Enhancement of On-grid PV System under Irradiance and Temperature Variations Using New Optimized Adaptive Controller

Solar Energy is one of the key solutions to future electrical power generation. Photovoltaic Plants (PV) are fast growing to satisfy electrical power demand. Different maximum power point tracking techniques (MPPT) are used to maximize PV systems generated power. In this paper, on grid PV system model in MATLAB SIMULINK is tested under sudden irradiance and cell temperature variations. Incremental Conductance MPPT is used to maximize generated power from the PV system with the help of new adaptive controller to withstand these heavy disturbances. The new adaptive controller is tuned for optimal operation using two different optimization techniques (Invasive weed and Harmony search).Optimization results for the two techniques are compared. .A robustness test is made to check system stability to withstand different random irradiance and cell temperature patterns without failure to track the maximum power point.Finally, a brief comparison is made with a previous literature and the new adaptive controller gives better results

Power Quality Improvement and Low Voltage Ride through Capability in Hybrid Wind-PV Farms Grid-Connected Using Dynamic Voltage Restorer

© 2018 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission.This paper proposes the application of a dynamic voltage restorer (DVR) to enhance the power quality and improve the low voltage ride through (LVRT) capability of a three-phase medium-voltage network connected to a hybrid distribution generation system. In this system, the photovoltaic (PV) plant and the wind turbine generator (WTG) are connected to the same point of common coupling (PCC) with a sensitive load. The WTG consists of a DFIG generator connected to the network via a step-up transformer. The PV system is connected to the PCC via a two-stage energy conversion (dc-dc converter and dc-ac inverter). This topology allows, first, the extraction of maximum power based on the incremental inductance technique. Second, it allows the connection of the PV system to the public grid through a step-up transformer. In addition, the DVR based on fuzzy logic controller is connected to the same PCC. Different fault condition scenarios are tested for improving the efficiency and the quality of the power supply and compliance with the requirements of the LVRT grid code. The results of the LVRT capability, voltage stability, active power, reactive power, injected current, and dc link voltage, speed of turbine, and power factor at the PCC are presented with and without the contribution of the DVR system.Peer reviewe

Photovoltaic and Wind Energy Conversion Systems

In the first decades of the current millennium, the contribution of photovoltaic and wind energy systems to power generation capacity has grown extraordinarily all around the world; in some countries, these systems have become two of the most relevant sources to meet the needs of energy supply. This Special Issue deals with all aspects of the development, implementation, and exploitation of systems and installations that operate with both sources of energy

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

Novel Night and Day Control of a PV Solar System as a STATCOM (PV-STATCOM) for Damping of Power Oscillations

Installations of large scale PV solar farms are rapidly increasing, worldwide. This is causing a growing apprehension that inertialess power injections from these inverter based generators will result in a decline in power system stability. Instead, this thesis presents novel applications of a patent pending technology whereby the PV solar farms actually help significantly increase system stability. A novel 24/7 (night and day) control of a large-scale PV solar farm as a dynamic reactive power compensator STATCOM, termed PV-STATCOM, is presented for damping low-frequency electromechanical power oscillations resulting in a significant improvement in power transfer capability of existing power transmission systems. A new real and reactive power modulation based control of PV-STATCOM is demonstrated during daytime that combines the functionalities of both a STATCOM and a Battery Energy Storage System (BESS) to provide significantly enhanced levels of power oscillation damping than that achieved by either a STATCOM or a BESS. The effectiveness of the proposed PV-STATCOM Power Oscillation Damping (POD) control techniques based on modulation of reactive power, real power or a combination of both is evaluated through both small signal and Electromagnetic Transients simulations studies. Participation factor analysis is utilized for selection of appropriate control signals and damping controllers. The POD controllers are designed through small signal Residue analysis and validated through Simplex Optimization technique in electromagnetic transient simulations. The efficacy of the proposed PV-STATCOM controls is demonstrated on three power systems: Single Machine Infinite Bus SMIB system, Two-Area system, and the 12 bus FACTS power system, which exhibit different power oscillation modes. New ramp up techniques for power restoration from solar farms are also presented, which are substantially faster than those specified by grid codes. A methodology for coordination of proposed PV-STATCOM controls with existing Power System Stabilizers (PSSs) on synchronous generators is further described for further damping enhancement. This thesis thus presents a novel technology that can not only help increase the penetration of large scale PV solar farms but utilize them for reducing the need for construction of expensive new lines or use of costly Flexible AC Transmission systems for stability improvement

Low voltage ride-through strategies for a 3-phase grid-connected PV system

Grid codes is a technical specification which defines the parameters a power system that are connected to the national power systems has to ensure safe, secure and eco-nomic proper functioning of the electric system. One of these requirements is to stay connected to the grid during faults. In such scenarios, the generating unit should remain connected to the grid for a certain period and provide reactive power to support the grid. This is called low voltage ride-through capability. At the early stage, low voltage ride-through requirements were imposed for large scale generators connected to the trans-mission network. However, with the increased penetration of distributed generation, such as PV panels implemented in the distribution network, the low voltage ride-through requirements are also required for distributed generation. With the maturity of PV technology, the cost of PV generation has decreased. Therefore, the total installed capacity of grid-connected PV generation has increased; this has cre-ated new challenges to the low voltage ride-through. Power quality and transient per-formance are the most critical aspects of the grid-connected PV systems under grid faults. PV generation is permitted to switch off from the grid during a fault; however, with the high penetration of the installed PV system, it will degrade the power quality if the same method applied. It is necessary to make sure that the inverter currents remain sinusoidal and within the acceptable limits at the instant of the fault, during and after the fault clearance for different types of faults. Accordingly, this thesis proposes two low voltage ride-through strategies for a 3-phase grid-connected PV system in different reference frames. The presented low voltage ride-through control algorithm in the synchronous reference frame, which fulfils a voltage compensation unit and the reactive power injection block is designed to protect the inverter from overcurrent failure under both symmetrical and asymmetrical faults, reduce the double grid frequency oscillations and provides reac-tive power support by applying a voltage compensation unit. The inverter can also inject sinusoidal current during asymmetrical faults. The method does not require a hard switch from the Maximum Power Point Tracking to a non-Maximum Power Point Tracking algorithm, which ensures a smooth transition. The proposed method in the stationary reference frame provides a fast post-fault recov-ery, which is essential to minimize the fault impacts on the loads and the converter. The method, which consists of a new reference currents calculation block and the voltage compensation unit, maintains the converter current within acceptable limits, produces sinusoidal current even during asymmetrical faults, improves the post-fault recovery performance, and provides independent control for active and reactive powers

Advanced Grid-Tied Photovoltaic Micro-Inverter

Along with the damaged environment and the emerging energy crisis, many problems have been caused by utilizing fossil fuels. Green energy, also known as renewable energy, has been trusted as a good alternative for the conventional energy resources and effort has been contributed in the development of modern green energy. Solar energy is one of the renewable energy resources. Owing to its advantages of being nearly unlimited, pollution free, noise free and relatively easy to maintain, photovoltaic (PV) systems have experienced a significant increase in the past few decades. In this thesis, a grid-tied solar micro inverter has been presented and several key technology issues on this PV system are investigated: 1. Maximum power point tracking (MPPT) strategies. Under changing atmospheric conditions, intensity of the sunlight irradiation and shading problems, the output of a solar panel varies nonlinearly. MPPT techniques are designed to enable PV panels always operate at the optimal power point and produce maximum power. In this paper, different MPPT strategies are compared and analysed. An improved variable step-size P&O MPPT strategy is also proposed to compensate those drawbacks from conventional MPPT techniques. Simulation results are also given. 2. Control strategies of a single-phase grid-tied inverter. A deadbeat controller, named the OSAP control, is proposed for the inverter. This inverter is analysed into two states: standalone inverter and grid-tied inverter. In each state, the OSAP controller is applied to control the inverter. Some disadvantages are also shown for the OSAP controllers. An improved OSAP controller is then introduced to compensate these drawbacks. Simulation results are given to support the theory. 3. Experiment of this solar inverter. An interleaved boost converter is shown to implement the MPPT techniques. Experiments of the stand-alone inverter and grid-tied inverter are also conducted with the OSAP control strategies. The experiment of this PV system under some environmental changes are also conducted and the transient response is given. Chapter 1 deals with the background introduction and literature review. A model of solar cell is introduced in Chapter 2 and the simulation model is also built to analysis the characteristics of solar panel output power. Several Maximum Power Point Tracking (MPPT) techniques are evaluated and an improved variable step-size MPPT technique is proposed to overcome the disadvantages. In Chapter 3, a control strategy is developed for a grid-tied PV micro-inverter, which is called one-sampling-ahead-preview (OSAP) control. Firstly a full-bridge inverter is analysed. Two states of this inverter are introduced, one is the stand-alone inverter and the other is the grid-tied inverter. Mathematical and simulation model have been built for each inverter. Then an OSAP voltage controller is proposed for the stand-alone inverter and an OSAP current controller is proposed the grid-tied inverter. However, since OSAP controllers belong to the deadbeat control category, these exists a deadbeat response in the output. And another problem is that OSAP controllers highly depend on the inverters have accurate parameters for the components, which is not practical in real life. So an improved OSAP controller is introduced to solve these problems, which is the OSAP with a resonant controller. Simulation results are also given to support the theory. In Chapter 4, the experiment of this system has been shown and experimental results have been provided. Chapter 5 explains the conclusions and some developments need to be done in the future work

POWER CONDITIONING UNIT FOR SMALL SCALE HYBRID PV-WIND GENERATION SYSTEM

Small-scale renewable energy systems are becoming increasingly popular due to soaring fuel prices and due to technological advancements which reduce the cost of manufacturing. Solar and wind energies, among other renewable energy sources, are the most available ones globally. The hybrid photovoltaic (PV) and wind power system has a higher capability to deliver continuous power with reduced energy storage requirements and therefore results in better utilization of power conversion and control equipment than either of the individual sources. Power conditioning units (p.c.u.) for such small-scale hybrid PV-wind generation systems have been proposed in this study. The system was connected to the grid, but it could also operate in standalone mode if the grid was unavailable. The system contains a local controller for every energy source and the grid inverter. Besides, it contains the supervisory controller. For the wind generator side, small-scale vertical axis wind turbines (VAWTs) are attractive due to their ability to capture wind from different directions without using a yaw. One difficulty with VAWTs is to prevent over-speeding and component over-loading at excessive wind velocities. The proposed local controller for the wind generator is based on the current and voltage measured on the dc side of the rectifier connected to the permanent magnet synchronous generator (PMSG). Maximum power point tracking (MPPT) control is provided in normal operation under the rated speed using a dc/dc boost converter. For high wind velocities, the suggested local controller controls the electric power in order to operate the turbine in the stall region. This high wind velocity control strategy attenuates the stress in the system while it smoothes the power generated. It is shown that the controller is able to stabilize the nonlinear system using an adaptive current feedback loop. Simulation and experimental results are presented. The PV generator side controller is designed to work in systems with multiple energy sources, such as those studied in this thesis. One of the most widely used methods to maximize the output PV power is the hill climbing technique. This study gives guidelines for designing both the perturbation magnitude and the time interval between consecutive perturbations for such a technique. These guidelines would improve the maximum power point tracking efficiency. According to these guidelines, a variable step MPPT algorithm with reduced power mode is designed and applied to the system. The algorithm is validated by simulation and experimental results. A single phase H-bridge inverter is proposed to supply the load and to connect the grid. Generally, a current controller injects active power with a controlled power factor and constant dc link voltage in the grid connected mode. However, in the standalone mode, it injects active power with constant ac output voltage and a power factor which depends on the load. The current controller for both modes is based on a newly developed peak current control (p.c.c.) with selective harmonic elimination. A design procedure has been proposed for the controller. Then, the method was demonstrated by simulation. The problem of the dc current injection to the grid has been investigated for such inverters. The causes of dc current injection are analyzed, and a measurement circuit is then proposed to control the inverter for dc current injection elimination. Characteristics of the proposed method are demonstrated, using simulation and experimental results. At the final stage of the study, a supervisory controller is demonstrated, which manages the different operating states of the system during starting, grid-connected and standalone modes. The operating states, designed for every mode, have been defined in such a hybrid model to allow stability and smooth transition between these states. The supervisory controller switches the system between the different modes and states according to the availability of the utility grid, renewable energy generators, the state of charge (SOC) of energy storage batteries, and the load. The p.c.u. including the supervisory controller has been verified in the different modes and states by simulation