Research On The Key Techniques Of Shunt Active Power Filter

In modern electric power systems, the use of a large number of non-linear loads results in harmonics and reactive power. It has becoming an increasingly serious problem. Active power filter (APF) can suppress harmonics and compensate reactive power, with fast response and dynamic characteristics of a good compensation effect. The active power filter has become a research hot spot in power electronics field, because of its predominant compensation performanceIn this paper, shunt active power filter has been systematically researched, including the harmonics current detection, reactive power current detection and current tracking control. On this basis, proposed an improved system. The system based on a harmonic detection method with separation of active and reactive fundamental, based on the improved method of current predictive control, and controlling SVPWM pulses by transforming reference volume (grid voltage, current, and compensation orders current) into DC form.First of all, this paper classifies and introduces the system structure and main circuit of active power filter, analyzes the application of four switch three phase converter in shunt active power filter, elaborates the basic principle of voltage shunt active power filter. Secondly, it describes ip-iq harmonic detection method based on instantaneous reactive power theory and another method which based on separation of active and reactive fundamental in detail. Then, in the applications of single-phase systems and three-phase system, elaborates both advantages and disadvantages of the detection techniques mentioned above; proposes a method to set up three-phase current d-q transform by delaying 60°of single-phase current, so that ip-iq detection can be achieved in a single-phase system. This paper applies an improved current predictive control to the shunt active power filters, compared with traditional PI (Proportion Integral) control, hysteresis control and traditional predictive control method, this method decreased the amount of calculation reduced model complexity and also improved compensation performance. In addition, this paper introduces and improves the voltage control policy which based on space vector. The improvement strategy implements by transforming reference volume into DC form and calculating the AC output voltage of converter in the aim of controlling the SVPWM pulses. It can simplify the system and resolve a problem of employing the steady DC side capacitor vohage of converter, which can't be achieved by other strategies.Finally, according to the system design, this paper makes a reasonable choice of some main parameters, sets up a shunt active power filter system simulation model by SIMULINK. Depending on kinds of harmonic and reactive current detection methods, and non-linear load compensation control strategy, the model simulates the compensation performance of various systems. Simulation results show that compared with the traditional shunt active power filter system, this improved solution presented in this paper can get a faster response and better tracking performance. Moreover, the improved system solution can effectively compensate the system harmonic and reactive power. For different loads, it has a good ability to eliminate harmonics and improve power factors. The improved filter system can compensate current with good dynamic performance, even though the load current varying fiercely.