A Seven-level Inverter with Self-balancing and Low Voltage Stress

ABSTRACT:  

Based on the switched-capacitor (SC) principle, a seven-level inverter is proposed, which can synthesize seven levels containing a single dc source. Moreover, it can further generate more levels by a cascaded extension. Meanwhile, the proposed topology does not require any sensor due to the use of SC technology. Furthermore, the capacitor voltage is self-balanced without utilizing the complicated control strategy and additional control circuits. The phase disposition pulse width modulation (PD-PWM) is adopted to reduce the total harmonic distortion (THD). The topology can generate the different levels with a wide range of modulation index. In addition, the topology can also work in over modulation. Compared with the traditional SC multilevel inverter (MLI), the absence of H-bridge makes low-voltage stress in proposed topology. The voltage stress of all switches is not more than the input voltage. Operational principles, modulation strategy, and voltage stress analysis are discussed. Simulation and experiment are conducted in low power to verify the feasibility of the proposed topology.

KEYWORDS:

1.      Multilevel inverters

2.       Low-voltage stress

3.      Switched-capacitor

4.      Voltage self-balancing

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig. 1. The circuit of the proposed seven-level inverter.

EXPERIMENTAL RESULTS:

Fig. 2. Simulation waveforms of the output voltage and current. (a) Output voltage and current. (b) THD of the output voltage.

CONCLUSION:

In this paper, the seven-level inverter is proposed by utilizing the switched capacitor technology. In addition, the inverter can be used as the basic cell to construct more output levels through a cascaded configuration. With the PD-PWM modulation, the capacitor voltage can be self-balanced without any sensor to detect the voltage. Moreover, the topology can work in different modulation index and can generate a different number of voltage levels. The working principle and capacitor parameters are analyzed in detail. In addition, the performances are compared with the existing topologies to prove the advantages. A low-power prototype is constructed to prove the feasibility of the proposed topology, and good performance of steady and transient state is testified.

REFERENCES:

[1] E. Samadaei, A. Sheikholeslami, S. A. Gholamian, and J. Adabi, “A Square T-Type (ST-Type) Module for Asymmetrical Multilevel Inverters,” IEEE Trans. Power Electron., vol. 33, no. 2, pp. 987–996, Feb. 2018.

[2] R. Barzegarkhoo, M. Moradzadeh, E. Zamiri, H. M. Kojabadi, and F. Blaabjerg, “A New Boost Switched-Capacitor Multilevel Converter with Reduced Circuit Devices,” IEEE Trans. Power Electron., vol. 33, no. 8, pp. 6738–6754, Aug. 2018.

[3] M. Norambuena, S. Kouro, S. Dieckerhoff, and J. Rodriguez, “Reduced Multilevel Converter: A Novel Multilevel Converter With a Reduced Number of Active Switches,” IEEE Trans. Ind. Electron., vol. 65, no. 5, pp. 3636–3645, May. 2018.

[4] S. Kouro, M. Malinowski, K. Gopakumar, J. Pou, L. G. Franquelo, B. Wu, J. Rodriguez, M. A. Pérez, 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.

[5] A. Nabae, I. Takahashi, and H. Akagi, “A new neutral-point-clamped PWM inverter,” IEEE Trans. Ind. Appl., vol. IA-17, no. 5, pp. 518–523, Sep. 1981.

A Hybrid Boundary Conduction Modulation for a Single-Phase H-bridge Inverter to Alleviate Zero-Crossing Distortion and Enable Reactive Power Capability

ABSTRACT:  

Boundary Conduction Modulation (BCM) featuring zero voltage switching has caught researchers’ eyes recently. In single-phase full-bridge inverter with one leg operating in high switching frequency and one leg in line frequency, it is easy to achieve high conversion efficiency for low power applications. However, severe distortion will be introduced during zero voltage crossing area due to too low switching frequency around this area, and reactive power generation is not allowed under this modulation scheme due to zero voltage crossing issue. This paper proposes a hybrid BCM strategy for a single-phase full-bridge inverter to both alleviate voltage zero-crossing distortion and enable reactive power generation by reshaping the triangular waveform of inductor current into quadrangle waveform through rearranging the driving signals during voltage zero crossing area. This alleviates zero-crossing distortion by avoiding too low switching frequency and enables reactive power generation by employing the hybrid BCM around voltage zero crossing area. High efficiency can be maintained by combining the proposed hybrid BCM employed only for a small portion of zero crossing area and the conventional BCM for the rest. The principle of operation, theoretical analysis and simulation results are presented in this paper. A 300W microinverter prototype was built to verify the feasibility and effectiveness of the proposed hybrid BCM scheme.

KEYWORDS:

1.      Microinverter

2.      BCM operation

3.      Hybrid  modulation strategy

4.       High efficiency

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. The control diagram of the prototype proposed.

                

 EXPERIMENTAL RESULTS:

Fig. 2. The simulated wave forms of inverter operated in the proposed

control scheme (a) full load (b) half load.

Fig. 3. The simulated waveforms of BCM inverter when output reactive

power. (a)output current leads grid voltage 30o phase. (b)output current lags

grid voltage 30o phase.

Fig. 4. The detailed wave forms of hybrid BCM when output reactive power.

CONCLUSION:

This paper proposes a hybrid BCM for single-phase full bridge inverters to both overcome the current distortion at voltage zero-crossing region and have capability of reactive power generation. By combining the proposed hybrid BCM and unipolar BCM, the inverter will alleviate the current distortion without lowering efficiency. The hybrid modulation scheme is explained in details and the design considerations are also given for selecting control parameters and driving signal arrangement. To verify the proposed control scheme, a two-stage 300W microinverter prototype has been built. Simulation and experimental results verify the feasibility and effectiveness of the proposed control scheme.

 REFERENCES:

[1] Z. Zhang, X. F. He, and Y. F. Liu, “An optimal control method for  photovoltaic grid-tied-interleaved flyback microinverters to achieve high efficiency in wide load range,” IEEE Trans. Power Electron., vol. 28, no. 11,pp. 5074–5087, Nov. 2013.

[2] D. M. Scholten, N. Ertugrul, and W. L. Soong, “Micro-inverters in small scale PV systems: A review and future directions,” in Proc. Australas. Univ. Power Eng. Conf., Hobart, Tas., Australia, 2013, pp. 1–6.

[3] Z. Zhang, M. Chen, W. Chen, C. Jiang, and Z. Qian, “Analysis and implementation of phase synchronization control strategies for BCM  interleaved flyback microinverters,” IEEE Trans. Power Electron., vol. 29, no. 11, pp. 5921–5932, Nov. 2014.

[4] R. C. Beltrame, J. R. Zientarski, M. L. Martins, and J. R. Pinheiro, “Simplified zero-voltage-transition circuits applied to bidirectional poles: Concept and synthesis methodology,” IEEE Trans. Power Electron., vol. 26, no. 6, pp. 1765–1776, Jun. 2011.

[5] C. M. de Oliveira Stein, H. A. Grundling, H. Pinheiro, J. R. Pinheiro,  and H. L. Hey, “Zero-current and zero-voltage soft-transition commutation cell for PWM inverters,” IEEE Trans. Power Electron., vol. 19, no. 2, pp. 396–403, Mar. 2004.

A Highly Effective Fault-Ride-Through Strategy For a Wind Energy Conversion System with Doubly Fed Induction Generator

ABSTRACT:  

 This paper proposes an improved fault-ride through (FRT) system for a wind turbine with doubly fed induction generator (DFIG) that is based on the proper stator voltage control to address symmetrical as well as unsymmetrical and unbalanced grid voltage sags. This is accomplished by adopting a properly modified topology of the conventional wind energy con-version system (WECS) with DFIG that provides the ability to regulate the stator voltage through the system of the rotor power converters. Therefore, significant improvement of the FRT capability is attained, since any oscillations of both the stator and ro-tor currents that may be caused by the voltage dip can be considerably reduced and they can remain within predefined safety limits. The implementation of the new topology as well as the corresponding control system are cost effective, since no additional hardware is required, and it is accomplished by the reconfiguration of the conventional topology. Selective simulation and experimental results obtained by a high and low scale WECS with DFIG, respectively, are presented to validate the effective-ness of the proposed FRT control method and demonstrate the operational improvements.

KEYWORDS:

1.      Fault-ride through

2.      Doubly-fed induction generator

3.      Wind power generation

4.      Wind turbine

5.      Reliability

6.      Voltage control

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Comparison of the structure of a variable speed WECS with DFIG: (a) conventional and (b) improved FRT capability system.

EXPERIMENTAL RESULTS:

Fig. 2. Simulation results of the performance of the proposed FRT wind sys-tem with DFIG of 1.6-MW, when a symmetrical grid voltage disturbance from 100% to 20% and then 100% of the nominal value occurs, for a low wind speed of 4.5 m/s.

Fig. 3. Simulation results of the performance of the proposed FRT wind system with DFIG of 1.6-MW, when a symmetrical grid voltage disturbance from 100% to 20% and then 100% of the nominal value occurs, for a high wind speed of 9 m/s.

Fig. 4. Zoom of the simulation results of Fig. 5 (WECS with DFIG of 1.6- MW), at the time that the grid voltage disturbance from 100% to 20% of the nominal value occurs (wind speed 9 m/s).

CONCLUSION:

A highly effective FRT control system for a WECS with DFIG has been proposed in this paper. A new WECS topology has been adopted that gives the ability to control the stator of the DFIG. Specifically, by properly controlling the rotor side converter of the DFIG, the stator voltage can be kept constant at the nominal value and thus, a fault diagnosis system is not required. Therefore, the WECS can continue the operation without being affected by any symmetrical, unsymmetrical and unbalanced grid voltage disturbances, and thus, no transient current and voltages are caused. The implementation of the proposed FRT control system does increase the cost of WECS compared to the conventional system, since it is based on the proper modification by replacing expensive components of the conventional system with low cost components and vice-versa. The effectiveness and the high performance of the pro-posed FRT control scheme have been validated with several simulation results obtained by a high power WECS-DFIG of 1.6-MW and experimentally in a laboratory low power scaling emulated WECS with DFIG of 5.5-kW.

REFERENCES:

[1] E. Hau, Wind Turbines: Fundamentals, Technologies, Application, Economics, Springer-Verlag: 2013, 3rd Edition.

[2] A. El-Naggar and I. Erlich, ‘Fault current contribution analysis of dou-bly fed induction generator-based wind turbines’, IEEE Trans. Energy Conv., vol. 30, no. 3, pp. 874-882, Sept. 2015.

[3] D. Xiang, L. Ran, P.J. Tavner, and S. Yang, ‘Control of a doubly fed induction generator in a wind turbine during grid fault ride-through’, IEEE Trans. Energy Conv., vol. 21, no. 3, pp. 652-662, Sep. 2006.

[4] S. Seman, J. Niiranen, and A. Arkkio, ‘Ride-through analysis of doubly fed induction wind-power generator under unsymmetrical network dis-turbance’, IEEE Trans. Power Syst., vol. 21, no. 4, pp. 1782–1789, Nov. 2006.

[5] J. Morren and S.W.H. de Haan, ‘Ridethrough of wind turbines with doubly-fed induction generator during a voltage dip’, IEEE Trans. En-

ergy Conv., vol. 20, no. 2, pp. 435-441, June 2005.

A 500-W Wireless Charging System with Lightweight Pick-Up for Unmanned Aerial Vehicles

ABSTRACT:  

This letter develops a wireless charging system based on a novel orthogonal magnetic structure and primary-side power control to simplify the structure and reduce the weight of on-board pick-up for recharging the unmanned aerial vehicles (UAVs). The novel magnetic structure has a polarized transmitter with a flat U-type core and a perpendicular air-cored receiving coil, guaranteeing the magnetic flux operation space away from UAV body by coil structure itself and also reducing the weight of magnetic receiver. The power flow to the battery is controlled by the primary-side based on charging current and voltage feedback by pick-up. Simulations based on ANSYS Maxwell and experiments are carried out to validate the proposal. The weight of magnetic receiver is 130g. And the system can deliver 500W with a DC-to-Battery efficiency of 90.8%, meanwhile 10A constant current/50V constant voltage charging for 12S lithium-ion battery is achieved by the closed-loop system.

KEYWORDS:

1.      Unmanned aerial vehicles (UAVs)

2.      Wireless charging

3.      Magnetic structure

4.      Primary-side control

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. (a) Wireless charging system structure. (b) The gate drive signals and

output voltage of the inverter. (c) Equivalent circuit model.

 EXPERIMENTAL RESULTS:

Fig. 2. Power transfer ability test. (a) Measured waveforms of system, (b) Input and output power test.

Fig. 3. Closed-loop system operation test. (a) Change the equivalent load  resistance RB from 3 to 33 . (b) Change the equivalent load resistance RB from 3 to 8

CONCLUSION:

A novel orthogonal magnetic structure, which has a lightweight magnetic receiver, for UAVs, has been proposed and verified throughout this letter. The air-cored receiving coil is placed vertically in the middle of a polarized transmitter, possessing a large magnetic flux captured surface for enough power transfer and also constraining magnetic field operation space away from UAV’s body by coil-structure itself. The primary-side power control method is adopted to regulate the power flow to battery, which further reduces the weight of on-board pick-up circuit. A prototype was built for experiment.  It is shown that the system can successfully deliver 500W to UAV with a DC-to-Battery efficiency of 90.8%. The simulation and experimental results confirm the effectiveness of the proposal.

REFERENCES:

[1] T. Kan, R. Mai, P. P. Mercier and C. C. Mi, “Design and Analysis of a Three-Phase Wireless Charging System for Lightweight Autonomous Underwater Vehicles,” IEEE Trans. Power Electron., vol. 33, no. 8, pp. 6622-6632, Aug. 2018.

[2] M. Budhia, J. T. Boys, G. A. Covic and C. Huang, “Development of a  Single-Sided Flux Magnetic Coupler for Electric Vehicle IPT Charging Systems,” IEEE Trans. Ind. Electron., vol. 60, no. 1, pp. 318-328, Jan. 2013.

[3] P. Si, A. P. Hu, S. Malpas and D. Budgett, “A Frequency Control Method for Regulating Wireless Power to Implantable Devices,” IEEE Trans.  Biomed. Circuits Syst., vol. 2, no. 1, pp. 22-29, Mar. 2008.

[4] A. B. Junaid, Y. Lee, Y. Kim, “Design and implementation of  autonomous wireless charging station for rotary-wing UAVs,” Aerospace Science and Technology, vol. 54, pp. 253-266, Apr. 2016.

[5] S. Kumar, Jayprakash, G. K. Mandavi, “Wireless Power Transfer for Unmanned Aerial Vehicle (UAV) Charging,” International Research Journal of Engineering and Technology, vol. 4, no. 8, pp. 1939-1942, Aug. 2017.

Power Quality Analysis and Enhancement of Grid Connected Solar Energy System

ABSTRACT:  

In recent years, renewable energy resources are utilized to meet the growing energy demand. The  integration of renewable energy resources with the grid incorporates power electronic converters for conversion of energy. These power electronic converters introduce power quality issues such as a harmonics, voltage regulation etc. Hence, to improve the power quality issues, this work proposes a new control strategy for a grid interconnected solar system. In this proposed work, a maximum power point tracking (MPPT) scheme has been used to obtain maximum power from the solar system and DC/DC converter is implemented to maintain a constant DC voltage. An active filtering method is utilized to improve the power quality of the grid connected solar system. The proposed system is validated through dynamic simulation using MATLAB/Simulink Power system toolbox and results are delivered to validate the effectiveness of the work.

KEYWORDS:

1.      Power Quality

2.      Active Power Filter

3.      Fuzzy Controller

4.      Harmonics Compensation

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Figure 1. Configurations of a photovoltaic interactive shunt active power filter system.

EXPERIMENTAL RESULTS:

Figure 2. Source current for nonlinear load before compensation.

Figure 3. Voltage and current of source after compensation

Figure 4. Voltage and current of source after compensation.

 CONCLUSION:

This work has presented a novel control of an existing grid interfacing inverter to improve the quality of power at PCC. It has been proved that the grid-interfacing inverter can be effectively utilized for power conditioning without affecting its normal operation of real power transfer. This approach eliminates the need for additional power conditioning equipment to improve the quality of power. Extensive MATLAB/Simulink simulation results have validated the proposed approach and have shown that the grid-interfacing inverter can be utilized as a multi-function device.

REFERENCES:

[1] Akagi, H. (2006) Modern Active Filters and Traditional Passive Filters. Bulletin of the Polish Academy of Sciences Technical Sciences, 54, 255-269.

[2] Kazem, H.A. (2013) Harmonic Mitigation Techniques Applied to Power Distribution Networks. Advances in Power Electronics. http://dx.doi.org/10.1155/2013/591680

[3] Ravindra, S., Veera Reddy, V.C., Sivanagaraju, S. and Gireesh Kumar, D. (2012) Design of Shunt Active Power Filter to Eliminate the Harmonic Currents and to Compensate the Reactive Power under Distorted and or Imbalanced Source Voltages in Steady State. International Journal of Engineering Trends and Technology, 3, 1-6.

[4] Kumar, A. and Singh, J. (2013 Harmonic Mitigation and Power Quality Improvement Using Shunt Active Power Filter. International Journal of Electrical, Electronics and Mechanical Control, 2, 13 p.

[5] Gligor, A. (2009) Design and Simulation of a Shunt Active Filter in Application for Control of Harmonic Levels. Acta Universitatis Sapientiae, Electrical and Mechanical Engineering, 53-63.