Mitigation of Lower Order Harmonics in a Grid Connected Three Phase Pv Inverter

In this paper simple single-phase grid connected photovoltaic (PV) inverter topology consisting of a boost section, a low voltage Threephase inverter with an inductive filter, and a step-up transformer interfacing the grid is considered. Ideally, this topology will not inject any lower order harmonics into the grid due to high-frequency pulse width modulation operation. However, the non ideal factors in the system such as core saturation-induced distorted magnetizing current of the transformer and the dead time of the inverter, etc., contribute to a significant amount of lower order harmonics in the grid current. A novel design of inverter current control that mitigates lower order harmonics is presented in this paper. An adaptive harmonic compensation technique and its design are proposed for the lower order harmonic compensation. In addition, a proportional-resonant-integral (PRI) controller and its design are also proposed. This controller eliminates the dc component in the control system, which introduces even harmonics in the grid current in the topology considered. The dynamics of the system due to the interaction between the PRI controller and the adaptive compensation scheme is also analyzed Keywords—adaptive filter, harmonic distortion, Inverters, Solar energy. INTRODUCTION Renewable sources of energy such as solar, wind and geothermal have gained popularity due to the depletion of conventional energy sources. Hence, many distributed generation (DG) systems making use of the renewable energy sources are being designed and connected to a grid. In this paper, one such DG system with solar energy as the source is considered. The topology of the solar inverter system is simple. It consists of the following three stages:  A boost converter stage to perform maximum power point tracking (MPPT).  A low-voltage Three-phase H-bridge inverter.  An inductive filter and a step-up transformer The switches are all rated for low voltage which reduces the cost and lesser component count in the system improves the overall reliability. This topology will be a good choice for low-rated PV inverters of rating less than a kilowatt. The disadvantage would be the relatively larger size of the interface transformer compared to topologies with a highfrequency link transformer. The basic circuit will not have any lower order harmonics in the ideal case. However, the following factors result in lower order harmonics in the system: The distorted magnetizing current drawn by the transformer due to the nonlinearity in the B– HCurve of the transformer core, the dead time introduced between switching of devices of the same leg, on-state voltage drops on the switches, and the distortion in the grid voltage itself. There can be a dc injection into the transformer primary due to a number of factors. These can be the varying power reference from a fast MPPT block from which the ac current reference is generated, the offsets in the sensors, and A/D conversion block in the digital controller. This dc injection would result in even harmonics being drawn from the grid, again International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 02 Issue: 05 | Aug-2015 www.irjet.net p-ISSN: 2395-0072 © 2015, IRJET ISO 9001:2008 Certified Journal Page 1037 contributing to a lower power quality. II REVIEW OF LITERATURE 1. Adaptive harmonic compensation technique in Three phase PV Inverter PWM inverters ideally shift the output voltage spectrum around the switching frequency. Thus ideally PWM inverters do not introduce any significant lower order harmonics. However, in real systems, due to dead-time effect, device drops and other non-idealities lower order harmonics are present. In order to attenuate these lower order harmonics and hence to improve the quality of output current, this paper presents an adaptive harmonic elimination technique 2. Review of Three-Phase Grid-Connected Inverter for Photovoltaic Modules This review focuses on inverter technologies for connecting photovoltaic (PV) modules to a singlephase grid. The inverters are categorized into four classifications: The number of power processing stages in cascade. The type of power decoupling between the PV module(s) and the single phase grid. 3. Compensation Method Eliminating Voltage Distortions in PWM Inverter The switching lag-time and the voltage drop across the power devices cause serious waveform distortions and fundamental voltage drop in pulse width-modulated inverter output. These phenomenon’s are conspicuous when both the output frequency and voltage are low. To estimate the output voltage from the PWM reference signal it is essential to take account of these imperfections and to correct them. In this paper, on-line compensation method is presented. 4. Systematic Method for Damping of the LCL Filter for Three-Phase Grid-Connected PV Inverters The Proportional Resonant (PR) current controller provides gains at a certain frequency (resonant frequency) and eliminates steady state errors. Therefore, the PR controller can be successfully applied to single grid-connected PV inverter current control. On the contrary, a PI controller has steadystate errors and limited disturbance rejection capability. Compared with the Land LC filters, the LCL filter has excellent harmonic suppression capability, but the inherent resonant peak of the LCL filter may introduce instability in the whole system. 5. A strategy for harmonic reduction using complete Solution: One of the major problems in electric power quality is the harmonic contents. There are several Methods of indicating the quantity of harmonic contents. These parameters of power quality measurement are four in number, of which Total Harmonic Distortion is most widely used. In electrical systems, harmonics increase business operating costs by increasing downtime, placing burden on the electrical infrastructure, making power factor correction difficult and causing poor total power factor. Harmonics are a circumstance of progress, and they affect all the operating systems. 6. Harmonic Reduction in Cascaded Multilevel Inverter It presents method of selecting switching angles of a cascaded multilevel inverter so as to produce required fundamental voltage along with improved staircase waveform in terms of harmonics. Cascaded multilevel inverter uses number of DC sources, for k sources number of levels will be 2k+1 and leads to k number of non-linear equations to be solved. Many approaches can be made regarding the solution but this focuses on Specific Harmonic Elimination (SHE) technique for angle International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 02 Issue: 05 | Aug-2015 www.irjet.net p-ISSN: 2395-0072 © 2015, IRJET ISO 9001:2008 Certified Journal Page 1038 optimization. NewtonRaphson method is used and the difficulty with this method is a closed initial guess. Variation of angles with modulation index is observed and THD is calculated for selected modulation indexes and all attempts are made so as to get lowest THD. Results are simulated in MATLAB/Simulink environment. CONVENTIONAL POWER CIRCUIT TOPOLOGY 2.1 CIRCUIT DIAGRAM: Fig.2.1 Power circuit topology of the single phase PV system connected to grid 2.2 PULSE WIDTH MODULATION (PWM): Pulse Width Modulation (PWM) is the most effective means to achieve constant voltage battery charging by switching the solar system controller’s power devices. When in PWM regulation, the current from the solar array tapers according to the battery’s condition and recharging needs consider a waveform such as this: it is a voltage switching between 0v and 12v. It is fairly obvious that, since the voltage is at 12v for exactly as long as it is at 0v, then a 'suitable device' connected to its output will see the average voltage and think it is being fed 6v exactly half of 12v. So by varying the width of the positive pulse we can vary the 'average' voltage. Similarly, if the switches keep the voltage at 12 for 3 times as long as at 0v, the average will be 3/4 of 12v or 9v, as shown below and if the output pulse of 12v lasts only 25% of the overall time, then the average is by varying or 'modulating' the time that the output is at 12v (i.e. the width of the positive pulse) we can alter the average voltage.. Fig2.2. Pulse width modulation The triangle waveform, which has approximately equal rise and fall slopes, is one of the commonest used, but you can use a saw tooth (where the voltage falls quickly and rinses slowly). .