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Abstract Frequency‐adaptive prefilters are widely used in the phase‐locked loop (PLL) to suppress input disturbances. However, the parameters of the PLL and prefilters are often designed separately or based on an inaccurate model. The positive feedback effect introduced by the frequency adaption (FA) is usually ignored, leading to non‐optimal performance. Based on the accurate small‐signal model with a particular focus on the FA, this paper proposes an optimal design method for these advanced PLLs. The PLL based on dual second‐order generalized integrator (DSOGI) is taken as an example to demonstrate the principle. With different gain margins, the optimal damping factors of DSOGI and PLL, as well as the natural frequency of PLL, are obtained using the proposed method. Then the global optimal parameters are obtained by evaluating the settling time and overshoot. The analysis shows that the truly optimal parameters are quite different with those provided in the literature, and the dynamic performance is significantly enhanced without degrading the steady‐state performance. Experimental results are presented to verify the theoretical analysis.

Antibiotics are commonly overused to prevent livestock from diseases and to increase production performance. As potential substitutes of antibiotics, plant extracts have attracted the attention of researchers. It was known to all that addition of Macleaya cordata extract (MCE) to the food could advance immunity, intestinal health and animal performance. Thus, it was conducted to investigate the influence of MCE (0, 100, 150 and 200 mg/kg, with six replicate pens/treatment and 24 hens/pen) on intestinal morphology and microbial diversity in different intestinal segments in Xuefeng black-boned chicken in this study. The results showed that MCE supplement (100, 150 and 200 mg/kg) significantly diminished (P

The addition of Hermetia illucens larvae meal (HILM) to the feed could contribute to particular antimicrobial and intestinal health in animal husbandry. This study was conducted to investigate the effects of HILM on intestinal morphology and microbial diversity in different intestinal segments of Xuefeng black-bone chickens. All of 432 birds (45 weeks old) were randomly assigned to four equal groups with six replicates and 18 hens in each replicate: (A) basal diet, (B) basal diet with 1% HILM, (C) basal diet with 3% HILM, and (D) basal diet with 5% HILM. The results showed that, compared with the basal diet group, the HILM supplement significantly increased the abundance-based coverage estimator (ACE) and Chao index in cecum (p < 0.05). Diet with 1% HILM significantly increased the villus height (VH) of the duodenum (p < 0.05) and cecum microbial diversity as represented by the Simpson index (p < 0.05). In particular, 1% HILM displayed a markedly increase in the genus unclassified Bacteroidales (cecum, p < 0.05). A basal diet with 3% HILM markedly increased the beneficial genus Romboutsia (jejunum, p < 0.05). Also, principal component analysis (PCA) cluster analysis showed that 3% of HILM was more individual than other groups (p < 0.05). However, 5% HILM decreased the VH and the ratio of villus height to crypt depth (VH/CD) of the jejunum and increased beneficial bacteria such as Staphylococcus (p < 0.05), which was regarded as pathogenetic genera. In conclusion, we found that HILM improved intestinal morphology and increased microbiological diversity and species abundance. Together, dietary supplementation of 1 or 3% HILM might benefit the intestinal morphology and intestinal microbiota of Xuefeng black-bone chicken. However, the addition of 5% HILM could decrease VH and the ratio of VH/CD of the jejunum and increased pathogenetic genera. HILM was an excellent protein substitute for Xuefeng black-bone chickens, which could meet the nutritional requirements under the condition of less feed. These results provide information for HILM meal as an alternative source of soybean meal in Xuefeng black-bone chickens’ feed.

The abuse of antibiotic growth promoters (AGPs) in feed has led to drug resistance and ecological damage would threaten human health eventually. Natural plants have become a hotspot in the research and application of substituting AGPs because of their advantages of safety, efficiency, and availability. This study was conducted to investigate the effects of Macleaya cordata extract (MCE) in the diet of Xuefeng black-bone chicken on laying performance, egg quality, and serum indices. In this study, 576 birds (47-week-old) were evenly distributed between 4 treatments with 6 replicates of 24 hens each. The control group was fed a basal diet without MCE and the remaining groups received 100, 150, or 200 mg/kg MCE for 84 d. Results revealed that the strength and thickness of the eggshell increased significantly with the dietary addition of MCE (P

With the integration of wind energy, the widely used doubly fed induction generator wind turbines (DFIG-WT) could induce Power System forced oscillations (FOs), which threaten the safety of power grid. In this paper, an accurate FOs location method is proposed to pinpoint sources of FOs to the specific components inside a DFIG-WT and a participation assessment method is proposed to evaluate the role of DFIG-WTs in the FOs event. Firstly, the energy structure of the DFIG-WT is constructed and the correspondence between the physical components and energy structure of the DFIG-WT is established. Thus, the sources of FOs can be located by the energy flow among the converter, wind turbine and induction generator. Furthermore, the port-controlled Hamiltonian (PCH) method is used to analyze the influence of external disturbances to the potential energy of DFIG-WT, based on which the participation factor of the DFIG-WT in FOs event can be defined. The simulation results demonstrate that the proposed method is able to locate the oscillation sources accurately and reveal the participation of the DFIG-WT in FOs events effectively.

The existing model predictive control schemes for the matrix converter perform well under ideal input conditions, but are not optimal when source voltages are unbalanced and distorted. The analysis shows that, under input disturbances, the input filter capacitors cause active power fluctuation and further output power quality degradation, which has been ignored in literature. Therefore, a method is proposed to extract the fluctuation with a digital filter and compensate it in the reference generation of source active power, so as to eliminate the output low-frequency harmonics. In the case of input voltage unbalance, a method is proposed to generate the reference source reactive power which could achieve sinusoidal source currents, without the need of separating sequence components. Moreover, effects of source voltage distortions, which degrade the input power quality significantly and are ignored in literature, are suppressed with the proposed generation method of reference reactive power. The extensive experimental results in nine cases have verified the satisfactory steady-state and dynamic performance of the proposed methods.

Forced oscillations (FOs), which are caused by sustained cyclic disturbances, threaten the safe and stable operation of power system. The most effective way to eliminate FOs is to locate the oscillation source and take corresponding measures. In this paper, a two-level method for forced oscillations source location is proposed. First, the energy structure of the generator is analyzed based on Hamiltonian function. The energy injected into generator is divided into two parts, i.e., energy injected by the prime mover system and excitation system. Then, as to the energy injected into power grid, the phasor relation between the variances of branch variables is analyzed to identify the energy flow direction. Based on the former analysis, the proposed method includes two levels. The bus level location of the oscillation source is realized according to the energy flow direction obtained with phasor analysis. Furthermore, the control device level location within the generator is realized according to the injected energy of the prime mover system and excitation system of generator. This method has good robustness for the measurement of data quality issue and is able to locate multimode oscillations with multiple disturbances. The simulation results in four-machine two-area system, East China power grid and the WECC 179-bus system as well as the comparison with classic energy-based method demonstrate the effectiveness and improvement of the proposed method.

With the integration of renewable energy resources and variable loads into power grid, power oscillations caused by persistent external fluctuating forces are becoming more prevalent. Termed as “forced oscillations (FO)”, such phenomena could happen even when the grid is with good damping characteristics. Therefore, conventional mitigation methods based on improving damping are rendered less effective. By leveraging the new control capability offered by static synchronous compensator with energy storage (E-STATCOM), a novel approach to mitigate FOs is proposed in this paper. A control strategy based on resonant controllers is adopted to modulate active and reactive power supplied by E-STATCOM. It is theoretically shown that FOs propagating from the disturbed area to other areas can be effectively eliminated by this method. Besides, we derived the analytical relationship among the location, the capacity of E-STATCOM and the suppression performance. Case studies demonstrate the effectiveness of the proposed method.

This paper applies the emerging hybrid active third-harmonic current injection converter (H3C) to the battery energy storage system (BESS), forming a novel H3C-BESS structure. Compared with the commonly used two-stage VSC-BESS, the proposed H3C-BESS has the capability to reduce the passive components and switching losses. The operation principle of the H3C-BESS is analyzed and the mathematical model is derived. The closed-loop control strategy and controller design are proposed for different operation modes of the system, which include the battery current/voltage control and the injected harmonic current control. In particular, active damping control is realized through the grid current control, which could suppress the LC-filter resonance without the need of passive damping resistors. Simulation results show that the proposed topology and its control strategy have fast dynamic response, with a setup time of less than 4 ms. In addition, the total harmonic distortions of battery current and grid currents are only 2.54% and 3.15%, respectively. The amplitude of the injected harmonic current is only half of the grid current, indicating that the current injection circuit generates low losses. Experimental results are also provided to verify the validity of the proposed solution.

A current source converter (CSC) is a promising topology for interfacing aircraft generators with the onboard DC microgrid. In this paper, a hybrid predictive control is proposed for the CSC with an output LC filter in such application. Deadbeat predictive control with larger sampling time is applied to the output circuit, generating reference source currents. Finite-set model predictive control with smaller sampling time is applied to the input circuit to achieve sinusoidal source currents, which is simplified by saving the source current predictions. The proposed scheme eliminates both the proportional-integral controller and the weighting factor, which are required in the existing studies. Besides, it has lower control complexity. A SiC-MOSFET-based prototype is used to verify the validity of the proposed scheme. Experimental results under 150 V/350−800 Hz AC input and 270 V DC output demonstrate the superior control performance.

This paper presents general design considerations of a partitioned stator switched flux hybrid magnet memory machine (PS-SF-HMMM). The armature windings and permanent magnets (PMs) are placed on two separate stators, respectively, in the PS-SF-HMMM, and thus both high torque density and wide flux regulation capability can be obtained. The topology and working principle of the machine are introduced briefly first, and then different magnet arrangements and stator/rotor pole combinations are investigated. In addition, various design parameters are optimized based on finite element (FE) methods. Finally, a prototype is fabricated to experimentally validate the FE results.

In this paper, an improved model predictive control (MPC) is proposed for the matrix converter (MC). First, the conventional MPC which adopts the separately discretized prediction models is discussed. It shows that the conventional MPC ignores the input−output interaction in every sampling period. Consequently, additional prediction errors arise, resulting in more current harmonics. Second, the principle of the improved MPC is presented. With the interaction considered, the integral state-space equation of the whole MC system is constructed and discretized to obtain the precise model. The eigenvalue analysis shows that the proposed prediction model has the same eigenvalues with the continuous model, and thus is more accurate than the conventional one to describe the MC’s behavior in every sampling period. Finally, experimental results under various working conditions prove that the proposed approach can always increase the control accuracy and reduce the harmonic distortions, which in turn requires smaller filter components.

This paper proposes an input voltage disturbance suppression control strategy for the unidirectional matrix converter (UMC) with a new modulation scheme enhancing the stability. In the new scheme, the modulation index is directly, rather than reversely, proportional to the instantaneous amplitude of input filter capacitor voltages. Contrary to traditional schemes, the stability of the UMC with this new scheme is even better with the increase of the transferred active power, which is particularly suitable for applications with sinusoidal and balanced input conditions. As to the disturbed input conditions, the new scheme could introduce low-frequency harmonics into output currents. To address this issue, a feedback control strategy of output current amplitude is further proposed to eliminate the additional harmonics. Stability analysis of a UMC with the proposed modulation scheme and feedback control strategy is presented. Experimental results have verified the validity of the proposed control solution.

Considering reducing the airspace congestion and the flight delay simultaneously, this paper formulates the airway network flow assignment (ANFA) problem as a multiobjective optimization model and presents a new multiobjective optimization framework to solve it. Firstly, an effective multi-island parallel evolution algorithm with multiple evolution populations is employed to improve the optimization capability. Secondly, the nondominated sorting genetic algorithm II is applied for each population. In addition, a cooperative coevolution algorithm is adapted to divide the ANFA problem into several low-dimensional biobjective optimization problems which are easier to deal with. Finally, in order to maintain the diversity of solutions and to avoid prematurity, a dynamic adjustment operator based on solution congestion degree is specifically designed for the ANFA problem. Simulation results using the real traffic data from China air route network and daily flight plans demonstrate that the proposed approach can improve the solution quality effectively, showing superiority to the existing approaches such as the multiobjective genetic algorithm, the well-known multiobjective evolutionary algorithm based on decomposition, and a cooperative coevolution multiobjective algorithm as well as other parallel evolution algorithms with different migration topology.

This study proposes an improved hybrid modular multilevel converter (MMC) topology with enhanced fault ridethrough capability and fast pre-charging strategies. This improved MMC topology mainly consists of the half-bridge sub-modules (HBSMs), the modified series connected double sub-modules (MSDSMs), and the adjustable damping sub-module (ADSM). In the improved topology, in addition to being configured on the MMC AC-side, resistors are also configured in MSDSMs and ADSM, respectively, in the MMC. This type of resistance configuration based on the improved MMC topology benefits adjusting the value of the total equivalent current limiting resistance during the pre-charging process, leading to a higher pre-charging speed and a lower SM voltage drop risk. Three different pre-charging strategies can cope with changes in resistance configuration caused by the increasing number of SMs. Furthermore, the resistances in MSDSM and ADSM also help dissipate the energy caused by the DC short-circuit fault so that the fault ride-through capacity is enhanced. The simulation and experimental results validate the effectiveness of the proposed topology and the corresponding pre-charging strategies. [ABSTRACT FROM AUTHOR]

The constant power control strategy of matrix converter (MC), which is commonly adopted in practice to suppress input disturbances, could result in system instability and oscillations of source currents and input voltages. To stabilise the system, a novel control method is proposed in this study, which is based on filtering the input voltages in stationary frame with digital high-pass filters of zero gain at the fundamental frequency. The filtered signals are injected to input currents so as to increase the input admittances for stability improvement. Since the filtered signals do not contain any fundamental frequency components, the proposed method would not affect the normal operation of MC. No matter the operation mode of MC is motoring or generating, the proposed method is always effective to improve system stability by adjusting the proportional coefficient and time constant of the digital filters. The feasibility and validity of the proposed method is verified by experimental results. [ABSTRACT FROM AUTHOR]