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.

PMSG Based Wind Energy Generation System: Energy Maximization and its Control

ABSTRACT:

This paper deals with the energy maximization and control analysis for the permanent magnet synchronous generator (PMSG) based wind energy generation system (WEGS). The system consists of a wind turbine, a three-phase IGBT based rectifier on the generator side and a three-phase IGBT based inverter on the grid side converter system. The pitch angle control by perturbation and observation (P&O) algorithm for obtaining maximum power point tracking (MPPT). MPPT is most effective under, cold weather, cloudy or hazy days. A designed control technique is proposed for the MPPT mechanism of the system. This paper will explore in detail about the control analysis for both the generator and grid side converter system. Further, it will also discuss about the pitch angle control for the wind turbine in order to obtain maximum power for the complete wind energy generation system. The proposed WEGS for maximization of power is modelled, designed and simulated using MATLAB R2014b Simulink with its power system toolbox and discrete step solver incorporated in the simulation tool.

KEYWORDS:

1.      Maximum power point tracking (MPPT)

2.      Permanent magnet synchronous generator (PMSG)

3.      Pitch angle control (PAC)

4.      Wind energy generation system (WEG)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 Fig. 1. Control issue in PMSG based wind turbine system

EXPECTED SIMULATION RESULTS:

Fig.2. Wind speed (15 m/s).

Fig.3. Pitch angle ( 26 Degree).

Fig.4. Active power output (1.49 MW).

Fig.5. Stator voltage of PMSG (per unit).

Fig.6. Stator current of PMSG (per unit).

Fig.7. Wind speed (m/s).

Fig.8. Pitch control.

Fig.9. Electrical torque of PMSG.

 

Fig.10. Wind turbine power with pitch control.

CONCLUSION:

This paper has briefly discussed about the energy maximization and control analysis for the PMSG based wind energy generation system. The paper also explored in detail about the different control algorithm for both the machine and grid side converter system and has used VSC control for our proposed mechanism. A brief discussion on the pitch angle control for the wind turbine has been described which aims to obtain maximum power for the complete wind energy generation system. A designed control technique named as (P&O) has also been proposed for the MPPT mechanism of the system whose results has been validated using MATLAB R2014b Simulink. As discussed before the presented technique includes maximum power point tracking module, pitch angle control and average model for machine side and grid side converters. Also, the integrated control system controls the generator speed, DC-link voltage and active power along with the above-mentioned factors.

REFERENCES:

[1] M. Benadja and A. Chandra, “A new MPPT algorithm for PMSG based grid connected wind energy system with power quality improvement features”, IEEE Fifth Power India Conference, Murthal, pp. 1-6, 2012.

[2] S. Sharma and B. Singh, “An autonomous wind energy conversion system with permanent magnet synchronous generator”, International Conference on Energy, Automation and Signal, Bhubaneswar, Odisha, pp. 1-6, 2011.

[3] M. Singh and A. Chandra, “Power maximization and voltage sag/swell ride-through capability of PMSG based variable speed wind energy conversion system”,34th Annual Conference of IEEE Industrial Electronics, Orlando, FL, pp. 2206-2211, 2008.

[4] T. Tafticht, K. Agbossou, A. Cheriti and M. L. Doumbia, “Output Power Maximization of a Permanent Magnet Synchronous Generator Based Stand-alone Wind Turbine”,IEEE International Symposium on Industrial Electronics, Montreal, pp. 2412-2416, 2006.

[5] N. A. Orlando, M. Liserre, R. A. Mastromauro and A. D. Aquila, “A Survey of Control Issues in PMSG-Based Small Wind-Turbine Systems”, IEEE Transactions on Industrial Informatics, vol. 9, no. 3, pp. 1211-1221, Aug. 2013.

Power Management in PV-Battery-Hydro Based Standalone Microgrid

 ABSTRACT:

This paper proposes a high-efficiency two stage three-level grid-connected photovoltaic inverter. This work deals with the frequency regulation, voltage regulation, power management and load levelling of solar photovoltaic (PV)-battery-hydro based microgrid (MG). In this MG, the battery capacity is reduced as compared to a system, where the battery is directly connected to the DC bus of the voltage source converter (VSC). A bidirectional DC–DC converter connects the battery to the DC bus and it controls the charging and discharging current of the battery. It also regulates the DC bus voltage of VSC, frequency and voltage of MG. The proposed system manages the power flow of different sources like hydro and solar PV array. However, the load levelling is managed through the battery. The battery with VSC absorbs the sudden load changes, resulting in rapid regulation of DC link voltage, frequency and voltage of MG. Therefore, the system voltage and frequency regulation allows the active power balance along with the auxiliary services such as reactive power support, source current harmonics mitigation and voltage harmonics reduction at the point of common interconnection. The experimental results under various steady state and dynamic conditions, exhibit the excellent performance of the proposed system and validate the design and control of proposed MG.

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig. 1 Microgrid Topology and MPPT Control

(a) Proposed PV-battery-hydro MG,

EXPECTED SIMULATION RESULTS:

Fig. 2 Dynamic performance of PV-battery-hydro based MG following by solar irradiance change

(a) vsab, isc, iLc and ivscc, (b) Vdc, Ipv, Vb and Ib, (c) vsab, isa, iLa and ivsca, (d) Vdc, Ipv, Vb and Ib

.

Fig.3 Dynamic performance of hydro-battery-PV based MG under load perturbation

(a) vsab, isc, Ipv and ivscc, (b) Vdc, Ipv, Vb and Ib, (c) vsab, isc, Ipv and ivscc, (d) Vdc, Ipv, and Vb

CONCLUSION: 

In the proposed MG, an integration of hydro with the battery, compensates the intermittent nature of PV array. The proposed system uses the hydro, solar PV and battery energy to feed the voltage (Vdc), solar array current (Ipv), battery voltage (Vb) and battery current (Ib). When the load is increased, the load demand exceeds the hydro generated power, since SEIG operates in constant power mode condition. This system has the capability to adjust the dynamical power sharing among the different RES depending on the availability of renewable energy and load demand. A bidirectional converter controller has been successful to maintain DC-link voltage and the battery charging and discharging currents. Experimental results have validated the design and control of the proposed system and the feasibility of it for rural area electrification.

REFERENCES:

[1] Ellabban, O., Abu-Rub, H., Blaabjerg, F.: ‘Renewable energy resources: current status, future prospects and technology’, Renew. Sustain. Energy Rev.,2014, 39, pp. 748–764

[2] Bull, S.R.: ‘Renewable energy today and tomorrow’, Proc. IEEE, 2001, 89, (8), pp. 1216–1226

[3] Malik, S.M., Ai, X., Sun, Y., et al.: ‘Voltage and frequency control strategies of hybrid AC/DC microgrid: a review’, IET Renew. Power Gener., 2017, 11, (2), pp. 303–313

[4] Kusakana, K.: ‘Optimal scheduled power flow for distributed photovoltaic/ wind/diesel generators with battery storage system’, IET Renew. Power Gener., 2015, 9, (8), pp. 916–924

[5] Askarzadeh, A.: ‘Solution for sizing a PV/diesel HPGS for isolated sites’, IET Renew. Power Gener., 2017, 11, (1), pp. 143–151

High-Efficiency Two-Stage Three-Level Grid-Connected Photovoltaic Inverte

ABSTRACT:

This paper proposes a high-efficiency two stage three-level grid-connected photovoltaic inverter. The proposed two-stage inverter comprises a three-level step up converter and a three-level inverter. The three-level step up  converter not only improves the power-conversion efficiency by lowering the voltage stress but also guarantees the balancing of the dc-link capacitor voltages using a simple control algorithm; it also enables the proposed inverter to satisfy the VDE 0126-1-1 standard of leakage current. The three-level inverter minimizes the overall power losses with zero reverse-recovery loss. Furthermore, it reduces harmonic distortion, the voltage ratings of the semiconductor device, and the electromagnetic interference by using a three-level circuit configuration; it also enables the use of small and low cost filters. To control the grid current effectively, we have used a feed-forward nominal voltage compensator with a mode selector; this compensator improves the control environment by presetting the operating point. The proposed high-efficiency two-stage three-level grid-connected photovoltaic inverter overcomes the low  efficiency problem of conventional two-stage inverters, and it provides high power quality with maximum efficiency of 97.4%. Using a 3-kW prototype of the inverter, we have evaluated the performance of the model and proved its feasibility.

KEYWORDS:

1.      Transformerless

2.      Multilevel

3.      Dc-ac power conversion

4.      Single-phase

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Proposed high-efficiency two-stage three-level grid-connected PV inverter circuit diagram.

EXPECTED SIMULATION RESULTS:

Fig.2. Simulation results for the leakage current of the proposed twostage

inverter.

Fig.3. Simulation results for the leakage current using a conventional three-level step-up converter of Fig. 2(b) as dc-dc power conversion stage of two-stage inverter.

CONCLUSION: 

A high-efficiency two-stage three-level grid-connected PV inverter and control system are introduced. Also, a theoretical analysis is provided along with the experimental results. By using the novel circuit configuration, the proposed two-stage inverter performs power conversion with low leakage current and high efficiency; in dc-dc power conversion stage, the connection of midpoints of capacitors enables the proposed two-stage inverter to limit the leakage current below 300mA; in dc-ac power conversion stage, the overall power losses are minimized by eliminating the reverse-recovery problems of the MOSFET body diodes. Besides, the proposed inverter with three voltage levels reduces the power losses, harmonic components, voltage ratings, and EMI; it also enables using small and low cost filters. For the control system, the feedforward nominal voltage compensator also improves the control environment by presetting the operating point. This developed control algorithm makes the proposed inverter feasible. Thus, the proposed high-efficiency two-stage three-level grid connected PV inverter provides high power quality with high power-conversion efficiency. By using a 3-kW prototype, this experiment has verified that the proposed inverter has high efficiency, and the developed control system is suitable for the proposed inverter.

REFERENCES:

[1] B.K. Bose, “Global energy acenario and impact of power electronics in 21st century,” IEEE Transactions on Industrial Electronics, vol. 60, no. 7, pp. 2638-2651, July. 2013.

[2] Y. Zhou, D. C. Gong, B. Huang, and B. A. Peters, “The impacts of carbon tariff on green supply chain design,” IEEE Transactions on Automation Science and Engineering, July. 2015. Available: DOI: 10.1109/TASE.2015.2445316

[3] Y. Wang, X. Lin, and M. Pedram, “A near-optimal model-based control algorithm for households equipped with residential photovoltaic power generation and energy storage systems,” IEEE Transactions on Sustainable Energy, vol. 7, no. 1, pp. 77-86, Jan. 2016.

[4] Y. W. Cho, W. J. Cha, J. M. Kwon, and B. H. Kwon, “Improved  single-phase transformerless inverter with high power density and high efficiency for grid-connected photovoltaic systems,” IET Renewable Power Generation, vol. 10, no. 2, pp. 166-174, Feb. 2016.

[5] A. Shayestehfard, S. Mekhilef, and H. Mokhlis, “IZDPWMBased feedforward controller for grid-connected inverters under unbalanced and distorted conditions,” IEEE Trans. Ind. Electron., vol. 64, no. 1, pp. 14-21, Jan. 2017.

A Three-Phase Symmetrical DC-Link Multilevel Inverter with Reduced Number of DC Sources

ABSTRACT:

 This paper presents a novel three-phase DC-link multilevel inverter topology with reduced number of input DC power supplies. The proposed inverter consists of series-connected half-bridge modules to generate the multilevel waveform and a simple H-bridge module, acting as a polarity generator. The inverter output voltage is transferred to the load through a three-phase transformer, which facilitates a galvanic isolation between the inverter and the load. The proposed topology features many advantages when compared with the conventional multilevel inverters proposed in the literatures. These features include scalability, simple control, reduced number of DC voltage sources and less devices count. A simple sinusoidal pulse-width modulation technique is employed to control the proposed inverter. The performance of the inverter is evaluated under different loading conditions and a comparison with some existing topologies is also presented. The feasibility and effectiveness of the proposed inverter are confirmed through simulation and experimental studies using a scaled down low-voltage laboratory prototype.

KEYWORDS:

1.      Hybrid multilevel inverter

2.      DC-link inverter

3.      half-bridge module

4.      symmetric DC voltage supply

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1 The proposed three-phase CMLI with two half-bridge cells per phase leg

 EXPECTED SIMULATION RESULTS:

Fig. 2 Simulation results of the output line voltages and line currents for (a) load of nearly 0.8–lagging power factor and (b) load of nearly unity power factor

Fig. 3 Simulation results for a dynamic change in the load from nearly unity PF (100.31∠4.49°Ω) to 0.8 lagging PF (127.13∠38.13°Ω): (a) level generator output voltage, (b) polarity generator output voltage (phase voltage) and (c) line voltage and line current

Fig. 4 Simulation results for a dynamic change in the load magnitude with the same PF: (a) Line voltage, (b) Line current

Fig. 5 Simulation results for a dynamic change in the load from nearly 0.9 lagging PF (108.01∠22.21°Ω) to 0.7 lagging PF (142.88∠45.58°Ω): (a) level generator output voltage, (b) polarity generator output voltage (phase voltage) and (c) line voltage and line current

Fig. 6 Simulation results for carrier frequency of 8 kHz: (a) line voltages and currents, (b) line current THD, (c) line voltage THD

CONCLUSION

This paper presents a new symmetrical multilevel inverter topology with two different stages. The proposed inverter requires less power electronic devices and features modularity, hence simple structure, less cost, and high scalability. The number of input DC-supplies for the proposed topology is found to be nearly 67% less than the similar symmetric half-bridge topologies, which is a great achievement for industrial applications. This phenomenon will reduce the complexity of DC voltage management. As being a symmetric structure, all the switching devices experience same voltage stress, which is a very important factor for high voltage applications. The feasibility of the proposed inverter is confirmed through simulation and experimental analysis for different operating conditions.

REFERENCES:

[1] L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo, and M. A. Prats, "The age of multilevel converters arrives," IEEE Ind. Electron. magazine, vol. 2, pp. 28-39, 2008.

[2] A. Nabae, I. Takahashi, and H. Akagi, "A new neutral-point-clamped PWM inverter," IEEE Trans. Ind. Appl., pp. 518-523, 1981.

[3] S. Kouro, M. Malinowski, K. Gopakumar, J. Pou, L. G. Franquelo, B. Wu, et al., "Recent advances and industrial applications of multilevel converters," IEEE Trans. Ind. Electron., vol. 57, pp. 2553-2580, 2010.

[4] J. Rodriguez, J.-S. Lai, and F. Z. Peng, "Multilevel inverters: a survey of topologies, controls, and applications," IEEE Trans. Ind. Electron., vol. 49, pp. 724-738, 2002.

[5] B. Xiao, L. Hang, J. Mei, C. Riley, L. M. Tolbert, and B. Ozpineci, "Modular cascaded H-bridge multilevel PV inverter with distributed MPPT for grid-connected applications," IEEE Trans. Ind. Appl., vol. 51, pp. 1722-1731, 2015.