Herbert L. Ginn

An optimization based method for selection of resonant harmonic filter branch parameters

Resonant harmonic filters (RHFs) are effective devices for reducing supply current harmonics when only those load generated harmonics for which they are tuned are present. Other current harmonics as well as supply voltage harmonics may reduce the effectiveness of RHFs in harmonic suppression. To counter such reductions in effectiveness, an optimization based method for selection of filter branch parameters is developed for the conventional RHF. It takes into consideration the interaction of the filter with the distribution system and provides filter parameters that give the maximum effectiveness with respect to harmonic suppression. To accomplish this, a cost function is developed, its behavior examined, and appropriate constraint functions are developed. The results for optimized filters, applied in a test case, are given.

Flexible Active Compensator Control for Variable Compensation Objectives

In this paper, a new approach is proposed to increase the flexibility of the reference current generation for active compensators. Although compensating all useless components of the current is ideal, it is sometimes desirable to target a subset of the possible components of the current due to power electronic converter power, switching speed limitations, etc. Furthermore, power quality objectives may vary over time. The proposed strategy utilizes a novel reference signal generator to provide online flexibility with respect to the compensation objectives. The reference signal generator utilizes a computationally efficient moving-window discrete Fourier transform along with an orthogonal decomposition of the current instead of the filters typically used to extract the desired components of the current. Each orthogonal component of the current can be adjusted independently in any percentage, thus providing the selective current compensation. The proposed reference signal generator also allows for easy extrapolation of the measured current, effectively canceling the delay inherent in the digital current control loop. Cancellation of the delay allows for the elimination of the spikes that typically occur due to poor tracking of fast slope transitions of the current reference. The advantages of the proposed control architecture have been verified by an experimental prototype.

Comprehensive review of wind energy maximum power extraction algorithms

With the advancements in the variable speed direct drive design and control of wind energy systems, the efficiency and energy capture of these systems is also increasing. As such, many maximum power point tracking methods have been developed and implemented. These MPPT algorithms can be broadly categorized into three types: Tip-Speed control, Power-Signal feedback, and Hill climb search based. However, so many variations have been proposed over the last 30 years that it has become difficult to adequately determine which method, newly proposed or existing, is most appropriate for a given wind system. Recent papers have shorter literature review and a comprehensive review of all the variations of algorithms was not done. There is also little agreement in the energy gain results mentioned in various papers that were using the same or different algorithms. Therefore, a comprehensive review of various maximum power tracking algorithms proposed has been done by the authors, while further categorizing them into nine categories based on sensor requirements, speed, effectiveness, memory requirements, etc. Also, merits, demerits and comprehensive comparison of various algorithms are performed. The authors hope this paper would serve as a single point reference for the work that has been done on this topic and would be helpful for future researchers.

High-Impedance Fault Detection in the Distribution Network Using the Time-Frequency-Based Algorithm

A new high-impedance fault (HIF) detection method using time-frequency analysis for feature extraction is proposed. A pattern classifier is trained whose feature set consists of current waveform energy and normalized joint time-frequency moments. The proposed method shows high efficacy in all of the detection criteria defined in this paper. The method is verified using real-world data, acquired from HIF tests on three different materials (concrete, grass, and tree branch) and under two different conditions (wet and dry). Several nonfault events, which often confuse HIF detection systems, were simulated, such as capacitor switching, transformer inrush current, nonlinear loads, and power-electronics sources. A new set of criteria for fault detection is proposed. Using these criteria, the proposed method is evaluated and its performance is compared with the existing methods. These criteria are accuracy, dependability, security, safety, sensibility, cost, objectivity, completeness, and speed. The proposed method is compared with the existing methods, and it is shown to be more reliable and efficient than its existing counterparts. The effect of choice of the pattern classifier on method efficacy is also investigated.

Attenuation of Electromagnetic Interference in a Shunt Active Power Filter

Shunt active power filters (APF) are commonly used for the reduction of current harmonics and improvement of the power factor in power systems with nonlinear loads, such as diode rectifiers. A pulsewidth modulation (PWM) power converter constitutes the main component of the APF. The low-order harmonics of the line current are attenuated, but the switch-mode operation of the converter results in electromagnetic interference (EMI) spreading to the grid. Specifically, clusters of harmonics appear in the frequency spectra of voltages and currents of the converter at multiples of the switching frequency. In this paper, transferring the discrete spectral power of those harmonics to the continuous spectral power density is proposed as means for mitigation of the EMI. It is accomplished by randomization of the switching periods using a novel random PWM method (RPWM II). In contrast to the existing random PWM methods, in RPWM II the sampling frequency of the digital modulator is constant and equal to the average switching frequency. Computer simulations and experimental investigation of an APF designed for shipboard power systems are described, and the results are presented. They demonstrate significant reduction of the EMI, a feat achieved at practically no expense.

Hardware in the Loop Test for Power System Modeling and Simulation

This paper presents a design procedure of hardware in the loop (HIL) test for power system modeling and simulation. A HIL simulation refers to a system in which parts of a pure simulation have been replaced with actual physical components. HIL simulation is often used to understand the behavior of a new device, or to predict an outcome under different system conditions without knowing the detail of device design. Additionally, a HIL test could help to build a model and validate a data model of a new power device. To efficiently evaluate the various design of controller, HIL testing is beneficial. Requirements of a real-time system simulator for active compensator systems are discussed and a general function blocks are presented. Examples of power system modeling for active compensator and relay HIL tests are presented in this paper. Finally, preliminary results and future work of HIL for relay test is presented

The effect of the design method on efficiency of resonant harmonic filters

Distribution voltage harmonics and load current harmonics other than harmonics to which a resonant harmonic filter (RHF) is tuned, deteriorate the filter efficiency in reducing harmonic distortion. The paper presents results of a study on dependence of this deterioration on the method of the filter design. The study was confined to four-branch RHFs of the 5th, 7th, 11th, and 13th order harmonics, installed on buses that predominantly supply six-pulse ac/dc converters or rectifiers. The filters under investigation were designed according to two different approaches: a traditional approach and an approach based on an optimization procedure. In the traditional approach, the reactive power allocated to particular branches of the filter and their tuning frequencies are selected at the designers discretion, according to recommended practices. In the optimization based approach, the reactive power allocated to particular branches and tuning frequencies are resultants of an optimization procedure that minimizes the bus voltage and the supply current THD in the system with the filter under design.

Multifunctional VSC Based on a Novel Fortescue Reference Signal Generator

This paper presents a novel reference signal generator (RSG) for voltage-source converters (VSCs) that enables the maximization of its functionality. The proposed RSG is based on a combination of the Fortescue decomposition with recursive discrete Fourier transform. The method is characterized by computational efficiency, excellent detection accuracy, and fast dynamic response. An experimental prototype of a multifunctional VSC with the proposed RSG has been built, and experimental results are presented. The functionality of the VSC can be extended to such modes of operation as harmonic compensator, active power filter, pulsewidth modulator (PWM) rectifier, PWM inverter, balancing compensator, and STATCOM, with the update of only six coefficients in the RSG.

Digital Control Method for Grid-Connected Converters Supplied With Nonideal Voltage

When employed in systems with higher frequency variability and nonideal supply voltage, the synchronization method used in grid-connected power electronic converter control systems must be considered. A method is presented here that achieves synchronization implicitly through the use of a discrete Fourier transform in combination with the computation of an effective admittance. It is shown that the method is suitable for systems with high frequency variability as well as for systems with nonideal supply voltage including heavy voltage asymmetry.

A Computationally Efficient RDFT-Based Reference Signal Generator for Active Compensators

Several methods for generation of the control reference signals for active compensators have been proposed. Many of those reference signal generation techniques use Alters to extract the desired components of the current. Frequency domain methods are generally not used due to high computational complexity as well as susceptibility to frequency variation and numerical errors. In this paper a computationally efficient and robust Recursive Discrete Fourier Transform based reference signal generator is proposed for use in active compensator applications. In addition to mathematical analysis, discussions and simulations, an experimental prototype of an active compensator with the proposed reference signal generator has been built and experimental results have been obtained.