Font Size: a A A

The Research On Active Power Filter Based On Cascade H-Bridge

Posted on:2008-12-31Degree:MasterType:Thesis
Country:ChinaCandidate:R LiuFull Text:PDF
GTID:2178360245497864Subject:Power system and its automation
Abstract/Summary:PDF Full Text Request
The development of power electronics contributes the prevailing of their used in electric network, they bring great convenient as well as inject massive harmonic. One of the solutions to harmonic problem is installing active power filters(APF). At present, APF are mainly used in low and moderate situation. When comes to high power situation, the prime problem is that high power devices'low work frequency makes they are not suitable for PWM modulation method. The main solution to the harmonic problem is developing new circuit topology or control method. In order to fix the contradiction between power capacity and work frequency, this paper carries out some research on the APF with cascade H bridges.This paper analyses the fundamental theory and mathematical model of cascade H bridge APF. The research focus on the parameters of the main circuit. The simulation model of cascade H bridge APF is developed, the simulation result justify the validity and effectiveness of the system.There is independent DC side capacitor in the main circuit of cascaded H bridge APF, so it is important to keep all the capacitor voltage in line. This paper yields a new control method of DC side capacitor which can keep the three phase voltage and capacitor voltage in balance.In the real electric network, there are always asymmetries with the three phase voltage. When we use the traditional ip-iq method to detect harmonic and reactive power, the phase of A voltage detected by PLL is not the fundamental positive sequence phase of phase A. There is power inaccuracy when compensation harmonic and reactive power because of the reactive power component in fundamental positive sequence current . This paper derive the mathematic expression of power inaccuracy using instantaneous reactive power theory and come up with a new PI based reference current calculation method. The method produced can rectify the phase A voltage detected by PLL through PI closed loop control. Also the method can effectively eliminate the reactive power component in and realize the accuracy detection of harmonic and reactive power. Carrier Phase Shift SPWM(CPS-SPWM) is an excellent modulation strategy that suitable for high power switch devices, it can realize the equivalent high switch frequency while working at low switch frequency. It is necessary to use digital method to generate PWM in the real applications. This paper use the DSP+CPLD solution to realize the generation of PWM, DSP is in charge of calculating the duty ratio of PWM while CPLD is in charge of generating the multi-channel PWM. This paper completes the designation of PWM generation modulation.
Keywords/Search Tags:Active power filter, Cascade-H bridge, DC-side voltage, Harmonic detection
PDF Full Text Request
Related items