AC voltage controllers performance and applications

A voltage controller, also called an AC voltage controller or AC regulator is an electronic module based on either thyristors, TRIACs,SCRs or IGBTs, which converts a fixed voltage, fixed frequency alternating current (AC) electrical input supply to obtain variable voltage in output delivered to a resistive load. This varied voltage output is used for dimming street lights, varying heating temperatures in homes or industry, speed control of fans and winding machines and many other applications, in a similar fashion to an autotransformer. AC voltage controllers (ac line voltage controllers) are employed to vary the RMS value of the alternating voltage applied to a load circuit by introducing Thyristors between the load and a constant voltage ac source. The RMS value of alternating voltage applied to a load circuit is controlled by controlling the triggering angle of the Thyristors in the ac voltage controller circuits. In brief, an ac voltage controller is a type of thyristor power converter which is used to convert a fixed voltage, fixed frequency ac input supply to obtain a variable voltage ac output. The RMS value of the ac output voltage and the ac power flow to the load is controlled by varying (adjusting) the trigger angle ‘’ The ac voltage controllers are classified into two types based on the type of input ac supply applied to the circuit.  Single Phase AC Controllers.  Three Phase AC Controllers. Single phase ac controllers operate with single phase ac supply voltage of 230V RMS at 50Hz in our country. Three phase ac controllers operate with 3 phase ac supply of 400V RMS at 50Hz supply frequency. Each type of controller may be sub divided into  Uni-directional or half wave ac controller.  Bi-directional or full wave ac controller. In brief different types of ac voltage controllers are  Single phase half wave ac voltage controller (uni-directional controller).  Single phase full wave ac voltage controller (bi-directional controller).  Three phase half wave ac voltage controller (uni-directional controller).  Three phase full wave ac voltage controller (bi-directional controller). APPLICATIONS OF AC VOLTAGE CONTROLLERS  Lighting / Illumination control in ac power circuits.  Induction heating.  Industrial heating & Domestic heating.  Transformers tap changing (on load transformer tap changing).  Speed control of induction motors (single phase and poly phase ac induction motor control).  AC magnet controls. 4. AC VOLTAGE CONTROL TECHNIQUES There are two different types of thyristor control used in practice to control the ac power flow  Phase control  On-Off control These are the two ac output voltage control techniques. In On-Off control technique Thyristors are used as switches to connect the load circuit to the ac supply (source) for a few cycles of the input ac supply and then to disconnect it for few input cycles. The Thyristors thus act as a high speed contactor (or high speed ac switch). 4.1 PHASE CONTROL TECHNIQUE In phase control the Thyristors are used as switches to connect the load circuit to the input ac supply, for a part of every input cycle. That is the ac supply voltage is chopped using Thyristors during a part of each input cycle. The thyristor switch is turned on for a part of every half cycle, so that input supply voltage appears across the load and then turned off during the remaining part of input half cycle to disconnect the ac supply from the load. By controlling the phase angle or the trigger angle ‘’ (delay angle), the output RMS voltage across the load can be controlled. The trigger delay angle ‘’ is defined as the phase angle (the value of t) at which the thyristor turns on and the load current begins to flow. Thyristor ac voltage controllers use ac line commutation or ac phase commutation. Thyristors in ac voltage controllers are line commutated (phase commutated) since the input supply is ac. When the input ac voltage reverses and becomes negative during the negative half cycle the current flowing through the conducting thyristor decreases and falls to zero. Thus the ON thyristor naturally turns off, when the device current falls to zero. Phase control Thyristors which are relatively inexpensive, converter grade Thyristors which are slower than fast switching inverter grade Thyristors are normally used. For applications up to 400Hz, if Triacs are available to meet the voltage and current ratings of a particular application, Triacs are more commonly used. Due to ac line commutation or natural commutation, there is no need of extra commutation circuitry or components and the circuits for ac voltage controllers are very simple. Due to the nature of the output waveforms, the analysis, derivations of expressions for performance parameters are not simple, especially for the phase controlled ac voltage controllers with RL load. But however most of the practical loads are of the RL type and hence RL load should be considered in the analysis and design of ac voltage controller circuits. PRINCIPLE OF ON-OFF CONTROL TECHNIQUE (INTEGRAL CYCLE CONTROL) The basic principle of on-off control technique is explained with reference to a single phase full wave ac voltage controller circuit shown below. The thyristor switches and are turned on by applying appropriate gate trigger pulses to connect the input ac supply to the load for ‘n’ number of input cycles during the time interval . The thyristor switches and are turned off by blocking the gate trigger pulses for ‘m’ number of input cycles during the time interval . The ac controller ON time usually consists of an integral number of input cycles. Referring to the waveforms of ON-OFF control technique in the above diagram, Two input cycles. Thyristors are turned ON during for two input cycles. One input cycle. Thyristors are turned OFF during for one input cycle Thyristors are turned ON precisely at the zero voltage crossings of the input supply. The thyristor is turned on at the beginning of each positive half cycle by applying the gate trigger pulses to as shown, during the ON time . The load current flows in the positive direction, which is the downward direction as shown in the circuit diagram when conducts. The thyristor is turned on at the beginning of each negative half cycle, by applying gating signal to the gate of , during . The load current flows in the reverse direction, which is the upward direction when conducts. Thus we obtain a bi-directional load current flow (alternating load current flow) in a ac voltage controller circuit, by triggering the thyristors alternately. This type of control is used in applications which have high mechanical inertia and high thermal time constant (Industrial heating and speed control of ac motors). Due to zero voltage and zero current switching of Thyristors, the harmonics generated by switching actions are reduced.

BLDC motor Drive and applications in real time systems

Before there were brushless DC motors there were brush DC motors, which were brought on in part to replace the less efficient AC induction motors that came before. The brush DC motor was invented all the way back in 1856 by famed German inventor and industrialist Ernst Werner von Siemens. Von Siemens is so famous that the international standard unit of electrical conductance is named after him. Von Siemens studied electrical engineering after leaving the army and produced many contributions to the world of electrical engineering, including the first electric elevator in 1880. Von Siemens’s brush DC motor was fairly rudimentary and was improved upon by Harry Ward Leonard, who nearly perfected the first effective motor control system near the end of the 19th century. This system used a rheostat to control the current in the field winding, which resulted in adjusting the output voltage of the DC generator, which in turn adjusted the motor speed. The Ward Leonard system remained in place all the way until 1960, when the Electronic Regulator Company’s thyristor devices produced solid state controllers that could convert AC power to rectified DC power more directly. It supplanted the Ward Leonard system due to its simplicity and efficiency. Advent of Brushless DC Motors Once the Electronic Regulator Company maximized the efficiency of the brush DC motor, the door was opened for an even more efficient motor device. Brushless DC motors first made the scene in 1962, when T.G. Wilson and P.H. Trickey unveiled what they called “a DC machine with solid state commutation.” Remember that the key element of brushless DC motors as opposed to brush DC motors is that the brushless DC motor requires no physical commutator, a revolutionary difference. As the device was refined and developed, it became a popular choice for special applications such as computer disk drives, robotics and in aircraft. In fact, brushless DC motors are used in these devices today, fifty years later, so great is their effectiveness. The reason these motors were such a great choice for these devices is that in these devices brush wear was a big problem, either because of the intense demands of the application or, for example, in the case of aircraft because of low humidity. Because brushless DC motors had no brushes that could wear out, they represented a great leap forward in technology for these types of devices. The problem was that as reliable as they were, these early brushless DC motors were not able to generate a great deal of power. Modern Brushless DC Motors That all changed in the 1980s, when permanent magnet materials became readily available. The use of permanent magnets, combined with high voltage transistors, enabled brushless DC motors to generate as much power as the old brush DC motors, if not more. Near the end of the 1980s, Robert E. Lordo of the POWERTEC Industrial Corporation unveiled the first large brushless DC motors, which had at least ten times the power of the earlier brushless DC motors. Today, there are probably no major motor manufacturers that do not produce brushless DC motors capable of high power jobs. Naturally, NMB Tech offers a wide variety of brushless DC motors for you to choose from, in sizes from 15mm in diameter to 65mm in diameter, from 0.7 maximum Watts output to 329.9. If you’re starting a new project that requires motors for its applications, you’ll want to seriously consider using brushless DC motors. Industries with motor needs have relied on brushless DC motors for nearly fifty years, and there is every reason to believe that they will continue to do so for decades to come. Take a look at some brushless DC motors today. The brushless DC (BLDC) motor can be envisioned as a brush DC motor turned inside out, where the permanent magnets are on the rotor, and the windings are on the stator. As a result, there are no brushes and commutators in this motor, and all of the disadvantages associated with the sparking of brush DC motors are eliminated. This motor is referred to as a "DC" motor because its coils are driven by a DC power source which is applied to the various stator coils in a predetermined sequential pattern. This process is known as commutation. However, "BLDC" is really a misnomer, since the motor is effectively an AC motor. The current in each coil alternates from positive to negative during each electrical cycle. The stator is typically a salient pole structure which is designed to produce a trapezoidal back-EMF waveshape which matches the applied commutated voltage waveform as closely as possible. However, this is very hard to do in practice, and the resulting back-EMF waveform often looks more sinusoidal than trapezoidal. For this reason, many of the control techniques used with a PMSM motor (such as Field Oriented Control) can equally be applied to a BLDC motor. Another misconception about the BLDC motor is related to how it is driven. Unlike an open-loop stepper application where the rotor position is determined by which stator coil is driven, in a BLDC motor, which stator coil is driven is determined by the rotor position. The stator flux vector position must be synchronized to the rotor flux vector position (not the other way around) in order to obtain smooth operation of the motor. In order to accomplish this, knowledge of the rotor position is required in order to determine which stator coils to energize. Several techniques exist to do this, but the most popular technique is to monitor the rotor position using hall-effect sensors. Unfortunately, these sensors and their associated connectors and harnesses result in increased system cost, and reduced reliability. In an effort to mitigate these issues, several techniques have been developed to eliminate these sensors, resulting in sensorless operation. Most of these techniques are based upon extracting position information from the back-EMF waveforms of the stator windings while the motor is spinning. However, techniques based on back-EMF sensing fall apart when the motor is spinning slowly or at a standstill, since the back-EMF waveforms are faint or non-existent. As a result, new techniques are constantly being developed which obtain rotor position information from other signals at low or zero speed. BLDC motors reign supreme in efficiency ratings, where values in the mid-nineties percent range are routinely obtained. Current research into new amorphous core materials is pushing this number even higher. Ninety six percent efficiency in the 100W range has been reported. They also compete for the title of fastest motor in the world, with speeds on some motors achieving several hundred thousand RPM (400K RPM reported in one application). The most common BLDC motor topology utilizes a stator structure consisting of three phases. As a result, a standard 6-transistor inverter is the most commonly used power stage, as shown in the diagram. Depending on the operational requirements (sensored vs. sensorless, commutated vs. sinusoidal, PWM vs. SVM, etc.) there are many different ways to drive the transistors to achieve the desired goal, which are too numerous to cover here. This places a significant requirement on the flexibility of the PWM generator, which is typically located in the microcontroller.

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

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.

Power Electronics, converters, research and Applications: A Brief overview

Power electronics is the application of solid-state electronics for the control and conversion of electric power. It also refers to a subject of research in electronic and electrical engineering which deals with design, control, computation and integration of nonlinear, time varying energy processing electronic systems with fast dynamics. The capabilities and economy of power electronics system are determined by the active devices that are available. Their characteristics and limitations are a key element in the design of power electronics systems. Formerly, the mercury arc valve, the high-vacuum and gas-filled diode thermionic rectifiers, and triggered devices such as the thyratron and ignitron were widely used in power electronics. As the ratings of solid-state devices improved in both voltage and current-handling capacity, vacuum devices have been nearly entirely replaced by solid-state devices. Power electronic devices may be used as switches, or as amplifiers. An ideal switch is either open or closed and so dissipates no power; it withstands an applied voltage and passes no current, or passes any amount of current with no voltage drop. Semiconductor devices used as switches can approximate this ideal property and so most power electronic applications rely on switching devices on and off, which makes systems very efficient as very little power is wasted in the switch. By contrast, in the case of the amplifier, the current through the device varies continuously according to a controlled input. The voltage and current at the device terminals follow a load line, and the power dissipation inside the device is large compared with the power delivered to the load. Several attributes dictate how devices are used. Devices such as diodes conduct when a forward voltage is applied and have no external control of the start of conduction. Power devices such as silicon controlled rectifiers and thyristors (as well as the mercury valve and thyratron) allow control of the start of conduction, but rely on periodic reversal of current flow to turn them off. Devices such as gate turn-off thyristors, BJT and MOSFET transistors provide full switching control and can be turned on or off without regard to the current flow through them. Transistor devices also allow proportional amplification, but this is rarely used for systems rated more than a few hundred watts. The control input characteristics of a device also greatly affect design; sometimes the control input is at a very high voltage with respect to ground and must be driven by an isolated source. As efficiency is at a premium in a power electronic converter, the losses that a power electronic device generates should be as low as possible. Devices vary in switching speed. Some diodes and thyristors are suited for relatively slow speed and are useful for power frequency switching and control; certain thyristors are useful at a few kilohertz. Devices such as MOSFETS and BJTs can switch at tens of kilohertz up to a few megahertz in power applications, but with decreasing power levels. Vacuum tube devices dominate high power (hundreds of kilowatts) at very high frequency (hundreds or thousands of megahertz) applications. Faster switching devices minimize energy lost in the transitions from on to off and back, but may create problems with radiated electromagnetic interference. Gate drive (or equivalent) circuits must be designed to supply sufficient drive current to achieve the full switching speed possible with a device. A device without sufficient drive to switch rapidly may be destroyed by excess heating. Power electronic circuit’s process and control electrical energy, and are critical elements in many kinds of systems. The rapid evolution of technology is generating a demand for power electronics whose capabilities greatly exceed what is presently achievable. Challenges of particular importance include miniaturization and integration of power electronics, and improving their cost and dynamic performance. Miniaturization is difficult in part because the magnetic components used in most power circuits scale down poorly in size. Likewise, achieving integration and low cost is difficult because of the diverse materials and assembly methods that are required for contemporary designs. My research interest includes working to address these challenges through a combination of new technologies. One research focus is on the development of improved power passive components. Passive components such as inductors and capacitors often dominate the size and cost of power circuits, and limit their efficiency, noise attenuation, and transient performance. In one effort, we are developing means to improve the performance of passive filter components by compensating for their parasitic. These efforts have led to new integrated filter components with much better performance than conventional passives. Likewise, we are developing new types of power passive components that better scale to small sizes and high frequencies. Construction of these components using micro fabrication techniques is also being explored, with the goal of enabling integrated fabrication of power converters. A second research focus is the development of techniques to achieve greatly increased switching frequencies in power converters. Higher frequencies are desirable because they enable faster transient response and reduce passive component requirements. Moreover, at sufficiently high frequencies, batch fabrication of many circuit components may become possible, enabling higher levels of integration to be achieved. We are exploring new system architectures, circuit designs, and control methods that together enable substantial increases in operating frequency over the present state of the art. It is anticipated that the technologies under development will lead to miniaturized, highly integrated power electronics. In addition to developing fundamental power conversion technologies, we are applying them in a variety of applications. Automotive power generation and control is one such area. For example, we have investigated the application of power electronics to enhance the efficiency, power, and transient performance of automotive alternators. We have also developed dc/dc converters and other power electronics for automotive applications, with the goal of enabling improved performance, safety, and comfort in vehicles. Other areas of interest include power components and circuits for industrial, commercial, consumer, and medical applications where improved size, efficiency, and performance are of importance. Applications of power electronics range in size from a switched mode power supply in an AC adapter, battery chargers, fluorescent lamp ballasts, through variable frequency drives and DC motor drives used to operate pumps, fans, and manufacturing machinery, up to gigawatt-scale high voltage direct current power transmission systems used to interconnect electrical grids. Power electronic systems are found in virtually every electronic device. For example: • DC/DC converters are used in most mobile devices (mobile phones, PDA etc.) to maintain the voltage at a fixed value whatever the voltage level of the battery is. These converters are also used for electronic isolation and power factor correction. A power optimizer is a type of DC/DC converter developed to maximize the energy harvest from solar photovoltaic or wind turbine systems. • AC/DC converters (rectifiers) are used every time an electronic device is connected to the mains (computer, television etc.). These may simply change AC to DC or can also change the voltage level as part of their operation. • AC/AC converters are used to change either the voltage level or the frequency (international power adapters, light dimmer). In power distribution networks AC/AC converters may be used to exchange power between utility frequency 50 Hz and 60 Hz power grids. • DC/AC converters (inverters) are used primarily in UPS or renewable energy systems or emergency lighting systems. Mains power charges the

DC battery. If the mains fail, an inverter produces AC electricity at mains voltage from the DC battery. Solar inverter, both smaller string and larger central inverters, as well as solar micro-inverter are used in photovoltaic as a component of a PV system. Motor drives are found in pumps, blowers, and mill drives for textile, paper, cement and other such facilities. Drives may be used for power conversion and for motion control. For AC motors, applications include variable-frequency drives, motor soft starters and excitation systems. In hybrid electric vehicles (HEVs), power electronics are used in two formats: series hybrid and parallel hybrid. The difference between a series hybrid and a parallel hybrid is the relationship of the electric motor to the internal combustion engine (ICE). Devices used in electric vehicles consist mostly of dc/dc converters for battery charging and dc/ac converters to power the propulsion motor. Electric trains use power electronic devices to obtain power, as well as for vector control using pulse width modulation (PWM) rectifiers. The trains obtain their power from power lines. Another new usage for power electronics is in elevator systems. These systems may use thyristors, inverters, permanent magnet motors, or various hybrid systems that incorporate PWM systems and standard motors.

Power Electronics Devices & converters A K Tyagi

Cycloconverters or frequency changers

Project ideas: Design and analysis of three phase cycloconverter for variable load

The objective of this study is to observe the correlations between variable operating conditions and power quality parameters for a three-phase to single-phase cycloconverter. The cycloconverter is examined in its most straightforward form without additional output filters or elaborate control methods. Variable operating conditions include input frequency, output frequency, and resistive load size. The power quality parameters of interest are power factor, input current total harmonic distortion (THD), output voltage THD, and efficiency. The scope of the project includes analytical calculations, Matlab/Simulink simulations, and /or hardware implementation. The results show that output frequency has minimal effect on power quality. Total harmonic distortion undesirably peaks at a combination of low input frequency and high output frequency. Extrapolations can be made for the cycloconverter operating at different frequencies and loads based on the trends observed within the test matrix. This can be a good design and innovative exercise to perform.

Student Project: Energy generation by excercise

In this project, students learn about the energy generation and usage. Emphasis is placed on potential sources of renewable energy, and on how power demands vary from country to country. The students learn how energy is measured, and experiment with generating and storing energy themselves, using an AC or DC generator connected to a bicycle and lead-acid batteries. They can measure how long common household appliances can be run on the stored energy, and in the process gain a better understanding of their own personal energy usage. Design of different energy efficient converters can be undertaken in this project. 

Lecture on Power Electronics Improvements

Speed control of DC Motor

Controlled full wave rectifier

PWM Rectifier

Boost chopper/ step up chopper simulation

Three phase to single phase Matrix Converter

A model of three phase to single phase matrix converter is shown in Fig. 11.13. The three phase input waves are modeled in a similar manner. The input frequency is taken as 50 Hz and the output frequency as 100 Hz. The three switches taken are ideal switches. Modulating signals for this converter are obtained by Venturini method as obtained previous case. Switching pulses from these modulating signals are obtained by applying PWM modulation.

More info: Matlab & simulink for Engineers

180 DEGREE THREE PHASE VOLTAGE SOURCE INVERTER

Model of a three phase 180 degree VSI and its ouput. More design and project ideas Follow Matlab & simulink for Engineers