Showing papers by "Juan Carlos Balda published in 2012"

Placement of energy storage coordinated with smart PV inverters

Abstract: Energy storage (ES) is increasing used in electrical transmission and distribution systems because it can perform many functions. These include peak shaving, voltage regulation, frequency regulation, spinning reserve, and aiding integration of renewable generation by mitigating the effects of intermittency. This work focuses on the usage of energy storage for peak shaving and voltage regulation on a distribution system having a high penetration of photovoltaic (PV) generation. The PV stations considered make use of smart PV inverters as proposed by the Electric Power Research Institute (EPRI). These inverters assist the energy storage with voltage regulation. Additionally, the proposed method includes support for varying energy storage unit (ESU) sizes, non-radial distribution systems, and reverse power flow, both real and reactive. The method is applied to the worst-case voltage regulation scenario. The impact of the placement and voltage regulation on the profitability of energy storage is assessed. This is accomplished by adding voltage regulation as a constraint to the problem scheduling energy storage in order to maximize profit. Applying the method shows that the best place to put an ESU is near the end of a feeder. Validation of the method shows that it does not impact the ability of ES to be scheduled in order to maximize economic benefits with time-ofuse pricing.

Selection of converter topologies for distributed energy resources

Abstract: Distributed energy resources (DER) are becoming increasingly common on the electrical grid. Depending on the operating conditions of the DER, which depend on the application, different topologies need to be selected in order to achieve the maximum efficiency of each DER. Complicating the selection is the fact that operating conditions vary over time. For example, the voltage and current drawn from a PV panel varies over the course of a day. To calculate the overall efficiency, the efficiency of a topology at each operating point and the amount of time spent at that operating point must be considered. This work extends existing analytical methods for loss calculations by taking this into account. The specific DER applications considered are a three-phase ultracapacitor energy storage unit (UC-ESU), battery energy storage unit (B-ESU), and photovoltaic array (PV). This work determines for each application if an inverter-only (single-stage) or an inverter plus boost converter (double-stage) topology is more efficient. The results show that a single-stage topology is better for the B-ESU and PV, while the double-stage topology is better for the UC-ESU. The method is applicable to other DER types, including wind turbines, micro-hydro generators, variable-speed gensets, and microturbines.

Smart grid applications of selected energy storage technologies

Abstract: Large-scale energy storage has recently been discussed as part of the future of the smart grid because of the many opportunities for improvement in the reliability and quality of the electric grid that can stem from their use. Information exchange from utility to consumer and vice versa makes it possible to send real-time signals regarding electricity prices and consumption. This enables many applications such as arbitrage, electric reserves, and load following to be served immediately by energy storage systems that are on the grid. For this reason, large-scale energy storage technologies must be implemented that have the ability to serve these applications. This paper examines three energy storage technologies that appear to be well suited for large-scale implementation: sodium-sulfur, vanadium-redox flow batteries, and lithium-ion batteries. These technologies were examined along with many other current technologies and chosen due to the potential to operate at grid-scales. Also, several of their potential applications are discussed.

A unified silicon/silicon carbide IGBT model

Abstract: A new physics-based IGBT compact model has been developed for circuit simulation of silicon (Si) or silicon carbide (SiC) devices. The model accurately predicts the steady-state output, transfer and switching characteristics of the IGBT under a variety of different conditions. This is the first IGBT model to predict the behavior of p-channel SiC IGBTs. Previous work on IGBT models has focused on Si n-channel IGBTs [1]. The unified model is not limited to SiC p-channel IGBTs; the user has the option to select between Si or SiC, and n-channel or p-channel, making it the first IGBT model that captures the physics of all of these device and material types. The model also accounts for temperature effects, often referred to as temperature scaling. The model have been experimentally validated up to 125 °C for silicon and 300 °C for SiC. Validation of n-channel and p-channel devices for both Si and SiC was accomplished by fitting the steady-state characteristics and inductive load switching transient waveforms. 15-kV p-channel IGBTs supplied by Cree were among those used for validation. The fitting was achieved using Certify, a software tool developed at the University of Arkansas. A parameter extraction recipe for the model was developed for simple parameter extraction using data that are readily available from datasheets. That fitting tool is available to the public through the National Center for Reliable Electric Power Transmission website (ncrept.eleg.uark.edu). The model and parameter extraction recipe will also be made available to the public through NCREPT.

A 4 kV Silicon Carbide solid-state fault current limiter

Abstract: Due to increased demand and deployment of new technologies, such as electric vehicles, utilities face increasing fault currents in their systems. As a consequence protection devices must have higher ratings. Replacing existing infrastructure can prove expensive and complicated. Fault current limiters promise an upgrade solution that will mitigate the need for replacing existing breakers to keep fault currents within the ratings of existing protection equipment. SiC offers several key advantages to grid-connected power electronics, such as smaller footprint, faster switching speeds, and simpler cooling systems. This paper describes a 4 kV Silicon Carbide (SiC) fault current limiter that demonstrated the technologies' potential.1

A 6.5kV wire-bondless, double-sided cooling power electronic module

Abstract: A 6.5kV, wire-bondless power electronics module with a double-sided cooling is proposed and evaluated. A direct solder attachment is employed to minimize parasitic circuit elements and increase current handling capability as well as to enable a double-sided cooling capability with mechanical robustness. Finite element simulations were performed to investigate the thermal performance, critical breakdown voltage and mechanical stresses of the power electronic module. The active devices in the proposed modules were demonstrated to withstand a 6.5kV breakdown voltage with a reasonable leakage current. The parasitic inductance is also modeled and compared between wire-bonded and wire-bondless power module. The mechanical and electrical performance of the power module agreed well with simulation results.

An indirect matrix converter for CCHP microturbines in data center power systems

Abstract: Data centers (DCs) are considered critical loads that require premium power from utilities to ensure reliability at all times. Microturbine (MT) generation systems are becoming important in DCs, not only as distributed generation (DG) for supplying electricity, but also for providing cooling and heating functions, which is known as combined cooling, heat and power (CCHP) or tri-generation. This paper considers the use of an indirect matrix converter (IMC) as the power electronic interface (PEI) to connect a permanent magnet synchronous generator (PMSG) with the power grid in a DC. First, the paper analyzes the semiconductor losses for the IMC and the conventional back-to-back converter (BBC) as a function of the switching frequency in order to determine the favorable operating conditions for the IMC. It then presents a new control strategy that does not require measuring the grid voltages to inject the commanded power into the grid at unity power factor. Simulation results of a 15-kVA, 480-Vrms IMC-based MT generation system show the effectiveness of the proposed control technique for this particular application.

Wind farm layout for mitigating output power intermittency

Abstract: The placement of wind turbines (WTs) on a terrain to form a wind farm (WF) has significant impact on the total output power resulting from aggregating the WT powers at the point of common coupling (PCC). Output power intermittency is inherent in a WT as the wind speed invariably changes in intensity and direction. A combination of fast-acting energy storage (ES) and (relative) slow-acting spinning reserve may be used for smoothing the WF total output power when connected to the power grid. ES adds to the WF capital and operating costs. Thus, the main purpose of this paper is to present a simple methodology for evaluating the output power intermittency and ES requirements for a given WF layout. This methodology should minimize the number of WF layouts requiring more complex analysis before final siting. The methodology is illustrated by considering the spatial smoothing effects in three WF layouts having 16 WTs; namely, the straight-line, circular and square layouts. The total harmonic distortion (THD) of the total output power at the PCC when the wind direction varies from 0 to 90 degrees is used as a comparative figure of merit. For the direction with the worst THD, the amount of ES needed to limit the worst-case power ramp is calculated using a first-order approximation of the ES unit. The best layout is the one whose output power characteristic is least affected by changes in the wind direction, and thus, having the lowest THD and requiring the least amount of ES; this is the circular one for the analyzed layouts.

Enhancing power quality on distribution systems with Fault-Current Limiters

Abstract: High levels of power quality are required in electric power systems to ensure safe and continuous operation for most loads. Voltage sags, one of the most critical power quality problems that utilities and customers alike may face, are short voltage-reduction events representing probably one of the main causes of costly shutdowns in companies.

A nano-composite polyamide imide passivation for 10 kV power electronics modules

Abstract: High current and voltage handling capabilities are desired in many high-performance power electronic modules. One of the main challenges when integrating a power module is having a high-voltage insulation material that is reliable at all operating temperatures. In this work, the use of a polyamide imide (PAI) material as the high-voltage passivation for the power electronic modules was investigated. The power modules were integrated with a two-step passivation-encapsulation process using the PAI material. The fabricated modules were tested up to 10 kV to evaluate the material insulation properties.

The modeling and characterization of Silicon carbide gate turn off thyristors

Abstract: Over the past decade Silicon carbide (SiC) power semiconductor devices have shown great promise for next generation power electronic applications. New intelligent systems that will require advanced power electronic circuitry range from electric vehicles to smart grid interfaces. Several devices have been developed for use in these power electronic circuits including diodes, MOSFETs, JFETs, thyristors, gate turn-off thyristors, and IGBTs. The model development, characterization and experimental validation of a SiC p-type Gate Turn-off Thyristor (GTO) is presented in this paper. The developed model is a level-3 physics-based model that predicts on-state and switching behavior with high accuracy. The model also incorporates temperature effects, and accurately predicts device performances from 25 °C to +175 °C. Test configurations were designed to accurately characterize and test an 8 kV ptype SiC GTO provided by Cree. The measured data was used to validate the model's performance.