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Four-switch buck-boost (FSBB) converter is widely used in battery applications due to the simple structure and the excellent performance of both voltage step-up and step-down. With the quadrangle control method, FSBB converter can realize zero voltage switching (ZVS) of all power switches, and thus can adapt to the high-frequency trends. However, the conventional quadrangle control method has two problems: 1) the efficiency degradation caused by the large root mean square (RMS) current of the inductor, and 2) the instability caused by the coupling relationship between multiple control variables. In this article, an improved quadrangle control method is proposed to solve the two problems, making FSBB converter a good candidate for high-frequency battery applications. First, the loss analysis is built to determine the relationship between loss and the control variables. Then, the conditions to achieve the minimum loss are obtained. Second, the decoupling compensation strategy is applied to free the coupling relationship to improve the stability. The proposed strategy can achieve three control goals: 1) ZVS of all power switches; 2) minimize the total loss; and 3) stable closed-loop system. Finally, a 1MHz 280W FSBB prototype is built to verify the proposed control method. The prototype achieves all control goals and 98.1% peak efficiency. more...

Critical conduction mode (CrCM) active clamp flyback (ACF) converter is regarded as a good candidate to be applied in high-frequency small power supplies. This article focuses on the modeling, analysis, and controller design of CrCM-ACF converter. The small signal model of the converter is derived based on a zero-input resonant equivalent circuit and extended describing function (EDF) method for the first time, then the obtained full-order model is simplified to a low-order model. This procedure establishes an insightful understanding about the effects of the converter parameters and working conditions. Based on the simplified model, a control loop compensator is designed in a single-loop voltage-feedback control scheme for high dynamic performance. An experimental prototype of digital controlled CrCM-ACF converter is built, the accuracy of the derived model is verified by comparing with experimental and simulation results. The performance of the compensator is experimentally evaluated by applying abrupt load current and reference voltage changes in the operating conditions of the converter. From the experimental results, it is demonstrated that the derived analytical model and designed compensator are effective in regulating the output voltage in CrCM-ACF converter. more...

Two-stage cascade architecture is widely used in the modular power supply applications. In order to reduce the additional component number caused by the cascading structure, the power switch integration technique is proposed in numerous literature studies. However, the power switch integration leads to both the efficiency degradation and the abnormal gain of the stage employed. In this article, the four-switch noninverting buck–boost converter is merged with the LLC resonant converter. The proposed integration method has no awful influence on the efficiency and the gain of the LLC stage. Meanwhile, the soft switch capability of the integrated bridge can be enhanced due to the accumulation of the two currents of the buck–boost stage and the LLC stage during dead time. Moreover, the current of the two-stage will commutate to cancel out with each other during the conduction period, reducing the conduction loss and improving the overall efficiency. The benefits of the integrated bridge make the proposed converter appropriate for the high-frequency and high-efficiency application. Finally, a 720-W 1-MHz prototype is built to prove the performance of the proposed converter. The prototype achieves a peak efficiency of 96.4% and the input voltage range of 250–420 V. more...

Critical conduction mode (CrCM) active clamp flyback (ACF) converter is regarded as a good candidate for low power adaptor applications. However, the most adopted control strategy of variable-frequency peak current mode (VF-PCM) and discrete zero voltage switch (ZVS) control makes it difficult to get the accurate small signal model. Therefore, by using sampled-data modeling method, this paper proposes an exact small signal model of CrCM ACF converter for the first time. In the modeling process, the influence of discrete-ZVS control is firstly considered. The conduction time of power switch is regarded as the control signal, which is different from constant-frequency converter. The total current close-loop transfer function is simplified by the linear combination of single VF-PCM and discrete-ZVS control model. After considering the sampling effect and the modulator gain from the derived sampled-data model respectively, the control-to-output transfer function of CrCM ACF converter is developed. The analytical results are analyzed by comparing with single VF-PCM and the widely used average model. Finally, to validate the accuracy of the proposed model, a 65W 20V output CrCM ACF converter is simulated and measured. The verification shown that the proposed sampled-data model is basically agreement with the simulation and experimental results. more...

Double-clamped zero voltage switching (ZVS) buck-boost converter with primary side sampled feedback control that is suitable for converter Chip modules has been widely used for defense and industrial applications. Aiming at the double-clamped ZVS buck-boost converter with previous primary-side sampling and voltage-mode control, this paper proposes a novel primary-side sampling scheme, which can not only calculate the output voltage, but also the output current, and can use current-mode control and optimize the duration of the dead-times. The novel control scheme gives the converter a better dynamic performance and lower switching loss. more...

High switching frequency, high efficiency and high power density are critical in portable AC-DC adapters. The active clamp flyback (ACF) converter can achieve zero voltage switching (ZVS) and recycle leakage energy of transformer to maintain high efficiency in high frequency operation. This paper presents a digital PWM control method of secondary resonant ACF converter. A proposed adaptive period modulation is used to choose the optimum period under different conditions which can contribute to efficiency improvement. Meanwhile, a digital PI compensator is adopted to regulate the output voltage. A 65W prototype of ACF converter with digital microcontroller is implemented. With proposed digital control method, the prototype operates with 500-900 kHz frequency range and realizes maximum efficiency of 91.2% which is 2% better than control method at fixed frequency. more...

Ultra-high power density power module presents many design and optimization challenges of power supply. How to effectively interfaces the wide input range, high efficiency, with higher power density is a great challenge for power supply designers. Traditional DC-DC converters usually need considerable space with relatively low operating frequency and transmission efficiency. In this paper, a novel control method based on Double-Clamp ZVS converter is proposed to realize the ultra-high power density for power module. According to simulations, the topology realizes high transmission efficiency (96.33%) in 1MHz with wide input voltage range (200V-420V DC ). Moreover, the voltage ratings applied to switches can be decreased obviously, which is very suitable for the design of ultra-high power density power module. more...

This paper proposed a novel primary side voltage sampling (PVS) system, which use the gate signal of secondary synchronous rectifier as a trigger to generate a short sampling pulse, and let this sampling pulse to control a switch to realize a short-on-time sampling. The proposed PVS system is based on a Double-Clamp, Zero Voltage Switching (DCZVS) converter. An auxiliary transformer, which is completely separate with the main transformer, is used to isolate primary side and secondary side. The auxiliary transformer using air as the core and can bury in the printed circuit board (PCB) to avoid occupying surface area and using demagnetization circuit. The area of the surface devices is about 13.86 mm2 while the auxiliary transformer cost a 270 mm2, 4 layers space inside the PCB. Power loss of the auxiliary transformer is about 2.83 W in a worst case, and the maximum loss of the surface devices is about 129.3 mW more...

Active Clamp flyback converter (ACF) is a good candidate to replace the traditional flyback converter to be used in high frequency small power applications. Due to the circuit delay and intrinsic characteristic, PCM controlled ACF converter has a slow output dynamic response. Therefore, by associating the PCM with V2 control method, a novel PCM-V2 control scheme is proposed to improve the output dynamic response of PCM controlled ACF converter. The control scheme is illustrated, and the modeling strategy of the proposed PCM-V2 control is given. After comparing the frequency response curve, the presented PCM-V2 control method has a larger bandwidth than PCM control. To verify the effect of the proposed method, a 65W 20V output ACF converter is simulated ant tested. The simulation and experimental results between PCM-V2 and PCM control are compared and presented. The results show that the output dynamic response of the proposed PCM-V2 is faster than PCM control method in ACF converter. more...

Secondary side resonant active clamp flyback (SSR-ACF) converter is a better candidate than primary side resonant active clamp flyback (PSR-ACF) converter to be used in high frequency small power supply applications. Based on the resonant capacitor voltage in SSR-ACF converter, this paper proposes an accurate synchronous rectification (SR) control method to turn off the synchronous rectifier (SRer) at the right point. Compared with the current widely used SR detecting method, the turn off point of SRer based on the presented method can not be affect by noise or voltage oscillation, and not need complicated sensing circuit. To verify the proposed SR control method, the simulation and experimental results of a 65w 19.5v output SSR-ACF converter are given. The results show that the SRer can be switched off at the right point by the proposed method. Compared with the current widely used SR detecting method, the efficiency in heavy load is improved by 0.3%. more...

An accurate small signal model of active clamp flyback (ACF) converter is proposed in this paper. To obtain a precise model, the ESR of output capacitor was considered. Different to traditional flyback converter, because of the resonant effect, at the three to five times of switching frequency, ACF converter was added two poles which result in high oscillation in frequency responses curve. To get sufficient phase margin and avoid resonant inductor oscillation affect, a fundamental error compensator was given to keep control loop stabled. Then a 65W prototype was implemented to verify the performance of the designed control loop, the simulation and experimental results showed that the adjusted process between different load status haven't result in much voltage overshoot or undershoot and need a long regulate time. more...

Adaptive synchronous rectification (SR) is a good solution to solve duty cycle loss for LLC resonant converter. Usually, whether the synchronous rectifier is turned off prematurely or late can be detected by whether the body diode is conducted on or not. However, when the switching frequency is below the resonant frequency, both SR turning- off prematurely and late may generate body diode conduction (BDC), which will cause logic errors in the conventional adaptive SR strategy. Then, a large reverse current from load to source will occur, which damages the efficiency. To solve the problem, the time-domain modeling of the SR drain-to-source voltage is established to analyze the mechanism of BDC caused by SR turning- off late. Moreover, an improved adaptive SR driving scheme is proposed, which can identify the two different types of BDC and tune SR to be turned off exactly. Finally, a 280 W LLC prototype is built to verify the established model and the proposed SR method. The prototype proves that both the duty cycle loss and the reverse current are eliminated and efficiency improvement of 0.54% is achieved. more...

The paper presents a temperature gradient based method for device state evaluation, taking the insulated Gated Bipolar Transistor (IGBT) modules as an example investigation. Firstly, theoretical basis of this method is presented and the results from example calculation on temperature gradient indicate that the increased thermal resistance and power loss of IGBT modules would increase the temperature gradient. Then an electrical-thermal- mechanical finite element method (FEM) model of IGBT modules, which takes the material temperature-dependent characteristic into account, is utilized to estimate the temperature gradient distribution for both healthy and fatigue conditions. It is found that the temperature gradient varies with power loss. Furthermore, both the experimental and simulation investigation on the temperature gradient for different conditions were conducted, and it is concluded that the temperature gradient can not only track the change of power loss, but have a better sensitivity compared with temperature distribution. In addition, the temperature gradient can reflect the defects location and distinguish failures degree. In the end the influence on the temperature gradient distribution caused by solder fatigue, void and delamination are discussed. more...