Abstract-This paper presents a new concept in active damping techniques using a reduced model of a LCLfiltered grid connected inverter. The presence of the LCL filter complicates the design of the inverter control scheme, particularly when uncertainties in the system parameters, especially in the grid inductance, are considered. The proposed control algorithm is addressed to overcome such difficulties using a reduced model of the inverter in a state observer. In this proposal, two of the three state variables of the system are obviated from the physical inverter model and only the inverter side current is considered. Therefore, the inverter side current can be estimated emulating the case of an inverter with only one inductor, thus eliminating the resonance problem produced by the LCL filter. Besides, in the case of a distorted grid, the method allows to estimate the voltages at the point of common coupling free of noise and distortion without using any PLL-based synchronization algorithm. This proposal provides the following features to the closed-loop system: 1) robust and simple active damping control under system parameters deviation, 2) robustness against grid voltage unbalance and distortion, and 3) an important reduction in the computational load of the control algorithm which allows to increase the switching frequency. To complete the control scheme, a theoretical stability analysis is developed considering the effect of the observer, the system discretization and the system parameters deviation. Experimental and comparative evaluation results are presented to validate the effectiveness of the proposed control scheme.
A thorough analysis of the Concentrating Solar Thermal Power (CSP) development in Spain in the period 1998-2013 has been carried out in order to identify the main drivers behind the bubble-like behaviour exhibited by this renewable technology. Tending a parallelism with the basic principles of the control systems theory has facilitated the identification of the main shortcomings in the design of the various control frameworks governing the CSP deployment in the studied period. The CSP 2 disorderly proliferation propitiated by inefficient control mechanisms has resulted in an overrun cost to the electricity system that has tried to be mitigated with the application of retroactive measures seriously harmful for the investors. It is expected that the conclusions drawn from this comprehensive review of the Spanish case have a general relevance for other countries undertaking the development path of renewable technologies.
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