Olga Lavrova

Small signal stability of the western North American power grid with high penetrations of renewable generation

The goal of this effort was to assess the effect of high penetration solar deployment on the small signal stability of the western North American power system (wNAPS). Small signal stability is concerned with the system response to small disturbances, where the system is operating in a linear region. The study area consisted of the region governed by the Western Electricity Coordinating Council (WECC). General Electrics Positive Sequence Load Flow software (PSLF®) was employed to simulate the power system. A resistive brake insertion was employed to stimulate the system. The data was then analyzed in MATLAB1® using subspace methods (Eigensystem Realization Algorithm). Two different WECC base cases were analyzed: 2022 light spring and 2016 heavy summer. Each base case was also modified to increase the percentage of wind and solar. In order to keep power flows the same, the modified cases replaced conventional generation with renewable generation. The replacements were performed on a regional basis so that solar and wind were placed in suitable locations. The main finding was that increased renewable penetration increases the frequency of inter-area modes, with minimal impact on damping. The slight increase in mode frequency was consistent with the loss of inertia as conventional generation is replaced with wind and solar. Then, distributed control of renewable generation was assessed as a potential mitigation, along with an analysis of the impact of communications latency on the distributed control algorithms.

Evaluation of communication requirements for voltage regulation control with advanced inverters

A central control algorithm was developed to utilize photovoltaic system advanced inverter functions, specifically fixed power factor and constant reactive power, to provide distribution system voltage regulation and to mitigate voltage regulator tap operations by using voltage measurements at the regulator. As with any centralized control strategy, the capabilities of the control require a reliable and fast communication infrastructure. These communication requirements were evaluated by varying the interval at which the controller sends dispatch commands and evaluating the effectiveness to mitigate tap operations. The control strategy was demonstrated to perform well for communication intervals faster than the delay on the voltage regulator (30 seconds). The communication reliability, latency, and bandwidth requirements were also evaluated.

PV System Component Fault and Failure Compilation and Analysis.

This report describes data collection and analysis of solar photovoltaic (PV) equipment events, which consist of faults and failures that occur during the normal operation of a distributed PV system or PV power plant. We present summary statistics from locations where maintenance data is being collected at various intervals, as well as reliability statistics gathered from that data, consisting of fault/failure distributions and repair distributions for a wide range of PV equipment types.

Communication requirements for hierarchical control of volt-VAr function for steady-state voltage

A hierarchical control algorithm was developed to utilize photovoltaic system advanced inverter volt-VAr functions to provide distribution system voltage regulation and to mitigate 10-minute average voltages outside of ANSI Range A (0.95–1.05 pu). As with any hierarchical control strategy, the success of the control requires a sufficiently fast and reliable communication infrastructure. The communication requirements for voltage regulation were tested by varying the interval at which the controller monitors and dispatches commands and evaluating the effectiveness to mitigate distribution system over-voltages. The control strategy was demonstrated to perform well for communication intervals equal to the 10-minute ANSI metric definition or faster. The communication reliability impacted the controller performance at levels of 99% and below, depending on the communication interval, where an 8-minute communication interval could be unsuccessful with an 80% reliability. The communication delay, up to 20 seconds, was too small to have an impact on the effectiveness of the communication-based hierarchical voltage control.

Comparison of electroluminescence image capture methods

In the field of photovoltaics, electroluminescence (EL) imaging has proven useful in determining the degradation of solar panels, primarily through use of expensive equipment within a confined lab setting. This study explored the potential of conducting EL imaging using relatively inexpensive equipment. Factors that heavily influenced the quality of EL images included voltage/current settings for the purpose of forward biasing the test panel, camera settings (aperture, shutter speed, and ISO), and amount of external light (not EL) detected by the camera. Once EL images were captured, the images with the best quality were analyzed and modified through image processing and photo editing. The quality of the final images was then validated through comparison with images captured in a controlled lab with higher quality equipment. Moreover, the results of transporting a solar panel are shown to be clearly observable using low-cost EL imaging.

Reconfigurable photovoltaic integrated with CMOS for a fault tolerant system

For space applications, photovoltaic cells provide the best power to weight ratio than any other power source. But, overexposure to electromagnetic radiations and hostile environment in space can damage the photovoltaic cells. In addition, manual intervention in space is too expensive. These issues can be overcome by making PV module reconfigurable by introducing a MOSFET transistor as a switch in a Photovoltaic module. We are presenting a novel addressable reconfigurable PV module which can be integrated with fault detection and mitigation algorithm. Moreover, such kind of architecture enables the creation of real-time reconfigurable power buses or a power island. Additionally, the architecture can be integrated with PV cells monolithically.

Automatic fault classification of photovoltaic strings based on an in situ IV characterization system and a Gaussian process algorithm

Current-voltage (I-V) curve traces of photovoltaic (PV) systems can provide detailed information for diagnosing fault conditions. The present work implemented an in situ, automatic I-V curve tracer system coupled with Support Vector Machine and a Gaussian Process algorithms to classify and estimate abnormal and normal PV performance. The approach successfully identified normal and fault conditions. In addition, the Gaussian Process regression algorithm was used to estimate ideal I-V curves based on a given irradiance and temperature condition. The estimation results were then used to calculate the lost power due to the fault condition.

Reconfigurable power management for monolithic CMOS-on-Photovoltaic under partial and complete shading

The Photovoltaic (PV) cells of a module can be made to operate in various load and lighting condition by using switches to connect in series or parallel for various load requirements in the field, such as high voltage and low current versus high current and low voltage. Compared to having external switches monolithic CMOS-on-PV cells improves the module efficiency by providing better reliability and lifetime. In this paper, a partial and complete shading detection algorithm is presented. Also, a model for calculating the output current and voltage equation for the monolithic CMOS-on-PV cell is presented.

PV Systems Reliability Final Technical Report: Ground Fault Detection

We have examined ground faults in PhotoVoltaic (PV) arrays and the efficacy of fuse, current detection (RCD), current sense monitoring/relays (CSM), isolation/insulation (Riso) monitoring, and Ground Fault Detection and Isolation (GFID) using simulations based on a Simulation Program with Integrated Circuit Emphasis SPICE ground fault circuit model, experimental ground faults installed on real arrays, and theoretical equations.

Characterization of fire hazards of aged photovoltaic balance-of-systems connectors

Three balance of systems (BOS) connector designs common to industry were investigated as a means of assessing reliability from the perspective of arc fault risk. These connectors were aged in field and laboratory environments and performance data captured for future development of a reliability model. Comparison of connector resistance measured during damp heat, mixed flowing gas and field exposure in a light industrial environment indicated disparities in performance across the three designs. Performance was, in part, linked to materials of construction. A procedure was developed to evaluate new and aged connectors for arc fault risk and tested for one of the designs. Those connectors exposed to mixed flowing gas corrosion exhibited considerable Joule heating that may enhance arcing behavior, suggesting temperature monitoring as a potential method for arc fault prognostics. These findings, together with further characterization of connector aging, can provide operators of photovoltaic installations the information necessary to develop a data-driven approach to BOS connector maintenance as well as opportunities for arc fault prognostics.