A Single DC Source Cascaded Seven-Level Inverter Integrating Switched Capacitor Techn

 ABSTRACT:

 In this paper, a novel cascaded seven-level inverter topology with a single input source integrating switched capacitor techniques is presented. Compared with the traditional cascade multilevel inverter (CMI), the proposed topology replaces all the separate dc sources with capacitors, leaving only one H-bridge cell with a real dc voltage source and only adds two charging switches. The capacitor charging circuit contains only power switches, so that the capacitor charging time is independent of the load. The capacitor voltage can be controlled at a desired level without complex voltage control algorithm and only use the most common carrier phase-shifted sinusoidal pulse width modulation (CPS-SPWM) strategy. The operation principle and the charging-discharging characteristic analysis are discussed in detail. A 1kW experimental prototype is built and tested to verify the feasibility and effectiveness of the proposed topology.

KEYWORDS:

1.      Cascaded seven-level inverter

2.       Switched capacitor techniques

3.       Carrier phase-shifted sinusoidal pulse width modulation

4.       Charging and discharging characteristic

SOFTWARE: MATLAB/SIMULINK

 CONTROL DIAGRAM:

Fig. 1. Topologies of the proposed inverter. (a) The novel single dc source cascaded seven-level inverter. (b) Three-input cascaded seven-level inverter for PV systems.

 EXPECTED SIMULATION RESULTS:

Fig. 2. Output voltage and current waveforms. (a) At resistive load. (b) At inductive load. (c) THD value of the output voltage

Fig. 3. Voltage waveforms of the charging-switch. (a) S_C1. (b) S_C3.

Fig. 4. The capacitor voltage and the charging current waveforms of capacitors C₁. (a) R_ESR=5mΩ. (b) R_ESR=200mΩ.

CONCLUSION:

A novel single DC source cascaded seven-level inverter integrating switched capacitor techniques is developed in this paper. In the proposed topology, the transformerless charging circuit only contains power switches and capacitors, and the charging time is independent of the load. The operation principle and the charging-discharging characteristic analysis are investigated in depth. With the common CPS-SPWM strategy, the sinusoidal output voltage can be well obtained. Moreover, the capacitors are properly charged without complex voltage balancing control algorithm. The peak charging current and the charging loss can be reduced with appropriate circuit parameters. The proposed topology has the features of modularity, low cost and simplicity of control and makes it attractive in DC-AC power applications. A 1Kw experimental prototype verifies the feasibility of the proposed inverter. The proposed inverter is also suitable for photovoltaic-battery multi-input application with high redundancy.

REFERENCES:

[1] S. Kouro, M. Malinowski, K. Gopakumar, J. Pou, L. G. Franquelo, B. Wu, J. Rodriguez, M. A. Perez, and J. I. Leon, “Recent advances and industrial applications of multilevel converters,” IEEE Trans. Ind. Electron. , vol. 57, no. 8, pp. 2553–2580, Aug. 2010.

[2] H. Abu-Rub, J. Holtz, J. Rodriguez, and G. Baoming, “Medium-voltage multilevel converters; state of the art, challenges, and requirements in industrial applications,” IEEE Trans. Ind. Electron. , vol. 57, no. 8, pp. 2581–2596, Aug. 2010.

[3] J. Dixon, J. Pereda, C. Castillo, and S. Bosch, “Asymmetrical multilevel inverter for traction drives using only one dc supply,” IEEE Trans. Veh. Technol., vol. 59, no. 8, pp. 3736–3743, Oct. 2010.

[4] S. Lu, K. A. Corzine, and M. Ferdowsi, “A unique ultracapacitor direct integration scheme in multilevel motor drives for large vehicle propulsion,” IEEE Trans. Veh. Technol., vol. 56, no. 4, pp. 1506–1515, Jul. 2007.

[5] J. Rodriguez, S. Bernet, P. K. Steimer, and I. E. Lizama, “A survey on neutral-point-clamped inverters,” IEEE Trans. Ind. Electron. , vol. 57, no. 7, pp. 2219–2230, Jul. 2010.

Modelling and analysis of modular multilevel converter for solar photovoltaic applications to improve power quality

ABSTRACT:

The design of control circuit for a solar fed cascaded multilevel inverter to reduce the number of semiconductor switches is presented in this study. The design includes ‘binary’, ‘trinary’ and ‘modified multilevel connection’ (MMC)-based topologies suitable for varying input sources from solar photovoltaic’s (PV). In binary mode, 2Ns +1 − 1 output voltage levels are obtained where Ns is the number of individual inverters. This is achieved by digital logic functions which includes counters, flip-flops and logic gates. In trinary mode, 3Ns levels are achieved by corresponding look-up table. MMC intends design in both control and power circuits to provide corresponding output voltage levels by appropriate switching sequences. Hence to obtain a 15-level inverter, the conventional method requires 28 switches and in binary mode 12 switches are needed. In trinary mode with the same 12 switches, 27 levels can be obtained whereas in MMC only 7 switches are employed to achieve 15 levels. The advantage of these three designs is in the reduction of total harmonic distortion by increasing the levels. Simulations are carried out in MATLAB/Simulink and comparisons were made. All the three topologies are experimentally investigated for a 3 kWp solar PV plant and power quality indices were measured.

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig.1 Single stage 15-level inverter power circuit

 EXPECTED SIMULATION RESULTS:

Fig. 2 Solar PV with partial shaded condition for a 15-level CMLI

a Variation of panel irradiance

b 15-level output voltage waveform

Fig. 3 15-level output voltage waveform achieved from three stage inverter

a 15-level output voltage waveform

b FFT analysis for three stage 15-level CMLI

Fig. 4 Output voltage waveform and its corresponding harmonic spectrum

a 27-level output voltage waveform

b FFT analysis for three stage 27-level CMLI

Fig. 5 Output voltage waveform and its corresponding harmonic spectrum

a 15-level output voltage waveform

b FFT analysis for one stage 15-level CMLI

 CONCLUSION:

The power quality improvement for a solar fed CMLI with reduced number of semiconductor switches is investigated in this paper. The required 15-level output is achieved with only 12 switches in binary mode and 7 switches in MMC mode. In addition, 27-level output is obtained with 12 switches through trinary mode. The mathematical model for solar PV is carried out which is considered as the input to the inverter stages. A detailed simulation study is carried out for various levels and comparison has been made. A 3 kWp solar PV fed CMLI is implemented for all the three topologies and harmonics analysis was made. Based on the observations, the proposed method provides the multiple advantages which include reduced THD, less cost, simple design, minimum computational complexity and the absence of transformers, boost converters, detailed look-up table and filter circuit. Moreover, these methods are much suitable for standalone/grid interacted PV systems to improve power quality.

REFERENCES:

1 Rahim, N.A., Selvaraj, J.: ‘Multistring five-level inverter with novel PWM control scheme for PV application’, IEEE Trans. Ind. Electron., 2010, 57, (6), pp. 2111–2123

2 Selvaraj, J., Rahim, N.A.: ‘Multilevel inverter for grid-connected PV system employing digital PI controller’, IEEE Trans. Ind. Electron., 2009, 56, (1), pp. 149–158

3 Rahim, N.A., Chaniago, K., Selvaraj, J.: ‘Single-phase seven-level grid-connected inverter for photovoltaic system’, IEEE Trans. Ind. Electron., 2011, 58, (6), pp. 2435–2443

4 Barbosa, P.G., Braga, H.A.C., do Carmo Barbosa Rodrigues, M., Teixeira, E.C.: ‘Boost current multilevel inverter and its application on single-phase grid-connected photovoltaic systems’, IEEE Trans. Power Electron., 2006, 21, (4), pp. 1116–1124

5 Villanueva, E., Correa, P., Rodríguez, J., Pacas, M.: ‘Control of a single-phase cascaded H-bridge multilevel inverter for grid-connected photovoltaic systems’, IEEE Trans. Ind. Electron., 2009, 56, (11), pp. 4399–4406

Hybrid Active Filter with Variable Conductance for Harmonic Resonance Suppression in Industrial Power Systems

ABSTRACT:

Unintentional series and/or parallel resonances, due to the tuned passive filter and the line inductance, may result in severe harmonic distortion in the industrial power system. This paper presents a hybrid active filter to suppress harmonic resonance and reduce harmonic distortion as well. The proposed hybrid filter is operated as variable harmonic conductance according to the voltage total harmonic distortion, so harmonic distortion can be reduced to an acceptable level in response to load change or parameter variation of power system. Since the hybrid filter is composed of a seventh-tuned passive filter and an active filter in series connection, both dc voltage and Kva rating of the active filter are dramatically decreased compared with the pure shunt active filter. In real application, this feature is very attractive since the active power filter with fully power electronics is very expensive. A reasonable trade-off between filtering performances and cost is to use the hybrid active filter. Design consideration are presented and experimental results are provided to validate effectiveness of the proposed method. Furthermore, this paper discusses filtering performances on line impedance, line resistance, voltage unbalance and capacitive filters.

KEYWORDS:

1.      Hybrid active filter

2.       Harmonic resonance

3.       Industrial power system

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. The proposed hybrid active filter unit (HAFU) in the industrial power

system and its associated control.

EXPECTED SIMULATION RESULTS:

Fig. 2. Line voltage e, source current is, load current iL, and filter current

i in case of NL1 initiated. X axis: 5ms/div.

Fig. 3. Line voltage e, source current is, load current iL, and filter current i in case of NL2 initiated. X axis: 5ms/div.

(a)     Terminal voltage

(b) Source current.

(c) Filter current.

(d) Load current.

Fig. 4 The HAFU is off for single-phase nonlinear load.

(a) Terminal voltage.

(b) Source current

     

(c) Filter current.

(d) Load current.

Fig. 5. The HAFU is on for single-phase nonlinear load.

CONCLUSION:

This paper presents a hybrid active filter to suppress harmonic resonances in industrial power systems. The proposed hybrid filter is composed of a seventh harmonic-tuned passive filter and an active filter in series connection at the secondary side of the distribution transformer. With the active filter part operating as variable harmonic conductance, the filtering  performances of the passive filter can be significantly improved. Accordingly, the harmonic resonances can be avoided  and the harmonic distortion can be maintained inside an acceptable level in case of load changes and variations of line impedance of the power system. Experimental results verify the effectiveness of the proposed method. Extended discussions are summarized as follows:

• Large line inductance and large nonlinear load may result in severe voltage distortion. The conductance is increased to maintain distortion to an acceptable level.

• Line resistance may help reduce voltage distortion. The conductance is decreased accordingly.

• For low line impedance, THD_ should be reduced to enhance filtering performances. In this situation, measuring voltage distortion becomes a challenging issue.

• High-frequency resonances resulting from capacitive filters is possible to be suppressed by the proposed method.

• In case of unbalanced voltage, a band-rejected filter is needed to filter out second-order harmonics if the SRF is realized to extract voltage harmonics.

REFERENCES:

[1] R. H. Simpson, “Misapplication of power capacitors in distribution systems with nonlinear loads–three case histories,” IEEE Trans. Ind. Appl., vol. 41, no. 1, pp. 134–143, Jan./Feb. 2005.

[2] T. Dionise and V. Lorch, “Voltage distortion on an electrical distribution system,” IEEE Ind. Appl. Mag., pp. 48–55, Mar./Apr. 2010.

[3] E. J. Currence, J. E. Plizga, and H. N. Nelson, “Harmonic resonance at a medium-sized industrial plant,” IEEE Trans. Ind. Appl., vol. 31, no. 3, pp. 682–690, May/Jun. 1995.

[4] C.-J. Wu, J.-C. Chiang, S.-S. Yen, C.-J. Liao, J.-S. Yang, and T.-Y. Guo, “Investigation and mitigation of harmonic amplification problems caused by single-tuned filters,” IEEE Trans. Power Del., vol. 13, no. 3, pp. 800–806, July 1998.

[5] B. Singh, K. Al-Haddad, and A. Chandra, “A review of active filters for power quality improvement,” IEEE Trans. Ind. Electron., vol. 46, no. 5, pp. 960–971, Oct. 1999.

High-Frequency AC-Link PV Inver

ABSTRACT:

In this paper, a high-frequency ac-link photovoltaic (PV) inverter is proposed. The proposed inverter overcomes most of the problems associated with currently available PV inverters. In this inverter, a single-stage power-conversion unit fulfills all the system requirements, i.e., inverting dc voltage to proper ac, stepping up or down the input voltage, maximum power point tracking, generating low-harmonic ac at the output, and input/output isolation. This inverter is, in fact, a partial resonant ac-link converter in which the link is formed by a parallel inductor/capacitor (LC) pair having alternating current and voltage. Among the significant merits of the proposed inverter are the zero-voltage turn-on and soft turn-off of the switches which result in negligible switching losses and minimum voltage stress on the switches. Hence, the frequency of the link can be as high as permitted by the switches and the processor. The high frequency of operation makes the proposed inverter very compact. The other significant advantage of the proposed inverter is that no bulky electrolytic capacitor exists at the link. Electrolytic capacitors are cited as the most unreliable component in PV inverters, and they are responsible for most of the inverters’ failures, particularly at high temperature. Therefore, substituting dc electrolytic capacitors with ac LC pairs will significantly increase the reliability of PV inverters. A 30-kW prototype was fabricated and tested. The principle of operation and detailed design procedure of the proposed inverter along with the simulation and experimental results are included in this paper. To evaluate the long-term performance of the proposed inverter, three of these inverters were installed at three different commercial facilities in Texas, USA, to support the PV systems. These inverters have been working for several months now.

KEYWORDS:

1.      Inverters

2.      Photovoltaic (PV) systems

3.      Zero voltage switching

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Proposed PV inverter.

EXPECTED SIMULATION RESULTS:

Fig. 2. PV current and voltage at full power.

Fig. 3. AC-side current and voltage at full power.

Fig. 4. Link voltage at full power.

Fig. 5. Link current at full power.

         Fig. 6. Link current and voltage at full power, using 0.1-μF link capacitance.

Fig. 7. Link current and voltage at 15 kW.

Fig. 8. AC-side current and voltage when the irradiance drops from 850 to

650 w/m2.

Fig. 9. AC-side current and voltage when the temperature changes from

25 ◦C to 50 ◦C.

Fig. 10. AC-side current and voltage when the AC-side voltage drops to 10%

of its nominal value (at t = 0.016 s).

Fig. 11. PV current and voltage when the AC-side voltage drops to 10% of its

nominal value (at t = 0.016 s).

CONCLUSION:

In this paper, a reliable and compact PV inverter has been proposed. This inverter is a partial resonant ac-link converter in which the link is formed by an LC pair having alternating current and voltage. The proposed converter guarantees the isolation of the input and output. However, if galvanic isolation is required, the link inductance can be replaced by a singlephase high-frequency transformer. The elimination of the dc link and low-frequency transformer makes the proposed inverter more compact and reliable compared with other types of PV inverters. In this paper, the principle of operation of the proposed converter along with the detailed design procedure has been presented. The performance of the proposed converter has been evaluated through both simulation and experimental results.

 REFERENCES:

[1] S. Chakraborty, B. Kramer, and B. Kroposki, “A review of power electronics interfaces for distributed energy systems towards achieving low-cost modular design,” Renew. Sustain. Energy Rev., vol. 13, no. 9, pp. 2323–2335, Dec. 2009.

[2] Y. Huang, F. Z. Peng, J. Wang, and D. W. Yoo, “Survey of the power conditioning system for PV power generation,” in Proc. IEEE PESC, Jun. 18–22, 2006, pp. 1–6.

[3] S. Atcitty, J. E. Granata, M. A. Quinta, and C. A. Tasca, Utility-scale gridtied PV inverter reliability workshop summary report, Sandia National Labs., Albuquerque, NM, USA, SANDIA Rep. SAND2011-4778. [Online].

Available: http://energy.sandia.gov/wp/wp-content/gallery/uploads/  Inverter_Workshop_FINAL_072811.pdf

[4] Y. C. Qin, N. Mohan, R. West, and R. Bonn, Status and needs of power electronics for photovoltaic inverters, Sandia National Labs., Albuquerque, NM, USA, SANDIA Rep. SAND2002-1535. [Online]. Available: www.prod.sandia.gov/techlib/access-control.cgi/2002/021535. pdf

[5] T. Kerekes, R. Teodorescu, P. Rodríguez, G. Vázquez, and E. Aldabas, “A new high-efficiency single-phase transformerless PV inverter topology,” IEEE Trans. Ind. Electron., vol. 58, no. 1, pp. 184–191, Jan. 2011.