As solar photovoltaic power generation becomes more commonplace, the inherent intermittency of the solar resource poses one of the great challenges to those who would design and implement the next generation smart grid. Specifically, grid-tied solar power generation is a distributed resource whose output can change extremely rapidly, resulting in many issues for the distribution system operator with a large quantity of installed photovoltaic devices. Battery energy storage systems are increasingly being used to help integrate solar power into the grid. These systems are capable of absorbing and delivering both real and reactive power with sub-second response times. With these capabilities, battery energy storage systems can mitigate such issues with solar power generation as ramp rate, frequency, and voltage issues. Beyond these applications focusing on system stability, energy storage control systems can also be integrated with energy markets to make the solar resource more economical. Providing a high-level introduction to this application area, this paper presents an overview of the challenges of integrating solar power to the electricity distribution system, a technical overview of battery energy storage systems, and illustrates a variety of modes of operation for battery energy storage systems in grid-tied solar applications. The real-time control modes discussed include ramp rate control, frequency droop response, power factor correction, solar time-shifting, and output leveling.

Battery Energy Storage for Enabling Integration of Distributed Solar Power Generation

Although wind power as a renewable energy is assumed to be an advantageous source of energy, its intermittent nature causes difficulties especially in the islanding mode of operation. Conventional synchronous generators can help to compensate for wind fluctuations, but the slow behavior of such systems may result in stability concerns. Here, the virtual inertia method, which imitates the kinetic inertia of synchronous generator, is used to improve the system dynamic behavior. Since the proposed method focuses on short-term oscillations and incorporates no long-term power regulation, it needs no mass storage device. Thus, the method is economical. To prevent any additional cost, the rotating mass connected to the DFIG shaft or a super-capacitor connected to the DC-link of a back-to-back inverter of a wind power generator could be used. The concept and the proposed control methods are discussed in detail. Eigen-value analysis is used to study how the proposed method improves system stability. The advantages and disadvantages of using DFIG rotating mass or super-capacitor as the virtual inertia source are compared. The proposed approach also shows that while virtual inertia is not incorporated directly in long-term frequency and power regulation, it may enhance the system steady-state behavior indirectly. A time domain simulation is used to verify the results of the analytical studies.

Implementing Virtual Inertia in DFIG-Based Wind Power Generation

This paper investigates an improved active power control method for variable speed wind turbine to enhance the inertial response and damping capability during transient events. The optimized power point tracking (OPPT) controller, which shifts the turbine operating point from the maximum power point tracking (MPPT) curve to the virtual inertia control (VIC) curves according to the frequency deviation, is proposed to release the “hidden” kinetic energy and provide dynamic frequency support to the grid. The effects of the VIC on power oscillation damping capability are theoretically evaluated. Compared to the conventional supplementary derivative regulator-based inertia control, the proposed control scheme can not only provide fast inertial response, but also increase the system damping capability during transient events. Thus, inertial response and power oscillation damping function can be obtained in a single controller by the proposed OPPT control. A prototype three-machine system containing two synchronous generators and a PMSG-based wind turbine with 31% of wind penetration is tested to validate the proposed control strategy on providing rapid inertial response and enhanced system damping.

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Control of PMSG-Based Wind Turbines for System Inertial Response and Power Oscillation Damping

Accurate state estimation is of paramount importance to maintain normal operations of smart power grids. However, recent research shows that carefully produced attacks with the knowledge of the grid topology, i.e., Jacobian matrix, can bypass the bad data detection (BDD) system. The BDD is used to ensure the integrity of state estimation to filter faulty measurements introduced by device malfunctions or malicious attacks. However, to construct the false data injection attack vectors, a common assumption in most prior works on false data injection attacks is that the attacker has complete knowledge about the power grid topology and transmission-line admittances. By contrast, this paper studies the general problem of blind false data injection attacks using the principal component analysis approximation method without the knowledge of Jacobian matrix and the assumption regarding the distribution of state variables. The proposed attack is proven to be approximately stealthy.
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 The performance of the proposed attack is analyzed. Simulations confirm the performance of the proposed method.

Blind False Data Injection Attack Using PCA Approximation Method in Smart Grid

Creation of a Smart Grid provides utilities and their customers a significant improvement in power reliability and services. To date, Smart Grid has attracted various researchers from different perspectives. This paper presents a review of Smart Grid technologies and its characteristics. An extensive literature review is introduced. One can see variety of problems and challenges in the field of Smart Grid. Hence, this paper can provide a help to find a new research point in this field.

Survey on Smart Grid

As interest in renewable energy continues to gain momentum, use of power electronics in both generation and transmission systems has become increasingly important. One device that has enjoyed much interest as of late is the Battery Energy Storage System. Advancements in battery technology coupled with modern power electronics has resulted in a plethora of possibilities for such systems. This paper provides an overview of battery energy storage systems. It also divulges the views and experiences of one particular manufacturer, General Electric, and its experience with Battery Energy Storage projects. It also discusses some possibilities for future applications including frequency regulation, peak shaving, and integration of renewables.

Utility scale Battery Energy Storage Systems

As system planners consider improvements and/or enhancements to the grid, compatibility with existing devices is a key-determining factor as to the preferred solution. The Variable Frequency Transformer (VFT) has proven itself to be compatible with all types of power system equipment. Through simulations and examples of actual and potential VFT installations, the VFT demonstrates compatibility and in many cases has also shown to enhance the performance of existing devices. This paper will discuss the compatibility of the VFT with traditional grid components like generators and PARs, nearby FACTS devices like STATCOMs, and existing power electronic interconnection technologies including HVDC. Whether a VFT is desired for synchronous or asynchronous power transfer, stability enhancements, or a grid shock absorber, its proven compatibility with the smart grid of the future is assured.

VFT - a smart transmission technology that is compatible with the existing and future grid

Many transmission entities around the world are considering the use of modern synchronous condensers as part of their overall transmission solution. This paper explores the performance characteristics of synchronous condensers and provides reasons why this time-proven technology is now again seen as offering many beneficial characteristics to the transmission grid. Of particular interest are applications in small isolated systems with high penetrations of renewable power sources. Such systems magnify the benefits provided by the synchronous condenser. Another common application involves placement of synchronous condensers electrically near HVDC installations to increase the system short circuit MVA. This paper reports on observations from one particular system that has been studied which involves all of the above situations.

Modern synchronous condenser performance considerations

As wind power achieves higher penetration levels and becomes a more and more substantial portion of our electric energy supply, more stringent requirements are being placed on wind plants. As wind plants displace traditional synchronous generators in terms of percentages, the wind plants must also do their part to maintain stability and reliability of the power system. Modern power electronics are being used in GE's wind offerings to allow wind plants to fulfill the requirements of modern grid codes. A critical component of modern wind generation is the power electronics. The power electronics enable advanced designs and controls that greatly improve the grid integration and functionality of modern wind plants. This paper discusses the GE WindCONTROL*, GE WindINERTIA*, GE WindFREE*, and GE WindRIDE-THROUGH* functions and offers a comparison to traditional thermal or hydro plants.

Facts on grid friendly wind plants

Vermont Electric Power Company recently commissioned a Synchronous Condenser based reactive power device in the Granite substation as part of the Northwest Vermont Reliability Project. The reactive power device consisted of four +25/−12.5 MVAr synchronous condensers and four 25MVAr shunt capacitor banks. This synchronous condenser based reactive power device was chosen over Static Var Compensators or STATCOM. This installation is significant in that it represents the first new conventional synchronous condenser provided by GE for a utility application in more than thirty years. This paper examines the needs surrounding the Granite Substation Reactive Power Device and provides a comparison of the different technologies considered. This paper also discusses both the technical and business reasons why synchronous condenser technology made the most sense in this application.

Paul E. Marken

Papers

Utility scale Battery Energy Storage Systems

VFT - a smart transmission technology that is compatible with the existing and future grid

Modern synchronous condenser performance considerations

Facts on grid friendly wind plants

Selection of Synchronous Condenser technology for the Granite Substation