Improved P-F/Q-V And P-V/Q-F Droop Controllers For Parallel Distributed Generation Inverters In AC Microgrid

ABSTRACT:

Distributed generation inverters are generally operated in parallel with P-f/Q-V and P-V/Q-f droop control strategies. Due to mismatched resistive and inductive line impedance, power sharing and output voltage of the parallel DG inverters deviate from the reference value. This leads to instability in the microgrid system. Adding virtual resistors and virtual inductors in the control loop of droop controllers improve the power sharing and stability of operation. But, this leads to voltage drop. Therefore, an improved P-f/Q-V and P-V/Q-f droop control is proposed. Simulation results demonstrate that the proposed control and the selection of parameters enhance the output voltage of inverters.

KEYWORDS:

1.      Distributed generation inverters

2.      Droop control

3.      Microgrid

4.      Output impedance

5.      Virtual resistors

6.      Virtual inductors

SOFTWARE: MATLAB/SIMULINK

 DROOP CONTROL BLOCK DIAGRAM.:

Fig. 1. Droop control block diagram.

EXPERIMENTAL RESULTS:

Fig. 2. Parallel inverter output voltage using P-V/Q-f droop control with virtual resistor under resistive line impedance.

Fig. 3. Active power sharing using secondary control with virtual resistor under resistive line impedance.

Fig. 4. Reactive power sharing using secondary control with virtual resistor under resistive line impedance.

Fig. 5. Parallel inverter output frequency using secondary control with virtual resistor under resistive line impedance.

Fig. 6. Parallel inverter output voltage using secondary control with virtual resistor under resistive line impedance.

Fig. 7. Active power sharing using P-V/Q-f droop control under inductive line impedance.

Fig. 8. Reactive power sharing using P-V/Q-f droop control under inductive line impedance.

Fig. 9. Active power sharing using P-f/Q-V droop control with virtual inductor under inductive line impedance.

Fig. 10. Reactive power sharing using P-f/Q-V droop control with virtual inductor under inductive line impedance. 

Fig. 11. Parallel inverter output frequency using P-f/Q-V droop control with virtual inductor under inductive line impedance.

Fig. 12. Parallel inverter output voltage using P-f/Q-V droop control with virtual inductor under inductive line impedance.

Fig. 13. Active power sharing using secondary control with virtual inductor under inductive line impedance.

Fig. 14. Reactive power sharing using secondary control with virtual inductor under inductive line impedance.

Fig. 15. Parallel inverter output frequency using secondary control with virtual inductor under inductive line impedance.

Fig. 16. Parallel inverter output voltage using secondary control with virtual inductor under inductive line impedance.

Fig. 17. Active power sharing using secondary control with different DG ratings under resistive line impedance.

Fig. 18. Reactive power sharing using secondary control with different DG ratings under resistive line impedance.

Fig. 19. Parallel inverter output frequency using secondary control with different DG ratings under resistive line impedance.

Fig. 20. Parallel inverter output voltage using secondary control with different DG ratings under resistive line impedance.

Fig. 21. Active power sharing using secondary control with different DG ratings under inductive line impedance.

Fig. 22. Reactive power sharing using secondary control with different DG ratings under inductive line impedance.

Fig. 23. Parallel inverter output frequency using secondary control with different DG ratings under inductive line impedance.

Fig. 24. Parallel inverter output voltage using secondary control with different DG ratings under inductive line impedance.

CONCLUSION:

In this paper, analysis of improved P-f/Q-V and P-V/Q-f droop control with secondary control for DG parallel inverters in microgrid is proposed considering line and output impedance. Proportional integral controller is adopted to ensure accurate tracking of the output voltage of the inverter to the reference value and the influence of the controller parameters on the voltage closed loop transfer function and the equivalent output impedance of the inverter is analyzed. In order to match the total output impedance of the inverter and line impedance in parallel, the P-V/Q-f and P-f/Q-V droop control strategy based on the inductive and resistive virtual impedance is adopted to improve the total output impedance of the inverter through the virtual impedance. The proposed P-f/Q-V and P-V/Q-f droop control, adaptively compensates the virtual resistor and inductor voltage drop to improve output voltage amplitude accuracy to the reference value. Simulation results show the rationality and effectiveness of the proposed improved control method.

REFERENCES:

Brabandere, K. D., Bolsens, B., & Van, J. (2007). A voltage and frequency droop control method for parallel inverters. IEEE Transactions on Power Electronics, 22(4), 1107–1115.

Chandorkar, M. C., Divan, D. M., & Adapa, R. (1993). Control of parallel connected inverters in standalone ac supply systems. IEEE Transactions on Industry Applications, 29(1), 136–143.

Chengshan, W., Zhaoxia, X., & Shouxiang, W. (2009). Multiple feedback loop control scheme for inverters of the microsource in microgrids. Transactions of China Electro Technical Society, 24(2), 100–107 [in Chinese].

Chengshan, W., Zhangang, Y., Shouxiang, W., & Yanbo, C. (2010). Analysis of structural characteristics and control approaches of experimental microgrid systems. Automation of Electric Power Systems, 34(1), 99–105 [in Chinese].

Chowdhury, A. A. S., & Agarwal, K. (2003). Dono Koval Reliability modeling of distributed generation in conventional distribution systems planning and analysis. IEEE Transactions on Industry Applications, 39(5), 1493–1498.

A Novel Control Strategy for a Variable Speed Wind Turbine with a Permanent Magnet Synchronous Generator

ABSTRACT:

This paper presents a novel control strategy for the operation of a direct drive permanent magnet synchronous generator (PMSG) based stand alone variable speed wind turbine. The control strategy for the generator side converter with maximum power extraction is discussed. The stand alone control is featured with output voltage and frequency controller capable of handling variable load. The potential excess of power is dissipated in the damp resistor with the chopper control and the dc link voltage is maintained. Dynamic representation of dc bus and small signal analysis are presented. Simulation results show that the controllers can extract maximum power and regulate the voltage and frequency under varying wind and load conditions. The controller shows very good dynamic and steady state performance.

KEYWORDS:

1.      Permanent magnet synchronous generator

2.      Maximum power extraction

3.      Switch-mode rectifier

4.      Variable speed

5.      Wind turbine

6.      Voltage and frequency control

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

 Figure 1. Control Structure of a PMSG based standalone variable speed wind turbine.

 EXPERIMENTAL RESULTS:

Figure 2. Response of the system for a step change of wind speed from 10 m/s

to 12 m/s to 9 m/s to 10 m/s.

Figure 3. Optimum torque and generator torque.

Figure 4. Turbine mechanical input power and Electrical output power.

Figure 5. Voltage and current responses at a constant load.

Figure 6. Frequency response, DC link voltage and modulation index at

a constant load.

Figure 7. Voltage and current responses when load is reduced by 50%.

Figure 8. Frequency response, DC link voltage and modulation index when load is reduced by 50%.

CONCLUSION:

Control strategy for a direct drive stand alone variable speed wind turbine with a PMSG is presented in this paper. A simple control strategy for the generator side converter to extract maximum power is discussed and implemented using Simpower dynamic system simulation software. The controller is capable to maximize output of the variable speed wind turbine under fluctuating wind. The load side PWM inverter is controlled using vector control scheme to maintain the amplitude and frequency of the inverter output voltage. It is seen that the controller can maintain the load voltage and frequency quite well at constant load and under varying load condition. The generating system with the proposed control strategy is suitable for a small scale standalone variable speed wind turbine installation for remote area power supply. The simulation results demonstrate that the controller works very well and shows very good dynamic and steady state performance.

REFERENCES:

[1] Müller, S., Deicke, M., and De Doncker, Rik W.: ‘Doubly fed induction genertaor system for wind turbines’, IEEE Industry Applications Magazine, May/June, 2002, pp. 26-33.

[2] Polinder H., Van der Pijl F. F. A, de Vilder G. J., Tavner P. J.:  "Comparison of direct-drive and geared generator concepts for wind turbines," IEEE Trans. on energy conversion, 2006, . 21, (3), pp. 725- 733.

[3] Chan T. F., and Lai L. L., "Permanenet-magnet machines for distributed generation: a review," Proc. IEEE power engineering annual meeting, 2007, pp. 1-6.

[4] De Broe M., Drouilhet S., and Gevorgian V.: “A peak power tracker for small wind turbines in battery charging applications,” IEEE Trans. Energy Convers. 1999, 14, (4), pp. 1630–1635.

[5] Datta R., and Ranganathan V. T.: “A method of tracking the peak power points for a variable speed wind energy conversion system,” IEEE Trans. Energy Convers., 1999, 18, (1), pp. 163–168.

PMSG Wind Turbine System for Residential Applications

ABSTRACT:

This paper analyzes the operation of small wind turbine system with variable speed Permanent Magnet Synchronous Generator (PMSG) and a Lead Acid Battery (LAB) for residential applications, during wind speed variation. The main purpose is to supply 230 V/50 Hz domestic appliances through a single-phase inverter. The required power for the connected loads can be effectively delivered and supplied by the proposed wind turbine and energy storage systems with an appropriate control method. The models of the PMSG, boost converter with a control method for obtaining maximum power characteristic of wind turbine (MPPT), voltage source inverter (VSI) and LAB model with battery state of charge (SOC) control method, are presented. Energy storage devices are required for power balance and power quality in stand alone wind energy systems. Simulations and experimental results validate the stability of the supply.

KEYWORDS:

1.      Wind energy

2.      Variable-speed

3.      Permanent magnets generators and energy storage

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

                                          Fig. 1. Stand-alone wind system configuration.

 EXPERIMENTAL RESULTS:

Fig. 2. The PMSG rotor speed variation:

(a) Simulation results; (b) Experimental results.

Fig. 3. The PMSG electromagnetic torque:

(a) Simulation results; (b) Experimental results.

Fig. 4. The DC link rectifier bridge voltage variation:

(a) Simulation results; (b) Experimental results.

Fig. 5. The converter input current variation:

(a) Simulation results; (b) Experimental results.

Fig. 6. The LAB voltage variation:

(a) Simulation results; (b) Experimental results.

Fig. 7. The LAB current variation:

(a) Simulation results; (b) Experimental results.

Fig. 8. The LAB state of charge (SOC) variation:

(a) Simulation results; (b) Experimental results.

Fig. 9. The active power balance of the system:

(a) Simulation results; (b) Experimental results.

CONCLUSION:

In this paper, a PMSG wind turbine system for residential applications is analyzed. Simulation and experimental results show that the active power balance of the system proves to be satisfying during variable wind speed condition. The MPPT algorithm will ensure a maximum extraction of energy from the available wind. LAB always ensures the safe supply of the loads (households) regardless of the problems caused by wind speed variations. At the end one can conclude that the power system’s stability considered in terms of load power quality can be ensured by using the proposed configuration.

REFERENCES:

[1] Barton, J.P.; Infield, D.G.: Energy storage and its use with intermittent renewable energy, IEEE Transaction on Energy Conversion, vol.19, no.2, June 2004, pp. 441-448.

[2] Weissbach, R.; Teodorescu, R.; Sonnenmeier, J.: Comparison of Time-Based Probability Methods for Estimating Energy Storage Requirements for an Off-Grid Residence, IEEE Energy2030, Atlanta, November 2008.

[3] Lee, D. J.; Wang, L.: Small-Signal Stability Analysis of an Autonomous Hybrid Renewable Energy Power Generation/Energy Storage System Part I: Time-Domain Simulations, IEEE Transaction on Energy Conversion, vol. 19, no. 2, March 2008, pp. 311-320.

[4] El-Ali, A.; Kouta, J.; Al-Samrout, D.; Moubayed, N.; Outbib, R.: A Note on Wind Turbine Generator Connected to a Lead Acid Battery, International Conference on Electromechanical and Power Systems, SIELMEN’09, Iasi, Romania, October 2009, pp. 341- 344.

[5] Barote, L.; Marinescu, C.: Control of Variable Speed  PMSG Wind Stand-Alone System, Proc. of International Conference OPTIM’06, Brasov, vol. II, May, 2006, pp. 243-248.

Voltage and Frequency Control of a Stand-alone Wind-Energy Conversion System Based on PMSG

 ABSTRACT:

This paper presents a control strategy for a standalone wind-energy conversion system using Permanent Magnet Synchronous Generator (PMSG). The presented control strategy aims at regulating the load voltage in terms of magnitude and frequency under different operating conditions including wind speed variation, load variation and the unbalanced conditions. The wind generating-system under study consists of a wind turbine, PMSG, uncontrolled rectifier, DC-DC boost converter and voltage source inverter. The presented control strategy is based firstly upon controlling the duty cycle of the boost converter in order to convert the variable input dc-voltage, due to different operating conditions, to an appropriate constant dc voltage. Hence, a sinusoidal pulse width modulated (SPWM) inverter is used to regulate the magnitude and frequency of the load voltage via controlling the modulation index. In order to verify the performance of the employed wind generating-system, a sample of simulation results is obtained and analyzed. The presented simulation results show the effectiveness of the employed control strategy to supply the load at constant voltage and frequency under different operating conditions.

KEYWORDS:

1.      Wind turbine

2.      PMSG

3.      Voltage and frequency control

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1.Complete structure of the stand-alone wind-energy conversion system

 EXPERIMENTAL RESULTS:

Fig. 2.Effect of wind-speed variation on the generated voltage and frequency:

a) Wind speed b) generated line voltage c) frequency of the generated voltage

Fig. 3. DC-link voltage

Fig. 4. Load voltage and current during different periods of wind-speed

variation a) Effective value of the load voltage b) Instantaneous three-phase

load-current waveforms

Fig. 5. Effect of load variation on the generated voltage and frequency at

constant wind speed a) generated line voltage b) frequency of the generated

voltage

Fig. 6. Load voltage and current during different periods of load variations a)

Effective value of load voltage during different loads b) Instantaneous threephase

load-current waveforms

Fig. 7. DC Link Voltage during balanced and unbalanced

Fig. 8. Effective value of the load voltage during both balanced and

unbalanced loading condition

Fig. 9. Load current of each phase during both balanced and unbalanced

loading conditions (a) Instantaneous waveforms (b) Effective value

CONCLUSION:

This paper has presented a control strategy of a stand-alone wind-driven Permanent Magnet Synchronous Generator (PMSG) in order to regulate the magnitude and frequency of the load voltage under different operating conditions. In order to ensure the validity of the presented control strategy, the performance characteristics of the wind-generating system has been studied and discussed under three different operating conditions; wind-speed variation, load variation and unbalance operating condition. The presented simulation results have verified the effectiveness of the control strategy to maintain the load voltage and frequency at a constant level under different operating conditions. This has been achieved by controlling the duty cycle of the employed DC-DC boost converter in order to maintain the DC-link voltage constant at a predetermined value. In addition, the magnitude and frequency of the load voltage has been maintained constant via controlling the modulation index of the load-side SPWM inverter. A constant modulation index has been used in the case of balanced loading conditions. However, different modulation index for each phase has been used in case of unbalanced loading conditions.

REFERENCES:

[1] Aditya Venkataraman, Ali Maswood, Nirnaya Sarangan, Ooi H.P. Gabriel "An Efficient UPF Rectifier for a Stand-Alone Wind Energy Conversion System," IEEE Trans. on industry applications, vol. 50, NO.2, Marsh/April. 2014

[2] Y. Izumi, A. Pratap, K. Uchida, A. Uehara, T. Senjyu, A. Yona, "A control method for maximum power point tracking of a PMSG-based WECS using online parameter identification of wind turbine," Proc. Of the IEEE 9th International Conf. on Power Electronics and Drives Systems, Singapore, 5–8 Dec. 2011, pp. 1125–1130.

[3] M. Singh, A. Chandra, B. Singh, “Sensorless power maximization of PMSG based isolated wind-battery hybrid system using adaptive neuro fuzzy controller,” IEEE Ind. Appl. Soc. Annual Meeting, 2010, pp. 1-6.

[4] Nishad Menddis, Kashem M. Muttaqi, Sarath Perara "Management of Battery-Supercapacitor Hybrid Energy Storage and Synchronous Condenser for Isolated Operation of PMSG Based Variable-speed wind Turbine Generating Systems"IEEE Trans. ON SMART GRID, vol. 5, NO.2, MARCH 2014

[5] Luminita BAROTE, Corneliu MARINESCU "Modeling and Operational Testing of an Isolated Variable Speed PMSG Wind Turbine with Battery Energy Storage," Advances in Electrical and Computer Engineering, vol. 12, No. 2, 2012. For equivalent circuit of PMSG