A power inverter , inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC) .The resulting AC frequency obtained depends on the particular device employed. Inverters do the opposite of rectifiers which were originally large electromechanical devices converting AC to DC.
The inverter is known as voltage source inverter when the input of the inverter is a constant DC voltage source. The input to the voltage source inverter has a stiff DC voltage source. Stiff DC voltage source means that the impedance of DC voltage source is zero. Practically, DC sources have some negligible impedance. VSI are assumed to be supplied with ideal voltage sources (very low impedance sources). The AC output voltage is completely determined by the states of switching devices in the inverter and the applied DC source.
The voltage source inverter topology uses a diode rectifier that converts utility/line AC voltage (60 Hz) to DC. The converter is not controlled through electronic firing like the CSI drive. The DC link is parallel capacitors, which regulate the DC bus voltage ripple and store energy for the system.
The inverter is known as current source inverter when the input of the inverter is a constant DC current source. Stiff current is supplied to the CSI (current source inverter) from the DC source where the DC source have high impedance. Usually, a large inductor or closed loop-controlled current are used to provide stiff current. The resulting current wave is stiff which is not influenced by the load. The AC output current is completely determined by the states of switching devices in the inverter and the DC applied source.
The variable dc voltage source is converted into a variable current source by using inductance L. The current IL supplied to the single phase transistorised inverter is adjusted by the combination of variable dc voltage and inductance
A single-phase inverter converts DC input into Single phase output. The output voltage/current of single-phase inverter has exactly one phase which has a nominal frequency of 50HZ or 60Hz a nominal voltage. The Nominal voltage is defined as the voltage level at which Electrical system operates. There are different nominal voltages i.e. 120V, 220V, 440V, 690V, 3.3KV, 6.6KV, 11kV, 33kV, 66kV, 132kV, 220kV, 400kV and 765kV
The working principle of single phase full bridge inverter is based on the sequential triggering of thyristors placed diagonally opposite. This means, for half of time period, thyristors T3 & T4 will be triggered while for the remaining half of time period, T1 & T2 will be triggered. Only two thyristors are turned ON in half of the time period.
Three-phase inverters convert DC into three-phase power. Three-phase power provides three alternating currents which are uniformly separated in phase angle. Amplitudes and frequencies of all three waves generated at the output are same with slight variations due to load while each wave has a 120o phase shift from each other. Basically, a single 3-phase inverter is 3 single-phase inverters, where phases of each inverter are 120 degrees apart and each single-phase inverter is connected to one of the three load terminals.
The working principle of this inverter is that it consists of three inverter switches with a single phase. In which each switch can be connected to the load terminal. Three switches can be synchronized to the operation of the basic control system. So that a switch works to create a line / to-line output waveform, including six steps, at every 60 degrees of the basic output waveform.
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