Critical Conduction Mode Research Articles

A PFC Rectifier Based EV Charger for Harmonic Reduction

Abstract The current Indian scenario has marked adoption of Electric Vehicle (EV) to eradicate the atmosphere′s carbon footprint. However, the inclusion of nonlinear EV charger offers catastrophic effects to battery′s and EV′s circuitry. The AC-DC conversion of energy through conventional rectifier leads to the generation of large inrush current and obnoxious spikes in the input current. Moreover, the repercussions of interference of injected harmonics may be witnessed in the poor efficiency and degradation of the EV charger′s elements. Henceforth, the resultant low power factor and exaggerated total harmonic distortion (THD) makes it obvious to integrate a Power Factor Correction (PFC) circuit at the initial stage. Thus, an Orcad Pspice simulated PFC rectifier model has been proposed that eliminates the undesirable harmonics, hence, empowering the power factor. This is achieved by developing a sinusoidal input inductor current in phase with the input voltage waveform. The model adopts an easy control by using Critical Conduction Mode (CrCM) technique under which the switching operation takes place at zero as well as peak of the current waveform. Moreover, the circuit inculcates a closed loop strategy where the generated error at voltage sensing, current sensing, programmed and reference current waveform comparison is evaluated. Thus, the examination of achieved results explains the accurate working of model and realization of unity power factor.

A High-Efficiency High-Density Wide-Bandgap Device-Based Bidirectional On-Board Charger

This paper proposes a novel two-stage topology for a 6.6-kW on-board charger. The first stage, employing an interleaved bridgeless totem-pole ac/dc in critical conduction mode to realize zero-voltage switching, is operated at over 300 kHz. A bidirectional CLLC resonant converter operating at 500 kHz is chosen for the second stage. A variable dc-link voltage is adopted to track the wide battery voltage range, so that the CLLC resonant converter can always operate at its most efficient point. The 1.2-kV SiC devices are adopted for the ac/dc stage and the primary side of dc/dc stage, while 650-V GaN devices are used for the secondary side of dc/dc stage. In addition, PCB winding coupled inductors and integrated transformer are implemented in ac/dc stage and dc/dc stage, respectively, for the purpose of high density and manufacture automation. The proposed structure is demonstrated to have 37-W/in3 power density and above 96% efficiency over the entire battery voltage range, which far exceeds the current practice.

Improvement of Power-Conversion Efficiency of AC–DC Boost Converter Using 1:1 Transformer

This paper proposes a circuit structure that can improve the power-conversion efficiency $\eta _{e}$ of an AC–DC boost converter. The circuit uses a 1:1 transformer and a voltage boost circuit composed of an inductor, a capacitor, and a diode. The transformer forces the converter to operate in continuous conduction mode for input current, and thereby reduces input ripple. The voltage boost circuit enables the switch to operate in critical conduction mode, so the power loss due to turn- on of switch and reverse recovery of diode is minimized. The proposed converter has high $\eta _{e}$ over a wide range of AC input voltage $V_{{\rm{ac}}}:\,\eta _{e}= 92.9\% $ at $V_{{\rm{ac}}}= {\text{85}}\,{\text{V}}$ and $\eta _{e}= 97.4\% $ at $V_{{\rm{ac}}}= {\text{265}}\,{\text{V}}$ , when the converter was operated at DC output voltage of 400 V and output power of 500 W. The temperature of the switch stabilized at ∼84 °C for $V_{{\rm{ac}}}= {\text{85}}\,{\text{V}}$ , at ∼70 °C for $V_{{\rm{ac}}}= {\text{110}}\,{\text{V}}$ , and at ∼42 °C for $V_{{\rm{ac}}}= {\text{220}}\,{\text{V}}$ , whereas that in other AC–DC converters either failed or stabilized at much higher levels. The proposed converter is well suited to systems that require an input voltage range of 85–265 V in root-mean-square value.

Critical Conduction Mode Boost PFC Converter With Fixed Switching Frequency Control

Critical conduction mode (CRM) boost power factor (PF) correction converter features zero-current turn-on for the switch and no reverse recovery in diode, which is suitable for low-to-medium power applications. However, the switching frequency varies in a line cycle, and the wide variation range of the switching frequency is different under different input voltage and load conditions. This makes the conducted electromagnetic interference (EMI) spectra appearing great differences and complicates the design of EMI filter. In this paper, based on the expression of the switching frequency for traditional CRM control strategy, a variable on-time control strategy is proposed, and the implementation circuit is designed to realize a fixed switching frequency in a half-line cycle. The proposed strategy also achieves a lower output voltage ripple and a lower peak current for the power components. In spite of the PF decrease, the input current harmonic values are much lower than the IEC 61000-3-2 Class D limits. A 120 W prototype has been fabricated and tested in the laboratory and the experimental results are presented to verify the effectiveness of the proposed method.

A 12 mV Input, 90.8% Peak Efficiency CRM Boost Converter With a Sub-Threshold Startup Voltage for TEG Energy Harvesting

This paper proposed a high efficiency boost converter targeting thermoelectric generator energy harvesting. The proposed converter adopts the critical conduction mode rather than the discontinuous mode to reduce the conduction loss, which can improve the peak efficiency at high input power. To reduce the minimum input voltage, an adaptive on-resistance switch, which can automatically change the high side and low side on-resistance according to the input voltage, is used. To maximize the output power, a maximum power point tracking circuit is designed to track the internal source resistance. Radio frequency (RF) kick-up and low voltage startup are used to improve the cold start voltage. The proposed converter is implemented in a 0.18- $\mu \text{m}$ standard CMOS process, which occupies a chip area of about 0.48 mm2. Measurement results show that the peak efficiency of the converter can be up to 90.8% and 60% at 180 and 20 mV of the open-circuit voltage, respectively. Owing to the cold startup circuit, the proposed converter can start successfully with 260-mV open-circuit voltage or −16-dBm RF input. Moreover, the open-circuit voltage can be further lowered to 12 mV with 1.5- $\mu \text{W}$ output power after startup.

Quasi-Interleaved Current Control for Switch-Linear Hybrid Envelope-Tracking Power Supply

An envelope-tracking (ET) technique can greatly enhance the efficiency of the power amplifier in wireless communication system. Among the structures of the ET power supply, the switch-linear hybrid (SLH) structure can obtain both high-tracking bandwidth and high efficiency. An implementation of series–parallel-form SLH ET power supply is proposed in this paper, which includes one multilevel converter, one linear amplifier, and two buck converters. The two buck converters adopt current sensor-less prediction control and are operated at critical conduction mode (CRM). In order to ensure the operation of CRM and provide as much load current as possible, a quasi-interleaved current control scheme is proposed for the two buck converters. Moreover, a peak current restriction method is proposed to prevent the output current of the two interleaved buck converters from excessively exceeding the load current, avoiding the increase of the power loss in the linear amplifier. Finally, a prototype is fabricated with the specifications as 5-MHz tracking bandwidth, 9.6–26.4-V output voltage, and 20-W average output power. The overall measured efficiency is 81.0%, and the normalized-mean-square error is 0.28% when tracking the envelope of wideband code division multiple access signal.

Adaptive Constant Power Control of MHz GaN-Based AC/DC Converters for Low Power Applications

With offline single-phase power supplies moving toward the megahertz switching frequency range, the converter's bus capacitor becomes the bottleneck of further improvement of power density. Partial constant power operation is effective in reducing the bus capacitance and capacitor current stress for low-power applications. However, its impact on circuit design and operation design has not been studied thoroughly. With the developed circuit operation and loss model, this paper presents design considerations and power loss analysis of megahertz ac/dc converters in partial constant power operation. An adaptive constant power control is also proposed, based on the developed models, to improve the light-load efficiency and power factor. A 65 W, megahertz critical conduction mode GaN-based ac/dc converter prototype has been developed to validate the analysis and circuit operation method. Compared with power factor correction (PFC) operation, partial constant power control exhibits an efficiency drop of less than 1%. However, a 50% reduction of bus capacitance can be realized. With the proposed adaptive constant power control, the light-load efficiency and power factor can be improved to be a level similar to the PFC operation. This paper ends with a discussion of the possibility of extending the proposed operation method to higher power applications.

Compensation Technique for Current Sensorless Digital Control of Bridgeless PFC Converter under Critical Conduction Mode

Compensation Technique for Current Sensorless Digital Control of Bridgeless PFC Converter under Critical Conduction Mode

Achieving High Input PF for CRM Buck-Buck/Boost PFC Converter

When the on-time is constant during a line cycle, the input power factor (PF) of critical conduction mode buck-buck/boost power factor correction converter is low. A variable on-time control (VOTC) scheme is put forward in this paper to realize high PF. By utilizing the input and output voltage to modulate the on-time of buck and buck/boost switch, we can realize high-input PF with low-total harmonic distortion within the universal input voltage range. The operating principles and the comparative analysis of the converter with conventional constant on-time control (COTC) and VOTC are analyzed. The proposed control scheme achieves high PF and efficiency as compared with the COTC. A 100-W prototype was built up to verify the effectiveness of the proposed control strategy.

Variable-On-Time Control to Achieve High Input Power Factor for a CRM-Integrated Buck–Flyback PFC Converter

A variable-on-time (VOT) control scheme for a critical conduction mode (CRM) integrated buck–flyback power factor correction (PFC) converter with high power factor (PF) and low total harmonic distortion (THD) is proposed in this paper. By utilizing the input and output voltage to modulate the on-time of both buck and flyback switches, the input current harmonics can be eliminated and high PF will be obtained. The operating principles of both the conventional constant-on-time (COT) control and VOT control for the CRM buck–flyback PFC converter are analyzed. A 100-W prototype has been built and tested in the lab. The experimental results demonstrate that the THD and PF of the converter with VOT control are greatly improved compared to those with COT control.

Single-Stage Single-Switch Four-Output Resonant LED Driver With High Power Factor and Passive Current Balancing

A resonant single-stage single-switch four-output LED driver with high power factor and passive current balancing is proposed. By controlling one output current, the other output currents of four-output LED driver can be controlled via passive current balancing, which makes its control simple. When magnetizing inductor current operates in critical conduction mode, unity power factor is achieved. The proposed LED driver uses only one active switch and one magnetic component, thus it benefits from low cost, small volume, and light weight. Moreover, high-efficiency performance is achieved due to single-stage power conversion and soft-switching characteristics. The characteristics of the proposed LED driver are studied in this paper and experimental results of two 110-W four-output isolated LED drivers are provided to verify the studied results.

A High Performance Interleaved Bridgeless PFC for Nano-grid Systems

A high performance interleaved bridgeless boost power factor correction (PFC) rectifier operating under the critical current conduction mode (CrM) is proposed in this paper to improve the efficiency and system performance of various applications, such as nano-grid systems. By combining the interleaved technique with the bridgeless topology, the circuit contains two independent branches without rectifier diodes. The branches operate in interleaved mode for each respective half-line period. Moreover, when operating in CrM, all the power switches take on soft-switching, thereby reducing switching losses and raising system efficiency. In addition, the input current flows through a minimum amount of power devices. By employing a commercial PFC controller, an effective control scheme is used for the proposed circuit. The operating principle of the proposed circuit is presented, and the design considerations are also demonstrated. Simulations and experiments have been carried out to evaluate theoretical analysis and feasibility of the proposed circuit.

An E-capless AC-DC CRM Flyback LED Driver with Variable On-time Control

LED is a promising new generation of green lighting with the advantages of high efficiency, good optical performance, long lifetime and environmental friendliness. A pulsating current can be used to drive LEDs. However, current with a high peak-to-average ratio is unfavorable for LEDs. A novel control scheme for the ac-dc critical conduction mode (CRM) flyback LED driver is proposed in this paper. By using the input voltage, output voltage and average output current to control the turn-on time of the switch, the peak-to-average ratio of the output current can be reduced. The operation principle is analyzed and an implementation circuit is put forward. Experimental results show the effectiveness of the proposed scheme.

An Improved Variable On-Time Control Strategy for a CRM Flyback PFC Converter

The traditional critical conduction mode (CRM) flyback PFC converter with constant on-time control strategy usually suffers low power factor (PF) and high total harmonic distortion (THD) due to the nonsinusoidal input current waveform. In order to solve this problem, an improved variable on-time control strategy for the CRM flyback PFC converter is proposed in this letter. A simple analog divider circuit consisting of an operational amplifier, two signal switches, and an RC filter is proposed to modulate the turn-on time of the primary switch, and the PF and THD of the CRM flyback PFC converter can be evidently improved. The theoretical analysis is presented and the experiment results verify the advantages of the proposed control scheme.

Design of Inductors With Significant AC Flux

A design methodology is introduced to select a minimum core volume for an inductor or coupled inductors experiencing appreciable core loss. The geometric constant ( K gac) has been found to be a power function of the core volume for commercial toroidal, ER, and PQ cores, permitting the total loss to be expressed as a direct function of the core volume. The inductor is designed to meet specific loss or thermal constraints. An iterative procedure is described in which 2-D or 3-D proximity effects are first neglected and then subsequently incorporated via finite-element simulation. The methodology is demonstrated for coupled inductors in a 5-MHz converter in critical conduction mode. The core loss is verified using rectangular excitation and the winding loss is inferred from thermal measurements.

디지털 제어 기반의 경계점모드 브릿지리스 PFC 컨버터

Generally, in order to implement the CRM(Critical Conduction Mode), the analog controller is used rather than a digital controller because the control is simple and uses less power. However, according to the semiconductor technology development and various user needs, digital control system based on a DSP is on the rise. Therefore, in this paper, the CRM bridgeless PFC converter based on a digital control is proposed. It is necessary to detect the inductor current when it reaches zero and peak value, for calculating the on time and off time by using the current information. However, in this paper, the on-time and off-time are calculated by using the proposed algorithm without any current information. If the switching-times are calculated through the steady-state analysis of the converter, they do not reflect transient status such as starting-up. Therefore, the calculated frequency is out of range, and the transient current is generated. In order to solve these problems, limitation method of the on-time and off-time is used, and the limitation values are varied according to the voltage reference. In addition, in steady state, depending on the switching frequency, the inductance is varied because of the resonance between the inductor and the parasitic capacitance of the switching elements. In order to solve the problem, inductance are measured depending on the switching frequency. The measured inductance are used to calculate the switching time for preventing the transient current. Simulation and experimental results are presented to verify the proposed method.

High power factor and low total harmonics distortion using critical conduction mode boost converter-fed light-emitting diode driver

Summary This article presents a critical conduction mode (CRM)–based power factor correction (PFC) converter for multistring light-emitting diode (LED) driver. The application is targeted for high power projection application with brightness control of red-green-blue LED module. A pulse width modulation (PWM) technique is used for lighting control to achieve required brightness without compromising the efficiency (overall 82%) and power quality. The CRM boost PFC converter is used to feed a dual output flyback DC-DC converter, which supplies power to the forced cooling unit and the LED modules with galvanic isolation. The brightness control of LED is performed by synchronous buck converter using current PWM modulation. The CRM boost converter–based PFC converter is designed to operate in critical inductor current mode at universal AC mains. A prototype of proposed PFC converter–based LED driver is developed and experimentally verified. The power quality parameters of the proposed LED driver are evaluated at rated and light load conditions for universal AC mains (90–265 V) with brightness control. The power quality parameters are found within acceptable ranges of international harmonic standard IEC 61000-3-2 Class C for lighting systems.

Digital-Based Interleaving Control for GaN-Based MHz CRM Totem-Pole PFC

This paper presents a comparison between the performances of different interleaving control methods for gallium nitride devices-based MHz critical conduction mode (CRM) totem-pole power factor correction (PFC) circuit. Both closed-loop interleaving and open-loop interleaving are good for the 70-kHz CRM PFC; but for a MHz frequency CRM PFC with microcontroller (MCU) implementation, the open-loop interleaving outperforms the closed-loop interleaving with only a small and nonamplified phase error. After software optimization, the phase error of the open-loop interleaving is smaller than 3° at 1 MHz, when the control is implemented by a 60-MHz low-cost MCU. Significant ripple cancellation effect and differential-mode (DM) filter size reduction are achieved with good interleaving. For a 1.2-kW MHz totem-pole PFC, the DM filter size is reduced to one quarter when compared with the counterpart of a 100-kHz PFC. Last but not least, the stability of the open-loop interleaving is also analyzed indicating that the MHz CRM totem-pole PFC with voltage-mode control, open-loop interleaving, and turn-on instant synchronization can maintain critical mode operation with better stability compared with the 70-kHz CRM PFC.

Efficient Single-Switch Boost-Dual-Input Flyback PFC Converter With Reduced Switching Loss

This paper presents an efficient single-switch boost-dual-input flyback power factor correction (PFC) converter. To achieve a high power factor, a boost PFC cell operating in discontinuous conduction mode is presented. A dual-input flyback dc–dc module, which consists of parallel primary windings and serial secondary windings, operating in critical conduction mode is introduced for galvanic isolation and valley-switching operation. In addition, the proposed converter features high efficiency because the input power is equally divided, and some power is directly transferred to the load by the dual-input flyback dc–dc module. The remaining power is stored in dc-bus capacitors, and it is closely related to the holdup time. Moreover, the currents in the leakage inductors are absorbed by the dc-bus capacitors through a snubber diode, and they are reprocessed by the dual-input flyback dc–dc module. Consequently, the peak voltage in the MOSFET drain is clamped, and the total power conversion efficiency is improved. To verify the performance of the proposed converter, the operating principles, steady-state analysis, and experimental results from a 48 V, 100 W prototype are presented.

The virtual infinite capacitor

ABSTRACTWe define the virtual infinite capacitor (VIC) as a nonlinear capacitor that has the property that for an interval of the charge Q (the operating range), the voltage V remains constant. We propose a lossless approximate realisation for the VIC as a simple circuit with two controllers: a voltage controller acts fast to maintain the desired terminal voltage, while a charge controller acts more slowly and maintains the charge Q in the desired operating range by influencing the incoming current. The VIC is useful as a filter capacitor for various applications, for example, power factor compensators (PFC), as we describe. In spite of using small capacitors, the VIC can replace a very large capacitor in applications that do not require substantial energy storage. We give simulation results for a PFC working in critical conduction mode with a VIC for output voltage filtering.