents a system identification based minimum variance controller for active and reactive power control of Doubly Fed Induction Generator (DFIG). The controller is adaptive as the parameters in the control law are updated online based on system identification that relate the output (active and reactive power) and the input (direct and quadrature axis rotor voltages). The main advantage of the proposed controller is the simplicity in design, its adaptability under varying operating conditions and the ability of the controller to perform without the need to measure rotor side quantities. The paper discusses the design of the controller and presents the simulation results from tests performed using MATLAB SimPowerSystems. The results show that the proposed controller can be a better alternative to the existing PI based vector control for DFIG.

Transient Stability Enhancement of Power Grid with Integrated Wide-Area Control of Wind Farms and Synchronous Generators

This paper presents a Wide Area Control (WAC) design to enhance the transient stability of Doubly Fed Induction Generators (DFIG) integrated power grid. The proposed WAC design is based on a nonlinear optimal control algorithm using Reinforcement Learning (RL) and Neural Networks (NNs), which optimizes the closed-loop performance of the wind integrated power grid through Approximate Dynamic Programming (ADP). The aim of the WAC is to estimate the global energy function of the system, independent of the contingency, and derive supplementary damping control to augment the excitation system of synchronous generators and local active and reactive power control of DFIG. The controller objective is evolved from transient energy function terms developed for synchronous generators and wind farms within the framework of a coupled oscillatory system. The theoretical results are verified by conducting simulation studies on the modified IEEE 68-bus system with three aggregated wind farms modeled in electromagnetic transient simulator test-bed. It has been shown that the method improves transient stability of the test system and damps the interarea oscillations faster, including the active and reactive power support from DFIG during grid transient conditions.

Reduced order state observer based feedback control methodologies for doubly fed induction generator (DFIG)

In this paper, a reduced order state observer for DFIG is designed that estimate the states with just using DFIGs stator voltage and power measurements. Further, the proposed state observer is used to provide two control strategies for Rotor Side Converter (RSC) of DFIG a) state estimator based state feedback control and b) state estimator based vector control. The state observer and controllers were tested for varying wind conditions using a full order dynamic model of DFIG with a real-time simulation platform. The results verify that the proposed state observer can augment existing control for DFIG with better tracking of the system output without the need for feedback measurements, and at the same time it can reduce the controller design complexity. Also, these state estimator based controllers eliminate the need of rotor current sensors for DFIG control.

Parametrically robust dynamic speed estimation based control for doubly fed induction generator

This paper presents a speed estimation based vector control architecture for Doubly Fed Induction Generator (DFIG). The main advantage of the proposed architecture is that with this methodology the generator can be operated without a speed sensor and position encoder. The method calculates the machine parameters online using a recursive least square (RLS) technique based on identifying the transfer function relating to rotor speed and position error. A minimum variance regulator ensures that the position error is minimum by proper estimation of the speed. For illustration, first, the small signal model of the machine and the regulator design is discussed. Then, a methodology is proposed, in which machines mutual inductance is estimated online, so that the estimation approach is robust to changes in the machine parameters. Second, the control architecture with the speed estimation technique is discussed. The proposed approach is validated using a real-time simulation platform for a GE 1.5 MW wind turbine and with hardware-in-the-loop experimental set up for a 2kW Doubly Fed Induction Machine (DFIM).

Coordinated voltage control strategy for voltage regulators and voltage source converters integrated distribution system

Modern day distribution systems (DS) is now hosting increasing number of both small and large scale distributed energy resources (DERs). Even though these DERs have capability to support reactive power along with the active power they provide, practitioners are still hesitant in utilizing the reactive power potential from these DERs. One of the major concerns for the distribution system operator is the coordination between the existing voltage regulators and the inverter based reactive power sources in the DS. This paper presents a situational aware and agnostic coordinated control strategy for voltage regulation in the DS considering power electronic based inverters as reactive power sources that work in conjunction with the existing legacy controllers for an overall value based voltage regulation of the entire feeder. It has also been shown that this can be achieved without major changes in the communication framework currently utilized by the utility (another concern for DS operator). The proposed control technique has been tested in the field verified model of a real feeder. Results show that the proposed coordination approach has a major economic as well and power quality benefits in the operation of DS.

Operational cost value assessment and value based stacked energy storage management for active power distribution systems

In this paper, a formal procedure to evaluate the operational value of ancillary services provided by battery energy storage systems is presented along with a methodology on how to schedule the battery considering maximum benefits. The ancillary services considered are photovoltaic (PV) power output smoothing, voltage support and energy time shift (ETS). The benefits provided by energy storage applications are quantified in terms of monetary value. First, the issues related to such value studies are mentioned and a method has been proposed to resolve these issues. Second, utilizing the value information, an optimization method is developed to modify the algorithms for energy storage applications. It has been concluded that monetary value of different energy storage applications provides additional information that can be used schedule energy storage applications to yield maximum cost benefit of the applications. Results obtained using the field validated simulation model show the potential of proposed method.

Direct intelligent wide-area damping controller for wind integrated power system

In this paper an intelligent wide-area damping controller is proposed for a wind integrated power grid. The proposed design is based on an energy function based intelligent optimal controller evolved from adaptive critic design using reinforcement learning technique. A Lyapunov function candidate is derived that links the energy function and the transient stability of the integrated system with the wide-area controller. The proposed wide-area controller augments the excitation system of the synchronous generator and local Maximum Power Point (MPP) tracking control of wind generator Doubly Fed Induction Generator (DFIG). The theoretical results are validated by conducting simulation studies on 2-Area Kundur power system for damping the inter-area oscillations. It was observed that the method improves transient stability of the integrated system due to the active and reactive support from the DFIG and thus damping the inter-area oscillations much faster. It was also observed that the speed oscillations of DFIG is within the limits.

Control of grid connected inverters using minimum variance adaptive architecture

This paper presents a system identification based minimum variance architecture for active and reactive power control of a Grid Connected Inverter (GCI). The controller is adaptive as the parameters in the control law are updated online based on identification that relate the output (active and reactive power) and the input (direct and quadrature axis voltage references). The main advantage of the proposed controller is the simplicity in design and its adaptability under varying operating conditions. The paper discusses the design of the controller and presents the simulation results from tests performed using MATLAB SimPowerSystems along with the Hardware-in-the-loop (HIL) implementation. The results show that the proposed controller can be a better alternative to the existing cascaded PI based vector control for grid connected inverters.