Variable Switching Frequency PWM Strategy of Two-Level Rectifier for DC-link Voltage Ripple Control

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ABSTRACT

The switching frequency is an important control parameter of P WM rectifier to reduce switching losses and E MI noise. This paper proposed a variable switching frequency P WM (VS F P WM) strategy for DC-link voltage ripple control in two-level rectifier. DC-link current directly determines the DC-link voltage ripple, and predicts synchronously with P WM signals. A real-time prediction model of DC-link voltage ripple is derived for a common voltage oriented control (V O C) P WM rectifier.

Then,

introduced a VS F P WM control, which changes the switching frequency cycle to cycle with a restriction of DC-link voltage ripple peak value. Furthermore, also observes the dynamic behavior with  the adoption of the proposed VS F P WM control scheme. Detail simulation and experimental comparisons between V S F P WM and normal constant switching frequency P WM (CS F P WM) demonstrate the advantages of the proposed method.

 

BLOCK DIAGRAM:

Fig.1 Control structure of A FE rectifier

EXPECTED SIMULATION RESULTS

Fig.2 Comparison between the prediction and the simulation results of the

DC-link voltage ripple in one line-cycle

Fig.3 DC-link voltage ripple comparison

Fig.4 Switching frequency comparison

Fig.5 AC-side current

Fig.6 Spectrum comparison (a) AC-side (2) DC-link

Fig.7 Step response (a) Step response of DC-link voltage (f) The change of switching frequency with VS F P WM

CONCLUSION

The contribution of this paper is to develop the VS F P WM strategy for DC-link voltage ripple control. Different from the previous work on the AC-side current ripple or torque ripple, P WM current ripple of AC-side does not affects the DC-link voltage ripple. In a rectifier system, P WM method determines the DC-link voltage ripple and load current, and the peak value of it is important for DC-link capacitor design or selection. The proposed VS F P WM fully utilizes the freedom of switching frequency, which is often neglected in the P WM module.

However,

the proposed VS F P WM is different from the random P WM [24], which changes the switching frequency based on the statistics and no prediction model is used. It should be noted that the proposed technique can be applied to a different power factor than the unitary one and not can be applied direct to the rectifier with neutral wire (four wire). Few conclusions can be derived as follows:

(1)

DC-link voltage ripple prediction model can be built in the time-based-domain. With the three-phase duty cycles, AC-side current and load current measured by the current sensors, the DC-link voltage ripple peak can be predicted for updating the switching frequency in next cycle. The prediction method also applies to other P WM methods, and also be used for design and analysis of DC capacitors and DC battery reliability.

(2)

In a whole line period, the switching frequency of VS F P WM continuously varies below the designed constant switching frequency, keeping the DC-link voltage ripple always under the requirement. Using the proposed VS F P WM strategy, the switching losses decrease significantly, and E MI noise reduces markedly.

(3)

Typical closed-loop control system  investigates the dynamic property of VS F P WM. In fact, VS F P WM still has a good dynamic response, without nearly impairing the tracking performance shown in common CS F P WM. The open-loop Bode plot indicates the VS F P WM methods just decrease a little bit of bandwidth of both voltage control loop and the current in CS F P WM because of the reduction of average switching frequency.

 

REFERENCES

[1] J. Rodriguez, J. Dixon, J. Espinoza, J. P on t t, and P. Le z an a, “P WM regenerative rectifiers: State of the art,” IEEE Trans. Ind. Electron., vol. 52, no. 1, pp. 5–22, Feb. 2005.

[2] B., Singh; B. N., Singh; K., Al-Had dad; A., Pan d e y; and D. P., K o t ha r i,“A Review of Three-Phase Improved Power Quality AC-DC Converters,” IEEE Trans. on Industrial Electronics, Vol.51, pp.641–660, June 2004.

[3] A. Mar z o u k i, M. Ham o u d a, and F. F n a i e ch, “Sensor less Nonlinear Control for a Three-Phase P WM AC-DC Converter,” in Industrial Electronics (IS IE), 2010 IEEE International Symposium, Bar i, Italy, pp. 1052-1057, July 2010.

[4] M.Malinowski, M. P. K a z mi er k o w ski, and A. M. Tr z y n a d lo w ski, “A comparative study of control techniques for P WM rectifiers in ac adjustable speed drives,” IEEE Transaction on Power Electronics,vol.18,no.6,pp.1390–1396, Nov. 2003.

 

Comparison of DC/DC Converters in DCM for Reducing Low-Frequency Input Current Ripple of Single-Phase Two-Stage Inverters

ABSTRACT

DC/DC Converters  Single-phase two-stage inverters generally use an intermediate capacitor to buffer the power imbalance between DC input and AC output. However, the resultant low-frequency voltage ripple on this intermediate capacitor may produce low frequency ripple at the source side, especially when the front-end dc/dc converter operates in continuous conduction mode (CCM). Some common solutions to reducing this ripple are feed forward control and power decoupling circuits. Alternatively, this paper analyzes a two-stage inverter where the front-end is a dc/dc converter operating in discontinuous conduction mode (DCM). In general dc/dc converters operating in DCM have inherent natural capability to reduce this low-frequency input current ripple, without needing a sophisticated control or complex circuitry as compared with its CCM operation. Analysis with simulation verification is reported to demonstrate such capability.

KEYWORDS

  1. Dc/ac
  2. Low-frequency ripple
  3. Single-phase
  4. Two stage

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

dc/dc converters

Fig. 1. A simplified power-stage diagram of a single-phase two-stage inverter.

EXPECTED SIMULATION RESULTS

comparison dc dc converters

  • (a) CCM operation: _vin = 3:3V

  • comparison dc dc converters

(b) DCM operation: _vin = 0:88V

Fig. 2. DCM boost front-end converter has lower voltage ripple than CCM.

comparison dc dc converters

Fig. 3. DCM buck-boost front-end converter does not contain low-frequency ripple but only high-frequency ripple.

comparison dc dc converters                                               Fig. 4. SEPIC front-end converter operating in DCM+CCM contains negligible

low-frequency ripple but only high-frequency ripple.

comparison dc dc converters

Fig. 5. High-gain front-end converter operating in DCM does contains

significant low-frequency ripple.

CONCLUSION

This paper analyzes basic and several higher-order front-end dc/dc converters for single-phase two-stage inverter design. Through inspecting the instantaneous average input current of those converters in discontinuous conduction mode (DCM), it has confirmed that buck-boost converter and buck-boost derived converters such as ZETA are free of low-frequency (mainly double ac line frequency) input current ripple due to the lack of direct connection between input and output during switching actions. For boost converter based converters such as SEPIC and C´ uk converters, their input currents contain lower low-frequency content thanks to the cascaded design. For boost converter based high voltage gain converters, its input current may not necessarily reduce the low-frequency content effectively. It depends on how the high-gain sub circuit is constructed and interacts with the input inductor. Further research is necessary to identify suitable converter topologies which have both smooth input current and low frequency content.

REFERENCES

[1] K. Fukushima, I. Norigoe, M. Shoyama, T. Ninomiya, Y. Harada, and K. Tsukakoshi, “Input Current-Ripple Consideration for the Pulse-link DC-AC Converter for Fuel Cells by Small Series LC Circuit,” in 2009 Twenty-Fourth Annual IEEE Applied Power Electronics Conference and Exposition, Feb 2009, pp. 447–451.

[2] L. Jianguo, H. Wenbin, Y. Kai, L. Xiaoyu, W. Fuyun, and W. Junji, “Research on input current ripple reduction of two-stage single-phase PV grid inverter,” in 2014 16th European Conference on Power Electronics and Applications, Aug 2014, pp. 1–8.

[3] B. Ge, Y. Liu, H. Abu-Rub, R. S. Balog, F. Z. Peng, S. McConnell, and X. Li, “Current Ripple Damping Control to Minimize Impedance Network for Single-Phase Quasi-Z Source Inverter System,” IEEE Transactions on Industrial Informatics, vol. 12, no. 3, pp. 1043–1054,

June 2016.

[4] Y. Zhou, H. Li, and H. Li, “A Single-Phase PV Quasi-Z-Source Inverter With Reduced Capacitance Using Modified Modulation and Double- Frequency Ripple Suppression Control,” IEEE Transactions on Power Electronics, vol. 31, no. 3, pp. 2166–2173, March 2016.

[5] D. B. W. Abeywardana, B. Hredzak, and V. G. Agelidis, “An Input Current Feedback Method to Mitigate the DC-Side Low-Frequency Ripple Current in a Single-Phase Boost Inverter,” IEEE Transactions on Power Electronics, vol. 31, no. 6, pp. 4594–4603, June 2016.

[6] H. Hu, S. Harb, N. Kutkut, I. Batarseh, and Z. J. Shen, “A Review of Power Decoupling Techniques for Microinverters With Three Different Decoupling Capacitor Locations in PV Systems,” IEEE Transactions on Power Electronics, vol. 28, no. 6, pp. 2711–2726, June 2013.
[7] M. A. Vitorino, L. F. S. Alves, R. Wang, and M. B. de Rossiter Corrła, “Low-Frequency Power Decoupling in Single-Phase Applications: A Comprehensive Overview,” IEEE Transactions on Power Electronics, vol. 32, no. 4, pp. 2892–2912, April 2017.
[8] Z. Chao, H. Xiangning, and Z. Dean, “Design and control of a novel module integrated converter with power pulsation decoupling for photovoltaic system,” in 2008 International Conference on Electrical Machines and Systems, Oct 2008, pp. 2637–2639.
[9] D. Debnath and K. Chatterjee, “A buck-boost integrated full bridge inverter for solar photovoltaic based standalone system,” in 2013 IEEE 39th Photovoltaic Specialists Conference (PVSC), June 2013, pp. 2867– 2872.
[10] J. Kan, S. Xie, Y. Wu, Y. Tang, Z. Yao, and R. Chen, “Single-Stage and Boost-Voltage Grid-Connected Inverter for Fuel-Cell Generation System,” IEEE Transactions on Industrial Electronics, vol. 62, no. 9, pp. 5480–5490, Sept 2015.
[11] D. Zhou, “Synthesis of PWM dc-to-dc power converters,” Ph.D. dissertation, California Institute of Technology, Pasadena, California, 1996.