Model Predictive Control of PV Sources in A Smart DC Distribution System Maximum Power Point Tracking and Droop Control

ABSTRACT:

In a dc distribution system, where multiple power sources supply a common bus, current sharing is an important issue. When renewable energy resources are considered, such as photovoltaic (PV), dc/dc converters are needed to decouple the source voltage, which can vary due to operating conditions and maximum power point tracking (MPPT), from the dc bus voltage. Since different sources may have different power delivery capacities that may vary with time, coordination of the interface to the bus is of paramount importance to ensure reliable system operation. Further, since these sources are most likely distributed throughout\ the system, distributed controls are needed to ensure a robust and fault tolerant control system. This paper presents a model predictive control-based MPPT and model predictive control-based droop current regulator to interface PV in smart dc distribution systems. Back-to-back dc/dc converters control both the input current from the PV module and the droop characteristic of the output current injected into the distribution bus. The predictive controller speeds up both of the control loops, since it predicts and corrects error before the switching signal is applied to the respective converter.

KEYWORDS:

1.      DC microgrid

2.      Droop control

3.      Maximum power point tracking (MPPT)

4.      Model predictive control (MPC)

5.      Photovoltaic (PV)

6.      Photovoltaic systems

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Multiple-sourced dc distribution system with central storage.

EXPECTED SIMULATION RESULTS:

                                   

Fig. 2. Ideal bus voltage and load power as system impedance increases and loads are interrupted to prevent voltage collapse. (a) Bus voltage decreases in response to increased system impedance at t₁ to reach the operating point on the new P–V curve at t₂ . The new bus voltage is below the UVP limit, so control action cause load to be shed, moving to a new operating point on the same P–V curve at t₃ with a higher bus voltage. (b) Load power in the system changes as point-of-load converters are turned OFF to reduce total system load when the bus voltage drops below the UVP.

Fig. 3. Response of dc bus voltage to step changes in the power drained by

load.

Fig. 4. Response of dc bus voltage and output power to imbalanced input

PV sources

                                       

. Fig. 5. Response validation of dc bus voltage to step changes in the power

drained by load.

 

Fig. 6. Response validation of dc bus voltage and output power to imbalanced

input PV sources.

 

Fig. 7. Response of dc bus voltage and output power to the input PV sources

of Fig. 7.

CONCLUSION:

High efficiency and easy interconnection of renewable energy sources increase interests in dc distribution systems. This paper examined autonomous local controllers in a single-bus dc microgrid system for MPP tracked PV sources. An improved MPPT technique for dc distribution system is introduced by predicting the error at next sampling time using MPC. The proposed predictive MPPT technique is compared to commonly used P&O method to show the benefits and improvements in the speed and efficiency of the MPPT. The results show that the MPP is tracked much faster by using the MPC technique than P&O method.

In a smart dc distribution system for microgrid community, parallel dc/dc converters are used to interconnect the sources, load, and storage systems. Equal current sharing between the parallel dc/dc converters and low voltage regulation is required. The proposed droop MPC can achieve these two objectives. The proposed droop control improved the efficiency of the dc distribution system because of the nature of MPC, which predicts the error one step in horizon before applying the switching signal. The effectiveness of the proposed MPPT-MPC and droop MPC is verified through detailed simulation of case studies. Implementation of the MPPT-MPC and droop MPC using dSPACE DS1103 validates the simulation results.

REFERENCES:

[1] Z. Peng, W. Yang, X. Weidong, and L. Wenyuan, “Reliability evaluation of grid-connected photovoltaic power systems,” IEEE Trans. Sustain. Energy, vol. 3, no. 3, pp. 379–389, Jun. 2012.

[2] W. Baochao, M. Sechilariu, and F. Locment, “Intelligent DC microgrid with smart grid communications: Control strategy consideration and design,” IEEE Trans. Smart Grid, vol. 3, no. 4, pp. 2148–2156, Dec. 2012.

[3] R. Majumder, “A hybrid microgrid with DC connection at back to back converters,” IEEE Trans. Smart Grid, vol. 5, no. 1, pp. 251–259, Jun. 2013.

[4] R. Lasseter, A. Akhil, C. Marnay, J. Stephens, J. Dagle, R. Guttromson, A. S. Meliopoulous , R. Yinger, and J. Eto, “Integration of distributed energy resources. The CERTS microgrid concept,” U.S. Dept. Energy, Tech. Rep. LBNL-50829, 2002.

[5] T. Esram and P. L.Chapman, “Comparison of photovoltaic array maximum power point tracking techniques,” IEEE Trans. Energy Convers., vol. 22, no. 2, pp. 439–449, Jun. 2007.

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.