Although LLC converters are attractive in industrial applications due to its advantages of soft switching, high efficiency, and simple control, in wide voltage gain range applications, large ...switching frequency operating range is required, which may cause the loss of soft switching operation and existence of control instability issue. In this article, a novel LLC converter with two LLC resonant tanks is proposed. The proposed converter has three operation modes, namely, dual full-bridge operation mode, full-bridge operation mode, and half-bridge operation mode, which can cover the high voltage gain range, medium voltage gain range, and low voltage gain range operations, respectively. The operational principles of the proposed converter are presented, and brief design considerations are discussed. A 250 W experimental prototype with six times input voltage range (50-300 V) was built to validate the theoretical analysis of the proposed converter. Comparisons among different LLC topologies for wide voltage gain range applications are made.
Cryogenic power electronics is regarded as the next step to improve the power converter efficiency and power density. Thus, investigations on component and converter performances under low ...temperature operations are of great importance. Silicon carbide (SiC) devices have gradually replaced traditional Silicon (Si) devices in high voltage and high power applications. This is due to their fast switching speed and low switching loss. In this article, the performance of SiC device based power converters are investigated under low temperature operation. Firstly, the individual component performances are evaluated under low temperatures. Then, a 600 W resonant converter based DC transformer was built and tested under low temperatures. The efficiency for the tested converter with ferrite cores drops from 97.86% at room temperature (298 K) to 93.44% at 143 K. The converter power loss model under low temperature operation was developed to facilitate the understanding of converter performance at various operating temperatures.
Silicon carbide (SiC) MOSFET has many superior characteristics in high power applications. Paralleling the SiC devices is an effective approach to increase the current capacity of the system, which ...also leads to current sharing issues. In this paper, both transient and steady-state current sharing issues are studied for the high-power grid-tied inverters with paralleled SiC modules with an effective current balancing strategy proposed to address both issues simultaneously. The steady-state imbalance current due to the parameter mismatch is suppressed by the self-inductance of power cables used for paralleling connection. With the elimination of steady-state imbalance current, the transient imbalance current sensing is much simplified and can be realized by using low-cost current sensors. With the sensed imbalance current, a closed-loop control approach is proposed to adjust the modulation reference signal for each module to mitigate the remaining transient imbalance current. The proposed method is straightforward to implement with enhanced compatibility and flexibility compared to existing methods. Experimental studies are performed using inverters with 2 and 4 power modules paralleled in each phase to demonstrate the effectiveness of the proposed method.
With high-temperature power devices available, the support circuitry required for efficient operation, such as a gate driver, is needed as part of a complete high-temperature solution. The design of ...an integrated silicon carbide (SiC) gate driver using a 1.2-μm complementary metal-oxide-semiconductor (CMOS) process is presented. Adjustable drive strength is added to facilitate a minimal external component requirement for high-temperature power modules and lays the groundwork for dynamic adjustment of drive strength. The adjustable drive strength feature demonstrates a capability of reducing overshoot and controlling dv / dt dynamically. Measurement of the gate driver was performed driving a power mosfet gate over temperature, exceeding 500 °C. High-speed and high-voltage room temperature evaluation is provided, demonstrating a system capable of high performance over temperature. The driver accomplishes better than 75 ns of rise and fall time driving the Cree CPM3-0900-0065B from room temperature to over 500 °C indicating that it will be ideal for integration into an all-SiC power module where driver, protection circuits, and power devices are fabricated in SiC.
This article presents a comprehensive design and validation of a compact all-silicon carbide (SiC) 250-kW T-type traction inverter with a power density of 25 kW/l and 98.5% peak efficiency. All the ...operation modes and switching transitions in a T-type phase leg are analyzed to model the semiconductor power losses over a fundamental cycle. Special attention has been paid to investigate the behavior and losses due to the reverse conduction of the SiC MOSFETs. Then a loss model is built based upon this analysis to calculate the device loss distribution and system efficiency, which is further used to determine the optimal switching frequency. In addition, detailed inverter system design and prototyping procedure, including the selection of SiC modules and dc-link capacitors, and the optimization of a fourlayer laminated busbar, are presented. In this article, the T-type phase leg is formed by a normal half-bridge module and a common-source module. The switching performance and losses in this configuration are different from two-level topology that only uses one SiC module. Therefore, the switching performance and the associated switching energy in each switch position are characterized using a custom clamped inductive load (CIL) test setup designed for a T-type phase leg. The performance of the full power traction inverter prototype has been verified experimentally using pulse testing and continuous power testing.
Wide voltage gain range applications are challenging for dc/dc converters, and the system efficiency would be degraded in order to satisfy the voltage gain requirement. Inductor-inductor-capacitor ( ...LLC ) resonant converters have gained popularity owning to its high efficiency feature. However, wide voltage gain range applications also challenge the LLC converters from the following three aspects: 1) large switching frequency operating range is required to meet the voltage gain requirement, which degrades the converter electromagnetic interference (EMI) performance and challenges the optimization of magnetic components; 2) small inductor ratio is required to boost the voltage gain, which increases the resonant tank root-mean-square (rms) current and conduction loss; and 3) control instability issues may occur at both maximum voltage gain and minimum voltage gain, which reduce the converter reliability. To address these issues, in this article, a novel LLC converter with topology morphing control is proposed for wide voltage gain range applications. Three operation modes, dual full-bridge (DFB), hybrid full-bridge and half-bridge (HFBHB), and dual half-bridge (DHB), can be achieved by adopting the topology morphing control, which can cover a wide voltage gain operation range. Operational principles, design considerations, and experimental validations of the proposed converter are presented.
In this paper, a Multi-Input Multi-Output (MIMO) high step-up transformerless DC-DC converter is proposed. The proposed converter can expand the number of ports from both input and output terminals. ...Also, it has a modular structure using voltage multiplier cells (a switch, two diodes, a capacitor, and an inductor). The proposed converter is useful for a wide range of applications and has the merit of interfacing multiple hybrid voltage sources with each other to supply different loads with various voltage levels. All the output voltages of the output ports can be regulated at the same time by tuning separate controlling parameters. Since digital control has the benefit of (1) enhancing efficiency, (2) higher flexibility than analog electronics, (3) ease of use, (4) improving reliability and stability in hybrid energy conversion applications, this method of controlling implementation is adopted. The key contributions of this article would be 1) expandable modular MIMO converter with high performance for all range of duty cycles; 2) integration of hybrid energy sources and delivering to multiple loads; 3) nonlinear digital controlling approach to achieve fast transient response under the variation of input voltage sources and output loads, and 4) high voltage gain with low normalized power stress on switches. To simplify the analysis, first, single-input, dual-output (SIDO) mother-module, dual-input, three-output (DITO) and three-input, four-output (TIFO) developed modules are carefully analyzed and then, the MIMO structure is explained. To verify the theoretical results, a prototype of SIDO operation of the proposed converter with a digital controlling scheme is implemented for 30V input voltage /150V, 250V output voltages with the total power of 450W. Furthermore, experimental results of DITO operation with 30V and 40V input voltages/150V, 250V, 405V output voltages with the total power of 800W are extracted.
Cryogenic power electronics is regarded as the next step to improve the converter efficiency and power density. It is advantageous in many different applications, including aerospace, renewable ...energy, transportation and so on. Among all different semiconductors, gallium nitride (GaN) was found more advantageous with significant loss reduction at cryogenic temperature. In this paper, overcurrent test is performed and analyzed for a high-efficient commercial GaN high electron mobility transistor (HEMT). The experimental results demonstrate a significant improvement of the device overcurrent capability at cryogenic temperature (from 160 A at room temperature to 250 A at cryogenic temperature). The operating mechanisms behind the overcurrent test are investigated and discussed. Finally, a 5 kW GaN HEMT based cryogenic Buck converter is built and tested. Maximum efficiency of 98.5% is achieved at 1.5 kW output power and around 1% efficiency improvement can be achieved when compared to room temperature operation. Another GaN HEMT based four-switch Buck-boost converter is evaluated at cryogenic temperature, maximum efficiency improvement of 1.5% is observed when compared to room temperature.
In this article, a hybrid pulse frequency modulation (PFM) and pulse width modulation (PWM) modulation strategy is proposed for the stacked structure LLC resonant converter. Three-level operation of ...the resonant tank input voltage is achieved by introducing the half of input voltage level due to the adopted PWM modulation strategy. Therefore, two control freedoms, switching frequency and duty ratio, are available for the proposed converter. To optimize the system efficiency performance, a power loss model based on the time-domain analysis method was built. By setting the converter power loss as the optimization objective, the optimized combination result of switching frequency and duty ratio can be found. In addition, the proposed hybrid modulation strategy can be applied for wide input voltage range application. Compared with traditional PFM LLC resonant converter, the proposed converter has better efficiency performance and the required switching frequency operating range is reduced significantly. Compared with the PWM LLC resonant converter, the resonant inductor current peak value and root-mean-square (RMS) value are reduced greatly. Finally, a 115 W experimental prototype with a wide input voltage range of 160 V--340 V was built to validate the effectiveness of the proposed hybrid modulation strategy for the stacked structure LLC resonant converter.
In the field of electric mobility, in particular heavy-duty electric vehicles and long-haul trucks, the energy systems are susceptible to transients with different amplitudes and dynamics due to the ...high power demand. With the combination of high power and long distances, the available battery technologies become insufficient as a single energy source for such a system. Thus, the integration of hybrid energy storage systems (HESSs) with different energy capabilities, such as fuel cells, battery packs, and supercapacitors, is highly required. In this context, for leveraging HESSs in an efficient way, a resonant multiwinding transformer-based converter is proposed to interconnect these different energy storage systems (ESSs) since the resonant converters are able to operate at a wider range of switching frequencies and, hence, a wider soft-switching range. However, due to the multiple resonant circuits and possible parameter deviations, the control capability might be compromised. Thus, a multiport resonant dc/dc converter embedded with variable inductors is proposed to enhance the power flow management among these different ESSs with reduced conversion stages. Further, the proposed concept can also improve the immunity to parameter deviations on the resonant by compensating for possible variations at the resonant frequencies. Finally, simulations and experimental results of a <inline-formula><tex-math notation="LaTeX">\text{20} \;\text{kW}</tex-math></inline-formula> four-port resonant dc/dc converter embedded with variable inductors are shown to prove the effectiveness of the proposed concept.
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