There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

On robust estimation of the location parameter

In the world, wind power is rapidly becoming a generation technology of significance. Unpredictability and variability of wind power generation is one of the fundamental difficulties faced by power system operators. Good forecasting tools are urgent needed under the relevant issues associated with the integration of wind energy into the power system. This paper gives a bibliographical survey on the general background of research and developments in the fields of wind speed and wind power forecasting. Based on the assessment of wind power forecasting models, further direction for additional research and application is proposed.

A review on the forecasting of wind speed and generated power

http://pierrepinson.com/31761/Literature/foley2012.pdf

Current methods and advances in forecasting of wind power generation

In this paper we present a new approach to detect, localize, and investigate the feasibility of classifying various types of power quality disturbances. The approach is based on wavelet transform analysis, particularly the dyadic-orthonormal wavelet transform. The key idea underlying the approach is to decompose a given disturbance signal into other signals which represent a smoothed version and a detailed version of the original signal. The decomposition is performed using multiresolution signal decomposition techniques. We demonstrate and test our proposed technique to detect and localize disturbances with actual power line disturbances. In order to enhance the detection outcomes, we utilize the squared wavelet transform coefficients of the analyzed power line signal. Based on the results of the detection and localization, we carry out an initial investigation of the ability to uniquely characterize various types of power quality disturbances. This investigation is based on characterizing the uniqueness of the squared wavelet transform coefficients for each power quality disturbance.

Power quality assessment via wavelet transform analysis

By adding a variable external resistance to the rotor of an induction generator used in a wind turbine, it is possible to manipulate the torque-speed curve and control the output power. The hardware implementation is accomplished by a set of three-phase external resistors connected in series with the rotor windings. To vary the effective value of the external resistance, a three-phase diode bridge and a DC chopper with a variable duty cycle is commonly used. Thus, the wind turbine generator operates at variable slip above synchronous speed. This method is less flexible than a doubly-fed induction generator, but does not require the use of slip rings to access the rotor circuit. This paper describes the construction of a time-domain electromechanical model for a wind turbine. The model is used to evaluate control strategies for the output power based on stator power, the equivalent circuit, or aerodynamic torque. All are capable of maintaining a constant power beyond rated wind speed. The transient performance of the controllers is also compared and control based on the aerodynamic torque is found to be the fastest, albeit with high transient power deviations.

Variable rotor-resistance control of wind turbine generators

Power quality monitoring has expanded from a means to investigate customer complaints to an integral part of power system performance assessments Besides special purpose power quality monitors, power quality data are collected from many other monitoring devices on the system (intelligent relays, revenue meters, digital fault recorders, etc) The result is a tremendous volume of measurement data that is being collected continuously and must be analyzed to determine if there are important conclusions that can be drawn from the data It is a significant challenge due to the wide range of characteristics involved, ranging from very slow variations in the steady state voltage to microsecond transients and high frequency distortion This paper describes some of the problems that can be evaluated with both oine and online analyses of power quality measurement data These applications can dramatically increase the value of power quality monitoring systems and provide the basis for ongoing research into new analysis and characterization methods and signal processing techniques

/pdf/challenges-and-trends-in-analyses-of-electric-power-quality-5fx5mf02tp.pdf

Challenges and trends in analyses of electric power quality measurement data

Traditional impedance-based fault-locating methods implemented in modern overcurrent protection relays require voltage and current measurements to provide reasonable fault-location estimates. Although they capture voltage and current, depending on field condition or due to equipment failure, relays may record current measurements only. Voltage measurements are thus missing or unavailable. The objective of this paper is to develop practical impedance-based fault-locating algorithms with current data (magnitude or phasors) as the only input and demonstrate the efficacy of the algorithms with simulated and actual field data. These algorithms use the circuit model of the distribution feeder and Kirchhoff's circuit laws in estimating the fault voltage at the relay location and then use impedance-based methods for fault location. Based on the analysis conducted on actual fault data, error in estimation is generally less than 0.5 mi from the actual location of the fault.

Distribution Fault-Locating Algorithms Using Current Only

In recent years, voltage and reactive power control in distribution systems is becoming increasingly complex with the growing penetration levels of distributed energy resources (DER), electric vehicle loads, and new requirements like conservation voltage reduction (CVR). Traditional approaches of voltage control rely on slow acting electromechanical devices installed on the primary feeder. These approaches are not suitable for handling the changing paradigm in the distribution systems towards smart grid. Advanced volt-var control technologies like smart inverters and other distributed secondary-side voltage regulation devices are perceived to be the key enabling technologies to meet the requirements of future smart grid such as effective voltage control and ability for seamless integration of DER. This paper reviews existing and emerging volt-var control techniques in the distribution systems with DER.

Advances in volt-var control approaches in utility distribution systems

A disturbance locating system deployed within a power grid to estimate a location of a disturbance in a power system includes a voltage transducer, a current transducer and disturbance energy determination circuitry. The system may also include disturbance power determination circuitry. The voltage transducer couples to an output of a voltage transformer, the output of the voltage transformer representative of a voltage on a line within the power grid. The current transducer couples to an output of a current transformer, the output of the current transformer representative of the current flowing through the line, the output having a forward reference direction and a behind reference direction. The voltage and current transformers may be hard wired to the line. The disturbance energy determination circuitry couples to the voltage transducer and the current transducer. Based upon the inputs received, the disturbance energy determination circuitry determines disturbance energy flowing in the line and estimates a direction of disturbance energy flow with respect to the system as either in front of or behind of the disturbance locating system. The disturbance energy determination circuitry may include disturbance power determination circuitry that couples to the voltage transducer and the current transducer. In such case, the disturbance power is provided to the disturbance energy determination circuitry for estimating a relative direction to the disturbance.

Surya Santoso

Papers

Variable rotor-resistance control of wind turbine generators

Challenges and trends in analyses of electric power quality measurement data

Distribution Fault-Locating Algorithms Using Current Only

Advances in volt-var control approaches in utility distribution systems

System and method for locating a disturbance in a power system based upon disturbance power and energy