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Hydrogels with good flexibility and strong hydrophilicity can be candidates for excellent flexible electrolyte materials. However, the poor structural stability, uncontrollable swelling, and lower potential window of hydrogel electrolytes need to be improved. This work combined quaternized gelatin with cross-linked poly(acrylic acid-co-acrylamide) to form a semi-interpenetrating network and gelatinized in situ in a flexible porous wood skeleton. The flexible wood (FW) skeleton enhances the hydrogel and limits the swelling of the hydrogel. In addition, quaternary ammonium groups and FW act synergistically to provide the composite hydrogel electrolyte with a high ionic conductivity of 5.57 × 10

The extensive application of the power electronic transformers (PETs) in power systems poses a challenge as the accurate and high-speed electromagnetic transient (EMT) simulation of PET has been a critical issue. The computational time of the detailed EMT simulation of PET on EMT programs is unacceptable due to the large electrical node count, microsecond-range simulation steps, and high switching frequency of the devices and transformers. This article proposes a hierarchical modeling scheme for PET. Unlike the existing modeling methods, the proposed technique recursively decreases the dimension order of the admittance matrix to obtain the generalized Norton equivalent of each phase leg. The final admittance matrix overlaid onto the external system admittance matrix has a dimension order of magnitude remarkably smaller than that of the unreduced structure. By comparison with a detailed EMT model of a medium-voltage dc system, the performance of the proposed scheme has been assessed in PSCAD/EMTDC under various working conditions. With negligible loss of accuracy, approximately one to two orders of magnitude speedup over a straightforward EMT program is achieved.

The high-speed accurate electromagnetic transient (EMT) simulation of the power electronic transformers (PET) has become a challenge, due to the microsecond-range time steps and the large number of high-frequency semiconductor switches and isolating transformers. Taking the input-series-output-parallel (ISOP) connected cascaded H-bridge (CHB) type dual active bridge (DAB) based PET as an example, this paper proposes a general high-speed equivalent EMT modelling method of PET. First, the isolating transformer within each DAB is discretized into two-port Norton circuits. Second, each CHB-DAB is equivalent to two single-port circuits by eliminating the internal nodes. And the input-side is represented by a Thevenin circuit and the output-side is represented by a Norton circuit. Third, all the CHB-DABs are equivalent to a two-port circuit with all the internal node information preserved. Fourth, the implementation of PET blocking is also considered for startup and fault protective actions. Fifth, the stability of the proposed discrete decoupling method of the PET is verified that it does not introduce specific limitation on the simulation step size. Finally, the developed PET models on PSCAD/EMTDC are shown to be two orders of magnitude faster than the currently available fully-detailed models with negligible loss of accuracy.

The modular power electronic transformer (PET) faces difficulty carrying out microsecond-level electromagnetic transient (EMT) simulations. This paper provides a high-speed and high-precision simulation method capable of eliminating the internal nodes and reducing the order of the nodal admittance matrix. Meanwhile, the parallel computing is integrated into the whole solution process, which achieves a significant simulation speedup. A physical prototype is established to prove that the detailed model is sufficient to reflect the dynamics of physical devices. Moreover, simulations in PSCAD/EMTDC are carried out to compare the proposed method with the detailed model in terms of accuracy and time efficiency. Simulation results show that the proposed method is accurate to simulate the external and internal dynamics of PET with hundreds of times simulation speed acceleration.

Accurate and efficient electromagnetic transient (EMT) simulation of various types of solid-state transformers (SST) is extremely time-consuming due to the complex module structure, flexible topology connections, large number of electrical nodes and simulation time-steps limited in the range of micro-seconds. Therefore, it is urgent to develop the EMT equivalent modelling and fast simulation of SSTs for system level studies. Taking the modular multilevel converter (MMC) based SST as an example, this paper proposes an accelerated EMT model which focuses on the equivalence of the dual active bridge (DAB) based high-frequency link (HFL) in the SST. Compared with the existing algorithms, two critical factors of the proposed method that contribute the most to the efficiency improvement are the preprocessing of the nodal admittance equation and the conversion of the short-circuit admittance parameters. The proposed model is verified in PSCAD/EMTDC by comparing it with the detailed EMT model. The results show that the accelerated model is one to two orders of magnitude faster than the detailed model without sacrificing the accuracy. The experiment validation also confirms the validity of the proposed model.

Reducing the capacitor voltage ripples of the half-bridge submodules (HBSM) and full-bridge submodules (FBSM) in a hybrid modular multilevel converter (MMC) is expected to reduce the capacitance, volume, and costs. To address this issue, this article proposes a dual harmonic injection method which injects the second harmonic circulating current and third-order harmonic voltage into the conventional MMC control. First, the mathematical model of the proposed control is established and analyzed. Then, the general strategy of determining the amplitude and phase angle of each injection component is proposed to suppress the fluctuations of the fundamental- and double-frequency instantaneous power. The proposed strategy can achieve the optimal power fluctuation suppression under various operating conditions, which also has the advantage of reducing the voltage fluctuation difference between HB and FB SMs. The correctness and effectiveness of the proposed strategy are verified in simulations in PSCAD/EMTDC.

This paper proposes a high-speed modeling architecture for fast electromagnetic transient (EMT) simulation of PETs. Unlike the existing modeling methods, the proposed technique recursively decreases the dimension order of the admittance matrix to obtain the generalized Norton equivalent of each phase leg. The final admittance matrix overlaid onto the external system admittance matrix has a dimension orders of magnitude remarkably smaller than that of the unreduced structure. By comparison with a detailed EMT model of a medium-voltage dc (MVDC) grid, the performance of the proposed scheme has been assessed in PSCAD/EMTDC under various working conditions. With negligible loss of accuracy, approximately one to two orders of magnitude speedup over a straightforward EMT program is achieved.

Accurate and efficient electromagnetic transient (EMT) simulation of various types of power electronic transformers (PET) is extremely time consuming due to the complex module structure, flexible topology connections, large electrical node count and microsecond-range simulation time-steps. Therefore, the EMT equivalent modelling and fast simulation of PET topologies face very urgent needs for research and practical development. Taking the modular multilevel converter (MMC) based PET as an example, this paper proposes an enhanced EMT model which focuses on the equivalence of the dual active bridge (DAB) based DC/DC converter in the PET. Two critical factors of the proposed method that contribute the most to the efficiency improvement are the preprocessing of nodal admittance equation and the conversion of the short-circuit admittance parameters. The proposed model is verified in PSCAD/EMTDC by comparing with the detailed EMT model. The results show that the accelerated model is one to two orders of magnitude faster than the detailed model with negligible loss of accuracy.

Currently, Deep Neural Networks has achieved excellent results on many tasks. But recent studies have shown that these networks are easily influenced by adversarial examples, which are artificially crafted by adding perturbation to original image. Moreover, most of the models to which we can access are black-box, we don’t know the internal structure and parameters of the model. Thus, it is more practical and more challenging to study how to attack these models. In this article, we propose a cam(class activation map)-guided data augmentation attack method, which can improve the transferability of adversarial examples. Specifically, first use the trained network to get the class activation maps for an input image, then binarize the cam to get the mask, finally implement the data augmentation attack method on the masked area of the image. Experiments based on ImageNet prove that our proposed method can generate more transferable adversarial examples, and the attack success rates of our method have a certain improvement compared with the latest methods.

Recently, nonlinear components such as metal oxide arresters (MOA) are widely used in MMC-HVDC systems. Equivalent models are proposed to accelerate the simulation of complex nonlinear components. However, it is hard to evaluate the similarity of the original model and equivalent model. In this paper, a novel method is proposed to calculate the similarity of similar waveforms after removing the time delay and DC offset, and is capable to give the degree of the accuracy of the equivalent model. We eliminate the influence of DC offset by differentiating and calculate the time delay by finding the most similar interval between two discrete series. And then the DC offset of similar waveforms is obtained by integrating in the fitting interval. Finally, based on the concept of the coefficient of determination in statistics, the two waveforms similarity are evaluated. Then waveforms obtained from the detailed model and the equivalent model of nonlinear component in MOA are analyzed with the method.