Santosh Chalise

Impact of Active Power Curtailment of Wind Turbines Connected to Residential Feeders for Overvoltage Prevention

Overvoltage is a major limiting factor for the integration of distributed generation in distribution systems. Among various solutions to the overvoltage problem, active power curtailment is an attractive solution since only small adjustments in the controllers are necessary for implementing this technique. Furthermore, it is activated only when needed. In wind energy systems, this can be achieved by adjusting the pitch angle of a wind turbine. The objective of this paper is to develop an active power curtailment strategy for small wind turbines to prevent overvoltage by controlling the pitch angle of the turbine blades. The required blade pitch angle was calculated by using the voltage droop method. The developed control strategy was validated by a real time simulation of a rural feeder model developed using RT-Lab software. The feeder is based upon a North American rural distribution network consisting of 96 small wind turbines of 20 kW, a 30 MVA distribution substation with an On-Load Tap-Changing transformer, a rural feeder with 288 houses, a 120 kV/25 kV LV transformer, and rural loads. The results show the effectiveness of the method in keeping the voltage within acceptable limits and a reduction in network losses.

Solar Irradiance Forecasting in Remote Microgrids Using Markov Switching Model

Photovoltaic (PV) systems integration is increasingly being used to reduce fuel consumption in diesel-based remote microgrids. However, uncertainty and low correlation of PV power availability with load reduces the benefits of PV integration. These challenges can be handled by introducing reserve. However, this leads to increased operational cost. Solar irradiance forecasting helps to reduce reserve requirement, thereby improving the utilization of PV energy. This paper presents a new solar irradiance forecasting method for remote microgrids based on the Markov switching model. This method uses locally available data to predict one-day-ahead solar irradiance for scheduling energy resources in remote microgrids. The model considers past solar irradiance data, clear sky irradiance, and Fourier basis expansions to create linear models for three regimes or states: high, medium, and low energy regimes for days corresponding to sunny, mildly cloudy, and extremely cloudy days, respectively. The case study for Brookings, SD, USA, discussed in this paper, resulted in an average mean absolute percentage error of 31.8% for five years, from 2001 to 2005, with higher errors during summer months than during winter months.

Power management of remote microgrids considering battery lifetime

xiv CHAPTER 1: INTRODUCTION 1 1.1. Background 1 1.2. Previous work 7 1.2.1. Remote microgrid operation 7 1.2.1.1. Traditional methods 7 1.2.1.2. Schedule and dispatch methods 11 1.2.2. Battery lifetime 15 1.3. Summary of previous work 15 1.4. Motivation 16 1.5. Objectives 16 1.6. Contributions 17 1.7. Dissertation outline 17 CHAPTER 2: THEORY 19 2.1. Remote microgrid components 19

Reducing fuel consumption in microgrids using PV, batteries, and generator cycling

Diesel generators are the most common source of electricity for remote microgrids. Typically, remote microgrids have load profiles with large peak to average ratios which results in frequent operation of the generators at low loading. Generators are most efficient near rated load and operation at low loading results in poor fuel utilization and increased cost. Photovoltaics (PV) can be added to microgrids to reduce the cost of energy but can aggravate the problem of low generator loading. This paper analyses several methods to reduce fuel consumption in microgrids: PV, batteries, and generator cycling. The performance of these methods was evaluated through simulations using the software HOMER and an economic analysis. Results show the effectiveness of PV generator cycling, and batteries to reduce fuel consumption and energy costs.

Day ahead schedule of remote microgrids with renewable energy sources considering battery lifetime

Remote microgrids are a viable option for electrification where the main grid expansion is either impossible or not economical. Typically, remote microgrid consists of diesel generator as a primary source of energy which has a high fuel cost. Renewable energy sources can be used to reduce the fuel consumption with proper coordination and scheduling methods. Storage devices, usually battery, used in remote microgrid are expensive and toxic in nature; therefore battery lifetime is another important parameter to be considered during microgrid scheduling. In this paper, four test cases were developed for the study of fuel consumption. Problems were formulated as mixed integer programming (MIP) and solved using GAMS/CPLEX 12.6 solver. Furthermore, the battery lifetime model was included in the optimization model and fuel consumption was compared with other cases. Results show the slight increment in fuel consumption when the battery lifetime model was included.

Overvoltages in LV rural feeders with high penetration of wind energy

Overvoltage is a major limiting factor for the integration of distributed generation into the grid. This paper, discusses the use of active power curtailment of wind energy systems using pitch angle control and a voltage droop function as means to mitigate the overvoltage problem. This method is validated by a simulation study in PSCAD using typical low voltage rural feeder parameters and 24 hours wind velocity and residential load profiles. Results showed the effectiveness of the method keeping the voltage within acceptable limits.

Data center energy systems: Current technology and future direction

Data centers are becoming a significant energy consumer. Server workload, cooling, and supporting infrastructure represents large loads for the grid. This paper intends to present a comprehensive literature review that account for generation, loads, storage, and topology of data centers. It is shown that green data centers are emerging which incorporate renewable energy sources to cap their carbon footprint. Different data center metrics have been introduced which shows data center efficiency and utilization of resources. Utilization of different power supply topologies and storage to improve the availability, and how various components can play role in energy management to improve the performance of data centers are presented.

Economic analysis of a data center virtual power plant participating in demand response

Data centers represent a large load for the grid, and the number of data centers are increasing at a high rate. The transmission network in the grid is becoming congested as a result of the load growth. Data centers have underutilized energy resources, such as backup generators and battery storage, which can be used for demand response (DR) to benefit both the electric power system and the data center. Therefore, in this paper, data center energy resources, including renewable energy, are aggregated and controlled using an energy management system (EMS) to operate as a virtual power plant (VPP). The data center as a VPP participates in a day-ahead DR program to relieve network congestion and improve market efficiency. A case study is conducted in which the data center is connected to bus 8 of the modified IEEE 30-bus test system to evaluate the potential economic savings by participating in the DR program, coordinated by the Independent System Operator (ISO). We show that the savings of the data center operating as a VPP and participating in the DR program far outweighs the expense due to operating its own generators.

Feasibility study of energy storage technologies for remote microgrid's energy management systems

Energy storage improves system reliability and efficiency in remote microgrid by optimizing the power demand and generation to reduce operational costs. A lead acid battery is widely used as an energy storage device in remote microgrid due to its low cost; however, the response rate, short life cycle and depth of discharge (DoD) lead to high operational costs. Although, the ultracapacitor has considerably longer life cycle, its energy density is low and the initial cost is very high. Lithium-ion and hybrid ion batteries may have comparatively better economical prospective in terms of DoD, life cycle, and operational cost. In this paper, different energy storage technologies are considered for remote microgrid energy management systems. Results showed that the wear cost is an important factor to consider while designing the energy management system.

Operation of datacenter as virtual power plant

Datacenters are becoming a significant energy consumer and ideal candidates to operate as virtual power plant (VPP). In order to provide reliable power, datacenters are provided with on-site generators and large backup resources. These resources are designed to provide power during grid failure, therefore they are underutilized most of the time. In addition, load demand of the datacenter is flexible and the datacenters resources are designed to meet the peak load. Resource use during average load conditions is very low and they remain idle. These characteristics make datacenters ideal candidates for VPP. This paper presents a new method to operate a datacenter as a virtual power plant and participate in the power market. A benchmark for datacenters to operate as VPP was developed and two different cases were analyzed to demonstrate the effectiveness of the proposed method.