Antonio de la Villa Jaén

Increasing the efficiency of the passive loading strategy for wave energy conversion

The control strategy applied to the oscillating system of the wave energy converters largely determines the overall system efficiency and thus the energy production. One of the first proposed control strategies for this type of device is the passive control. This type of control continues currently to be considered because it can be implemented in a simple way: short-term predictions about the performance of the wave are not needed when passive control is applied. Moreover, the power flow is unidirectional, and the extraction system is subjected to moderate peak powers so that costs and dimensions of the wave energy converter components can be reduced. The main disadvantage of passive loading control is the low energy production compared with other control strategies, such as the so-called reactive control which requires bidirectional power flow between the oscillating system and the generator. This way, the device can extract more energy from the waves, but the global system requires large energy exchanges between the oscillating device and the generator. These energy exchanges cause high losses, and thus the overall system efficiency significantly decreases. Furthermore, the reactive control system involves high oscillating excursions that can become unacceptable. In this paper, a point absorber converter that uses a linear direct-drive generator and power electronics converters jointly is considered. This article presents a passive control strategy that optimizes the power transferred from the generator to the power electronic converter considering the copper losses in the electric generator. Applying this approach, the generation system efficiency increases significantly, and similar values of the oscillating systems heave excursions and the peak-to-average power ratio for both the conventional and the proposed passive loading are found. The formulation of the proposed method is presented as well as time domain wave-to-wire simulations in both regular and irregular waves.

Improvements in the Reactive Control and Latching Control Strategies Under Maximum Excursion Constraints Using Short-Time Forecast

Control strategies are essential for the proper functioning of point absorbers. One of them is reactive control, which requires the system to work as a motor during part of the wave cycle and typically places stringent requirements on the efficiency of the power take-off (PTO) machinery. On the other hand, latching control consists of locking the oscillator into position in an intermittent and timely fashion to improve performance over linear damping. This way, the PTO system always works as a generator. This paper proposes latching and reactive control strategies in irregular waves considering short-term predictions on the oscillating system performance. If it is predicted that the end-strokes are going to be reached by the oscillating system, then the damping coefficient will be calculated in order to extract energy so that the velocity vanishes when the end-strokes are reached. The power absorbed by the PTO system significantly increases when the proposed control strategies are applied. Moreover, the oscillating system velocities decrease and the peak-to-average power ratios present acceptable values. The formulation of the proposed methods are presented as well as numerical simulations in regular and irregular waves.

DC Link Operation in Smart Distribution Systems With Communication Interruptions

DC Links are proposed in the literature as a mean to enhance the system performance and facilitate the integration of dispersed generators in distribution grids. Their operation relies on a centralized controller which gathers the measurements acquired along the network to compute their adequate set points. This system architecture provides several technical benefits but strongly depends on communication infrastructures (meters, data concentrators, etc.) which may fail. When this happens the DC links may not work properly, even forcing the system operator to disconnect them until the communications are restored. This paper proposes operational strategies to avoid the malfunction or disconnection of DC links when communication interruptions occur. Several simulations are done to assess how these strategies affect the performance of the DC links. An actual Spanish 100-bus distribution system with a DC link is used as a test bench in different situations.

Equality-constrained bilinear state estimation

This paper generalizes the recently introduced bilinear formulation of the weighted least squares (WLS) state estimation problem to those cases in which equality constraints must be explicitly considered. This leads to augmented equation systems in which both state variables and Lagrange multipliers get updated throughout the three stages arising in the bilinear approach (two linear filters with a nonlinear transformation in between). The proposed formulation prevents the ill-conditioning typically arising when exact-injection constraints are handled as virtual measurements with huge weights, while the excellent convergence speed of the bilinear scheme, which for practical purposes reaches the optimal solution in a single iteration, is fully preserved.

Assessment of generalized state estimators including ampere measurements

Conventional state estimators (SE) cannot take advantage of all available measurements, like currents flowing through circuit breakers and individual external injections. Current measurements are frequent at the lower levels and their loss implies a reduction of the global redundancy and hence a deterioration of the SE filtering capability. In this paper, a methodology is presented allowing all current measurements to be included in the model. A generalized state estimator (GSE) is used and the substations are represented in an efficient way by means of an implicit model. To illustrate the performance of the proposed formulation, several simulations are presented. Results are validated by checking the accuracy of the estimated states and by showing the improved ability to detect and identify bad data and topology errors.

DC link operation in smart distribution systems with communication interruptions

DC Links are proposed in the literature as a mean to enhance the system performance and facilitate the integration of dispersed generators in distribution grids. Their operation relies on a centralized controller which gathers the measurements acquired along the network to compute their adequate set points. This system architecture provides several technical benefits but strongly depends on communication infrastructures (meters, data concentrators, etc.) which may fail. When this happens the DC links may not work properly, even forcing the system operator to disconnect them until the communications are restored. This paper proposes operational strategies to avoid the malfunction or disconnection of DC links when communication interruptions occur. Several simulations are done to assess how these strategies affect the performance of the DC links. An actual Spanish 100-bus distribution system with a DC link is used as a test bench in different situations.