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For gallium nitride (GaN) based triangular current mode (TCM) applications, the dead-time has a significant effect on the switching loss. However, previous GaN high electron mobility transistor (HEMT) models focus on the turn-on/off process without fully considering the effect of the dead-time. Hence, this article analyzes the switching transients under the superfluous and insufficient dead-time and evaluates the dead-time loss with an improved GaN HEMT model. The proposed model improves an existing GaN HEMT model by adding the voltage rising/falling time of the gate driver, the dynamic threshold voltage of Schottky-type GaN HEMTs, and an equivalent gate-drain capacitance obtained from the datasheet. Verified by a GaN-based double-pulse test, the proposed model can more accurately calculate the gate-source voltage and the self-commutated reverse conduction voltage. Verified by a GaN-based TCM Buck converter, the proposed model can predict the dead-time loss well and has higher simulation accuracy for the turn-on process induced by the inappropriate dead-time. [ABSTRACT FROM AUTHOR]

Data centers require high efficiency and high power-density dc–dc converter with wide input range and galvanic isolation. To overcome the drawbacks of traditional single-stage LLC and two-stage solutions, a novel partial power regulation topology with wide input range is proposed in this article. The proposed topology delivers the load power through a three-ports LLC-based dc transformer regulated DCX (DCX). A pulsewidth modulation (PWM) converter is cascaded with one of the input ports of the DCX and then in series with the other input port to regulate the output voltage. Since a single transformer and a partial power PWM converter are employed, high power density can be achieved. Furthermore, only a portion of the load power is transferred by the PWM converter, the efficiency sacrifice is reduced. By introducing an appropriate negative current, the zero voltage switching of the PWM is also achieved. Furthermore, when the input voltage approaches the lower or the upper limit, the switching frequency of the PWM regulator can be ultralow. As a result, switching losses and core losses are further reduced. Finally, a prototype with 190—475 V input and 12 V/500 W output is demonstrated, which achieves a peak efficiency of up to 97.2% and a power density of 153 W/in3. [ABSTRACT FROM AUTHOR]

The double-side cooling (DSC) packaging becomes more and more popular with the great demands of high power and fast speed, especially for silicon carbide metal oxide semiconductor field effect transistors. Measurements and modeling of thermal resistance are critical for thermal management of DSC module. However, the thermal resistance of DSC module is still unclear due to the asymmetric dual thermal paths. In this article, a clear understanding of thermal resistance of DSC module measured by transient dual-interface method (TDIM) is explained. The thermal impedance of DSC module is analyzed through time- and frequency-domain response of the DSC thermal model. The cooling conditions in TDIM have no influence on the measured thermal resistance of DSC module. The measured thermal resistance from junction to top case (or bottom case) is half of the actual value. The important conclusions are verified by transient simulations and experiments. Based on the results, a new definition of thermal resistance of DSC module is proposed for exact evaluation of thermal resistance and reliability. [ABSTRACT FROM AUTHOR]

Conventional fast Fourier transform analysis is limited in conducted electromagnetic interference (EMI) prediction for triangle current mode (TCM) based converters. Several prediction strategies based on EMI receiver modeling have been published for this issue, but the prediction range was below 1 MHz. Such a narrow frequency range cannot meet the demands of EMI prediction for MHz converter. In this article, a more accurate differential mode (DM) EMI prediction is proposed for MHz TCM-based single-phase inverter. The accurate drain-to-source voltage model considering the TCM resonant transition is established for different TCM-derived strategies at first. Passive components of the propagation path are also modeled with the measured impedance for more accurate transfer gain. An improved envelope detector model of the EMI receiver is proposed for an accurate quasi-peak spectrum. The prediction range can be extended to 5 MHz. Moreover, the EMI of TCM, hybrid triangle current mode, and sinusoidal triangle current mode are analyzed and compared with the established prediction strategy. The worst spectrum can be determined, and the DM filter can be designed without repetitive measurements. Finally, A 500 W MHz single-phase inverter prototype is built, and the evaluation of the measured conducted EMI spectrum and the EMI filter design can verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

The dynamic current imbalance between paralleled SiC mosfets will cause unbalanced losses and reduce current capacity. The existing current balancing methods will make the circuit more complex or hard to design and implement. Hence, this article proposes a dynamic current balancing method by connecting monolithic Si-RC snubber between paralleled mosfets, which maintains a simple circuit structure and is easy to implement. Balanced dynamic currents can be achieved by adjusting the RC snubber connecting location. Meanwhile, low voltage spike and low switching oscillation can be achieved by using RC snubber. First, an analytical current sharing model is established for paralleled SiC mosfets. The key parameter affecting the balance of the drive circuit and then affecting the dynamic current sharing is obtained for the first time. Based on the conclusions of the model, this article then presents the current balancing method using RC snubber. Then, a power module with monolithic Si-RC snubber is designed, fabricated, and tested. Experimental results verify the current sharing model and the current balancing method. The current difference of the optimized module is reduced by more than 50% under different conditions. Finally, the effectiveness of this method in the module with more paralleled mosfets is verified. [ABSTRACT FROM AUTHOR]

Wind turbines (WTs) are prone to lose the synchronization during severe grid faults due to the absence of equilibrium point. To cope with the issue, this letter proposes a power compensation control for doubly fed induction generator based WT to enhance the transient synchronization stability from the new perspective of active power balance. In the method, the active power of WT is controlled to compensate the power loss on the network. Compared with the existing methods, the proposed method has more widely application scenarios because it avoids using the frequency error as control signal. Experimental tests are performed to validate proposed method. [ABSTRACT FROM AUTHOR]

The LCC series–parallel resonant converter with a voltage doubler rectifier, widely used in X-ray machines, is required to meet an extremely wide output range. However, state-of-the-art models are based on fundamental harmonic approximation and cannot maintain good accuracy over the entire output range. The state trajectory method has the potential to achieve a full range of high accuracy without high complexity, but it only applies to simple topologies, like LCC with a full-bridge rectifier. For LCC with a voltage multiplier, the capacitors in the multiplier are involved in the resonance, which can be modeled as a five-element resonant circuit. Moreover, the conduction sequence of components in the minor mode is different from that in the major mode, which is usually ignored in the steady-state model. The influence of the output capacitance of power transistors on the state trajectory is so unclear that the model accuracy decreases considerably at high frequencies. In this article, the equivalent parallel resonant capacitance is derived through the current distribution. The steady-state model of the LCC converter with a voltage doubler rectifier is developed for both major mode and minor mode. The deviation of the state trajectory and modeling accuracy induced by the output capacitor is investigated. Based on the proposed model and device stress analysis, the design procedure for LCC under a wide operation range is presented. The simulations and experiments verify the accuracy of the model and the validity of the design method. The simulation mismatches are less than 2.3% over the entire output range. The maximum experimental mismatch is 15%. [ABSTRACT FROM AUTHOR]

Integrated buck-boost-LLC (IBBL) dcconverter is a good solution for high efficiency and high power density applications. However, the bridge leg integration causes asymmetrical zero-voltage-switching process and asymmetrical secondary current. The method of high quality factor or symmetric phase shift modulation proposed in the existing research can improve the asymmetrical current issue under heavy load, but is ineffective for light load conditions. This article proposes a novel Interleaved IBBL converter to improve the asymmetry issue for whole load range. Interleaving makes the secondary current be symmetric naturally. In addition, a comprehensive optimal design method for phase-shift angle and choke inductor is proposed to minimize the total power loss of all primary elements. A 600 W/1 MHz prototype verifies that the proposed IIBBL converter achieves symmetric secondary current in whole load range, and it achieves 95.7% efficiency and 180 W/in3 under the proposed comprehensive optimal design method. [ABSTRACT FROM AUTHOR]

Multilevel circuits can achieve high-voltage level, power density, and performance. This article considers a dual active bridge (DAB) based on the active neutral-point-clamped (ANPC) three-level circuit (ANPC–DAB). The soft-switching characteristics of the ANPC circuit during the switching process between switching states are analyzed, and the conditions for enabling all 12 switching devices to achieve zero-voltage switching (ZVS) on all the turn-on switching transitions are obtained. Based on this, the distribution of hard-switching turn-off and conduction losses of power devices is further analyzed, and an optimized switching strategy that can balance the loss distribution of power devices is proposed by the evaluation of all zero states and analysis of a switching-state sequence. Moreover, this article examines the effect of the proposed switching strategy by analyzing the loss distribution of power devices and efficiency of the ANPC–DAB. Finally, experiments are conducted using a 1-kW prototype. The simulation and experimental results show that the proposed switching strategy can effectively improve the loss distribution of power devices while all the power devices realize ZVS. [ABSTRACT FROM AUTHOR]

Benefited from the fast switching speed, Gallium nitride (GaN) high electron mobility transistors (HEMTs) have been widely used in high switching frequency converters. However, due to the significant correlation between the turn-off time and operating conditions (more than 20 times difference of the turn-off time between the high load current and small load current for GaN HEMTs), using a fixed dead time will introduce extra dead-time (DT) losses in inverters where the output voltage and current are constantly varying. Therefore, this article proposes a high-efficiency adaptive method to dynamically adjust the GaN-inverter DT with operating conditions. An improved transient model including the parasitic inductance and output voltage with bidirectional solution flow has been proposed for GaN HEMTs to increase the accuracy of DT adjustment. Based on this model, the dynamic DT adjustment can be realized without extra sensors for GaN-inverters. Using the dynamic DT adjustment, the experimental results show a peak efficiency of 98.25% in a 1200 W inverter with triangular current mode modulation. Compared with using the fixed DT, the dynamic DT method can reduce the power loss by 26.7% under full load and 49.14% under light load. [ABSTRACT FROM AUTHOR]