Low Switching Frequency Based Asymmetrical Multilevel Inverter Topology With Reduced Switch Count

ABSTRACT:

The inceptions of multilevel inverters (MLI) have caught the attention of researchers for medium and high power applications. However, there has always been a need for a topology with a lower number of device count for higher efficiency and reliability. A new single-phase MLI topology has been proposed in this paper to reduce the number of switches in the circuit and obtain higher voltage level at the output. The basic unit of the proposed topology produces 13 levels at the output with three dc voltage sources and eight switches. Three extentions of the basic unit have been proposed in this paper. A detailed analysis of the proposed topology has been carried out to show the superiority of the proposed converter with respect to the other existing MLI topologies. Power loss analysis has been done using PLECS software, resulting in a maximum efficiency of 98.5%. Nearest level control (NLC) pulse-width modulation technique has been used to produce gate pulses for the switches to achieve better output voltage waveform. The various simulation results have been performed in the PLECS software and a laboratory setup has been used to show the feasibility of the proposed MLI topology.

KEYWORDS:

1.      DC/AC converter

2.      Multilevel inverter

3.      Reduce switch count

4.      Nearest level control (NLC)

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Figure 1. Basic unit of the proposed topology.

 EXPERIMENTAL RESULTS:

Figure 2. Simulation results with (a) dynamic change of modulation

index (b) FFT of 13 level output voltage and current with ZD10C100mH

and (c) output voltage and current waveforms with change of load from

ZD50 to ZD50C100mH.

CONCLUSION:

The paper presents a novel MLI topology with multiple extension capabilities. The basic unit of the proposed topology produces 13 levels using eight unidirectional switches and three dc voltage sources. Three different extension of the basic unit has been proposed. The performance analysis of the basic unit of the proposed topology has been done and the comparative results with some recently proposed topologies in literature have been presented in the paper. Further, a power loss analysis of the dynamic losses (switching and conduction) in the MLI has also been presented, which gives the maximum efficiency of the basic unit as 98.5%. The power loss distribution in all the switches for different combination of loads have also been demonstrated in the paper. The performance of the proposed topology has been simulated with dynamic modulation indexes and different combination of loads using PLECS software. A prototype of the basic unit has been developed in the laboratory and the simulation results have been validated using the different experimental results considering different modulation indexes.

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. Aburub, J. Holtz, and J. Rodriguez, ``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, Dec. 2010.

[3] H. Akagi, ``Multilevel converters: Fundamental circuits and systems,'' Proc. IEEE, vol. 105, no. 11, pp. 2048_2065, Nov. 2017.

[4] J. I. Leon, S. Vazquez, and L. G. Franquelo, ``Multilevel converters: Control and modulation techniques for their operation and industrial applications,'' Proc. IEEE, vol. 105, no. 11, pp. 2066_2081, Nov. 2017.

[5] J. Venkataramanaiah, Y. Suresh, and A. K. Panda, ``A review on symmetric, asymmetric, hybrid and single DC sources based multilevel inverter topologies,'' Renew. Sustain. Energy Rev., vol. 76, pp. 788_812, Sep. 2017.

A Novel Multilevel DC/AC Inverter Based on Three-Level Half Bridge With Voltage Vector Selecting Algorithm

ABSTRACT:

A novel multilevel inverter based on a three-level half bridge is proposed for the DC/AC applications. For each power cell, only one DC power source is needed and five-level output AC voltage is realized. The inverter consists of two parts, the three-level half bridge, and the voltage vector selector, and each part consists of the four MOSFETs. Both positive and negative voltage levels are generated at the output, thus, no extra H-bridges are needed. The switches of the three-level half bridge are connected in series, and the output voltages are (Vo, Vo/2, and 0). The voltage vector selector is used to output minus voltages (􀀀Vo and 􀀀Vo/2) by different conducting states. With complementary working models, the voltages of the two input capacitors are balanced. Besides, the power cell is able to be cascaded for more voltage levels and for higher power purpose. The control algorithm and two output strategies adopted in the proposed inverter are introduced, and the effectiveness is verified by simulation and experimental results.

KEYWORDS:

1.      Bridge circuits

2.      DC-AC power converters

3.      Modular multilevel converters

4.      Pulse width modulation converters

5.      Voltage control

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Figure 1. The proposed hybrid ZVS bidirectional DC/AC inverter topology.

EXPERIMENTAL RESULTS:

Figure 2. Waveforms with LFF strategy.

Figure 3. Waveforms with HFSPWM strategy.

Figure 4. Voltages of input capacitors C1 and C2.

Figure 5. Output waveforms of 2-level cascaded topologies.

CONCLUSION:

A novel multilevel inverter based on a three-level half bridge is proposed for DC/AC applications in this paper. For each power cell, only one DC power source is needed and 5-level output AC voltage is realized. Both positive and negative voltage levels are generated at the output, thus no extra H bridges are needed. The non-isolated topology (transformerless) eliminates magnetic losses. The operating principle and the working stages of the proposed inverter are introduced, while the two output strategies are discussed in detail. Besides, voltage balance strategy is adopted to balance the bus capacitor voltages, and stage optimization method is applied to further reduce the switching losses. Finally, a simulation is carried out to verify the two output strategies, voltage balance strategy and the cascaded ability, and a laboratorial experiment is carried out to test the THD losses and the total efficiency.

REFERENCES:

[1] A. Jahid, M. K. H. Monju, M. E. Hossain, and M. F. Hossain, ``Renewable energy assisted cost aware sustainable off-grid base stations with energy cooperation,'' IEEE Access, vol. 6, pp. 60900_60920, Oct. 2018.

[2] S. Xie, W. Zhong, K. Xie, R. Yu, and Y. Zhang, ``Fair energy scheduling for vehicle-to-grid networks using adaptive dynamic programming,'' IEEE Trans. Neural Netw. Learn. Syst., vol. 27, no. 8, pp. 1697_1707, Aug. 2016.

[3] A. Garcia-Bediaga, I. Villar, A. Rujas, and L. Mir, ``DAB modulation schema with extended ZVS region for applications with wide input/output voltage,'' IET Power Electron., vol. 11, no. 13, pp. 2109_2116, Nov. 2018.

[4] G. Xu, D. Sha, Y. Xu, and X. Liao, ``Hybrid-bridge-based DAB converter with voltage match control for wide voltage conversion gain application,'' IEEE Trans. Power Electron., vol. 33, no. 2, pp. 1378_1388, Feb. 2017.

[5] Y. Cho, W. Cha, J. Kwon, and B. Kwon, ``High-efficiency bidirectional DAB inverter using a novel hybrid modulation for stand-alone power generating system with low input voltage,'' IEEE Trans. Power Electron., vol. 31, no. 6, pp. 4138_4147, Jun. 2015.

A Novel Seven-Level Active Neutral Point Clamped Converter with Reduced Active Switching Devices and DC-link Voltage

ABSTRACT:

 This paper presents a novel seven-level inverter topology for medium-voltage high-power applications. It consists of eight active switches and two inner flying-capacitor units forming a similar structure as in a conventional Active Neutral Point Clamped (ANPC) inverter. This unique arrangement reduces the number of active and passive components. A simple modulation technique reduces cost and complexity in the control system design without compromising reactive power capability. In addition, compared to major conventional 7-level inverter topologies such as the Neutral Point Clamped (NPC), Flying Capacitor (FC), Cascaded H-bridge (CHB) and Active NPC (ANPC) topologies, the new topology reduces the dc-link voltage requirement by 50%. This recued dc-link voltage makes the new topology appealing for various industrial applications. Experimental results from a 2.2 kVA prototype are presented to support the theoretical analysis presented in this paper. The prototype demonstrates a conversion efficiency of around 97.2% ± 1% for a wide load range.

KEYWORDS:

1.      Multilevel Inverter

2.      7-level inverter

3.      Active Neutral Point Clamped (ANPC) inverter

4.      Flying Capacitor

5.      Voltage Source Converter

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Proposed seven-level three-phase inverter circuit

 EXPERIMENTAL RESULTS:

Fig. 2. Some key simulated waveforms of the proposed seven-level inverter: (a) input voltage, flying capacitors voltages, phase voltage (with and without filter), and (b) voltage stress on switches, (c) current stress on switches, and (d) harmonic spectrum of the output voltage.

Fig. 3. Operation of the inverter during: (a) lagging power factor of φ𝑝𝑓 = −450 (RL load of 60 Ω + 200 mH), and (b) leading power factor of φ𝑝𝑓 = +450 (RC load of 60 Ω + 50 μF).

Fig. 4. Dynamic performance of the converter under several changes in the active power (a step change in load from no load to full load (30 Ω ), b step change in load from full load (30 Ω) to half load (60 Ω), and c step change in load from half load (60 Ω) to full load (30 Ω)).

CONCLUSION:

In this paper, a novel eight-switch seven-level Active Neutral Point Clamped inverter is proposed. Modulation techniques are explored and operation under both active and reactive power factor conditions are systematically analyzed. A comparative analysis and a set of design guidelines are presented and followed by simulation and experimental verification. Compared to conventional seven-level inverter topologies, the ANPC inverter topology requires only eight power devices for a single-phase design and halves the dc-link voltage required to produce a given ac voltage output magnitude when compared to similar circuits. For applications such as for a grid-connected PV system, this may help eliminate additional power conversion stages (boost converters) and therefore increase the efficiency and reliability of the system. Further, this reduces the voltage stress on the dc-link capacitor, which reduces the cost and size of the system design. The inverter can operate at any power factor (leading or lagging) without requiring any changes to the modulation scheme. Compared with other seven-level configurations, the performance demonstrated by the new inverter is highly competitive, potentially making it an appropriate topology choice for a wide-range of power conversion applications, e.g. variable-speed drives, electric vehicles (V2G/G2V technologies), grid-connected renewable energy systems.

REFERENCES:

[1] M. Schweizer, T. Friedli, and J. W. Kolar, “Comparative Evaluation of Advanced Three-Phase Three-Level Inverter/Converter Topologies Against Two-Level Systems,” IEEE Trans. Ind. Electron., vol. 60, no. 12, pp. 5515-5527, Dec. 2012.

[2] H. Tian, Y. Li, Y. W. Li, “A Novel Seven-Level Hybrid-Clamped (HC) Topology for Medium Voltage Motor Drives,” IEEE Trans. Power Electron., vol. 33, no. 7, pp. 5543-5547, Jul. 2018.

[3] 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.

[4] J. Rodríguez, J. S. Lai, and F. Z. Peng, “Multilevel Inverters: A Survey of Topologies, Controls, and Applications,” IEEE Trans. Ind. Electron., vol. 49, no. 4, pp. 724-738, Aug. 2002.

[5] J. I. Leon, S. Vazquez, and L. G. Franquelo, “Multilevel Converters: Control and Modulation Techniques for their Operation and Industrial Applications,” Proc. of the IEEE, vol. 105, no. 11, pp. 2066-2081, Nov. 2017.

Improved MPPT method to increase accuracy and speed in photovoltaic systems under variable atmospheric conditions

ABSTRACT:

The changes in temperature and radiation cause visible fluctuations in the output power produced by the photovoltaic (PV) panels. It is essential to keep the output voltage of the PV panel at the maximum power point (MPP) under varying temperature and radiation conditions. In this study, a maximum power point tracking (MPPT) method has been developed which is based on mainly two parts: the first part is adapting calculation block for the reference voltage point of MPPT and the second one is Fuzzy Logic Controller (FLC) block to adjust the duty cycle of PWM applied switch (Mosfet) of the DC-DC converter. In order to evaluate the robustness of the proposed method, Matlab/Simulink program has been used to compare with the traditional methods which are Perturb & Observe (P&O), Incremental Conductance (Inc. Cond.) and FLC methods under variable atmospheric conditions. When the test results are observed, it is clearly obtained that the proposed MPPT method provides an increase in the tracking capability of MPP and at the same time reduced steady state oscillations. The accuracy of the proposed method is between 99.5% and 99.9%. In addition, the time to capture MPP is 0.021 sec. It is about four times faster than P&O and five times faster than for Inc. Cond. and, furthermore, the proposed method has been compared with the conventional FLC method and it has been observed that the proposed method is faster about 28% and also its efficiency is about 1% better than FLC method.

KEYWORDS:

1.      PV

2.      MPPT methods

3.      FLC based MPPT

4.      DC-DC converter

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Block diagram of the designed system.

 EXPERIMENTAL RESULTS:

Fig. 2. The PV power with four MPPT algorithm.

Fig. 3. The speed of MPPT algorithms.

Fig. 4. The PV voltage with four MPPT algorithm.

Fig. 5. The generated PV current with four MPPT methods.

Fig. 6. The reference voltage produced by the MPPT algorithm.

Fig. 7. PV array current and load current.

Fig. 8. Fuzzy logic controller output (D).

Fig. 9. PV array voltage and load voltage.

Fig. 10. PV power for four different MPPT techniques under variable irradiance (fixed temperature).

Fig. 11. PV currents for proposed MPPT technique.

Fig. 12. PV voltages for proposed MPPT technique under variable irradiance (fixed temperature).

Fig. 13. PV power for four different MPPT techniques under variable temperature (fixed irradiance).

Fig. 14. PV currents for proposed MPPT technique.

Fig. 15. PV voltages for proposed MPPT technique under variable temperature (fixed irradiance).

Fig. 16. (a) P-V characteristics curve, (b) Tracking global peak point for proposed MPPT technique.

CONCLUSION:

This study proposes a novel MPPT method and the detailed performance comparison with commonly used methods such as P&O, Incremental conductance and FLC techniques is achieved. Under sudden change in atmospheric operating conditions, the proposed MPPT method performs better performance than other methods to determine MPP. The efficiency of proposed MPPT method is between 99.5% and 99.9%, while P&O is between 91% and 98%, Inc. Cond. Is between 96% and 99% and FLC is between 98.8% and 99.4% for all case studies. The proposed MPPT method has achieved the lowest oscillation rate at the MPP compared to commonly used methods. This brings the method to the forefront in terms of efficiency. The duration of the proposed MPPT technique to reach a steady state has been measured as 0.021 sec. It is about four times faster than P&O and five times faster than for Inc. Cond. and, furthermore, the proposed method has been compared with the conventional FLC method and it has been observed that the proposed method is faster about 28% than FLC method this means the speed of proposed MPPT technique is the best. At the same time, the amount of oscillation is very low compared to conventional methods. The accuracy of the algorithm is high (%99.9 in many study cases) and also the proposed method is easy to implement in the system.

REFERENCES:

[1] Luo HY, Wen HQ, Li XS, Jiang L, Hu YH. Synchronous buck converter based low cost and high-efficiency sub-module DMPPT PV system under partial shading conditions. Energy Convers Manage 2016;126:473–87.

[2] Babaa SE, Armstrong M, Pickert V. Overview of maximum power point tracking control methods for PV systems. J Power Energy Eng 2014;2:59–72.

[3] Dolara AFR, Leva S. Energy comparison of seven MPPT techniques for PV systems. J Electromagn Anal Appl 2009;3:152–62.

[4] Ngan MS, Tan CW. A study of maximum power point tracking algorithms for standalone photovoltaic systems. Applied Power Electronics Colloquium (IAPEC): IEEE. 2011. p. 22–7.

[5] Liu JZ, Meng HM, Hu Y, Lin ZW, Wang W. A novel MPPT method for enhancing energy conversion efficiency taking power smoothing into account. Energy Convers Manage 2015;101:738–48.