An Improved Beatless Control Method of AC Drives for Railway Traction Converters


The traction converter consists of a single phase AC DC rectifier and a three phase DC AC invert er. Due to special structural characteristics of single phase rectifier, a fluctuating voltage component with the frequency twice of the grid’s, exists in DC link voltage. Fed by fluctuating DC link voltage, a beat phenomenon occurs in traction motor, and harmonic components appear in both stat or current and electromagnetic torque, especially when motor operates near the ripple frequency. In this paper, the mechanism and influence of fluctuating voltage are analyzed in detail. Based on modeling analysis of motor and switching function of invert er, a frequency compensation factor is derived in vector control of induction motor. Then an improved frequency compensation control method is proposed to suppress beat phenomenon without LC resonant circuit. Finally the simulation verifies the modified scheme.


  1. Fluctuating DC voltage
  2. Beat phenomenon
  3. Vector control
  4. Beat less control



 Fig. 1. F O C with frequency compensation for Induction Motor


 Fig. 2. Waves of stat or current and electromagnetic torque of traction Motor

Fig. 3. FF T of stat or current and electromagnetic torque before adding frequency compensation method

Fig. 4. FF T of stat or current and electromagnetic torque after adding traditional frequency compensation method

Fig. 5. FF T of stat or current and electromagnetic torque after adding improved frequency compensation method


 In high power traction converters, without LC filter circuit paralleled in DC link, a fluctuating voltage twice of the grid frequency contains in DC link voltage. This paper aims at adopting software control method to suppress beat phenomenon in traction motor caused by DC ripple voltage. According to theoretical analysis, output power of motor, DC link capacitor and power factor influenced the DC ripple voltage. Then, the aspect of switching function and motor model analyzed the influences of fluctuating voltage in detail. Based on above analysis, combining with rotor field oriented control of traction motor, the frequency of switching function is modified to suppress beat phenomenon. An improved frequency compensation control method is proposed. Simulation model is built to verify the proposed scheme. Finally, the drag experiment on a dynamo meter test platform verified the proposed control method.


[1] J. K l i ma, M. Ch  o mat, L. Sch re i e r, “Analytical Closed-form Investigation of P WM Invert er Induction Motor Drive Performance under DC Bus Voltage Pulsation,” I ET Electric Power Application, Vol. 2, No. 6, pp. 341–352, Nov, 2008.

[2] H. W. van d e r Bro e ck and H. C. S k u d e l n y, “Analytical analysis of the harmonic effects of a P WM AC drive,” in IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 216-223, Apr 1988.

[3] K Na k at a, T N a k a m a chi , K Na k am u r a, “A beat less control of invert er-induction motor system driven by a rippled DC power source,” Electrical Engineering in Japan, Vol.109, No.5, pp.122-131,1989.

[4] Z Sal am, C.J. Goodman, “Compensation of fluctuating DC link voltage for traction invert er driver,” Power Electronics and Variable Speed Drives, 1996. Sixth International Conference on (Conf. Pub l. No. 429), pp. 390-395, 1996.

[5] S. K o u r o, P. Le z an a, M. An g u lo and J. Rodriguez, “Multi carrier P WM With DC-Link Ripple Feed forward Compensation for Multilevel Invert er s,” IEEE Transactions on Power Electronics, vol. 23, no. 1, pp. 52- 59, Jan. 2008.

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