Ramtin Hadidi

Reinforcement Learning Based Real-Time Wide-Area Stabilizing Control Agents to Enhance Power System Stability

In this paper, the design of a network of real-time close-loop wide-area decentralized power system stabilizers (WD-PSSs) is investigated. In this approach, real-time wide-area measurement data are processed and utilized to design a set of stability agents based on a Reinforcement Learning (RL) method. Recent technological breakthroughs in wide-area measurement system (WAMS) make the use of the system-wide signals possible in designing power system controllers. The main design objectives of these controllers are to stabilize the system after severe disturbances and mitigate the oscillations afterward. The proposed stability agents are decentralized and autonomous. The proposed method extends the stability boundary of the system and achieves the above goals without losing any generator or load area and without any knowledge of the disturbances causing the response. This paper describes the developed framework and addresses different challenges in designing such a network. A case study is provided to illustrate and verify the performance and robustness of the proposed approach.

Hardware-in-the-Loop Testing of Utility-Scale Wind Turbine Generators

Historically, wind turbine prototypes were tested in the field, which was--and continues to be--a slow and expensive process. As a result, wind turbine dynamometer facilities were developed to provide a more cost-effective alternative to field testing. New turbine designs were tested and the design models were validated using dynamometers to drive the turbines in a controlled environment. Over the years, both wind turbine dynamometer testing and computer technology have matured and improved, and the two are now being joined to provide hardware-in-the-loop (HIL) testing. This type of testing uses a computer to simulate the items that are missing from a dynamometer test, such as grid stiffness, voltage, frequency, rotor, and hub. Furthermore, wind input and changing electric grid conditions can now be simulated in real time. This recent advance has greatly increased the utility of dynamometer testing for the development of wind turbine systems.

Design of a fixed-order robust controller using loop shaping method for damping inter-area oscillations in power systems

The inter-area oscillations are common in power system and can occur due to the changes in the load or generation power especially in long transmission lines. This paper presents the design of a robust fixed-order loop shaping controller to damp out the inter-area oscillations and to enhance the stability of the power system. The proposed loop shaping method is based on the shaping of the open-loop transfer function in the Nyquist diagram through minimizing the quadratic error between the actual and the desired open loop transfer functions in the frequency domain. The proposed method is robust with respect to multi-model uncertainty. Despite other robust controller design methods, the proposed approach deals with the entire system i.e. there is no need to reduce the system and still leads to a lower order controller. The proposed method is applied on the two area four machine system under different load conditions and different wind generations. The effectiveness and robustness of the proposed method in damping inter-area oscillations are validated using case studies.

Optimal operation of microgrids under conditions of uncertainty

This paper proposes a method to optimally operate microgrids under conditions of uncertainty introduced by renewable energy sources, under both grid connected and islanded mode. Uncertainty is quantified with probability distribution and confidence levels are used to establish likelihood of forecast error. The optimization problem is formulated as a quadratic programming problem and the optimality of the solution is shown mathematically by proving the convexity of the problem. The optimization is carried out with the combined objective of minimizing total operating cost and carbon emission. The proposed optimization method is then tested against a priority controller for an extended time-horizon of 24 hours. Furthermore, under islanded mode of operation, for extended time-horizon, a key decision making task of whether to provide energy to non-critical loads or to store excess energy is addressed.

Real-time modeling of multi-level megawatt class power converters for Hardware-In-the-Loop testing

Hardware-In-the-Loop (HIL) testing using real-time simulation allows system designers to lower risks associated with system integration of new technology. Controller HIL (CHIL) is used here to verify the controller platform of a 15 MW amplifier that will be used as a grid simulator in Power HIL (PHIL) configuration. This allows elements of a smart electrical distribution system to be tested in an anticipated power system in a controlled laboratory environment. Details include a description of CHIL testing with simulation results and experimental results of the hardware implementation with open circuit measurements at the 24 kV experimental bus.

A MILP formulation for utility scale optimal demand side response

A detailed mathematical model for optimal utilization of demand side response is formulated. Formulations for constrained controllable load (dependent load) is modeled, whose operation is dependent on certain other loads completing their schedule prior to the constrained controllable loads start time. In addition, several other types of load models, including electric vehicles (EV), adjustable and constant power loads are modeled. The ensuing problem is that of mixed integer linear programming (MILP) type. Using the developed MILP formulation optimal solution to utility scale demand response (DR) scheme is obtained in real-time (duration between dispatches). In particular, the work is aimed at reliability based DR schemes used by independent system operators (ISOs) and regional transmission organizations (RTOs). Applicability to utility scale DR schemes is shown by formulation and solution of large problems with more than one million variables - solved in real-time.

Experimental PWM method validation of a 9-level 4.16 kV series connected H-bridge grid simulator

Controllable ac sources, sometimes referred to as grid simulators, are becoming more common for grid integration testing of inverters as new grid interactive inverter functions develop. Due to the relatively niche application, high power grid simulators are often made by repurposing commercial drives with additional systems integration by the manufacturer or end user including filters, transformers, and control features. Simulation models, invaluable for pre-test simulations and future retrofits to the drive, are not usually provided with the drive and must therefore be developed by end users. Pulse-width modulation details are often overlooked in this process, using defaults within the simulation environment. Validating the digital implementation of PWM, including sampling method, is beneficial as it can have significant effects on control bandwidth especially on multi-level and interleaved converters. The grid simulator considered here utilizes 9-level series-connected H-bridge topology. Experimental setup and results are shown for two carrier frequencies, 600 Hz and 2 kHz, verifying an effective phase shifted carrier each with double-edge sampling.

Snubber circuit design considerations for medium-voltage solid-state switches for high-power inverter-based testing applications: A case study

This paper investigates a common problem in the snubber circuits of medium-voltage solid-state AC switches in industrial environments where PWM voltage-source converters are prevalent. The switches considered here were designed to evaluate fault ride-through capabilities for megawatt scale wind turbine generators and other generators with grid-connected stators. It is shown in the paper that, if left unchecked, high-frequency harmonics inherent in the output of inverter-based voltage sources can produce failures in the snubber circuits of AC switches. A case study is presented to analyze this issue, and different solutions are analyzed and implemented to tackle the problem. The experimental results validate the proposed solutions.

Heat generation and failure in padmount transformers due to zero sequence saturation

After a transformer failed following a double phase fault, there was an interest in understanding how the fault mechanism led to the failure. This paper investigate this fault condition in detail and demonstrate the underlying challenges in correcting the failure. The system electrical and thermal models were developed and simulated to analyze the transformer response under double phase fault conditions. Experimental measurements validated the simulation results on a real three phase distribution transformer. This paper presents the results from simulated and experimental analysis from double phase fault on a Yg-Yg distribution transformer.

Arc flash risk assessment for a megawatt scale medium voltage research and testing facility

Arc flash is one of the leading causes of injury and death in electrical work-related incidents. In recent years, arc flash risk mitigation and protection solutions have become the forefront topics in the electrical industry studies. Conventional techniques provide ways to lower incident energy on installed systems but they add to the system limitations. This is a case study which explores arc flash risk assessment process and mitigation techniques used for an operating research facility consisting of 7.5 MW and 15 MW wind turbine mechanical testbeds in addition to a 15 MVA experimental power grid.