Converter Operating In Continuous Conduction Mode Research Articles

Boundary-Based Hybrid Control Algorithm for Switched Boost Converter Operating in CCM and DCM

It is essential to have enhanced efficiency for the DC-DC converters operating in continuous conduction mode (CCM) and discontinuous conduction mode (DCM). This requires a hybrid controller designed using pulse width modulation (PWM) and pulse frequency modulation (PFM) schemes. This paper fixates on a boundary-based hybrid control algorithm for the second-order DC-DC converter - the switched boost converter. The proposed algorithm works in PWM control scheme for CCM operation, whereas DCM operation uses PFM control scheme. The boundary conditions are defined by the load current, output voltage, and switching frequency. Here, an attempt is carried out to have the advantages of both the control schemes. The boost converter is represented by the switched system operating in three modes. Violating transition guards condition orchestrates the switching among these modes. A supervisor detects the CCM and DCM operations, and subsequently switches between PWM and PFM control scheme. Extensive circuit-level simulations are carried out in MATLAB to show the efficacy of the suggested algorithm under the fluctuating line, load, and set-point.

A Simple, Accurate Small-Signal Model of a Coupled-Inductor-Based DC-DC Converter Including the Leakage Inductance Effect

This brief proposes a method to dynamically modeling the coupled-inductor double-boost converter operating in continuous-conduction mode. Such method has the advantage of including the leakage inductance effect on the dynamic behavior of the converter in a simple, straightforward approach. The presence of the leakage inductance is initially neglected and a traditional circuit-averaging technique is used. The averaged models are then refined by accounting the impacts of the reported inductance. Since its major impact is on the damping factor of the system, this dynamic change is modeled by equivalent resistors. Equations for describing the equivalent resistors are derived based on the analysis of the duty cycle loss caused by leakage inductance in the static gain of the converter. The effect on the averaged small-signal model is shown by a closed-form control-to-output transfer function and experimental results demonstrate its accurate performance.

Accurate Loop Gain Modeling of Digitally Controlled Buck Converters

For the digitally controlled buck converters, the nonlinearity and time periodicity, caused by the pulsewidth modulator (PWM) and sample and hold, make the accurate frequency-domain analysis intractable. In this article, based on the harmonic transfer function (HTF) approach, a precise small-signal continuous-time modeling for the digitally controlled Buck converter operating in continuous-conduction mode (CCM) under constant-frequency voltage-mode control is presented. The sideband components on the closed-loop control are embedded in the model. Thus, this model is accurate within the full frequency domain region, which breaks the limit of Nyquist frequency. Furthermore, by overcoming the barrier of infinite series introduced by the sideband effects, the analytical loop gain expression is derived, which contributes to accurate stability assessment and reduction of computation burden. In addition, the proposed exact small-signal model has explained the reasons why different information injection points lead to different measured loop gains. Simulations and experimental results are conducted to verify the effectiveness of the proposed method.

Open‐loop transfer functions of buck–boost converter by circuit‐averaging technique

This study shows the derivation of the power-stage transfer functions and input and output impedances of a buck–boost pulse width-modulated (PWM) dc–dc converter operating in continuous-conduction mode. The expressions are derived using the small-signal model obtained by the circuit-averaging technique. Using the small-signal dynamic model, both transient and frequency domain characteristics are determined. An example buck–boost converter with the following specifications was considered: supply voltage 12 V, output voltage 5 V, switching frequency 200 kHz, and output power 10 W. The modification of the power-stage transfer function to include the time delay between the MOSFET gate drive and the duty cycle is considered and is modelled by the first-order Padè approximation. The theoretical predictions were verified by experiments and excellent agreement between the results was observed.

Unified model of Sepic converter in continuous and discontinuous conduction modes

Aiming at the problems of the modelling methods for Sepic converter, they were described as in inexact, large amount of calculation and complicated expressions. A suitable hybrid switching model for both continuous conduction mode (CCM) and discontinuous conduction mode (DCM) is proposed. Firstly, according to the working process of the Sepic converter, the switching conditions of Sepic converter between different working conditions are formulated. Secondly, by introducing the logic proposition and the equivalent translation principle, the switching conditions of the converter in different modes can be transformed into mixed logical inequalities, moreover then, a unified model of Sepic converter in CCM and DCM modes is obtained. Finally, the simulation experiment of Sepic converter operating in CCM, BCM (boundary conduction mode) and DCM modes were conducted, and compared with the state space averaging method, the validity of effectiveness of the proposed approach was shown.

Cross-Regulation Suppression and Stability Analysis of Capacitor Current Ripple Controlled SIDO CCM Buck Converter

For a single-inductor dual-output (SIDO) dc–dc converter operating in continuous conduction mode (CCM), load variation of one output will affect the voltage of the other output, i.e., there exists cross regulation between its two outputs. To suppress the cross regulation of the SIDO dc–dc converter operating in CCM, a novel ripple based control technique, called capacitor current ripple (CCR) control technique, is proposed in this paper. The operation principle of the SIDO CCM buck converter and the proposed CCR control technique are presented. The small signal model of the CCR-controlled SIDO CCM buck converter is established by the state space averaging method. Bode plots based on small signal model show that the proposed CCR-controlled SIDO CCM buck converter significantly reduces cross regulation and improves the transient performance compared with the peak current mode controlled SIDO CCM buck converter. In addition, the effect of the variation of loads on the stability of the proposed CCR-controlled SIDO CCM buck converter is analyzed by eigenvalues analysis. Finally, experimental results are provided to verify the analysis results.

A New Transformerless Buck–Boost Converter With Positive Output Voltage

A new transformerless buck–boost converter with simple structure is proposed in this study. Compared with the traditional buck–boost converter, the proposed buck–boost converter’s voltage gain is squared times of the former’s and its output voltage polarity is positive. These advantages enable it to work in a wider range of positive output. The two power switches of the proposed buck–boost converter operate synchronously. In the continuous conduction mode (CCM), two inductors are magnetized and two capacitors are discharged during the switch-on period, while two inductors are demagnetized and two capacitors are charged during the switch-off period. The operating principles, the steady-state analyses, and the small-signal model for the proposed buck–boost converter operating in CCM are presented in detail. The power electronics simulator (PSIM) and the circuit experiments are provided to validate the effectiveness of the proposed buck–boost converter.

An Improved Modeling and Analysis Technique for Peak Current-Mode Control-Based Boost Converters

A modeling approach is presented that calculates an accurate open-loop transfer characteristic for a boost converter that employ peak current-mode control (PCMC). Many techniques exist for modeling a PCMC-based boost converter; however, all these techniques focus on purely resistive loads and are not always accurate for a purely capacitive load. In this paper, a new modeling technique is presented, which is simple and gives accurate results for both capacitive and resistive loads. Furthermore, the useful expressions for dc gain and pole locations of a boost converter operating in continuous-conduction mode with PCMC are derived and compare well to simulations and measurements.

A Simple Average Current Control With On-Time Doubler for Multiphase CCM PFC Converter

This paper proposes a new modulated carrier control method for an interleaved continuous conduction mode (CCM) power factor correction (PFC) boost converter. The proposed method allows precise sinusoidal line current shaping for a PFC boost converter operating in CCM. This is accomplished by simply comparing modulated carrier signal with switch current, such that inner current loop compensation design and rectified line voltage sensing are not required. The proposed control method greatly simplifies current sensing and control circuitry of multiphase converters since average current control is available by just sensing the switch current for each module. This also enables simple current balancing between parallel converters by employing modulated carrier signals with same amplitude. The principle of the control method is presented. The performance of the proposed control method is experimentally verified on a 600-W PFC converter. The measured power factor remains above 94.9% down to 20% of a full load for $110\hbox{-}V_{\rm rms}$ and $220\hbox{-}V_{\rm rms}$ line voltages. The line current harmonics also meet the IEC61000-3-2 Class D standard.

Low-frequency oscillation of continuous conduction mode buck converter with pulse skipped modulation

Low-frequency oscillation phenomenon in pulse skipped modulation (PSM) buck converter operating in continuous conduction mode (CCM) is reported in this paper. Energy transfer difference between the PSM-controlled buck converter operating in discontinuous conduction mode (DCM) and that in CCM is studied. The mechanism of low-frequency phenomenon in PSM-controlled CCM buck converter is revealed, and a discrete-time model of PSM-controlled buck converter operating in CCM is established. Based on this model, the border collision bifurcation with variations of the ESR is studied; meanwhile, the inhibition effect of output capacitor equivalent series resistance (ESR) on low-frequency oscillation is presented. Based on the above analysis, a capacitor current pulse skipped modulation (CC-PSM) technology is proposed; the energy transfer principle of CC-PSM controlled buck converter is analyzed. The control pulse of CC-PSM is generated by the comparison between the sampled capacitor current and preset peak reference current, and thus the range of inductor current ripple is limited. Results show that CC-PSM effectively eliminates the low-frequency oscillation in CCM buck converter under classical PSM when the ESR is low. Finally, the experimental results validate the correctness of theory and simulation analysis

Distortion Behavior Analysis of General Pulse-Width Modulated Zeta PFC Converter Operating in Continuous Conduction Mode

For most actual power applications, power-factor correction (PFC) converters usually operate in the stable continuous conduction mode (CCM), but input current distortion will occur as long as these converters operate in oscillatory condition. This distortion usually manifests itself as a local oscillation within one line cycle. Typically, a Zeta PFC converter under the general pulse-width modulated (GPWM) control possesses high performance, and requires simpler control circuitry with fewer external components. However, due to the large-signal nonlinearity of the GPWM controller, the dynamic analysis and modeling of the input current distortion in its PFC converters remains vacant. In this paper, a large-signal average SPICE model is derived to capture the time-domain waveforms of the input current and output voltage. A power-balance approach for the PFC converter operating in CCM is developed, which can predict the steady-state values of the converters by using the Fourier series expansion. Analysis of the distortion behavior is provided in terms of the proposed model and the unbalanced power transfer mode. Experimental results are presented to verify the proposed method.

HOPF BIFURCATION AS AN INTERMEDIATE-SCALE INSTABILITY IN SINGLE-STAGE POWER-FACTOR-CORRECTION POWER SUPPLIES: ANALYSIS, SIMULATIONS AND EXPERIMENTAL VERIFICATION

This paper reports intermediate-scale instability in a single-stage power-factor-correction (PFC) power supply that employs a cascade configuration of a boost stage operating in discontinuous conduction mode (DCM) and a forward stage operating in continuous conduction mode (CCM). The two stages combine into a single stage by sharing one main switch and one control loop to achieve input PFC and tight output regulation. The main results are given by "exact" cycle-by-cycle circuit simulations. The effect of the intermediate-scale instability on the attainable power factor is illustrated in terms of total harmonic distortion (THD) which is found by taking the Fast Fourier Transform (FFT) of the input current. The intermediate-scale instability usually manifests itself as local oscillations within a line cycle. Based on the stability analysis of a buck converter operating in CCM, the underlying mechanism of such instability can be attributed to the Hopf bifurcation that occurred in CCM forward stage. Finally, experimental results are presented for verification purposes.

Voltage-Loop Power-Stage Transfer Functions With MOSFET Delay for Boost PWM Converter Operating in CCM

Open-loop transfer functions can be used to create closed-loop models of pulsewidth-modulated (PWM) converters. The closed-loop small-signal model can be used to design a controller for the switching converter with well-known linear control theory. The dynamics of the power stage for boost PWM dc-dc converter operating in continuous-conduction mode (CCM) are studied. The transfer functions from output current to output voltage, from duty cycle to output voltage including MOSFET delay, and from input voltage to output voltage are derived. The derivations are performed using an averaged linear circuit small-signal model of the boost converter for CCM. Experimental Bode plots and step responses were used to test the accuracy of the derived transfer functions. The theoretical and experimental responses were in excellent agreement, confirming the validity of the derived transfer functions

Voltage loop of boost PWM DC-DC converters with peak current-mode control

A new transfer function from control voltage to duty cycle, the closed-current loop, which captures the natural sampling effect is used to design a controller for the voltage-loop of a pulsewidth modulated (PWM) dc-dc converter operating in continuous-conduction mode (CCM) with peak current-mode control (PCM). This paper derives the voltage loop gain and the closed-loop transfer function from reference voltage to output voltage. The closed-loop transfer function from the input voltage to the output voltage, or the closed-loop audio-susceptibility is derived. The closed-loop transfer function from output current to output voltage, or the closed loop output impedance is also derived. The derivation is performed using an averaged small-signal model of the example boost converter for CCM. Experimental verification is presented. The theoretical and experimental results were in good agreement, confirming the validity of the transfer functions derived.

Open-loop power-stage transfer functions relevant to current-mode control of boost PWM converter operating in CCM

This paper presents the analysis of open-loop power-stage dynamics relevant to current-mode control for a boost pulsewidth-modulated (PWM) dc-dc converter operating in continuous-conduction mode (CCM). The transfer functions from input voltage to inductor current, from duty cycle to inductor current, and from output current to inductor current are derived. The delay from the MOSFET gate drive to the duty cycle is modeled using a first-order Pade/spl acute/ approximation. The derivations are performed using an averaged linear small-signal circuit model of the boost converter for CCM. The transfer functions can be used in modeling the complete boost PWM converter when current-mode control is used. The theory was in excellent agreement with the experimental results, enforcing the validity of the transfer functions derived.