Harsha Ravindra

Study of photovoltaic integration impact on system stability using custom model of PV arrays integrated with PSS/E

This paper focuses on the impact of large solar plants on power systems due to rapid variation in power injection caused by various factors such as the intermittency of solar radiation, changes in temperature and tripping out of power electronic based converters connected to the system. In the first step of this research, incorporating the Maximum Power Point Tracking (MPPT) algorithm, a mathematical model of PV (Photovoltaic) array based solar plant has been developed. The model produces changes in DC power output for changes in its two inputs; (1) solar irradiance and (2) temperature. In the next step, the mathematical model is integrated with the dynamic simulation software PSS/E through user written model integration technique. The dynamic model for the inverter and the electrical controller are used from the PSS/E library. The PV plants are added to the 39-bus New England test system at three different locations. To demonstrate a high penetration of PV, the power generation from PV has been increased up to 20% and was randomly distributed between three plants. The dynamic behavior of the system was studied by changing the solar irradiance, tripping of the PV plant and by simulating a three phase fault at PV connected buses. The responses obtained from these studies indicate that vulnerability of the system increases with the increase in penetration of PV power.

Dynamic interactions between distribution network voltage regulators for large and distributed PV plants

This paper summarizes the initial investigation of dynamic interactions of voltage regulating equipment when allowed to act together with one or more large voltage-controlled solar photovoltaic (PV) generation plants. The study results are based on an existing large PV plant and distribution circuit in the service area of a major electric utility. The existing feeder does not have any voltage regulating equipment and the PV plant is not allowed to control voltage, hence injects real power only. However, in light of the growing interest in allowing PV plants to control voltage, several scenarios are considered by allowing PV plants to control the voltage at the Point of Common Coupling (PCC) along with the traditional voltage regulators. Further case studies are performed by distributing the large PV plant into six PV plants of equal power rating connected at different feeder locations. This configuration has been investigated to determine possible differences in interactions of voltage regulators between a large plant and distributed plants. The voltage regulating equipment considered are On-Load Tap-Changing Transformers (OLTC), Switched Capacitor Banks (SCB) and also PV plant inverters capable of controlling the voltage at the PCC. The 12.6 MW (peak a.c.) PV plant and its controls, the regulating equipment, and the distribution network are modeled using a Real Time Digital Simulator (RTDS). Initial study suggests that allowing PV plants to actively participate in the voltage control process requires a coordinated control to minimize the number of operations of traditional voltage regulators.

Impact of PV on distribution protection system

This paper investigates the impacts of PV interconnection on the protection systems of a distribution network, especially when power flow is reversed in high penetration scenarios. A Florida based substation and its six-feeders were selected for the study. The system was slightly modified to make it a notional system that still closely represents the actual system behavior from the point of view of system protection. The main modification is in the representations of loads, where all the loads were represented by fewer aggregated loads on each feeder. One of the feeders is 9 miles long and has a 12.6 MW (AC) PV plant connected to the primary side of the feeder at a distance of 4.8 miles from the substation. The feeder has an average load of approximately 11 MVA that makes it a contender for a high penetration (more than 100%) feeder when PV reaches its peak generation. The model of the entire substation, its feeders and protection system has been built using a high fidelity transient simulation tool RSCAD. Initial simulation results indicate that if protection devices are coordinated properly, a reverse power flow does not create any nuisance trip or malfunction of the protection system. However, based on the location of the PV plant with respect to the fault, slight change in the trip time of the time-overcurrent relays was observed.

Graph traversal-based automation of fault detection, location, and recovery on MVDC shipboard power systems

This paper describes a graph traversal-based method for automating system-wide programming of differential fault protection and generation of fault isolation steps in MVDC shipboard power systems (SPS). Automation is highly desired due to the increased complexity of isolating faults using disconnect switches rather than breakers. The method in this paper describes the derivation of a graph abstraction from the electrical system that is then used for computing a minimal but sufficient isolation sequence consisting of commands issued to breakers and switching converters.

Voltage stability preserving invariants for smart grids

Voltage stability analysis is essential in any power system. This paper addresses the voltage stability in a typical smart grid type system with multiple independent entities. A typical smart grid operation involves various loading excursions (changes in power, both generated and consumed) undertaken by all these independent entities. For a smooth functioning of any generic smart grid type system, correct behavior of all these independent entities must be preserved when one or more of these entities are subjected to various loading levels. Correct behavior of all the entities (sub-systems) will ensure correct behavior of the overall system (smart grid). Invariants, if forced to be true, ensure correct behavior on a subsystem level and thus preserve the overall system correctness. An invariant is a logical predicate on a system state that should not change its truth value if satisfied by system execution [1]. This paper derives an invariant that preserves voltage stability. This invariant is based on an online indicator which is derived from fundamental Kirchhoff s laws and will predict the proximity of voltage collapse at one or more entities in a smart grid. The efficiency of the invariant in predicting voltage collapse has been verified with simulations performed on a typical seven node smart grid system. Thus an online monitoring of the system parameters gives an indication of the system voltage stability. The voltage stability invariant works for both static and dynamic states. This method is also a fast and powerful tool to predict the voltage stability margin of a generic smart grid system by a simple monitoring of the system parameters.

High Penetration Solar PV Deployment Sunshine State Solar Grid Initiative (SUNGRIN)

Disclaimer: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Acknowledgments The work described herein was made possible by the dedication and commitment of the SUNGRIN projects electric utility partners and industry suppliers who provided information on high penetration PV circuits for analysis, valuable input and perspective on real-world issues and challenges, review of project activities and results, and in-kind cost share contributions to completion of the total effort: University partners also played a vital role, particularly in completing the research and analytical work. (UCF) made major contributions in data collection and studies of the solar resource throughout the course of the project, and

Modeling and validation of a utility feeder for study of voltage regulation in the presence of high PV penetration

A Florida utility feeder with a high penetration level of solar photovoltaic (PV) generation was modeled in RTDS/RSCAD. The feeder model was validated by comparing the results in different simulation tools, and using field measurements and short circuit data provided by the utility. The feeder has 2.6 MW of PV which is approximately 30% penetration (comparing with peak load). The feeder has a step voltage regulator (SVR) and 4 switched capacitor banks (SCBs) installed to regulate voltage. Studies were conducted to analyze feeder voltage characteristic for the existing circuit configuration and operating scenarios. Additional studies were conducted to determine the potential impact of additional PV penetration that might happen in the future. Validation results show full agreement with the software based validation and a reasonably acceptable match with the field data collected from different locations on the feeder.

Conversion of PSS®E models into RSCAD models: Lessons learned

The use of real time digital simulation of large power systems is widely spreading due to its high precision result and increasing computing capability. However, in many cases, especially when large power system networks are to be modeled, the interconnection data and parameter data are available in flies which are used as input to simulation programs. Most transmission utilities use dynamic studies using PSS®E, PSLF or similar type of tools. Since most of the system data are available in PSS®E data format, it will be easier to develop an electromagnetic transient model if those data files can be used without putting much effort. Considering the benefit in huge savings in time, RTDS® Technologies Inc. has developed a conversion routine to generate transient model of power system network using the data files available in PSS®E. This paper discusses the conversion process and uses two test cases to verify the accuracy of the conversion tool. IEEE 39 bus test system and a notional 311 bus system were used for this purpose. Both steady state and transient test results of PSS®E and RSCAD model are then compared with each other. This paper also discusses the limitations and challenges of the conversion process, as well as potential solutions. In essence, this study evaluates the accuracy of model conversion from PSS®E to RSCAD for large power systems and highlights the lessons learned from the whole exercise.

Effectiveness of Superconducting Fault Current Limiting Transformers in Power Systems

Superconducting devices have emerged in many applications during the last few decades. They offer many advantages, including high efficiency, compact size, and superior performance. However, the main drawback of these devices is the high cost. An option to reduce the high cost and improve the cost-benefit ratio is to integrate two functions into one device. This paper presents the superconducting fault current limiting transformer (SFCLT) as a superior alternative to normal power transformers. The transformer has superconducting windings and also provides fault current limiting capability to reduce high fault currents. The SFCLT is tested in two power system models: a 7 bus wind farm-based model simulated in PSCAD and on the 80 bus simplified Australian power system model simulated in real-time digital simulator. Various conditions were studied to investigate the effectiveness of the fault current limiting transformer.

Advances to megawatt scale demonstrations of high speed fault clearing and power restoration in breakerless MVDC shipboard power systems

The studies shown in this paper extend the work conducted previously for the megawatt scale demonstration of high speed fault clearing and power restoration in MVDC systems using modular multi-level converters (MMC) and fast disconnect switch. Enhancements were made to the MMC controllers to improve the performance and response times for certain trigger events during fault isolation and re-energization of MVDC systems. The time required for process of fault management, i.e., fault detection, location, isolation and re-energization has been reduced from previously achieved time of 80 ms to less than 25 ms. Moreover, the dynamic performance of the converters has been improved substantially. This work paves the way towards a breaker less architecture with fault clearing times approaching one 60 Hz cycle.