Sliding Mode Control Methods Time-Varying and Constant Switching Frequency Based Trans- former less DVR Employing Half-Bridge VSI

sliding mode control  IEEE Transactions on Industrial Electronics, 2016

 ABSTRACT:

sliding mode control This paper presents time-varying and constant switching frequency based sliding mode control (SMC) methods for three-phase transformerless dynamic voltage restorers (TDVRs) which employ half-bridge voltage source inverter (VSI). An equation is derived for the time-varying switching frequency. However, since the time-varying switching frequency is not desired in practice, a smoothing operation is applied to the sliding surface function within a narrow boundary layer with the aim of eliminating the chattering effect and achieving a constant switching frequency operation. The control signal obtained from the smoothing operation is compared with a triangular carrier signal to produce the PWM signals. The feasibility of both SMC methods has been validated by experimental results obtained from a TDVR operating under highly distorted grid voltages and voltage sags. The results obtained from both methods show excellent performance in terms of dynamic response and low total harmonic distortion (THD) in the load voltage. However, the constant switching frequency based SMC method not only offers a constant switching frequency at all times and preserves the inherent advantages of the SMC, but also leads to smaller THD in the load voltage than that of time-varying switching frequency based SMC method.

 

KEYWORDS:

  1. Constant switching frequency
  2. Dynamic voltage restorer
  3. Sliding mode control
  4. Time-varying switching frequency.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Block diagram of three-phase TDVR with the proposed SMC methods. (a) Time-varying switching frequency based SMC method, (b) Constant switching frequency based SMC method.

 

EXPECTED SIMULATION RESULTS:.

Fig.2. Simulated responses of sk v , se k v , and Lk v obtained by the constant switching frequency based SMC under three-phase-to-ground fault. (a) sk v , (b) se k v , and (c)Lk v .

Fig. 3. Simulated responses of vsk , se k v , and Lk v obtained by the constant switching frequency based SMC under single-phase-to-ground fault. (a)sk v , (b) se k v , and (c)Lk v .

 

Fig. 4. Simulated responses of sk v , se k v , and Lk v obtained by the SMC method presented in [15]. (a) sk v , (b) se k v , and (c) Lk

 

Fig. 5. Simulated responses of sk v , se k v , and Lk v obtained by the time-varying switching frequency based SMC. (a) sk v , (b) se k v , and (c)Lk v .

Fig. 6. Simulated responses of sk v , se k v , and Lk v obtained by the constant switching frequency based SMC. (a) sk v , (b) se k v , and (c)Lk v .

 

CONCLUSION:

In this study, time-varying and constant switching frequency based SMC methods are presented for three-phase TDVR employing half-bridge VSI. An analytical equation is derived to compute the time-varying switching frequency. Since, the time-varying switching frequency is not desired in a real application, a smoothing operation is applied to the sliding surface function within a narrow boundary layer with the aim of eliminating the chattering effect and achieving a constant switching frequency. The control signal obtained from the smoothing operation is compared with a triangular carrier signal to produce the PWM signals. It is observed that the smoothing operation results in a constant switching frequency operation at all times. The feasibility of both SMC methods has been validated by experimental results obtained from the TDVR operating under highly distorted grid voltages and voltage sags. The results obtained from both methods show excellent performance. However, the constant switching frequency based SMC method not only offers a constant switching frequency at all times and preserves the inherent advantages of the SMC, but also leads to smaller THD in the load voltage than that of time-varying switching frequency based SMC method.

 

REFERENCES:

  • Bollen, Understanding Power Quality Problems. New York, NY, USA: IEEE Press, 2000.
  • Singh, A. Chandra, and K. Al-Haddad, Power Quality: Problems and Mitigation Techniques. West Sussex, United Kingdom: John Wiley & Sons Inc., 2015.
  • W. Li, F. Blaabjerg, D. M. Vilathgamuwa, and P. C. Loh, ”Design and comparison of high performance stationary-frame controllers for DVR implementation,” IEEE Trans. Power Electron., vol. 22, no. 2, pp. 602-612, Mar. 2007.
  • Kim, and S. K. Sul, ”Compensation voltage control in dynamic voltage restorers by use of feed forward and state feedback scheme,” IEEE Trans. Power Electron., vol. 20, no. 5, pp. 1169-1177, Sep. 2005.

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