THD Analysis of Cascaded H-Bridge Inverter with Fuzzy Logic Controller

In recent days, the multilevel inverter technology is widely applied to domestic and industrial applications for medium voltage conversion. But the power quality issues of the multilevel inverter limit the usage of much sensitive equipment like medical instruments. The lower distortion level of the output voltage and current can generate a quality sinusoidal output voltage in inverters and they can be used for many applications. The harmonics can cause major problems in equipment due to the nonlinear loads connected with the power system. So, it is necessary to minimize the losses to raise its overall efficiency. In this paper, a new topology of seven-level asymmetrical cascaded H-bridge multilevel inverter with a fuzzy logic controller had been implemented to reduce the Total Harmonic Distortion (THD) and to improve the overall performance of the inverter.

The proposed model was well suited for use with a solar PV application. In this topology, only six IGBT switches were used with three different voltage ratings of PV modules (1:2:4). The lower number of semiconductor switches led to minimizing overall di/dt ratings and voltage stress on each switches and switching losses. The gate pulses generated by Sinusoidal Pulse Width Modulation (SPWM) technique with a Fuzzy logic controller were also introduced. A buck-boost converter was used to maintain the constant PV voltage level integrated by an MPPT technique and the Perturb and Observer algorithm was also implemented. The MPPT was used to harness the maximum power of solar radiations under its various climatic conditions. The new topology was evaluated by a Matlab/Simulink model and compared with a hardware model.

The results proved that the THD achieved by this topology was 1.66% and realized that it met the IEEE harmonic standards. And the use of different voltage ratings of PV module was recommended for the proposed asymmetric inverter with less number of switches. The overall cost of the proposed model was also reduced. So, the quality of the improved output voltage provided an improved efficiency which was suitable for PV fed inverter.

Article by Sivakumar N. and Sumathi A., from India.

Full access: http://mrw.so/2IMxP4

Image by Teodor BACIU, from Flickr-cc.