Thomas E. McDermott

An open source platform for collaborating on smart grid research

An open-source distribution system simulator has been developed for distributed resource planning, harmonic studies, neutral-earth voltage studies, volt-var control studies, and other special applications. The software includes several means of interfacing user code, including compiled dynamic link library, COM automation, and text scripting. Co-simulation interfaces are under development for interfacing with proprietary vendor-supplied models, and communication system overlays. The simulator, called OpenDSS, has been used to conduct several smart grid research projects, including advanced automation, electric vehicle penetration, state estimation, and green circuits. The software architecture and solution methods are described, in the effort to foster more collaborative research.

Distributed generation impact on reliability and power quality indices

Properly sited distributed generation (DG) can increase the feeder capacity limit, but this does not necessarily produce an improvement in system reliability or power quality, as quantified by standard indices. The DG may have a positive impact on reliability through faster system restoration following a fault. The DG can also improve reliability for the owner, and may reduce the severity of voltage sags near the DG. Indices normalized to the number of customers dilute these positive benefits. The DG often has a negative impact on reliability indices through sympathetic tripping, required changes to utility overcurrent device settings, and increased fuse blowing. The utility cannot assume DG automatically improves system reliability, and action may be required to ensure that reliability does not actually degrade for other customers.

PQ, reliability and DG

The distributed generation (DG) owners reliability, measured by the sustained interruption indices, should improve markedly if DG has been installed and operated properly. However, because this is just one customer out of hundreds or thousands on the feeder, the improvement does not show up the utilitys traditional reliability indices. There can be a positive or negative impact on the utility-level indices in these cases: DG can reduce the number or the duration of sustained interruptions if automated switches are available to restore power in DG-supplied islands or to DG-supported alternate feeds; the loss of fuse-saving on laterals can significantly degrade the utility-level indices. There is little opportunity for DG to affect the PQ of other customers, as measured by the indices for voltage sags, which are related to faults and interruptions. DG can still have adverse impacts on harmonics and steady-state voltage regulation, which are other aspects of PQ. Utilities should consider tracking ASIFI, ASIDI, and other indices that are based on load size rather than the number of customers. As a supplement to the traditional reliability indices, these would better show the positive impacts of DG, assuming DG owners tend to be larger customers.

Distribution System Analysis to support the Smart Grid

The “Smart Grid” refers to various efforts to modernize the power grid through the application of intelligent devices. This paper describes current thinking by members of the Distribution System Analysis Subcommittee (DSA SC) on how distribution system analysis might evolve to support the Smart Grid. Various issues related to Smart Grid and distribution system analysis are identified. The essential characteristics of distribution system analysis tools to support these issues are discussed. Relevant activities of the DSA SC are described.

Smart inverter settings for improving distribution feeder performance

Photovoltaic (PV) generation is increasingly prevalent throughout power distribution systems. The increased presence of this variable resource can cause adverse impacts to the system due to cloud-induced power output fluctuations. These adverse impacts can be mitigated by allowing PV inverters to absorb and provide reactive power in response to voltage swings. Additionally, properly chosen reactive power response settings can improve distribution feeder metrics such as system losses, number of regulator tap changes, customer consumption, and voltage variability. This paper will assess the impact of smart inverter settings on the performance of a distribution feeder in the United States, identify relationships between suitable settings and feeder variables that may be applicable to other feeders, and show the potential benefit of integrated control.

Roadmap for the IEEE PES test feeders

The Distribution System Analysis Subcommittee (DSAS) of the IEEE PES Power System Analysis, Computing, and Economics Committee has been developing benchmarks for distribution system analysis tools. A number of test cases have already been developed may be easily downloaded on the Internet. Other test cases have been requested. This paper describes the purpose and planned direction for these test cases in the near future. Participation from the power industry is solicited.

A microgrid co-simulation framework

Microgrids have been proposed as a key piece of the Smart Grid vision to enable the potential of renewable energy generation. Microgrids are required to operate in both grid connected and standalone island mode using local sources of power. A major challenge in implementing microgrids is the communications and control to support transition to and from grid connected mode and operation in island mode. Microgrids consists of two interdependent networks, namely; the power distribution and data communication networks. To accurately capture the overall operation of the system, we propose a co-simulation model driven by embedded power controllers. Further, we propose a novel co-simulation scheduler taking into account events from both the power and communication network simulators, as well as the timing of each embedded controllers execution loop to adaptively synchronize both simulators efficiently. The approach ensures minimal synchronization error while still providing the ability to simulate extended operational scenarios. The numerical results illustrate the novelty of the propose co- simulation to study the microgrid power and communication networks interactions, and the effect on the power stability.

Interconnecting single-phase backup generation to the utility distribution system

One potentially large source of underutilized distributed generation (DG) capacity exists in single-phase standby backup gensets on farms served from single-phase feeder laterals. Utilizing the excess capacity would require interconnecting to the utility system. Connecting single-phase gensets to the utility system presents some interesting technical issues that have not been previously investigated. This paper addresses several of the interconnection issues associated with this form of DG including voltage regulation, harmonics, overcurrent protection, and islanding. A significant amount of single-phase DG can be accommodated by the utility distribution system, but there are definite limitations due to the nature and location of the DG. These limitations may be more restrictive than is commonly assumed for three-phase DG installed on stronger parts of the electric distribution system.

Analysis of an offshore medium voltage DC microgrid environment — Part I: Power sharing controller design

The AC microgrid is proposed as a plug-and-play interface for various types of renewable generation resources. The fundamental microgrid requirements include the capability of operating in islanding mode and/or grid connected modes. The high-level technical challenges associated with microgrids include (1) operation modes and transitions that comply with IEEE1547 and (2) control architecture and communication. Proposed control layers and respective functions have been defined in the microgrid literature. These layers include the primary, secondary and tertiary control. In this work, the focus is on the design of a power management secondary control for an offshore DC microgrid serving induction motor drives. The power is managed through a secondary controller to adjust the power delivered through bidirectional DC/DC converters, which intertie with the inverters connected to the machine loads. Simulations in Matlab/Simulink demonstrate the system performance under a mechanical torque step change for one motor drive unit with other conditions fixed. Part I of the concept emphasizes the electrical layout and part II, a communication layout of the offshore platform is described.

Guidelines for high penetration of single-phase PV on power distribution systems

A study was performed to determine the impact of single-phase photovoltaic (PV) generation on distribution laterals at high penetration levels. The study addresses concerns about the impact on load balance, fault current balance, power quality and islanding conditions. Methods and tools used for this study, which are appropriate for general analysis of PV on single-phase laterals, are discussed. Guidelines for the acceptance of single-phase PV connections without detailed study also are presented.