Varying Phase Angle Control In Isolated Bidirectional DC–DC Converter For Integrating Battery Storage And Solar PV System In Standalone Mode

 ABSTRACT:

This study proposes a varying phase angle control (VPAC) in isolated bidirectional dc–dc converter (IBDC) for integrating battery storage unit to a DC link in a standalone solar photovoltaic (PV) system. The IBDC is capable of power transfer using high step up/down ratio between DC link and battery. The VPAC control proposed in this study effectively manage the power flow control between the battery storage unit and the solar PV fed DC link by continuously varying the phase angle between high voltage and low voltage (LV) bridge voltage of the IBDC. The solar PV system is incorporated with the maximum power point tracking using DC–DC converter. In order to control the voltage across the AC load a voltage source inverter is used. The study also presents the design aspects of the IBDC converter for the application considered. The performance of the proposed power flow control strategy has been studied through PSCAD/EMTDC simulation and validated using LPC 2148 ARM processor.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1 Block diagram for proposed standalone system

(a) Generalised block diagram, (b) Mode 1 operation, (c) Mode 2 operation, (d) Mode 3 operation

 EXPECTED SIMULATION RESULTS:

.

Fig. 2 Simulation results of IBDC

(a) Battery current during change in mode 1 to mode 2, (b) Battery current during change in mode 2 to mode 1, (c) Solar PV power, load power and battery power during change in

mode 1 to mode 2, (d) Solar PV power, load power and battery power during change in mode 2 to mode 1

CONCLUSION: 

The proposed variable phase angle control of IBDC converter balances the power flow between the solar PV system, battery storage unit and AC load in all the modes. The VPAC algorithm ensures that the, (i) solar PV system delivers maximum demanded power corresponding to the load and battery gets charged/ discharged through the available excess/short power. The governing mathematical formulation of problem reveals the dependency of average battery current on phase angle between the voltages of LV and HV side of the IBDC converter and hence provides a strategy to control the power flow. The analysis presented can be used to design the passive components and switches of the IBDC. From the obtained results, the performance of the proposed VPAC has been established with smooth transition of power flow between the PV fed DC link and the battery through the IBDC converter. The maximum power is extracted from the solar PV and AC load voltage is controlled in all the modes.

REFERENCES:

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

[2] Solodovnik, E.V., Liu, S., Dougal, R.A.: ‘Power controller design for maximum power tracking in solar installations’, IEEE Trans. Power Electron., 2004, 19, (5), pp. 1295–1304

[3] Kuo, Y.-C., Liang, T.-J., Chen, J.-F.: ‘Novel maximum-power-point tracking controller for photovoltaic energy conversion system’, IEEE Trans. Ind. Electron., 2001, 48, (3), pp. 594–601

[4] Koutroulis, E., Kalaitzakis, K., Voulgaris, N.C.: ‘Development of a microcontroller-based, photovoltaic maximum power point tracking control system’, IEEE Trans. Power Electron., 2001, 16, (1), pp. 46–54

Single-phase solar PV system with battery and exchange of power in grid-connected and standalone modes

ABSTRACT:

A grid tied photovoltaic (PV) power conversion topology is presented in this study with a novel scheme of resynchronization to the grid. This scheme serves the purpose of supplying continuous power to the load along with feeding power to the grid. The control approach helps in mitigation of harmonics and improving the power quality while extracting the optimum power from the PV array. Depending on the availability of grid voltage, the proposed configuration is controlled using three approaches, defined as grid current control, Point of Common Coupling (PCC) voltage control and intentional islanding with re-synchronisation. A simple proportional integral controller manages the grid current, load voltage, battery current and DC Direct Current (DC) link voltage within these modes. Moreover, a control scheme for quick and smooth transitions among the modes is described. The robustness of the system under erratic behaviour of solar insolation, load power and disturbances in grid supply makes it a suitable choice for a residential application. The control, design and simulation results are presented to demonstrate the satisfactory operation of the proposed system.

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig. 1 Proposed system topology

 EXPECTED SIMULATION RESULTS:

Fig. 2 Performance of the system under grid isolation

(a)   GCC to PVC, (b) Harmonic spectrum of grid current (ig), (c) Harmonic spectrum of load voltage (vL)

Fig. 3 Performance of the system under grid reconnection

(a) Mode change from PVC to IIRS, (b) Grid voltage (vg) vs. load voltage (vL) during

intentional islanding

Fig. 4 Performance of the system for insolation change from 1000 W/m2

to 500/m2

 CONCLUSION: 

The proposed scheme has combined the solar PV power generating unit to single-phase grid with a unique feature of resynchronization of grid to the system after overcoming the grid failures. The ability of the system to generate maximum power for varying insolation, feeding active power to the grid as well as load and store/extract power to/from the battery has been validated by the dynamic performance. This helps in increasing the efficiency of the system. The scheme has utilised minimum number of switches resulting in lower switching losses. The VSC has the ability to diminish the switching harmonics in grid current and load voltages resulting in <5% THD as demanded by the IEEE 519 standard. The system has ability to re-synchronise with the grid within five cycles of grid voltage for any phase difference. This helps in achieving the fast time response of the system, thus making it a suitable choice for residential applications. The obtained results have authenticated the robustness and feasibility of the proposed system under various disturbances.

REFERENCES:

[1] Zheng, H., Li, S., Bao, K., et al.: ‘Comparative study of maximum power point tracking control strategies for solar PV systems’. IEEE Conf. on Transmission, Distribution and Exposition, May 2012, pp. 1–8

[2] Weihang, Y., Jianhui, W., Wenzhong, G., et al.: ‘A MPPT algorithm based on extremum seeking with variable gain for microinverters in microgrid’. IEEE Conf. on Control (CCC), July 2015, pp. 7939–7944

[3] Zhang, Q., Hu, C., Chen, L., et al.: ‘A center point iteration MPPT method with application on the frequency-modulated LLC microinverter’, IEEE Trans. Power Electron., 2014, 29, (3), pp. 1262–1274

[4] Li, Q., Wolfs, P.: ‘A review of the single phase photovoltaic module integrated converter topologies with three different DC link configurations’, IEEE Trans. Power Electron., 2008, 23, (3), pp. 1320–1333

[5] Gloire, N., Lei, D., Xiaozhong, L., et al.: ‘Single phase grid-connected PV inverter applying a boost coupled inductor’. IEEE Conf. on Transportation Electrification (ITEC Asia-Pacific), August–September 2014, pp. 1–5

Novel High Performance Stand Alone Solar PV System with High Gain, High Efficiency DC-DC Converter Power Stages

ABSTRACT:  

This paper proposes a novel 3- stand-alone solar PV system configuration that uses high gain, high efficiency (96%) dc-dc converters both in the forward power stage as well as the bidirectional battery interface. The high voltage gain converters enable the use of low voltage PV and battery sources. This results in minimization of partial shading and parasitic capacitance effects on the PV source. Series connection of a large number of battery modules is obviated, preventing the overcharging and deep discharging issues that reduce the battery life. Also, the proposed configuration facilitates "required power tracking (RPT)" of the PV source as per the load requirements eliminating the use of expensive and 'difficult to manage' dump loads. High performance inverter operation is achieved through abc to dq reference frame transformation, which helps in generating precise information about the load's active power component for RPT, regulation of ac output voltage and minimization of control complexity. Inverter output voltage is regulated by controlling the modulation index of sinusoidal pulse width modulation, resulting in a stable and reliable system operation. The active power demand is controlled by regulating the dc link voltage. All the analytical, simulation and experimental results of this work are presented.

KEYWORDS:

1.      Power conversion

2.      Pulse width modulation converters

3.      Power conditioning, Inverters

4.      Three-phase electric power

5.      Power control

6.      Photovoltaic cells

7.      Energy conversion

8.      Solar power generation

9.      High gain DC-DC Converter

10.  MPPT

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Simplified block diagram of a two stage stand alone PV system

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results of the proposed system during the sequence of events considered

Fig.3 Dynamic response of the dc link: (a) An effective load (Reff) connected across the dc link; (b) Response to step change in effective load (200W to 400W); (c) Response to step change in reference dc link voltage, *

Vdc from 250V to 400V.

CONCLUSION:

This paper has described and implemented a novel 3- solar PV inverter system for stand-alone applications. Considering that high PV side voltage leads to several drawbacks, a low voltage PV source is used in the system. The limitation of low voltage PV source is overcome by using a special high voltage gain front end dc-dc converter capable of operating at high efficiency and MPPT. The proposed scheme is particularly conducive to long battery life by as it ensures no battery overcharge or deep discharge. For this purpose, the   conventional MPPT scheme is replaced by RPT, which ensures only the required power is tracked from the PV source. This prevents the drawing of excess power from the PV source and the use and management of expensive 'dump' loads. Not only the main power stage, but the battery interfacing bi-directional stage also supports high voltage gain with high efficiency. Due to the use of special high gain, high efficiency converters in the power stage, the overall efficiency of the system is 94%. Preliminary investigations have yielded encouraging results. The capacity of the proposed control strategy can be enhanced for high power operation by interfacing other renewable sources (fuel cell stack, wind etc.) to the dc link of the proposed system without significantly altering the control strategy. In spite of the good performance of the proposed system, as verified through several simulation and experimental results, there are some limitations too, as listed below:

1. The high gain, high efficiency dc-dc converters used in the proposed system may be difficult to design for high power levels.

2. In the proposed system, battery is interfaced with the high voltage (400V) dc link requiring a high voltage gain, high efficiency dc-dc converter. Battery interfacing to the low voltage (40V) dc bus should be explored.

3. The proposed system uses a large number of sensors, which may increase the cost and complexity. All these issues are being currently investigated and the findings will be reported in a future paper.

REFERENCES:

[1] S.R. Bhat, A. Pittet and B.S. Sonde, "Performance optimization of induction motor-pump system using photovoltaic energy source," IEEE Transactions on Industry Applications, vol. IA- 23, no. 6, pp. 995–1000, Nov. 1987.

[2] S. Duryea, S. Islam and W. Lawrence, "A battery management system for stand alone photovoltaic energy systems," 34th IEEE IAS Annual Meeting, vol. 4, pp. 2649-2654, Phoenix, AZ , 3rd - 7th Oct., 1999.

[3] M. Uzunoglu, O. C. Onar, and M. S. Alam, “Modeling, control and simulation of a PV/FC/UC based hybrid power generation system for stand-alone applications” Renewable Energy, vol. 34, no. 3, pp. 509-520, Mar. 2009.

[4] R. M. Cuzner and G. Venkataramanan, "The status of dc microgrid protection," IEEE Industry Applications Society Annual  Meeting, pp. 1-8, 5th-9th Oct. 2008

[5] P. Sharma and V. Agarwal, "Exact maximum power point tracking of grid-connected partially shaded PV source using current compensation concept," IEEE Transactions on Power Electronics, vol. 29, no. 9, pp. 4684-4692, Sep. 2014.

Control and Implementation of a Standalone Solar Photo-Voltaic Hybrid System

ABSTRACT:  

 A control algorithm for a standalone solar photovoltaic (PV)-diesel-battery hybrid system is implemented in this paper. The proposed system deals with the intermittent nature of the energy generated by the PV array and it also provides power quality improvement. The PV array is integrated through a DC-DC boost converter and controlled using a maximum power point tracking (MPPT) algorithm to obtain the maximum power under varying operating conditions. The battery energy storage system (BESS) is integrated to the diesel engine generator (DG) set for the coordinated load management and power flow within the system. The admittance based control algorithm is used for load balancing, harmonics elimination and reactive power compensation under three phase four-wire linear and nonlinear loads. A four-leg voltage source converter (VSC) with BESS also provides neutral current compensation. The performance of proposed standalone hybrid system is studied under different loading conditions experimentally on a developed prototype of the system.

KEYWORDS:

1.      Admittance based control algorithm

2.      BESS

3.      DG set

4.      Four-leg VSC

5.      Neutral current compensation

6.      Power quality

7.      Solar photovoltaic array

8.      Standalone system

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Schematic diagram of the proposed system

EXPECTED SIMULATION RESULTS:

Fig.2 Performance of proposed system under unbalance nonlinear load

CONCLUSION:

The admittance based control technique has been used for a PV-diesel-battery hybrid system for an uninterrupted power supply and power quality improvement. The incremental based MPPT algorithm has delivered maximum solar array power under varying conditions of temperature and insolation radiation. The technique has been demonstrated to eliminate harmonics, load balancing and to provide neutral current compensation by incorporating four-leg VSC in the system. The PCC voltage and frequency have been maintained constant. Satisfactory performance of the system has been observed through test results obtained for steady state and dynamic conditions under both linear/nonlinear loads.

REFERENCES:

[1] Z. Jiang, “Power Management of Hybrid Photovoltaic-Fuel Cell Power Systems”, Proc. of IEEE Power Engg. Society General Meeting, Montreal Quebec, Canada, 2006.

[2] A. Naik, R.Y. Udaykumar and V. Kole, “Power management of a hybrid PEMFC-PV and Ultra capacitor for stand-alone and grid connected applications”, Proc. of IEEE Int. Conf. Power Electron. Drives and Energy Sys. (PEDES), 2012, pp. 1-5.

[3] J. Philip, C. Jain, , K. Kant, B. Singh, S. Mishra, A. Chandra and K. Al- Haddad “Control and implementation of a standalone solar photo-voltaic hybrid system”, Proc. of IEEE Industry Applications Society Annual Meeting, Addison, TX, 18- 22 Oct. 2015, pp.1-8.

[4] J. Philip, B. Singh and S. Mishra, “Design and operation for a standalone DG-SPV-BES microgrid system”, Proc. of 6thIEEE Power India Int. Conf. (PIICON), Delhi, 5-7 Dec, 2014, pp.1-6.

A Unified Control Strategy for Three-phase Inverter in Distributed Generation

ABSTRACT:  

This paper presents a unified control strategy that enables both islanded and grid-tied operation of three-phase inverter in distributed generation (DG), with no need for switching between two corresponding controllers or critical islanding detection. The proposed control strategy composes of an inner inductor current loop, and a novel voltage loop in the synchronous reference frame (SRF). The inverter is regulated as a current source just by the inner inductor current loop in grid-tied operation, and the voltage controller is automatically activated to regulate the load voltage upon the occurrence of islanding. Furthermore, the waveforms of the grid current in grid-tied mode and the load voltage in islanding mode are distorted under nonlinear local load with the conventional strategy. And this issue is addressed by proposing a unified load current feed forward in the paper. Additionally, the paper presents the detailed analysis and the parameter design of the control strategy. Finally, the effectiveness of the proposed control strategy is validated by the simulation and experimental results.

KEYWORDS:

1.      Distributed generation

2.      Three-phase inverter

3.      Islanding

4.      Unified control

5.      Seamless transfer

6.      Load current

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1 Schematic diagram of the distributed generzation based on the proposed control strategy.

 EXPECTED SIMULATION RESULTS:

Fig. 2 Bode plot of the transfer function from load current to grid current with

and without the load current feedforward, when DG operates in grid-tied

mode.

Fig. 3 Simulation waveforms of load voltage vCa, grid current iga and inductor

current iLa when DG is in grid-tied mode under condition of the step down of

the grid current reference from 9A to 5A with: (a) conventional voltage mode

control, and (b) proposed unified control strategy.

Fig. 4 Simulation waveforms of load voltage vCa, grid current iga and inductor

current iLa when DG is transferred from grid-tied mode to islanded mode with:

(a) conventional hybrid voltage and current mode control, and (b) proposed

unified control strategy.

CONCLUSION:

A unified control strategy is proposed for three-phase inverter in DG to operate in both islanded and grid-tied mode, with no need for switching between two different control architectures or critical islanding detection. A novel voltage controller is presented. It is inactivated in grid-tied mode, and the DG operates as a current source with fast dynamic performance. Upon the utility outage, the voltage controller can automatically be activated to regulate the load voltage. Moreover, a novel load current feedforward is proposed, and it can improve the waveform quality of both the grid current in grid-tied mode and the load voltage in islanded mode. The proposed unified control strategy is verified by the simulation and experimental results.

REFERENCES:

[1] R. C. Dugan and T. E. McDermott, "Distributed generation," IEEE Ind. Appl. Mag., vol. 8, no. 2, pp. 19-25, Mar./Apr. 2002.

[2] R. H. Lasseter, "Microgrids and distributed generation," J. Energy Eng., vol. 133, no. 3, pp. 144-149, Sep. 2007.

[3] C. Mozina, "Impact of Green Power Distributed Generation," IEEE Ind. Appl. Mag., vol. 16, no. 4, pp. 55-62, Jul./Aug. 2010.

[4] IEEE Recommended Practice for Utility Interface of Photovoltaic(PV) Systems, IEEE Standard 929-2000, 2000.

[5] IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems, IEEE Standard 1547-2003, 2003.