Advance Three Phase Power Factor Correction Schemes for Utility Interface of Power Electronic Systems



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Modern power electronic systems operate with different voltage and/or frequency rating such as Adjustable speed drive, Micro Grid, Uninterruptable Power Supplies (UPS) and High Voltage DC Transmission Systems. To match power electronic systems with the mains supply, DC link converters are used. The first stage of the DC link converter is the AC/DC conversion (rectifier). The rectifier type utility interface has substantial harmonics result in poor power quality due to low power factor and high harmonic distortion.

Power Factor Correction (PFC) schemes are effective methods to mitigate harmonics and address this issue. In this thesis, analyses of three approaches for high power density rectifiers are developed. In the first study, modular three phase boost rectifiers operating in DCM are coupled in order to increase the power density. Major drawback of this rectifier is the high currents ripple in both the source and the DC link sides which require large EMI filter size -could be larger than the rectifier component size- and large DC filter capacitor size. This thesis proposes coupling modular three phase boost DCM rectifiers, the currents in both source and DC link sides are interleaved and consequently the currents ripple dramatically decreased results in small component size of the EMI filter and the DC filter capacitor leading to high power density rectification. Also, optimization of the number of the rectifier modules to achieve maximum power density is presented. Moreover, the switching function of each rectifier employs harmonic injection technique to reduce the low order harmonics. And, the DC output voltage is varied with the load power such that the operation is at the boundary between CCM and DCM to achieve maximum power density tracking.

In the Second study, a resonant three phase single switch PFC is presented to overcome the high 5th and 7th order current harmonics drawback in the conventional single switch three phase PFC circuits. The input current has low THD for each individual low order harmonics with high current ripple at the switching frequency. Interleaving the input current by coupling modular rectifiers is also presented to reduce the input current ripple. System equations and modes of operation is analyzed and derived to design the circuit parameters, switching frequency and duty ratio for the desired output voltage and load power.

In the Third study, an advancement of existing modular T-connected single phase PFCs by means of replacing the low frequency transformer with medium frequency electronic phase shifter to reduce the size and weight of the system. The approach has higher power density compared with the Y, delta and T-connected single phase PFC modules. The study examines the 3 to 2 phase conversion, system harmonics, switching technique for the AC chopper and the power flow of the system.