This project is based on cascaded H bridge inverter and various topologies. Inverters are mainly used for commercial and industrial purposes. The multilevel inverter is low harmonics in output voltage. There are different types of multilevel inverters. As the number of level increases the harmonic content of output voltage waveform decreases. This project is normal cascaded multilevel inverter only, but input voltage is applied through sepic converter. The sepic converter is converts the low voltage dc supply into high voltage dc voltage.
Multilevel inverter provides a suitable solution for medium and high power systems to synthesize an output voltage which allows a reduction of harmonic content in voltage and current waveforms. The solar photovoltaic (PV) modules directly converts the light energy into the electrical energy, but energy obtained from the PV module acts as low voltage DC source and has relatively low conversion efficiency. In order to improve the efficiency and convert low voltage DC source into usable AC source, the power electronics converters are used to transform DC into AC.
In normal five level cascaded inverter is used for two single phase inverter circuits. The two inverters are connected in cascaded connections. This multilevel inverter circuit contains 8 power switches. This inverter wants the external supply source. This project is mainly suitable for renewable energy sources. The solar PV is produced low voltage dc, that dc voltage is converts high voltage dc voltage by using sepic converter.
This proposed multilevel inverter is reduced the switching losses and total harmonics distortion(THD).And also easy to control the voltage of the multilevel inverter. The solar PV voltage is applied to sepic converter, that sepic converter is converts the low voltage dc into high voltage dc. That voltage is applied to the cascaded multilevel inverter circuits. The multilevel inverter is produces the five level step output.
Block Diagram Explanation
- Pulse generator: - Here we have used PIC microcontroller (PIC 16F877A) to make a switching signal.
- Driver circuit: -It can be used to amplify the pulses and provided isolations by using opto coupler. It has two functions,
- Bridge Rectifier: It converts AC to DC Supply.
- SEPIC Converter : It converts low voltage DC voltage into high voltage DC.
- Inverter: It converts DC to AC Supply.
Pic Controller Board
The five level cascaded inverter by employing sepic converter output waveforms are shown in below.
The pic controller is used to generate the PWM pulses for converter and inverter circuit. The pic controller pulses are given to the driver circuit as input. Driver board is mainly used to isolate and amplify the input signals from the controller. The amplified driver output will be connected to the main power circuit devices. And the devices are turned on by using the PWM pulses. The power transformer is directly connected to the bridge rectifier. The bridge rectifier converts the ac voltage into dc voltage. That DC voltage converts into high voltage DC voltage. Dc voltage is converted into ac voltage by using multilevel inverter circuit. The multilevel inverter output waveform is shown in below.
Circuit Diagram for Sepic Converter
Circuit Diagram for Multilevel Inverter
- Reduce the switching loss.
- High efficiency.
- Reduced THD.
- Industrial machines
- Automobiles medical equipment
- Solar PV applications
In this project it reduces the uneven degradation of power switches, switching losses when compared to the conventional PWM technique and harmonics are reduced and the output waveform level is increased. And also increase the efficiency. This project is mainly used for solar power applications.
Sepic Converter Output Waveform
Multilevel Inverter Output