Small-Signal Modeling of Phase-Shifted Digital PWM in Interleaved and Multilevel Converters

Abstract

In this article, small-signal modeling of digital pulsewidth modulators (DPWMs) used in multi-cell voltage source converters (VSCs) is addressed. In addition to sampling and computation, DPWM introduces delay, which impairs VSC's dynamic performance and robustness. In order to take into account the influence of modulation delay, an accurate small-signal representation of DPWM is necessary. Here, modeling of multisampled bipolar and unipolar phase-shifted DPWMs for single-, double-, and multi-update strategies is presented. The simplest multilevel modulation of single-cell full-bridge VSCs, unipolar DPWM, is also covered by the analysis. The derived operatingpoint-dependent small-signal DPWM models are verified using simulated and experimental frequency response measurements up to four times the Nyquist frequency. Comparisons are also made with the models conventionally considered in the literature. Additionally, an approximate method is presented to model the influence of dead-time on DPWM's small-signal dynamics. For the purposes of showcasing the importance of the proposed DPWM models, high-frequency admittance of a VSC employing multi-sampled multi-update unipolar DPWM is modeled and verified in simulations and experiments.

Switching Noise Propagation and Suppression in Multisampled Power Electronics Control Systems

“…1 is assumed, with the only difference being the modulator. For multilevel and interleaved converters, symmetric 12 phase-shifted PWM (PS-PWM), consisting of N w phase-shifted triangular carriers, is assumed [28]. There, an often implemented control strategy is multi-sampled PS-PWM (MS-PS-PWM), in which N = N c = 2N w .…”

“…There, an often implemented control strategy is multi-sampled PS-PWM (MS-PS-PWM), in which N = N c = 2N w . Due to frequency multiplication of PS-PWM, MS-PS-PWM is often considered as equivalent to DS-PWM in two-level converters, and used in this article as a benchmark [28]. Similar to MR-DS-PWM control aimed at enhancing noise suppression for two-level converters, multirate multi-sampled PS-PWM control (MR-MS-PS-PWM) is considered.…”

Nonlinearities of Multisampled Phase-Shifted PWM in Unbalanced Multicell Converters

“…In multi-sampled single-and double-update PS-DPWM, the modulating signal for each cell is updated at the peaks or/and valleys of the carrier corresponding to that cell [16], [18]. This results in only horizontal intersections between the modulating signal and the carrier.…”

“…A widely used modulation strategy for MC-VSCs is the digital phase-shifted pulsewidth modulation (PS-DPWM) [2]- [5], [7], where the carriers of the subsequent cells are phaseshifted with respect to each other, so that harmonic cancellation is achieved at the output [10], [11]. Under balanced conditions, this yields an increased frequency of the output current ripple, i.e., frequency multiplication [12], enabling output filter reduction [7], [12] and control loop bandwidth improvement [6], [13]- [17].…”

“…For regulating the output current of PS-DPWM MC-VSCs, multi-sampled multi-update (MSMU) control is a widely adopted strategy, due to improved dynamic performance and robustness, offered by a significant reduction of the modulation delay [13]- [16], [18]- [21]. In MSMU-PS-DPWM, the sampling of the output current and update of the modulating signal are performed at peaks, valleys, and intersections of all triangular carriers.…”