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In this paper, eight different SRAM cells are studied and evaluated with a 65nm CMOS technology. The cells were designed with radiation-hardening-by-design approaches including schematic and layout techniques. The eight types of cells were placed into eight pages of an SRAM test chip. The alpha and proton irradiation demonstrated that the Dual Interlocked Cell (DICE) has the best radiation-tolerant performance, but requires the largest area. The 6T and 11T cells designed with charge cancellation techniques can reduce soft errors up to 2-3 times with less area overhead. Several DICE variants were developed with reduced area overhead and showed SEU resilience performance equivalent to DICE. Simulation results are also presented in this paper to validate the findings.

A triple modular redundancy SRAM was designed as the embedded high-speed memory for a radiation-tolerant ARM processor with ST Microelectronics 28-nm FDSOI technology. The single event upset (SEU) cross-section of the SRAM was tested by using heavy ions with the linear energy transfer of 15.0 meV.cm2.mg−1 in both non-TMR and TMR modes with different accumulated fluence. The SRAM cell was also simulated by using Cogenda TCAD simulation suite and the cross section was calculated by using analytic method. The results showed the cross-section is around 2E-10 cm2/bit in non-TMR mode, and in TMR mode it varied from one to several orders lower than the non-TMR mode according to the specific accumulated fluence. As a scrubbing circuit was designed to reduce the accumulated number of SEUs in the SRAM, the Failure In Time (FIT) rate at sea level in New York City could be as low as 8E-11, which is robust enough for the whole circuit.

The high frequency (HF) isolation transformer is the core element of a dual-active-bridge (DAB) bi-directional high-power DC-DC converter. At high frequency high power conversion, providing compact and efficient transformer design solutions need to consider the magnetic, electric as well as thermal aspect thoroughly and carefully to ensure the reliability and efficiency of the whole system. Detailed design considerations for a HF isolation transformer in a DAB conversion system are presented in this paper taking into consideration the insulation, high frequency magnetics characteristics, skin-proximity effects at high switching frequency as well as the thermal-fluid interaction analysis. Special attention is paid to the leakage inductance since improper value leads to an undesirable overshoot on the device voltage which may cause the SiC failure. This paper also presents the a multi-objective optimization design methodology applied to a 25kVA/25kHz, 1500V/750V transformer intended for DC-DC stage in 1MVA SiC-based solid state transformer (SST) and the Pareto optimal sets under different cooling methods are derived and analyzed. Comparison between different magnetic materials and different operation conditions are also carried out to find the characteristics variation of the designed transformer. The merit of the optimal design are validated through finite element modeling (FEM) and computational fluid dynamics (CFD) simulations.

In order to effectively control vessel rudder under the random interference, this paper presented an innovative method based on extended linear-quadratic regulator (LQR) control method and adaptive genetic algorithm (AGA). With respect to the actual vessel navigation environment, the extended LQR control method is explored by using a series of calculus transformation under the random interference. Besides, the AGA is utilized to optimize two kinds of weighted matrices in Riccati differential equation. What's more, the crossover and mutation probabilities are adaptively computed in the process of AGA. The numeric simulation indicated that the proposed method can effectively control vessel rudder with the satisfactory robustness.

Medium-frequency (MF) transformer has gained much popularity in power conversion systems. Temperature control is a paramount concern, as the unexpected high temperature declines the safety and life expectancy of transformer. The scrutiny of losses and thermal-fluid behavior are thereby critical for the design of MF transformers. This paper proposes a coupled, semi-numerical model for electromagnetic and thermal-fluid analysis of MF oil natural air natural (ONAN) transformer. An analytical model that is based on spatial distribution of flux density and AC factor is exploited to calculate the system losses, while the thermal-hydraulic behavior is modelled numerically leveraging the computational fluid dynamics (CFD) method. A close-loop iterative framework is formulated by coupling the analytical model-based electromagnetic analysis and CFD-based thermal-fluid analysis to address the temperature dependence. Experiments are performed on two transformer prototypes with different conductor types and physical geometries for validation purpose. Results suggest that the proposed model can accurately model the AC effects, losses, and the temperature rises at different system components. The proposed model is computationally more efficient than the full numerical method but it reserves accurate thermal-hydraulic characterization, thus it is promising for engineering utilization. Published version

Nowadays, medium frequency transformers are widely employed with power electronic converters, offering obvious benefits for modern power system. Rising the switching frequency leads to the need for accurate estimation of the characteristics of a designed transformer. This paper refines the existing analytical frequency-dependent method for accurately calculating leakage inductance in the medium frequency range based on the magnetic field intensity distribution and the stored magnetic energy method. Unlike the previous expressions, the proposed method employs mean turn length of individual layer which makes the calculation more precise. The advantages and impacts of interleaved winding structure to minimize the leakage inductance are also shown by comparing different winding patterns. Transformer prototypes with specifications as 10kW, 500/5000V, 5kHz have been manufactured and tested. The presented equations for inductance calculation are benchmarked to the experimental results on the developed transformer prototypes as well as the finite element analysis (FEM) simulation results.

The maximum current carrying capacity of a power cable (Ampacity) is determined by the thermal characteristics of the cable components and surrounding medium in which they are buried. Power cable ampacity calculations are based on typical standard tables defined with predetermined parameters. In realtime, the environment of installation plays significant role in cable current carrying capacity. This paper presents FEM approach to determine the maximum current capacity within the safe operating limits of the cable by modeling electro-magnetic heat transfer. The study includes complex thermo-electric coupling and heat transfer in different zones surrounding the cable and its effect on the conductor operating temperature. The results show the difference between the proposed approach and standard calculations and improvements to accurate rating of the cables.

Nowadays, medium frequency transformers have gained growing attention in modern power system. Higher power density, which is realized by increasing the operating frequency, leads to the reduction of the magnetic components size. Along with it, cooling surface is consequently reduced which results in high thermal stress. Careful attention must be paid on the loss mechanisms and thermal analysis of a medium frequency transformer at the design stage. This paper develops an equivalent thermal circuit of an oil-immersed medium frequency transformer to predict its temperature profile. Thermal resistance, capacitance and the losses generated in the core and winding are carefully estimated. Two oil-immersed shell-type transformer prototypes with specifications as 5kW, 500/5000V, 5kHz, interleaved winding construction have been developed and built for verification purpose. Loss and temperature measurements have been performed to verify the presented framework. The accuracy of the proposed thermal model is benchmarked and corroborated through experimental measurements as well as FEM-CFD study with good agreement.

To find balance among multiple design objectives of a medium/high-frequency (MF/HF) high-power (HP) transformer is best addressed employing an optimization technique. In this paper, MF HP transformer design is formulated as a multi-variable optimization problem, where efficiency, power density and temperature rise are chosen as design objectives. Total loss, core volume and maximum temperature rise are modeled as respective cost functions and amalgamated using weighted-sum approach to derive objective function. It is minimized using Steepest descent method. Being a gradient-based search technique, it preserves correlation among design variables during minimization. Using the proposed methodology, optimal design of a 10 kW, 0.5/5 kV, 1 kHz natural oil-cooled transformer with amorphous core and concentric foil winding, is derived. It is estimated to have an efficiency of 99.55% at a power density of 19.79 and maximum node temperature of 52.92 °C. These merit of figures are validated using FEM and CFD studies. Cost-effectiveness of proposed methodology is discussed with the help of a hardware prototype, built from off-the-shelf amorphous core. Benefits like design flexibilities and plausible cost-effectiveness, are inherent to gradient-based optimization method, which augur well for its applicability for MF HP transformer design.

A medium/high-power conversion system using power electronic (PE) converter along with a medium/high-frequency transformer, offers many desirable features that are beneficial for present-day power system topologies. Leakage inductance is identified to be one of the key parameters to characterize performances of such a medium-frequency (MF) high-power (HP) transformer. In this paper, existing analytical method to calculate leakage inductance of a concentric winding is further refined employing mean turn length of individual layer and winding porosity factor. Impact of interleaving to reduce leakage inductance is studied. Consequently different winding dispositions (normal and interleaved) and conductor geometries (foil, round) are investigated for a 10 kW, 0.5/2.5 kV, 1 kHz transformer design. Finally generalized method to deduce leakage inductance of fractional-interleaved winding is introduced in scope of this paper. Analytical calculations are corroborated with PEMag simulation results. With proper selection of wire and core geometry, good agreement between analytical and PEMag results is achieved at medium switching frequency, which substantiates aptness of presented methodology.

A medium/high-power conversion system, using power electronic (PE) converter in conjunction with a medium/high-frequency transformer, has many desirable effects suitably oriented for modern power system architecture. Switching at high frequency results in lesser volume of magnetics but induces higher loss density. Thus design and characterization of a medium-frequency (MF) high-power (HP) transformer has significant ramification on its performance and application. Thermal management of a MF HP transformer is one of key aspects for its characterization. In this paper, an equivalent thermal model of a multi-layer concentrated winding is derived. Core and copper losses are carefully estimated. Thermal resistance and capacitance are accurately calculated. Time-domain response of proposed thermal network is obtained using Heun's method (Modified Euler) and validated with PLECS. Effects of temperature change on thermal properties of material and coolant (transformer oil) are also discussed. Furthermore, accuracy of said thermal network is corroborated through FEM-CFD study of a 10kW, 0.5/2.5kV, 1kHz natural oil-cooled transformer. Close agreement between analytical and simulation results is observed which substantiates proposed thermal model in terms of accuracy and efficacy of computation.