Richard J. Bravo

Load modeling in power system studies: WECC progress update

This paper provides an update on a composite load model development in Western Electricity Coordinating Council (WECC). A composite load model structure is described. The two salient features of the new load model are: (a) the model recognizes electrical distance between the transmission bus and the end-uses and (b) the model represents the diversity in composition and dynamic characteristics of various electrical end-uses. The load model data includes (a) data for a distribution equivalent model, (b) load component model data and (c) load component fractions. The paper presents tests and modeling of various electrical end-uses. The paper in particular focuses on modeling compressor motors in single-phase air-conditioners. Load composition methodology is also discussed. The model structure was implemented and tested in a production-level grid simulator.

Power hardware-in-the-loop testing of a 500 kW photovoltaic array inverter

The testing of a 500 kW photovoltaic array inverter using power hardware-in-the-loop simulation is described. A real-time simulator is used with a DC amplifier in order to emulate a photovoltaic (PV) array and an AC amplifier to emulate a power grid. The test setup is described in detail and a range of tests that were conducted on the inverter are summarized.

The system impact of air conditioner under-voltage protection schemes

This paper presents the results of simulating and evaluating an under-voltage protection scheme, which takes stalled air-conditioner (a/c) units offline so that the slow voltage recovery phenomena can be prevented in areas heavily loaded with a/c motors during summer peak periods. First, a three-feeder test-bed was used to quantify the effectiveness of the protection scheme and the sensitivity of the under-voltage relay settings. Then, two real system events from the Western US power grid were simulated to evaluate the area-level impact of the protection scheme proposed by Southern California Edison. The study demonstrates that after 75% or more of the stalled a/c units are disconnected, the feeder voltage recovers in a few seconds, much quicker than the tens of seconds that standard thermal relays need to trip the stalled motor offline. The drawback is that after the voltage recovered, it settles at a higher value than prior to the faults because a large proportion of load is shed. Therefore, the coordination among the capacitor bank operation is recommended to suppress the overvoltage caused by tripping of the a/c motor load.

Results of residential air conditioner testing in WECC

This paper summarizes the key results of testing work performed by three organizations (EPRI, SCE, and BPA) on a total of twenty seven air conditioning units in order to better understand and thus characterize their behavior for power system simulations. The diversity of the tested air conditioner units included sizes (tonnage), compressor technology (reciprocating and scroll), type of refrigerant (R-22 and R-410A), efficiencies (between 10 and 13 SEER), and vintage (new and old). A common test plan was developed by the three organizations. The tests were then performed independently by each of the three organizations. The EPRI work was sponsored by APS and SRP. This effort was part of the current load modeling effort going on in WECC under the load modeling task force. The key findings of this work are presented here together with a description of the testing methodology. All three organizations found very similar results despite testing a variety of different sizes and manufacturer units. The key results presented are associated with the stalling behavior of the units at different outdoor temperatures, the behavior of thermal overload tripping, contactor dropout, and the behavior of the units in response to different emulated types of system events.

Solar PV inverter testing for model validation

This paper will cover the solar PV inverter tests required for model development and validation including but not limited to voltage transients, frequency deviations, grid disconnection, short circuit, harmonics generation, and voltage oscillations. Additionally, it will cover the test results acquired from our tests of 3-phase 480VAC commercial solar PV inverters. Finally, it will cover proposed recommendations for solar PV inverter performance to accommodate high penetration of solar PV inverter generation.

Fault current contribution from single-phase PV inverters

A significant increase in photovoltaic (PV) system installations is expected to come on line in the near future and as the penetration level of PV increases, the effect of PV may no longer be considered minimal. One of the most important attributions of additional PV is what effect this may have on protection systems. Protection engineers design protection systems to safely eliminate faults from the electric power system. One of the new technologies recently introduced into the electric power system are distributed energy resources (DER). Currently, inverter-based DER contributes very little to the power balance on all but a few utility distribution systems. As DER become prevalent in the distribution system, equipment rating capability and coordination of protection systems merit a closer investigation. A collaborative research effort between the National Renewable Energy Laboratory (NREL) and Southern California Edison (SCE) involved laboratory short-circuit testing single-phase (240 VAC) residential type (between 1.5 and 7kW) inverters. This paper will reveal test results obtained from these short-circuit tests.

Advanced Volt/VAr control element of Southern California Edison's Irvine smart grid demonstration

Southern California Edison is developing a Smart Grid Demonstration project in Irvine California under ARRA funding from the DOE. The project, named the Irvine Smart Grid Demonstration (ISGD) is an integrated deployment of smart grid elements from transmission to the home. Subprojects of the ISGD include 1) Zero Net Energy Homes (ZNE), 2) a Solar Shade EV charging station, 3) Distribution Circuit Constraint Management using Energy Storage, 4) Advanced Volt/VAr Control, 5) Self Healing Circuits, 6) Deep Grid Situational Awareness, 7) Secure Energy Networking, and 8) Workforce of the Future. The demonstration site substation will also host a High Temperature Superconducting Fault Current Limiting Transformer being separately developed by a team headed by Waukesha Electric Systems. This paper describes the Advanced Volt VAr Control (AVVC) element.

Experimental evaluation of the harmonic behavior of LED light bulb

During the recent few years the residential lighting market has completely altered by the introduction of new energy efficient lighting solid state lamps known as LED lamps. This will affect the power distribution grid harmonic behavior under high penetration of these light sources. This paper evaluates the harmonic behavior of different commercially available residential LED light bulbs under different operating conditions. The paper presents the test setup and recommendations for residential LED lights bulbs specification to minimize their impact on the distribution system harmonic distortion. The results database can be used to assess the effect of high penetration of this type of loads on the power quality of the distribution grid and to develop and test the dynamic and electromagnetic transient models for this type of loads.

Fault Induced Delayed Voltage Recovery (FIDVR) indicators

This paper presents Fault Induced Delayed Voltage Recovery (FIDVR) indicators observed before, during and after several events in Southern California. The purpose of this paper is to educate utilities, independent system operators (ISOs), generator owners, customers, equipment manufacturers, and other entities involved with the production, transmission, distribution, and consumption of electricity based on our observations from our own experiences and from our review of the experiences of others. We believe the information in this paper can be used by ISOs for real-time FIDVR identification so that appropriate measures are used to stabilize the system. The observations presented may also be useful to load equipment manufacturers when designing electrical equipment with the capability of riding through these events.

Evaluation of German 3-phase solar PV inverter

This paper provides the test results for a solar photovoltaic (SPV) inverter designed to operate according to German standards. The testing was performed in Southern California Edisons (SCE) Distributed Energy Resources (DER) Laboratory in Westminster, California. The primary reason for testing this inverter is to explore features not used in inverters must comply with U. S, standards. These features include the ability to: communicate, adjust ramp-up power rates, perform voltage ride-through, adjust power factor (PF) based on real power output, inject or absorb reactive power (vars) during voltage deviations, and reduce output real power during over-frequencies. The results detailed here provide information that can be used to develop national standards for advanced features. The test data can also be used for model development and validation to assess grid performance with a high penetration of inverters with these characteristics.