Burst-mode Control Research Articles

A Charge Normalization Based Burst Mode Control Strategy for the LLC Converter Without Current Sensing

A Charge Normalization Based Burst Mode Control Strategy for the <i>LLC</i> Converter Without Current Sensing

A Burst Mode and Variable Frequency Voltage Sharing Control Mechanism for an Adjustable High Voltage Pulsed Converter

This article presents a modular adjustable high-voltage pulse (MAHVP) generation system. The proposed MAHVP generation system uses a combination of full-bridge LLC resonant converters whose input terminals are connected in parallel and whose output terminals are in series to boost the output voltage; input parallel output series configuration efficiently increases the power holding capabilities of the overall system. The MAHVP generation system uses a novel burst mode and variable frequency voltage sharing (BMVFVS) control mechanism, the BMVFVS control mechanism senses the type of load if the MAHVP generation system needs to operate at a heavy load, it uses the variable frequency voltage sharing method to divide the power equally between the modules to enhance the overall performance. For light load conditions, the MAHVP generation system operates in burst mode, and the BMVFVS control mechanism combined with the frequency modulation technique is used to control the amplitude and pulsewidth of the output voltage smoothly and efficiently. A hardware prototype of 2.4 kW is developed, and experimental results are taken to verify the feasibility and validity of the proposed system, the maximum output voltage of the developed two-module prototype is tested up to 6 kV at the high efficiency of 97%.

Variable-Frequency and Phase-Shift With Synchronous Rectification Advance On-Time Hybrid Control of LLC Resonant Converter for Electric Vehicles Charger

The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter has been widely used in the power supply industry, such as server power, TV power, and adapter, because this converter can realize the zero-voltage switching (ZVS) at the power <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s of the primary side. Thus, the switch losses can be decreased, and the conversion efficiency can also be improved. The electric vehicle (EV) charger has been recently widely used in research and development. However, designing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converters for the wide battery voltage range is difficult because this converter is usually utilized in pulse-frequency modulation (PFM) to regulate the output voltage. This converter will also be limited to the low operating frequency range for the high conversion efficiency due to the switching frequency. By contrast, the phase-shift modulation (PSM) control for the wide output voltage range has been used at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converters. However, the ZVS will be lost due to the lagging leg of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter when the phase-shift angle is remarkably excessive. The burst-mode control has also been proposed for the converter to regulate the output voltage and maintain high conversion efficiency at light-load conditions. Therefore, this article utilized the combination of PFM, PSM, and burst-mode control for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter operating at the wide output voltage range for EV charge applications. Furthermore, this article proposed a synchronous rectification advance on-time control for PFM control, which can help address the ZVS at the lagging leg when the phase-shift angle is excessive. Detailed analysis and design of this control method are also described. The performance evaluation of the proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter with hybrid control was finally realized under the following conditions: 3.75 kW, dc input voltage of 400 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> , dc output voltage of 75–475 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> , and maximum conversion efficiency around 97%.

Design and Analysis of LLC Resonant Converter With Valley Switching Control for Light-Load Conditions

The LLC converter has been widely used in the power supply industry for its high conversion efficiency. When the output load is low, the LLC resonant converter will substantially increase the operating frequency, thereby reducing the conversion efficiency and exceeding the limited operating frequency of the specification. Thus, burst-mode control is applied to increase the ability of regulation at light-load conditions. Even so, the switching period of power switches still occurs at a high switching frequency. Burst-mode control will also result in an extremely low-frequency output voltage ripple. In this study, a valley switching control (VSC) for the LLC resonant converter at light-load conditions is proposed. The VSC control strategy maintains the output voltage by modulating the pulsewidth signals of drivers and achieves valley switching by modulating the switching frequency. Thus, the VSC strategy can reduce the operating frequency compared with the frequency modulation strategy. Compared with burst-mode operations, the proposed VSC effectively reduces the switching loss and has the advantage of high-frequency output voltage ripple. The VSC increases the efficiency and the power quality of the converter. Detailed analysis and design of the proposed method are described. Experimental results are recorded for a prototype converter with a dc input voltage of 400 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {DC}}$ </tex-math></inline-formula> , an output voltage of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$48~V_{\mathrm {DC}}$ </tex-math></inline-formula> , and an output current of 12.5 A.

Slam Control Method for Improving Light Load Efficiency of Boost Converter

The burst-mode control is one of the most effective methods to improve the efficiency of a converter at the light load condition, but it inevitably reduces the voltage conversion ratio of the converter. In this letter, we propose a slam control for improving light load efficiency of the boost converter while maintaining its voltage conversion ratio. The proposed control method applies the full duty–ratio to the switch during predetermined time, which significantly increases the light load efficiency and sufficiently boosts the output voltage. In addition, the quasi-resonant operation enables zero voltage switching at the switch; thus, reducing further switching loss. This slam control can be easily implemented by adopting “OR gate” to synthesize the slam carrier and switching carrier. The feasibility and effectiveness of the proposed control were verified by the experimental results from a 20-W prototype. The power conversion efficiency was increased by more than 20% at the light load condition.

Improved Circuit Design and Adaptive Burst Mode Control in PSFB Converters for Higher Efficiency Over a Wide Power Range

This paper presents an improved circuit design of Gallium Nitride (GaN) based phase shifted full bridge (PSFB) converters along with a new adaptive burst mode control strategy, to achieve high efficiency over a wide power range, including light loads. The main challenges of PSFB converters addressed in this paper are: load-dependent zero-voltage switching (ZVS), transformer saturation, and secondary side ringing. Since switching losses of GaN FETs are dominant at light loads, adaptive burst mode control can be employed to improve the efficiency at lower output power. By periodically switching output current between 0 A and minimum ZVS current, adaptive burst mode control can enable both smaller effective switching frequency and lower switching losses. A correction factor ‘k’ is adopted in the adaptive burst mode control’s current loop PI calculation so that the output current can switch fast without any overshoot that increases switches’ current stress. To verify the effectiveness of the proposed circuit and controller design, a 375 V input, 70 V output, 800 W PSIM simulation model as well as experimental prototype are developed and tested. The experimental results demonstrate the practical benefits of the proposed adaptive burst mode control.

High-Efficiency Multiphase Capacitive Power Transfer in Sliding Carriages With Closed-Loop Burst-Mode Current Control

Sliding carriages or gantries that use journal bearings for support are common in industrial automation, e.g., assembly lines, spindle heads, and xy tables, and their moving parts are powered through a flexible wireway or cable track. This paper eliminates the cable connection by using the parasitic capacitance of the stock sliding bearings to capacitively transfer power between stationary and moving parts. At high frequency, ac current can safely pass through the journal-rail capacitance where it is ultimately rectified on a carriage/gantry for final use. A 3.4-MHz resonant voltage sourced inverter utilizing gallium nitride (GaN) high-electron mobility transistors in a three-phase configuration enables this approach. The salient features of this paper are: 1) characterization of commercial-off-the-shelf bearings; 2) development of a three-phase matching network between the tank circuit and GaN inverter for high efficiency; and 3) control of the dc output current on the secondary (moving carriage/gantry) side using only primary (stationary) side sensed quantities and burst-mode control. A controller developed from a small signal operating point model uses average bearing displacement current, measured by ac sense coils embedded in the tank inductors, to accurately regulate dc output current. The experimental tests at a tank resonance of 3.4 MHz demonstrate >100-W power transfer through an off-the-shelf bearing to a sliding carriage load with 95% efficiency. This system, when paired with a burst-mode frequency of 10 kHz, demonstrates current regulation on the carriage load with a bandwidth of 200 Hz.

Burst-Mode and Phase-Shift Hybrid Control Method of LLC Converters for Wide Output Range Applications

For an LLC converter, it is difficult to realize the wide output range with conventional pulse frequency modulation control because of the limited operating frequency. This paper proposes a new hybrid control method. The proposed strategy combines the burst-mode control and phase-shift control methods for the LLC converter. The burst-mode control can regulate the output voltage from zero to its maximum value, and the phase-shift control can reduce the increased resonant current during burst-on time. By using this method, the wide output voltage range is realized with the low resonant current during burst-on time and zero-voltage switch (ZVS) for all switches. The reliability and efficiency of the converter can be improved accordingly. The burst duty ratio is regulated by the reference output voltage, and the phase-shift angle is derived when realizing ZVS for lagging-leg switches. Moreover, the resonant parameters and the maximum phase-shift angle are optimized under the constraints of current stress and ZVS condition. This method is easy to be implemented in a low-cost microcontroller because high-frequency real-time calculations are not necessary. A 1.5-kW prototype is built to verify the feasibility and validity of the proposed control method.

Power Density and Efficiency Enhancement in ICN DC–DC Converters Using Topology Morphing Control

This paper introduces a new approach for output voltage regulation in impedance control network (ICN) resonant dc–dc converters, in which the rectifier of the ICN converter alternates between full-bridge and half-bridge topologies. This approach, termed topology morphing control, allows the ICN converter to maintain soft switching across power levels while substantially reducing the output capacitance requirement and improving partial-power efficiencies compared to the conventional burst mode ( on/off ) control. A closed-loop control architecture for the ICN converter is also introduced, which regulates the converter's output voltage under input voltage and load variations while ensuring smooth transitions between the multiple operating modes of the proposed topology morphing control. A prototype 1-MHz, 120-W step-down ICN resonant converter designed for an input voltage range of 18–36 V, an output voltage of 12 V, and a 10:1 output power range has been built and tested with both burst mode control and the proposed topology morphing control. The topology morphing control reduces the output capacitance requirement in the prototype ICN converter by 57% and reduces converter losses at partial power levels by up to 46.5%. The prototype ICN converter is also tested under closed-loop control and is shown to successfully regulate its output voltage in the face of input voltage and load variations.

A 100-mV–2.5-V Burst Mode Constant on-Time- Controlled Battery Charger With 92% Peak Efficiency and Integrated FOCV Technique

In this paper, a burst mode constant ON-time-controlled, energy harvesting charger is presented. The proposed boost converter system uses the burst mode control to improve the efficiency by 11%, compared to the conventional single-mode energy transfer implementation with an ultralow-power input comparator. A technique to deduce an optimum inductor energizes time across the given input range, for which the maximum converter efficiency is demonstrated. An internally triggered, capacitor-less sample-and-hold block addresses the leakage issue in the conventional fractional open-circuit voltage maximum power point tracking systems. The system is capable of charging a super-capacitor of 4.7 mF, from 1.8 to 3.3 V from an input power of 50 μW to 100 mW by maintaining the maximum power at the input. The entire system is designed and fabricated in the standard 180-nm CMOS technology, and the measurement results show a peak efficiency of 92% at 98-mW input power for the output voltage of 3 V and efficiency ≥65% across the range of input voltages more than 0.3 V for the output voltage of 1.8 V.

Digital Implementation of Light-Load Efficiency Improvement for High-Frequency LLC Converters With Simplified Optimal Trajectory Control

The light-load efficiency has drawn more and more attention for the LLC resonant converters in information technology industry. Burst mode is an effective and popular method to improve the light-load efficiency. The conventional burst-mode control has limited efficiency improvement on LLC converter due to the dynamics of the resonant tank. The simplified optimal trajectory control (SOTC) for burst mode can solve this issue by using optimal switching pattern for burst-on time. High-frequency LLC converters are emerging in recent years, thanks to the high power density and integrated magnetics. In this paper, the digital implementation of SOTC for burst mode and its limitation in high-frequency LLC converter are investigated. SOTC for adaptive burst mode is proposed and implemented by low-cost microcontrollers (MCUs) for high-frequency LLC converters. Furthermore, the digital implementation of SOTC for fast transient response between burst mode and normal operation of high-frequency LLC converter is proposed. The experimental results are demonstrated on a 500-kHz 1-kW 400 V/12 V LLC converter with a 60-MHz MCU, and the proposed control can achieve burst-mode operation from no load up to 26% load, 92.5% efficiency at 10% load, 91.8% efficiency at 2.4% load, and fast transient response between burst mode and normal operation.

Step-Down Impedance Control Network Resonant DC–DC Converter Utilizing an Enhanced Phase-Shift Control for Wide-Input-Range Operation

This paper introduces an isolated step-down impedance control network (ICN) resonant dc–dc converter that utilizes enhanced inverter and rectifier phase-shifts to achieve both soft switching and output voltage regulation. Compared to previously presented ICN converters, which utilize burst-mode control to achieve output voltage regulation, this ICN converter with the proposed enhanced phase-shift control has dramatically reduced output capacitance requirement. The avoidance of burst-mode control also simplifies the design of the converter's input electromagnetic interference filter, reduces switch stresses due to overshoots during repeated startup transitions, and improves converter efficiency by eliminating startup and shutdown losses as well as by reducing conduction losses when backing off in power. A closed-loop control architecture for the ICN converter operated under enhanced phase-shift control is also proposed, wherein state-feedback control is incorporated to guarantee stability and achieve good dynamic performance across wide variations in input voltage and output power. A prototype 1-MHz, 120-W step-down ICN converter designed for an input voltage range of 18–75 V, an output voltage of 12 V, and a 10:1 output power range is built and tested with both burst-mode control and the proposed enhanced phase-shift control. When operated with enhanced phase-shift control, the prototype ICN converter achieves a peak efficiency of 95.7% and maintains full-power efficiency above 91.7% across its 4:1 input voltage range. Compared to when operated under burst-mode control, the ICN converter with enhanced phase-shift control reduces converter losses by up to 30% and reduces the output capacitance requirement by two orders of magnitude. The prototype ICN converter is also operated under closed-loop control using a digitally implemented controller based on the proposed architecture, and is shown to successfully regulate its output voltage in the face of input voltage and load variations.

An Average Input Current Sensing Method of LLC Resonant Converters for Automatic Burst Mode Control

Burst mode control techniques have been studied for LLC resonant dc-dc converters to improve power conversion efficiencies at light load conditions. However, there are not many studies about how to detect the load conditions at burst mode not even at normal mode, at the primary side of LLC resonant dc-dc converters. In this paper, we propose and implement a lossless load detection technique for normal and burst modes by a novel average input current sensing method at the primary side of LLC resonant converters. Detailed theoretical analysis at normal and burst modes is presented and a load detection circuit is proposed with the consideration of integrated circuits. To verify the analysis, an LLC resonant offline converter with 400 V input and 16 V/10 A output is simulated using PSIM and a prototype board is built. The experimental results show that the proposed load detection technique is valid and practical. As a result, an automatic burst mode control for LLC resonant converters at light load conditions is realized with the proposed average input current sensing method.

同軸型 DBD プラズマアクチュエータの電圧波形が噴流に与える影響

In this study, coaxial type DBD plasma actuator was designed for flow diffusion control. Induced flow is generated by a coaxial type DBD plasma actuator mounted on the tip of the converging nozzle and gives the turbulence on the boundary layer flow. In this experiment, we experimented continue control and burst-mode control. Both Reynolds number is 2000, the wave form using sin wave and square wave, the voltage is 14kV. Frequency of continue control is 8kHz. Frequency of burst-mode control is 7480Hz, and the voltage applied in 187 Hz. This frequency was determined by we counting generation cycle of voltex from the video taken by the high-speed camera. When the AC voltage is applied and to generate a induced flow, it was successful in flow diffusion. In continue control, we found generating small voltex. In burst-mode control, we found generating large voltex. and, appling a voltage frequency was changed to 1/4times, 1/2times, 2times, 3times. When 1/4times and 1/2times, it was found to generate voltex of the 187 Hz and 1/4times or 1/2times Hz.

A Parabolic Voltage Control Strategy for Burst Mode Converters with Constant Burst Frequency and Eliminated Audible Noise

To improve the conversion efficiency at light load, burst mode control is widely employed by power converters. One drawback of hysteresis burst mode control is that the burst frequency changes with different load, which would introduce audible noise to the system if burst frequency falls into audible frequency range. To solve the frequency variation and audible noise problems of burst-mode-controlled power converters, a parabolic voltage control method is proposed in this paper. A hysteresis burst-mode-controlled quasi-resonant boost converter is employed as an example. First, the operation principles of the boost converter are analyzed and the simplified circuit is obtained. Based on the simplified circuit, the frequency variation problem is studied and burst frequency change over different loads is calculated. Second, by analyzing the constitutive equations of the simplified circuit, inspired the derivation of parabolic current control, a pair of parabolic control carriers are obtained. The proposed parabolic carriers serve as the control band to achieve constant burst frequency, eliminating audible noise, and extending the light load efficiency to the whole load range. A comparison between parabolic voltage control and parabolic current control is conducted. It is found that parabolic voltage control can be seen as the dual of parabolic current control. In addition, the convergence process of the proposed parabolic voltage control is analyzed. The performance of the proposed control strategy is experimentally verified with prototype hardware.

A Bidirectional Dual Buck-Boost Voltage Balancer with Direct Coupling Based on a Burst-Mode Control Scheme for Low-Voltage Bipolar-Type DC Microgrids

DC microgrids are considered as prospective systems because of their easy connection of distributed energy resources (DERs) and electric vehicles (EVs), reduction of conversion loss between dc output sources and loads, lack of reactive power issues, etc. These features make them very suitable for future industrial and commercial buildings’ power systems. In addition, the bipolar-type dc system structure is more popular, because it provides two voltage levels for different power converters and loads. To keep voltage balanced in such a dc system, a bidirectional dual buck-boost voltage balancer with direct coupling is introduced based on P-cell and N-cell concepts. This results in greatly enhanced system reliability thanks to no shoot-through problems and lower switching losses with the help of power MOSFETs. In order to increase system efficiency and reliability, a novel burst-mode control strategy is proposed for the dual buck-boost voltage balancer. The basic operating principle, the current relations, and a small-signal model of the voltage balancer are analyzed under the burst-mode control scheme in detail. Finally, simulation experiments are performed and a laboratory unit with a 5kW unbalanced ability is constructed to verify the viability of the bidirectional dual buck-boost voltage balancer under the proposed burst-mode control scheme in low-voltage bipolar-type dc microgrids.

New Integrated Control Technique for Two-Stage Server Power to Improve Efficiency Under the Light-Load Condition

A new control technique for two-stage server power is proposed in this paper. The proposed technique will significantly reduce power consumption under the light-load condition. The basic idea of the proposed control technique is to control both the dc-link voltage of the power factor corrector (PFC) stage and the switching method of the full-bridge stage. Under the light-load condition, the output voltage of the PFC stage is no more fixed and is dynamically adjusted to significantly reduce the switching losses. Moreover, under the light-load condition, the full-bridge stage is with pulsewidth-modulation (PWM) and burst-mode control to reduce the circulating current losses. The former approach will reduce the switching losses due to the reduction of voltage across the power devices. The latter approach will dramatically reduce the circulating current losses caused by the phase-shift control method since phase-shift switching control is replaced by PWM switching control. Moreover, due to the reduction of the dc-link voltage, the switching losses for PWM and burst-mode control can be further reduced, as compared to those for fixed dc-link voltage. Experimental results of 480-W server power are presented. It is shown that the efficiency of the two-stage power converter can be improved up to 8% and 3.9% under light-load and 10% load conditions for $\mbox{input voltage}=110 \mbox{V}$ , respectively. For the 220-V input voltage, the efficiency improvement using the proposed method is 6.4% and 4.2% under light-load and 10% load conditions, respectively.

Design and Implementation of Self-Oscillating Flyback Converter With Efficiency Enhancement Mechanisms

This paper presents a self-oscillating flyback converter with efficiency enhancement mechanisms using lossless snubber and the energy recovery winding. The conventional self-oscillating flyback converter with resistor–capacitor–diode snubber has the issues of low conversion efficiency and high no-load power loss. Furthermore, in order to fulfill the $95 \mbox{V}_{\mathrm{p-p}}$ voltage limitation of the IEC62684 Common-Mode (CM) Standard, the parasitic capacitor of a transformer between the primary and secondary windings has to be reduced, which leads to large leakage inductance for the transformer. However, the larger leakage inductance stores more energy to cause the high voltage spike on the main switch during the turnoff transition period. Therefore, the lossless snubber is employed to suppress the voltage spike and increase the conversion efficiency. In order to increase more conversion efficiency, the energy recovery winding is employed to recycle the energy discharged from the gate–source capacitor of the main switch. Furthermore, the burst-mode control mechanism is utilized to reduce the power consumption at the no-load and light-load conditions. Finally, a prototype circuit of the 7.5-W self-oscillating flyback converter with efficiency enhancement mechanisms is built to verify the performance feasibility, such as the CM voltage, the voltage stress on the switch, the conversion efficiency, and the no-load power loss.

A Novel Choice Procedure of Magnetic Component Values for Phase Shifted Full Bridge Converters with a Variable Dead-Time Control Method

Magnetic components are important parts of the phase shifted full bridge (PSFB) converter. During the dead-time of switches located in the same leg, the converter can achieve zero-voltage-switching (ZVS) by using the energies stored in magnetic components to discharge or charge the output capacitances of switches. Dead-time is usually calculated under a given set of pre-defined load condition which results in that the available energies are insufficient and ZVS capability is lost at light loads. In this paper, the PSFB converter is controlled by variable dead-time method and thus full advantage can be taken of the energies stored in magnetic components. Considering that dead-time has a great effect on ZVS, the relationship between available energies and magnetic component values is formulated by analyzing the equivalent circuits during dead-time intervals. Magnetic component values are chosen based on such relationship. The proposed choice procedure can make the available energies greater than the required energies for ZVS operation over a wide range of load conditions. Moreover, the burst mode control is adopted in order to reduce the standby power loss. Experimental results coincide with the theoretical analysis. The proposed method is a simple and practical solution to extend the ZVS range.

Impedance Control Network Resonant dc-dc Converter for Wide-Range High-Efficiency Operation

This paper introduces a new resonant converter architecture that utilizes multiple inverters and a lossless impedance control network (ICN) to maintain zero-voltage switching and near zero-current switching across wide operating ranges. Hence, the ICN converter is able to operate at fixed frequency and maintain high efficiency across wide ranges in input and output voltages and output power. The ICN converter architecture enables increase in switching frequency (hence reducing size and mass), while achieving very high efficiency. Three prototype 200-W 500-kHz ICN resonant converters, one with low-Q, one with medium-Q, and one with high-Q resonant tanks, designed to operate over an input voltage range of 25 to 40 V and an output voltage range of 250 to 400 V are built and tested. The low-Q prototype ICN converter achieves a peak efficiency of 97.1%, maintains greater than 96.4% full power efficiency at 250 V output voltage across the nearly 2:1 input voltage range, and maintains full power efficiency above 95% across its full input and output voltage range. It also maintains efficiency above 94.6% over a 10:1 output power range across its full input and output voltage range owing to the use of burst-mode control.