Rotor-craft unmanned aerial vehicle (UAV) has been applied rapidly in the domestic electric power system. However, endurance time of the drone loaded with equipment is limited in 20 minutes. Therefore, this paper proposes a key technology of automatic leapfrog-type charging control based on machine vision. Leapfrog-type charging platform is composed of UAV platform, UAV automatic charging platform and ground control system. According to both flight control and intelligent control, with the aid of machine vision and image recognition technology on positioning and intelligent landing UAV with high precision, and effective docking of preset slots and charging interfaces between ground charging platform and UAV, the battery of UAV charges automatically reliably, so as to realize the take-off and landing and automatically recharging UAV. The experimental results show that the problem of high precision positioning in charging process of UAV is effectively solved by implementing the leapfrog charging platform, machine vision, image recognition and shutdown technology.
Variable frequency transformer (VFT), a new type of flexible alternating current transmission equipment, is easier to operate under dual-side harmonic distorted grid voltages for its windings are directly connected to two power grids. This paper presents a novel topology of non-grid-side-converter-based VFT (NGSC-VFT). Operations of proposed NGSC-VFT under ideal and harmonically polluted grid voltages are detailed. Control strategy for two series converters is proposed to eliminate the torque and power fluctuations at different frequencies. The effectiveness of proposed topology of NGSC-VFT and corresponding control strategy is verified via simulation studies.
The work of this paper focuses on oxygen excess ratio control, for the oxygen excess ratio has a great influence on the performance of the proton exchange membrane (PEM) fuel cell. To model dynamics of air supply system and oxygen excess ratio, a validated three-order model is used for controller design. Because the pressure of the cathode is unmeasurable in the actual system, a state observer is designed to observe the cathode pressure based on the third-order model. A controller combining with feedforward control and feedback control based on LQR method and map that can output the equilibrium state, feedforward control signal and feedback gain calculated off-line at different equilibrium points through the input of the expected oxygen excess ratio and load current is then designed. At last, oxygen excess ratio control strategy under different working conditions is realized and the simulation results verify the effectiveness of the proposed controller.
In order to solve the problem of endurance in the process of unmanned aerial vehicle (UAV) line patrol, an autonomous UAV line patrol system based on leapfrog charging is designed and implemented. The key to achieving the goal of autonomous line patrol for UAVs is autonomous positioning technology and automatic charging control technology. This paper focuses on the research of autonomous positioning technology for UAVs based on GPS/RTK. First of all, the system structure and operating principle of leapfrog-type charging UAV is proposed, and the combined GPS/RTK navigation control module and automatic identification module are developed. Then, in order to ensure that the UAVs can precise positioning, accurate calibration of cameras and targets are studied. Finally, this paper conducts experimental simulations in the three main links of attitude solving, acceleration compensation and delay compensation in line patrol technology. The experimental results show that the attitude solving algorithm can accurately estimate the flight attitude of the UAVs in flight, and can compensate for the motion acceleration in a timely and fast manner. The delay compensation algorithm can effectively solve the problem of positioning sensor delay. When the barometer output altitude data is unhealthy, the system can identify the health of the data and automatically fuse the altitude data output by GPS. Therefore, the methods and research conclusions proposed in this paper have important engineering guiding significance for the autonomous line patrol of UAVs.
Both variable frequency transformer (VFT) and high voltage direct current converter are feasible solutions for asynchronous interconnection of different power grids. The VFT possesses inherent natural damping and high overloading capability, which is important for stability and reliability of power grids. The VFT, however, has not been widely used, since it cannot well solve some grid faults like asymmetrical grid faults. In this paper, a novel control strategy is designed on a single series compensation converter (SCC) of traditional VFT. With only replacement of this proposed strategy, the traditional VFT is immune to dual-side asymmetrical grid faults. In detail, three controllers are designed and implemented in a single SCC, i.e., two negative sequence controllers are designed to deal with asymmetrical grid faults at stator and rotor sides of the VFT, respectively; A positive sequence controller is adopted to control the reactive power flowing through the VFT, which reserves the original function of the SCC. Detailed theoretical analysis and hardware-in-loop experiments are carried out to verify the proposed control strategy.
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