Steven B. Leeb

Transient event detection in spectral envelope estimates for nonintrusive load monitoring

This paper describes the theoretical foundation and prototype implementation of a power system transient event detector for use in a nonintrusive load monitor (NILM). The NILM determines the operating schedule of the major electrical loads in a building from measurements made at the electric utility service entry. The transient event detector extends the applicability of the NILM to challenging commercial and industrial sites. A spectral preprocessor for use in the transient event detector is introduced first. Then, the transient event detection algorithm is developed. The performance of the algorithm is illustrated with results from a prototype event detector. >

Non-intrusive electrical load monitoring in commercial buildings based on steady-state and transient load-detection algorithms

Abstract Increased interest in energy scorekeeping, load forecasting and improved control of electricity-consuming equipment has focused attention on the instrumentation required to obtain the desired data. Work performed by the authors and other researchers has shown that individual loads can be detected and separated from rapid sampling of power at a single point serving a number of pieces of equipment, for example the electrical service entrance for an entire house or all of the central space-conditioning equipment in a commercial building. This technique has worked well in tests in houses but faces more difficult challenges in commercial buildings. We present our results for this centralized or non-intrusive load monitoring technique, applied to the space-conditioning equipment in an office/laboratory building in which equipment start-up and shut-down was centrally observed and analyzed on the basis of changes in steady-state power. We further describe our enhanced technique for distinguishing loads by matching start-up transients to known patterns, and present laboratory tests of fully automated detection hardware and software.

Nonintrusive Load Monitoring and Diagnostics in Power Systems

This paper describes a transient event classification scheme, system identification techniques, and implementation for use in nonintrusive load monitoring. Together, these techniques form a system that can determine the operating schedule and find parameters of physical models of loads that are connected to an AC or DC power distribution system. The monitoring system requires only off-the-shelf hardware and recognizes individual transients by disaggregating the signal from a minimal number of sensors that are installed at a central location in the distribution system. Implementation details and field tests for AC and DC systems are presented.

An adaptive digital controller for a unity power factor converter

This paper describes an adaptive digital controller for a unity power factor AC-DC power converter. The controller is based on a linear large-signal model of the boost power converter. A hardware design is presented and analyzed, followed by the software implementation of the control algorithm. Issues in digital control of power converters, such as quantization effects and fixed-point representation of system parameters, are examined in the context of this system. Experimental results are presented and compared with simulations.

Fast controller for a unity-power-factor PWM rectifier

This paper presents an analog implementation of a fast controller for a unity-power-factor (UPF) PWM rectifier. The best settling times of many popular controllers for this type of power converter are on the order of a few line cycles, corresponding to bandwidths under 20 Hz. The fast controller demonstrated in this paper can exercise control action at a rate comparable to the switching frequency rather than the line frequency. In order to accomplish this while maintaining unity power factor during steady-state operation, the fast controller employs a ripple-feedback cancellation scheme.

Identification of induction motor parameters from transient stator current measurements

This paper describes three methods for estimating the lumped model parameters of an induction motor using startup transient data. A three-phase balanced induction motor is assumed. Measurements of the stator currents and voltages are required for the identification procedure, but no measurements from the motor shaft are needed. The first method presented applies simple models with limited temporal domains of validity and obtains parameter estimates by extrapolating the model error bias to zero. This method does not minimize any specific error criterion and is presented as a means of finding a good initial guess for a conventional iterative maximum-likelihood or least-squares estimator. The second method presented minimizes equation errors in the induction motor model in the least-square sense using a Levenburg-Marquardt iteration. The third identification method is a continuation of the Levenburg-Marquardt method, motivated by observed properties of some pathological loss functions. The third method minimizes errors in the observations in the least-squared sense and is, therefore, a maximum-likelihood estimator under appropriate conditions of normality. The performance of the identification schemes is demonstrated with both simulated and measured data, and parameters obtained using the methods are compared with parameters obtained from standard tests.

A Multilevel Inverter Topology for Inductively Coupled Power Transfer

This paper describes a multilevel inverter for delivering power to a set of frequency selectable induction heating targets for stimulating temperature sensitive polymer actuators. The proposed inverter topology overcomes the capacitor voltage balancing issue common to traditional multilevel inverters. This inverter is suitable for sustained real power transfer.

Estimation of variable-speed-drive power consumption from harmonic content

Nonintrusive load monitoring can be used to identify the operating schedule of individual loads strictly from measurements of an aggregate power signal. Unfortunately, certain classes of loads present a continuously varying power demand. The power demand of these loads can be difficult to separate from an aggregate measurement. Variable-speed drives (VSDs) are industrially important variable-demand loads that are difficult to track non-intrusively. This paper proposes a VSD power estimation method based on observed correlations between fundamental and higher harmonic spectral content in current. The technique can be generalized to any load with signature correlations in harmonic content, including many power electronic and electromechanical loads. The approach presented here expands the applicability and field reliability of nonintrusive load monitoring.

An envelope-following approach to switching power converter simulation

The implementation of an envelope-following method that is particularly efficient for open-loop switching power converters with fixed clock frequencies is described. A simple method for computing envelopes that involves solving a sequence of two-point boundary value problems is derived. The two-point boundary value problems are solved with a shooting or Newton method. The computations involved are explained and their implementation in the Nitswit program, along with results from using it to simulate several switching power circuits, is described. Results demonstrating the methods effectiveness are presented. >

Transient event detection for nonintrusive load monitoring and demand side management using voltage distortion

This paper describes a simple system that can be used for autonomous demand-side management in a load site such as a home or commercial facility. The system identifies the operation of individual loads using transient patterns observed in the voltage waveform measured at an electric service outlet. The theoretical foundation of the measurement process is introduced, and a preprocessor that computes short-time estimates of the spectral content of the voltage waveform is described. The paper presents several example measurements demonstrating the ability of the system to obtain estimates of the spectral content of the voltage waveform.