Grid-Connected PV-Wind-Battery-Based multi input transformer coupled bidirectional dc-dc converter for household applications

 ABSTRACT:

In this paper, a control strategy for power flow management of a grid-connected hybrid photovoltaic (PV)–wind battery- based system with an efficient multi-input transformer coupled bidirectional dc–dc converter is presented. The proposed system aims to satisfy the load demand, manage the power flow from different sources, inject the surplus power into the grid, and charge the battery from the grid as and when required. A transformer-coupled boost half-bridge converter is used to harness power from wind, while a bidirectional buck– boost converter is used to harness power from PV along with battery charging/discharging control. A single-phase full-bridge bidirectional converter is used for feeding ac loads and interaction with the grid. The proposed converter architecture has reduced number of power conversion stages with less component count and reduced losses compared with existing grid-connected hybrid systems. This improves the efficiency and the reliability of the system. Simulation results obtained using MATLAB/Simulink show the performance of the proposed control strategy for power flow management under various modes of operation. The effectiveness of the topology and the efficacy of the proposed control strategy are validated through detailed experimental studies to demonstrate the capability of the system operation in different modes.

KEYWORDS:

1.      Battery charge control

2.      Bidirectional buck–boost converter

3.      Full-bridge bidirectional converter

4.      Hybrid system

5.      Maximum power-point tracking

6.      Solar photovoltaic (PV)

7.      Transformer-coupled boost dual-half-bridge bidirectional converter

8.      Wind energy

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Grid-connected hybrid PV–wind-battery-based system for household

applications.

CIRCUIT DIAGRAM

                                               

Fig 2. Proposed converter configuration.

EXPECTED SIMULATION RESULTS:

 

Fig. 3. Steady-state operation in the MPPT mode.

 

Fig. 4. Response of the system for changes in an insolation level of source-1

(PV source) during operation in the MPPT mode.

Fig. 5. Response of the system for changes in wind speed level of source-2

(wind source) during operation in the MPPT mode.

Fig. 6. Response of the system in the absence of source-1 (PV source),

while source-2 continues to operate at MPPT.

Fig. 7. Response of the system in the absence of source-2 (wind source),

while source-1 continues to operate at MPPT.

Fig. 8. Response of the system in the absence of both the sources and

charging the battery from the grid.

CONCLUSION:

A grid-connected hybrid PV–wind-battery-based power evacuation scheme for household application is proposed. The proposed hybrid system provides an elegant integration of PV and wind source to extract maximum energy from the two sources. It is realized by a novel multi-input transformer coupled bidirectional dc–dc converter followed by a conventional full-bridge inverter. A versatile control strategy which achieves a better utilization of PV, wind power, battery capacities without effecting life of battery, and power flow management in a grid-connected hybrid PV–wind-battery-based system feeding ac loads is presented. Detailed simulation studies are carried out to ascertain the viability of the scheme. The experimental results obtained are in close agreement with simulations and are supportive in demonstrating the capability of the system to operate either in grid feeding or in stand-alone modes. The proposed configuration is capable of supplying uninterruptible power to ac loads, and ensures the evacuation of surplus PV and wind power into the grid.

 REFERENCES:

[1] F. Valenciaga and P. F. Puleston, “Supervisor control for a stand-alone hybrid generation system using wind and photovoltaic energy,” IEEE Trans. Energy Convers., vol. 20, no. 2, pp. 398–405, Jun. 2005.

[2] C. Liu, K. T. Chau, and X. Zhang, “An efficient wind–photovoltaic hybrid generation system using doubly excited permanent-magnet brushless machine,” IEEE Trans. Ind. Electron., vol. 57, no. 3, pp. 831–839, Mar. 2010.

[3] W. Qi, J. Liu, X. Chen, and P. D. Christofides, “Supervisory predictive control of standalone wind/solar energy generation systems,” IEEE Trans. Control Syst. Technol., vol. 19, no. 1, pp. 199–207, Jan. 2011.

[4] F. Giraud and Z. M. Salameh, “Steady-state performance of a grid connected rooftop hybrid wind-photovoltaic power system with battery storage,” IEEE Trans. Energy Convers., vol. 16, no. 1, pp. 1–7, Mar. 2001.

[5] S.-K. Kim, J.-H. Jeon, C.-H. Cho, J.-B. Ahn, and S.-H. Kwon, “Dynamic modeling and control of a grid-connected hybrid generation system with versatile power transfer,” IEEE Trans. Ind. Electron., vol. 55, no. 4, pp. 1677–1688, Apr. 2008.

Dual-Bridge LLC Resonant Converter With fixed frequency PWM control for wide input applications

ABSTRACT:

This paper proposes a dual-bridge (DB) LLC resonant converter for wide input applications. The topology is an integration of a half-bridge (HB) LLC circuit and a full-bridge (FB) LLC circuit. The fixed-frequency pulse width-modulated (PWM) control is employed and a range of twice the minimum input voltage can be covered. Compared with the traditional pulse frequency modulation (PFM) controlled HB/FB LLC resonant converter, the voltage gain range is independent of the quality factor, and the magnetizing inductor has little influence on the voltage gain, which can simplify the parameter selection process and benefit the design of magnetic components as well. Over the full load range, zero-voltage switching (ZVS) and zero-current switching (ZCS) can be achieved for primary switches and secondary rectifier diodes, respectively. Detailed analysis on the modulation schedule and operating principle of the proposed converter is presented along with the converter performance. Finally, all theoretical analysis and characteristics are verified by experimental results from a 120-V to 240-V input 24 V/20 A output converter prototype.

KEYWORDS:

1.      Dual bridge (DB)

2.      Fixed frequency

3.      LLC

4.      Wide input voltage range

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 Fig. 1. (a) Proposed DB LLC resonant converter. (b) Equivalent circuit when the proposed DB LLC resonant converter operates in the HB mode. (c) Equivalent circuit when the proposed DB LLC resonant converter operates in the FB mode.

 EXPECTED SIMULATION RESULTS:

 

Fig. 2. Measured steady-state voltage and current waveforms at full load with different input voltages. (a) V_in = 120 V; (b) V_in = 130 V; (c) V_in = 190 V; (d) V_in = 240 V.

Fig. 3. ZVS waveforms of switches Q₁ and Q₂ with the converter operating at (a) full load with 120 V input, (b) full load with 240 V input, (c) 10% load with 120 V input, and (d) 10% load with 240 V input.

 

Fig. 4. Experimental results of the DB LLC resonant converter with closed loop control in response to ramp changes in the input voltage V_in. (a) Ramp increase of the input voltage V_in from 130 to 190 V. (b) Ramp decrease of the input voltage V_in from 190 to 130 V.

Fig. 5. Experimental results of the DB LLC resonant converter with closed loop

control in response to step changes in the load. (a) Step increase of load

from light load to full load. (b) Step increase of load from full load to 10% load.

Fig. 6. Measured power stage efficiency of the converter prototype for

different input voltages.

CONCLUSION:

A fixed-frequency-controlled DB LLC resonant converter with a wide input range has been proposed in this paper. In the proposed DBLLC resonant converter, two operating modes (HB and FB modes) are identified and utilized to regulate the output voltage within a wide input voltage range. The modulation strategy, operating principle and characteristics are investigated in depth. Compared with a conventional PFM-controlled LLC converter, the proposed DB LLC resonant converter adopts the fixed-frequency PWM control. The voltage gain range is independent of the quality factor Q and the magnetizing inductance has little impact on the dc voltage gain characteristics. Thus, the process of parameter design can be simplified and also a larger inductor ratio can be chosen to reduce the conduction loss. The structure and control strategy of the DB LLC resonant converter are simpler compared with conventional fixed-frequency TL LLC resonant converters. The performance of the proposed DB LLC resonant converter is experimentally verified on a 120–240 V input 24 V/20 A output converter prototype. All primary-side switches operate with ZVS and secondary-side diodes turn off with ZCS within wide input voltage and full-load ranges. Also, good dynamic performance with respect to input variations and load changes can be achieved under the closed-loop control. Therefore, the DB LLC resonant converter is a good candidate for wide input voltage applications.

REFERENCES:

[1] M.M. Jovanovi´c and B. T. Irving, “On-the-fly topology-morphing control efficiency optimization method for LLC resonant converters operating in wide input- and/or output-voltage range,” IEEE Trans. Power Electron., vol. 31, no. 3, pp. 2596–2608, Mar. 2016.

[2] J. Deng, C. C. Mi, R. Ma, and S. Li, “Design of LLC resonant converters based on operation-mode analysis for level two PHEV battery chargers,” IEEE Trans. Mechatronics, vol. 20, no. 4, pp. 1595–1606, Aug. 2015.

[3] D. Moon, J. Park, and S. Choi, “New interleaved current-fed resonant converter with significantly reduced high current side output filter for EV and HEV applications,” IEEE Trans. Power Electron., vol. 30, no. 8, pp. 4264–4271, Jun. 2015.

[4] F. Musavi, M. Craciun, D. S. Gautam, and W. Eberle, “Control strategies for wide output voltage range LLC resonant DC–DC converters in battery chargers,” IEEE Trans. Veh. Technol., vol. 63, no. 3, pp. 1117–1125, Jun. 2014.

[5] C.W. Tsang, M. P. Foster, D. A. Stone, and D. T. Gladwin, “Analysis and design of LLC resonant converters with capacitor-diode clamp current limiting,” IEEE Trans. Power Electron., vol. 30, no. 3, pp. 1345–1355, Mar. 2015

A Three-Phase Grid Tied SPV System with Adaptive dc link voltage for CPI voltage variations

ABSTRACT:

This paper deals with a three-phase two-stage grid tied SPV (solar photo-voltaic) system. The first stage is a boost converter, which serves the purpose of MPPT (maximum power point tracking) and feeding the extracted solar energy to the DC link of the PV inverter, whereas the second stage is a two-level VSC (voltage source converter) serving as PV inverter which feeds power from a boost converter into the grid. The proposed system uses an adaptive DC link voltage which is made adaptive by adjusting reference DC link voltage according to CPI (common point of interconnection) voltage. The adaptive DC link voltage control helps in the reduction of switching power losses. A feed forward term for solar contribution is used to improve the dynamic response. The system is tested considering realistic grid voltage variations for under voltage and over voltage. The performance improvement is verified experimentally. The proposed system is advantageous not only in cases of frequent and sustained under voltage (as in the cases of far radial ends of Indian grid) but also in case of normal voltages at CPI. The THD (total harmonics distortion) of grid current has been found well under the limit of an IEEE-519 standard.

KEYWORDS:

1.      Adaptive DC link

2.      MPPT

3.      Overvoltage

4.      Solar PV

5.      Two-stage

6.      Three phase

7.      Under voltage

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. System configuration.

 CONTROL SYSTEM

                                 

Fig. 2. Block diagram for control approach.

 EXPECTED SIMULATION RESULTS:

Fig. 3. Simulated performance for, (a) change in solar insolation without feedforward for PV contribution,

(b) change in solar insolation with feed forward for PV contribution,

(c) normal to under voltage (415 V to 350 V),

(d) CPI voltage variation from normal to over voltage (415 V to 480 V).

CONCLUSION:

A two-stage system has been proposed for three-phase grid connected solar PV generation. A composite InC based MPPT algorithm is used for control of the boost converter. The performance of proposed system has been demonstrated for wide range of CPI voltage variation. A simple and novel adaptive DC link voltage control approach has been proposed for control of grid tied VSC. The DC link voltage is made adaptive with respect to CPI voltage which helps in reduction of losses in the system. Moreover, a PV array feed forward term is used which helps in fast dynamic response. An approximate linear model of DC link voltage control loop has been developed and analyzed considering feed forward compensation. The PV array feed forward term is so selected that it is to accommodate for change in PV power as well as for CPI voltage variation. A full voltage and considerable power level prototype has verified the proposed concept. The concept of adaptive DC link voltage has been proposed for grid tied VSC for PV application however, the same concept can be extended for all shunt connected grid interfaced devices such as, STATCOM, D-STATCOM etc. The proposed system yields increased energy output using the same hardware resources just by virtue of difference in DC link voltage control structure. The THDs of the grid currents and voltages are found less than 5% (within IEEE-519 standard). The simulation and experimental results have confirmed the feasibility of proposed control algorithm.

REFERENCES:

 [1] M. Pavan and V. Lughi, “Grid parity in the Italian commercial and industrial electricity market,” in Proc. Int. Conf. Clean Elect. Power (ICCEP’13), 2013, pp. 332–335.

[2] M. Delfanti, V. Olivieri, B. Erkut, and G. A. Turturro, “Reaching PV grid parity: LCOE analysis for the Italian framework,” in Proc. 22nd Int. Conf. Exhib. Elect. Distrib. (CIRED’13), 2013, pp. 1–4.

[3] H.Wang and D. Zhang, “The stand-alone PV generation system with parallel battery charger,” in Proc. Int. Conf. Elect. Control Eng. (ICECE’10), 2010, pp. 4450–4453.

[4] M. Kolhe, “Techno-economic optimum sizing of a stand-alone solar photovoltaic system,” IEEE Trans. Energy Convers., vol. 24, no. 2, pp. 511–519, Jun. 2009.

[5] D. Debnath and K. Chatterjee, “A two stage solar photovoltaic based stand alone scheme having battery as energy storage element for rural deployment,” IEEE Trans. Ind. Electron., vol. 62, no. 7, pp. 4148–4157, Jul. 2015.

Control Scheme for a Stand-Alone Wind Energy Conversion System

ABSTRACT

Present energy need heavily relies on the conventional sources. But the limited availability and steady increase in the price of conventional sources has shifted the focus toward renewable sources of energy. Of the available alternative sources of energy, wind energy is considered to be one of the proven technologies. With a competitive cost for electricity generation, wind energy conversion system (WECS) is nowadays deployed formeeting both grid-connected and stand-alone load demands. However, wind flow by nature is intermittent. In order to ensure continuous supply of power suitable storage technology is used as backup. In this paper, the sustainability of a 4-kW hybrid of wind and battery system is investigated for meeting the requirements of a 3-kW stand-alone dc load representing a base telecom station. A charge controller for battery bank based on turbine maximum power point tracking and battery state of charge is developed to ensure controlled charging and discharging of battery. The mechanical safety of the WECS is assured by means of pitch control technique. Both the control schemes are integrated and the efficacy is validated by testing it with various load and wind profiles in MATLAB/SIMULNIK.

KEYWORDS

1.      Maximum power point tracking (MPPT)

2.       Pitch control

3.      State of charge (SoC)

4.      Wind energy conversion system (WECS).

SOFTWARE: Matlab/Simulink

BLOCK DIAGRAM:

Fig. 1. Layout of hybrid wind–battery system for a stand-alone dc load.

SIMULATION RESULTS:

Fig. 2. (a) WT and (b) battery parameters under the influence of gradual variation of wind speed.

Fig. 3. (a)WT and (b) battery parameters under the influence of step variation of wind speed.

Fig. 4. (a) WT and (b) battery parameters under the influence of arbitrary variation of wind speed.

CONCLUSION

The power available from a WECS is very unreliable in nature. So, a WECS cannot ensure uninterrupted power flow to the load. In order to meet the load requirement at all instances, suitable storage device is needed. Therefore, in this paper, a hybrid wind-battery system is chosen to supply the desired load power. To mitigate the random characteristics of wind flow the WECS is interfaced with the load by suitable controllers. The control logic implemented in the hybrid set up includes the charge control of battery bank using MPPT and pitch control of the WT for assuring electrical and mechanical safety. The charge controller tracks the maximum power available to charge the battery bank in a controlled manner. Further it also makes sure that the batteries discharge current is also within the C/10 limit. The current programmed control technique inherently protects the buck converter from over current situation. However, at times due to MPPT control the source power may be more as compared to the battery and load demand. During the power mismatch conditions, the pitch action can regulate the pitch angle to reduce the WT output power in accordance with the total demand. Besides controlling the WT characteristics, the pitch control logic guarantees that the rectifier voltage does not lead to an overvoltage situation. The hybrid wind-battery system along with its control logic is developed in MATLAB/SIMULINK and is tested with various wind profiles. The outcome of the simulation experiments validates the improved performance of the system.

REFERENCES

[1]   D. Sahin, “Progress and recent trends in wind energy,” Progress in Energy Combustion Sci., vol. 30, no. 5, pp. 501–543, 2004.

[2]   R. D. Richardson and G. M. Mcnerney, “Wind energy systems,” Proc. IEEE, vol. 81, no. 3, pp. 378–389, Mar. 1993.

[3]   R. Saidur, M. R. Islam, N. A. Rahim, and K. H. Solangi, “A review on global wind energy policy,” Renewable Sustainable Energy Rev., vol. 14, no. 7, pp. 1744–1762, Sep. 2010.

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