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The paper proposes a Current Source Multilevel Inverter (CSMLI) with single rating inductor topology. Multilevel inverters are most familiar with power converter ’ s applications due to reduced dv/dt, di/dt stress, and very efficient for reducing harmonic distortion in the output voltage and output current. The proposed nine-level current source inverter has been tested under symmetrical and asymmetrical modes of operation, and their activities are compared using PI and Fuzzy PI (Proportional Integral) controllers with multicarrier PWM (Pulse Width Modulation) strategy. MATLAB/Simulink simulation has been made for the proposed converter to obtain its performance measures. Some experimental results are given to verify the presented Current Source Multilevel Inverter.

Multilevel inverters can offer substantial benefits for higher power applications, including reduced harmonics, and increased power ratings because of reduced switching device voltage and current stresses. Multilevel inverters have been shown more consideration [

Current Source Inverters with pulse width modulation strategies are employed to deliver a minimum distorted input and output waveforms. This inverter circuit is the double cascaded H-bridge multilevel Current Source Inverter. Tragically, the need for isolated DC sources, power devices, and their gating circuits are a few issues of this inverter circuit. Reference [

This paper presents a nine-level single phase single inductor current source inverter using multicarrier PWM strategy controlled with PI and Fuzzy PI Controller. The Fuzzy PI control algorithm that combines the fuzzy logic control results in suitable non- linear characteristics and efficiently reduces the error in power extraction [

A current source inverter converts the input DC to an AC at its output terminals. In these inverters, the input voltage is kept constant, and the amplitude of output voltage does not depend on the load. Nevertheless, the wave form of load current, as well as its magnitude, depends on the nature of the load impedance. In this inverter, the input current is constant, but adjustable. The amplitude of output current from CSI independent of the load. A DC source supplies current Source Inverter. In an adjustable speed drive (ASD), DC source is usually an AC/DC rectifier with a large inductor to provide stable current supply. Usually, a CSI has a boost operation function, its output voltage peak value can be higher than the DC-link voltage [

In the proposed CSI topology, a level based multicarrier PWM strategy implemented for firing the gate terminals of the MOSFET to obtain the current waveform of nine- level CSI. Multicarrier PWM strategy is a comparison of a reference waveform, with vertically shifted carrier signals. In multicarrier PWM technique, m − 1 triangular carriers are used for m-level inverter output voltage or current. In this proposed topology,

eight triangular carriers are preferred. In Phase Opposition Disposition (POD), the carriers above the Sinusoidal reference zero points are 180 out of phase with those below the zero point. _{a} = 0.9 and the carrier frequency of 2 kHz. The carrier waveforms have same amplitude Ac and frequency f_{c}. Similarly, the reference waveforms have frequency f_{ref} and amplitude A_{ref}. At every instant, the response of the comparator is decoded to generate the correct switching sequences with respect to the output of the inverter. The frequency modulation index (m_{f}) and amplitude modulation index (ma) calculated in Equations (1) and (2) [

Level | S_{11} | S_{12} | S_{13} | S_{14} | S_{21} | S_{22} | S_{23} | S_{24} | S_{31} | S_{32} | S_{33} | S_{34} | S_{41} | S_{42} | S_{43} | S_{44} |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|

+4 | On | Off | Off | On | On | Off | Off | On | On | Off | Off | On | On | Off | Off | On |

+3 | On | Off | Off | On | On | Off | Off | On | On | Off | Off | On | On | Off | On | Off |

+2 | On | Off | Off | On | On | Off | Off | On | on | Off | On | Off | On | Off | On | Off |

+1 | On | Off | Off | On | On | Off | On | Off | On | Off | On | Off | On | Off | On | Off |

0 | On | Off | On | off | Off | On | Off | On | on | off | On | Off | Off | On | Off | On |

-1 | Off | On | On | Off | Off | On | Off | On | Off | On | Off | On | Off | On | Off | on |

-2 | Off | On | On | Off | Off | On | On | Off | Off | On | Off | On | Off | On | Off | On |

-3 | Off | On | on | Off | Off | On | On | Off | Off | On | On | Off | Off | On | Off | On |

-4 | off | on | on | off | off | on | on | off | off | on | on | off | off | on | on | off |

asymmetrical current source inverter. From this figure, it is observed that the circuit model is obtained by connecting two H-bridge, unidirectional controlled power devices and a DC source with inductors. It is implemented using the power circuit consists of eight IGBT switches, and two pairs of inductors of L11 and L12 whose values are 300 mH and L21 and L22 are 100 mH with a common current source. The switching sequences for nine level single rating inductor asymmetrical current source inverter shown in

The Simulink representation of nine level single rating inductor type symmetrical current source inverter is implemented and this power circuit consists of sixteen IGBT

Level | S_{11} | S_{12} | S_{13} | S_{14} | S_{21} | S_{22} | S_{23} | S_{24} |
---|---|---|---|---|---|---|---|---|

+4 | On | Off | Off | On | On | Off | Off | on |

+3 | On | Off | On | Off | On | Off | Off | on |

+2 | Off | On | On | Off | On | Off | off | on |

+1 | On | Off | Off | On | On | Off | on | off |

0 | On | Off | On | Off | Off | On | Off | On |

−1 | Off | On | On | Off | Off | On | off | on |

−2 | On | Off | Off | On | Off | On | On | off |

−3 | Off | On | Off | On | Off | On | On | off |

−4 | off | on | on | off | off | on | on | off |

switches and eight identical inductors with rating of 100 mH with a common current source generated from PV array. The current source shared by the four H-bridge inverter with suitable switching sequences generate the nine level output. Multi-carrier pulse width modulation is tuned with proposed PI and Fuzzy PI Controller.

_{rms} tuned with PI controller and fuzzy PI controller respectively with a set value of I_{rms} as 2 A.

Similarly, the

Multicarrier pulse width modulation strategy is implemented for IGBT switching with PI and Fuzzy PI Controller.

Controller | Nominal Case | Servo Response | Regulatory Response | |||||||
---|---|---|---|---|---|---|---|---|---|---|

Rise Time (sec) | Settling Time (sec) | Supply Increase 33% | Supply Decrease 33% | Load Increase 33% | Load Decrease 33% | |||||

Rise Time (sec) | Settling Time (sec) | Rise Time (sec) | Settling Time (sec) | Rise Time (sec) | Settling Time (sec) | Rise Time (sec) | Settling Time (sec) | |||

PI | 0.3027 | 0.7258 | 0.352 | 0.614 | 0.416 | 0.690 | 0.3501 | 0.7549 | 0.240 | 0.468 |

Fuzzy PI | 0.1281 | 0.2306 | 0.181 | 0.119 | 0.093 | 0.212 | 0.1447 | 0.2658 | 0.086 | 0.149 |

Figures 11-15 shows the overall simulated responses of the asymmetrical nine level single rating inductor current source inverter with PI and fuzzy PI controllers. _{rms} tuned with PI controller and fuzzy PI controller respectively with a set value of I_{rms} of 2 A.

current response comparison of PI and Fuzzy Controller of asymmetrical CSI for change in load current. During this regulatory response, the fuzzy PI controller response has been settled very fast with its reference current without any oscillation compared with PI controller. Similarly, the

Controller | Nominal Case | Servo Response | Regulatory Response | |||||||
---|---|---|---|---|---|---|---|---|---|---|

Rise Time (sec) | Settling Time (sec) | Supply Increase 33% | Supply Decrease 33% | Load Increase 33% | Load Decrease 33% | |||||

Rise Time (sec) | Settling Time (sec) | Rise Time (sec) | Settling Time (sec) | Rise Time (sec) | Settling Time (sec) | Rise Time (sec) | Settling Time (sec) | |||

PI | 0.260 | 0.646 | 0.251 | 0.790 | 0.337 | 0.935 | - | 0.540 | - | 0.320 |

Fuzzy PI | 0.094 | 0.386 | 0.158 | 0.432 | 0.167 | 0.361 | - | 0.193 | - | 0.105 |

From the simulated performance the asymmetrical nine-level inverter produced good results with less number of power electronics components. So the best circuit also implemented for experimental verification. The proposed asymmetrical nine level CSI was built and tested to assess its performance. 3 A DC used as a source by using 36 V and 100 W solar panel fed to the input of CSI circuit. The maximum power available was 100 W, at an irradiance level of 1000 W/m^{2}, and a temperature of 25˚C. This power circuit consists of four IGBT switches IRG4PC40UD, 600 V and 20 A, and two pairs of inductors of L11 and L12 whose values are 15 mH and L21 and L22 are 5 mH. Arduino controller was programmed to provide the controlled switching sequences of the asym- metrical nine level CSI using fuzzy tuned PI controller technique. Finally, the output of nine level CSI generated and verified with different load changing conditions. Figures 16-20 show the experimental results of proposed asymmetrical nine level CSI.

Description | Symmetrical | Asymmetrical |
---|---|---|

%THD | 14.31 | 14.26 |

I_{rms} in Amps | 4.015 | 4.096 |

No. of switched required | 16 | 8 |

No. of inductors required | 8 | 4 |

of proposed CSI.

number of switches and is able to produce the desired output current while the current balance between current-sharing inductors is guaranteed using appropriate control method. Output current waveform and current balance between current-sharing inductors are completely satisfied.

In this work, an important assessment of Current Source Multilevel Inverter (CSMLI) has been presented. It draws a low-ripple current from the PV cells, therefore maximizing its performance. The inverter is built with state-of-the-art power devices that have fast switching times. The overall performance analysis of proposed symmetrical and asymmetrical nine-level single phase single inductor current source inverter is tabulated in Tables 3-5. From the

Tamilarasi, D. and Sivakumaran, T.S. (2016) Analysis of Symmetrical and Asymmetrical Current Source Multilevel Inverter. Circuits and Systems, 7, 3469-3484. http://dx.doi.org/10.4236/cs.2016.711295