Matteo Carraro

Effect of Control Strategies and Power Take-Off Efficiency on the Power Capture From Sea Waves

The choice of the most suitable control strategy for wave energy converters (WECs) is often evaluated with reference to the sinusoidal assumption for incident waves. Under this hypothesis, linear techniques for the control of the extracted power, as passive loading and optimum control, are well known and widely analyzed. It can be shown, however, how their performances are fundamentally different when irregular waves are considered and the theoretical superiority of optimum control is questionable under real wave conditions. Moreover, the global optimization of WECs implies a rational design of the power electronics equipment. This requires the analysis of the instantaneous extracted power in addition to the average one. In this paper, the impact of irregular waves on the power extraction when using different control techniques is analyzed in the case of a point absorber in heave. It is also shown how a convenient tradeoff between high average power extraction and limited power electronics overrating can be obtained by applying simple power saturation techniques. Moreover, the impact of power conversion efficiency on the control strategy is analyzed.

Maximum-Torque-Per-Ampere Operation of Anisotropic Synchronous Permanent-Magnet Motors Based on Extremum Seeking Control

This paper presents a theoretical analysis of a maximum-torque-per-ampere control strategy based on the extremum seeking control working principle, which provides useful insights for the definition of a systematic and quantitative design procedure. The focus is on the convergence properties to the optimal operating point, and a method for evaluating an upper bound of the convergence time is proposed. The analysis is supported by several experimental tests performed on an interior permanent-magnet synchronous motor.

Analysis of power extraction from irregular waves by all-electric power take off

The choice of the most suitable control strategy for Wave Energy Converters (WECs) is often evaluated with reference to the sinusoidal assumption for incident waves. Under this hypothesis, linear techniques for the control of the extracted power, as passive loading and optimum control are well-known and widely analyzed. It can be shown, however, how their performances are fundamentally different when irregular waves are considered and the theoretical superiority of optimum control is questionable under real wave conditions. Moreover, the global optimization of WECs requires a rational design of the power electronics equipment. This requires the analysis of the instantaneous extracted power in addition to the average one. In this paper the impact of irregular waves on the power extraction when using different control techniques is analyzed in the case of a point absorber in heave. It is also shown how a convenient trade-off between high average power extraction and limited power electronics overrating can be obtained by applying simple power saturation techniques. Moreover, the impact of power conversion efficiency on the control strategy is analyzed.

Convergence Analysis and Tuning of a Sliding-Mode Ripple-Correlation MPPT

The development of fast maximum power point tracking (MPPT) algorithms for photovoltaic (PV) systems with high bandwidth and predictable response to irradiation transients is attractive for mobile applications and installations under fast changing weather conditions. This paper proposes the convergence analysis of a sliding-mode version of the MPPT based on ripple correlation control (RCC). The contribution of this paper is a dynamic model, useful to derive a set of design guidelines to tune the sliding-mode RCC-MPPT and achieve a desired dynamic performance under irradiation transients. The research is based on sliding control theory and it includes both the chattering phenomena analysis, and a discussion on the effects of reactive parasitic elements in the PV module. The proposed analysis and design have been validated by MATLAB simulations first, and then with experimental tests on a 35-W panel with a boost converter charging a 24-V battery. The results support the effectiveness of the proposed modeling procedure and design guidelines, showing good agreement between the model prediction and the experimental transient response.

Automatic Parameter Identification of Inverter-Fed Induction Motors at Standstill

As a step toward the self-commissioning of the next generation of ac drives, this work deals with an automatic procedure for the identification of the inverse- Γ equivalent circuit of inverter-fed induction motors (IM) at standstill. The algorithm, cut out for the modern microprocessors combines different test signals with the aim of extracting and mapping the magnetic model nonlinearity. As a key feature, the procedure uses the existing inverter as a precise voltage probe to get the complete parameter set usually required by the advanced control of ac drives. The theoretical investigations are supported by experimental results and are reported in the paper. A distinguishing characteristic of the proposed method among the other existing solutions is the accuracy of the results confirmed by the comparison with finite-element analysis tools and tailored to the laboratory IM prototypes.

Hierarchical Scaled-States Direct Predictive Control of Synchronous Reluctance Motor Drives

This paper presents the design and experimental validation of a finite-state direct predictive control (DPC) for synchronous reluctance motor (SynRM) drives. The main features are the hierarchical selection policy of the optimal voltage vector and the dynamic scaling of the voltage amplitude, which keeps the current ripple limited even in the presence of low switching frequencies, as required by medium and high-power applications. The implementation is simple, intuitive, and low-demanding. This study is fully supported by experimental evidences.

Energy-Efficient Autonomous Solar Water-Pumping System for Permanent-Magnet Synchronous Motors

This paper presents a novel stand-alone solar-powered water-pumping system, especially suited for usage in rural or remote areas. The system is primarily designed to reduce both cost and complexity, while simultaneously guaranteeing optimal utilization of the photovoltaic generator. The use of standard hardware and control architectures ensures ease of installation, service, and maintenance. The proposed solution consists of a water pump driven by a permanent-magnet synchronous motor, controlled by a conventional field oriented control scheme. The photovoltaic array is directly connected to the dc bus of the inverter, with no intermediate power conversion stages. A perturbation based extremum-seeking controller adjusts the motor speed reference to attain the maximum power point operation of the photovoltaic array. Both simulations and experimental results on a full-scale prototype support the effectiveness of the proposed system.

Theory and implementation of a MTPA tracking controller for anisotropic PM motor drives

Energy saving will be the key-factor of the next-generation electrical drives. Extremum-seeking techniques, and the derived injection-based Maximum Torque per Ampere (MTPA) strategies, are a step towards the optimal drive efficiency, combining implementation easiness and robustness against parameter variations. Nevertheless, due to both the heavy motor non-linearity and the presence of mixed frequency signal dynamic, not all the implementation issues have been successfully addressed yet. Along this path, the paper offers a comprehensive theoretical and experimental validation of the MTPA tracking algorithm based on high frequency signal injection, including the stability numerical proof and an extended batch of commented experimental results.

Estimation of the direct-axis inductance in PM synchronous motor drives at standstill

The call for human mobility reduction pushes research in electrical drives towards the implementation of efficient self-commissioning procedures. As a preliminary and crucial step, an accurate estimation of motor parameters is necessary. As a part of a process of careful review of existing and often either rough-and-ready or bulky estimation methods, this work copes with the light and precise estimation of the direct flux linkage in permanent magnet motors at standstill. The estimation is based on multi-sinusoidal signal injection, and signal post-processing through Goertzel algorithm, for the sake of very low computational complexity. The procedure considers both iron losses and saturation effects. A set of experimental results show the feasibility of the method, while the comparison with finite element analysis confirms the accuracy of the estimation.

Convergence analysis and tuning of ripple correlation based MPPT: A sliding mode approach

The development of fast MPPT (Maximum Power Point Tracking) algorithms for photovoltaic (PV) systems able to track variable irradiation conditions with high bandwidth is becoming attractive, especially for mobile applications. This paper focuses on the well known ripple correlation technique, proposing an analysis that provides an upper bound to the convergence time in response to solar irradiation steps. The availability of an upper bound enables the prediction of the dynamic behaviour of the MPPT, and gives a set of guidelines for a proper tuning of the controller to fit specific dynamic requirements. The analysis is based on a simple application of sliding control theory, and it also includes chattering phenomena and the effects of parasitic reactive elements of the PV module. Matlab simulation and experimental tests are provided on a 35W panel interfaced to a 24V battery through a boost converter. A controllable LED illuminator has been used as solar generator, able to provide irradiation step changes with a bandwidth of 1kHz. The results confirm the effectiveness of both the analysis and tuning.