ECE464 Power Electronics Assignment Solution

ECE464 Power Electronics Assignment Solution

ECE464 Power Electronics Assignment Solution

1.

(a) Define a non-renewable energy source.
A non-renewable resource (also known as a finite resource) is a resource that does not renew itself at a sufficient rate for sustainable economic extraction in meaningful human timeframes. Example: Fossil fuels (Coal, Petroleum, and Natural-Gas), and certain aquifers.

(b) Name two originating sources of renewable energy.
Sunlight & Biomass

(c) Detail at least three types of energy derived from them.
Solar Energy, Hydrogen Energy, Biofuels (Ethanol & Biodiesel)

ECE464 Power Electronics Assignment Solution

2. Factors to take into consideration for a renewable energy facility and how these factors differ from a non-renewable energy facility.

The renewableenergy facilities must be located where the resource is abundantly available. Therefore, sitingrenewable energy facilities involves geographic constraints that do not apply to traditional powerplants (non-renewable energy facilities). For example:
A. Ideal locations for harnessing a resource may lack easy access to transmissioninfrastructure – a problem in particular for wind farms in remote rural areas.
B. Locating a biomass plant for ready access to a feedstock mayinvolve transporting the energy produced over a longer distance to population centres.

Several other factors need to be taken into account for siting, like restrictions on the use of rooftop solar panels. Barriers can also consist of regulatory gaps - the absence of standards needed to support grid interconnection. Moreover, other factors in the form of siting-related incentives or benefits that areavailable only or predominantly for non-renewable generation. For example, the availability of statutory benefits for utility-scale projects mayoperate in the inverse as a measurable barrier to smaller non-utilityprojects relative to their larger counterparts. Similarly, other laws outlining the cost recovery for siting and related pre-construction costs for nuclear power plants, irrespective of whether thefacility is in fact built, provide a significant incentive to build nuclear power plants.Without the same provision for large-scale renewable projects, it may function as an inverse regulatory barrier relative to non-renewable facilities.

3. Outline the application of Power Electronics in renewable energy systems

Power Electronics are widely applied in renewable energy systems for power generation, transmission and distribution in order to produce a flexible AC/DC power output for a given load and enhance affordability of the developed technology. Different semiconductor-based power-conversion represents a key enabling technology to meet the challenges of tomorrows electricity supply. Power electronics technologies have been widely used inrenewable energy systems such as hydro power, municipal solid wastes, biomass, geothermal,solar thermal, solar photovoltaic, wind power, and tidal andwave. The latest research on fuel cells has made them the no.1 contender for a future distribution energy resource.

Some exemplary details of the renewable energy systems deploying power electronic systems are as follows:

  • Wind Power
    • Synchronous Generator with rectifier and inverter for grid interconnects
    • Induction Generator with AC-DC convertor for frequency and power control
  • Solar Power
    • Solar Cells to convert sunlight into electrical energy based on solar photovoltaic principles
    • First Stage AC-DC Converterfor circuit power conditioning

4. Design and sketch a photovoltaic array configuration to power an AC circuit load of 1.1KW through an adequately sized inverter, requiring a 60 to 80VDC input and capable of 95% energy transmission. The PV modules or panels to be used are rated 12V at 60W each.

1. Determination of Actual Power Demand
AC Load to be powered = 1100 W
Transmission Efficiency = 0.95
Actual Power requirement = 1100/0.95 = 1157.89 W

2. Sizing of PV Modules
Assuming Panel-generation factor of 3, the total Watt-peak rating of the PV Module required = 1157.89/3 = 385.97 W
Therefore, No. of PV Panels required = 385.97/60 = 6.43 or 7 (approximately)
Result of the calculation is the minimum number of PV panels. If more PV modules are installed, the system will perform better and battery life will be improved. If fewer PV modules are used, the system may not work at all during cloudy periods and battery life will be shortened.

Sizing of PV Modules

3. Inverter sizing
The input rating of the inverter should never be lower than the total watt of appliances. The inverter must have the same nominal voltage as your battery.The inverter size should be 25-30% bigger than total load in Watts.
Therefore, Inverter Size = 1430 W

4. Battery Sizing
Total Load = 1100 W
Nominal Battery Voltage = 70 V (average)
Therefore Battery Ampere Rating = 1100/70 = 15.71 Amp
The Solar Charge Controller can be similarly designed if the ratings are specified.

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5. Sketch a simple grid-connected photovoltaic system and describe how the main components function.

The grid-connected photovoltaic power systems feed excess power to the grid, which in this case acts as a battery for the system. This feedback is done through a meter to monitor the amount of power transferred based on the concept of Net-metering. Moreover, the photovoltaic wattage may be less than average consumption and require the consumer to purchase a lesser amountof grid energy. On the other hand, if the photovoltaic wattage substantially exceeds the average consumption, the excessenergy produced by the panels can yield revenue by selling it to the grid. Therefore, the consumer only needs to pay the cost of electricity consumed less the value of electricity generated.

grid-connected photovoltaic system

6. What are the characteristics of a good wind power site and why are they important?

The main characteristics for siting wind turbines and assessing the feasibility of a proposed wind power siteinclude the following:

  1. Wind resource characteristics, including extreme wind conditions
  2. Setback requirements (distance to publicly accessible areas), and spacing between turbines
  3. Proximity to existing infrastructure including transmission lines and roads with adequate capacityto serve the wind plant
  4. Environmental impact, including avian, bat and other biological considerations
  5. Seismic activity, noise constraints, altitude, corrosion, and extreme temperatures
  6. Community acceptance and compatibility with adjacent land uses
  7. MW-scale wind turbines cannot be located in densely populated areas.Site-specific characteristics greatly influence the scope of construction.
  8. Engineering, Procurement and Construction (EPC) considerations: Wind turbine foundations, Wind turbine installation/erection, Balance of Plant (supporting infrastructure such as sub-station), Offsite and onsite access roads capable of accommodating significant weight, including localcounty roads and highways

A wind turbine site is built on arelatively small area on the groundthat is expected to receive continuous vibrations due to rotatingblades. Therefore, the dynamic properties of the groundat construction site can beespecially pertinent from geotechnical engineering perspectives. The seismic survey is a thorough and appropriate approach for sitecharacterization than conventional drilling because it does not need the bulky, heavy equipment thatdrilling does, the convenient accessibility to the site is anotheradvantage.  Overall cost is also usually some fraction of the drillingcost.

7. A wind farm is to be located on a flat grassed tableland with a scattering of small trees of up to 5m in height and small thickets of brush up to 2m high.  The site is a nature reserve so trees and thickets may not be cleared.  Specify guidelines for wind turbine location and height for this situation.

Guidelines for wind turbine location

  • Locate the infrastructure (including turbines, underground cables and power lines) and other elements associated with the development (such as access tracks and construction laydown areas) at least 50 metres from important stands of this community

  • Undertake a detailed botanical survey to provide suitable compensation for the loss of the community where the damages cannot be avoided
  • The layout concerning the position of turbines, providing the overallconfiguration of the wind energy development and its perceived density or complexity should be of a uniform type, whether asingle line, staggered line, splayed line, random or grid,rather than a mixture

Height Considerations
Height is related to the full extent of turbines (comprising tower,nacelle and maximum blade length in an upright position) and involves the actual height andthe perceived height relativeto topography. Differentpossibilities are acceptable, depending on context:

  • Turbine height is critical in landscapes of relatively smallscale, or comprising features and structures such as houses,and must be carefully considered so as to achieve visualbalance and not to visually dominate.
  • Awind energy development comprising two distinct turbineheights may be acceptable to achieve anaesthetic effect by thecombination of an old and a new wind energy developmentor where certain turbines would be critically visible froma sensitive viewpoint. Other than the height difference, thewind energy developments in the same view-shed shouldrelate with regard to their main design features and colour.

8. Rough out a bid specification profile for a renewable power plant at an ecologically sensitive site.

Introduction:
It is proposed to construct a renewable energy facility at an ecologically sensitive site in ABC Town, XYZ City. To construct this plant, 250 Solar Panels (100 x 100) would be installed and integrated into the electric grid to serve PQR region of this town. Other considerations have been outlined below.

Site details:
Site Name: PQR Region (Total Area of a1b2c3 Sq. Miles)
Location: ABC Town, XYZ City
Capacity: 100 kWp
Latitude: nnnnnn’N
Longitude: eeeeee’E
Elevation: hhhh ft.

Scope of work:

  1. Site survey and layout planning.
  2. Design, development and supply of all components (including LED Street Lights with Poles)of the SPV Power Plants.
  3. Transportation of SPV Power system hardware up to site.
  4. Civil works (construction of control rooms) and related electricaland other works.
  5. Installation and commissioning of SPV Power system (LED Street Lights with poles).
  6. Operation & maintenance of system for a period of 5 years from the date of installation.
  7. Training to JREDA/Local staff for up-keep and routine maintenance.
  8. Any other job essential for smooth completion of the project, not mentioned in “Jobs in the outlined Scope” below.

Jobs in the outlines Scope
i. Arranging a shadow-free area for SPV array installation & control rooms.
ii. Providing statutory clearance of any type, wherever required.

Technical Specifications:
Each of the 100 kWp Power Plant suitable to operate the above mentioned loads should have the followingsub-systems:

Detailed Specification of Components
Detailed Specification of Components

9. Sketch and name six different types of wind turbine rotor. Research and state one advantage for each?

a. Savonius Wind Turbine:This drag-type Vertical-Axis-Wind-Turbine turns relatively slowly, butyields a high torque. Its slowrotational speeds make itunsuitable for generatingelectricity on a large-scale.

Savonius Wind Turbine
b. Flapping Panel Wind Turbine:The wind canactually come from any direction and thewind turbine will work the same way.

Flapping Panel Wind Turbine
c. Darrieus Wind Turbine:It is characterised byits C-shaped rotor blades whichgive it its eggbeater appearance.It is normally built withtwo or three blades.

Darrieus Wind Turbine
d. Giromill Wind Turbine:It is powered by twoor three vertical aerofoils attached tothe central mast by horizontal supports.Giromill turbines work well in turbulentwind conditions and are an affordableoption where a standard horizontal axiswindmill type turbine is unsuitable.

Giromill Wind Turbine
e. Up-Wind Turbines:designed to operate in anupwind mode (with the blades upwind of the tower).Large wind turbines use a motor-driven mechanismthat turns the machine in response to a wind direction.

Up-Wind Turbines
f. Shrouded Wind Turbines:have an added structural designfeature called an augmentor to increase the amount of wind passingthrough the blades.

Shrouded Wind Turbines

10. Calculate the mechanical shaft power that can be generated from the following wind turbine:

a.    Hub height 36m
b.    Rotor turbine swept diameter 16m
c.    Power coefficient 0.48
d.    Specific wind power 342W/m2
e.    Hub altitude above sea level 230m
Swept Area = πr^2 = 22*8*8/7 = 201.062 m2
Density Correction Factor for Air:
Density Correction Factor for Air
Pressure (230 m) = 0.973 atm.
Density Correction Factor (230 m) = 0.973
Corrected Specific Wind Power = 0.973*342 = 332.766

This corrected specific wind power need to be further corrected for effect of change in wind velocity due to hub-height of 50 m.
Assuming a friction coefficient of 0.3,Wind Velocity can be calculated as follows:

Wind Velocity

Therefore, wind speed at base height (10 m) = 8.43 m/s
Therefore, wind speed correction factor for a hub height of 50 m = (50/10)0.3= 1.62
Corrected Specific Wind Power = 332.766*(1.62)3 = 1416.5 W/m2
Mechanical Shaft Power Generated = Corrected Specific Wind Power * Area * Power coefficient = 1416.5*201.06*0.48 = 136.7 kW

11. Define overall efficiency of a wind generator

The fraction of the wind’s power that is extracted bythe blades, also known as the efficiency of the rotor, is the overall efficiency of any wind-generator

wind-generator

Where, the ratio of downstream to upstreamwind-speed is defined as:

upstreamwind-speed

13. Name three hybrid energy systems and describe a scenario for each in which they might be selected to provide power.

1. Biomass-Wind-Fuel Cell
2. Photovoltaic-Wind Energy
3. Renewable Hybrid Power Plant
A hybrid power plant consisting of these renewable energy sources can be made into operation by proper utilization of these resources in a completely controlled manner.

14. Discuss the main electrical threat that needs to be considered for a wind turbine installation and the systems used to protect the wind power system.

Earthing, lightning and overvoltage effects constitute important electrical threats to wind power systems. The main systems used to protect wind-power installations are as follows:

  1. low-voltage surge protection devices
  2. medium and high-voltage surge arresters
  3. earthing and lightning protection systems

Actual variable-speed wind turbines are equipped with PWM (Pulse with Modulation) controlled inverters in order to regulate their output voltage and frequency. These technologies, if not filtered properly, generate peak transient over-voltages super-imposed on the PWM control voltage. These peaks, of several kV, will be seen by a standard surge protection device as transient over-voltages due to lightning, creating unwanted triggering of the surge arresters with a high frequency and therefore reducing considerably their life time. That’s why it is necessary to use SPDs with a specific withstand to these PWM, the peak repetitive voltage withstand characteristics.

15. Describe three maintenance tasks and their purpose required for a solar photovoltaic installation.

1. Battery Maintenance:

  • Battery Inspection & Cleaning: To assess the condition of the system’sbatteries
  • Checking the Electrolyte Level: To assess the correct acid volume
  • Checking Battery Voltage: To determine the battery state of charge

2. Solar Panel Maintenance:To ensure the optimal use ofthe solar panels by checking for defects in the modules such as cracks, chips, de-lamination, fogged glazing, water leaks and dis-coloration. The array mounting frame should also be noted including the array mounting bolts (e.g. bolt rusting) and checks to ensure that the frame and modules are firmly secured. The junction boxes should also be checked to ensure that the wires are not damaged.

3.Wiring and Connections:To check for any cracks, breaks or deterioration in the insulation/conduits. Inspect panel boxes to ensure that they have not become a home for rodents and insects. Also inspect connections for any corrosion and/or burning. The following sections of conduit and wiring should be checked for any signs of damage:

  • Solar panels to the charge controller
  • Charge controller to the battery bank
  • Inverter/charger to the battery bank
  • Generator to Inverter/charger
  • Inverter/charger and Generator to the AC outlets
  • Battery bank to the DC outlets/load.

16. Describe how earthing works?

An earthing system works by keeping the exposed conductive surfaces of a device at earth potential. For Example: If a fault within an electrical device connects a "hot" (unearthed) supply conductor to an exposed conductive surface, anyone touching it while electrically connected to the earthwill complete a circuit back to the earthed supply conductor and receive an electric shock. Furthermore, to avoid possible voltage drop no current is allowed to flow in this conductor under normal circumstances, but fault currents will usually trip or blow the fuse or circuit breaker protecting the circuit. But the most important example of a functional earth is the neutral in an electrical supply system. It is a current-carrying conductor connected to earth, often but not always at only one point to avoid earth currents.

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