Mehrdad Yazdanian

Distributed Control Techniques in Microgrids

The objective of this paper is to provide a review of distributed control and management strategies for the next generation power system in the context of microgrids. This paper also identifies future research directions. The next generation power system, also referred to as the smart grid, is distinct from the existing power system due to its extensive use of integrated communication, advanced components such as power electronics, sensing, and measurement, and advanced control technologies. At the same time, the need for increased number of small distributed and renewable energy resources can exceed the capabilities of an available computational resource. Therefore, the recent literature has seen a significant research effort on dividing the control task among different units, which gives rise to the development of several distributed techniques. This paper discusses features and characteristics of these techniques, and identifies challenges and opportunities ahead. The paper also discusses the relationship between distributed control and hierarchical control.

Estimation of Electromechanical Oscillation Parameters Using an Extended Kalman Filter

Estimation of electromechanical modes of a power system has attracted attention in the past few decades because it can provide vital information about the stability of the system. In this paper, a new state-space model is proposed for online detection of parameters of a ringdown signal using an extended Kalman filter (EKF). The proposed model can estimate both constant and time-varying parameters. Furthermore, stability analysis of the proposed model is performed to demonstrate the convergence of the parameters. Simulation results confirm the desirable performance of the proposed method for ringdown parameter estimation.

Internal Model-Based Current Control of the RL Filter-Based Voltage-Sourced Converter

Power system operates close to its operational limit to achieve a higher level of utilization of the grid infrastructure. As a result, its transient behavior is of great importance to prevent violation of the operation limits. This paper proposes an internal model control (IMC)-based approach for voltage-sourced converters (VSC) to improve their dynamic behavior. This IMC controller is designed based on a detailed model of the VSC. The proposed control approach has superior performance, i.e., faster step response and less overshoot, and higher axes decoupling than the conventional dq-current control method. The proposed IMC-based controller has a straightforward design procedure, and can be implemented using simple PI and PID controllers. Several case studies are presented to evaluate and compare the transient performance of the IMC-based controller with conventional dq current control subsequent to step changes in the set points of direct and quadrature axes current, single-phase fault, and three-phase fault.

Washout Filter-Based Power Sharing

Microgrid control practice has been dominated by droop control for over a decade. The main reason is that droop control can ensure voltage and frequency stability, and proper sharing of the load among distributed generation units without communication links. However, droop control causes undesirable voltage and frequency deviations. Using a dynamic feedback incorporating washout filters, this letter proposes a novel approach to perform power sharing without any communication links, and without compromising voltage and frequency regulation. Simulation results in PSCAD/EMTDC environment validate the performance of the proposed approach.

Small-Signal Stability Analysis of an Inverter-Based Microgrid With Internal Model-Based Controllers

Several microgrid control strategies are proposed and studied in the literature. However, there are still gaps in improving their transient behavior and studying their stability. This paper uses small-signal analysis to explore the behavior of internal model-based current and voltage controllers by deriving a state-space model and performing eigenvalue and sensitivity analysis on an islanded inverter-based microgrid system. The results are compared with those of the same microgrid but with PI-based current and voltage controllers. Simulation case studies are performed in the PSCAD/EMTDC environment to compare the transient behavior of both methods. Results show that internal model-based controllers have superior eigenvalue patterns that lead to increased stability and improved transient behavior.

A novel approach for ringdown detection using extended Kalman filter

Estimation of electromechanical modes has attracted attention during past few decades because the estimation of these modes provides vital information about the stability of the power system. In this paper, a new state-space model is developed for online detection of a ringdown signal using extended Kalman filter (EKF). The proposed model not only can estimate constant parameters, but it can also track time-varying parameters. Simulation results demonstrate the desirable performance of the proposed method for ringdown parameter estimation.

Smooth Reference Modulation to Improve Dynamic Response in Electric Drive Systems

Response overshoot is an undesired behavior that can be experienced by a dynamic system. Reduction of overshoot, without compromising the speed of the system response, increases the permissible operational range by enabling the system to operate closer to its limits. Previous work related to set point modulation proposed an effective strategy to improve set point tracking by temporarily modifying the set point based on the trend of the response and its proximity to the set point. However, this strategy is designed for solid-state units with no inertia and is not directly applicable to applications such as electric drive systems, in which frequent step changes in the set point may cause mechanical stress. This paper addresses this issue and proposes an alternate strategy based on continuous, rather than step, changes in the set point. The proposed approach is implemented for an electric drive system. Simulation and experimental results confirm the desirable performance of the proposed approach.

Estimation of electromechanical oscillation parameters using an extended Kalman filter

Estimation of electromechanical modes of a power system has attracted attention in the past few decades because it can provide vital information about the stability of the system. In this paper, a new state-space model is proposed for online detection of parameters of a ringdown signal using an extended Kalman filter (EKF). The proposed model can estimate both constant and time-varying parameters. Furthermore, stability analysis of the proposed model is performed to demonstrate the convergence of the parameters. Simulation results confirm the desirable performance of the proposed method for ringdown parameter estimation.

Overshoot control of the electromagnetic torque during fault recovery for an SCIG with a STATCOM

Squirrel cage induction generators (SCIG) are one of the widely used generators in the wind turbines. The popularity of the SCIG is because of their relatively low price. However, speed and torque control in SCIGs is not as well studied as doubly fed induction generators (DFIG). This leads to more stress in the mechanical parts and more fatigue in the gearbox. In this paper a control method is proposed for limiting the electromagnetic torque overshoot during the recovery process subsequent to a fault. The idea behind the proposed method is to utilize the set point automatic adjustment with correction enabled (SPAACE) method to modify the voltage control loop of the static synchronous compensator (STATCOM) installed at the terminal of the SCIG to limit the torque overshoot.

Internal model-based current control of the RL filter-based voltage-sourced converter

Power system operates close to its operational limit to achieve a higher level of utilization of the grid infrastructure. As a result, its transient behavior is of great importance to prevent violation of the operation limits. This paper proposes an internal model control (IMC)-based approach for voltage-sourced converters (VSC) to improve their dynamic behavior. This IMC controller is designed based on a detailed model of the VSC. The proposed control approach has superior performance, i.e., faster step response and less overshoot, and higher axes decoupling than the conventional dq-current control method. The proposed IMC-based controller has a straightforward design procedure, and can be implemented using simple PI and PID controllers. Several case studies are presented to evaluate and compare the transient performance of the IMC-based controller with conventional dq current control subsequent to step changes in the set points of direct and quadrature axes current, single-phase fault, and three-phase fault.