Current Tracking Delay Effect Minimization for Digital Peak Current Mode Control of DC–DC Boost Converter

Digital peak current mode (DPCM) control is widely used for dc-dc converters operating in continuous current mode. However, current tracking delay (CTD) in the system is normally neglected in the modeling stage, which leads to poor compensator design and degraded performance. This paper investigates CTD effect in boost converter with different DPCM controls. Based on dynamic relationship between the reference current and actual inductor current, the CTD transfer functions are derived, which improves the accuracy of small signal model. Since CTD degrades the phase margin of the system, equivalent migration of right half plane zero is proposed to model CTD effect. This method is very simple and straightforward, which facilitates the compensator design. Furthermore, two novel DPCM control strategies with minimized CTD are proposed, and they are based on duty cycle restriction and duty cycle extension, respectively. Both controls greatly reduce the CTD effect and improve the response speed. Besides, the duty cycle extension benefits from an extended pulsewidth modulation (ExPWM). This optimizes the calculation algorithm and speed, while improving the time margin for digital calculations. Combined with the proposed models and controls, the CTD effect is greatly reduced. The effectiveness is verified through detailed simulations and experiments.

I. Introduction

In Recent years, digital control strategies are widely applied for power converters, since they provide advantages of programmability, less sensitive to component aging, robustness to noise and possibility to realize complicated algorithm, etc. [1]–[4]. However, they suffer from a reduced bandwidth owing to the inherent delays caused by samplings and computational time. In order to improve performance, various digital control strategies are proposed, such as digital sliding mode control, digital charge balance control, and predictive DPCM control [5]–[8]. Combined with current prediction algorithms, predictive DPCM control is an effective way to enlarge the bandwidth of current loop [9]–[13]. With limited current sampling frequency, the inductor current is predicted ahead of the next sampling point, so the delay of current sampling can be minimized.