Converter Operating In Discontinuous Conduction Mode Research Articles

SEPIC converter in discontinuous conduction mode: Small signal modeling and analysis

AbstractIn this article, a new approach is applied to solve the small signal state space average (SSA) model for pulse width modulated (PWM) single ended primary inductor converter (SEPIC) under discontinuous conduction mode (DCM) of operation. Authors proposed a novel approach to get duty ratio constrains that is based on variation of current in inductor. The approach used a unique correction matrix (M) in the modeling process and obtained better results for DCM. To demonstrate the whole technique, the SEPIC‐based power supply of 75 W is designed and system loop gain is derived with the help of this new technique. The frequency response of the proposed system is captured with the help of linearization technique using MATLAB Simulink platform. The frequency plot from the proposed techniques is much closer to simulation results as compared to conventional method. This claims high predictions for dc–dc converter operating in DCM with wide range of input supply. The proposed model is analyzed with previous SSA small signal modeling for comparative results on the basis of frequency analysis and stability. The experiment results of designed power supply have shown good power quality performance at 220‐V AC mains for light‐emitting diode (LED) lighting application.

Spectral analysis of switch voltage for dual randomized PWM DC-DC converters operating in DCM

ABSTRACT This paper addresses the spectral characteristics of a dual randomised pulse width modulation scheme (RCFM-RPPM) for reducing conducted EMI in the basic DC-DC converters (buck, boost, and buck-boost) operating in discontinuous conduction mode (DCM). It combines two simple schemes, random carrier frequency modulation (RCFM), and a random pulse position (RPPM). First, the modulating principle of the dual randomised PWM is presented. Then, a mathematical model of power spectral density (PSD) that characterises the switch voltage of the three basic DC-DC converters is derived. The mathematical model is validated by simulation of a buck converter operating in DCM. Analytical and simulation results show the effectiveness of PSD spreading of the dual randomised scheme compare to the simple randomised schemes. Moreover, the PSD analysis is confirmed by FFT (Fast Fourier Transform) analysis of the switch voltage. Finally, the effect of randomness levels on the PSD spreading is studied.

Voltage‐extrapolative charge balance controller with charge compensation for flyback converter operating in DCM

This study presents a voltage-extrapolative charge balance (VECB) controller with charge compensation for flyback converter operating in discontinuous conduction mode (DCM). Compared with conventional charge balance controller, the VECB controller benefits from voltage extrapolation, which improves the transient response to load disturbance. Based on the output voltage differential value, a voltage extrapolator calculates the output voltage after two switching cycles under the influence of discharge. Furthermore, the extrapolated voltage is used to calculate the reference charge for the next switching cycle. The VECB controller eliminates the lag in calculating the reference charge, which improves the transient response to load disturbance. Closed-loop small signal models under VECB and conventional charge balance controls are derived and compared to prove the improvement. Furthermore, charge damping and its influence to the output voltage are intensely studied. To minimise the influence, a constant factor is adopted to carry out charge compensation, which is proved to be adequate. Finally, the effectiveness of VECB controller is verified on a flyback converter prototype.

An Optimized Sensorless Charge Balance Controller Based on a Damped Current Model for Flyback Converter Operating in DCM

This paper presents an Optimized Sensorless Charge Balance (OSCB) controller based on a damped current model for flyback converter operating in Discontinuous Conduction Mode (DCM). By solving total differential equations of non-ideal transformer currents, the damped current model is derived with consideration of parasitics, leakage inductance of transformer, and the Resistor-Capacitor-Diode (RCD) snubber circuit. Based on the proposed model, current observation and control algorithms of the Sensorless Charge Balance (SCB) controller are optimized, which forms the OSCB control strategy. The average current damping is considered in the equivalent discrete-time small signal model. Furthermore, frequency analyses show that OSCB controller achieves higher closed-loop bandwidth and lower overshoot than a SCB controller, which indicates an improved transient performance. Finally, both OSCB and conventional SCB controllers are experimentally evaluated on a flyback converter prototype.

Small-Signal Model of the Two-Phase Interleaved Coupled-Inductor Boost Converter

A coupled-inductor dc–dc converter has several modes of operation in continuous-conduction mode (CCM) and discontinuous-conduction mode (DCM), and is quite complex. This paper presents the derivation of the complete small-signal model of a two-phase interleaved dc–dc boost converter utilizing a single-core coupled-inductor operating in both CCM and DCM. Several small-signal models are required to fully model the converter due to the complexity of the converter operating in DCM. The transfer functions are then derived from these small-signal models. The theoretical analysis is validated experimentally using frequency sweeps from a 1-kW prototype.

Primary Side Control For Flyback Converter Operating in DCM and CCM

Primary side regulation (PSR) technology has the characteristics of lower cost and standby power losses. However, there is no algorithm suitable for discontinuous conduction mode (DCM) and continuous conduction mode (CCM) operations of primary side control for flyback converter because of the difficulty in estimating the output voltage correctly. In this paper, a PSR control algorithm suitable for DCM/CCM flyback converter is proposed and implemented with digital micro controller. The voltage drop on the secondary winding and output diode at CCM operation is compensated by sensing the secondary side current at the instant when primary side switch is being turned-on. The secondary side current is zero at the voltage sensing instant and equal to the current at the instant when primary side switch is being turned-on as flyback operated at DCM. In addition, the proposed algorithm can be used to regulate either the output voltage or current very well. An experimental prototype with 150 W rated power is built to verify the feasibility of the proposed control. Experimental results show that the output voltage can be controlled with error less than 0.25%, and the output current error is less than 5%. The conversion efficiency is up to 92.8%.

Uniform Model and Analysis of PWM DC–DC Converter for Discontinuous Conduction Mode

ABSTRACTIn this paper, a modified small signal state space average model is proposed to analyze the pulse width modulated converter operating in discontinuous conduction mode (DCM). It is based on a unique correction matrix (Mc) and new duty ratio constrain which is derived on the basic properties of inductor current. A 12 volt, 5 watt power supply based on Cuk converter is designed to demonstrate this proposed methodology. Transfer functions (input-to-output and control-to-output) of this power supply are calculated theoretically with the help of proposed modelling procedure. Bode plots of those transfer function are achieved using MATLAB toolboxes. To validate the proposed model, a simulation is also performed in MATLAB and frequency response is captured at run time using linearization technique. Bode plots from proposed model are very much in line with simulation results and offer improved predictions for high frequency dynamics of converter operating in DCM. The validity of presented work is reconfirmed by experimental set-up. The presented work is also compared with conventional small signal modelling on the basis of frequency analysis.

Chaos control of voltage mode controlled buck-boost converter

Due to the limitation to the development level of modern science and technology, DC-DC (where DC stands for direct current) converters operating in chaotic state cannot be used to achieve some desired goals yet and the chaotic phenomena occurring in DC-DC converters are almost restrained. For DC-DC converter operating in continuous conduction mode (CCM), its characteristic has been widely studied, but DC-DC converter needs to operate in discontinuous conduction mode (DCM) at light load. Because if it always works in CCM, the inductor current will be less than zero when the load is light, which will increase conduction loss and reduce conversion efficiency. Moreover, DCM operation is frequently encountered, since power converters are usually required to operate with loads removed. For buck-boost converter, the obvious oscillation will appear when it works under the condition of varying operating point, so it is difficult to control. Considering the reasons above, the voltage mode controlled buck-boost converter operating in DCM is chosen to be studied to verify the validity of the two control methods presented in this paper. Under a certain condition, chaos and bifurcation will occur in the voltage mode controlled buck-boost converter operating in DCM. Having discussed its chaotic phenomenon, in this paper we present two ways to control the system to operate stably in one-cycle state. The first way is the self-controlling delayed feedback control method. The basic idea of this method is to use the difference between the delayed output signal and the output signal to form a feedback signal, and return it to the control circuit in a form of negative feedback to control the output signal. The simulation results show that the self-controlling delayed feedback control method can make the system which has already entered into chaos operate stably in one-cycle state. Besides, its dynamic response speed is fast and it does not change the system frequency. However, this method fails to work when the disturbance is too large. Therefore, the self-controlling delayed feedback control method is more suitable for small disturbance condition. The second way is the improved sliding mode control method. The basic idea of the sliding mode control is to design a switching function to determine a switching surface which represents a desired system dynamics, then, design a variable structure control law to drive any state to reach the switching surface, therefore, the sliding mode takes place and the system follows the desired dynamics. The simulation results show that the improved sliding mode control method can force the system which has already entered into chaos to operate stably in one-cycle state even when the system encounters large disturbance. In addition, although it is more complicated to design, it has great dynamic response characteristics and excellent robustness. Because the methods presented in this paper do not rely on the buck-boost converter itself, both methods can be used to control other DC-DC converters. When the disturbance is small, the self-controlling delayed feedback control method should be considered first, for it is easier to achieve. When the system encounters large disturbances the sliding mode control method has the priority, because this method is valid while the self-controlling delayed feedback control method may fails under such a condition.

Isolated Single-phase High Power Factor Rectifier Using Zeta Converter Operating in DCM With Non-Dissipative Snubber

This paper presents the study of a single-stage, single-phase, unity power factor converter, isolated by a high frequency transformer, based on a Zeta converter operating in discontinuous conduction mode (DCM). The main feature of the proposed converter is its ability to naturally emulate an apparent resistance to the ac input source, without current sensor or current controller. Circuit operation, theoretical analysis and design example are included in this paper, along with experimental results taken from a laboratory prototype rated at 400W, input voltage equal to 127 V, output voltage equal to 200 V, switching frequency of 25 kHz and efficiency of 92 %. In order to reduce the commutation losses and limit the peak voltage across the power semiconductors, a non- dissipative snubber has been included in the laboratory prototype. With the advent of new low losses power semiconductor technologies, such as SiC and GaN, power converters operating in DCM will become very attractive, due to their simplicity and robustness, even for high power applications. This is the main motivation of the study presented hereafter.

Stability issues and modelling of ripple‐based constant on‐time control schemes operating in discontinuous conduction mode

Ripple-based constant on-time (RBCOT) control schemes have recently received much attention for the DC converters used in many applications, mainly because of the relatively high efficiency under light-load condition while preserving other features such as fast step-load response and small component count. Since the converter is usually operated under discontinuous conduction mode (DCM) under light-load condition, an effort to investigate the RBCOT schemes under DCM is practically important. Rigorous mathematical analyses are used to investigate the feedback stability issues of the buck converters using RBCOT control schemes operating in DCM. Two RBCOT control schemes are considered: the basic RBCOT scheme and the basic RBCOT with virtual-inductor-current signal (VICRBCOT). It is proved that it is always stable for the basic RBCOT converter operating in DCM, but that is not the case for the VICRBCOT converters. A proper design procedure to maintain stability for both the continuous conduction mode and the DCM operations in VICRBCOT converters is proposed and verified.

LED Lamp Power Supply without Electrolytic Capacitors based on Integrated Double Buck-Boost Converter Operating in Full DCM

In this paper the integrated double buck-boost converter (IDBBC) operating with both stages in discontinuous conduction mode (DCM) is analyzed. The converter is intended to supply high-voltage LED lamps from the mains, typically in street lighting applications. A high input power factor is assured by operating the first stage in DCM, thus complying with current harmonic injection standards. In this work, the second stage is also operated in DCM as an option to the continuous conduction mode (CCM) that has been studied in a previous paper. The behavior of the converter with both stages in DCM is compared with that of the converter operation with the second stage in CCM. It is demonstrated that with both converters operating in DCM the filter capacitances are reduced even further, allowing for the use of long-life non-electrolytic capacitors. A laboratory prototype to supply a 70 W LED lamp with nominal voltage of 200 V from a 230 V/50 Hz mains maintaining the same design conditions as in the previous work is presented. A comparison of both prototypes is also carried out.

A reduced sensor PFC BL-Zeta converter based VSI fed BLDC motor drive

This papers aims at the design of BL-Zeta (bridgeless Zeta) converter fed BLDC (Brushless DC) motor drive. A single voltage sensor is used for achieving PFC (Power Factor Correction) and DC link voltage control. Unlike the conventional approach of using a PWM (Pulse Width Modulation) switching of VSI (Voltage Source Inverter), a new approach of speed control is used to control the voltage at the DC link of VSI. A fundamental frequency switching is used for electronic commutation of BLDC motor for achieving reduced switching losses in the VSI. A voltage follower approach is employed for DC link voltage control in BL-Zeta converter operating in DCM (Discontinuous Conduction Mode). Moreover, the conduction losses in the DBR (Diode Bridge Rectifier) are also eliminated in a bridgeless topology of Zeta converter. A satisfactory performance of proposed drive is achieved for a wide range of speed control of BLDC motor and varying supply voltage to study the behaviour of proposed drive in practical supply conditions. Switches stresses are also analyzed for their selection and heat sink design. The power quality indices at AC mains obtained are found within the recommended limits by International power quality standards such as IEC 61000-3-2.

Discontinuous-Conduction Mode DC/DC Converters Feeding Constant-Power Loads

One of the major issues in multiconverter power-electronic systems, which exist in different land, sea, air, and space vehicles, is the stability problem imposed by constant-power loads (CPLs). The research work done in this field has been focused mainly on continuous-conduction mode of operation. In this paper, we study the case when the loaded converter operates in discontinuous-conduction mode (DCM). We prove that the open-loop DC/DC converters operating in DCM are stable when they are loaded by CPLs. Furthermore, we present that the problem of feedback design for a converter operating in DCM and loaded by a CPL can be translated into a conventional feedback-design task for the same converter with a resistive load. Simulation and experimental results verify the presented discussion.

Winding losses caused by harmonics in high-frequency flyback transformers for pulse-width modulated dc–dc converters in discontinuous conduction mode

High-frequency transformers used in pulse-width modulated (PWM) converters conduct periodic non-sinusoidal currents, which give rise to additional winding losses because of harmonics. This study presents expressions for winding power losses in a two-winding transformer subject to non-sinusoidal excitation operated in discontinuous conduction mode (DCM). Dowell's equation is used to determine the winding resistances because of eddy currents as a function of frequency. Both skin and proximity effects are taken into account. Fourier series of the primary and secondary triangular current waveforms in isolated dc–dc power converters and the primary and secondary winding resistances are used to determine the primary and secondary winding power losses at various harmonics, respectively. The harmonic winding loss factors FRph and FRsh are introduced. The theory is illustrated by the case study of the two-winding flyback converter operating in DCM. Plots of the winding power losses are given as functions of the output power and the dc input voltage.

Pulse Regulation Control Technique for Flyback Converter

Pulse regulation, a fixed frequency control technique, is introduced and applied to flyback converter operating in discontinuous conduction mode (DCM). The control parameters are designed in a way that the converter operates as close as possible to the critical conduction mode. In contrast to the conventional pulsewidth modulation control scheme, the principal idea of pulse regulation is to achieve output voltage regulation using high and low-power pulses. Pulse regulation is simple, cost effective, and enjoys a fast dynamic response. The proposed technique is applicable to any converter operating in DCM. However, this work mainly focuses on flyback topology. In this paper, the main mathematical concept of the new control algorithm is introduced and simulations as well as experimental results are presented.

Pulse Regulation Control Technique for Integrated High-Quality Rectifier-Regulators

The pulse regulation control scheme is presented and applied to the boost integrated flyback rectifier/energy storage dc/dc (BIFRED) converter as the most popular member of the integrated high-quality rectifier-regulators (IHQRR). In contrast to the conventional control techniques, the principal idea of pulse regulation is to regulate the output voltage using a series of high- and low-power pulses generated by the current of the input inductor, which is operating in discontinuous conduction mode (DCM). Analysis of the BIFRED converter operating in DCM is presented. Fundamentals of pulse regulation as well as its stability analysis and the estimation of the output voltage ripple are introduced. Experimental results on a prototype converter are also presented to validate the analytical and simulation results.

Suitability of pulse train control technique for BIFRED converter

Pulse Train/spl trade/ control scheme is presented and applied to a boost integrated flyback rectifier/energy storage dc-dc (BIFRED) converter operating in discontinuous conduction mode (DCM), which avoids the light-load high-voltage stress problem. In contrast to the conventional control techniques, the principal idea of Pulse Train technique is to regulate the output voltage using a series of high and low energy pulses generated by the current of the inductor. The applicability of the proposed technique to both the input and magnetizing inductances of BIFRED converter is investigated. Analysis of BIFRED converter operating in DCM as well as the output voltage ripple estimation is given. Experimental results on a prototype converter are also presented.

Pulse Train Control Technique for Flyback Converter

Pulse Train/spl trade/ control technique is introduced and applied to flyback converter operating in discontinuous conduction mode (DCM). In contrast to the conventional pulse width modulation (PWM) control scheme, the principal idea of Pulse Train is to achieve output voltage regulation using high and low power pulses. The proposed technique is applicable to any converter operating in DCM. However, this work mainly focuses on flyback topology. In this paper, the main mathematical concept of the new control algorithm is introduced and simulations as well as experimental results are presented.

Estimative Current Mode Control Technique for DC–DC Converters Operating in Discontinuous Conduction Mode

A new control technique for DC-DC converters is introduced and applied to a boost converter operating in discontinuous conduction mode (DCM). In contrast to conventional control methods, the principal idea of the proposed control scheme is to obtain samples of the required signals and estimate the required switch-on time. The proposed technique is applicable to any converter operating in DCM, including power factor correctors (PFC), however, this letter mainly focuses on boost topology. In this letter, the main mathematical concept of a new control algorithm is introduced, as well as the robustness investigation of the proposed method with simulation and experimental results.