A Management of power flow for DC Microgrid with Solar and Wind Energy Sources

ABSTRACT:

Today there is a rapid proliferation of DC loads into the market and DC micro grid with renewable energy sources is emerging as a possible solution to meet growing energy demand. As different energy sources like solar, wind, fuel cell, and diesel generators can be integrated into the DC grid, Management of power flow among the sources is essential. In this paper, a control strategy for Management of power flow in DC micro grid with solar and wind energy sources is presented. As the regulation of voltage profile is important in a standalone system, a dedicated converter is to be employed for maintaining the DC link voltage. DC link voltage is regulated by the battery circuit while maximum power is extracted from Solar and Wind to feed the loads connected at the DC bus. A power flow algorithm is developed to control among three sources in the DC Microgrid. The algorithm is tested for various load conditions and for fluctuations in solar and wind power in MATLAB/SIMULINK environment.

KEYWORDS:

1.      DC microgrid

2.      Power flow administration

3.      Photovoltaics

4.      Wind conversion systems

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1 Block diagram of the DC microgrid with Solar and wind energy sources

 EXPERIMENTAL RESULTS:

Fig 2 . Response of the system for increase in load

power

Fig 3. Response of the system for decrease in load power

Fig .4. Response of the system during change in Ppv

Fig .5. Response of the system during change in Pw

 CONCLUSION:

A Management of power flow and control algorithm for DC microgrid with solar and wind energy sources is presented. As the system involves different intermitted energy sources and load whose demand can vary, it is necessary to develop a Management of power flow and control algorithm for the DC Microgrid. To provide ceaseless power supply to the loads and balance the power flow among the different sources at any time, a Management of power flow algorithm is developed. The feasibility of the algorithm has been tested for various load conditions and for  changes in solar and wind power.

REFERENCES:

[1] F. Katiraei, M. R. Iravani, A. L. Dimeas, and N. D. Hatziargyriou, "Microgrids management: control and operation aspects of microgrids, "IEEE Power Energy Mag., vol. 6, no. 3, pp. 54-65, May/Jun. 2008.

[2] W. Jiang and B. Fahimi, “Active current sharing and source  management in fuel cell-battery hybrid power system,” IEEE Trans. Ind. Electron., vol. 57, no. 2, pp. 752–761, Jan. 2010.

[3] L. Xu and D. Chen, "Control and operation of a DC microgrid with variable generation and energy storage," IEEE Trans. Power Del., vol. 26, no. 4, pp. 25 I 3-2522, Oct. 2011.

[4] Jin C, Wang P, Xiao J, "Implementation of hierarchical control in DC microgrids,"IEEE Transaction of Industrial Electronics, vol.61(8), pp.4032-4042,2014.

[5] L. Xiaonan, J. M. Guerrero, S. Kai, and J. C. Vasquez, "An Improved Droop Control Method for DC Microgrids Based on Low Bandwidth Communication With DC Bus Voltage Restoration and Enhanced Current Sharing Accuracy," Power Electronics, IEEE Transactionson,vol.29,pp.1800-1812,2014.

Single Phase Bidirectional H6 Rectifier/Inverter

ABSTRACT:

Transformer-less photovoltaic (PV) inverters are more widely adopted due to high efficiency, low cost and light weight, etc. However, H5, HERIC, etc. transformer-less PV inverters do not have the bidirectional capability for solar energy storage system in the future. With topology derivation history reviewed from rectifier to inverter, the essence of bidirectional rectifier/inverter is revealed to find a reverse power flow approach. Therefore, this paper proposes an advanced bidirectional technique for a selected H6 inverter topology with only modulation strategy modified, while the others remain the same. For the H6 circuitry in both rectifier and inverter modes, excellent three level DM voltage feature is achieved, while leakage current issue is eliminated at the same time with improved modulation method. Simulations and experimental results verify the proposed single phase bidirectional H6 rectifier/inverter technique.

KEYWORDS:

1.      H6 inverter

2.      Rectifier

3.      Improved modulation

4.      Bidirectional power flow

5.       Leakage current

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Figure 1 Selected H6 inverter

 EXPERIMENTAL RESULTS:

(a)     Ac grid voltage, ac current, DM voltage and CM voltage in rectifier mode

(b) Switching pulses S1&S4, S2&S3, S5, S6 in rectifier mode

(c) Expanded switching pulses S1&S4, S2&S3, S5, S6 in rectifier mode

(d) Ac grid voltage, ac current, DM voltage and CM voltage in inverter mode

(e) Switching pulses S1&S4, S2&S3, S5, S6 in inverter mode

(f) Expanded switching pulses S1&S4, S2&S3, S5, S6 in inverter mode

Figure 2 Bidirectional H6 rectifier/inverter modulation method simulation Results

(a) Current stress

(b) Voltage stress

Figure 3 H6 rectifier device stress

CONCLUSION:

Aiming solar energy storage system, this paper improves a grid-tied single phase H6 PV inverter from unidirectional power flow to bidirectional power flow. A unified hybrid modulation method is proposed for both rectifier and inverter modes. The main advantages of the proposed solution can be summarized as:

1) Compared with the traditional hybrid modulation method for power rejection to grid only, a simple modification in the switching patterns is just needed for solar energy storage system with H6 type topology.

2) Battery storage is adopted for emergency usage in small solar energy storage system. Therefore, a slight cost of efficiency decreases in rectifier mode due to the partly used body diodes is acceptable, and the excellent DM/CM voltage features of the H6 circuitry in both rectifier and inverter modes are totally achieved.

3) The improved hybrid modulation method would be easily modified and applied to other H6 and similar topologies.

REFERENCES:

[1] R. Teodorescu, M. Liserre, and P. Rodriguez, Grid converters for photovoltaic and wind power systems. Hoboken, NJ, USA: Wiley, 2011.

[2] Rik W. De Doncker. Power Electronics – key enabling technology for a CO2 neutral electrical energy supply. Available: http://www.ifeec.tw/rik.html

[3] Generators connected to the low-voltage distribution network. Available: https://www.vde-verlag.de/standards/0105029/vde-ar-n-4105- anwendungsregel-2011-08.html.

[4] T. Kerekes, R. Teodorescu, P. Rodriguez, G. Vazquez, and E. Aldabas, "A  new high-efficiency single-phase transformerless PV inverter topology, " IEEE Trans. Ind. Electron., vol. 58, no. 1, pp. 184-191, 2011.

[5] R. Bojoi, L. R. Limongi, D. Roiu, and A. Tenconi, "Enhanced power quality control strategy for single-phase inverters in distributed generation systems," IEEE Trans. Power Electron., vol. 26, no. 3, pp. 798–806, 2011.

A Torque Ripple Compensation Technique for a Low Cost Brushless DC Motor Drive

ABSTRACT:

This paper presents a torque ripple compensation technique for a Brushless DC (BLDC) motor drive that is operated without a DC link capacitor. The motor drive, which uses a single switch control strategy, resembles that of a buck converter during operation at any switching state. A simple buck converter based model is therefore proposed to predict the behaviour of the BLDC motor drive at constant speed. Using the model, the impact of operation without the DC link capacitor on the torque produced by the BLDC motor drive is investigated in detail. Theoretical behaviour of the BLDC motor drive is compared with Matlab/Simulink based simulations to demonstrate the validity of the compensation technique and the analysis. Experimental results of a 250 W prototype motor drive are also presented to further validate the theoretical analysis as well as the effectiveness of the proposed technique. Results convincingly indicate that the BLDC motor drive with torque ripple compensation offers comparable performance.

KEYWORDS:

1.      Brushless machines

2.      Torque ripple compensation

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. (a) A typical BLDC motor drive; and (b) a BLDC motor drive without

a DC link capacitor.

 EXPERIMENTAL RESULTS:

Fig. 2. Case 1 with M1 for E = 95V: (a) vin(t) and E; (b) im(t) by theoretical

analysis; (c) im(t) by simulation; and (d) im(t) by experiment.

Fig. 3. Case 2 with M2 for E = 80V: (a) vin(t) and E; (b) im(t) by theoretical

analysis; (c) im(t) by simulation; and (d) im(t) by experiment.

Fig. 4. Case 3 with M1 for E = 65 V: (a) vin(t) and E; (b) im(t) by

theoretical analysis; (c) im(t) by simulation; and (d) im(t) by experiment.

Fig. 5. A comparison between the comprehensive model and the simple

model: (a) case 1 with M1; (b) case 2 with M2; and (c) case 3 with

M1.

Fig. 6. Proposed compensation for case 1: (a) simulated im(t) without a capacitor and with a 150 μF capacitor; (b) simulated im(t) with proposed compensation; (c) experimental im(t); and (d) DC link voltage with proposed compensation.

Fig. 7. Proposed compensation for case 3: (a) simulated im(t) without a capacitor and with a 150 μF capacitor; (b) simulated im(t) with proposed compensation; (c) experimental im(t); and (d) DC link voltage with proposed compensation.

CONCLUSION:

A simple mathematical model and a compensation technique for inherent torque ripples of a BLDC motor drive, operated without a DC link capacitor, have been proposed. The simplicity of the model permits the controller to be implemented on inexpensive microcontroller platforms with very low resources. With the proposed technique for compensating torque ripples, comparable performance to a conventional BLDC motor drive with a large DC link capacitor can be achieved. However, with the torque ripple compensation technique, the overall complexity of the motor drive has been increased, which is a major disadvantage. Based on the application, major augmentations in both hardware and firmware may be required. The good agreement between the theoretical results, simulated results and experimental results demonstrate the accuracy of the simple buck model and the effectiveness of the proposed compensation technique. The proposed compensation technique is expected to be useful for manufacturing low cost BLDC motor drives with comparable performance.

REFERENCES:

[1] R. Krishnan, Electric Motor Drives, Modeling, Analysis, and Control. Prentice Hall, 2001.

[2] R. Krishnan, Permanent Magnet Synchronous and Brushless DC Motor Drives. CRC Press, 2010.

[3] J. F. Gieras, Permanent Magnet Motor Technology - Design and Applications: CRC Press, 2010.

[4] V. Sankaran, F. Rees, and C. Avant, “Electrolytic capacitor life testing and prediction,” in Industry Applications Conference, 1997. Thirty- Second IAS Annual Meeting, IAS ’97., Conference Record of the 1997 IEEE, vol. 2, Oct. 1997, pp. 1058–1065.

[5] H. K. Samitha Ransara and U. K. Madawala, "A Low Cost Brushless DC Motor Drive," in 6th IEEE Conference on Industrial Electronics and Applications, (IEEE ICIEA), Jun. 2011, pp. 2723-2728.