Search

This paper presents a triple-mode average current control (TACC) strategy to achieve unity power factor and reduce the current stress for a boost PFC converter. The controller switches among different modes in each half-line cycle, and smooth transition is ensured by mapping of the operation region. By adaptive mode shifting, it reduces the current stress and current distortion caused by non-linear effects. With valley current shaping and comparisons, the TACC controller accordingly incorporates three control laws to adapt different modes. In discontinuous conduction mode (DCM), a variable on-time is calculated while the modulation is equivalent to PWM. In critical conduction mode (CRM), a constant on-time is derived, while the switching cycle is modified to regulate the current average value. For both DCM and CRM, the switching cycle is slightly extended to realize valley switching. Furthermore, with valley current shaping, the proposed controller reuses the CRM calculation to form continuous conduction mode (CCM) control law. To make the control laws compatible, normalized mapping and design rules are provided with respect to mode boundaries. This allows the TACC controller to automatically switch among different modes. Finally, experimental results prove the effectiveness of the controller in reducing the current stress and enlarging the preferable power range. [ABSTRACT FROM AUTHOR]

This article proposes a unified pulsewidth-cycle (UPWC) control strategy to achieve mixed-mode operation and consistent valley switching (VS) for boost power factor correction converter. Compared with conventional single-mode controllers, it has a unified scheme to achieve single discontinuous conduction mode (DCM), single critical conduction mode (CRM), or mixed DCM/CRM operations in each half-line cycle. To regulate the input current as a sinusoid, the UPWC controller adopts a variable pulsewidth and a near-constant switching cycle under DCM, while adopts a constant pulsewidth and a variable switching cycle under CRM. To facilitate analysis, normalized mapping of operation modes is provided, along with the final pulsewidth and switching cycle. Furthermore, to ensure consistent VS, a controlled zero current detection method is proposed to fix the turn-on point of the power switch. No matter in DCM or CRM, consistent VS reduces both the switching loss and current distortion caused by parasitic resonance. To further reduce the current distortion caused by fixing the turn-on point, a compensation gain is provided that reshapes the input current as a sinusoid. Finally, through mixed DCM/CRM operation and consistent VS, the proposed UPWC controller achieves preferable performances in the power range, efficiency, power factor, and current distortion. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]