Butterworth Filter And Its Application In Single Phase PLL

Nowadays, the economic and technology of human society develops in rapid pace, the utility power grade was in quick changing, as well its power structure, and day-by-day better orientingfunction. In the meantime, the industrial machines, especially high power reciprocating compressor, large motors andvariable frequency drives, arc furnace, etc., are quickly spreadedto achieve bettor performance to carry out more suitable product. And, energy crisis is becoming a more and more hot topic of human society, to tackle with this troublesome question and for human being’s own benefactor, renewable resources must be analyzed and be put into the source of our power. Fortunately, this is an unstoppable trend. With more and more renewable sources connected to the utility, power electronic devices are put into use. And, in another aspect, renewable sources, like wind and solar power are themselves unstable. With the fast developing speed of human society, the need of more stable and better power quality is urgent. Many power electronic devices are connected to the grid to achieve better performance. Some traditional power quality control device like high power compensator are connected to the utility.The complexity of the utility, high power impact and nonlinear industrial machines, more and more power electronic devices, the inherent instability of wind and solar power, all of them pose great threat to the stability of the utility. At the same time, the power quality, especially the harmonic pollution goes worse and worse. Under these background, the phase lock loop(PLL) of the weak utility has become a research point. Recently, digital PLL has become a hot point, especially single phase lock loop(SPLL). For a very noticeable reason, SPLL has to tackle with the lack of quadrature signal.In a SPLL, the quadrature signal generator(QSG) is an essential part. Many types of QSG has been researched, such as second order general integrator(SOGI), Kalman Filter, All Pass Filter(APF), delayed method. But, all of these method themselves has not enough harmonic attenuation ability, some can mere generate a quadrature signal of the utility voltage, totally lack of the ability to suppress the harmonics of the utility voltage. To tackle with this question, many method has been analyzed, such as the moving average filter(MAF), and recursive discrete Fourier transform. With these methods implemented in the right place of the single phase lock loop, the harmonics of the utility voltage sampled can be attenuated effectively.In this paper, a new method to utilize the Butterworth filter in SPLL is analyzed. In the save order with SOGI and Kalman filter, the Butterworth filter has a similar structure as well as performance. But when raising the filter order, a Butterworth filter will gain new ability which the other filters don’t have, saving the ability to avoid the DC component of the utilityvoltage. And, to improve the ability of attenuating harmonics especially the lower order harmonics, this paper put a notch filter after the Butterworth filter.When in the environment of a weak power grid, the frequency, phase and the amplitude of the utility voltage may present sudden changes, which needs the SPLL algorithm has adaptive ability. In this case, this paper first presents a look-up table method to update the filter parameter, which will greatly reduce the calculating burden of the control chip. In addition to that, this paper proposes another method, the compensation of the angle of a SPLL, which will slightly lose some accuracy, but has a better dynamic performance.At last, based on MATLAB and DSP, simulation and experimentation of the proposed methods are analyzed, all of them valid the efficiency and feasibility of the proposed methods.