Challenges in achieving high performance in boost PFC converter

Online Estimation of ESR for DC-Link Capacitor of Boost PFC Converter Using Wavelet Transform Based Time–Frequency Analysis Method

Abstract: Aluminum electrolytic capacitor (AEC) is one of the most age-affected components in ac–dc conversion, and its equivalent series resistance ( ESR ) is an important index for reflecting the healthy condition of AEC. In AEC-used boost power factor correction (PFC) converters, ESR of AEC causes a small jump in the switching ripple of output voltage at switching moments, especially at turn- off moments. This small jump is hardly observed at line-frequency scale, either using time-domain analysis or frequency-domain analysis. However using time–frequency analysis this jump is very prominent due to its singularity. In this article, an online ESR estimation method of AEC is proposed by using the wavelet transform (WT) based time–frequency analysis. The relationship between ESR and the jump amount of output voltage at turn- off moments is analyzed first, and then the ESR calculation model is derived using WT with the wavelet basis of the first derivative of Gaussian function. An appropriate sampling interval for the output voltage and the inductor current is determined. Besides, the online ESR estimation scheme is implemented including the hardware and software designs. Furthermore, a prototype of boost PFC converter with 220 V ac input and 360 V dc output is built, where an average current mode control chip UC3854 is used. Four factors are discussed for estimation accuracy in the experiment, and the estimated results are consistent with the results measured by LCR meter with a relative error less than 10%.

An Improved Digital Algorithm for Boost PFC Converter Operating in Mixed Conduction Mode

Abstract: This article proposes an improved digital algorithm based on predictive control for the operation of a boost power factor correction (PFC) converter in the mixed conduction mode (MCM). The proposed MCM algorithm comprises of a proposed digital conduction mode detection method, a proposed predictive discontinuous conduction mode (DCM) average current controller, a proposed digital compensation technique in DCM to account for the initial nonzero inductor current during switch turn-on and also a predictive continuous conduction mode (CCM) average current controller. The proposed algorithm flow is computationally efficient with no additional sensor/circuit requirements and ensures low harmonic content in the input current. The proposed MCM algorithm is verified experimentally on a 300-W boost PFC converter hardware prototype for converter operation in MCM, pure DCM, and pure CCM within a half line cycle. The proposed MCM algorithm is evaluated experimentally in terms of current tracking, current harmonics, and computation times.

A Computationally Simple Predictive CCM Average Current Controller With Nearly Zero Tracking Error for Boost PFC Converter

Abstract: Predictive current controllers offer superior control action in power factor correction (PFC) converters, however, cause tracking error in the average inductor current due to the unmodeled circuit parameters and variations which could lead to higher harmonic currents, higher input current THD and impact on the output voltage. Attempts to make the predictive current control equations accurate leads to increased computational complexity, thus limiting the switching frequency of operation or increasing the processing requirements. This article proposes a computationally simple predictive continuous conduction mode average current controller based on the concept of moving averages for the boost PFC converter and achieves nearly zero tracking error in the average inductor current. Additionally, a predictive current controller is derived for performance comparison by considering the effect of major converter nonidealities and digital implementation aspects. The performance of the proposed predictive current controller is compared with that of a PI current controller, an ideal predictive current controller and the derived predictive current controller with nonidealities included. Experimental studies on a boost PFC converter hardware prototype validate the effectiveness of the proposed predictive current controller.

Implementation Aspects of a Single Phase Boost PFC Converter

Abstract: The single phase boost PFC converter is used as a front end stage in equipments in order to conform to harmonic standards. Due consideration is to be given for the implementation issues in the boost PFC converter due to the large signal variations in the converter waveforms and its wide operating ranges. This paper highlights the practical challenges and implementation aspects with respect to the topology and control in a single phase boost PFC converter. The causes of input current distortion and conduction mode change are analysed. The effect of voltage loop bandwidth on the converter performance is discussed. Digital implementations with PI current controller and with predictive current controller are discussed. Inferences are presented based on equations and experimental results. The experimental tests are carried out on a 50 Hz universal AC input, 400 V DC output, 300 W single phase boost PFC converter hardware prototype operated at a switching frequency of 100 kHz.

Predictive Average Current Control Considering Non-Idealities for a Boost PFC Converter

Abstract: The design of the current control loop in a boost PFC converter plays a significant role due to the large signal variations in the input waveforms. A predictive average current control law based on triangular modulation considering the converter non-idealities, time variation of waveforms and computation delays is proposed and validated with simulation and experimental results. A digital method for the boost inductance value estimation is also proposed which could be used with predictive current control laws.

Single phase power factor correction: a survey

Abstract: New recommendations and future standards have increased the interest in power factor correction circuits. There are multiple solutions in which line current is sinusoidal. In addition, a great number of circuits have been proposed with nonsinusoidal line current. In this paper, a review of the most interesting solutions for single phase and low power applications is carried out. They are classified attending to the line current waveform, energy processing, number of switches, control loops, etc. The major advantages and disadvantages are highlighted and the field of application is found.

Average current mode control of switching power supplies

Abstract: Current mode control as usually implemented in switching power supplies actually senses and controls peak inductor current. This gives rise to many serious problems, including poor noise immunity, a need for slope compensation, and peak-to-average current errors which the inherently low current loop gain cannot correct. Average current mode control eliminates these problems and may be used effectively to control currents other than inductor current, allowing a much broader range of topological application.

On the zero-crossing distortion in single-phase PFC converters

Abstract: Input current distortion in the vicinity of input voltage zero crossings of boost single-phase power factor corrected (PFC) ac-dc converters is studied in this paper. Previously known causes for the zero-crossing distortion are reviewed and are shown to be inadequate in explaining the observed input current distortion, especially under high ac line frequencies. A simple linear model is then presented which reveals two previously unknown causes for zero-crossing distortion, namely, the leading phase of the input current and the lack of critical damping in the current loop. Theoretical and practical limitations in reducing the phase lead and increasing the damping factor are discussed. A simple phase compensation technique to reduce the zero-crossing distortion is also presented. Numerical simulation and experimental results are presented to validate the theory.

A Simple Digital DCM Control Scheme for Boost PFC Operating in Both CCM and DCM

Abstract: Digital average current controllers for boost power factor correctors (PFCs) are usually designed for continuous conduction mode (CCM). However, discontinuous conduction mode (DCM) appears in the inductor current near the zero crossings of the input current at light loads, resulting in input current distortion. It is caused by inaccurate average current values obtained in DCM and by the linear CCM PFC controller that is unable to ensure input current shaping in DCM whereby the converter exhibits nonlinear characteristic. This paper proposes a simple digital DCM control scheme that is achieved with minimal changes to the CCM average current control structure. It is mathematically and computationally simple. The result of all arithmetic operations in the proposed current control loop to obtain the desired control output can be achieved in a single clock cycle, whereas other DCM control schemes require multiple clock cycles. Good input current shaping is achieved in both CCM and DCM with the proposed CCM-DCM digital controller.