Nga Nguyen

An Analysis of the Effects and Dependency of Wind Power Penetration on System Frequency Regulation

The integration of renewable energy sources into power systems has gathered significant momentum globally because of its unlimited supply and environmental benefits. Within the portfolio of renewable energy, wind power is expected to have a soaring growth rate in the coming years. Despite its well known benefits, wind power poses several challenges in grid integration. The inherent intermittent and non-dispatchable features of wind power not only inject additional fluctuations to the already variable nature of frequency deviation, they also decrease frequency stability by reducing the inertia and the regulation capability. This paper closely examines these effects as well as the effect on tie-line flows and area control error, which causes a larger and longer frequency deviation in the integrated system. Further, the effect of wind power on frequency regulation capability at different penetration levels is also examined. The analytical and simulation results presented here provide some guidance on determining maximum wind power penetration level given a frequency deviation limit.

Estimation of penetration limit of variable resources based on frequency deviation

This paper presents a method to estimate the maximum level of variable energy resources that can be integrated into the grid based on the frequency security constraint. The method described uses the approximation of the frequency deviation extremum based on the sensitivity analysis. The approximated results are then employed to estimate the change of the maximum frequency deviation following the change of inertia and the equivalent regulation constant in the presence of variable energy resources. The frequency security constraint is then used to define the maximum level of variable energy resources penetration. The approximation model has been tested on two test systems and the obtained results are compared with those produced by the simulation. The comparison shows that the proposed method can be utilized to define the maximum level of variable energy resources penetration while securing the stability and reliability of the system without losing notable accuracy.

Reliability of Power System with High Wind Penetration Under Frequency Stability Constraint

This paper presents a new method to evaluate the reliability of a power system with high penetration of wind generation, considering the impact of not only the intermittence but also the low inertia characteristic of wind power. As wind generation gradually replaces conventional generation, the system stability and the reliability are negatively affected. Some of the measures employed to deal with the challenges resulting from increasing wind penetration include operating wind generators at lower levels than their available output and providing inertia so that wind generation is able to contribute to system frequency regulation. Apart from these measures, another factor that limits the amount of wind power that can be absorbed into the grid is the imposition of the frequency standard and this also affects the reliability of the system in the presence of wind penetration. The reliability evaluation approach proposed in this paper is developed using discrete convolution and implemented on an IEEE RTS-79 system with a suitable modification. Power system reliability with and without considering the impacts of wind intermittence and low inertia are compared to show the effectiveness of the proposed method.

Effect of wind power on load frequency control

The integration of wind power into power systems has been gaining momentum in the global energy industry due to its environmental benefits and abundance of supply. However, the natural intermittent and non-dispatchable features of wind negatively impact the systems frequency regulation capability. Wind power not only injects additional fluctuations to the already variable nature of frequency deviation, it also decreases frequency stability by reducing the inertia as well as the regulation capability. This reduction causes the decrease of overall system frequency response characteristic. These effects of wind integration will be examined closely in this paper. In addition, the effect of wind power on tie-line power flows and area control error will be investigated. The analytical and simulation model of load frequency control are utilized to show the impact of wind on system frequency regulation. Additionally, a range of wind penetration levels is considered to determine the maximum wind power penetration level given a frequency deviation limit.

A unified analysis of the impacts of stochasticity and low inertia of wind generation

This paper proposes a new method to model wind generation in power system reliability evaluation that not only considers the uncertainty of wind speed and mechanical failures of wind turbines but also includes the impacts of winds low inertia property. Due to the stochasticity and low inertia of wind generation, power system stability and reliability are significantly affected. When wind generators are integrated into the grid, a strategy to ensure the system stability is that wind generators are required to operate at a lower level than their maximum available output power. The effect of this requirement is that not all of the available wind power will be used in the system, which in turn affects the contribution of wind generation in power system availability. The proposed model is implemented using Monte Carlo methods. For every system state, the maximum integrated amount of wind power is determined based on frequency regulation requirements. Then, this amount of power is used along with the stochastic model of wind speed in the reliability modeling. The proposed method is demonstrated on the IEEE RTS system. Power system reliability with and without considering the impacts of wind stochasticity and low inertia are compared to show the effectiveness of the proposed method.

A visualization tool for real-time dynamic contingency screening and remedial actions

This paper proposes a real-time visual interactive transient stability screening and remedial action tool that uses an approach based on Lyapunov functions to enable the selection of appropriate remedial actions that stabilize power systems due to large disturbances and cascading failures. At present, there is no effective tool that enables making a well-informed choice from amongst a profusion of remedial action alternatives. Conventionally, transient stability analysis of power system is performed offline to assess the capability of the power system to withstand specific disturbances and to investigate the dynamic response of the power system as the network is restored to normal operation. In this paper, postfault stable and controlling unstable equilibrium points are determined using a homotopy-based approach. Subsequently, stability assessment of the system and the corresponding potential remedial actions are determined from the equilibrium points of the system dynamical model. The real-time transient stability analysis and remedial action algorithm are incorporated with the visualization tool to facilitate interactive decision making in real time. The transient stability analysis and remedial action algorithm, and the visualization tool are demonstrated on several test systems including the equivalent Western Electricity Coordinating Council system and the simplified New England 39 bus test system.

Environmental-economic dispatch of power system in the presence of wind generation

The presence of wind generation with intermittent and low inertia features increases the need for modification in power system operation and planning. One of the main problems of wind integration is the effect of wind on system frequency. This paper addresses the environmental-economic generation dispatch of the wind integrated system while considering the frequency stability condition as a constraint in the optimization problem. The proposed frequency stability constraint is represented by the minimum inertia required to keep the frequency deviation within a safe limit. A non-dominated sorting genetic algorithm II is utilized to investigate the multi-objective generation dispatch problem in the presence of stability constraint. Environmental-economic generation dispatch will be examined on the modified IEEE 30-bus system to demonstrate the impact of the proposed idea.

Cost benefit analysis for wind power penetration

Wind power has become a candidate to replace some or part of the conventional generation to meet the continually increasing electricity demand. Yet, the stochastic nature of the wind speed and the rapid changes of wind turbine output increases the complexity of planning and operation of power systems. In this paper, a cost benefit analysis is developed for measuring the benefits of integrating wind farms with the grid. The analysis considers both the dynamic operations and the reliability of the system. The dynamic operation of the system is considered to be the economic cost and the environmental impact. Both categories are converted to one, using market prices for emission levels. The system reliability is assumed to be a disjoint objective and is evaluated separately, and then the economic impact for the reliability is evaluated using the expected damage cost (EDC). The system analysis for the dynamic operation is performed over the yearly load profile on the IEEE RTS-79 system, with an hourly output of wind. The results for the system reliability and the environmental-economic dispatch are presented, and the performance for different wind penetration at different buses is analyzed and discussed.

Energy storage to improve reliability of wind integrated systems under frequency security constraint

The integration of wind power into the grid causes numerous stability and reliability issues due to its low inertia and intermittent nature. To ensure system stability, wind power production has to be restricted, which implies that the system cannot absorb the entire output available from wind generation, especially if the output is high. Consequently, the reliability of the integrated system is adversely affected. In order to improve the system reliability, energy storage can be used, which is emerging as a prominent solution for enhancing supply continuity. The complete utilization of an energy storage device can be achieved if it is properly coordinated with wind and conventional generation. This paper proposes a new method to coordinate energy storage with the existing system to improve the system reliability while maintaining the system frequency security. The effectiveness of the model is demonstrated on the IEEE RTS-79 system.

A Visualization Tool for Real-Time Dynamic Contingency Screening and Remedial Actions

This paper proposes a real-time visual interactive transient stability screening and remedial action tool that uses an approach based on Lyapunov functions to enable the selection of appropriate remedial actions that stabilize power systems due to large disturbances and cascading failures. At present, there is no effective tool that enables making a well-informed choice from amongst a profusion of remedial action alternatives. Conventionally, transient stability analysis of power system is performed offline to assess the capability of the power system to withstand specific disturbances and to investigate the dynamic response of the power system as the network is restored to normal operation. In this paper, postfault stable and controlling unstable equilibrium points are determined using a homotopy-based approach. Subsequently, stability assessment of the system and the corresponding potential remedial actions are determined from the equilibrium points of the system dynamical model. The real-time transient stability analysis and remedial action algorithm are incorporated with the visualization tool to facilitate interactive decision making in real time. The transient stability analysis and remedial action algorithm, and the visualization tool are demonstrated on several test systems including the equivalent Western Electricity Coordinating Council system and the simplified New England 39 bus test system.