Geothermal Energy: A brief Overview

Geothermal energy is the heat from the Earth. It's clean and sustainable. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth's surface, and down even deeper to the extremely high temperatures of molten rock called magma. Almost everywhere, the shallow ground or upper 10 feet of the Earth's surface maintains a nearly constant temperature between 50° and 60°F (10° and 16°C). Geothermal heat pumps can tap into this resource to heat and cool buildings. A geothermal heat pump system consists of a heat pump, an air delivery system (ductwork), and a heat exchanger-a system of pipes buried in the shallow ground near the building. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to provide a free source of hot water. In the United States, most geothermal reservoirs of hot water are located in the western states, Alaska, and Hawaii. Wells can be drilled into underground reservoirs for the generation of electricity. Some geothermal power plants use the steam from a reservoir to power a turbine/generator, while others use the hot water to boil a working fluid that vaporizes and then turns a turbine. Hot water near the surface of Earth can be used directly for heat. Direct-use applications include heating buildings, growing plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes such as pasteurizing milk. Hot dry rock resources occur at depths of 3 to 5 miles everywhere beneath the Earth's surface and at lesser depths in certain areas. Access to these resources involves injecting cold water down one well, circulating it through hot fractured rock, and drawing off the heated water from another well. Currently, there are no commercial applications of this technology. Existing technology also does not yet allow recovery of heat directly from magma, the very deep and most powerful resource of geothermal energy. Most power plants need steam to generate electricity. The steam rotates a turbine that activates a generator, which produces electricity. Many power plants still use fossil fuels to boil water for steam. Geothermal power plants, however, use steam produced from reservoirs of hot water found a couple of miles or more below the Earth's surface. There are three types of geothermal power plants:dry steam, flash steam, and binary cycle. Dry steam power plants draw from underground resources of steam. The steam is piped directly from underground wells to the power plant, where it is directed into a turbine/generator unit. There are only two known underground resources of steam in the United States: The Geysers in northern California and Yellowstone National Park in Wyoming, where there's a well-known geyser called Old Faithful. Since Yellowstone is protected from development, the only dry steam plants in the country are at The Geysers. Flash steam power plants are the most common. They use geothermal reservoirs of water with temperatures greater than 360°F (182°C). This very hot water flows up through wells in the ground under its own pressure. As it flows upward, the pressure decreases and some of the hot water boils into steam. The steam is then separated from the water and used to power a turbine/generator. Any leftover water and condensed steam are injected back into the reservoir, making this a sustainable resource. Binary cycle power plants operate on water at lower temperatures of about 225°-360°F (107°-182°C). These plants use the heat from the hot water to boil a working fluid, usually an organic compound with a low boiling point. The working fluid is vaporized in a heat exchanger and used to turn a turbine. The water is then injected back into the ground to be reheated. The water and the working fluid are kept separated during the whole process, so there are little or no air emissions. Small-scale geothermal power plants (under 5 megawatts) have the potential for widespread application in rural areas, possibly even as distributed energy resources. Distributed energy resources refer to a variety of small, modular power-generating technologies that can be combined to improve the operation of the electricity delivery system. When a person takes a hot bath, the heat from the water will usually warm up the entire bathroom. Geothermal reservoirs of hot water, which are found a couple of miles or more beneath the Earth's surface, can also be used to provide heat directly. This is called the direct use of geothermal energy. Geothermal direct use dates back thousands of years, when people began using hot springs for bathing, cooking food, and loosening feathers and skin from game. Today, hot springs are still used as spas. But there are now more sophisticated ways of using this geothermal resource. In modern direct-use systems, a well is drilled into a geothermal reservoir to provide a steady stream of hot water. The water is brought up through the well, and a mechanical system - piping, a heat exchanger, and controls - delivers the heat directly for its intended use. A disposal system then either injects the cooled water underground or disposes of it on the surface. Geothermal hot water can be used for many applications that require heat. Its current uses include heating buildings (either individually or whole towns), raising plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes, such as pasteurizing milk. With some applications, researchers are exploring ways to effectively use the geothermal fluid for generating electricity as well. The shallow ground, the upper 10 feet of the Earth, maintains a nearly constant temperature between 50° and 60°F (10°-16°C). Like a cave, this ground temperature is warmer than the air above it in the winter and cooler than the air in the summer. Geothermal heat pumps take advantage of this resource to heat and cool buildings. Geothermal heat pump systems consist of basically three parts: the ground heat exchanger, the heat pump unit, and the air delivery system (ductwork). The heat exchanger is basically a system of pipes called a loop, which is buried in the shallow ground near the building. A fluid (usually water or a mixture of water and antifreeze) circulates through the pipes to absorb or relinquish heat within the ground. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to heat water, providing a free source of hot water. Geothermal heat pumps use much less energy than conventional heating systems, since they draw heat from the ground. They are also more efficient when cooling your home. Not only does this save energy and money, it reduces air pollution.

Tidal Energy: A Introduction & Technical Aspects

Tidal energy is one of the oldest forms of energy used by humans. Indeed, tide mills, in use on the Spanish, French and British coasts, date back to 787 A.D.. Tide mills consisted of a storage pond, filled by the incoming (flood) tide through a sluice and emptied during the outgoing (ebb) tide through a water wheel. The tides turned waterwheels, producing mechanical power to mill grain. We even have one remaining in New York- which worked well into the 20th century. Tidal power is non-polluting, reliable and predictable. Tidal barrages, undersea tidal turbines – like wind turbines but driven by the sea – and a variety of machines harnessing undersea currents are under development. Unlike wind and waves, tidal currents are entirely predictable. Tidal energy can be exploited in two ways: 1. By building semi-permeable barrages across estuaries with a high tidal range. 2. By harnessing offshore tidal streams. Barrages allow tidal waters to fill an estuary via sluices and to empty through turbines. Tidal streams can be harnessed using offshore underwater devices similar to wind turbines. Most modern tidal concepts employ a dam approach with hydraulic turbines. A drawback of tidal power is its low capacity factor, and it misses peak demand times because of 12.5 hr cycle of the tides. The total world potential for ocean tidal power has been estimated at 64,000 MWe. The 25-30 ft tidal variations of Passamaquoddy Bay (Bay of Fundy) have the potential of between 800 to 14,000 MWe Tidal range may vary over a wide range (4.5-12.4 m) from site to site. A tidal range of at least 7 m is required for economical operation and for sufficient head of water for the turbines. Hammerfest Traditional tidal electricity generation involves the construction of a barrage across an estuary to block the incoming and outgoing tide. The dam includes a sluice that is opened to allow the tide to flow into the basin; the sluice is then closed, and as the sea level drops, the head of water (elevated water in the basin) using traditional hydropower technology, drives turbines to generate electricity. Barrages can be designed to generate electricity on the ebb side, or flood side, or both. Tidal range may vary over a wide range (4.5-12.4 m) from site to site. A tidal range of at least 7 m is required for economical operation and for sufficient head of water for the turbines. A 240 MWe facility has operated in France since 1966, 20 MWe in Canada since 1984, and a number of stations in China since 1977, totaling 5 mWw. Tidal energy schemes are characterised by low capacity factors, usually in the range of 20-35%. The waters off the Pacific Northwest are ideal for tapping into an ocean of power using newly developed undersea turbines. The tides along the Northwest coast fluctuate dramatically, as much as 12 feet a day. The coasts of Alaska, British Columbia and Washington, in particular, have exceptional energy-producing potential. On the Atlantic seaboard, Maine is also an excellent candidate. The undersea environment is hostile so the machinery will have to be robust. Currently, although the technology required to harness tidal energy is well established, tidal power is expensive, and there is only one major tidal generating station in operation. This is a 240 megawatt (1 megawatt = 1 MW = 1 million watts) at the mouth of the La Rance river estuary on the northern coast of France (a large coal or nuclear power plant generates about 1,000 MW of electricity). The La Rance generating station has been in operation since 1966 and has been a very reliable source of electricity for France. La Rance was supposed to be one of many tidal power plants in France, until their nuclear program was greatly expanded in the late 1960’s. Elsewhere there is a 20 MW experimental facility at Annapolis Royal in Nova Scotia, and a 0.4 MW tidal power plant near Murmansk in Russia. UK has several proposals underway. Studies have been undertaken to examine the potential of several other tidal power sites worldwide. It has been estimated that a barrage across the Severn River in western England could supply as much as 10% of the country’s electricity needs (12 GW). Similarly, several sites in the Bay of Fundy, Cook Inlet in Alaska, and the White Sea in Russia have been found to have the potential to generate large amounts of electricity. WHAT IS THE IMPACT ON THE ENVIRONMENT? Tidal energy is a renewable source of electricity which does not result in the emission of gases responsible for global warming or acid rain associated with fossil fuel generated electricity. Use of tidal energy could also decrease the need for nuclear power, with its associated radiation risks. Changing tidal flows by damming a bay or estuary could, however, result in negative impacts on aquatic and shoreline ecosystems, as well as navigation and recreation. The few studies that have been undertaken to date to identify the environmental impacts of a tidal power scheme have determined that each specific site is different and the impacts depend greatly upon local geography. Local tides changed only slightly due to the La Rance barrage, and the environmental impact has been negligible, but this may not be the case for all other sites. It has been estimated that in the Bay of Fundy, tidal power plants could decrease local tides by 15 cm. This does not seem like much when one considers that natural variations such as winds can change the level of the tides by several metres. WHAT ARE THE COSTS OF TIDAL ENERGY? Tidal power is a form of low-head hydroelectricity and uses familiar low-head hydroelectric generating equipment, such as has been in use for more than 120 years. The technology required for tidal power is well developed, and the main barrier to increased use of the tides is that of construction costs. There is a high capital cost for a tidal energy project, with possibly a 10-year construction period. Therefore, the electricity cost is very sensitive to the discount rate. The major factors in determining the cost effectiveness of a tidal power site are the size (length and height) of the barrage required, and the difference in height between high and low tide. These factors can be expressed in what is called a site’s “Gibrat” ratio. The Gibrat ratio is the ratio of the length of the barrage in metres to the annual energy production in kilowatt hours (1 kilowatt hour = 1 KWH = 1000 watts used for 1 hour). The smaller the Gibrat site ratio, the more desireable the site. Examples of Gibrat ratios are La Rance at 0.36, Severn at 0.87 and Passamaquoddy in the Bay of Fundy at 0.92. Offshore tidal power generators use familiar and reliable low-head hydroelectric generating equipment, conventional marine construction techniques, and standard power transmission methods. The placement of the impoundment offshore, rather than using the conventional “barrage” approach, eliminates environmental and economic problems that have prevented the deployment of commercial-scale tidal power plants. Three projects (Swansea Bay 30 MW, Fifoots Point 30 MW, and North Wales 432 MW) are in development in Wales where tidal ranges are high, renewable source power is a strong public policy priority , and the electricity marketplace gives it a competitive edge. Q. What are some of the devices for tidal energy conversion? The technology required to convert tidal energy into electricity is very similar to the technology used in traditional hydroelectric power plants. The first requirement is a dam or “barrage” across a tidal bay or estuary. Building dams is an expensive process. Therefore, the best tidal sites are those where a bay has a narrow opening, thus reducing the length of dam which is required. At certain points along the dam, gates and turbines are installed. When there is an adequate difference in the elevation of the water on the different sides of the barrage, the gates are opened. This “hydrostatic head” that is created, causes water to flow through the turbines, turning an electric generator to produce electricity. Electricity can be generated by water flowing both into and out of a bay. As there are two high and two low tides each day, electrical generation from tidal power plants is characterized by periods of maximum generation every twelve hours, with no electricity generation at the six hour mark in between. Alternatively, the turbines can be used as pumps to pump extra water into the basin behind the barrage during periods of low electricity demand. This water can then be released when demand on the system its greatest, thus allowing the tidal plant to function with some of the characteristics of a “pumped storage” hydroelectric facility. WHAT ARE SOME OF THE DEVICES FOR TIDAL ENERGY CONVERSION? The technology required to convert tidal energy into electricity is very similar to the technology used in traditional hydroelectric power plants. The first requirement is a dam or “barrage” across a tidal bay or estuary. Building dams is an expensive process. Therefore, the best tidal sites are those where a bay has a narrow opening, thus reducing the length of dam which is required. At certain points along the dam, gates and turbines are installed. When there is an adequate difference in the elevation of the water on the different sides of the barrage, the gates are opened. This “hydrostatic head” that is created, causes water to flow through the turbines, turning an electric generator to produce electricity. Electricity can be generated by water flowing both into and out of a bay. As there are two high and two low tides each day, electrical generation from tidal power plants is characterized by periods of maximum generation every twelve hours, with no electricity generation at the six hour mark in between. Alternatively, the turbines can be used as pumps to pump extra water into the basin behind the barrage during periods of low electricity demand. This water can then be released when demand on the system its greatest, thus allowing the tidal plant to function with some of the characteristics of a “pumped storage” hydroelectric facility. WHY TIDAL ENERGY? The demand for electricity on an electrical grid varies with the time of day. The supply of electricity from a tidal power plant will never match the demand on a system. But, due to the lunar cycle and gravity, tidal currents, although variable, are reliable and predictable and their power can make a valuable contribution to an electrical system which has a variety of sources. Tidal electricity can be used to displace electricity which would otherwise be generated by fossil fuel (coal, oil, natural gas) fired power plants, thus reducing emissions of greenhouse and acid gasses. Tidal power, also called tidal energy, is a form of hydropower that converts the energy of tides into useful forms of power, mainly electricity. Although not yet widely used, tidal power has potential for future electricity generation. Tides are more predictable than wind energy and solar power. Among sources of renewable energy, tidal power has traditionally suffered from relatively high cost and limited availability of sites with sufficiently high tidal ranges or flow velocities, thus constricting its total availability. However, many recent technological developments and improvements, both in design (e.g. dynamic tidal power, tidal lagoons) and turbine technology (e.g. new axial turbines, cross flow turbines), indicate that the total availability of tidal power may be much higher than previously assumed, and that economic and environmental costs may be brought down to competitive levels. Historically, tide mills have been used both in Europe and on the Atlantic coast of North America. The incoming water was contained in large storage ponds, and as the tide went out, it turned waterwheels that used the mechanical power it produced to mill grain. The earliest occurrences date from the Middle Ages, or even from Roman times. It was only in the 19th century that the process of using falling water and spinning turbines to create electricity was introduced in the U.S. and Europe. The world's first large-scale tidal power plant is the Rance Tidal Power Station in France, which became operational in 1966. Tidal power is taken from the Earth's oceanic tides; tidal forces are periodic variations in gravitational attraction exerted by celestial bodies. These forces create corresponding motions or currents in the world's oceans. Due to the strong attraction to the oceans, a bulge in the water level is created, causing a temporary increase in sea level. When the sea level is raised, water from the middle of the ocean is forced to move toward the shorelines, creating a tide. This occurrence takes place in an unfailing manner, due to the consistent pattern of the moon’s orbit around the earth.[5] The magnitude and character of this motion reflects the changing positions of the Moon and Sun relative to the Earth, the effects of Earth's rotation, and local geography of the sea floor and coastlines. Tidal power is the only technology that draws on energy inherent in the orbital characteristics of the Earth–Moon system, and to a lesser extent in the Earth–Sun system. Other natural energies exploited by human technology originate directly or indirectly with the Sun, including fossil fuel, conventional hydroelectric, wind, biofuel, wave and solar energy. Nuclear energy makes use of Earth's mineral deposits of fissionable elements, while geothermal power taps the Earth's internal heat, which comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%). A tidal generator converts the energy of tidal flows into electricity. Greater tidal variation and higher tidal current velocities can dramatically increase the potential of a site for tidal electricity generation. Because the Earth's tides are ultimately due to gravitational interaction with the Moon and Sun and the Earth's rotation, tidal power is practically inexhaustible and classified as a renewable energy resource. Movement of tides causes a loss of mechanical energy in the Earth–Moon system: this is a result of pumping of water through natural restrictions around coastlines and consequent viscous dissipation at the seabed and in turbulence. This loss of energy has caused the rotation of the Earth to slow in the 4.5 billion years since its formation. During the last 620 million years the period of rotation of the earth (length of a day) has increased from 21.9 hours to 24 hours; in this period the Earth has lost 17% of its rotational energy. While tidal power will take additional energy from the system, the effect is negligible and would only be noticed over millions of years.[8]

Design of marine half-ship electrical power system with base load, hotel load, bow thrusters and electric propulsion

The principal components of the system are: 30 MVA Gas Turbine, Round Rotor Alternator 5 MVA Diesel Generator, Salient Pole Alternator 11.5 MVA Base Load 6 MVA Switched Hotel Load 20 MVA Average-Value Propulsion Rectifier 1 MVA Direct Online Start, Squirrel Cage Bow Thrusters

The sequence of events during the simulation is: 10 seconds - Hotel Load disconnected 20 seconds - Propulsion begins ramping up 30 seconds - Full power ahead 40 seconds - Propulsion begins ramping down 50 seconds - Bow Thrusters start up 60 seconds - Hotel Load connected

Design of Three phase to DC zener regulated supply for DC battery charging

Description The Zener diode block modeled in this example presents a practical implementation that uses parameters commonly provided on datasheets. These parameters are (1) Zener Voltage Vz (2) Dynamic Impedance Zzt (3) Knee Impedance Zzk (4) Max Continuous Current Izm (5) Forward Voltage Drop Vf (6) On Resistance Ron This block can effectively model three regions of operation of the zener diode I-V characteristics - forward-biased, reverse-biased before breakdown and reverse-biased after breakdown. Beyond the maximum reverse continuous current Izm, the zener is assumed to burn up and is treated as an open circuit. The implementation of the zener diode can be seen by looking under the mask of the block. Zener diodes are commonly employed in applications as voltage regulators. The circuit shows an AC source fed to a step-down transformer. The output of the transformer is then rectified using a diode bridge and smoothened using a capacitive filter. The zener diode then acts to regulate the output voltage to the zener voltage 10V. The input current into the zener is limited by the resistor Rlimit to permissible values. The programmable voltage source is setup to increase its output voltage at 0.1s. As the source output increases, so does the voltage applied at the input of the zener. However, the zener can regulate the output only as long as its input current is below the maximum specified value. This current increases as we increase the source voltage and the zener ultimately fails at about 0.112s. With the zener acting as an open-circuit at fault, voltage regulation is lost and the output of the capacitive filter gets applied to the load. Result:

Modelling of Electrical components in Simpower system

Advantages of MATLAB modelling: • Libraries of application-specific models, including models of common AC and DC electric drives, flexible AC transmission systems (FACTS), and renewable energy systems • Discretization and phasor simulation modes for faster model execution • Ideal switching algorithm for accelerated simulation of power electronic devices • Analysis methods for obtaining state-space representations of circuits and computing load flow for machines • Basic models for developing key electrical technologies • Ability to extend component libraries using the Simscape language • Support for C-code generation SimPowerSystems model (left) of an asynchronous motor and diesel-generator uninterruptible power supply (UPS). The Simulink scope (right) shows stator currents and speed of the asynchronous machine.

SimPowerSystems supports the development of complex, self-contained power systems, such as those in automobiles, aircraft, manufacturing plants, and power utility applications. The models you create support your entire development process, including hardware-in-the-loop simulations. Modeling Electrical Power Systems SimPowerSystems provides libraries for modeling electric machines, transformers, and power converters. You can connect components, such as generators, transmission lines, breakers, and motors, to model electrical power systems. Application-specific libraries are also provided, enabling you to model electric drives, aircraft power networks, and renewable energy systems. Connecting these systems with control systems modeled in Simulink lets you test integrated electrical power systems in a single environment. In addition to the traditional input-output or signal flow connections used in Simulink, SimPowerSystems uses physical connections that permit the flow of power in any direction. Models of electrical power systems built using physical connections (or acausal models) closely resemble the network they represent, and are easy to understand and share. You can define your three-phase connections using individual connections for each phase, enabling you to perform tests such as injecting a single-line-to-ground fault. You can also create single-line diagrams, where the three phases are represented by a single line, making the diagram easy to read. SimPowerSystems components are parameterized using the per-unit system, which is widely used in the power system industry and simplifies the parameterization and analysis of your system.

SimPowerSystems model (left) of a permanent magnet synchronous motor and inverter sized for use in a typical hybrid vehicle. The model includes the electrical connections (single-phase and three-phase) and signal flow connections, and the scope (right) shows the stator currents in the PMSM. Creating Custom Components You can add components from other physical modeling products to your SimPowerSystems model. The Foundation libraries in Simscape contain blocks in hydraulic, thermal, magnetic, and other physical domains. Integrating these domains into your SimPowerSystems model using physical connections helps you model other aspects of your system in a single environment. The Simscape language is an object-oriented language based on MATLAB that enables you to create your own physical modeling components and libraries. You can define custom components complete with parameterization, physical connections, and equations represented as acausal implicit differential algebraic equations (DAEs). Within your component’s Simscape language file, you can use MATLAB to analyze parameter values, perform preliminary computations, and initialize system variables. The Simulink block and dialog box for your custom component are automatically created from the file.

Using the Simscape language, you can control exactly which effects are captured in the models of your physical components. This approach enables you to balance the tradeoff between model fidelity and simulation speed. Custom Simscape implementation of a permanent magnet synchronous motor, used as a generator. The MATLAB editor shows Simscape language source code of the electrical and mechanical equations, and the scope shows the three-phase AC currents and DC current at the load. Simulating Models You can simulate your SimPowerSystems models using any of three solution methods for your power system network, as well as an ideal switching algorithm that improves simulation performance for systems with high-frequency switching. Selecting SimPowerSystems Simulation Mode Choose simulation mode (continuous, discrete, or phasor) using SimPowerSystems™. Analyze transient effects and magnitudes of circuit voltages. Continuous methods perform highly accurate simulations of power system models, varying the step size to capture the dynamics of your system. Discrete methods enable you to control the precision of your simulation by selecting the size of the time step. Phasor simulation replaces the differential equations representing the network with a set of algebraic equations at a fixed frequency, making it possible to do transient stability studies of systems with multiple machines. The ideal switching algorithm in SimPowerSystems enables fast and accurate simulation of systems containing power electronic devices. This algorithm uses an improved method of calculating the state-space representation of the system instead of relying on current sources with high-impedance snubbers to model power electronic devices. This method gives you greater flexibility in selecting a solver and results in shorter simulation times. SimPowerSystems interface for selecting simulation options. Continuous, discrete, and phasor simulation modes are supported, with the option of enabling an ideal switching algorithm for faster simulation. Analyzing Models SimPowerSystems provides tools for analyzing models, visualizing simulation results, and calculating advanced block parameters, enabling you to: • Display steady-state voltage and currents • Display and modify initial state values • Perform load flows and machine initialization • Perform harmonic analysis • Display impedance vs. frequency measurements The load flow computational engine computes initial currents of synchronous and asynchronous machines. You specify the desired steady-state machine conditions in your circuit, and SimPowerSystems computes the load flow. The resulting rotor position, initial currents, and internal fluxes are automatically entered into the parameters for the machines. SimPowerSystems lets you analyze the electrical network topology and compute the equivalent state-space model of your circuit without running a simulation. You can link the state-space model to the Linear System Analysis app in Control System Toolbox™ to obtain time-domain and frequency-domain responses. The SimPowerSystems FFT analysis tool. The frequency spectrum of a voltage waveform is displayed, and power quality is measured by calculating total harmonic distortion.

SimPowerSystems Release Notes R2015a

Simscape Components Asynchronous machines with SI parameterization Synchronous Machine Model 2.1 blocks Zigzag-Delta1-Wye and Zigzag-Delta11-Wye Transformer blocks Average-Value Inverter block Ideal Rectifier block name change Featured Examples Specialized Technology PV Array block Annotation and export options for Load Flow Tool power_customize function for creating custom Specialized Technology blocks Three-limb core option for three-phase transformer blocks Interpolation and Store State-Space Matrices options for Tustin solver​​ New machine block dialog boxes and function access New powergui dialog box and tools Block library changes Phasor Simulation Method examples

Simulating AC to DC to AC PWM converter

A 60 Hz, voltage source feeds a 50 Hz, 50 kW load through an AC-DC-AC converter. The 600V, 60 Hz voltage obtained at secondary of the Wye/Delta transformer is first rectified by a six pulse diode bridge. The filtered DC voltage is applied to an IGBT two-level inverter generating 50 Hz. The IGBT inverter uses Pulse Width Modulation (PWM) at a 2 kHz carrier frequency. The circuit is discretized at a sample time of 2 us The load voltage is regulated at 1 pu (380 V rms) by a PI voltage regulator using abc_to_dq and dq_to_abc transfomations. The first output of the voltage regulator is a vector containing the three modulating signals used by the PMW Generator to generate the 6 IGBT pulses. The second output returns the modulation index. The Multimeter block is used to observe diode and IGBT currents. In order to allow further signal processing, signals displayed on Scope1 block (sampled at simulation sampling rate of 2us ) are stored in a variable named 'psbbridges_str' (structure with time). Simulation Start the simulation. After a transient period of approximately 50 ms, the system reaches a steady state. Observe voltage waveforms at DC bus, inverter output and load on Scope1. The harmonics generated by the inverter around multiples of 2 kHz are filtered by the LC filter. As expected the peak value of the load voltage is 537 V (380 Vrms). In steady state, the mean value of the modulation index is m = 0.80 and the mean value of the DC voltage is 778 V. The fundamental component of 50 Hz voltage buried in the chopped inverter voltage is therefore: Vab = 778 V * 0.612 * 0.80 = 381 V rms Once simulation is completed, open the Powergui and select 'FFT Analysis' to display the 0 - 7000 Hz frequency spectrum of signals saved in the 'psbbridges_str' structure. The FFT will be performed on a 2-cycle window starting at t=0.1-2/50 (last 2 cycles of recording). Select input labeled 'Vab Load' . Click on Display and observe the frequency spectrum of last 2 cycles. Notice harmonics around multiples of the 2 kHz carrier frequency. Maximum harmonic is 1.4 % of fundamental and THD is 2%. Observe diode currents on trace 1 of Scope2, showing commutation from diode 1 to diode 3. Also observe on trace 2 currents in switches 1 and 2 of the IGBT/Diode bridge (upper and lower switches connected to phase A). These two currents are complementary. A positive current indicates a current flowing in the IGBT, whereas a negative current indicates a current flowing in the antiparallel diode.