Abstract. This paper presents an analysis of the properties of pulse width modulator with a single (symmetrical regular sampled PWM) and double (asymmetrical regular sampled PWM) control sampling of the input signal (low-frequency control input wave) in presence of a triangular auxiliary signal. In this paper, a comparison of the characteristics of these modulators used in the control system with a linear proportional controller is presented. The article provides the relations derived for the maximum amplification of regulators for which the control system operates stably. Analysis results have been confirmed by simulation and experimental studies of a commercial active filter installed in an industrial plant. Simulation studies show an increase of the critical proportional controller gain with symmetrical regular sampled PWM with a doubled number of samples in the period of the triangular auxiliary signal for which the control system is stable. Also, the analysis included in this article demonstrates the possibility of increasing the value of the gain of the proportional controller in a closed system with asymmetrical regular sampled PWM. Publications [8][9][10][11][12][13][14] devoted to applications in power electronics systems with the asymmetrical regular sampled PWM are not related to control systems with a proportional controller. From the point of view of the topics covered in this article, the most interesting paper is publication [15]. This paper addresses the digital control system with asymmetrical regular sampled PWM with different types of controllers, but the issues critical to the gain of the proportional controller addressed in the present article are not discussed.One of the objectives of the work presented is to compare the dynamic and static properties of the control system with a proportional controller and symmetrical regular sampled or asymmetrical regular sampled PWM.Carried out in this article is an analysis taking into account the time between the instant of measurement of the controlled value and the actual determination of the magnitude of the sampled reference (PWM computation delay [15]).Control system with proportional controller has non-zero value of disturbance error. From the point of view of minimizing the disturbance errors and the reducing the time of decay of transient component of this error advantages of asymmetrical regular sampled PWM compared to the symmetrical regular sampled PWM manifest themselves only under the condition of an appropriately small value of the PWM computation delay.The article also describes a mechanism allowing for elimination of the impact of this error on the output current of the APF. This is a feature of APF with supervisory system of DC link voltage which allows the use of output current proportional controller.

Installation and operation of rail vehicles powered by multiple system voltages forces the construction of multi-system traction substation. The article describes a traction substation power supply with 15 kV output voltage and frequency Hz and 25 kV at 50 Hz. The topology of the power electronics system and the control structure of the power supply enables parallel connection of several power supplies. The selected topology and control structure ensures minimizing the rms value of the LCRL filter capacitor current used at the output of the inverters. The article analyses the influence of harmonics consumed by the active front end (AFE) rectifier used in traction vehicles on the rms current of the LCRL filter capacitor.