Frequency domain analysis of beatless control method for converter‐inverter driving systems applied to AC electric cars

Abstract

SUMMARYIn inverter-converter driving systems for AC electric cars, the DC input voltage of an inverter contains a ripple component with a frequency that is twice the line voltage frequency, due to the use of a single-phase converter. The ripple component of the inverter input voltage causes pulsations in the torque and current of driving motors. To decrease the pulsations, a beatless control method, which modifies the slip frequency depending on the ripple component, is applied to the inverter control. In the present paper, the beatless control method is analyzed in the frequency domain. In the first step of the analysis, transfer functions which revealed the relationship among the ripple component of the inverter input voltage, the slip frequency, the motor torque pulsation, and the current pulsation were derived with a synchronous rotating model of induction motors. An analytical model of the beatless control method was then constructed using the transfer functions. The optimal setting of the control method was obtained according to the analytical model. The transfer functions and the analytical model were verified by simulations.

Beat‐less algorithm based on dual‐frequency compensation in railway traction applications

“…The torque pulsation can be suppressed by these three beat-less algorithms. Some small terms in ( 9), ( 18), (19), and (20) are ignored in the calculation process. Besides, the principle of the DFC method is to shift the beat voltages to a higher-frequency region, rather than cancel them out.…”

“…After PWM process, the phase voltage with modified modulation signal in (19) can be derived as follows (noted φ dc = θ+2ω g t):…”

“…To get rid of the limitation of high control bandwidth, the modulation index compensation (MIC) [15,16] and singlefrequency compensation (SFC) [17][18][19] methods are proposed to modify the modulation signals directly. With the MIC method, the modulation index is varied against the actual DClink voltage inversely [20,21].…”