Embedded Files
In this chapter the basic information like definition of inverter, classification of inverter, basic principle of inverter, performance parameters of inverter and applications of inverter are described.
What is an inverter?
What is an inverter?
Inverter is a static circuit which converts power from DC source to AC at specified output voltage and frequency. The output voltage can be fixed or variable at a fixed or variable frequency.
DC inputs to the inverter
- Rectifier
- Batteries
- Fuel cell
- Photovoltaic array
- Magneto hydrodynamic generator
Classification of inverter
Classification of inverter
Table 3.1 Classification of inverter
Basic Principle of inverter
Basic Principle of inverter
Figure 3.1(a) shows the power topology of a half-bridge Inverter, Switches Q1 and Q2 are the gate commutated devices such as power BJTs, MOSFETs, GTO, IGBT, MCT, etc. When closed, these switches conduct and current flows in the direction of arrow. The operation of the circuit can be divided into two periods. The switching states of inverter are shown in Table 3.1.
Where T0=1/f and f is the frequency of the output voltage waveform. Figure 3.1(b) shows the waveforms for the output voltage and switch pulse for a resistive load.
Fig. 3.1(a) Circuit Diagram of Half Bridge inverter
Fig. 3.1(b) Wave forms of Half Bridge inverter
Table 3.2 Switching States of Half bridge inverter
Switch Q1 is closed for half-time period (T0/2) of the desired ac output. It connects point p of the dc source to point A and the output voltage e0 becomes equal to +Vs/2. At t=T0/2, gating signal is removed from Q1 and it turns-off. For the next half-time period (T0/2 t T0), the gating signal is given to Q2. It connects point N of the dc source to point A and the output voltage reverses. Thus, by closing Q1 and Q2 alternately, for half-time periods, a square-wave ac voltage is obtained at the output. With resistive load, wave shape of load current is identical to that of output voltage.
Performance Parameters of inverter
Performance Parameters of inverter
The output voltage obtained from inverters is not a sine wave. It consists of fundamental component plus certain harmonics. The presence of harmonics in the output voltage waveform of inverters leads to poor load performance and reduced system efficiency. Lower the harmonic content in the output voltage waveform better is the quality of an inverter. Several performance parameters which evaluate the quality of inverters are described below:-
- Harmonic factor of nth Harmonic (HFn)
Harmonic factor is a measure of the individual harmonic contribution in the output voltage of an inverter.
It is defined as the ratio of rms voltage of a particular harmonic component to the rms value of fundamental component.
Enrms is rms value of nth order harmonic component; Erms is rms value of fundamental harmonic component.
- Total Harmonic Distortion (THD):
A Total harmonic distortion is a measure of closeness in shape between output voltage waveform and its fundamental component.
It is defined as the ration of rms value of total harmonic components of output voltage to the rms value of the fundamental component.
Enrms is rms value of nth order harmonic component; E1rms is rms value of fundamental harmonic component.
- Distortion factor (DF)
A distortion factor indicates the amount of harmonic remains in output voltage waveform after the waveform has been subjected to second order attenuation.
- Lowest order harmonic (LOH)
The lowest frequency harmonic with a magnitude greater than or equal to 3% of the magnitude of the fundamental component of the output voltage is known as LOH.
Applications of inverter
Applications of inverter
Some of the important industrial applications of inverter are
1. Variable speed AC motor drives
2. Induction heating
3. Uninterruptible power supplies(UPS)
4. High voltage DC transmission (HVDC)
5. Air craft power supplies
6. Battery operated vehicle drives
7. Regulated voltage and frequency power supplies
Google Sites
Report abuse