Robert Joseph Broderick

Time series simulation of voltage regulation device control modes

The integration of photovoltaic systems (PV) on distribution feeders may result in unfavorable increases in the number of operations of voltage regulation devices, or may decrease the effectiveness of their settings, resulting in the need for mitigation. Voltage regulation devices commonly use controllers that have time delay settings and sample power system parameters at a high frequency. Quasi-static time series (QSTS) power flow simulation is necessary to properly analyze the impact of distributed PV integration on voltage regulation device operations. It is possible to properly simulate complex control algorithms through a COM interface program, resulting in more realistic and valuable results.

Smart inverter capabilities for mitigating over-voltage on distribution systems with high penetrations of PV

As the penetration level of PV on the distribution system grows, the current injection by PV can create over-voltage issues around the location of the interconnection of PV. Often, the voltage regulation in the feeder is not setup to handle these reverse current flows and inverse feeder voltage profile shape. The PV inverter can be used to absorb or inject reactive power to help negate the voltage change caused by the real power generation. Detailed analysis is performed to investigate the impact of PV output power factor and reactive power on the distribution system voltage. Several reactive control methods are demonstrated in simulation for a real distribution system with coincident high time-resolution measured load and irradiance data.

Improving distribution network PV hosting capacity via smart inverter reactive power support

Many utilities today have a large number of interconnection requests for new PV installations on their distribution networks. Interconnections should be approved in a timely manner but without compromising network reliability. It is thus important to know a networks PV hosting capacity, which defines the upper bound of PV sizes that pose no risk to the network. This paper investigates how implementing reactive power control on the PV inverter impacts the PV hosting capacity of a distribution network. A local Volt-Var droop control is used and simulations are performed in OpenDSS and Matlab. Multiple feeders are tested and it is found that the control greatly improves the overall hosting capacity of the feeder as well as the locational hosting capacity of most voltage constrained buses.

Locational dependence of PV hosting capacity correlated with feeder load

With rising adoption of solar energy, it is increasingly important for utilities to easily assess potential interconnections of photovoltaic (PV) systems. In this analysis, we show the maximum feeder voltage due to various PV interconnections and provide visualizations of the PV impact to the distribution system. We investigate the locational dependence of PV hosting capacity by examining the impact of PV system size on these voltages with regard to PV distance and resistance to the substation. We look at the effect of increasing system size on line loading and feeder violations. The magnitude of feeder load is also considered as an independent variable with repeated analyses to determine the effect on the PV impact analysis. A technique is presented to determine and visualize the maximum capacity for possible PV installations for distribution feeders.

Reduction of distribution feeders for simplified PV impact studies

With increasing connections of distributed rooftop PV to the distribution system, a method for simplifying the complex system to an equivalent representation of the feeder is useful to streamline the interconnection impact studies. This paper presents a method of reducing feeders to specified buses of interest while retaining equivalent electrical characteristics of the system. These buses of interest can be potential interconnection locations or buses where distribution engineers want to evaluate circuit performance. A methodology is presented showing equivalence of the reduction method with supporting equations and examples. Validation is performed for snapshot and time-series simulations with variable load and solar energy to demonstrate equivalent performance of the reduced circuit with the interconnection of PV.

PV interconnection risk analysis through distribution system impact signatures and feeder zones

High penetrations of PV on the distribution system can impact the operation of the grid and may require interconnection studies to prevent reliability problems. In order to improve the interconnection study process, the use of feeder zones and PV impact signatures are proposed to group feeders by allowable PV size as well as by their limiting factors for the interconnection. The feeder signature separates feeders into different impact regions with varying levels of PV interconnection risk, accounting for impact mitigation strategies and associated costs. This locational information improves the speed and accuracy of the interconnection screening process. The interconnection risk analysis methodology is based on the feeder and interconnection parameters such as: feeder type, feeder characteristics, and location and size of PV. PV impact signatures, hosting capacity, and feeder risk zones are demonstrated for four realistic distribution systems.

Analysis of PV Advanced Inverter Functions and Setpoints under Time Series Simulation.

Utilities are increasingly concerned about the potential negative impacts distributed PV may have on the operational integrity of their distribution feeders. Some have proposed novel methods for controlling a PV systems grid - tie inverter to mitigate poten tial PV - induced problems. This report investigates the effectiveness of several of these PV advanced inverter controls on improving distribution feeder operational metrics. The controls are simulated on a large PV system interconnected at several locations within two realistic distribution feeder models. Due to the time - domain nature of the advanced inverter controls, quasi - static time series simulations are performed under one week of representative variable irradiance and load data for each feeder. A para metric study is performed on each control type to determine how well certain measurable network metrics improve as a function of the control parameters. This methodology is used to determine appropriate advanced inverter settings for each location on the f eeder and overall for any interconnection location on the feeder.

Clustering methodology for classifying distribution feeders

The screening process for DG interconnection procedures needs to be improved in order to increase the penetration of PV systems on the distribution grid. A significant improvement in the current screening process could be achieved by finding a method to classify the feeders in a utility service territory and determine the sensitivity of particular groups of distribution feeders to the impacts of high PV deployment levels. This paper presents a method for separating a utilitys distribution feeders into unique clusters using the k-means clustering algorithm. An approach for determining the feeder variables of interest for use in a clustering algorithm is also described. The Cubic Clustering Criterion is used as a quality metric for determining the optimum number of clusters in a large dataset of over 3000 feeders from western utilities. An approach is illustrated for choosing the feeder variables to be utilized in the clustering process and a method is identified for determining the optimal number of representative clusters.

Distribution system low-voltage circuit topology estimation using smart metering data

Operating distribution systems with a growing number of distributed energy resources requires accurate feeder models down to the point of interconnection. Many of the new resources are located in the secondary low-voltage distribution circuits that typically are not modeled or modeled with low level of detail. This paper presents a practical and computational efficient approach for estimating the secondary circuit topologies from historical voltage and power measurement data provided by smart meters and distributed energy resource sensors. The accuracy of the algorithm is demonstrated on a 66- node test circuit utilizing real AMI data. The algorithm is also utilized to estimate the secondary circuit topologies of the Georgia Tech distribution system. Challenges and practical implementation approaches of the algorithm are discussed. The paper demonstrates the computational infeasibility of exhaustive secondary circuit topology estimation approaches and presents an efficient algorithm for verifying whether two radial secondary circuits have identical topologies.

High temporal resolution load variability compared to PV variability

While solar variability has often been quantified and its impact to distribution grids simulated, load variability, especially high-frequency (e.g., 1-second) load variability, has been given less attention. The assumption has often been made that high-frequency load variability is much smaller than PV variability, but with little evidence. Here, we compare load and PV variability using 1-second measurements of each. The impact on voltage regulator tap change operations of using low-resolution (e.g., 15- or 30-minute) interpolated load profiles instead of 1- second is quantified. Our results generally support the assumption that distribution feeder aggregate PV variability is much greater than aggregate load variability.