Abstract
This paper proposes a control scheme for seven level asymmetrical cascaded H-bridge multi level inverter (ACHBMLI) based on fractional order calculus. The seven level ACHBMLI consists of two H-bridges that are connected in series and are excited by different dc voltage sources. A simplified model is developed by assuming the small signal variation component is equal in both the H-bridges. A fractional order PID (FO-PID) controller is designed for the ACHBMLI using the simplified model. Simulation study shows the adequacy of FO-PID controller in giving an output voltage with minimum distortions. A conventional PID controller is also designed for ACHBMLI using the same simplified model. The performance of the ACHBMLI with FO-PID controller is compared with the performance of ACHBMLI with conventional PID controller. The simulation results prove the superiority of FO-PID controller in maintaining the output voltage of the ACHBMLI close to the reference voltage and in reducing the harmonic distortion of output voltage of the inverter. The simulation was done using MATLAB and the parameters of FO-PID controller was designed using FOMCON tool box.
Highlights
Multilevel inverter is a power electronic circuit that provides the required ac output by using an input of multiple low level DC voltages
Fractional order -PI controller is used as a controller to maintain the output voltage of the inverter constant and to reduce the total harmonic distortions
Total harmonic distortion (THD) of yield voltage of asymmetrical cascaded H-bridge multi level inverter (ACHBMLI) for different modulation index and level shifted techniques with open loop and closed loop IO-PID and fractional order PID (FO-PID) controllers are shown in Table 6 and Table 7
Summary
Multilevel inverter is a power electronic circuit that provides the required ac output by using an input of multiple low level DC voltages. A sinusoidal waveform can be achieved using multiple output levels which can be obtained through multi level inverters (MLIs) Because of their features such as superior electromagnetic capability, low switching losses, and low harmonics, MLIs have received increasing attention recently, especially in high power applications. Due to their switching frequencies, decreased use of output filters, MLI topologies at the same power ratings, have advantages over two level inverter topologies [1,2]. Cascaded multi level inverter can have symmetrical and asymmetrical structure These two types of CHBMLIs can be used to create a required yield voltage from different DC voltage sources [3,4]. If the isolated voltage sources are unequal in magnitude the structure is asymmetrical
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