Philip Irminger

Real and reactive power control of a three-phase single-stage PV system and PV voltage stability

Grid-connected photovoltaic (PV) systems with power electronic interfaces can provide both real and reactive power to meet power system needs with appropriate control algorithms. This paper presents the control algorithm design for a three-phase single-stage grid-connected PV inverter to achieve either maximum power point tracking (MPPT) or a certain amount of real power injection, as well as the voltage/var control. The switching between MPPT control mode and a certain amount of real power control mode is automatic and seamless. Without the DC-to-DC booster stage, PV DC voltage stability is an important issue in the control design especially when the PV inverter is operating at maximum power point (MPP) with voltage/var control. The PV DC voltage collapse phenomenon and its reason are discussed. The method based on dynamic correction of the PV inverter output is proposed to ensure PV DC voltage stability. Simulation results of the single-stage PV system during system disturbances and fast solar irradiation changes confirm that the proposed control algorithm for single-stage PV inverters can provide appropriate real and reactive power services and ensure PV DC voltage stability during dynamic system operation and atmospheric conditions.

Impacts of varying penetration of distributed resources with & without volt/var control: Case study of varying load types

This paper provides a follow-up to an earlier one on impacts of distributed energy resources (DR) on distribution feeders. As DR penetration level on the feeder increases, there can be impacts to distribution system/feeder capacity, line losses, and voltage regulation. These can vary as the penetration level reaches the capacity of the distribution feeder/system or loading. The question is how high of a DR level can be accommodated without any major changes to system operation, system design and protection. Our objective for this work was to address the question of how the DR impacts vary in regards to both DR voltage regulation capability and load mix. A dynamic analysis was used to focus on the impacts of DR with and without volt/var control with different load composition on the distribution feeder. The study considered an example 10MVA distribution feeder in which two inverter-based DRs were used to provide voltage regulation. The results due to DR without voltage regulation capability are compared with DR capable of providing local (at its bus) voltage regulation. The analysis was repeated for four different feeder load compositions consisting of (1) constant power, (2) constant impedance, (3) constant current and (4) ZIP (equal combination of the previous three).

Advanced Energy Storage Management in Distribution Network

With increasing penetration of distributed generation (DG) in the distribution networks (DN), the secure and optimal operation of DN has become an important concern. In this paper, an iterative mixed integer quadratic constrained quadratic programming model to optimize the operation of a three phase unbalanced distribution system with high penetration of Photovoltaic (PV) panels, DG and energy storage (ES) is developed. The proposed model minimizes not only the operating cost, including fuel cost and purchasing cost, but also voltage deviations and power loss. The optimization model is based on the linearized sensitivity coefficients between state variables (e.g., node voltages) and control variables (e.g., real and reactive power injections of DG and ES). To avoid slow convergence when close to the optimum, a golden search method is introduced to control the step size and accelerate the convergence. The proposed algorithm is demonstrated on modified IEEE 13 nodes test feeders with multiple PV panels, DG and ES. Numerical simulation results validate the proposed algorithm. Various scenarios of system configuration are studied and some critical findings are concluded.

The impact of synchronized human activities on power system frequency

It has been demonstrated in previous studies that nation-wide or largely synchronous societal activities have impacts on the power grid frequency responses. This paper investigates NFL Super Bowl games as an example to evaluate the influence of synchronized human activities on the power system using data collected from a wide-area frequency monitoring network (FNET/GridEye). The statistics and plots of several frequency fluctuation phenomena and relevant analysis are presented. Featured characteristics drawn from the frequency data detected during the Super Bowl games are discussed.

Air conditioning stall phenomenon - Testing, model development, and simulation

Electric distribution systems are experiencing power quality issues of extended reduced voltage due to fault-induced delayed voltage recovery (FIDVR). FIDVR occurs in part because modern air conditioner (A/C) and heat pump compressor motors are much more susceptible to stalling during a voltage sag or dip such as a sub-transmission fault. They are more susceptible than older A/C compressor motors due to the low inertia of these newer and more energy efficient motors. There is a concern that these local reduced voltage events on the distribution system will become more frequent and prevalent and will combine over larger areas and challenge transmission system voltage and ultimately power grid reliability. The Distributed Energy Communications and Controls (DECC) Laboratory at Oak Ridge National Laboratory (ORNL) has been employed to (1) test, (2) characterize and (3) model the A/C stall phenomenon.

Design and implementation of real-time off-grid detection tool based on FNET/GridEye

Real-time situational awareness tools are of critical importance to power system operators, especially during emergencies. The availability of electric power has become a linchpin of most post disaster response efforts as it is the primary dependency for public and private sector services, as well as individuals. Knowledge of the scope and extent of facilities impacted, as well as the duration of their dependence on backup power, enables emergency response officials to plan for contingencies and provide better overall response. Based on real-time data acquired by Frequency Disturbance Recorders (FDRs) deployed in the North American power grid, a real-time detection method is proposed. This method monitors critical electrical loads and detects the transition of these loads from an on-grid state, where the loads are fed by the power grid to an off-grid state, where the loads are fed by an Uninterrupted Power Supply (UPS) or a local backup generation system. The details of the proposed detection algorithm are presented, and some case studies and off-grid detection scenarios are also provided to verify the effectiveness and robustness. Meanwhile, how to implement the detection tool in real-time environment and its achievements in detecting off-grid situations are discussed in this paper.

Architecture and implementation of microgrid controller

A microgrid controller, the Complete System-level Efficient and Interoperable Solution for Microgrid Integrated Controls (CSEISMIC), is presented in this paper. The architecture and major components of the microgrid are introduced, followed by a discussion of the functions and implementation of the microgrid controller, including the Energy Management System (EMS) and Supervisory Control and Data Acquisition (SCADA). Testing results are provided to validate and demonstrate the effectiveness of the proposed microgrid controller.

Economic feasibility analysis and operational testing of a community energy storage system

A study of the impact of utility rates on the economic viability of Community Energy Storage (CES) is presented in this paper. Using the U.S. Utility Rate Database, the residential rate structures available at each available zip code in the continental United States were analyzed to see how viable CES is for that zip code. An operational CES hardware system was also tested to verify the results from economic analysis for the specific regions.

Software-defined intelligent grid research integration and development platform

A complication to control schemes is the fact that models can only represent the systems to the fidelity of the model. There is a need for hardware testing which can truly represent the dynamics of the system and the integration of the controls. A flexible and reconfigurable hardware low-power microgrid testbed platform is proposed in this paper for the verification of control schemes, protection and cyber-security. The design of multi-microgrid hardware configuration, shadow network architecture, and data collection and analytics are discussed.

Implementation of system level control and communications in a Hardware-in-the-Loop microgrid testbed

A Hardware-in-the-Loop (HIL) microgrid testbed for the evaluation and assessment of microgrid operation and control is presented in this paper. The HIL testbed is composed of a Real-Time Digital Simulator (RTDS) for modeling of the microgrid, multiple National Instruments (NI) CompactRIOs for Intelligent Electronic Device (IED) control, a prototype Energy Management System (EMS), and a Supervisory Control and Data Acquisition system (SCADA). The implementation of the system level control and communication is described, and testing results are presented to demonstrate the functionality of the proposed HIL microgrid testbed and microgrid controller.