Cascaded Multilevel Converter With Carrier Phase-Shifted SPWM Technique And Its Application To Active Power Filter

Together with the continual develop of high power self-turn-off devices and intelligent high-speed micro-controller, high power electronic equipment is increasingly deeply studied and is more and more widely applied in large capacitance motor drive, power transmission and so on. On the realization of high power electronic equipment, an important problem is that the working frequency of high power devices is too low to apply excellent modulated technique such as PWM. In order to overcome this problem, Carrier phase-shifted SPWM technique has been researched. On basis of it, its application to Active Power Filter in power system has been investigated in this paper.In the beginning, the basic principle of Carrier phase-shifted SPWM (abbreviated as CPS-SPWM) technique has been analyzed in this paper. The key idea of this approach is the combination of multi-modular technique and SPWM technique. The high equivalent switching frequency can be obtained with low switching frequency devices. Some characteristics of CPS-SPWM such as linearity and transmission bandwidth have been investigated.In reactive power compensation and active power filter, cascaded H-bridge multilevel converter with separated dc sources seems to be the most feasible topology for many reasons. The cascaded converter topology not only simplifies hardware manufacturability, but also makes the entire system flexible in term of power capability. In addition, for the same power capability, the cascaded converter requires less number of main power components. The operation principal of cascaded multilevel converter has been deeply analyzed. Cascaded multilevel converter based on CPS-SPWM has been proposed in this paper, which shows attractive perspective in large power application.Cascaded multilevel converter with CPS-SPWM technique has been discussed in application of Active Power Filter (APF). A closed-loop detecting circuit of harmonic and reactive current based on instantaneous reactive power theory has been analyzed. The dc-side and ac-side control algorithms of presented APF system have been proposed in this paper. All algorithms have been verified by simulation.To verify the proposed solution, a 5 kVA prototype of APF based on cascaded multilevel converter has been build. The prototype contains some modules such asmain circuit, detecting circuit, DSP micro-controller and multi-channel PWM waveform generator. All the design rules of the modules above have been deeply investigated. The experiment result shows good performance can be achieved even under low switching frequency.