Pseudo-continuous Conduction Mode Research Articles

Optimization Control Strategy for Light Load Efficiency of Four-Switch Buck-Boost Converter

The four-switch buck-boost (FSBB) converter usually adopts a pseudo-continuous conduction mode (PCCM) soft switching (ZVS) control strategy, but there is a problem with the low efficiency of FSBB converters under light loads. Firstly, the constraints that the control variables of the FSBB converter need to satisfy are analyzed, and it is pointed out that the fixed frequency constraint is not necessary. Then, the switching frequency is used to control the degree of freedom, and the quantitative relationship between the FSBB converter loss and the switching frequency is obtained. Finally, for different input voltages and loads, the switching frequency corresponding to the minimum power loss is calculated offline. By optimizing the switching frequency, the light-load efficiency of the FSBB converter is improved. A prototype with an input voltage range of 210 V–330 V, an output voltage of 270 V, and an output power of 3 kW was developed. The loss was reduced by 15% at 20% load, and the peak efficiency of the converter reached 99.23%. The experimental results verified the effectiveness of the proposed control strategy.

A Multi-Frequency PCCM ZVS Modulation Scheme for Optimizing Overall Efficiency of Four-Switch Buck–Boost Converter With Wide Input and Output Voltage Ranges

The pseudo-continuous conduction mode (PCCM) zero-voltage-switching (ZVS) modulation scheme is widely used in the four-switch buck-boost (FSBB) converter to achieve high efficiency and voltage step-up/step-down without modulation mode transition. There are two degrees of modulation freedom in the PCCM ZVS modulation scheme. The previous schemes typically only optimize one of them to reduce root mean square (rms) inductor current, which results in relatively lower efficiency in the condition when the difference between input voltage and output voltage is large. In this paper, a multi-frequency PCCM ZVS modulation scheme is proposed for the FSBB converter with wide input and output voltage ranges. By optimizing both of the two degrees of modulation freedom to reduce rms inductor current, the heavy-load efficiency can be effectively improved when the difference between input voltage and output voltage is large. Thus, the overall efficiency of the FSBB converter can be optimized. A 1500W FSBB prototype with input and output voltage ranges of 200-400V is built to verify the proposed modulation scheme.

Dynamic Freewheeling Control for SIDO Buck Converter With Fast Transient Performance, Minimized Cross-Regulation, and High Efficiency

Slow load transient performance, potential cross-regulation, and low efficiency are the major drawbacks for pseudocontinuous conduction mode single-inductor dual-output (SIDO) dc–dc converters. To overcome these drawbacks, this article proposes a voltage-ripple (VR)-based dynamic freewheeling (DF) control technique for hybrid conduction mode (HCM) SIDO buck converter. With the employment of VR controller, the proposed control technique improves the load transient performance significantly. As the fast recovery during load transition, the cross-regulation is minimized. Additionally, due to the DF controller, the freewheel current value automatically updates in each switching period, which can improve the efficiency of the HCM SIDO buck converter, especially under the light load conditions. Finally, the proposed converter has been verified through experimental results. The transient response time on 0.5 A load change takes only 1–2 switching periods. No observable cross- regulation is found and maximum efficiency of 92.03% is achieved. Finally, the experimental waveforms are presented to verify the theoretical research.

PT controlled PCCM buck converter with adaptive pulse train generator and NMOS current sensor

A pulse train controlled buck converter operating in pseudo continuous conduction mode (PCCM) is implemented in the 0.18-μm CMOS process in this paper. An adaptive pulse train generator, which adjusts duty cycle based on the output power, is proposed to improve the output voltage range and transient response. To operate in PCCM, an NMOS current sensor using a double common-gate amplifier with a high slew rate is utilized to detect the falling inductor current. Simulation results demonstrate that the converter obtains a well regulated variable output voltage from 1 V to 4 V, providing a maximum load current of 1000 mA at the switching frequency of 1 MHz. The transient spike is smaller than 35 mV and recovery time is less than 6.3μs for a 300 mA load current step. The peak efficiency is 94.4% at 300-mA load current.

Modeling and Analysis of Voltage Ripple-Controlled SIDO Buck Converter in Pseudo-Continuous Conduction Mode with Limited Cross-Regulation and Fast Load Transient Performance

Typical voltage mode-controlled DC–DC converters with single-inductor dual-output (SIDO) in pseudo-continuous conduction mode (PCCM) have slow load transient performance, and cross-regulation still exists between their two outputs. For the purposes of suppressing the cross-regulation and improving the load transient performance, a voltage ripple control technique for a PCCM SIDO buck converter is proposed in this study. A description of the PCCM SIDO buck converter and the voltage ripple control technique is provided in detail. In addition, the small-signal model was established, and the cross-regulation was further compared by Bode plots, as well as the load range and the power losses being analyzed. The cross-regulation and load transient performance of the voltage ripple-controlled PCCM SIDO buck converter was studied and compared with the conventional voltage mode-controlled. Using the proposed voltage ripple control for PCCM SIDO buck converters, we found no cross-regulation or rapid load transient behavior, which was validated by experimental results.

A high-power PCCM LED driver based on GaN eHEMT with hybrid dimming modes

PurposeThe purpose of this study is to design a more flexible and larger range of the dimming circuit that achieves the independence of multiple LED strings drive and can time-multiplex the power circuit.Design/methodology/approachThe state-space method is used to model the BUCK circuit working in Pseudo continuous conduction mode, analyze the frequency characteristics of the system transfer function and design the compensation network. Build a simulation platform on the Orcad PSPICE platform and verify the function of the designed circuit through the simulation results. Use Altium Designer 16 to draw the printed circuit board, complete the welding of various components and use the oscilloscope, direct current (DC) power supply and a signal generator to verify the circuit function.FindingsA prototype of the proposed LED driver is fabricated and tested. The measurement results show that the switching frequency can be increased to 1 MHz, Power inductance is 2.2 µH, which is smaller than current research. The dimming ratio can be set from 10% to 100%. The proposed LED driver can output more than 48 W and achieve a peak conversion efficiency of 91%.Originality/valueThe proposed LED driver adopts pulse width modulation (PWM) dimming at a lower dimming ratio and adopts DC dimming at a larger dimming ratio to realize switching PWM dimming to analog dimming. The control strategy can be more precise and have a wide range of dimming.

Single-Inductor Multiple-Output (SIMO) Buck Hybrid Converter for Simultaneous Wireless and Wired Power Transfer

In this article, a nonisolated single-inductor multiple-output (SIMO) dc–ac buck-derived hybrid converter for simultaneously driving multiple independent ac and dc loads using only a single inductor in the power stage is proposed. Compared with the prior art, the proposed SIMO-based hybrid converter carries the conspicuous advantages of 1) a simple, compact, and low-cost implementation of the power stage; 2) reduced component count; 3) high power density; 4) increased output power, better flexibility, and scalability in realizing any combinations of ac and/or dc loads; and 5) high efficiency. By operating in pseudocontinuous conduction mode (PCCM), this hybrid converter enables wireless and wired power transfer at medium-power level without cross regulation. In practice, this converter can serve as a Qi-compliant hybrid charger with multiple transmitting coils and universal serial bus (USB) charging ports for quick and concurrent multidevice charging. A hardware prototype of a single-inductor four-output (SIFO) buck-derived hybrid converter is constructed. The experimental results show that the SIFO converter produces a rated output power of 20 W and a maximum efficiency of around 88%.

Buck-Boost Single-Inductor Multiple-Output High-Frequency Inverters for Medium-Power Wireless Power Transfer

In this paper, a nonisolated buck-boost single-inductor multiple-output (SIMO) dc–ac inverter for driving multiple independent high-frequency ac outputs of medium power is proposed. Compared with traditional bridge-type inverters, the proposed buck-boost SIMO inverter achieves 1) a smaller component count, 2) fully independent power control of its outputs, 3) better scalability in increasing the number of ac output channels, and 4) higher power efficiency. Operating in pseudo-continuous conduction mode, the rated power of each output channel of this inverter can be high while attaining zero cross regulation. The scalability factor of the proposed inverter is formally investigated and the theoretical maximum number of ac outputs is analytically derived. The targeted application of this SIMO-based inverter is for driving multiple transmitter coils to realize versatile multidevice medium-power wireless power transfer. A hardware prototype of a single-inductor three-output buck-boost inverter delivering a medium power of 8.4 W per output channel has been constructed. It is experimentally verified that precise and independent current regulation of individual transmitter coil is achievable with the proposed inverter.

Unified discrete‐map modelling and dynamical behaviour analysis of current mode controlled tri‐state dc–dc converters

Through analysing the operating principle of current mode controlled (CMC) tri-state dc-dc converters, the inductor current borders are obtained and a unified discrete-map model of CMC tri-state dc-dc converters with ramp compensation is established. According to this model, the dynamical behaviour of the tri-state dc-dc converters is analysed by utilising bifurcation diagram. In addition, the boundary equation of tri-state dc-dc converters from stable pseudo-continuous conduction mode (PCCM) period-1 state to unstable state is derived. The expressions of the minimum slope of ramp compensation for the converter shifting from unstable state to stable PCCM period-1 state are also obtained. Meanwhile, the operating regions are divided effectively by the boundary equation. The research results indicate that border collision bifurcation could occur when the circuit parameters vary, including a bifurcation from one periodic orbit to another periodic orbit, such as period-1 to period-2 or period-2 to period-4 and so on, or a bifurcation from a period orbit to chaotic orbit. By using ramp compensation, the stable working range of the CMC tri-state dc-dc converter could be broadened. Finally, an experimental circuit is built and the experiment results verify the theoretical analysis.

Analysis and design of a novel tri-state Flyback PFC converter with high load power

A novel tri-state pseudo-continuous conduction mode (PCCM) Flyback power factor correction (PFC) converter and its corresponding control strategy are proposed to improve load power. The proposed converter is built with double MOSFET formed half bridge and operated in PCCM, which provides an additional degree of control freedom for simplifying the PFC controller. The tri-state PCCM Flyback converter can improve the load power effectively compared with the conventional DCM Flyback PFC converter at constant switching frequency. Analyses and 200W prototypes of the tri-state PCCM Flyback PFC converter and conventional DCM Flyback PFC converter have been presented. The results show that the proposed tri-state PCCM Flyback PFC converter is suitable for heavier load power compared with conventional DCM Flyback PFC converter.

Analysis of Pulse Train Controlled PCCM Boost Converter With Low Frequency Oscillation Suppression

For pulse train (PT) controlled switching converter, when it operates in continuous conduction mode (CCM) and discontinuous conduction mode (DCM), there exist disadvantages of low frequency oscillation and narrow load range, respectively. To avoid these disadvantages of PT controlled switching converter in CCM and DCM, a PT controlled boost converter operating in pseudo continuous conduction mode (PCCM) is taken as the research object in this paper, its working principle has been analyzed in detail. Based on the analysis of output voltage ripple during one switching cycle, the combination of high- and low-power control pulses in a repetition cycle is analyzed and the expression of output voltage ripple is derived for different load conditions. Finally, simulation and experiment are performed to verify the correctness of the control pulse combinations and the output voltage ripple analysis. Results show that compared with DCM and CCM boost converters, the PT controlled PCCM boost converter not only has wider load range, but also can suppress low frequency oscillation.

A Novel PCCM Voltage-Fed Single-Stage Power Factor Correction Full-Bridge Battery Charger

A novel pseudo-continuous conduction mode (PCCM) voltage-fed single-stage power factor correction (PFC) full-bridge battery charger is proposed in this paper. By connecting a freewheeling transistor in parallel with an input inductor, the PFC cell can operate in the PCCM with a constant duty ratio. Thus, the dc/dc stage can be designed using this constant duty ratio and the restriction on the duty ratio of the PFC cell is eliminated. As a result, the input current distortion is less and the dc bus voltage becomes controllable over the wide output power range of the battery charger. Moreover, the operation principle of the dc/dc stage is designed to be similar to that of a conventional phase-shifted full-bridge converter. Therefore, it is easy to implement. In this paper, the operation of the new converter is explained, and the design considerations of the controller and key parameters are presented. Simulation and experimental results obtained from a 1 kW prototype are given to confirm the operation of the proposed converter.

Modeling and Characteristics Analysis for a Buck-Boost Converter in Pseudo-Continuous Conduction Mode Based on Fractional Calculus

In recent days, fractional calculus (FC) has been accepted as a novel modeling tool that can extend the descriptive power of the traditional calculus. Fractional-order descriptiveness can increase the flexibility and degrees of freedom of the model by means of fractional parameters. Based on the fact that real capacitors and inductors are “intrinsic” fractional order, fractional calculus is introduced into the modeling process to establish a fractional-order state-space averaging model of the Buck-Boost converter in pseudo-continuous conduction mode (PCCM). Orders of the model are considered as extra parameters, and these parameters have significant influences on the performance of the model. The inductor current, the inductor current ripple, the amplitude of the output voltage, and the transfer functions of the fractional-order model are all related to orders. The contrast simulation experiments are conducted to investigate the performance of integer-order and fractional-order Buck-Boost converters in PCCM. Results of numerical and circuit simulations demonstrate that the proposed theoretical analysis is effective; the fractional-order model of the Buck-Boost converter in PCCM has certain theoretical and practical significance for modeling and performance analysis of other electrical or electronic equipment.

DSP-Based Control of Tri-State Boost PFC Converter with High Input Power Factor for Wide Range of Load Variations

Tri-state boost power factor correction (PFC) converter operating in pseudo-continuous-conduction mode (PCCM) is analyzed in this paper. The connection of power switch in parallel with inductor makes the boost converter operate in PCCM, which provides an additional degree of control freedom by inductor current freewheeling operation mode. Compared with boost PFC converter operating in continuous conduction mode (CCM) and discontinuous conduction mode (DCM), tri-state boost PFC converter extends the load range and is therefore more suitable for wide range of load variation. However, for universal input applications, the input power factor (PF) of the tri-state boost PFC converter is relatively low when the sinusoidal reference current control strategy is used. To improve the PF over the whole input voltage range, the input current and PF expressions of the tri-state boost PFC converter is derived and the non-sinusoidal reference current control strategy is proposed. A 400 W prototype of the tri-state boost PFC converter is built by using digital signal processing (DSP) as the controller. The experimental results verify the analysis results.

Dynamical modeling and analysis of buck converter operating in pseudo-continuous conduction mode

Taking buck converter operating in pseudo-continuous conduction mode (PCCM) for example, through a detailed description of the switch state of the switching converter, its accurate discrete-time model is established in this paper. On the basis of the model, bifurcation diagrams of the PCCM buck converter with the variations of circuit parameters are obtained, including load resistance, equivalent series resistance (ESR) of inductor, inductance, capacitance, reference current, and input voltage. And the complex dynamical behaviors existing in PCCM buck converter, such as subharmonic oscillation, period-double bifurcation and chaos, are revealed. Under different load resistances, time-domain simulation waveforms and phase portraits of PCCM buck converter are obtained by Runge-Kutta algorithm based on the piecewise smooth switch model. The working states of PCCM buck converter, reflected by the time-domain waveforms and phase portraits, are consistent well with those described by the bifurcation diagrams. It is shown that the time-domain simulation results verify the validation of the discrete-time model.#br#From theoretical analysis and simulation results, some conclusions can be obtained below. 1) When the load resistance gradually decreases, PCCM buck converter has a unique bifurcation route, i. e. , from PCCM period-1 state, PCCM multi-period oscillation via period-double bifurcation, chaos, CCM-PCCM multi-period oscillation, to CCM period-1 state via inverse period-double bifurcation. What is more, the bifurcation analysis with the load resistance serving as parameter indicates that the PCCM buck converter is more suitable for light load conditions, and its stable state will be lost and operation mode can be shifted (from PCCM to CCM) with increasing the load. 2) The ESR of inductor is closely related to the power loss and will affect the stability of the PCCM converter. The larger the ESR, the more the power loss will be. However, the PCCM converter is more stable if the ESR is larger. 3) Period-double bifurcation or inverse period-double bifurcation exists in the PCCM buck converter with the other circuit parameters varied in a wide range except for the load resistance, and there are three working states of buck operating in PCCM, i.e., stable period-1 state, multi-period sub-harmonic oscillation, and chaos. The research results in this paper are useful for designing and controlling PCCM switching converter.

Modeling and simulation analysis of fractional-order Boost converter in pseudo-continuous conduction mode

Based on the fact that the inductor and the capacitor are fractional in nature, the fractional order mathematical model of the Boost converter in pseudo-continuous conduction mode is established by using fractional order calculus theory. According to the state average modeling method, the fractional order state average model of Boost converter in pseudo-continuous conduction mode is built. In view of the mathematical model, the inductor current and the output voltage are analyzed and the transfer functions are derived. Then the differences between the integer order and the fractional order mathematical models are analyzed. On the basis of the improved Oustaloup fractional order calculus for filter approximation algorithm and the model of fractional order inductance and capacitance, the simulation results have been compared between the mathematical model and circuit model with Matlab/Simulink software; the origins of model error are analyzed and the correctness of the modeling in fractional order and the theoretical analysis is verified. Finally, the differences and the relations of Boost converter among the continuous conduction mode, the discontinuous conduction mode, and the pseudo-continuous conduction mode are indicated.

Non-linear control for the fractional boost converter in pseudo continuous conduction mode

Based on the fact that the inductor and the capacitor are of fractional order in nature, the mathematical model of the fractional order boost converter in pseudo continuous conduction mode is established by using the fractional order calculus theory. Due to the affine non-linear nature in this mathematical model and a similar Lyapunov stability theorem of the fractional order system, a fractional order non-linear controller is designed. On the basis of chain fractance and the improved Oustaloup algorithm, the circuit model of fractional order inductor and capacitor are built. The fractional order controller is verified by the Matlab/Simulink software. Simulation results show that the controller enhances the dynamic and steady-state performance, so as to realize the stability and achieve good dynamic performance of the fractional order system during large fluctuation of power supply and load disturbance.

High‐efficiency two‐switch tri‐state buck–boost power factor correction converter with fast dynamic response and low‐inductor current ripple

Two-switch tri-state buck-boost power factor correction (PFC) converter operating in pseudo-continuous conduction mode is proposed and analysed in this study. Different from tri-state boost PFC converter, the proposed two-switch tri-state buck-boost PFC converter does not need additional power switch to provide the additional degree of control freedom. Therefore it does not increase the complexity and affect the power conversion efficiency of the PFC converter as in the case of tri-state boost PFC converter. For the proposed two-switch tri-state buck-boost PFC converter, the current control loop and voltage control loop are decoupled, a simple voltage control loop with faster dynamic response can be designed to realise output voltage regulation and the additional degree of control freedom introduced by inductor current freewheeling stage helps to achieve unity power factor control. The operation principle, the input current, the inductor current ripple, the switch component stress and the small-signal characteristics of the proposed two-switch tri-state buck-boost PFC converter are analysed. The simulation and experimental results show that the proposed two-switch tri-state buck-boost PFC converter benefits with fast dynamic response, high-efficiency and low-inductor current ripple over single-switch buck-boost PFC converter or two-switch buck-boost PFC converter operating in continuous conduction mode and discontinuous conduction mode.

Monolithic quasi-sliding-mode controller for SIDO buck converter with a self-adaptive free-wheeling current level

An analog implementation of a novel fixed-frequency quasi-sliding-mode controller for single-inductor dual-output (SIDO) buck converter in pseudo-continuous conduction mode (PCCM) with a self-adaptive freewheeling current level (SFCL) is presented. Both small and large signal variations around the operation point are considered to achieve better transient response so as to reduce the cross-regulation of this SIDO buck converter. Moreover, an internal integral loop is added to suppress the steady-state regulation error introduced by conventional PWM-based sliding mode controllers. Instead of keeping it as a constant value, the free-wheeling current level varies according to the load condition to maintain high power efficiency and less cross-regulation at the same time. To verify the feasibility of the proposed controller, an SIDO buck converter with two regulated output voltages, 1.8 V and 3.3 V, is designed and fabricated in HEJIAN 0.35 μm CMOS process. Simulation and experiment results show that the transient time of this SIDO buck converter drops to 10 μs while the cross-regulation is reduced to 0.057 mV/mA, when its first load changes from 50 to 100 mA.

Adaptive pseudo-continuous conduction mode operation schemes and circuit designs for single-inductor multiple-output switching converters

As single-inductor multiple-output (SIMO) switching converters proliferate in integrated power management designs, pseudo-continuous conduction mode (PCCM) operation with freewheel switching has been well adopted owing to its effectiveness on cross-regulation, voltage ripple and switching noise issues, especially in heavy load scenarios. However, the technique faces a direct challenge in unbalanced loading conditions. Potential lengthy freewheel switching periods and high I dc current levels could lead to conduction and switching power losses, degrading the efficiency of the converters. To alleviate this problem, this paper presents adaptive PCCM operation schemes with the respective distributed and unified freewheel switching schemes. The optimal freewheel switching durations are achieved in various load conditions by adaptively adjusting the phase durations and freewheel switching I dc current level, thereby reducing the conduction and switching losses effectively. The switching power loss is further reduced by turning on/off the freewheel switch less frequently, without compromising the performance of operation. The proposed schemes have been implemented and verified in digital and analog-based SIMO power converters designed with 130 nm CMOS process.