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In flywheel energy storage system (FESS), multi-phase motor can be used to drive the flywheel for its high power density and fault-tolerance performance. Aiming at the two-phase fault in different sets of three-phase windings in twelve-phase permanent magnetic synchronous motor (PMSM), afault-tolerant control strategy based on motor model reconstruction is proposed in this paper. The set of three-phase windings that has phase failure is controlled as single-phase motor. Therefore, the twelve-phase PMSM is treated as an integration of two three-phase motors and two single-phase motors. The proposed strategy maintains stable torque and power during fault-tolerant operation. Theoretical analysis and simulation are carried out in this paper, and the results demonstrate that the proposed strategy has good effectiveness on two-phase faults in two sets of wingdings, no matter the two phases are orthogonal or not.

Computed tomography angiography (CTA) is a powerful tool for the diagnosis of vascular diseases and its radiation dose is widely concerned. Limited scan within vessel region, deemed as region-of-interest (ROI), is a particularly apt dose reduction strategy for CTA since clinical assessment mainly depends on vessel structures. However, insufficient raw data may induce noise and artifacts in images reconstructed by conventional analytic and iterative methods. In this paper, we introduced an ultra-low-dose scan protocol for CTA, by modifying the contrast-enhanced stage with a low-mA, few-view ROI scan. Accordingly, a previous-stage-based ROI reconstruction method (PSBROI) was proposed with weighted projections and voxels and a dual-dictionary learning (DDL) strategy. Experiments showed that under the ultra-low-dose scan protocol, the proposed method performed better in artifact removal, noise suppression and structure preservation within ROI than the conventional methods. The ultra-low-dose scan with 30 mAs, 60 projection views and 34.1 mm ROI size could reduce dose to about 0.305% of normal dose.

Energy Internet is a hot spot of research and practice in the field of energy at home and abroad. DC power distribution technology has the characteristics of bidirectional controllable power flow, convenient access to distributed resources, improved power quality, transmission capacity and reliability of power supply, and reduced system loss, which has a wide application prospect in energy Internet. The safety and reliability of ubiquitous distributed generation (DG) and multi load access to DC distribution network is an important problem to be studied and solved in the planning and operation of energy Internet. In this paper, the different ways and operation characteristics of AC-DG and DC-DG connected to DC distribution network are analyzed, in which AC-DG is connected through voltage source inverter, and DC-DG is connected through full bridge DC / DC converter. Based on PSCAD / EMTDC, and taken Shenzhen flexible DC distribution network demonstration project as an example, the dynamic operation characteristics of DGs under different modes of connecting to the DC distribution network are analyzed and verified.

Energy Internet is a hot spot of research and practice in the field of energy at home and abroad. DC power distribution technology is an important element of energy Internet. How to plan the type and capacity of energy storage system (ESS) is a problem worthy of attention when designing the optimal energy conversion path in the energy Internet, especially in the DC distribution network. The proper type and capacity of ESS can effectively suppress DC voltage flicker and improve the system operation stability and fault crossing ability. In this paper, the hybrid energy storage scheme of energy storage battery and super capacitor is adopted in DC distribution network, and the discrete Fourier spectrum analysis of power demand sample data is carried out to obtain the basic power in low frequency and fluctuating power in high frequency. The energy storage battery with slow dynamic response speed is used to match the power demand of low-frequency segment, and the super capacitor with slow dynamic response speed is used to match the power demand of high-frequency segment. The influence index of SOC over limit times of energy storage system is introduced to seek the critical value of ESS capacity planning. Finally, the proposed hybrid energy storage planning method is verified by the case studying.

Compressed sensing (CS) reconstruction methods employing sparsity regularization and prior constraints are successfully applied in sparse-view computed tomography (CT) reconstruction and yield high-quality images compared with other low-dose imaging methods. In this paper, we proposed an adaptive prior patch size (APPS) strategy in sparse-view CT reconstruction. The method adopts sparse representation (SR) using adaptive patch size instead of a constant one to synthesize prior image of higher quality, because the optimal patch size should vary from each distribution range of local feature. The simulation experiments show that the proposed strategy has the better performance than the method with fixed patch size in terms of artifact reduction and edge preservation.

Flywheel energy storage system (FESS) is qualified with high dynamic response performance in active power supply. The virtual synchronous generator (VSG) technique enables grid-connected converters to simulate the operation mechanism of synchronous generators. Applying VSG in FESS helps to improve the stability of the grid. This paper established the model of FESS, and a low voltage ride through (LVRT) control method for this combining system is developed. Simulation results in MATLAB/Simulink verified the effectiveness of the proposed method. During the fault of the power grid, both the voltage source characteristics and the inertia characteristics of the VSG control method can be ensured, and the FESS can provide certain amount of active and reactive power for the grid.

Multi-phase motors are applied in flywheel energy storage system (FESS) to improve the power level, and at the same time offer phase redundancy characteristics. This paper investigates the fault-tolerant control of 12-phase permanent magnetic synchronous motor (PMSM) with one phase open-circuit in FESS. The 12 phases have 4 sets of stator windings and each set is connected to one 3-phase converter. In case of one phase open-circuit, the converter containing the fault-phase is not cut off but operates as a single-phase driver while the left three still operate as 3-phase drivers. Thus the output capability of the converter containing fault-phase is utilized. Moreover, a compensation method is developed to solve the power fluctuation caused by the single-phase motor. Consequently, the fault-tolerant control of FESS is achieved and the power rating is not reduced. The model for FESS based on 12-phase PMSM is developed in Matlab/Simulink, and the results validate the effectiveness of the proposed fault-tolerant control method.