Inverter Circuits Design
A power inverter is an electronic system designed to convert direct current (DC) into alternating current (AC). Its design of the circuitry is what dictates the I/O voltage, frequency and the power handling capability. This inverter is incapable of producing any power that is provided by the DC source.
Two types of waveforms used in power inverters
There are two types of waveforms that a power inverter uses – square wave and sine wave.
● Square wave: The power inverter utilizing the square waveforms is of the simplest kind and is suited for low-sensitivity applications, such as lighting and heating. It is not suited for sensitive electronics, since it produces a humming sound when connected to audio equipment.
● Sine wave: The power inverter with sine waveform produces a multiple step sinusoidal AC waveform. This makes the inverter produce outputs with much less distortion, as compared to square wave. The sine wave inverts with over three-step wave output are more complex and, consequently, more expensive. These are ideal for personal computers and DVD players.
Basic inverter circuit design
In the simplest of inverter circuits, the DC power is connected to a transformer by means of the center tap. It operates by switching back and forth of the primary winding. This allows the DC source to flow back via two alternate paths – first through one end of the primary winding and then the other. This produces AC in the secondary circuit.
However, the electromechanical version of the switching device, consisting of two stationary contacts and a spring supported moving contact, involves the following steps:
● The movable contact is held by the spring against one of the stationary contacts and a spring supported moving contact.
● An electromagnet pulls the moveable contact to the opposite stationary contact. This interrupts the current in the electromagnet and the switch continuously switches back and forth.
● The result of this action is production of a square voltage waveform due to simple on and off mechanism. In contrast, the sinusoidal waveform of more complex inverter circuit is the result of AC power supply.
The electromechanical inverter switch is known as a vibrator or buzzer. It is used in vacuum tube automobile radios, door bells and buzzers, and even tattoo machines. For improved power ratings, the circuit designs of such inverters are incorporated with transistors and semiconductor switches.
Three-phase inverter design
The inverters used for variable-frequency drive applications and high-power applications are called three-phase inverters. It is called three-phase because it contains three single-phase inverter switches, separately connected to the three load terminals. This inverter is primarily used in high-power applications, such as air conditioners, induction motors, ventilation fans, etc.
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