MPPT oscillations minimization in PV system by controlling non-linear dynamics in SEPIC DC-DC converter

Solar PV power generation has achieved rapid growth in developing countries which has many merits such as absence of noise, longer life, no pollution, less time for installation, and ease of grid interface. A maximum power point tracking circuit (MPPT) consists of DC-DC power electronics converters that are used to improve the energy attainment from solar PV array. This paper presents a detailed analysis to control of chaos, a non-linear dynamic in SEPIC DC-DC converter interfaced solar PV system, to minimize the oscillations near to MPP. In SEPIC DC-DC converter, the input inductor current is continuous and capable of sweeping the whole I-V curve of a PV module from open circuit voltage (Voc) to short circuit current (Isc) operating points. To trace the true maximum power point and to nullify the oscillations near to MPP, the yield output voltage needs to ensure period-1 operation

Analysis of Grid-Interactive PV-Fed BLDC Pump Using Optimized MPPT in DC–DC Converters

In solar photovoltaic (PV) system-based Brushless DC (BLDC) motors for water pumping application, the role of DC/DC converters is very important. In order to extract the maximum power from the PV array, an efficient DC/DC converter is essential at the intermediate stage. In this work, different DC/DC converter topologies suitable for BLDC motors are proposed. The converters are supported by an optimized maximum power point tracking system to provide a reliable operation. Recent optimization algorithms such as fuzzy logic, perturb and observe, grey wolf, and whale optimization are implemented with the PI controller in maximum power point tracking to maximize the conversion efficiency. The obtained results using SEPIC, LUO, and interleaved LUO converters provide a comparative study in the case of converter output, motor parameters, and grid output. The performance analysis on three different converters and multiple optimization methods are carried out. By analyzing the performance of different converter topologies, the interleaved LUO converter outperforms the other two converters with the results of a voltage gain ratio of 1:22, conversion efficiency of 98.3%, and grid current THD of 2.9%. Moreover, regarding the power quality aspect, the total harmonic distortion of the grid current is maintained below the IEEE-519 standard. In addition, the developed system has an advantage of operating both in stand-alone and grid-connected operation modes.publishedVersio

Indirect Sliding Mode Control for DC-DC SEPIC Converters

This article presents an indirect sliding mode control (SMC) for single-ended primary-inductor converters (SEPIC). Unlike the conventional SMC methods, the proposed SMC method employs a sliding surface function based on the input current error only. The use of such sliding surface function not only simplifies the implementation but also reduces the cost of implementation. It is shown that the output voltage control can be achieved indirectly. The input current reference is generated by a proportional-integral (PI) regulator. The existence condition and the region of the closed-loop system are determined for all possibilities of the PI gains. The performance of the proposed SMC method is investigated on a laboratory prototype converter, operated in buck and boost modes, in terms of the voltage regulation ability under abrupt changes in the input voltage and load resistance. Simulation and experimental results are presented and discussed

Control of Proton Exchange Membrane Fuel Cell System

265 p.In the era of sustainable development, proton exchange membrane (PEM) fuel cell technology has shown significant potential as a renewable energy source. This thesis focuses on improving the performance of the PEM fuel cell system through the use of appropriate algorithms for controlling the power interface. The main objective is to find an effective and optimal algorithm or control law for keeping the stack operating at an adequate power point. Add to this, it is intended to apply the artificial intelligence approach for studying the effect of temperature and humidity on the stack performance. The main points addressed in this study are : modeling of a PEM fuel cell system, studying the effect of temperature and humidity on the PEM fuel cell stack, studying the most common used power converters in renewable energy systems, studying the most common algorithms applied on fuel cell systems, design and implementation of a new MPPT control method for the PEM fuel cell system

Simulation of various DC-DC converters for photovoltaic system

This work explains the comparison of various dc-dc converters for photovoltaic systems. In recent day insufficient energy and continues increasing in fuel cost, exploration on renewable energy system becomes more essential. For high and medium power applications, high input source from renewable systems like photovoltaic and wind energy system turn into difficult one, which leads to increase of cost for installation process. So the generated voltage from PV system is boosted with help various boost converter depends on the applications. Here the various converters are like boost converter, buck converter, buck-boost converter, cuk converter, sepic converter and zeta converter are analysed for photovoltaic system, which are verified using matlab / simulink

Sliding mode control of DC/DC switching converters for photovoltaic applications

2011 - 2012The maximum power point tracking (MPPT) is one of the most important features of a system that process the energy produced by a photovoltaic generator must hold. It is necessary, in fact, to design a controller that is able to set the value of voltage or current of the generator and always ensure the working within its maximum power point. This point can considerably change its position during the day, essentially due to exogenous variations, then sunshine and temperature. The MPPT techniques presented in literature and adopted in commercially devices operate a voltage control of the photovoltaic generator and require careful design of the control parameters. It is in fact complex obtain high performance both in stationary that strongly variable conditions of sunshine without a careful choice of some parameters that affect in both conditions the performance of the algorithm for the MPPT. In this thesis has been addressed the analysis of an innovative current-based MPPT technique: the sensing of the current in the capacitor placed in parallel with the photovoltaic source is one of the innovative aspects of the proposal. The controller is based on a nonlinear control technique called ”sliding mode” of which has been developed an innovative model that allow to obtain a set of conditions and enable the designing of the controller with extreme simplicity. The model also allow to demonstrate how the performance of this MPPT control tecnique are independent not only from the characteristics and operating conditions of the photovoltaic generator, but also by the parameters of the switching converter that implements the control. This property allows a significantly simplification in the designing of the controller and improve the performance in presence of rapid changes of the irradiance. An approach to the dynamic analysis of a class of DC/DC converters controlled by a sliding mode based maximum power point tracking for photovoltaic applications has been also presented. By referring to the boost and SEPIC topologies, which are among the most interesting ones in photovoltaic applications, a simple analytical model is obtained. It accounts for the sliding mode technique that allows to perform the maximum power point tracking of the photovoltaic generator connected at the converters input terminals. Referring to the previous approach, a correction term allowing to have an increased accuracy of the model at high frequencies has been also derived. The control technique proposed has been implemented by means of low cost digital controller in order to exploit the potential offered by the hardware device and optimize the performance of the controller. An extensive experimental analysis has allowed to validate the results of the research. The laboratory measurements were conducted on prototypes of DC/DC converters, boost and SEPIC, carried out by Bitron SpA. There are a considerable experimental tests both in the time and in the frequency domain , both using source generator in laboratory than photovoltaic panels. The results and theoretical simulations have found a large validation through laboratory measurements. [edited by author]XI n.s

Survey on Photo-Voltaic Powered Interleaved Converter System

Renewable energy is the best solution to meet the growing demand for energy in the country. The solar energy is considered as the most promising energy by the researchers due to its abundant availability, eco-friendly nature, long lasting nature, wide range of application and above all it is a maintenance free system. The energy absorbed by the earth can satisfy 15000 times of today’s total energy demand and its hundred times more than that our conventional energy like coal and other fossil fuels. Though, there are overwhelming advantages in solar energy, It has few drawbacks as well such as its low conversion ratio, inconsistent supply of energy due to variation in the sun light, less efficiency due to ripples in the converter, time dependent and, above all, high capitation cost. These aforementioned flaws have been addressed by the researchers in order to extract maximum energy and attain hundred percentage benefits of this heavenly resource. So, this chapter presents a comprehensive investigation based on photo voltaic (PV) system requirements with the following constraints such as system efficiency, system gain, dynamic response, switching losses are investigated. The overview exhibits and identifies the requirements of a best PV power generation system

Nonlinear Control Methods for Single-Ended Primary-Inductor Power Converters

This paper investigates nonlinear control methods for single-ended primary-inductor converters (SEPIC). The fastswitching and average models show the converter nonlinearity in terms of inductor currents, capacitor voltages, and the switching duty cycle. The control law intuitively should be nonlinear to drive and guarantee the system stability. Two different control laws based on the passivity and back-stepping technique are examined and designed to have asymptotically global stability in the system. Unlike the passivity method which regulates the duty cycle directly, the back-stepping method adjusts the switching duty by a driver integrator/low pass filter system. The simulation results have shown the benefits from the passivity control law over the back-stepping one. Moreover, an observer is introduced in order to reduce the number of voltage and current sensors for the control system. The nonlinear control law is thus a combination of the measured signal and the estimated ones. Simulation results are also presented to verify the effectiveness of the observer in the control system

Sliding mode control of renewable energy generation systems

As a result of decades of research and innovation in the renewable energy industry, advanced technologies have been developed for both wind and solar energy conversion systems. However, there are still some aspects of the systems that need to be enhanced to enable maximum and cost effective energy conversion. Wind is emerging as an alternative source for electrical power generation. Small-scale wind power generation system applications are becoming widespread because of rising fuel prices and the demand for reducing carbon emission. For such applications, vertical axis wind turbines (VAWT) appeal due to their ability to capture wind from different directions and their low noise-pollution. Wind energy and its conversion system are studied first. The need for advanced maximum power point tracking (MPPT) controllers is discussed in literature focusing on widely implemented algorithms. Sliding mode control theory has been studied and implemented in controlling wind power generation system (WPGS). The dynamic performance of the WPGS using sliding mode control has shown improved dynamic performance, overshoot errors eliminations and higher energy conversion ratios than the widely used proportional integral (PI) control. A new approach in WPGS control strategy by development of a novel soft control strategy based on the mathematical residue theorem has been introduced. The idea of using the residue theorem is to set a soft dynamic boundary for controlled variables around a reference point, so that controlled variables lie on a point inside this boundary. The stability of the system has been ensured by following the Forward Euler method. The developed control strategy has been implemented in different control techniques of a small-scale permanent magnet synchronous generator (PMSG) based WPGS. The introduction of the new control approach based on residue theorem has further improved the energy conversion ratio by 2:5%. Moreover, a wind speed estimation algorithm is provided and implemented to the proposed controllers to overcome the wind speed measurements issues, i.e. cost and accuracy. Furthermore, an improved back-EMF observer based on residual theorem has been designed to estimate the mechanical rotor speed of the PMSG using the stator current and voltage measurements. The improved back-EMF observer has overcome the well-known limitation of the classical back-EMF at low speed observation. In addition, the wind speed has been estimated using the calculated power obtained from the PMSG voltage and current measurements as well as the estimated rotor speed. Based on the wind and rotor speeds, the tip speed ratio (TSR) is calculated and controlled to its optimal value. A MPPT controller has been developed for photovoltaic power generation systems based on a sliding mode control scheme in stand-alone configuration. The developed controller provides a solution to atmospheric conditions measurement issues and it enhances the efficiency of the PV power system. In addition, the developed controller overcomes the power oscillation around the operating point which appears in most implemented MPPT techniques. The MPPT operation is achieved by regulating the input voltage of the PV system using DC-DC boost converter topology. Moreover, a single-ended primary inductor converter (SEPIC) topology has been employed in PV power systems. The restrictions on the application of SEPIC have been solved based on sliding mode control. The efficiency of the PV system has significantly improved

Modified SEPIC Converter Performance for Grid-connected PV Systems under Various Conditions

Step-up converter is widely used to increase DC voltage level on PV systems either off-grid or grid connected. One of the step-up converters often used in PV systems is SEPIC converter. To improve its performance, many SEPIC converters have been modified. However, performance on various conditions has not been further investigated. In this study, the modified SEPIC converter was investigated under various change conditions for grid-connected PV applications. This converter was modelled and simulated using PSIM software. The modified SEPIC converter received input from PV array 15 kWp, and its output was connected to the three-phase inverter with grid and load. The irradiance level and ambient temperature were varied to test its performance and compared to Boost converter and SEPIC converter. For all tests, the performance of modified SEPIC converter was better than other step-up converters because it was able to rectify the quality of output voltage and more efficient