Palle Andersen

Modal identification of output-only systems using frequency domain decomposition

In this paper a new frequency domain technique is introduced for the modal identification of output-only systems, i.e. in the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical approach where the modal parameters are estimated by simple peak picking. However, by introducing a decomposition of the spectral density function matrix, the response spectra can be separated into a set of single degree of freedom systems, each corresponding to an individual mode. By using this decomposition technique close modes can be identified with high accuracy even in the case of strong noise contamination of the signals. Also, the technique clearly indicates harmonic components in the response signals.

Using heat pump energy storages in the power grid

The extensive growth of installed wind energy plants lead to increasing balancing problems in the power grid due to the nature of wind fields and diurnal variations in consumption. One way to overcome these problems is to move consumption to times where wind power otherwise cause overproduction and large fluctuations in prices. The paper presents a method which takes advantage of heat capacity in single-family houses using heat pumps which are anticipated to be installed in large numbers in Denmark in next decade. This type of heating gives a large time constant and it is shown possible to move consumption without compromising the comfort of house residents. In the paper an optimization exploiting forecasts of weather and energy prices combined with prediction models of house dynamics is presented. The results show that with the presented method it will be possible to move a substantial amount of energy from one time to another.

Congestion management in a smart grid via shadow prices

Abstract We consider a distribution grid interconnecting a number of consumers with flexible power consumption. Each consumer is under the jurisdiction of exactly one balancing responsible party (BRP), who buys energy at a day-ahead electricity market on behalf of the consumer. We illustrate how BRPs can utilize the flexibility of the consumers to minimize the imbalance between the consumed and the purchased energy thereby avoiding trading balancing energy at unfavorable prices. Further we show how shadow prices on the distribution lines can be used to resolve grid congestion without information sharing between the BRPs.

Primary Control by ON/OFF Demand-Side Devices

We consider an aggregator managing a portfolio of ON/OFF demand-side devices. The devices are able to shift consumption in time within certain energy limitations; moreover, the devices are able to measure the system frequency and switch ON and OFF accordingly. We show how the aggregator can manage the portfolio of devices to collectively provide a primary reserve delivery in an unbundled liberalized electricity market setting under current regulations. Furthermore, we formulate a binary linear optimization problem that minimizes the aggregators cost of providing a primary reserve delivery of a given volume, and demonstrate this method on numerical examples.

Linear quadratic controller with fault detection in compact disk players

The design of the positioning controllers in optical disk drives are today subjected to a trade off between an acceptable suppression of external disturbances and an acceptable immunity against surfaces defects. In this paper an algorithm is suggested to detect defects of the disk surface combined with an observer and a linear quadratic regulator. As a result, the mentioned trade off is minimized and the playability of the tested compact disk player is considerably enhanced.

Smart grid dispatch strategy for ON/OFF demand-side devices

We consider an aggregator managing a portfolio of runtime and downtime constrained ON/OFF demand-side devices. The devices are able to shift consumption in time within certain energy limitations. We show how the aggregator can manage the portfolio of devices to collectively provide upward and downward regulation. Two control strategies are presented enabling the portfolio to provide regulating power while respecting the runtime, downtime, and energy constraints of the devices. The first strategy is a predictive controller requiring complete device information; this controller is able to utilize the full flexibility of the portfolio but can only handle a small number of devices. The second strategy is an agile controller requiring less device information; this controller is able to handle a large number of devices but not able to utilize the full flexibility of the portfolio.

A study on the surface defects of a compact disk

Optical disk drives are widely used today. However, even though the technology has been available to the consumer during 20 years, there are still performance issues to be improved. This study reveals a way of dealing with the photo diode signals in the optical pick-up to improve the performance of the optical disk drives.

Derivation and validation of a coal mill model for control

Abstract This paper presents a coal mill model to be used for improved mill control, which may lead to a more optimal load following capability of power plants fired by pulverized coal. The model is relatively simple, yet it captures all significant dynamics of mills from different manufactures. The model is validated using data from four mills of a similar type from two different producers. Model parameters are estimated using an efficient evolutionary algorithm called Differential Evolution. The model parameters are similar for all four mills, indicating that the model structure is reliable.

Detection of surface defects and servo signal restoration for a compact disc player

Compact disc (CD) players have been on the market for more than two decades, and the involved technologies, including control are very mature. Some problems, however, still remain with respect to playing CDs having to surface defects like scratches and fingerprints. Two servo control loops are used to keep the optical pick-up unit (OPU) focused and radially locked to the information track of the CD. The problem is to design servo controllers which are well suited for both handling surface defects and disturbances like mechanical shocks. The handling of surface defects requires a low-controller bandwidth which is in conflict with the requirement for the handling of disturbances. This control problem can be solved by the use of a fault tolerant control strategy, where the fault detection is very important. The OPU feeds the controllers with detector signals. Based on these, focus and radial distances can be estimated and a pair of residuals can be computed. This paper introduces a model-based method to estimate focus and radial distances as well as residuals, which have the potential to improve the control of a CD player in case of a surface defect. The methods are applied to experimental data of a scratch. The results of this experimental work show the potential of the method.

Aggregation and Control of Flexible Consumers: A Real Life Demonstration

Abstract In this paper, we present an architecture for aggregation and control of a portfolio of flexible consumers. The architecture makes it possible to control the aggregated consumption of the portfolio to follow a power reference while honoring local consumer constraints. Hereby, an aggregator is able to utilize a portfolio of consumers as a virtual power plant to deliver services in the electricity markets. The architecture is implemented and demonstrated in a field test on a portfolio consisting of 54 heat pumps each located in an inhabited household. In this demonstration, a power reference varying between 15 kW and 35 kW is followed over a 7 day period. The field test showed satisfactory performance in terms of following the power reference and assuring comfort for the inhabitants. To the best knowledge of the authors, this is the first real life demonstration where a power reference is followed based on the aggregated consumption of a larger number of devices – and consequently a significant step towards the smart grid vision.