Performance Analysis of Maximum Power Point Tracking Algorithms Under Varying Irradiation

Photovoltaic (PV) system is one of the reliable alternative sources of energy and its contribution in energy sector is growing rapidly. The performance of PV system depends upon the solar insolation, which will be varying throughout the day, season and year. The biggest challenge is to obtain the maximum power from PV array at varying insolation levels. The maximum power point tracking (MPPT) controller, in association with tracking algorithm will act as a principal element in driving the PV system at maximum power point (MPP). In this paper, the simulation model has been developed and the results were compared for perturb and observe, incremental conductance, extremum seeking control and fuzzy logic controller based MPPT algorithms at different irradiation levels on a 10 KW PV array. The results obtained were analysed in terms of convergence rate and their efficiency to track the MPP.Keywords: Photovoltaic system, MPPT algorithms, perturb and observe, incremental conductance, scalar gradient extremum seeking control, fuzzy logic controller.Article History: Received 3rd Oct 2016; Received in revised form 6th January 2017; Accepted 10th February 2017; Available onlineHow to Cite This Article: Naick, B. K., Chatterjee, T. K. & Chatterjee, K. (2017) Performance Analysis of Maximum Power Point Tracking Algorithms Under Varying Irradiation. Int Journal of Renewable Energy Development, 6(1), 65-74.http://dx.doi.org/10.14710/ijred.6.1.65-7

Uniform quasi-convex optimisation via Extremum Seeking

The paper deals with a well-known extremum seeking scheme by proving uniformity properties with respect to the amplitudes of the dither signal and of the cost function. Those properties are then used to show that the scheme guarantees the global minimiser to be semi-global practically stable despite the presence of local saddle points. To achieve these results, we analyse the average system associated with the extremum seeking scheme via arguments based on the Fourier series

Investigation of Some Self-Optimizing Control Problems for Net-Zero Energy Buildings

Green buildings are sustainable buildings designed to be environmentally responsible and resource efficient. The Net-Zero Energy Building (NZEB) concept is anchored on two pillars: reducing the energy consumption and enhancing the local energy generation. In other words, efficient operation of the existing building equipment and efficient power generation of building integrated renewable energy sources are two important factors of NZEB development. The heating, ventilation and air conditioning (HVAC) systems are an important class of building equipment that is responsible for large portion of building energy usage, while the building integrated photovoltaic (BIPV) system is well received as the key technology for local generation of clean power. Building system operation is a low-investment practice that aims low operation and maintenance cost. However, building HVAC and BIPV are systems subject to complicated intrinsic processes and highly variable environmental conditions and occupant behavior. Control, optimization and monitoring of such systems desire simple and effective approaches that require the least amount of model information and the use of smallest number but most robust sensor measurements. Self-optimizing control strategies promise a competitive platform for control, optimization and control integrated monitoring for building systems, and especially for the development of cost-effective NZEB. This dissertation study endorses this statement with three aspects of work relevant to building HVAC and BIPV, which could contribute several small steps towards the ramification of the self-optimizing control paradigm. This dissertation study applies self-optimizing control techniques to improve the energy efficiency of NZEB from two aspects. First, regarding the building HVAC efficiency, the dither based extremum seeking control (DESC) scheme is proposed for energy efficient operation of the chilled-water system typically used in the commercial building ventilation and air conditioning (VAC) systems. To evaluate the effectiveness of the proposed control strategy, Modelica based dynamic simulation model of chilled water chiller-tower plant is developed, which consists of a screw chiller and a mechanical-draft counter-flow wet cooling tower. The steady-state performance of the cooling tower model is validated with the experimental data in a classic paper and good agreement is observed. The DESC scheme takes the total power consumption of the chiller compressor and the tower fan as feedback, and uses the fan speed setting as the control input. The inner loop controllers for the chiller operation include two proportional-integral (PI) control loops for regulating the evaporator superheat and the chilled water temperature. Simulation was conducted on the whole dynamic simulation model with different environment conditions. The simulation results demonstrated the effectiveness of the proposed ESC strategy under abrupt changes of ambient conditions and load changes. The potential for energy savings of these cases are also evaluated. The back-calculation based anti-windup ESC is also simulated for handling the integral windup problem due to actuator saturation. Second, both maximum power point tracking (MPPT) and control integrated diagnostics are investigated for BIPV with two different extremum seeking control strategies, which both would contribute to the reduction of the cost of energy (COE). In particular, the Adaptive Extremum Seeking Control (AESC) is applied for PV MPPT, which is based on a PV model with known model structure but unknown nonlinear characteristics for the current-voltage relation. The nonlinear uncertainty is approximated by a radial basis function neural network (RBFNN). A Lyapunov based inverse optimal design technique is applied to achieve parameter estimation and gradient based extremum seeking. Simulation study is performed for scenarios of temperature change, irradiance change and combined change of temperature and irradiance. Successful results are observed for all cases. Furthermore, the AESC simulation is compared to the DESC simulation, and AESC demonstrates much faster transient responses under various scenarios of ambient changes. Many of the PV degradation mechanisms are reflected as the change of the internal resistance. A scheme of detecting the change of PV internal shunt resistance is proposed using the available signals in the DESC based MPPT with square-wave dither. The impact of the internal resistance on the transient characteristics of step responses is justified by using the small-signal transfer function analysis. Simulation study is performed for both the single-string and multi-string PV examples, and both cases have demonstrated successful results. Monotonic relationship between integral error indices and the shunt internal resistance is clearly observed. In particular, for the multi-string, the inter-channel coupling is weak, which indicates consistent monitoring for multi-string operation. The proposed scheme provides the online monitoring ability of the internal resistance condition without any additional sensor, which benefits further development of PV degradation detection techniques

Zwei-Freiheitsgrade-Struktur zur robusten Radschlupfregelung für Antiblockiersysteme

Die Regelung des gebremsten Rades eines gummibereiften Fahrzeugs stellt seit vier Jahrzehnten Generationen von Ingenieuren vor schwierige Herausforderungen und es wurden bereits zahlreiche Ansätze dazu erdacht und implementiert. Eine wesentliche Herausforderung der Regelstrecke ist die mit der Fahrzeuggeschwindigkeit skalierte Dynamik, wenn der Radschlupf als relative Geschwindigkeitsdifferenz zwischen Fahrzeug und Radaufstandspunkt geregelt werden soll, sowie die hohe Nichtlinearität der Reifenkraftschlusskennlinie in Abhängigkeit des Schlupfes. In der tatsächlichen Implementierung kommt darüber hinaus noch der Abtastcharakter der Regelung auf einem digitalen Mikrocontroller hinzu, der im Rahmen dieser Arbeit systematisch in den Entwurf mit einbezogen werden soll. Dazu wird zuerst ein physikalisches Modell des Fahrzeugs einschließlich der Bremsenaktorik aufgestellt und dieses anschließend mittels Strukturmaßen untersucht sowie Schlüsse für die notwendige Reglerstruktur aus dieser Untersuchung abgeleitet. In dieser Arbeit wird ein modellbasierter Ansatz zur Regelung des Radschlupfes vorgeschlagen, der aus einer Zwei-Freiheitsgrade-Struktur mit nichtlinearer modellbasierter Vorsteuerung und einer robust entworfenen Rückführung mittels Gain-Scheduling besteht. Für die Vorsteuerung wird ein Ansatz über die exakte Eingangs-/Ausgangslinearisierung gewählt, mit dem sich das nichtlineare System bezogen auf das Ein-/Ausgangsverhalten wie ein lineares System regeln lässt. Für die Rückführung wird ein Gain-Scheduling über die Schedulingparameter Fahrzeuggeschwindigkeit und Radschlupf durchgeführt, um den durch die hohe Parameterunsicherheit in der Reifenkennline und die reziproke Abhängigkeit der Systemdynamik von der Geschwindigkeit variablen Parameterbereich in kleinere Unsicherheitsbereiche zu unterteilen, für die anschließend ein linearer Regler mit fester Struktur über die Methode der robusten Polbereichsvorgabe entworfen wird. Basierend auf diesem Schlupfregler wird in einem zweiten Schritt ein Algorithmus verwendet, der in der Lage ist, das Maximum der Reibwertkennlinie einzuregeln, um den verfügbaren Kraftschluss bestmöglich auszunutzen, das sog. Extremum Seeking. Der gesamte Reglerentwurf erfolgt dabei rein zeitdiskret, um die charakteristischen Effekte der Diskretisierung bei einer digitalen Regelung behandeln zu können. Die vorgeschlagene Reglerstruktur wird dabei in Simulationen für unterschiedliche Reibwerte der modellbasierten Vorsteuerung und der realen Strecke untersucht und dabei gezeigt, dass die Regelung mit Extremwertsuche auch in der Lage ist, das Maximum zu finden, wenn die Reibwertkurve ihr Maximum verändert