In this paper, a load adaptive control method to improve the efficiency and dynamic performance of the Phase-Shifted Full-Bridge (PSFB) converter which works under a wide range of load conditions is presented. The proposed control method can be used as a battery charger since this application demands a wide range of load conditions. The composition of the PSFB converter’s losses and the loss analysis model are both discussed. According to this model, the optimum switching frequency which results in minimum power loss is adopted to improve the efficiency. The relationship between switching frequency and power loss is formulated over a wide load range. Indicated by this kind of relationship, the proposed controller adjusts the switching frequency at different load currents. Moreover, an adaptive gain adjustment controller is applied to replace the traditional controller, with the aim to improve the dynamic performance which is influenced by the changes of the switching frequency and load current. In addition, the experimental results show that the maximum improvement of efficiency is up to 20%. These results confirm the effectiveness of the proposed load adaptive control method.

First, the measuring principle, the weight function, and the magnetic field of the novel downhole inserted electromagnetic flowmeter (EMF) are described. Second, the basic design of the EMF is described. Third, the dynamic experiments of two EMFs in oil-water two-phase flow are carried out. The experimental errors are analyzed in detail. The experimental results show that the maximum absolute value of the full-scale errors is better than 5%, the total flowrate is 5–60 m³/d, and the water-cut is higher than 60%. The maximum absolute value of the full-scale errors is better than 7%, the total flowrate is 2–60 m³/d, and the water-cut is higher than 70%. Finally, onsite experiments in high-water-cut oil-producing wells are conducted, and the possible reasons for the errors in the onsite experiments are analyzed. It is found that the EMF can provide an effective technology for measuring downhole oil-water two-phase flow.

As a basic building block in power systems, the three-phase voltage-source inverter (VSI) connects the distributed energy to the grid. For the inductor-capacitor-inductor (LCL)-filter three-phase VSI, according to different current sampling position and different reference frame, there mainly exist four control schemes. Different control schemes present different impedance characteristics in their corresponding determined frequency range. To analyze the existing resonance phenomena due to the variation of grid impedances, the sequence impedance models of LCL-type grid-connected three-phase inverters under different control schemes are presented using the harmonic linearization method. The impedance-based stability analysis approach is then applied to compare the relative stability issues due to the impedance differences at some frequencies and to choose the best control scheme and the better controller parameters regulating method for the LCL-type three-phase VSI. The simulation and experiments both validate the resonance analysis results.

Due to the characteristics of high power factor and low total harmonic distortion in discontinuous conduction mode, the power factor correction (PFC) converter based on isolated single-ended primary-inductor converter (SEPIC) is more suitable for medium-line-frequency avionics applications. However, the inherent defects of isolated SEPIC PFC converter, such as the voltage-spike issue and the hard-switching operations of semiconductor components, severely limit the utilization of such topologies. In this article, a high-performance isolated bridgeless resonant SEPIC PFC converter is proposed. Instead of typical SEPIC-type operational mode, the proposed converter operates in resonant mode, and hence, all switches and diodes in this topology can achieve soft switching and the voltage-spike issue is effectively solved. Moreover, different from the existing isolated SEPIC PFC converters, the transformer in this topology can transfer energy through the whole switching cycle, which greatly improves the core utilization. The overall performance of the proposed topology is illustrated in terms of its working principles, control scheme, and the parameter design considerations. Finally, the analysis is validated by a 400-Hz experimental prototype with soft-switching capability.

Oil-air-water three-phase flow patterns in small-diameter vertical measurement channels are complex, making it difficult to establish techniques for interpretation of logging information. In this study, dynamic experiments involving oil-air-water three-phase flows were performed using a novel production logging tool that combined a petal-type turbine flowmeter, a conductance sensor, and an optical fiber sensor in a simulation well. Sensor response characteristics were researched, and a new method of measuring the oil-air-water three-phase flow rate was proposed. The measurement range and resolution of the gas flow rate were 3 ∼ 20 m³/d and 1 m³/d, respectively, and the relative error range of gas flow rate interpretation was 5 ∼ 10%. The measurement range and relative interpretation error range of the total liquid flow rate were 10 ∼ 60 m³/d and 5 ∼ 10%, respectively. The measurement range and resolution of the water cut were 50 ∼ 100% and 2%, respectively. The absolute error range of interpretation of the water cut ranged from 3.2% to 5%. Currently, the technique is valid for laboratory use under ideal conditions.

The Andronov-Hopf based virtual oscillator control (AHO) is a novel nonlinear grid-forming (GFM) control strategy that has better dynamic performance compared with droop and virtual synchronous generator. However, the grid voltage drop can affect the synchronization between the AHO inverter and the grid. In extreme cases, the system may lack a stable operating point, leading to transient stability issues. This paper establishes a dynamic power angle model that takes into account the voltage characteristics of the inverter. Subsequently, the influence of AHO parameters on transient stability is analysed under current unconstrained operation, and the impacts of current limitation strategy are discussed. On this basis, a transient stability enhanced control strategy for AHO inverters is proposed from the perspective of optimizing voltage characteristics and compensating power setpoints (OVCP). A small-signal model is then established to analyse the stability of the proposed strategy. Finally, simulations and hardware-in-the-loop simulations based on RT-BOX are conducted to verify the effectiveness of the proposed transient stability enhanced control strategy.