K.J. Olejniczak

Harmonic estimation with random sensor delay

A nonstationary discrete-time model is used for representing the harmonic components of nonsinusoidal signals observed in electric power systems. The signal measurement devices are assumed to possess a random delay that introduces stochastic parameters into the dynamic model used in estimation. A finite-time, linear, unbiased, reduced-order, minimum-variance state estimator is applied to predict the future behavior of this model. This is desired in order to annihilate the harmonic components which pollute the 50/60 Hz fundamental frequency in the electric power system.

Numerical optimization of a heat sink used for electric motor drives

To maximize the performance of a finned heat sink used to cool power modules for motor drives rated up to five horsepower, fluid and thermal effects were modeled using the commercially available software packages ANSYS and FLUENT. In particular, a heat sink used to cool a power module with an average power dissipation of 203 Watts was numerically studied to assess the feasibility of using the same heat sink to cool a power module with an average power dissipation of 265 Watts. Results indicate that, if the geometric configuration is unchanged, the volumetric flow rate must be increased by nearly 65%-increasing the pressure drop by 250% and the required fan power by 410%-or the ambient temperature must be lowered by almost 15/spl deg/C, relative to the base case.

Reduced-order harmonic estimation with probable sensor failures

A nonstationary discrete-time model is used for representation of harmonic components of nonsinusoidal signals observed in electric power systems. The measurement devices utilized are assumed to have nonzero failure probabilities that introduce stochastic parameters into the dynamic model used in estimation. A finite-time, linear, unbiased, reduced-order, minimum-variance state estimator is derived to predict the future behavior of this model. This is desired in order to annihilate the harmonic components which pollute the electric power system. Simulation results are provided to illustrate the use of this estimator and support the theoretical results.

Reduced-order estimation of power system harmonics using set theory

In this work, we consider state estimation of harmonic signals with time-varying magnitudes. The presence of such signals has been increasing in electric power systems due to the increased use of power electronics circuits possessing nonlinear voltage vs. current characteristics. In this work, harmonic signals are modelled using ellipsoidal set-theoretic methods and an optimal reduced-order estimator, which has one-half the dimension of the state vector, is introduced for predicting the unknown time-varying harmonic magnitudes. The optimality is in the sense of minimizing both the sum of the lengths of the principal axes and the volume of the ellipsoid for estimation error. This new estimator is compared with a full-order set-theoretic estimator in an example where each frequency component has a randomly changing magnitude.

Operating characteristics of MCTs in resonant DC link inverters

Improved performance of inverters may be obtained by increasing the switching frequency of the power semiconductor devices. Switching frequencies greater than the hard-switched limits may be obtained by using soft-switching techniques, The MOS-controlled thyristor (MCT) is a relatively new device showing a great potential in soft-switching applications involving high-power densities. Hence, the main objective of this paper is to extend the research work done on both soft-switched (resonant) inverters and MCTs by evaluating the operating characteristics of MCTs for switching frequencies up to approximately 75 kHz under a zero-voltage switching condition. A PCB is developed to subject the MCTs and passive components to stresses similar to those actually occurring in the resonant and actively-clamped resonant DC link inverter topologies. In addition, operation results of the operation of the MCT-based active clamp in the actively-clamp resonant DC link inverter and some practical implementation considerations are included.<<ETX>>

The Electromagnetic Transients Program (EMTP) as an effective tool to evaluate active power filters for harmonic compensation

Abstract The Institute of Electrical and Electronic Engineers (IEEE) ‘Recommended Practices and Requirements for Harmonic Control in Electric Power Systems’ sets limits for the current and voltage harmonic distortions at the point of common coupling in order to maintain an acceptable quality of electric power in the presence of nonlinear loads. Both the utility and its customers share a common responsibility since enforcement of the above practice by the utility would require that the affected customer use a suitable harmonic mitigating method. To this effect, this paper demonstrates how the Electromagnetic Transients Program (EMTP) may be used to investigate two harmonic mitigating methods, namely, the use of shunt passive power filters and the combination of a series active (APF) and shunt passive (PPF) power filters. Both methods reduce the harmonic currents injected into the distribution system; however, the combination of the series APF and shunt PPFs has a better compensation characteristic with a higher capital cost than only shunt PPFs. Before a final decision is reached, the cost of the higher harmonic losses throughout the distribution system when using only shunt PPFs must be taken into account.

Modeling and estimation of harmonic signals using ellipsoidal set theory

The objective of this paper is to demonstrate the use of ellipsoidal set theoretic methods for modelling and estimation of power system harmonic signals. The voltage or current signal to be estimated is assumed to be corrupted by measurement and process noises. Also, the magnitude of each harmonic component is assumed to be unknown and time-varying. Three ellipsoidal set theoretic estimation techniques are presented to estimate the harmonic signal when corrupted by noise. These methods are then compared with the optimal Kalman filter based on an equivalent stochastic model using Monte Carlo techniques.

On the use of diamond in a multichip power module (MCPM) based induction motor drive

The unique combination of excellent thermal, electrical, and mechanical properties makes synthetic diamond a legitimate material candidate for thermal management strategies in integrated drive modules. Over the past several years, joint research programs between academe have resulted in substantial diamond synthesis and post-synthesis processing time and cost, This is largely attributed to major advances in diamond synthesis using chemical vapor deposition (CVD) techniques. In this paper, an overview of diamond synthesis and post-synthesis processing is presented followed by a comparison of thermal heat spreading efficacy of silicon and CVD-diamond substrates for power electronic applications.

An analysis of active power line conditioners using the Electromagnetic Transients Program

The authors describe how the Electromagnetic Transients Program (EMTP) can be used as a tool to evaluate the effectiveness of active power line conditioners (APLC) in reducing harmonic distortion in distribution systems. The system under study consists of a three-phase diode bridge rectifier served by three single-phase distribution transformers. A shunt APLC and/or shunt passive power filters (PPFs) are used to reduce harmonic distortion. Special attention is given to the shunt APLC rating when it is used with shunt PPFs for harmonic distortion reduction.<<ETX>>