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Phasor-based interdependencies of multiple harmonic sources, especially Distributed Energy Resources, on distribution networks are analyzed in this paper. A new index, Phasor Harmonic Index (IPH), is proposed by the authors. IPH considers both harmonic source magnitude and phase angle for different harmonic orders. Other commonly used harmonic indices are based solely on magnitude of waveforms. A very detailed model of a distribution network is used in the harmonic assessment. With the help of the detailed distribution network model, the phase couplings and the phase balancing impacts on harmonic propagation between three phases are investigated. Moreover, effects of harmonic source phase angle deviations are analyzed at both the customer side and the substation side. This paper investigates the importance of phase angles in harmonic assessment and how distribution network characteristics can be analyzed appropriately with phasor-based harmonic studies. In addition to device level harmonics, system level harmonic propagation need to be considered.

California is striving to achieve 33% renewable penetration by 2020 in accordance with the state’s Renewable Portfolio Standard (RPS). The behavior of renewable resources and electric vehicles in distribution systems is creating constraints on the penetration of these resources into the distribution system. One such constraint is the ability of present-­‐‑day voltage management methodologies to maintain proper distribution system voltage profiles in the face of higher penetrations of PV and electric vehicle technologies. This white paper describes the research gaps that have been identified in current Volt/VAR Optimization and Control (VVOC) technologies, the emerging technologies which are becoming available for use in VVOC, and the research gaps which exist and must be overcome in order to realize the full promise of these emerging technologies.

Presented paper – COMPENG 2010: Complexity in Engineering

A presentation for the i4Energy Seminar Series for Spring 2011, February 4, 2011, UC Berkeley, Berkeley, California

Developed and conducted a demonstration of two real-time software tools to provide a grid operator a display of information and alarms from a network of phasor monitoring units and analysis of voltage security. Performed a scoping study that examined and prioritized options for data collection to improve the load and generator models used by CAISO and its control member utilities.

In this paper, we illustrate the effect of adding a hypothetical 100-MW doubly fed induction generator (DFIG) wind power plant to a weak transmission system. The effects of various wind plant load factors (100, 60 and 25 % of nameplate rating) are investigated. System performance is compared to a 100-MW conventional synchronous generator interconnected at the same location. The conventional generator is installed some distance away. The simulations demonstrated that DFIG generators provide a good damping performance under these conditions. These results support the conclusion that modern wind power plants, equipped with power electronics and low-voltage ride-through capability, can be interconnected to weak power grids without reducing stability. To conduct the studies, we selected an area of the Western Electricity Coordinating Council power system that is electrically far from major generation centers and is weakly connected to the bulk transmission system. The area contains large motor loads. We observed the dynamic response of large motors in the vicinity, especially their ability to ride through fault events. The studies were conducted using positive sequence phasor time-domain analysis. Index Terms--Low voltage ride through, power system, renewable energy, stability, variable-speed generation, weak grid, wind energy, wind farm, wind power plant, wind turbine.

Renewable-energy systems that are under development need a simulation-based analysis to ensure system stability, power quality, and reliability. Such an analysis may reveal design modifications that need to be made before the system is implemented in the field. The modular simulator RPM-Sim, available on the National Renewable Energy Laboratory Web site (http://wind.nrel.gov/designcodes/simulators/rpmsim/), facilitates a low-cost application-specific study of the dynamics of the wind-solar-diesel hybrid power systems. This paper discusses the principal modules of the simulator and provides several examples of a simulation-based analysis of the renewable-energy systems. These examples illustrate the importance of a simulation-based study of the grid-connected and stand-alone or autonomous systems. The RPM-Sim is open-ended and can be easily expanded. Index Terms--Modeling and simulation of power systems, peak-power tracker (PPT), renewable-energy systems, stiff grid, water pumping, weak grid, wind-farm aggregation.

We analyzed a power system network that consisted of two types of power generation: wind turbine generation and diesel generation. The power quality and the interaction of diesel generation, the wind turbine, and the local load were the subjects of investigation. From an energy-production standpoint, producing as much wind energy as possible is advantageous in terms of decreasing the fuel consumption of the diesel engines and reducing the level of pollution. From the customer point of view, good power quality at the receiving end is important. The purpose of this paper is to show the impact of the wind power plant on the entire system. In addition, we discuss how the startup of the wind turbine and the transient condition during load changes affect the system's voltage and frequency. Index Terms--Diesel generator, hybrid power system, power quality, renewable energy, wind turbine.

Permanent-magnet (PM) generators have been used for wind turbines for many years. Many small wind-turbine manufacturers use direct-drive PM generators. For wind-turbine generators, the design philosophy must cover the following characteristics: low cost, light weight, low speed, high torque, and variable-speed generation. The generator is easy to manufacture and the design can be scaled up for a larger size without major retooling. A modular PM generator with axial flux direction was chosen. The permanent magnet used is NdFeB or ferrite magnet with flux guide to focus flux density in the air gap. Each unit module of the generator may consist of one, two, or more phases. Each generator can be expanded to two or more unit modules. Each unit module is built from simple modular poles. The stator winding is formed like a torus. Thus, the assembly process is simplified and the winding insertion in the slot is less tedious. We built a prototype of one unit module and performed preliminary tests in our laboratory. Follow-up tests will be conducted in our laboratory to improve the design. Index Terms - Axial flux, modular generator, permanent magnet, wind energy.

To optimize the operation of a wind turbine, variable turbine speeds are desirable. To determine the advantages of a variable-speed turbine, the annualized energy production of the turbine needs to be considered. This is done by using a Rayleigh probability distribution to determine the number of hours of a particular wind speed which occur in a given year. This distribution is used with the aerodynamic power generated at a given average wind speed to determine the total energy generated during the year. The total energy for fixed- and variable-speed turbine control are compared. The variable-speed turbines show improved energy production over the constant-speed systems. Index Terms - Variable speed, wind energy, wind turbine.

The application of photovoltaics (PV's) has been increasingly popular, especially in remote areas, where power from a utility is not available or is too costly to install. PV-powered water pumping is frequently used for agriculture and in households. Among many available schemes, the system under study consists of a PV array, a variable-frequency inverter, an induction motor, and a water pump. The inverter feeds the induction motor, which drives the water pump. To seek the optimum power output of the PV array, the inverter is operated at variable frequency, to vary the output of the water pump. The inverter is operated to generate a six-step quasi-square wave, instead of a pulsewidth modulated (PWM) voltage output, to reduce the switching losses. The inverter acts as both a variable-frequency source and a peak-power tracker of the system, thus, having the number of switches minimized. The system is a low-cost design, with a simple control strategy. The dc bus is supported by a dc capacitor; thus, a balance-of-power flow must be maintained to avoid the collapse of the dc-bus voltage. Another advantage of the system is that the current is limited to an upper limit of the PV-array current. Thus, in case a short circuit is developed, the motor winding and the power semiconductor switches can be protected against excessive current flow. Index Terms - Peak-power tracker, photovoltaic, PV array, renewable energy, village electrification, water pumping.

This paper proposes a new series compensated induction generator/battery supply topology which provides a constant voltage and frequency at the terminals, allowing minimum current harmonic distortion while at the same time providing a source and sink of real and reactive power. With appropriate control of the reactive power, the speed of the generator is allowed to vary within a relatively wide range. This technique can be further expanded by applying ac capacitors in parallel with the load to lessen the burden of the PWM inverter. Both simulation and experimental results are in agreement with the theory which leads to the conclusion that the system could be feasible for isolated power generation systems (wind, hydro, diesel, or hybrid generation).

The most common practice for starting a single-phase induction machine (SPIM) is to install a starting capacitor in series with the auxiliary winding. In some applications, two capacitors are used. One is used during the starting period to help create the starting torque. The other one is used during the running condition to improve efficiency. This paper discusses the possibility of using an electronic switch in parallel with the running capacitor, thereby providing the equivalent of a starting capacitor. The capacitor is shorted during each cycle to vary the effective size of the ac capacitor. By using this method, only one capacitor is used for both the starting and running condition, and a similar starting performance can be obtained when compared with the conventional method using two capacitors.