Vahan Gevorgian

Understanding inertial and frequency response of wind power plants

The objective of this paper is to analyze and quantify the inertia and frequency responses of wind power plants with different wind turbine technologies (particularly those of fixed speed, variable slip with rotor-resistance controls, and variable speed with vector controls). The fundamental theory, the operating range, and the modifications needed for the wind turbine to contribute to the inertial and primary frequency response during the frequency drop will be presented in this paper. We will demonstrate practical approaches to allow variable slip and speed wind turbines to contribute inertia to the host power system grid. The approaches are based on the inclusion of frequency error and the rate of change of frequency signals in the torque control loop and pitch control actions for wind speeds below and above its rated value. Detailed simulation models in the time domain will be conducted to demonstrate the efficacy of the approaches.

Market Designs for the Primary Frequency Response Ancillary Service—Part I: Motivation and Design

The first part of this two-paper series discusses the motivation of implementing a primary frequency response (PFR) market in restructured pool-based power markets, as well as the market design that would create the right incentives to provide the response reliably. PFR is the immediate, autonomous response of generation and demand to system frequency deviations. It is the critical response required to avoid triggering under- and over- frequency relays or instability that could lead to machine damage, load-shedding, and in the extreme case, blackouts. Currently, in many restructured power systems throughout the world, ancillary services markets have been developed to incent technologies to provide the services to support power system reliability. However, few ancillary services markets include a market explicitly incentivizing the provision of PFR. Historically, PFR was an inherent feature available in conventional generating technologies, and in most systems, more was available than needed. Yet, recent trends in declining frequency response, the introduction of emerging technologies, and market behavior may soon require innovative market designs to incent resources to provide this valuable service.

Short circuit current contribution for different wind turbine generator types

An important aspect of wind power plant (WPP) impact studies is to evaluate the short circuit (SC) current contribution of the plant into the transmission network under different fault conditions. This task can be challenging to protection engineers due to the topology differences between different types of wind turbine generators (WTGs) and the conventional generating units.

Investigating the Impacts of Wind Generation Participation in Interconnection Frequency Response

The electrical frequency of an interconnection must be maintained very close to its nominal level at all times. Excessive frequency deviations can lead to load shedding, instability, machine damage, and even blackouts. There is rising concern in the power industry in recent years about the declining amount of inertia and primary frequency response (PFR) in many interconnections. This decline may continue due to increasing penetrations of inverter-coupled generation and the planned retirements of conventional thermal plants. Inverter-coupled variable wind generation is capable of contributing to PFR and inertia; however, wind generation PFR and inertia responses differ from those of conventional generators, and it is not entirely understood how this will affect the system at different wind power penetration levels. The simulation work presented in this paper evaluates the impact of the wind generation provision of these active power control strategies on a large, synchronous interconnection. All simulations were conducted on the U.S. Western Interconnection with different levels of wind power penetration levels. The ability of wind power plants to provide PFRand a combination of synthetic inertial response and PFRsignificantly improved the frequency response performance of the system. The simulation results provide insight to designing and operating wind generation active power controls to facilitate adequate frequency response performance of an interconnection.

Analysis of permanent magnet generator for wind power battery charging

One type of wind-powered battery charging is explored in this paper. It consists of a wind turbine driving a permanent magnet alternator and operates at variable speed. The alternator is connected to a battery bank via a rectifier. The characteristic of the system depends on the wind turbine, the alternator, and the system configuration. If the electrical load does not match the wind turbine, the performance of the system will be degraded. By matching the electrical load to the wind turbine, the system can be improved significantly. This paper analyzes the properties of the system components. The effects of parameter variation and the system configuration on the system performance are investigated. Two basic methods of shaping the torque-speed characteristic of the generator are presented. The uncompensated as well as the compensated systems are discussed. Control strategies to improve the system performance are explored.

Market Designs for the Primary Frequency Response Ancillary Service—Part II: Case Studies

The second part of this two-paper series analyzes the primary frequency response (PFR) market design developed in its companion paper with several case studies. The simulations will show how the scheduling and pricing change depending on whether requirements for PFR are included as well as how the requirements are defined. We first perform simulations on the base case IEEE RTS and show differences in production costs, prices, and amount of PFR when incorporating the PFR constraints. We show how new market designs can affect other linked markets when performing co-optimization. We then test a system with a significant amount of wind power, which does not provide PFR or synchronous inertia, to see how the incorporation of PFR constraints may become more critical on future systems. We then show how pricing can reduce make-whole payments and ensure resources needed for reliability reasons are incentivized. Lastly, we show how resources that improve their capabilities can earn additional profit if the improvement is needed ensuring the incentives can work for innovation in PFR capabilities.

Achieving a 100% Renewable Grid: Operating Electric Power Systems with Extremely High Levels of Variable Renewable Energy

What does it mean to achieve a 100% renewable grid? Several countries already meet or come close to achieving this goal. Iceland, for example, supplies 100% of its electricity needs with either geothermal or hydropower. Other countries that have electric grids with high fractions of renewables based on hydropower include Norway (97%), Costa Rica (93%), Brazil (76%), and Canada (62%). Hydropower plants have been used for decades to create a relatively inexpensive, renewable form of energy, but these systems are limited by natural rainfall and geographic topology. Around the world, most good sites for large hydropower resources have already been developed. So how do other areas achieve 100% renewable grids? Variable renewable energy (VRE), such as wind and solar photovoltaic (PV) systems, will be a major contributor, and with the reduction in costs for these technologies during the last five years, large-scale deployments are happening around the world.

Interarea Oscillation Damping Controls for Wind Power Plants

This paper investigates the potential for wind power plants (WPPs) to damp interarea modes. Interarea modes may be the result of a single or a group of generators oscillating against another group of generators across a weak transmission link. If poorly damped, these power system oscillations can cause system instability and potentially lead to blackouts. Power conversion devices, particularly, megawatt-scale converters that connect wind turbines and photovoltaic power plants to the grid, could be used to damp these oscillations by injecting power into the system out of phase with the potentially unstable mode. In our model, this power may be provided by a WPP. Over time, the net energy injection is near zero; therefore, providing this static damping capability is not expected to affect the energy production of a WPP. This is a measurement-based investigation that employs simulated measurement data. It is not a traditional small-signal stability analysis based on Eigenvalues and knowledge of the power system network and its components. Kundurs well-known two-area, four-generator system and a doubly fed induction generator (DFIG)-based WPP are modeled in PSCAD/EMTDC. The WPP model is based on the Western Electricity Coordination Council (WECC) standard model. A controller to damp interarea oscillations is added to the WECC DFIG model, and its effects are studied. Analysis is performed on the data generated by the simulations. The sampling frequency is set to resemble the sampling frequency at which data are available from phasor measurement units in the real world. The YuleWalker algorithm is used to estimate the power spectral density of these signals.

Different Factors Affecting Short Circuit Behavior of a Wind Power Plant

A wind power plant consists of a large number of turbines interconnected by underground cable. A pad-mount transformer at each turbine steps up the voltage from generating voltage (690 V) to a medium voltage (34.5 kV). All turbines in the plant are connected to the substation transformer where the voltage is stepped up to the transmission level. An important aspect of wind power plant (WPP) impact studies is to evaluate the short-circuit (SC) current contribution of the plant into the transmission network under different fault conditions. This task can be challenging to protection engineers due to the topology differences between different types of wind turbine generators (WTGs) and the conventional generating units. This paper investigates the short circuit behavior of a wind power plant for different types of faults. The impact of wind turbine types, the transformer configuration, and the reactive compensation capacitor will be investigated. The voltage response at different buses will be observed. Finally, the SC line currents will be presented along with its symmetrical components

Short-circuit modeling of a wind power plant

An important aspect of wind power plant (WPP) impact studies is to evaluate short-circuit current (SCC) contribution of the plant into the transmission network under different fault conditions. This information is needed to size the circuit breakers, to establish the proper system protection, and to choose the transient suppressor in the circuits within the WPP. This task can be challenging to protection engineers due to the topology differences between different types of wind turbine generators (WTGs) and the conventional generating units. This paper investigates the short-circuit behavior of a WPP for different types of wind turbines. The short-circuit behavior will be presented. Both the simplified models and detailed models are used in the simulations and both symmetrical faults and unsymmetrical faults are discussed.