Research And Implementation On Detection Algorithms Of Harmonics In Ship Electric Propulsion System

Ship electric propulsion technology is widely used thanks to the rapid development of power electronics and automation technologies. A variety of non-linear power electronic devices are being used, which brings a lot of harmonics to marine electric propulsion system, leading to overheating of electrical equipment and reducing reliability, even affecting the safe navigation of the ship, therefore, harmonic problems should be solved immediately. As the prerequisite and basis for harmonic governance, accurate detection of harmonics has important significance.Fourier transform is a classical harmonic analysis method. Firstly, the harmonic detection algorithm based on the Fast Fourier Transform was researched in depth in this paper. Comparing with other algorithms, Fast Fourier Transform has great advantages on the computation and operation speed, but it has a spectrum leakage and fence effect in non-synchronous sampling, and conventional Fast Fourier Transform cannot accurately detect interharmonics. Besides, the amount of computation of common interpolation windowed algorithms is very large. Considering the inefficiencies above, four interpolation Nuttall windowed Fast Fourier Transform algorithm is proposed in this paper, which has the advantages of high precision harmonic analysis and a small amount of computation. So this algorithm is suitable for application in engineering practice. Secondly, a power quality monitoring device with DSP as the core was designed in this paper. The function and composition of the hardware were introduced in detail. As the core processor, TMS320F28335 of TI can meet the requirements of high-speed processing of complex algorithms. As the sampling chip, AD7606 of ADI has 8 channels simultaneously for high-speed sampling. CCS3.3 was used as the software platform to complete the main program and subroutine by C programming language. With the hardware platform to complete the data acquisition and processing, the calculation of harmonic content, the calculation of basic power parameters and so on.Under laboratory conditions, the commission of each hardware circuits was completed, and the four interpolation Nuttall windowed FFT algorithm was actualized successfully in the power quality monitoring device. The test results show that the system can accurately measure the power parameters and harmonics and interharmonics content of a variety of conditions with real-time.