Thermal effect of wind generation on conventional generator in a microgrid

In order to reduce CO2 emissions, which is one of the key strategy in combatting global warming, development of wind energy technology as source of renewable energy has become more important globally. However, the variability of the wind speeds leads to the intermittent nature of wind power generation. The conventional generators in the system must be able to compensate this fluctuation to maintain system stability and meet the load demand in the grid. This in turn may increase the temperature of the conventional generators beyond what normally occurs without wind generation in the grid. The aim of the paper is to inestigate the effect of thermal heating of the generators due to the variable output of wind generation in different time of the year in a microgrid by proposing proper modelling in the simulation. The simulations are done in 24 hours period in four different time of the years corresponding to different seasons of the year

Non-intrusive monitoring algorithm for resident loads with similar electrical characteristic

Non-intrusive load monitoring is a vital part of an overall load management scheme. One major disadvantage of existing non-intrusive load monitoring methods is the difficulty to accurately identify loads with similar electrical characteristics. To overcome the various switching probability of loads with similar characteristics in a specific time period, a new non-intrusive load monitoring method is proposed in this paper which will modify monitoring results based on load switching probability distribution curve. Firstly, according to the addition theorem of load working currents, the complex current is decomposed into the independently working current of each load. Secondly, based on the load working current, the initial identification of load is achieved with current frequency domain components, and then the load switching times in each hour is counted due to the initial identified results. Thirdly, a back propagation (BP) neural network is trained by the counted results, the switching probability distribution curve of an identified load is fitted with the BP neural network. Finally, the load operation pattern is profiled according to the switching probability distribution curve, the load operation pattern is used to modify identification result. The effectiveness of the method is verified by the measured data. This approach combines the operation pattern of load to modify the identification results, which improves the ability to identify loads with similar electrical characteristics

Reactive power control of DFIG wind turbines for power oscillation damping under a wide range of operating conditions

This study analyses the effect of replacing existing synchronous generators (SGs) equipped with power system stabilisers (PSS) by doubly fed induction generator (DFIG) based wind farms on the damping of power system oscillations in a multi-machine power system. A power system stabiliser was designed to enhance the capability of DFIG to damp power systems oscillations. The validity and effectiveness of the proposed controller are demonstrated on the widely used New England 10-machine 39-bus test system that combines conventional SGs and DFIG based wind farms using eigenvalue analysis and non-linear simulation. The non-linear simulation is used to demonstrate how the damping contribution of DFIG based wind farms is affected by different operating conditions within the same wind farm and stochastic wind speed behaviour. The results show that installing conventional fixed parameters PSS within reactive power control loop of DFIG rotor side converter has a positive damping contribution for a wide range of operating conditions. Furthermore, the results clearly show that DFIG based wind farms equipped with the proposed farm level PSS can damp power system oscillations more effectively than SGs PSS

Impacts of high penetration of DFIG wind turbines on rotor angle stability of power systems

With the integration of wind power into power systems continues to increase, the impact of high penetration of wind power on power system stability becomes a very important issue. This paper investigates the impact of doubly fed induction generator (DFIG) control and operation on rotor angle stability. Acontrol strategy for both the rotor-side converter (RSC) and grid-side converter (GSC) of the DFIG is proposed to mitigate DFIGs impacts on the system stability. DFIG-GSC is utilized to be controlled as static synchronous compensator (STATCOM) to provide reactive power support during grid faults. In addition, a power system stabilizer (PSS) is implemented in the reactive power control loop of DFIG-RSC. The proposed approaches are validated on a realistic Western System Coordinating Council (WSCC) power system under both small and large disturbances. The simulation results show the effectiveness and robustness of both DFIG-GSC control strategy and PSS to enhance rotor angle stability of power system

Power oscillation damping capabilities of doubly fed wind generators

With the increased levels of wind power penetration into power systems, the influence of wind power on stability of power systems requires more investigation. Conventional synchronous generators are increasingly replaced by wind turbines and thus wind turbines have to contribute to power system stability. In this paper, the effects of double fed induction generator (DFIG) based wind farms and their controllers on small signal stability are investigated. Moreover, since wind turbines have to contribute to power system oscillation damping, a power oscillation damping controller within DFIG rotor side converter is developed in this study. The proposed damping control is validated on realistic Western System Coordinating Council (WSCC) power system consisting of DFIG based wind farm and synchronous generators. The simulation results show the effectiveness of the proposed power oscillation damping controller. With the proposed controller, DFIG based wind farm improves the system small signal stability dramatically by damping the system oscillations effectively

Impact of DFIG based offshore wind farms connected through VSC-HVDC link on power system stability

With the increased levels of offshore wind power penetration into power systems, the impact of offshore wind power on stability of power systems require more investigation. In this paper, the effects of a large scale doubly fed induction generator (DFIG) based offshore wind farm (OWF) on power system stability are examined. The OWF is connected to the main onshore grid through a voltage source converter (VSC) based high voltage direct current (HVDC) link. A large scale DFIG based OWF is connected to the New England 10-machine 39-bus test system through a VSC-HVDC. One of the synchronous generators in the test system is replaced by an OWF with an equivalent generated power. As the voltage source converter can control the active and reactive power independently, the use of the onshore side converter to control its terminal voltage is investigated. The behaviour of the test system is evaluated under both small and large grid disturbances in both cases with and without the offshore wind farm

Modelling the impact of social network on energy savings

It is noted that human behaviour changes can have a significant impact on energy consumption, however, qualitative study on such an impact is still very limited, and it is necessary to develop the corresponding mathematical models to describe how much energy savings can be achieved through human engagement. In this paper a mathematical model of human behavioural dynamic interactions on a social network is derived to calculate energy savings. This model consists of a weighted directed network with time evolving information on each node. Energy savings from the whole network is expressed as mathematical expectation from probability theory. This expected energy savings model includes both direct and indirect energy savings of individuals in the network. The savings model is obtained by network weights and modified by the decay of information. Expected energy savings are calculated for cases where individuals in the social network are treated as a single information source or multiple sources. This model is tested on a social network consisting of 40 people. The results show that the strength of relations between individuals is more important to information diffusion than the number of connections individuals have. The expected energy savings of optimally chosen node can be 25.32% more than randomly chosen nodes at the end of the second month for the case of single information source in the network, and 16.96% more than random nodes for the case of multiple information sources. This illustrates that the model presented in this paper can be used to determine which individuals will have the most influence on the social network, which in turn provides a useful guide to identify targeted customers in energy efficiency technology rollout programmes

Coordination of PSSs and SVC damping controller to improve probabilistic small-signal stability of power system with wind farm integration

A modified fruit fly optimization algorithm (MFOA) combined with a probabilistic approach are proposed in this paper to coordinate and optimize the parameters of power system stabilizers (PSSs) and static VAR compensator (SVC) damping controller for improving the probabilistic small-signal stability of power systems with large-scale wind generation, taking into consideration the stochastic uncertainty of system operating conditions. It is generally accepted that there is a threat to the stability of power system with penetration of wind farm. In addition, the stochastic fluctuations of wind generation make PSSs tuning more difficult. In this paper, PSSs and SVC damping controller are employed for suppressing local and inter-area low frequency oscillation. In order to eliminate the adverse effect between PSSs and SVC damping controller, the MFOA based on the probabilistic eigenvalue is applied to coordinate and optimize their parameters. The effectiveness of the proposed approach is verified on two test systems

Microwave and Millimeter Wave Techniques

Contains reports on four research projects.Joint Services Electronics Program (Contract DAAB07-74-C-0630)National Science Foundation (Grant MPS-73-05043-A01

Radio Astronomy

Contains reports on four research projects.National Aeronautics and Space Administration (Grant NGL 22-009-016)National Aeronautics and Space Administration (Grant NGR 22-009-421)National Science Foundation (Grant GP-20769)National Science Foundation (Grant GP-21348)California Institute of Technology Contract 952568Sloan Fund for Basic Research (M. I. T. Grant 241