Quantization resolution and limit cycling in digitally controlled PWM converters

Abstract

Abstract-This paper discusses the presence of steady-state limit cycles in digitally controlled pulse-width modulation (PWM) converters, and suggests conditions on the control law and the quantization resolution for their elimination. It then introduces single-phase and multi-phase controlled digital dither as a means of increasing the effective resolution of digital PWM (DPWM) modules, allowing for the use of low resolution DPWM units in high regulation accuracy applications. Bounds on the number of bits of dither that can be used in a particular converter are derived. Finally, experimental results confirming the theoretical analysis are presented.

High-resolution phase shift and digital implementation of a fuel cell powered UPS system

“…The problem can also be stated as insufficient time resolution in the digital modulator to satisfy specified output voltage regulation accuracy. The general quantization effects and no-limit-cycle conditions have been extensively analyzed in [5] and [6]. To increase the effective resolution of the DPWM, a few techniques such as dithering, multiphase averaging [5] and so-called cycle-skip [7] can be applied.…”

“…Furthermore, the inclusion of an integral term in the control law is necessary to eliminate LCO [5]. The digital integrator is intended to fine-tune the output voltage; therefore it has to be able to adjust the phase shift command by steps as small as a least significant bit (LSB).…”

Frequency response analysis of proposed digital control system for DPWM-POL

“…For the control purpose, pulse width modulation (PWM) control is a one of appropriate technique. Digital control or DPWM can accomplish robust and flexible power control with soft-tuned parameters and will become popular control technique [1][2][3][4][5][6][7][8][9][10][11][12]. Although, there are some disadvantages in cost and speed, against analog control circuit.…”

Analysis of limit cycles in a PI digitally controlled buck converter

“…Digital control has numerous potential advantages over the more traditional analog control. These include low power consumption, lower sensitivity to parameter variations, and the possibility for increased complexity and flexibility of control laws [1]. The buck converter is widely used in a variety of applications in power electronics, for example in portable electronic devices.…”