Anish Prasai

A new architecture for offshore wind farms

Offshore wind farms using HVDC links can be positioned a large distance from shore, opening up new opportunities for wind generation. Conventional approaches using 60 Hz generators and transformers are not appropriate in such applications, as they are heavy and result in expensive and complex installation and maintenance issues. This paper proposes an alternative architecture for such wind farms, using permanent magnet generators, medium frequency transformers and simple power converters to realize a compact and light system. It is possible that in the long term, the proposed approach may prove attractive for land-based wind farms as well.

Zero Energy Sag Correctors - Optimizing Dynamic Voltage Restorers for Industrial Applications

Plants and processes with a high level of industrial automation are most severely affected by short duration power disturbances. Such plants are most frequently fed from highly reliable utility grids, with measured reliability levels that are consistently in excess of 3 - 5 nines, yet face hours of unscheduled downtime resulting from short duration voltage sags. Extensive data confirms that such plants experience, on an average 30 power disturbances annually, of which over 95% are short duration disturbances lasting on an average no more than 6 cycles. Data also confirms that over 90% of these disturbances are asymmetrical faults. This paper shows a new approach to protecting industrial plants from power disturbances by building on the fact that it is prohibitively expensive to protect against all possible power disturbances, and that cost-effective protection is based on a statistical assessment of disturbances recorded and equipment susceptibility. This paper shows that it is possible to use a new family of zero energy sag correctors to realize protection against over 96-98% of all power disturbances. The paper also develops the design guidelines for such sag correctors, and shows simulation and experimental results for the new DVR system.

Thin AC converters — A new approach for making existing grid assets smart and controllable

Existing techniques for realizing dynamic grid control have involved the use of FACTS devices such as STATCOMs, where the desired functionality is obtained in a single dasiablack-boxpsila device. These devices are deployed in addition to resources that already exist on the grid. This paper proposes a new approach for using dasiathin AC converterspsila to convert existing dasiadumbpsila grid assets into dasiasmart and controllablepsila assets, resulting in significant cost reduction and enhanced asset availability. The technique is seen to be scalable to high power levels, and can convert shunt VAR capacitors into STATCOMs, and can convert load tap changing transformers into dynamic network control devices. New dasiathin AC converterpsila topologies for realizing high-voltage and high-power are detailed along with analysis, control and operating results.

Power Electronics at the Grid Edge : The key to unlocking value from the smart grid

Utilities implementing diverse grid modernization initiatives are observing greater volatility at the grid edge that cannot be managed using traditional electromechanically switched centralized command and control solutions. The decentralized, distributed, and dynamic capabilities required can only be achieved with semiconductor-based power electronics solutions that are deployed appropriately along the grid edge. The key control objective is the fast and granular control of volts and vars at hundreds of points along the feeder, a functionality typically associated with static synchronous compensators (STATCOMs) and unified power flow controllers (UPFCs), albeit in a distributed manner and at lower voltage levels. Several companies are now offering grid-edge power-electronics solutions to solve this new set of challenges, with substantial data from the field validating the benefits that such solutions can provide. This article discusses the challenges, solutions, and some of the results that point to the benefits that power electronics at the grid edge can provide for utilities.

Protection of meshed microgrids with communication overlay

The higher reliability of meshed grids, whether in power or communication, when compared with radial grids is well established. However, while meshed grids provide higher reliability, protection of meshed grids is challenging. In smaller systems such as microgrids, line impedances can be small and many branches may experience approximately the same level of fault current. Locating faults quickly before damage to the equipment and system occurs becomes a non-trivial task and cannot be achieved without communication. This paper discusses a comprehensive scheme for protecting meshed microgrids with multiple levels of protection for redundancy. Power line carrier (PLC) technology is proposed as cost effective and robust means of communication, obviating the need for additional cabling.

Minimizing emissions in microgrids while meeting reliability and power quality objectives

Fossil fuel generators like diesel and natural gas gen-sets are the mainstays of microgrids for reliable power generation. This paper investigates different methods or modes to maximize fuel efficiency of the online generators in a microgrid where a substantial portion of the total generation capacity comes from fossil fuel generators. Energy storage is used to facilitate high efficiency operation of the generators and ensure conformation with the power quality standards and reliability metrics. The methods to maximize fuel efficiency, involving generator scheduling, peak shaving, and power cycling, are discussed. Various case studies are simulated to determine the impact of these three methods or modes on fuel consumption for two particular types of load profiles.

Dynamic Capacitor (D-CAP): An Integrated Approach to Reactive and Harmonic Compensation

Industrial plants are faced with stringent requirements enforced by the utility to meet power factor and power quality requirements. These plants, in order to avoid very costly penalties, have traditionally utilized switchable shunt capacitor banks with detuning reactors for power factor correction, along with a separate active harmonic filter in cases where harmonic currents are an issue as well. Alternate solutions such as SVCs and STATCOMs have been considered to be too expensive for use in industrial power conditioning applications. This paper proposes a dynamic capacitor (D-CAP) based on the family of inverter-less active filters that is able to provide a dynamically controllable capacitance with active harmonic filtering integrated into the same unit. This new device is seen to be compact, and is likely to be cost competitive against simple switched shunt capacitors. It can maintain power factor close to unity, offering dynamic capabilities better than switched capacitors or SVCs, possibly lending itself for arc-furnace type of loads.

Dynamic Var/Harmonic Compensation with Inverter-Less Active Filters

Industrial plants are faced with stringent requirements enforced by the utility to meet power factor and power quality requirements. These plants, in order to avoid very costly penalties, have traditionally utilized switchable shunt capacitor banks with detuning reactors for power factor correction, along with a separate active harmonic filter in cases where harmonic currents are an issue as well. Alternate solutions such as SVCs and STATCOMs have been considered to be too expensive for use in industrial power conditioning applications. This paper proposes a dynamic capacitor (D-CAP) based on the family of inverter-less active filters (ILAF) that is able to provide a dynamically controllable capacitance with active harmonic compensation integrated onto the same unit. This new device is seen to be compact, and is likely to be cost competitive against simple switched shunt capacitors. It can maintain power factor close to unity, offering dynamic capabilities better than switched capacitors or SVCs, possibly lending itself for arc-furnace type of loads.

Optimal placement of Distributed Facts devices in power networks Using Particle Swarm Optimization

The concept of Distributed Flexible AC Transmission Systems (D-FACTS) was introduced in order to provide a cost-effective solution for power flow control. Determining the location and amount of distributed compensation to be employed is an important problem. Proper deployment of DFACTS is necessary for optimal control of the power flow in a large meshed network. Being a distributed solution, DFACTS provides flexibility in terms of deployment. This often makes the problem even more computationally intensive. Recent studies show that Particle Swarm Optimization (PSO) technique gives better results than classical optimization techniques, when applied to power engineering optimization problems. This paper shows the application of PSO for the optimal deployment of DFACTS. The technique is applied on the IEEE 39 bus system. Details of the method and the results obtained are presented in the paper.

Zero-Energy Sag Corrector With Reduced Device Count

Voltage sags are the leading cause of unscheduled downtime in industrial plants with high levels of automation. Zero-energy sag correctors (ZESCs) that utilize energy from those phases that have sufficient remaining voltage on them promise levels of protection that are comparable with conventional energy storage based sag correctors, but in a more compact package. This paper presents a ZESC topology with reduced device count using readily available device packages that can realize similar performance as the original ZESC circuit. The proposed ZESC behaves like a ldquothin AC converter,rdquo and can be integrated with existing assets such as transformers and switchgears. This paper presents details of the operation, design, and experimental results for such a ZESC circuit.