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With the increasing utilization of renewable energy generation, especially photovoltaic (PV) power generation, the technology for wide-range high-efficiency DC-DC converters is becoming increasingly important. This paper focuses on the control of high-efficiency step-up DC-DC converters with the multi-phase Boost and LLC (MPBLLC) converter. A control strategy based on intermediate bus voltage information is proposed to improve the efficiency over a wide input voltage range. The operation principle and the time domain model of the converter are analyzed first. Since the loss models in previous studies are not accurate and comprehensive enough, a loss modeling method for the variable voltage is proposed. It is based on the time domain analysis (TDA) and is available for a wide voltage range. By analyzing the level and influence factors of variables in the MPBLLC converter, a fast algorithm for loss modeling is also proposed. Further, the control strategy including the optimal bus voltage control is proposed for MPBLLC converter. Control modes are analyzed in detail. For the key part, four different control approaches are presented based on different variations of the intermediate bus voltage. Above all, the optimal bus voltage control is proposed based on the proposed variable bus loss model. Finally, a 500-W experimental prototype is built to verify the effectiveness of the proposed loss model and control strategy, which demonstrates good performance and high efficiency over a wide input voltage range.

The increasing number of low-frequency oscillation events has posed significant challenges to power system stability. It is imperative to accurately identify and properly control generators with poor or negative damping contribution for better oscillation damping. This paper proposes a hybrid energy and mode decomposition-based method for evaluating generators damping in multi-machine power systems. It is derived that the aggregate electric torque can be modeled as the superposition of electric torques in different modes. In each oscillation mode, the electric torque can be decomposed into the damping torque and the synchronizing torque. Moreover, a novel oscillation energy function is developed to evaluate generators' damping effect in each oscillation mode. The result proves that in each oscillation mode, generators with attenuated oscillation energies have negative damping effects. Simulation results in single and multinegative damping generators cases, as well as the comparison with other methods, demonstrate the effectiveness and robustness of the proposed method for damping evaluation.

Complementary sources concept and half-mode/quarter-mode substrate integrated waveguide (HMSIW/QMSIW) technology are introduced in this paper to improve the back-radiation suppression and bandwidth of microstrip patch antennas (MPAs). The HMSIW cavity as the feeding structure brings an additional resonant frequency to the inherent resonant mode of typical MPAs, which efficiently extends the bandwidth of the MPAs. In addition, while stimulating the MPA mode, the HMSIW cavity drives a monopole by slightly breaking the shorting wall of the HMSIW cavity and loading a printed monopole. The loaded monopole and the equivalent magnetic currents of the MPA construct an orthogonal complementary source model that indicates back radiation suppression. A differential feeding scheme is also employed to enhance the radiation performance. The dual-polarized model, achieved by replacing the HMSIW cavity with QMSIW cavities, is also addressed and even fabricated and tested. The measured results show a differential impedance bandwidth of 15.4% from 1.91 GHz to 2.23 GHz with a differential port-to-port isolation of 38 dB. In the operating band, the average gain is 7.5 dBi, and the front-to-back ratio (FBR) is over 18 dB with a maximum value of 34 dB.

The active distribution network management (ADNM) equipped by active distribution networks (ADNs) can enhance the resilience of the network after failure. This paper proposes a novel comprehensive post-event network restoration model and its chance-constrained variant for ADN that considering the dispatch of distributed generation (DG), energy storage system (ESS), demand response (DR), static var compensator (SVC), and network reconfiguration to fully investigate the potential of the ADNM in network restoration. In this paper, the line failure, bus failure, and the uncertainty from load and DG output forecast error are considered. Specifically, the line and bus failures are modeled by an enhanced fictitious network technique, while the uncertainty of load and DG output forecast is modeled by the chance-constrained optimization. The power flow is described by a linearized DistFlow model, and thus the deterministic and chance-constrained network restoration models are programmed by the mixed-integer linear programming (MILP). The proposed deterministic and chance-constrained restoration models are tested on the IEEE 33 bus system. Results demonstrate the effectiveness of the proposed deterministic and chance-constrained network restoration model.

This paper proposed a comprehensive evaluation (CE) framework concerning multivariate statistical analysis to provide a systematic assessment and a hierarchical analysis for the urban integrated transportation network (UITN). Specifically, this research contributed the following technical approaches: Firstly, 4 criteria (scale, structure, level of service (LOS), layout) was adopted and indexes were screened from heterogeneous aspects to establish the hierarchical model using correlation coefficient method (CCM). Built upon that, fuzzy comprehensive evaluation method (FCEM) and linear dimensionless (LD) were applied to quantify and nondimensionalize the qualitative and quantitative indexes. In order to improve accuracy and guarantee rationality, this paper then integrated analytic hierarchy process (AHP) with entropy weight method (EWM) to get the index weight. At last, the combination of value analysis (VA) and grey relational analysis (GRA) was used to calculate the CE value. The experimental study shows that our introduced CE framework can offer a thorough evaluation of the UITN, the CE value of UITN in Haimen city is 0.740 and its grade level is “Medium”. Pros and cons of the structural layout of each transport mode can also be judged through the hierarchical analysis of different indexes. In view of this, corresponding suggestions were given for future improved transportation planning.

Microgrids are localized electric grids that can operate independent of the main grid and help strengthen grid resiliency by working alongside backup generators to maintain electricity supply in the event of a large-scale grid disturbance. This research proposes a single-source capacitated facility location coverage problem (SS-CFLCP) to optimize the location, assignment and number of renewable distributed generators (DGs) within a utility-based microgrid during a large-scale grid disturbance, where the microgrid is operating independent of the main grid. Traditional analytical techniques for DG placement within microgrids tend to focus on minimizing power losses, minimizing electric energy losses, improving voltage profile and maximizing cost savings. To deter from these traditional techniques, the proposed SS-CFLCP combines the facility location and location coverage problems, with an aim to minimize the following: total investment costs, total operation and maintenance cost, the distance traveled for electricity distribution, the power outage levels (unmet electricity demand) experienced due to a large-scale grid disturbance, and the levels of excess renewable penetration, which can cause reverse power flow issues that damage the main grid, within a network. Additionally, the proposed SS-CFLCP is modeled with a budgetary constraint for installing the DGs, making it a more practical and applicable model for a utility company. A case study using solar/photovoltaic-based DGs is used to show the effectiveness of the proposed model.

In this paper, a novel circularly polarized (CP) antenna that achieves high gain by maximizing the radiation aperture utilization is proposed for vehicle applications. The realization of increasing the radiation aperture is based on the application environment, making full utilization of the vehicle roof, a large metal reflector beneath the antenna, which is indispensable in the vehicle application. Developed from the structure of typical microstrip patch antenna, the design extends the radiation patch to cover the side of the dielectric substrate, which increases the size of the radiating patch without increasing the antenna's outline size. To make CP antennas more suitable for special working environments with large reflecting surface, a sequential rotation feeding structure with 90° progressive phase difference is uniquely designed based on the active port impedance of the four-ended radiation structure. This co-design method introducing the active port impedance of a multi-port radiator into the design of feeding network as the loads can effectively guarantee the CP performance of the antenna, and can greatly simplify the optimization work in the subsequent stage. Based on this design idea, a prototype working at 1.48 GHz with a 50-MHz bandwidth is designed for vehicle satellite broadcasting application. Experimental results show that the antenna achieves a high CP gain greater than 7 dBic with a compact size of $50 \times 50 \times 10\,\,mm^{3}$ ($0.247\lambda _{0} \times 0.247\lambda _{0} \times 0.05\lambda _{0}$ , $\lambda _{0} $ is the wavelength of working frequency in free space).

A generation unit that is poorly damped or has periodical mechanical power outputs from its prime mover can become a source of oscillation in a bulk power system. Choosing the proper electric quantity to extract the oscillation characteristics is crucial for the location and mechanism analysis of the oscillation source. This paper proposes the concept of oscillation phasor to characterize a type of sustained power system oscillations that originate from power plants. On this basis, a two-stage scheme is presented to locate one type of the sustained oscillation source and discover its mechanism: first, Prony analysis and the first wave algorithm are applied to extract the oscillation phasors on active power and angular frequency; second, the phase relationships between the oscillation-source generator and other generators are derived to guide the location of the source; finally, damping estimation on these oscillation phasors help distinguish a forced oscillation from a poorly damped oscillation. The proposed scheme is first demonstrated in detail on a two-area four-machine system and then tested using historical oscillation event data.

Slip rate control is important in improving vehicle stability and driving efficiency. In this paper, a robust slip rate control system is designed for distributed drive electric vehicles that consists of two slip rate estimators for multi-driving conditions, a vehicle speed estimator, and an anti-windup robust variable structure slip rate tracking controller. Because there is no driven wheel in a four-in-wheel-motor distributed drive electric vehicle, the estimators for small and large slip rates are designed based on dynamic and kinematic methods, respectively, which can switch according to the slip conditions. The convergence of the estimation error is discussed with the Lyapunov stability law and is less than 2% under the condition of acceleration on a low-friction road. The slip rate tracking controller is designed based on the sliding mode control law and the proportional-integral (PI) control method to handle model nonlinearity, modelling and estimation errors, and disturbances and to control the input chattering and saturation. The asymptotic stability of the tracking error is proven by Lyapunov theory. A joint control variable composed of the wheel angular acceleration and slip rate is designed to improve the robustness of the controller against the slip rate estimation error. Simulations and experiments under various conditions are performed to verify the proposed anti-slip control method. The results show that compared with a distributed drive vehicle without a slip rate controller, the controlled vehicle can prevent serious wheel skid on low-adhesion roads and improve the driving performance.

The ocean surface current vector contains velocity and direction information, and its acquisition method has important research value in marine applications. Multi-aperture along-track interferometric (MA-ATI) SAR is a novel method of current vector detection. However, due to the lack of real experimental data validation, complex marine environment and diverse system parameters have an uncertain impact on the current measurement ability of MA-ATI SAR. Therefore it is necessary to analyze the measurement accuracy and error of this method in theory. Based on the current measurement principle of MA-ATI SAR, this article deduces and establishes the accuracy and error simulation model, and analyzes the influence of radar parameters and marine environment on the velocity and direction results. In the simulation results, the airborne MIMO-SAR radar parameters is more suitable to use MA-ATI method for accurate current measurement, and the accuracy of current measurement is higher for the current with high velocity and direction close to azimuth. It is found that the variation of wind direction will lead to obvious errors in MA-ATI current results, and it is pointed out that accurate current results can be obtained by iteratively correcting the velocity error of sub-apertures using M4S model.

This paper proposes a novel method for solving and tracing power flow solutions with changes of a loading parameter. Different from the conventional continuation power flow method, which repeatedly solves static AC power flow equations, the proposed method extends the power flow model into a fictitious dynamic system by adding a differential equation on the loading parameter. As a result, the original solution curve tracing problem is converted to solving the time domain trajectories of the reformulated dynamic system. A non-iterative algorithm based on differential transformation is proposed to analytically solve the aforementioned dynamized model in form of power series of time. This paper proves that the nonlinear power flow equations in the time domain are converted to formally linear equations in the domain of the power series order after the differential transformation, thus avoiding numerical iterations. Case studies on several test systems including a 2383-bus system show the merits of the proposed method.

In this paper, the feasibility of using the half-mode/quarter-mode of a substrate integrated waveguide (HMSIW/QMSIW) cavity to feed microstrip patch antennas (MPAs) is explored; based on this, a circularly polarized (CP) MPA fed by the sequential rotation QMSIW cavities is proposed. For more compact and higher integration, the active circuits are packaged inside the microstrip patch antenna. Correspondingly, the QMSIW cavities have also been chamfered, and slots are designed on the upper surface to reduce the influence of the chamfer operation. The SIW cavities introduced an additional resonant mode, which can essentially enhance the bandwidth of the MPAs. The fabricated prototype shows a bandwidth of about 9% (1.42GHz - 1.55GHz) with an average CP gain of 7 dBic. In addition, the adoption of HMSIW/QMSIW cavity excitation allows the microstrip patch antenna to retain a seamless ground plane as well, which facilitates further integration with other components of the communication system by printed circuit board lamination technology.

The early fault of a cable is usually a incipient fault, which is difficult to find and can easily develop into an insulation breakdown fault. Thus, it is of great significance to quickly and accurately find an incipient cable fault. This paper presents an fault location method for cable insulation based on the electric quantities of both ends. Based on the equivalent circuit model of three-phase single-core cable distribution parameters, the calculation method of the voltage along the cable is derived. The equivalent model of cable insulation in resistive and capacitive parallel is proposed and applied to the early fault modeling of cable. On the basis of the calculation formula of the voltage along the cable and the electric quantity at both ends of the cable, the analytical expression of the cable fault location is obtained by solving the fault equation directly. Extensive simulations show that the algorithm, this method can locate the incipient fault accurately, and is not affected by the fault point, fault resistance and fault inception angle.

The potential of using autonomous underwater vehicles (AUVs) for underwater exploration is confined by its limited on-board battery energy and data storage capacity. This problem has been addressed using docking systems by underwater recharging and data transfer for AUVs. In this paper, we propose a vision-based framework by addressing the detection and pose estimation problems for short-range underwater docking using these systems. For robust and credible detection of docking stations, we propose a convolutional neural network called docking neural network (DoNN). For accurate pose estimation, a perspective-n-point algorithm is integrated into our framework. In order to examine our framework in underwater docking tasks, we collected a dataset of 2D images, named underwater docking images dataset (UDID), which is the first publicly available underwater docking dataset to the best of our knowledge. In the field experiments, we first evaluate the performance of DoNN on the UDID and its deformed variations. Next, we examine the pose estimation module by ground and underwater experiments. At last, we integrate our proposed vision-based framework with an ultra-short baseline acoustic sensor, to demonstrate the efficiency and accuracy of our framework by performing experiments in a lake. The experimental results show that the proposed framework is able to detect docking stations and estimate their relative pose more efficiently and successfully, compared with the state-of-the-art baseline systems.

Vascular image registration is an essential approach to combine the advantages of preoperative 3D computed tomography angiography images and intraoperative 2D X-ray/digital subtraction angiography (DSA) images together. Cardiovascular deformation caused by heartbeat and respiration is one of the most vital factors that affect vascular image registration accuracy. Traditional optimized-based registration methods suffer severely from high computational complexity, which hinders the clinical applications of these methods seriously. To overcome these challenges, we developed a novel multi-channel convolutional neural network (MCNN) that combines a CNN with a periodic vascular diameter variation model. Our method is capable of registering simulated DSA images or real DSA images with their corresponding 3D models in a matter of milliseconds. Our presented MCNN model achieves excellent registration results of three different kinds of cardiovascular patients. The mean absolute error of all six transformation parameters of the MCNN model presented in this paper is less than 1 mm or 1°. The improvement to our MCNN model in registration accuracy is larger than 75% over a single-channel CNN model. Our MCNN method performs more effectively and stable than the state-of-the-art intensity-based methods, especially when vascular deformations occur.

Online decision support for effective mitigation actions against propagating cascading outages in a power grid still poses a big challenge to grid operators. This paper proposes an online mitigation strategy against cascading outages using an optimal power flow model based on a Dynamic Interaction Graph. For a given power grid, its interaction graph, also called an interaction model, was proposed in recent literature, which is composed of components and links that have large contributions to outage propagation. Differing from a conventional interaction graph, a Dynamic Interaction Graph can adaptively update its parameters with changes of grid topology and hence is more accurate in online identification of the most vulnerable transmission lines and likely outage propagation paths for mitigation. Further, the paper introduces an optimal power flow model based on the proposed Dynamic Interaction Graph for determining the optimal control strategy to maintain transfer margins of vulnerable transmission lines and effectively mitigate outage propagation. The numerical results on the IEEE 118-bus system demonstrate the effectiveness of the proposed models and associated control strategy.

Registration between the intraoperative 2D digital subtraction angiography (DSA) and the pre-operative 3D computed tomography angiography (CTA) is useful in the guidance of vascular interventional surgery (VIS). Because of the flow and diffusion of contrast in vessels, not all the vessels are visible in the DSA, which leads to difficulty in registration. Although the conventional mutual information (MI) and the normalized MI (NMI) perform well in orthopedic surgery, it cannot perform as well in VIS because of the missing vessel in DSA. In this paper, a novel similarity measure, WLMI (Weighted Local Mutual Information), is proposed to perform 2D-3D registration, which uses the patches selected in DSA to find the best match in the DRRs (digital radiography reconstruction) with weighted MI. At first, we choose several ways to measure the richness of block information to select small and scattered patches in the DSA image. Subsequently, different weights are assigned to these patches according to their information abundance by calculating the local MI. With the proposed WLMI, the 2D-3D registration experiments are conducted with the synthetic and real DSA images to CTA vessel model. In synthetic registration, the optimal way to measure information abundance and the optimal weight parameter value are selected. The registration with intact and partially absent vessels are compared with the conventional methods using MAE, mTREproj, and IoU metrics. In the registration of real DSA to CTA model, only IoU is used to compare the difference since the ground-truth cannot be derived. In synthetic registration with vessel excalation test, the mTREproj is 2.9 mm and the IoU is 96.7%. In a real registration test, the IoU reaches 81.3%. Both the synthetic and real DSA registration results show that the proposed WLMI can cope with the problem that partial vessel is invisible in the DSA, and outperformed the conventional methods such as MI and NMI. Therefore, the WLMI is more suitable to be used in the 2D/3D registration task in VIS.

Subsynchronous oscillation (SSO) phenomena caused by interactions between controllers of Doubly-fed induction generators (DFIGs) and series capacitor compensators has been well recognized. However, SSO can also happen on a DFIG-based wind farm without series compensation as reported in a recent real event. This paper firstly analyzes the recorded voltage waveform during this SSO event. Then an equivalent model of the system including the wind farm, static synchronous compensator (STATCOM) and the power grid was established. The paper derives the subsynchronous frequency response of the DFIG converter together with the STATCOM in detail and gives the criterion for SSO to occur, which is verified by both time domain simulation and spectrum analysis. The methodology adopted in this paper can be generalized to analyze the causes of a type of SSO that involves DFIGs and STATCOM but not series compensation. The paper also provides practical suggestions on adjustments of control parameters with the DFIG and STATCOM to prevent this type of SSO.

Many natural and manmade dynamical systems that are modeled as large nonlinear multioscillator systems like power systems are hard to analyze. For such systems, we propose a nonlinear modal decoupling (NMD) approach inversely constructing as many decoupled nonlinear oscillators as the system's oscillation modes so that individual decoupled oscillators can be easily analyzed to infer dynamics and stability of the original system. The NMD follows a similar idea to the normal form except that we eliminate inter-modal terms but allow intra-modal terms of desired nonlinearities in decoupled systems, so decoupled systems can flexibly be shaped into desired forms of nonlinear oscillators. The NMD is then applied to power systems toward two types of nonlinear oscillators, i.e. the single-machine-infinite-bus (SMIB) systems and a proposed non-SMIB oscillator. Numerical studies on a 3-machine 9-bus system and New England 10-machine 39-bus system show that: 1) decoupled oscillators keep a majority of the original system's modal nonlinearities and the NMD can provide a bigger validity region than the normal form and 2) decoupled nonSMIB oscillators may keep more authentic dynamics of the original system than decoupled SMIB systems.

Many steady-state power-flow-based models for cascading outage simulation have not considered frequency, which, however, is an important indicator of generation-load imbalance. This paper proposes a novel steady-state approach for simulating cascading outages. The approach employs a power-flow-based model that considers static power-frequency characteristics of both generators and loads. Thus, the frequency deviation due to active power imbalance can be calculated under cascading outages. Furthermore, a new ac optimal power-flow model considering frequency deviation is proposed to simulate the remedial control when system collapse happens as indicated by the divergence of power flows. Case studies first benchmark the steady-state frequency calculated by the power-flow-based model with time-domain simulation results on a two-area power system, and then test the proposed approach for simulation of cascading outages on the IEEE 39-bus system and an NPCC 48-machine 140-bus power system. The test results are compared with a traditional frequency-independent approach using the conventional power flow and ac optimal power-flow models, and verify that by capturing frequency variations under cascading outages, the proposed approach can more accurately simulate the mechanism of outage propagation.

This paper proposes a novel method for power system dynamic simulation that solves power system differential algebraic equations by a semi-analytical and semi-numerical approach using continued fractions. The method implements a two-stage scheme to enhance online performance of simulation: the offline derivation stage finds approximate analytical solutions, so-called “semi-analytical solutions,”for state variables of dynamic devices, such as generators in the form of power series of time with symbolic coefficients about system conditions; the online evaluation stage substitutes values on actual system conditions for symbolic coefficients, then transforms the solution into a continued fraction to prolong its time interval of accuracy, and finally calculates the system's trajectory over consecutive, adaptive time intervals for expected simulation results. A priori error bound for continued fractions is proposed to enable the simulation on adaptive time intervals. Compared with the conventional numerical simulation methods, the proposed continued fraction-based method has a fast simulation speed and a good suitability for parallel computing. The method is demonstrated and tested on the IEEE 9-bus system, the IEEE 39-bus system, and Polish 327-generator 2383-bus system.

It is well-known that ac power flows of a power system do not have a closed-form analytical solution in general. This paper proposes a multi-dimensional holomorphic embedding method that derives analytical multivariate power series to approach true power flow solutions. This method embeds multiple independent variables into power flow equations and hence, can, respectively, scale power injections or consumptions of selected buses or groups of buses. Then, via a physical germ solution, the method can represent each bus voltage as a multivariate power series about symbolic variables on the system condition so as to derive approximate analytical power flow solutions. This method has a non-iterative mechanism unlike the traditional numerical methods for power flow calculation. Its solution can be derived offline and then evaluated in real time by plugging values into symbolic variables according to the actual condition, so the method fits better into online applications, such as voltage stability assessment. The method is first illustrated in detail on a 4-bus power system and then demonstrated on the IEEE 14-bus power system considering independent load variations in four regions.