HARMONIC ANALYSIS OF SOLAR FED INVERTER
Engr. Simon Paul1, Engr. Shoaib Ahmed Khatri2, Engr. Waqas Ali Memon3, Engr. Haji Habibullah Memon4, Prof: Dr. Syed Asif Ali Shah5 and Prof: Dr. Anwar Ali Sahito6
1. Asst. Director (QA&Insp.), NTDC (WAPDA), Lahore, M.E. (Research Student), MUET Jamshoro2. Assistant Professor: Department of Electical Engineering, MUET, Jamshoro3. Asst. Director (Opertation), LESCO (WAPDA), Lahore
4. Asst. Director (QA&Insp.), NTDC (WAPDA), Lahore
5. Professor: Department of Electical Engineering, MUET, Jamshoro6. Professor: Department of Electrical Engineering, MUET, JamshoroABSTRACT
This paper studies the Photo-Voltaic systems and various switching techniques use to control the output of voltage source inverter. It emphasizes on the role of Photo-Voltaic systems in electricity generation. It surveys the usefulness of Photo-Voltaic systems, their environment friendly nature. The impact of Photo-Voltaic systems on power sector.
Inverters, are very important part of Photo-Voltaic systems. Inverters, serve as a hub for power conversion. They make Photo-Voltaic systems to supply energy to AC appliances.
These are however subjected to the issue of harmonics at their output. This if not addressed, results in life reduction of appliances being supplied.
The output of inverters is controlled by different switching techniques, which offer the control of output as well as support the control of harmonic levels in the inverter output.
The objective of the study covered in this paper, leads to the development of MATLAB SIMULINK model of a solar fed inverter, supplying a real AC load. (1 kW real load connected to inverter is acting as a domestic consumer, as per WAPDA consumer manuals 1977)
The Solar fed inverter, is thus harmonically analyzed under impact of different voltage control switching techniques, in terms of the percentage of Total Harmonic Distortion (THD) across the load by using FFT Tool of MATLAB SIMULINK.
THD percentage under impact of various switching techniques, subjected to solar fed inverter is compared to study and analyze the harmonic levels in the output of solar fed inverter.
Nowadays the trend utilization of renewable solar electricity as a backup source of electrical energy is tremendously increasing in Pakistan, specifically, among domestic electricity consumers (household consumers). The solar energy is rated among one of the reliable options among renewable energy resources available in Pakistan.
Despite of fact, solar – electric systems may have a high installation cost, these systems pay off their cost at once when they start operating. Pakistan is blessed with a rich solar capacity 1. The consumer who employs a solar – electricity system, finds it a healthy, cost saving and continuous alternative for production of electricity 2.
There are variety of Solar – electric systems, which utilize the application of Photovoltaic (PHOTO-VOLTAIC) systems. The Photo-Voltaic systems are ordered units (arrays and modules) composed of semiconductor material, which convert the solar irradiation into electricity. The output of these Photo-Voltaic systems is a DC supply 3,4.
There are different types of Photo-Voltaic systems available depending on the types of the semiconductor material and their composition (mono-crystalline and poly-crystalline etc). These Photo-voltaic systems depending on their composition provide different output efficiencies.
The role of Power Electronics is also very important in the Photo-Voltaic systems 3. It provides a great control and flexibility on use of solar energy. While using a Photo- Voltaic system as alternative source of electricity. Consumer has to go through two practical constraints to meet this requirement.
Use DC appliances which function on the output DC voltage level of the Photo – voltaic system.
Use some technical approach to change the output DC Voltage to AC voltage.
On surveying the Photo-Voltaic system market in Pakistan. One consumer can find both options depending on his need. Vast majority of the consumers require, DC voltage level obtained from Photo-Voltaic system be converted to AC voltage level. By accomplishing this they can use the maximum of their existing household appliances with ease.
The conversion of DC to AC voltage requires the use of Inverters. These inverters are the application of power electronics. Modern inverters use switching of high frequency switching devices for conversion of DC to AC voltage. Majority of the domestic consumers in Pakistan fall in the category of single phase consumers (as categorized by their utility provider). If such a consumer makes a Photo-Voltaic system as alternative source of electricity supply. It uses single phase type of inverter.
Quality of the final converted output of Photo-Voltaic system is a matter of great concern. It effects the life of household appliances. So, the better power quality requirement is always preferred.
2. SIGNIFICANCE OF INVERTERS IN PHOTO – VOLATIC SYSTEMS AND RELATED ISSUE OF HARMONICS
Inverters required to convert DC output of Photo-Voltaic cell generation to AC incorporates switching of power electronic switches resulting in harmonics and degradation of
Harmonics will result in improper function and reduction of operating life of consumer appliances. Hence it is important to perform harmonic analysis of the for small residential Photo-Voltaic inverter systems.
3. FOCUS OF RESEARCH
Our focus in this research paper is to develop Simulation modeling of single phase voltage source inverter for Photo-Voltaic cell generation.
After successful modeling have done Harmonic analysis of voltage source inverter under different switching techniques.
This Paper reviews solar Photo-Voltaic cell generation. Study of different switching techniques leading to development of simulation models for inverter with Photo-Voltaic cell using different switching techniques. Study of our system is based on the harmonic analysis of developed models using MATLAB/SIMULINK and comparison of results.
REVIEW OF PHOTO – VOLTAIC SYSTEMS GENERATING ELECTRICITY
The trend of utilizing solar energy or electricity is tremendously increasing in Pakistan. Solar energy being renewable energy is a environment friendly and healthy approach when utilized for electricity generation.
Pakistan has a abundant solar generation capacity. The natural climate and geographical conditions of Pakistan, support it as a huge stake holder in solar electricity generation in future.
Photo-Voltaic system are the basis that convert solar energy into electricity.
The Photo-Voltaic systems work on the principle of Photo-Voltaic effect which is the creation of voltage or electric current in a material upon exposure to sun light or light inherently a physical and chemical phenomena.
The electrical energy is obtained by the solar energy by the use of a solar cell which itself is a solid-state device. The efficiency of solar cell ranges from 10% to 30% with am life time of a solar cell is 20 to 30 years
The composition of a solar cell consists an ANODE (Positively charged) covered with anti- reflection coating. After anode, a layer of N- type silicon (extrinsic semiconductor) doped with Boron, Aluminum or Gallium which are Group II elements, which have strong acceptor capability. After a layer of N – type silicon, thick layer of P-type silicon which may probably composed of Phosphorous, Arsenic, antimony which are Group VI elements which have strong donor capability. After P- type, silicon layer a CATHODE (negatively charged) electrode
Junction of dissimilar materials (positive and negative silicon) creates a voltage and energy of sun knocks out electrons, thus creating a electron (photovoltaic effect), so connecting both junctions to external circuit flows a current.
The output of a solar cell is a small voltage of 0.5 volts DC with 0.5 Amperes to 2.5 Amperes of current
Photo-Voltaic cells are connected in series to add voltages or increase voltage capacity. If, cells are connected in parallel to add current or increase the amperage capacity.
But, Photo-Voltaic cells are connected in series -parallel combination to meet the desired voltage and current capacity of a load.
Photo-Voltaic cell is a single unit, or Photo-Voltaic cell is a single unit of generation on electricity.
Photo-Voltaic modules are combination of cells to give upto 12V DC and 50 Watts to 100 Watts of power output.
Photo-Voltaic array is a combination of modules to give any desired power output as per need.
Photo-Voltaic systems may be utilize in a number of applications a few of them may be listed as under:
1- Space shuttles
2- Telecommunication towers
3- Remote water pumping stations
4- Street lights
5- Electricity generation for homes
6- Electricity generation for national grid
1- Standalone photo-voltaic systems
2- Grid connected Photo-Voltaic system (with backup diesel generators)3- Grid connected Photo-Voltaic system (with backup batteries and diesel generator)
4- Hybrid Photo-Voltaic systems
Standalone Photo-Voltaic systems are the Photo-Voltaic systems, that work independently (for short period or for long continuous periods with backup) that are utilized to supply the house or domestic load without any integration with grid theses range from 1 kW to 5 kW, with optional backup comprising of batteries or Grid supply.
Grid connected Photo-Voltaic systems (with backup diesel generator) are systems that are designed to get synchronized with national grid and add their generated power to grid in coordination with supplying power to domestic or commercial use.
These systems utilize a diesel generator as backup so, as sunlight vanishes they automatically shift at their backup to supply their domestic or commercial loads.
These Photo-Voltaic systems are used to supply grids alongwith domestic or commercial loads but uses multiple backup sources consisting of batteries and diesel generator
These Photo-Voltaic systems are also known a advanced Photo-Voltaic systems are designed to synchronize and supply national grid.
These are flexible systems work efficiently as distributed Photo-Voltaic generation units.
1- Photo-Voltaic arrays
2- Charge Controllers (separate or integrated)
3- Batteries (primary, secondary, shallow and deep cycle)
5- Meters (Bi-Directional)
6- Protection equipments (DC and AC safety Equipment
The sun tracking system boosts the performance of Photo-Voltaic systems by 30% or more in summer and by 15% in winter.
these are the different type of silicon modules listed as under:
10 % to 12 % operational efficiency, square shaped cells fitted in modules (the design of these modules is susceptible to shading).
11% to 14% operational efficiency, circular shaped cells fitted in modules these are most expensive (the design of these modules is susceptible to shading.
These are most inexpensive with operational efficiency 6% to 8% , flexible in shape but give best performance in low light conditions.
As temperature increases from 25oC the Photo-Voltaic array output voltage decreases by 0.5% per degree centigrade.
output current of the Photo-Voltaic array decreases by decrease in sunlight as proportional amount while voltage remains roughly constant.
depending on the sun orientation or internal design of modules the shading may half or completely eliminate output of solar array.
Maximum performance of Photo-Voltaic systems may be achieved when Photo-Voltaic panels are perpendicular to sunlight, for around the year the optimum tilt angle in +/-
15 degrees latitude which is 35 degrees for winter and 20 degrees for summer.
Optimum solar window for a day is from 9 am morning to 3pm if array is not effected by shading during this solar window.
1- Liquid rechargeable battery
2- Secondary type dry battery: lithium ion rechargeable.
3- Shallow type dry battery: 20% Depth of Discharge
4- Deep cycle type battery: 50% to 80% Depth of Discharge
An MPPT circuit monitors array output and dynamically changes its resistance or input voltage to move the operating point of the Photo-Voltaic system towards the maximum power point of I-V curve.
1- Perturb and Observe MPPT technique.
2- Incremental Conductance MPPT technique.
3- Open Circuit voltage / constant voltage MPPT technique
Different types of inverters used in Photo-Voltaic systems are listed as under:
1- Standalone inverters
2- Interactive inverters: micro, central and solar inverters