Permanent Magnet Synchronous Generator-Based Standalone Wind Energy Supply System

ABSTRACT:

In this paper, a novel algorithm, based on dc link voltage, is proposed for effective energy management of a standalone permanent magnet synchronous generator (PMSG)-based variable speed wind energy conversion system consisting of battery, fuel cell, and dump load (i.e., electrolyzer). Moreover, by maintaining the dc link voltage at its reference value, the output ac voltage of the inverter can be kept constant irrespective of variations in the wind speed and load. An effective control technique for the inverter, based on the pulse width modulation (PWM) scheme, has been developed to make the line voltages at the point of common coupling (PCC) balanced when the load is unbalanced. Similarly, a proper control of battery current through dc–dc converter has been carried out to reduce the electrical torque pulsation of the PMSG under an unbalanced load scenario. Based on extensive simulation results using MATLAB/SIMULINK, it has been established that the performance of the controllers both in transient as well as in steady state is quite satisfactory and it can also maintain maximum power point tracking.

KEYWORDS:

1.      DC-side active filter

2.      Permanent magnet synchronous generator (PMSG)

3.      Unbalanced load compensation

4.      Variable speed wind turbine

5.      Voltage control

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. PMSG-based standalone wind turbine with energy storage and dump load.

EXPERIMENTAL RESULTS:

Fig. 2. Response of mechanical torque for change in wind velocity.

Fig. 3. (a) Load current; (b) wind speed.

Fig. 4. DC link voltage.

Fig. 5. RMS output voltage (PCC voltage).

Fig. 6. Instantaneous output voltage at s.

Fig. 7. Instantaneous output line current.

Fig. 8. Powers.

Fig. 9. Powers.

Fig. 10. DC link voltage.

Fig. 11. Powers.

Fig. 12. DC link voltage.

Fig. 13. Response of controllers.

Fig. 14. Three phase currents for unbalanced load.

Fig. 15. Electrical torque of PMSG with and without dc–dc converter controller.

Fig. 16. Instantaneous line voltages at PCC for unbalanced load.

Fig. 17. (a) RMS value of line voltages at PCC after compensation; (b) modulation

indexes.

Fig. 18. Instantaneous line voltages at PCC after compensation.

CONCLUSION:

Control strategies to regulate voltage of a standalone variable speed wind turbine with a PMSG, battery, fuel cell, and electrolyzer (acts as dump load) are presented in this paper. By maintaining dc link voltage at its reference value and controlling modulation indices of the PWM inverter, the voltage of inverter output is maintained constant at their rated values. From the simulation results, it is seen that the controller can maintain the load voltage quite well in spite of variations in wind speed and load. An algorithm is developed to achieve intelligent energy management among the wind generator, battery, fuel cell, and electrolyzer. The effect of unbalanced load on the generator is analyzed and the dc–dc converter control scheme is proposed to reduce its effect on the electrical torque of the generator. The dc–dc converter controller not only helps in maintaining the dc voltage constant but also acts as a dc-side active filter and reduces the oscillations in the generator torque which occur due to unbalanced Load. PWM inverter control is incorporated to make the line voltage at PCC balanced under an unbalanced load scenario. Inverter control also helps in reducing PCC voltage excursion arising due to slow dynamics of aqua elctrolyzer when power goes to it. The total harmonic distortion (THD) in voltages at PCC is about 5% which depicts the good quality of voltage generated at the customer end. The simulation results demonstrate that the performance of the controllers is satisfactory under steady state as well as dynamic conditions and under balanced as well as unbalanced load conditions.

REFERENCES:

[1] S. Müller, M. Deicke, and W. De DonckerRik, “Doubly fed induction generator system for wind turbines,” IEEE Ind. Appl. Mag., vol. 8, no. 3, pp. 26–33, May/Jun. 2002.

[2] H. Polinder, F. F. A. van der Pijl, G. J. de Vilder, and P. J. Tavner, “Comparison of direct-drive and geared generator concepts for wind turbines,” IEEE Trans. Energy Convers., vol. 21, no. 3, pp. 725–733, Sep. 2006.

[3] T. F. Chan and L. L. Lai, “Permanent-magnet machines for distributed generation: A review,” in Proc. 2007 IEEE Power Engineering Annual  Meeting, pp. 1–6.

[4] M. Fatu, L. Tutelea, I. Boldea, and R. Teodorescu, “Novel motion sensorless control of stand alone permanent magnet synchronous generator (PMSG): Harmonics and negative sequence voltage compensation under nonlinear load,” in Proc. 2007 Eur. Conf. Power Electronics and Applications, Aalborg, Denmark, Sep. 2–5, 2007.

[5] M. E. Haque, K. M. Muttaqi, and M. Negnevitsky, “Control of a stand alone variable speed wind turbine with a permanent magnet synchronous generator,” in Proc. IEEE Power and Energy Society General Meeting, Jul. 2008, pp. 20–24.

An Efficient UPF Rectifier for a Stand-Alone Wind Energy Conversion System

ABSTRACT:

 In this paper, a near-unity-power-factor front-end rectifier employing two current control methods, namely, average current control and hysteresis current control, is considered. This rectifier is interfaced with a fixed-pitch wind turbine driving a permanent-magnet synchronous generator. A traditional diode-bridge rectifier without any current control is used to compare the performance with the proposed converter. Two constant wind speed conditions and a varying wind speed profile are used to study the performance of this converter for a rated stand-alone load. The parameters under study are the input power factor and total harmonic distortion of the input currents to the converter. The wind turbine generator–power electronic converter is modeled in PSIM, and the simulation results verify the efficacy of the system in delivering satisfactory performance for the conditions discussed. The efficacy of the control techniques is validated with a 1.5-kW laboratory prototype, and the experimental results are presented.

KEYWORDS:

1.      Average current control (ACC)

2.      Hysteresis current control (HCC)

3.      Permanent-magnet synchronous generator (PMSG)

4.      Unity-power-factor (UPF) converter

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Schematic of the UPF converter in the wind generator system employing

the ACC method.

Fig. 2. Schematic of the UPF converter in the wind generator system employing the HCC method.

EXPERIMENTAL RESULTS:

Fig. 3. Performance parameters of the UPF rectifier using ACC at a rated wind speed of 12 m/s. (a) Input power factor of the front-end rectifier employing  ACC at a rated wind speed of 12 m/s. (b) FFT of phase “a” current to frontend rectifier employing ACC at a rated wind speed of 12 m/s. (c) Mechanical, PMSG, and dc output powers of the system employing ACC at a rated wind of speed 12 m/s. (d) DC bus capacitor voltages of the system employing ACC at a rated wind speed of 12 m/s.

Fig. 4. Performance parameters of the UPF rectifier employing ACC at a wind speed of 14 m/s. (a) Input power factor of the front-end rectifier employing ACC at a wind speed of 14 m/s. (b) FFT of phase “a” current to front-end rectifier employing ACC at a wind speed of 14 m/s. (c) Mechanical, PMSG, and dc output powers of the system employing ACC at a wind speed of 14 m/s.

Fig. 5. Wind speed variation and performance coefficient of wind turbine for

system operating with ACC.

Fig. 6. Performance parameters of the UPF rectifier using HCC at a rated wind speed of 12 m/s. (a) Input power factor of the front-end rectifier employing HCC at a rated wind speed of 12 m/s. (b) FFT of phase “a” current to frontend rectifier for HCC at a rated wind speed of 12 m/s. (c) Mechanical, PMSG, and dc output powers of the system for HCC at a rated wind speed of 12 m/s. (d) DC bus capacitor voltages for HCC at a rated wind speed of 12 m/s.

Fig. 7 Performance parameters of the UPF rectifier using HCC at a wind speed of 14 m/s. (a) Input power factor of the front-end rectifier employing HCC at a higher wind speed of 14 m/s. (b) FFT of phase “a” current to frontend rectifier for HCC at a higher wind speed of 14 m/s. (c) Mechanical, PMSG, and dc output powers of the system for HCC at a higher wind speed of 14 m/s.

Fig. 8.Wind speed variation and performance coefficient of wind turbine for

system operating with HCC.

Fig. 9. Performance parameters of the diode-bridge rectifier at a rated wind speed of 12 m/s. (a) Input power factor of the front-end diode-bridge rectifier at a rated wind speed of 12 m/s. (b) FFT of phase “a” current of front-end diode bridge rectifier at a rated wind speed of 12 m/s. (c) Mechanical, PMSG, and dc output powers of the system for front-end diode-bridge rectifier at a rated wind speed of 12 m/s.

Fig. 10. Wind speed variation and performance coefficient of wind turbine for

system operating without current control.

CONCLUSION:

In this paper, a WECS interfaced with a UPF converter feeding a stand-alone load has been investigated. The use of simple bidirectional switches in the three-phase converter results in near-UPF operation. Two current control methods, i.e., ACC and HCC, have been employed to perform active input line current shaping, and their performances have been compared for different wind speed conditions. The quality of the line currents at the input of the converter is good, and the harmonic distortions are within the prescribed limits according to the IEEE 519 standard for a stand-alone system. A high power factor is achieved at the input of the converter, and the voltage maintained at the dc bus link shows excellent voltage balance. The proposed method yields better performance compared to a traditional uncontrolled diode bridge rectifier system typically employed in wind systems as the front-end converter. Finally, a laboratory prototype of the UPF converter driving a stand-alone load has been developed, and the ACC and HCC current control methods have been tested for comparison. The HCC current control technique was found to be superior and  has better voltage balancing ability. It can thus be an excellent front-end converter in a WECS for stand-alone loads or grid connection.

REFERENCES:

[1] C. E. A. Silva, D. S. Oliveira, L. H. S. C. Barreto, and R. P. T. Bascope, “A novel three-phase rectifier with high power factor for wind energy conversion systems,” in Proc. COBEP, Bonito-Mato Grosso do Sul, Brazil, 2009, pp. 985–992.

[2] Online. Available: http://en.wikipedia.org/wiki/Wind_energy

[3] M. Druga, C. Nichita, G. Barakat, B. Dakyo, and E. Ceanga, “A peak power tracking wind system operating with a controlled load structure for stand-alone applications,” in Proc. 13th EPE, 2009, pp. 1–9.

[4] S. Kim, P. Enjeti, D. Rendusara, and I. J. Pitel, “A new method to improve THD and reduce harmonics generated by a three phase diode rectifier type utility interface,” in Conf. Rec. IEEE IAS Annu. Meeting, 1994, vol. 2, pp. 1071–1077.

[5] A. I. Maswood and L. Fangrui, “A novel unity power factor input stage for AC drive application,” IEEE Trans. Power Electron., vol. 20, no. 4, pp. 839–846, Jul. 2005.

Development of High-Performance Grid-Connected Wind Energy Conversion System for Optimum Utilization of Variable Speed Wind Turbines

ABSTRACT:

This paper presents an improvement technique for the power quality of the electrical part of a wind generation system with a self-excited induction generator (SEIG) which aims to optimize the utilization of wind power injected into weak grids. To realize this goal, an uncontrolled rectifier-digitally controlled inverter system is proposed. The advantage of the proposed system is its simplicity due to fewer controlled switches which leads to less control complexity. It also provides full control of active and reactive power injected into the grid using a voltage source inverter (VSI) as a dynamic volt ampere reactive (VAR) compensator. A voltage oriented control (VOC) scheme is presented in order to control the energy to be injected into the grid. In an attempt to minimize the harmonics in the inverter current and voltage and to avoid poor power quality of the wind energy conversion system (WECS), an filter is inserted between VOC VSI and the grid. The proposed technique is implemented by a digital signal processor (DSP TMS320F240) to verify the validity of the proposed model and show its practical superiority in renewable energy applications.

KEYWORDS:

1.      Grid connected systems

2.      Self-excited induction generator (SEIG)

3.      Voltage oriented control (VOC)

4.      Voltage source inverter (VSI)

5.      Wind energy conversion systems (WECSs)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Proposed SEIG-based WECS with VOC VSI.

 EXPERIMENTAL RESULTS:

Fig. 2. Line voltage of theVSI in frame (400 V/div–5ms). (a) Simulation.

(b) Experiment.

Fig. 3. Phase voltage of the VSI in frame (400 V/div–5 ms). (a) Simulation.

(b) Experiment.

Fig. 4. Grid phase voltage (50 V/div–10 ms) and injected current

(1 A/div–10 ms). (a) Simulation. (b) Experiment.

Fig. 5. Inverter phase voltage to be connected to the grid with only filter

(50 V/div–10 ms). (a) Simulation. (b) Experiment.

Fig. 6. Grid voltage (50 V/div–25 ms) and injected current (1 A/div–25 ms)

under step change in the reactive power injected into grid. (a) Simulation.

(b) Experiment.

Fig. 7. VSI response with filter for the grid and capacitor voltage

(100 V/div–10 ms) with the injected line current (5 A/div–10 ms). (a) Simulation.

(b) Experiment.

Fig. 8. Harmonic spectrum analysis with filter. (a) Injected current harmonic

content. (b) Filter capacitor voltage harmonic content.

CONCLUSION:

In this paper, the SEIG-based WECS dynamic model has been derived. The VOC grid connected VSI has been investigated for high performance control operation. The test results showed how the control scheme succeeded in injecting the wind power as active or reactive power in order to compensate the weak grid power state. An filter is inserted between VOC VSI and grid to obtain a clean voltage and current waveform with negligible harmonic content and improve the power quality. Also, this technique achieved unity power factor grid operation (average above 0.975), very fast transient response within a fraction of a second (0.4 s) under different possible conditions (wind speed variation and load variation), and high efficiency due to a reduced number of components (average above 90%) has been achieved. Besides the improvement in the converter efficiency, reduced mechanical and electrical stresses in the generator are expected, which improves the overall system performance. The experimental results obtained from a prototype rated at 250 W showed that the current and voltage THD (2.67%, 0.12%), respectively, for the proposed WECS with filter is less than 5% limit imposed by IEEE-519 standard. All results obtained confirm the effectiveness of the proposed system feasible for small-scale WECSs connected to weak grids.

REFERENCES:

[1] V. Kumar, R. R. Joshi, and R. C. Bansal, “Optimal control of matrix-converter-based WECS for performance enhancement and efficiency optimization,” IEEE Trans. Energy Convers., vol. 24, no. 1, pp. 264–272, Mar. 2009.

[2] Y. Zhou, P. Bauer, J. A. Ferreira, and J. Pierik, “Operation of grid connected DFIG under unbalanced grid voltage,” IEEE Trans. Energy Convers., vol. 24, no. 1, pp. 240–246, Mar. 2009.

[3] S. M. Dehghan, M.Mohamadian, and A. Y. Varjani, “A new variable speed wind energy conversion system using permanent-magnet synchronous generator and z-source inverter,” IEEE Trans Energy Convers., vol. 24, no. 3, pp. 714–724, Sep. 2009.

[4] K. Tan and S. Islam, “Optimum control strategies for grid-connected wind energy conversion system without mechanical sensors,” WSEAS Trans. Syst. Control, vol. 3, no. 7, pp. 644–653, Jul. 2008, 1991-8763.

[5] B. C. Rabelo, W. Hofmann, J. L. da Silva, R. G. de Oliveira, and S. R. Silva, “Reactive power control design in doubly fed induction generators for wind turbines,” IEEE Trans. Ind. Elect., vol. 56, no. 10, pp. 4154–4162, Oct. 2009.