In this paper, a reference current control strategy based on second-order generalized integrator and FBD method for shunt active power filter is proposed. The method uses the second-order generalized integrator and the symmetrical component method to obtain the fundamental sequence component of the grid voltage. And then the FBD method is used to decompose the load current under the fundamental positive-sequence voltage reference to obtain the reference value of the compensation current. This method does not need coordinate transformation, is simple to calculate, and has clear physical meaning. It can compensate harmonic current, reactive current and negative-sequence current at the same time even under complex grid voltage and load and frequency offset. The proposed method is compared with the existing method under a variety of experimental conditions. The experimental results prove the effectiveness and accuracy of the proposed method.

In view of the problems of poor safety, slow detection speed, and low accuracy of existing nondestructive testing (NDT) technologies, such as X-ray methods and ultrasonic detection in detecting electron beam weld defects in aluminum alloys, this study proposes a weak magnetic NDT method based on the geomagnetic field. Firstly, the finite element analysis method was used to establish a simulation model of aluminum alloy electron beam welding defects, and the distribution characteristics of the magnetic field around weld defects, such as cracks and pores, were obtained. Then, the magnetic anomaly signal at the crack weld was identified by combining the wavelet transform and the least squares method. Finally, experimental tests show that the proposed method can safely, quickly, and accurately detect the defects of aluminum alloy electron beam welds.