Elimination of Harmonics in a Five-Level Diode-Clamped Multilevel Inverter Using Fundamental Modulation

ABSTRACT:

In this study, elimination of harmonics in a five level diode-clamped multilevel inverter (DCMLI) has been implemented by using fundamental modulation switching. The proposed method eliminates harmonics by generating negative harmonics with switching angles calculated for selective harmonic elimination method. In order to confirm the proposed method, first Matlab/ Simulink and PSIM simulation results are given. Then the proposed method is also validated by experiments with Opal-RT controller and a 10 kW three phase, five-level DCMLI prototype.

KEYWORDS:

1.      Fundamental switching

2.      Harmonic elimination

3.      Multilevel inverter.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT  DIAGRAM:

EXPECTED SIMULATION RESULTS:

CONCLUSION:

The selected harmonic elimination is a popular issue in multilevel inverter design. The proposed selective harmonic elimination method for DCMLI has been validated in both simulation and experiment. The simulation and experimental results show that the proposed algorithm can be used to eliminate any number of specific lower order harmonics effectively and results in a dramatic decrease in the output voltage THD. In the proposed harmonic elimination method, the lower order harmonic distortion is largely reduced in fundamental switching. Furthermore, in the experiments reported here, an induction motor load is connected to the three-phase five-level DCMLI, and the current as well as the voltage waveforms are collected for analysis. The FFTs of these waveforms show that their harmonic content is close to the simulated values.

REFERENCES:

[1] J. Rodríguez, J. S. Lai, F. Z. Peng, “Multilevel inverters: a survey of topologies, controls, and applications,” IEEE Transactions on Industrial Electronics, vol.49, no.4, pp. 724-738, 2002.

[2] J. S. Lai, F. Z. Peng, “Multilevel converters-a new breed of power converters,” IEEE Transactions on Industry Applications, vol. 32, no.3, pp. 509-517, 1996.

[3] L. M. Tolbert, F. Z. Peng, T. G. Habetler, “Multilevel converters for large electric drives,” IEEE Transactions on Industry Applications, vol. 35, no. 1, pp. 36–44, Jan./Feb. 1999.

[4] S. Khomfoi, L. M. Tolbert, “Multilevel Power Converters,” Chapter 17, Power Electronics Handbook, 2nd Edition, Elsevier, ISBN 978-0- 12-088479-7, pp. 451-482, 2007.

[5] J. N. Chiasson, L. M. Tolbert, K. J. McKenzie, Z. Du, “A complete solution to the harmonic elimination problem,” IEEE Transactions on Power Electronics, vol. 19, no. 2, pp. 491-499, 2004.

Quasi Current Mode Control for the Phase-Shifted

Series Resonant Converter

ABSTRACT:

A novel indirect current mode control is applied in the phase-shifted series resonant converter system. The current is generated from resonant tank vector and the resonant current is regulated indirectly through quasi current mode control and thus the dynamic performance of the converter system is improved. Only single voltage feedback is required for the system. The proposed system consists of two control loops with one inner resonant vector and one outer voltage loop. Analysis and practical experiments are carried out and the results show the better performance compared with that of the conventional control.

KEYWORDS:

1.      Dynamic performance

2.      Dynamic response

3.      Phase shifted series resonant converter (PSRC)

4.       Quasi current mode control.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

BLOCK DIAGRAM:

EXPECTED SIMULATION RESULTS:

CONCLUSION:

The proposed control method based on the indirectly regulation of the resonant current is applied to the phase-shifted resonant converter. Only single voltage feedback is needed and it is converted to resonant tank vector components. Thus the output voltage is controlled more effectively and the dynamic performance is improved. Better performance has been verified through system analysis and experiments. In addition, the construction of the reformed control system is simple because only single voltage sensor is required. No current sensor is needed and the reformed control is monitored internally through quasi current vector.

REFERENCES:

[1] D. M. Sable and F. C. Lee, “The operation of a full bridge, zero voltage switched PWM converter,” in Proc. Virginia Power Electron. Ctr. Sem., 1989, pp. 92–97.

[2] A. J. Forsyth, P. D. Evans, M. R. D. Al-Mothafar, and K. W. E. Cheng, “A comparison of phase-shift controlled resonant and square-wave converters for high power ion engine control,” in Proc. Eur. Space Power Conf., 1991, pp. 179–185.

[3] H. L. Chan, K. W. E. Cheng, and D. Sutanto, “Phase-shift controlled DC-DC converter with bi-directional power flow,” Proc. Inst. Elect. Eng., vol. 148, no. 2, pp. 193–201, Mar. 2001.

[4] A. J. Forsyth, P. D. Evans, K. W. E. Cheng, and M. R. D. Al-Mothafar, “Operating limits of power converters for high power ion engine control,” in Proc. 22nd Int. Elect. Propul. Conf., 1991, [CD ROM].

[5] R. L. Steigerwald, “A comparison of half-bridge resonant converter topologies,” IEEE Trans. Power Electron., vol. PE-3, no. 2, pp. 174–182, Apr. 1988.

System Simulation of 3-phase PWM Rectifier Based on Novel Voltage Space Vector

ABSTRACT:

A novel voltage space vector control method based on Hysteresis Current Control is proposed. This method gives the optimal space vector by detecting the current error space vector and the system reference voltage space vector, and then controls the current error below the hysteresis width. Voltage space vector is introduced into the control system to eliminate the phase interference, and it can be realized simply without complicated vector transform. The proposed method has fast current response, and can limit the current error and the switching frequency with good current tracking performance. The system Mathematical mode is set up in this paper. The validity of the mathematical model and its control method are confirmed by MAT-LAB/SIMULINK simulation.

SOFTWARE: MATLAB/SIMULINK

  

BLOCK DIAGRAM:

EXPECTED SIMULATION RESULTS:

CONCLUSION:

In this paper a novel SVM-Based Hysteresis Current Control for 3-phase PWM VSR is suggested, which utilizes all advantages of the HCC and SVM technique. This method gives the optimal space vector by detecting the current error space vector and the system reference voltage space vector, and then controls the current error below the hysteresis width. The method can reduce the switching frequency, and has good current tracking performance. The validity of the mathematical model and its control method are confirmed by MAT-LAB/SIMULINK simulation.

REFERENCES:

[1] J. W. Dixon and B. T. Ooi, “Indirect current control of unity power factor sinusoidal current boost type three-phase rectifier,” IEEE Transactions on Industrial Electronics, vol. 35, no. 4, pp. 508-515, Nov. 1988.

[2] M. P. Kazmierkowski and L. Malesani, “Current control techniques for three-phase voltage-source PWM converters: A Surrey,” IEEE Transactions on Industrial Electronics, vol. 45, no. 5, pp. 691-703, Oct. 1998.

[3] B. T. Ooi, J. C. Salmon, J. W. Dixon, and A. B. Kulkarni, “A three phase controlled current PWM convert with leading power factor,” IEEE Transactions on Industry Applications, vol. IA-23, no. 1, pp. 78-84, 1987.

[4] R. Wu, S. B. Dewan, and G. R. Slemon, “PWM AC-to-DC converter with fixed switching frequency,” IEEE Transactions on Industry Applications, vol. 26, no. 5, pp. 880-885, Sep-Oct, 1990.

[5] T. G. Habetler, “A space vecter-based rectifier regulator for AC/DC/AC converters,” IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 30-36, Jan. 1993.

Improving the Dynamic Performance of Wind

Farms with STATCOM

ABSTRACT:

When integrated to the power system, large wind farms can pose voltage control issues among other problems. A thorough study is needed to identify the potential problems and to develop measures to mitigate them. Although integration of high levels of wind power into an existing transmission system does not require a major redesign, it necessitates additional control and compensating equipment to enable (fast) recovery from severe system disturbances. The use of a Static Synchronous Compensator (STATCOM) near a wind farm is investigated for the purpose of stabilizing the grid voltage after grid-side disturbance such as a three phase short circuit fault. The strategy focuses on a fundamental grid operational requirement to maintain proper voltages at the point of common coupling by regulating the voltage. The DC voltage at individual wind turbine (WT) inverters is also stabilized to facilitate continuous operation of wind turbines during disturbances.

KEYWORDS:

1.      Wind turbine

2.      Doubly-fed Induction Generator

3.      STATCOM

4.      Three phase fault

5.      Reactive power support.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

EXPECTED SIMULATION RESULTS:

CONCLUSION:

Wind turbines have to be able to ride through a fault without disconnecting from the grid. When a wind farm is connected to a weak power grid, it is necessary to provide efficient power control during normal operating conditions and enhanced support during and after faults. This paper explored the possibility of connecting a STATCOM to the wind power system in order to provide efficient control. An appropriately sized STATCOM can provide the necessary reactive power compensation when connected to a weak grid. Also, a higher rating STATCOM can be used for efficient voltage control and improved reliability in grid connected wind farm but economics limit its rating. Simulation studies have shown that the additional voltage/var support provided by an external device such as a STATCOM can significantly improve the wind turbine’s fault recovery by more quickly restoring voltage characteristics. The extent to which a STATCOM can provide support depends on its rating. The higher the rating, the more support provided. The interconnection of wind farms to weak grids also influences the safety of wind turbine generators. Some of the challenges faced by wind turbines connected to weak grids are an increased number and frequency of faults, grid abnormalities, and voltage and frequency fluctuations that can trip relays and cause generator heating.

REFERENCES:

 [1] http://www.awea.org/newsroom/releases/Wind_Power_Capacity_012307. html, accessed Nov. 2007.

[2] T. Sun, Z. Chen, F. Blaabjerg, “Voltage recovery of grid-connected wind turbines with DFIG after a short-circuit fault,” 2004 IEEE 35th Annual Power Electronics Specialists Conf., vol. 3, pp. 1991-97, 20-25 June 2004.

[3] E. Muljadi, C.P. Butterfield, “Wind Farm Power System Model Development,” World Renewable Energy Congress VIII, Colorado, Aug- Sept 2004.

[4] S.M. Muyeen, M.A. Mannan, M.H. Ali, R. Takahashi, T. Murata, J. Tamura, “Stabilization of Grid Connected Wind Generator by STATCOM,” IEEE Power Electronics and Drives Systems Conf., Vol. 2, 28-01 Nov. 2005.

[5] Z. Saad-Saoud, M.L. Lisboa, J.B. Ekanayake, N. Jenkins, G. Strbac, “Application of STATCOMs to wind farms,” IEE Proceedings – Generation, Transmission, Distribution, vol. 145, pp.1584-89, Sept 1998.

A Versatile Control Scheme for a Dynamic Voltage

Restorer for Power-Quality Improvement

ABSTRACT:

This paper presents a control system based on a repetitive controller to compensate for key power-quality disturbances, namely voltage sags, harmonic voltages, and voltage imbalances, using a dynamic voltage restorer (DVR). The control scheme deals with all three disturbances simultaneously within a bandwidth. The control structure is quite simple and yet very robust; it contains a feed forward term to improve the transient response and a feedback term to enable zero error in steady state. The well-developed graphical facilities available in PSCAD/EMTDC are used to carry out all modeling aspects of the repetitive controller and test system. Simulation results show that the control approach performs very effectively and yields excellent voltage regulation.

KEYWORDS:

1.      Dynamic voltage restorer (DVR)

2.      Harmonic distortion

3.      Power quality (PQ)

4.      Repetitive control

5.      Voltage sag.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

EXPECTED SIMULATION RESULTS:

CONCLUSION:

The use of dynamic voltage restorers in PQ-related applications is increasing. The most popular application has been on voltage sags amelioration but other voltage-quality phenomena may also benefit from its use, provided that more robust control schemes than the basic PI controller become available. A case in point is the so called repetitive controller proposed in this paper, which has a fast transient response and ensures zero error in steady state for any sinusoidal reference input and for any sinusoidal disturbance whose frequencies are an integer multiple of the fundamental frequency. To achieve this, the controller has been provided with a feed forward term and feedback term. The design has been carried out by studying the stability of the closed loop system including possible modeling errors, resulting in a controller which possesses very good transient and steady-state performances for various kinds of disturbances. A key feature of this control scheme is its simplicity; only one controller is required to eliminate three PQ disturbances, namely, voltage sags, harmonic voltages, and voltage imbalances. The controller can be implemented by using either a stationary reference frame or a rotating reference frame. In this paper, the highly developed graphical facilities available in PSCAD/EMTDC have been used very effectively to carry out all aspects of the system implementation. Comprehensive simulation results using a simple but realistic test system show that the repetitive controller and the DVR yield excellent voltage regulation, thus screening a sensitive load point from upstream PQ disturbances.

REFERENCES:

[1] M. H. J. Bollen, “What is power quality?,” Elect. Power Syst. Res., vol. 66, no. 1, pp. 5–14, July 2003.

[2] J. G. Nielsen and F. Blaabjerg, “A detailed comparison of system topologies for dynamic voltage restorers,” IEEE Trans. Ind. Appl., vol. 41, no. 5, pp. 1272–1280, Sep./Oct. 2005.

[3] V. K. Ramachandaramurthy, A. Arulampalam, C. Fitzer, C. Zhan, M. Barnes, and N. Jenkins, “Supervisory control of dynamic voltage restorers,” Proc. Inst. Elect. Eng., Gen., Transm. Distrib, vol. 151, no. 4, pp. 509–516, Jul. 2004.

[4] P. T. Nguyen and T. K. Saha, “Dynamic voltage restorer against balanced and unbalanced voltage sags: Modelling and simulation,” in Proc. IEEE Power Eng. Soc. General Meeting, Jun. 2004, vol. 1, pp. 639–644, IEEE.

[5] M. H. J. Bollen, Understanding Power Quality Problems: Voltage Sags and Interruptions.. Piscataway, NJ: IEEE Press, 2000.

Natural Harmonic Elimination of Square-Wave Inverter for Medium-Voltage Application

ABSTRACT:

In this paper, a low-frequency square-wave inverter with a series-connected pulse width modulation (PWM) inverter is investigated for high-power applications. The series compensators produce only the desired harmonic voltages to make the net output voltage sinusoidal with small PWM switching harmonics only. An open-loop control strategy for the series compensator is proposed in this paper. This strategy indirectly sets the compensator dc bus voltage to the desired level. No external dc source or active power at fundamental frequency is required to control this dc bus voltage. Different variations of this basic strategy are presented in this paper for medium voltage applications. Theoretical analysis of this strategy is presented in this paper with simulation and experimental results.

KEYWORDS:

1.      AC motor drives

2.      Power conversion

3.      Power conversion harmonics.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 EXPECTED SIMULATION RESULTS:

CONCLUSION:

In this paper, an open-loop natural control of voltage source inverter has been proposed mainly for high-power applications. The main square-wave inverter is built with high-voltage low switching- frequency semiconductor devices like integrated gate commutated thyristors (IGCTs). The series compensators are IGBT-based inverters and operate from relatively low dc bus voltages at high switching frequencies. The series compensators produce only the desired harmonic voltages to make the net output voltage sinusoidal. For medium-voltage application, several compensating PWM inverters are connected in series. Each cell compensates one particular harmonic only. As the order of harmonics increases, the required dc bus voltage level drops. This enables to exploit higher switching frequency for higher order harmonic cell. It has been established both theoretically and experimentally that the dc bus of the compensators do not require any external dc source or closed-loop controller for this proposed strategy. The active power at harmonic frequencies keeps the compensator dc bus voltage charged. For variable speed drives applications, the magnitude of the fundamental output voltage should be controlled by regulating the dc bus voltage of the square-wave inverter. For static synchronous compensator (STATCOM) applications, the limited variation of this dc bus voltage may also be required. This can be achieved by drawing small active power at fundamental frequency from the grid.

REFERENCES:

 [1] A. Nabae, I. Takahashi, and H. Akagi, “A new neutral point clamped PWM inverter,” IEEE Trans. Ind. Appl., vol. IA-17, no. 5, pp. 518–523, Sept./Oct. 1981.

[2] M. D.Manjrekar, P. K. Steimer, and T. A. Lipo, “Hybrid multilevel power conversion system: A competitive solution for high-power applications,” IEEE Trans. Ind. Appl., vol. 36, no. 3, pp. 834–841, May/Jun. 2000.

[3] R. H. Wilkinson, T. A. Meynard, and H. du T. Mouton, “Natural balance of multicell converters: The general case,” IEEE Trans. Power Electron., vol. 21, no. 6, pp. 1649–1657, Nov. 2006.

[4] H. Akagi, S. Inoue, and T. Yoshii, “Control and performance of a transformer less cascade PWM STATCOM with star configuration,” IEEE Trans. Ind. Appl., vol. 43, no. 4, pp. 1041 1049, Jul./Aug. 2007.

[5] S. S. Fazel, S. Bernet, D. Krug, and K. Jalili, “Design and comparison of 4-kV neutral-point-clamped, flying-capacitor, and series-connected Hbridge multilevel converters,” IEEE Trans. Ind. Appl., vol. 43, no. 4, pp. 1032–1040, Jul./Aug. 2007.

Improved Z-Source Inverter with Reduced Z-Source Capacitor Voltage Stress and Soft-Start Capability

ABSTRACT:

This paper proposes an improved Z-source inverter topology. Compared to the traditional Z source inverter, it can reduce the Z-source capacitor voltage stress significantly to perform the same voltage boost, and has inherent limitation to inrush current at startup. The control strategy of the proposed Z-source inverter is exactly the same as the traditional one, so all the existing control strategy can be used directly. A soft-start strategy is also proposed to suppress the inrush surge and the resonance of Z-source capacitors and inductors. The operation principle of the proposed topology and comparison with the traditional topology are analyzed in detail. Simulation and experimental results are given to demonstrate the new features of the improved topology.

KEYWORDS:

1.      Inrush current

2.      Soft start

3.      Z-source inverter.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 EXPECTED SIMULATION RESULTS:

CONCLUSION:

This paper has presented a new Z-source inverter topology. Compared to the previous Z-source inverter, the improved topology has several merits.

1) The Z-source capacitor voltage stress is reduced greatly to perform the same boost ability; thus, low-voltage capacitors can be utilized to reduce the system cost and volume;

2) The inrush current and resonance of Z-source capacitors and inductors in traditional topology can be suppressed with a proper soft-start strategy. Simulation and experimental results verified the aforesaid merits of the proposed topology.

REFERENCES:

 [1] F. Z. Peng, “Z-source inverter,” IEEE Trans. Ind. Appl., vol. 39, no. 2, pp. 504–510, Mar./Apr. 2003.

[2] Q. Tran, T. Chun, J. Ahn, and H. Lee, “Algorithms for controlling both the DC boost and AC output voltage of Z-source inverter,” IEEE Trans. Ind. Electron., vol. 54, no. 5, pp. 2745–2750, Oct. 2007.

[3] F. Z. Peng, M. Shen, and Z. Qian, “Maximum boost control of the Z-source inverter,” IEEE Trans. Power Electron., vol. 20, no. 4, pp. 833–838, Jul. 2005.

[4] M. Shen, J. Wang, A. Joseph, F. Z. Peng, L. M. Tolbert, and D. J. Adams, “ConstantBoost control of the Z-source inverter to minimize current ripple and voltage stress,” IEEE Trans. Ind. Appl., vol. 42, no. 3, pp. 770–777, May/Jun. 2006.

[5] P. C. Loh, D. M. Vilathgamuwa, Y. S. Lai, G. T. Chua, and Y. Li, “Pulsewidth modulation of Z-source inverters,” IEEE Trans. Power Electron., vol. 20, no. 6, pp. 1346–1355, Nov. 2005.