Design and Construction of a 1.5 Kva Inverter
Chapter One
OBJECTIVE OF THE PROJECT
The objective of this project is to design and construct a modified sine wave inverter which can be powered from the source of 12V battery to produce an output of 230vac. This inverter is rated 1.5kva which is capable of operating a wide variety of loads; electronic and household items including but not limited to TV, VCR, and satellite receiver, computers, and printers.
CHAPTER TWO
LITERATURE REVIEW
HISTORICAL BACKGROUND OF AN INVERTER
Early inverters from the late nineteenth century through the middle of the twentieth century, DC-to-AC power conversion was accomplished using rotary converters or motor generator sets (M-G sets). In the early twentieth century, vacuum tubes and gas filled tubes began to be used as switches in inverter circuits. The most widely used type of tube was the thyratron. The origins of electromechanical inverters explain the source of the term inverter. Early AC-to-DC converters used an induction or synchronous AC motor direct-connected to a generator (dynamo) so that the generator’s commutator reversed its connections at exactly the right moments to produce DC. A later development is the synchronous converter, in which the motor and generator windings are combined into one armature, with slip rings at one end and a commutator at the other and only one field frame. The result with either is AC-in, DC-out. With an M-G set, the DC can be considered to be separately generated from the AC; with a synchronous converter, in a certain sense it can be considered to be “mechanically rectified AC”. Given the right auxiliary and control equipment, an M-G set or rotary converter can be “run backwards”, converting DC to AC. Hence an inverter is an inverted converter. Controlled rectifier inverters Since early transistors were not available with sufficient voltage and current ratings for most inverter applications, it was the 1957 introduction of the thyristor or silicon controlled rectifier (SCR) that initiated the transition to solid state inverter circuits. The commutation requirements of SCRs are a key consideration in SCR circuit designs. SCRs do not turn off or commutate automatically when the gate control signal is shut off. They only turn off when the forward current is reduced to below the minimum holding current, which varies with each kind of SCR, through some external process. For SCRs connected to an AC power source, commutation occurs naturally every time the polarity of the source voltage reverses. SCRs connected to a DC power source usually require a means of forced commutation that forces the current to zero when commutation is required. The least complicated SCR circuits employ natural commutation rather than forced commutation. With the addition of forced commutation circuits, SCRs have been used in the types of inverter circuits described above. In applications where inverters transfer power from a DC power source to an AC power source, it is possible to use AC-to-DC controlled rectifier circuits operating in the inversion mode. In the inversion mode, a controlled rectifier circuit operates as a line commutated inverter. This type of operation can be used in HVDC power transmission systems and in regenerative braking operation of motor control systems. Another type of SCR inverter circuit is the current source input (CSI) inverter. A CSI inverter is the dual of a six-step voltage source inverter. With a current source inverter, the DC power supply is configured as a current source rather than a voltage source. The inverter SCRs is switched in a six-step sequence to direct the current to a three-phase AC load as a stepped current waveform. CSI inverter commutation methods include load commutation and parallel capacitor commutation. With both methods, the input current regulation assists the commutation. With load commutation, the load is a synchronous motor operated at a leading power factor.
As they have become available in higher voltage and current ratings, semiconductors such as transistors or IGBTs that can be turned off by means of control signals have become the preferred switching components for use in inverter circuits.
Rectifier and inverter pulse numbers
Rectifier circuits are often classified by the number of current pulses that flow to the DC side of the rectifier per cycle of AC input voltage. A single phase half wave rectifier is a one-pulse circuit and a single phase full wave rectifier is a two-pulse circuit. A three-phase half-wave rectifier is a three-pulse circuit and a three-phase full-wave rectifier is a six-pulse circuit. With three-phase rectifiers, two or more rectifiers are sometimes connected in series or parallel to obtain higher voltage or current ratings. The rectifier inputs are supplied from special transformers that provide phase shifted outputs. This has the effect of phase multiplication. Six phases are obtained from two transformers, twelve phases from three transformers and so on. The associated rectifier circuits are 12-pulse rectifiers, 18-pulse rectifiers and so on when controlled rectifier circuits are operated in the inversion mode, they would be classified by pulse number also. Rectifier circuits that have a higher pulse number have reduced harmonic content in the AC input current and reduced ripple in the DC output voltage. In the inversion mode, circuits that have a higher pulse number have lower harmonic content in the AC output voltage waveform.
CHAPTER THREE
CONSTRUCTION
BASIC DESIGNS OF AN INVERTER
In an inverter circuit, DC power is connected to a transformer through the center tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow back to the DC source following two alternate paths through one end of the primary winding and then the other. The alternation of the direction of current in the primary winding of the transformer produces alternating current (AC) in the secondary circuit.
Pulse generator: this is the signal processing and control circuit that generates the logic level control signals used to turn the power switch (semiconductor) ON and OFF. There are many different circuits that one can adopt and use a pulse generator or oscillator, in fact many ICs that need few external components to be connected are available in the market for use. Such IC is SG3524. The output of this circuit is either sent to the power switch (transistor) directly the or via the driver circuit for amplification before it is sent to the power switch as the case may be. Of course the choice depends on the designs and / or transistor used as power switch.
Driver circuits: this circuits amplifies the signal from pulse generator to levels required by the power switch and provides electrical isolation when required between the power switch and the logic level signal processing circuit (pulse generator).
Power switch: MOSFET is also known as switch. They are used here as the switching devices. They should stand to withstand the high current of the primary winding (low voltage side) of the transformer.
Transformer: transformer also belongs to output device. Transformers are of various types: step up, step down, auto-transformer etc. They comprises of primary and secondary windings which may not be isolated from each other. The winding are electrically interlinked by a common magnetic circuit and operate based on the principle of electromagnetic induction. The number of turns of the primary and secondary winding is related to their voltages and current with the following equation: The size of the transformer is proportional to its power. For an ideal transformer, the input power equals the output power; but in practice, there is no lossless transformer.
CHAPTER FOUR
RESULT ANALYSIS
CONSTRUCTION PROCEDURE AND TESTING
In building this project, the following procedures were properly considered,
- Purposing of the entire materials / Components needed
- Resistance check of the components bought with the help of ohmmeter before making the necessary connection with the components
- . Drafting out a schematic diagram or how to arrange the materials / components.
- Testing the completed system to see if the design works and
- Finally, implementation of design of the project.
Having procured all the materials, I processed into the arrangement of the components into the Vero board but we could not place the MOSFETs on the bread board because the heat it emit when we load it, proper soldering of the components then followed. The components were all soldered into the board after which it was correctly confirmed done.
CHAPTER FIVE
CONCLUSION
In the context of renewable energy, an inverter is a device that will convert DC battery/solar panel voltage into mains type AC power; suitable for use in your home or business.
Without this conversion from DC to AC, special appliances or adapters often need to be purchased – and DC appliances are often more expensive than their AC counterparts. The above two types of batteries are popular inverter batteries. Before buying the inverter and the battery, ask your dealer which suits your requirement better.
RECOMMENDATION
This project is designed to be used in our homes, offices and industries where the need for 24hrs supply is needed. And should be used and maintain by a qualified personnel.
REFERENCES
- The Authoritative Dictionary of IEEE Standards Terms, Seventh Edition, IEEE Press, 2000,ISBN 0-7381-2601-2, page 588
- Barnes, Malcolm (2003). Practical variable speed drives and power electronics. Oxford: Newnes. p. 97. ISBN0080473911.
- James, Hahn. “Modified Sine-Wave Inverter Enhanced”. Power Electronics.
- “Power Electronics: Energy Manager for Hybrid Electric Vehicles”. Oak Ridge National Laboratory Review(U.S. Department of Energy) 33 (3). 2000. Retrieved 2006-11-08.
- MIT open-courseware, Power Electronics, Spring 2007