A Multilevel Inverter Structure based on Combination of Switched-Capacitors and DC Sources

ABSTRACT:  

This paper presents a switched-capacitor multilevel inverter (SCMLI) combined with multiple asymmetric DC sources. The main advantage of proposed inverter with similar cascaded MLIs is reducing the number of isolated DC sources and replacing them with capacitors. A self-balanced asymmetrical charging pattern is introduced in order to boost the voltage and create more voltage levels. Number of circuit components such as active switches, diodes, capacitors, drivers and DC sources reduces in proposed structure.

This multi-stage hybrid MLI increases the total voltage of used DC sources by multiple charging of the capacitors stage by stage. A bipolar output voltage can be inherently achieved in this structure without using single phase H-bridge inverter which was used in traditional SCMLIs to generate negative voltage levels. This eliminates requirements of high voltage rating elements to achieve negative voltage levels. A 55-level step-up output voltage (27 positive levels, a zero level and 27 negative levels) are achieved by a 3-stage system which uses only 3 asymmetrical DC sources (with amplitude of 1Vin, 2Vin and 3Vin) and 7 capacitors (self-balanced as multiples of 1Vin). MATLAB/SIMULINK simulation results and experimental tests are given to validate the performance of proposed circuit.

KEYWORDS:
  1. Multi-level inverter
  2. Switched-capacitor
  3. Bipolar converter
  4. Asymmetrical
  5. Self-balancing

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig (1) Three stage structure of the proposed inverter

 EXPECTED SIMULATION RESULTS:

 

 Fig (2) Waveform of the output voltage in (a) 50Hz and pure resistive load (b)

the inset graphs of voltage and current

 Fig (3) waveform of the output voltage in 50Hz with resistive-inductive load

 Fig (4) Capacitor’s voltage in 50Hz (a) middle stage (b) last stage

CONCLUSION:

 In this paper, a multilevel inverter based on combination of multiple DC sources and switched-capacitors is presented. Unlike traditional converters which used H-bridge cell to produce negative voltage that the switches should withstand maximum output AC voltage, the suggested structure has the ability of generating bipolar voltage (positive, zero and negative), inherently. Operating principle of the proposed SCMLI in charging and discharging is carried out.

Also, evaluation of reliability has been done and because of high number of redundancy, there has been many alternative switching states which help the proposed structure operate correctly even in fault conditions. For confirming the superiority than others, a comprehensive comparison in case of number of devices and efficiency is carried out and shows that the proposed topology has better performance than others. For validating the performance, simulation and experimental results are brought under introduced offline PWM control method.

REFERENCES:

[1] L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo, and M. A. M. Prats, “The age of multilevel converters arrives,” IEEE Trans. Ind. Electron. Mag., vol. 2, no. 2, pp. 28–39, June, 2008.

[2] M. Saeedifard, P. M. Barbosa and P. K. Steimer,”Operation and Control of a Hybrid seven Level Converter,” IEEE Trans. Power Electron., vol. 27, no.2, pp. 652–660, February, 2012.

[3] A. Nami. “A New Multilevel Converter Configuration for High Power High Quality Application,” PhD Thesis, Queensland University of Technology, 2010.

[4] V. Dargahi, A. K. Sadigh, M. Abarzadeh, S. Eskandari and K. Corzine, “A new family of modular multilevel converter based on modified flying capacitor multicell converters IEEE Trans. Power Electron., vol. 30, no.

1, pp. 138-147, January, 2015.

[5] I. López, S. Ceballos, J. Pou, J. Zaragoza, J. Andreu, I. Kortabarria and V. G. Agelidis,” Modulation strategy for multiphase Neutral-Point Clamped converters,” IEEE Trans. Power Electron., vol. 31, no. 2, pp. 928–941, March, 2015.

A Highly Efficient and Reliable Inverter Configuration Based Cascaded Multi-Level Inverter for PV Systems

ABSTRACT:  

This paper presents an improved Cascaded Multi-Level Inverter (CMLI) based on a highly efficient and reliable configuration for the minimization of the leakage current. Apart from a reduced switch count, the proposed scheme has additional features of low switching and conduction losses. The proposed topology with the given PWM technique reduces the high-frequency voltage transitions in the terminal and common-mode voltages. Avoiding high-frequency voltage transitions achieves the minimization of the leakage current and reduction in the size of EMI filters. Furthermore, the extension of the proposed CMLI along with the PWM technique for 2m+1 levels is also presented, where m represents the number of Photo Voltaic (PV) sources.

The proposed PWM technique requires only a single carrier wave for all 2m+1 levels of operation. The Total Harmonic Distortion (THD) of the grid current for the proposed CMLI meets the requirements of IEEE 1547 standard. A comparison of the proposed CMLI with the existing PV Multi-Level Inverter (MLI) topologies is also presented in the paper. Complete details of the analysis of PV terminal and common-mode voltages of the proposed CMLI using switching function concept, simulations, and experimental results are presented in the paper.

KEYWORDS:
  1. Cascaded multi-level inverter
  2. Leakage current
  3. Common-mode voltage
  4. Terminal voltage

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 

Fig. 1. Proposed five-level grid-connected CMLI with PV and parasitic elements.

EXPECTED SIMULATION RESULTS:

 

Fig. 2. Simulation results of proposed five-level CMLI showing the waveforms of : (a) output voltage vuv; (b) grid current iac; (c) terminal voltage vxg; (d) terminal voltage vyg; (e) terminal voltage vzg; (f) leakage current ileak; (g) common-mode voltage vcm.

Fig. 3. Proposed five-level CMLI integrated with MPPT. The subplots give waveforms of : (a) voltage VPV1; (b) voltage VPV2; (c) current IPV1; (d) current IPV2; (e) power PPV1; (f) power PPV2; (g) resultant modulation index ma; (h) output power POUT; (i) modified reference wave vref_modified; (j) inverter output voltage vab.

CONCLUSION:

 In this paper, an improved five-level CMLI with low switch count for the minimization of leakage current in a transformerless PV system is proposed. The proposed CMLI minimizes the leakage current by eliminating the high-frequency transitions in the terminal and common-mode voltages. The proposed topology also has reduced conduction and switching losses which makes it possible to operate the CMLI at high switching frequency.

Furthermore, the solution for generalized 2m+1 levels CMLI is also presented in the paper. The given PWM technique requires only one carrier wave for the generation of 2m+1 levels. The operation, analysis of terminal and common-mode voltages for the CMLI is also presented in the paper. The simulation and experimental results validate the analysis carried out in this paper. The MPPT algorithm is also integrated with the proposed five-level CMLI to extract the maximum power from the PV panels. The proposed CMLI is also compared with the other existing MLI topologies in Table V to show its advantages.

REFERENCES:

[1] Y. Tang, W. Yao, P.C. Loh and F. Blaabjerg, “Highly Reliable Transformerless Photovoltaic Inverters With Leakage Current and Pulsating Power Elimination,” IEEE Trans. Ind. Elect., vol. 63, no. 2, pp. 1016-1026, Feb. 2016.

[2] W. Li, Y. Gu, H. Luo, W. Cui, X. He and C. Xia, “Topology Review and Derivation Methodology of Single-Phase Transformerless Photovoltaic Inverters for Leakage Current Suppression,” IEEE Trans. Ind. Elect., vol. 62, no. 7, pp. 4537-4551, July 2015.

[3] J. Ji, W. Wu, Y. He, Z. Lin, F. Blaabjerg and H. S. H. Chung, “A Simple Differential Mode EMI Suppressor for the LLCL-Filter-Based Single-Phase Grid-Tied Transformerless Inverter,” IEEE Trans. Ind. Elect., vol. 62, no. 7, pp. 4141-4147, July 2015.

[4] Y. Bae and R.Y.Kim, “Suppression of Common-Mode Voltage Using a Multicentral Photovoltaic Inverter Topology With Synchronized PWM,” IEEE Trans. Ind. Elect., vol. 61, no. 9, pp. 4722-4733, Sept. 2014.

[5] N. Vazquez, M. Rosas, C. Hernandez, E. Vazquez and F. J. Perez-Pinal, “A New Common-Mode Transformerless Photovoltaic Inverter,” IEEE Trans. Ind. Elect., vol. 62, no. 10, pp. 6381-6391, Oct. 2015.

A Multilevel Inverter Structure based on Combination of Switched-Capacitors and DC Sources

ABSTRACT:

This paper presents a switched-capacitor multilevel inverter (SCMLI) combined with multiple asymmetric DC sources. The main advantage of proposed inverter with similar cascaded MLIs is reducing the number of isolated DC sources and replacing them with capacitors. A self-balanced asymmetrical charging pattern is introduced in order to boost the voltage and create more voltage levels. Number of circuit components such as active switches, diodes, capacitors, drivers and DC sources reduces in proposed structure. This multi-stage hybrid MLI increases the total voltage of used DC sources by multiple charging of the capacitors stage by stage. A bipolar output voltage can be inherently achieved in this structure without using single phase H-bridge inverter which was used in traditional SCMLIs to generate negative voltage levels. This eliminates requirements of high voltage rating elements to achieve negative voltage levels. A 55-level step-up output voltage (27 positive levels, a zero level and 27 negative levels) are achieved by a 3-stage system which uses only 3 asymmetrical DC sources (with amplitude of 1Vin, 2Vin and 3Vin) and 7 capacitors (self-balanced as multiples of 1Vin). MATLAB/SIMULINK simulation results and experimental tests are given to validate the performance of proposed circuit.

KEYWORDS:

  1. Multi-level inverter
  2. Switched-capacitor
  3. Bipolar converter
  4. Asymmetrical
  5. Self-balancing

 SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig (1) Three stage structure of the proposed inverter

EXPECTED SIMULATION RESULTS

 

 Fig (2) Waveform of the output voltage in (a) 50Hz and pure resistive load (b the inset graphs of voltage and current

Fig (3) waveform of the output voltage in 50Hz with resistive-inductive load

Fig (4) Capacitor’s voltage in 50Hz (a) middle stage (b) last stage

CONCLUSION:

In this paper, a multilevel inverter based on combination of multiple DC sources and switched-capacitors is presented. Unlike traditional converters which used H-bridge cell to produce negative voltage that the switches should withstand maximum output AC voltage, the suggested structure has the ability of generating bipolar voltage (positive, zero and negative), inherently. Operating principle of the proposed SCMLI in charging and discharging is carried out. Also, evaluation of reliability has been done and because of high number of redundancy, there has been many alternative switching states which help the proposed structure operate correctly even in fault conditions. For confirming the superiority than others, a comprehensive comparison in case of number of devices and efficiency is carried out and shows that the proposed topology has better performance than others. For validating the performance, simulation and experimental results are brought under introduced offline PWM control method.

REFERENCES:

[1] L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo, and M. A. M. Prats, “The age of multilevel converters arrives,” IEEE Trans. Ind. Electron. Mag., vol. 2, no. 2, pp. 28–39, June, 2008.

[2] M. Saeedifard, P. M. Barbosa and P. K. Steimer,”Operation and Control of a Hybrid seven Level Converter,” IEEE Trans. Power Electron., vol. 27, no.2, pp. 652–660, February, 2012.

[3] A. Nami. “A New Multilevel Converter Configuration for High Power High Quality Application,” PhD Thesis, Queensland University of Technology, 2010.

[4] V. Dargahi, A. K. Sadigh, M. Abarzadeh, S. Eskandari and K. Corzine, “A new family of modular multilevel converter based on modified flying capacitor multicell converters IEEE Trans. Power Electron., vol. 30, no.

1, pp. 138-147, January, 2015.

[5] I. López, S. Ceballos, J. Pou, J. Zaragoza, J. Andreu, I. Kortabarria and V. G. Agelidis,” Modulation strategy for multiphase Neutral-Point Clamped converters,” IEEE Trans. Power Electron., vol. 31, no. 2, pp. 928–941, March, 2015.