Irradiance-adaptive PV Module Integrated Converter for High Efficiency and Power Quality in Standalone and DC Microgrid Applications

ABSTRACT:

The strive for efficient and cost-effective photovoltaic systems motivated the power electronic design developed here. The work resulted in a DC-DC converter for module integration and distributed maximum power point tracking (MPPT) with a novel adaptive control scheme. The latter is essential for the combined features of high energy efficiency and high power quality over a wide range of operating conditions. The switching frequency is optimally modulated as a function of solar irradiance for power conversion efficiency maximization. With the rise of irradiance, the frequency is reduced to reach the conversion efficiency target. A search algorithm is developed to determine the optimal switching frequency step. Reducing the switching frequency may, however, compromise MPPT efficiency. Furthermore, it leads to increased ripple content. Therefore, to achieve a uniform high power quality at all conditions, interleaved converter cells are adaptively activated. The overall cost is kept low by selecting components that allow for implementing the functions at low cost. Simulation results show the high value of the module integrated converter for DC standalone and microgrid applications. A 400 W prototype was implemented at 0.14 Euro/W. Testing showed efficiencies above 95% taking into account all losses from power conversion, MPPT, and measurement and control circuitry.
KEYWORDS:

1.      Boost converter

2.      Distributed maximum power point tracking (DMPPT)

3.      Microgrid

4.      Module integrated converter (MIC)

5.      Photovoltaics (PV)

6.      Power optimizer

7.      Power quality      

8.      Solar irradiance

9.      Switching frequency modulation (SFM)

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

A novel PV module integrated converter (MIC) suitable for boosting voltages for DC standalone and DC microgrid applications was designed, implemented, and tested. The proposed switching frequency modulation (SFM) selects an irradiance adapted switching frequency that is always high enough to avoid operation in discontinuous conduction mode. At a high irradiance, the switching frequency modulation sets a lower value for the frequency, guided by the strive for high efficiency through low switching losses. The proposed automated procedure has shown to be effective in searching for the optimal number and values of switching frequencies. Furthermore, an interleaved boost cell is activated at high irradiance to retain a high level of power quality. Hysteresis functions support the transitions between different discrete switching frequencies as the irradiance changes. The adaptive MIC control scheme is complemented by an MPPT designed for fast tracking. Thus, by combining the SFM with the adaptive usage of the boost converter interleaved cells and a fast MPPT, targets of efficiency and power quality are reached. The efficiency for the entire MIC including all power conversion and control functions was measured at around 95% or higher for irradiance levels ranging from 0.3 kW=m2 to 1.0 kW=m2. The voltage ripple remained below 0.7% during testing. The prototype was rated at 400 W to make the design well suited for integrating photovoltaics in DC microgrids or solar homes. Distributed maximum power point tracking is implicitly supported through the module integration. The prototype’s cost of parts amounted to 0.14 Euro/W when ordering parts individually in the year 2015. Scale effects will allow for further cost reductions. Together with the convincing technical performance, the cost effectiveness makes this MIC design a compelling candidate for renewable solutions of DC microgrids, DC buses, and solar home applications.

REFERENCES:

 [1] REN21. 2016, “Renewables 2016 Global Status Report,” Renewable Energy Policy Network for the 21st Century, Paris, Tech. Rep., 2016.

[2] E. Romero-Cadaval, G. Spagnuolo, L. G. Franquelo, C.-Andr´es Ramos- Paja, T. Suntio, and W.-Michael Xiao, “Grid-Connected Photovoltaic Generation Plants: Components and Operation,” IEEE Ind. Electron. Mag., vol. 7, no. 3, pp. 6–20, Sep. 2013.

[3] M. Das and V. Agarwal, “Design and Analysis of a High-Efficiency DCDC Converter With Soft Switching Capability for Renewable Energy Applications Requiring High Voltage Gain,” IEEE Trans. Ind. Electron., vol. 63, no. 5, pp. 2936–2944, May 2016.

[4] F. Wang, F. Zhuo, F. C. Lee, T. Zhu, and H. Yi, “Analysis of Existence- Judging Criteria for Optimal Power Regions in DMPPT PV Systems,” IEEE Trans. Energy Convers., vol. 31, no. 4, pp. 1433–1441, Dec. 2016.

[5] O. Khan, W. Xiao, and M. S. E. Moursi, “A New PV System Configuration Based on Submodule Integrated Converters,” IEEE Trans. Power Electron., vol. 32, no. 5, pp. 3278–3284, May 2017.

Intelligent Power Sharing of DC Isolated Microgrid Based on Fuzzy Sliding Mode Droop Control

ABSTRACT:

Linear droop control can realize power sharing among generators in DC microgrid without relying on critical communication links. However, the droop relationship between output power and voltage magnitude of renewable power generate system is nonlinear with uncertainties and disturbances from renewable sources and loads in practical DC microgrid. A novel droop scheme is proposed for an isolated DC microgrid to solve the nonlinear problem. The control strategy is proposed by using the Takagi-Sugeno (T-S) fuzzy model and sliding mode algorithm. The nonlinear droop characteristics can be represented by T-S model through taking advantage of locally measured output variables. The sliding mode droop controller is designed for compensating the uncertainties and disturbances to derive accurate power sharing based on T-S fuzzy model. The proposed scheme is proved to be effective under variable operating conditions through PSIM/Matlab simulation.

KEYWORDS

1.      Droop control

2.      Autonomous power sharing

3.      DC microgrid

4.      T-S fuzzy model

5.      Sliding mode control (SMC)

SOFTWARE: MATLAB/SIMULINK

 CONCLUSION:

The novel droop control strategy is proposed for accurate power sharing considering system parameters uncertainties and load disturbances. The technique is designed by using sliding mode controller based on T-S fuzzy model of the DC MG. The overall system stability can be assured. The conclusion is drawn that load changes of the DC MG can be regulated more adaptively. Meanwhile, the proportional load power sharing can be accurately achieved without any communication. The proposed method is verified in PSIM/Matlab simulation. Future extensions of the method can include nonlinear sliding mode droop control of multiple batteries or in AC/DC hybrid MG.

REFERENCES:

[1]. R. Lasseter, “Microgrids” in Proc. IEEE Power Eng. Soc. Winter Meet.,2002, pp. 305–308.

[2]. S. K. Mazumder, M. Tahir and K. Acharya, “Master – slave current-sharing control of a parallel DC-DC converter system over an RF communication interface”, IEEE Trans. Ind. Electron., vol. 55, no. 1, pp. 59-66, Jan. 2008.

[3]. M. N. Iyer, and M. C. Chandorkar, “A generalized computational method to determine stability of a multi-inverter microgrid,”IEEE Trans. Power. Electron., vol. 25, no. 9, pp. 2420-2432, Sept. 2010.

[4]. R. Majumder, B. Chaudhuri, A. Ghosh, and F. Zare, “Improvement of stability and load sharing in an autonomous microgrid using supplementary droop control loop,” IEEE Trans. Power Syst., vol. 25, no. 2, pp. 796-808, May. 2010.

[5]. P. C. Loh, D. Li, Y. K. Chai and F. Blaabjerg, “Autonomous operation of hybrid microgrid with AC and DC subgrids”, IEEE Trans. Power Electron., vol. 28, no. 5, pp. 2214-2223, May. 2013.

Improved secondary control for optimal total harmonic distortion compensation of parallel connected DGs in islanded microgrids

ABSTRACT:

This study proposes a two-layer hierarchical control to actualize optimal total harmonic distortion (THD) compensation in different buses of parallel-connected inverters in islanded microgrids which had not been studied so far. The proposed secondary layer is used to realize THD compensation of sensitive load bus (SLB) and make distributed generators (DGs) distribute the compensating efforts between them according to their rated capacity. It is noteworthy that improving THD at the SLB can lead to an increase in THD at local buses and/or DG terminals. Although the THD limitations of these buses are not as strict as the THD limitation of SLB, it is necessary to control them within their allowed range. This important problem is not well studied in the literature. A novel complementary part is designed and added to the secondary control to tune the compensation portion of each DG while the THD limitations in DG terminals and local buses are considered. The proposed method actualizes a multi-level voltage quality control in multi-bus islanded microgrids with parallel DGs through a simple yet effective solution. Furthermore, considering the DGs peak current limitation is added to the controller and a method for calculating this peak value is proposed.

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

A new two-level control hierarchy structure ,which had not been studied before, is proposed in this study to actualise the optimal compensation of voltage harmonics in islanded microgrids without any additional equipment installation. The primary layer controls the voltage and frequency and also the FPS power sharing. The secondary level controls the THD of SLB. Improving THD at the SLB can lead to an increase in THD at local buses and/or DG terminals. Although the THD limitations of these buses are not as strict as the THD limitation of SLB, it is necessary to control them within their allowed range. A complementary part is designed and added to the secondary control in order to tune the compensation efforts of each DG unit while considering the THD limitations in DG terminals and local buses. Furthermore, considering the DGs peak current limitation is added to the controller and a method for calculating this peak value is proposed. The proposed control structure realises a multi-power-quality level control for islanded microgrids with multi-bus and parallel DGs through a simple yet effective solution.

The design of the proposed control is very simple and it is not needed to have the microgrid parameters and structure. Therefore, it would be more functional and also the plug & play ability of DGs would be reserved as well. An example system is modeled and simulated. Simulation and comparison results are presented to demonstrate its effectiveness.

REFERENCES:

[1] Khodabakhshian, A., Andishgar, M.H.: ‘Simultaneous placement and sizing of DGs and shunt capacitors in distribution systems by using IMDE algorithm’, Int. J. Electr. Power Energy Syst., 2016, 82, pp. 599–607

[2] Andishgar, M.H., Fereidunian, A., Lesani, H.: ‘Healer reinforcement for smart grid using discrete event models of FLISR in distribution automation’, J. Intell. Fuzzy Syst., 2016, 30, pp. 2939–2951

[3] Micallef, A., Apap, M., Spiteri-Staines, C., et al.: ‘Reactive power sharing and voltage harmonic distortion compensation of droop controlled single phase islanded microgrids’, IEEE Trans. Smart Grid, 2014, 5, (3), pp. 1149– 1158

[4] Zeng, Z., Zhao, R., Yang, H.: ‘Coordinated control of multi-functional grid tied inverters using conductance and susceptance limitation’, IET Power Electron., 2014, 7, (7), pp. 1821–1831

[5] George, S., Agarwal, V.: ‘A DSP based optimal algorithm for shunt active filter under nonsinusoidal supply and unbalanced load conditions’, IEEE Trans. Power Electron., 2007, 22, (2), pp. 593–601

Improved Power Quality Switched Inductor Cuk Converter for Battery Charging Application

ABSTRACT:

Most of two-stage converters for electric bike battery charging comprise of boost converter for PFC followed by dc-dc converter with universal-input voltage. These two-stage conversions suffer from poor efficiency and increased component count. In this paper, a single- stage switched inductor Cuk converter based power factor correction converter is proposed which offers high step-down gain, low current stress, high efficiency and reduced component counts. The operational analysis and design equations for various components of proposed converter are carried out in continuous current mode (CCM). This paper presents mathematical modelling, analysis, simulation and experimentation on proposed converter rated for 500 W, 48V/10.4A. The performance investigation of proposed converter with respect to power quality indices like voltage THD, current THD and total power factor are carried out with various types of load such as resistive load and battery load in both constant voltage (CV) and constant current (CC). Furthermore, the dynamic performance of proposed converter with battery charging is investigated in constant voltage mode and constant current mode with respect to wide change of supply variations.

KEYWORDS:

1.      Diode Bridge Rectifier

2.      DC bus

3.      Power Factor Correction

4.      Harmonics

5.      Cuk converter

6.      Battery charging

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

The switched inductor Cuk converter based improved power quality AC-DC converter is proposed for battery charging application. The design, simulation and hardware implementation of proposed converter are carried out. The simulation results are obtained under various loading conditions and results demonstrate that the proposed converter is able to provide regulated output voltage irrespective of supply and load variations. The power quality indices like THD and PF at ac side are evaluated to assess the power quality performance of the converter. The converter is evaluated both under steady state and transient conditions. In battery charging application, the power quality indices are also evaluated both in CV and CC mode of battery charging and recorded. The simulation is validated with hardware implementation of same specifications. The experimental results showed good steady state and transient performance under load and source voltage disturbances. Therefore, it is well suited for various applications requiring power at high current at reduced output voltage such as battery charging for electric vehicles / EHV.

REFERENCES:

[1] Sheldon S. Williamson, “Energy Management strategies for Electric and Plug in Hybrid electric vehicles”, Springer, New York, USA, 2013

[2] Bruno Scrosati, Jürgen Garche and Werner Tillmetz, “Advances in Battery Technologies for Electric Vehicles,”Elsevier, UK, 2015

[3] R. Liu, L.Dow and E. Liu, “A survey of PEV impacts on electric utilities” in Proc. IEEE PES Innovative Smart Grid Technologies, pp.1- 8, 2011.

[4] G. A. Putrus, P.Suwanapingkarl , D.Johnston, E.C. Bentley and M. Narayana, “Impact of electric vehicles on power distribution networks”, in Proc. IEEE Vehicle Power and Propulsion Conference,, pp. 827-831, 2009.

[5] Suresh Mikkili, Anupkumar panda “Power Quality issues, current harmonics”, CRC Press, Boca Raton, USA, 2016.

 

Implementation of Solar PV- Battery and Diesel Generator Based Electric Vehicle Charging Station

ABSTRACT:

 In this paper, a solar PV (Photovoltaic) array, a battery energy storage (BES), a diesel generator (DG) set and grid based EV charging station (CS) is utilized to provide the incessant charging in islanded, grid connected and DG set connected modes. The charging station is primarily designed to use the solar photovoltaic PV array and a BES to charge the electric vehicle (EV) battery. However, in case of exhausted storage battery and unavailable solar PV array generation, the charging station intelligently takes power from the grid or DG (Diesel Generator) set. However, the power from DG set is drawn in a manner that, it always operates at 80-85% loading to achieve maximum fuel efficiency under all loading conditions. Moreover, in coordination with the storage battery, the charging station regulates the generator voltage and frequency without a mechanical speed governor. It also ensures that the power drawn from the grid or the DG set is at unity power factor (UPF) even at nonlinear loading. Moreover, the PCC (Point of Common Coupling) voltage is synchronized to the grid/ generator voltage to obtain the ceaseless charging. The charging station also performs the vehicle to grid active/reactive power transfer, vehicle to home and vehicle to vehicle power transfer for increasing the operational efficiency of the charging station. The operation of the charging station is experimentally validated using the prototype developed in the laboratory.

KEYWORDS:

1.      EV Charging Station

2.      Solar PV Generation

3.      Power Quality

4.      DG Set

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

An implementation of PV array, storage battery, grid and DG set based charging station has been realized for EV charging. The presented results have verified the multimode operating capability (islanded operation, grid connected and DG set connected) of the CS using only one VSC. Test results have also verified the satisfactory operation of charging station under different steady state conditions and various dynamics conditions caused by the change in the solar irradiance level, change in the EV charging current and change in the loading. The operation of charging station as a standalone generator with good quality of the voltage, has been verified by the presented results. Whereas, test results in DG set or grid connected mode, have verified the capability of ANC based control algorithm to maintain the power exchange with the grid at UPF or the optimum loading of the DG set. Moreover, the islanded operation, grid connected and DG set connected operations along with the automatic mode switching have increased the probability of MPP operation of the PV array and optimum loading of DG set along with increasing the charging reliability. The IEEE compliance operation of the charging station with voltage and current THD always less than 5% verifies the effectiveness of the control. Form the above mentioned point, it can be concluded that this charging station with the presented control have the capability to utilize the various energy sources very efficiently and provides the constant and cost effective charging to the EVs.

REFERENCES:

[1] International Energy Agency-Global EV Outlook 2018- Towards cross-modal electrification. [Online] Available: https://webstore.iea.org /download/direct/1045?fileName=Global_EV_Outlook_2018.pdf

[2] International Energy Agency- Renewables 2O18 - Analysis and Forecasts to 2O23 [Online]. Available: https://webstore.iea.org/ download/summary/2312?fileName=English-Renewables-2018ES.pdf.

[3] J. Ugirumurera and Z. J. Haas, “Optimal Capacity Sizing for Completely Green Charging Systems for Electric Vehicles,” IEEE Trans. Transportat. Electrificat.vol. 3, no. 3, pp. 565-577, Sept. 2017.

[4] G. R. Chandra Mouli, J. Schijffelen, M. van den Heuvel, M. Kardolus and P. Bauer, “A 10 kW Solar-Powered Bidirectional EV Charger Compatible With Chademo and COMBO,” IEEE Trans, Power Electron., vol. 34, no. 2, pp. 1082-1098, Feb. 2019.

[5] V. Monteiro, J. G. Pinto and J. L. Afonso, “Experimental Validation of a Three-Port Integrated Topology to Interface Electric Vehicles and Renewables With the Electrical Grid,” IEEE Trans. Ind. Informat., vol. 14, no. 6, pp. 2364-2374, June 2018

 

Implementation of Recurrent Neurocontrol Algorithm for Two Stage Solar Energy Conversion System

ABSTRACT:

A grid interactive photovoltaic generation system is developed in this work. A boost converter forms the initial stage and is used to obtain the maximum power from the PV array. It is controlled using an incremental conductance (INC) based algorithm. The second stage is a voltage source converter (VSC), which interfaces the PV system to the grid. A recurrent neurocontrol based algorithm is used to generate the switching pulses for the VSC. The solar energy conversion system (SECS) has the capabilities of harmonics reduction, reactive power compensation, unity power factor operation and grid currents balancing. The proposed system is validated under various operating conditions using simulation as well as experimental results.

KEYWORDS:

1.      Recurrent neurocontroller

2.      Solar Energy

3.      Conversion System

4.      Power Quality

5.      Incremental Conductance Based MPPT

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

The recurrent neuro control based control algorithm has been successfully implemented for a two stage solar energy conversion system. The first stage involves extracting the maximum available power from the PV generation system using a boost converter operated by INC based control. The performance of the recurrent neurocontrol based control algorithm is validated under various operating conditions, using simulation as well as experimental results. The SECS has provided reactive power compensation and exhibited fast response under dynamic conditions of sudden load variation and sudden insolation variation, and maintains the grid current THD within IEEE 519 standard.

REFERENCES:

[1] S. Bhattacharjee: Solar Electricity Generation, Narosa Publishing House, New Delhi, 2015.

[2] H. Tyagi, A. K. Agarwal, P.R. Chakraborty and S. Powar: Applications of Solar Energy, Springer Singapore, 2018.

[3] S. Kumar and B. Singh, “Seamless transition of three phase microgrid with load compensation capabilities,” IEEE Industry Applications Society Annual Meeting, Cincinnati, OH, pp. 1-9, 2017.

[4] C. C. Hua and Y. M. Chen, “Modified perturb and observe MPPT with zero oscillation in steady-state for PV systems under partial shaded conditions,” IEEE Conference on Energy Conversion (CENCON), Kuala Lumpur, Malaysia, pp. 5-9, 2017.

[5] Z. Xuesong, S. Daichun, M. Youjie and C. Deshu, “The simulation and design for MPPT of PV system Based on Incremental Conductance Method,” WASE International Conference on Information Engineering, Beidaihe, Hebei, pp. 314-317, 2010.

 

High Step-Up Quasi-Z Source DC-DC Converter

ABSTRACT:

In this paper, a high step-up Quasi-Z Source (QZS) DC-DC converter is proposed. This converter uses a hybrid switched-capacitors switched-inductor method in order to achieve high voltage gains. The proposed converter have resolved the voltage gain limitation of the basic QZS DC-DC converter while keeping its main advantages such as continuous input current and low voltage stress on capacitors. Compared to the basic converter, the duty cycle is not limited, and the voltage stress on the diodes and switch isn’t increased. In addition to these features, the proposed converter has a flexible structure, and extra stages could be added to it in order to achieve even higher voltage gains without increasing the voltage stress on devices or limiting the duty cycle. The operation principle of the converter and related relationships and waveforms are presented in the paper. Also, a comprehensive comparison between the proposed and other QZS based DC-DC converters is provided which confirms the superiority of the proposed converter. Simulations are done in PSCAD/EMTDC in order to investigate the MPPT capability of the converter. In addition, the valid performance and practicality of the converter are studied through the results obtained from the laboratory built prototype.

KEYWORDS:

1.      DC-DC converter

2.      High step-up

3.      Impedance network

4.      Quasi-Z source

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

An improved QZS based DC-DC converter with high step up capability was proposed. In addition to the QZS network, the proposed converter has used a combined method of switching-capacitors and switching-inductor. It could resolve the voltage gain limitation of the basic converter while keeping its main advantages such as continuous input current and low voltage stress on capacitors. The maximum duty cycle and voltage stress on the switch and diodes are remained unchanged. Therefore, they will not affect the voltage gain of the converter in practice. Extra stages can also be added to the converter to achieve even higher voltage gains. It was seen after increasing the stages.

Circuit operation principles, analysis, and necessary relationships were presented. A comparison between the proposed and other QZS based converters was also provided. Considering the results, the superiority of the proposed converter to other structures was confirmed. The simulations were done in PSCAD/EMTDC using a photovoltaic panel input. The results have confirmed the MPPT capability of the converter.

A 150W prototype of the proposed converter was also synthesized in the laboratory. The experimental results have confirmed the theoretical analysis, and, the practicality of the converter and its proper efficiency have been assured. Considering the approved advantages of the converter such as continuous input current, high voltage gain, low voltage stress on elements, and MPPT capability, it could be a suitable choice in a variety of industrial applications such as photovoltaic systems, fuel cells, PMSG based wind turbines, and, power systems based on battery banks and super capacitors. Also, in applications such as uninterruptable power supply (UPS), and LED lamps, low and varying voltage of the battery and fuel cell should be converted to the standard DC bus voltage (380-400V), which the proposed converter can be a suitable choice for them. The point which also should be mentioned is that, considering the non-isolated structure of the proposed converter, in applications which an isolation between the input and output side is required, an isolating transformer could be used in series with the converter.

REFERENCES:

[1] H. M. Maheri, E. Babaei, M. Sabahi, and S. H. Hosseini, “High step-up DC-DC converter with minimum output voltage ripple,” IEEE Trans. Ind. Electron., vol. 64, no. 5, pp. 3568-3575, May. 2017.

[2] D. Sha, Y. Xu, J. Zhang, Y. Yan, “A current-fed hybrid dual active bridge DC-DC converter for fuel cell power conditioning system with reduced input current ripple,” IEEE Trans. Ind. Electron., in press.

[3] B. Novakovic, A. Nasiri, “Modular multilevel converter for wind energy storage applications,” IEEE Trans. Ind. Electron., in press.

[4] Y. P. Siwakoti, F. Blaabjerg, P. C. Loh, “High step-up trans-inverse (TX-1) DC-DC converter for distributed generation system,” IEEE Trans. Ind. Electron., vol. 63, no. 7, pp. 4278-4291, July. 2016.

[5] Y. Hu, R. Zheng, W. Cao, J. Zhang, S. J. Finney, “Design of a modular, high step-up ratio DC-DC converter for HVDC applications integrating offshore wind power,” IEEE Trans. Ind. Electron., vol. 63, no. 4, pp. 2190-2202, April, 2016.