This paper highlights the power quality issues and explains the remedial measures taken by means of hybrid front-end third harmonic current injection rectifiers. Here zig-zag transformer is used as the current injection device so that the advantages pertaining to the zig-zag transformer is effectively utilized. The third harmonic current injection device along with three-level boost converter at the output stage will increase the DC-link voltage. With less boost inductance, generally half of the conventional boost converter inductance is sufficient to implement the proposed converter structure resulting in reduced ripple current and also the device rating is reduced by half of the output voltage. Moreover, the power quality is well improved using third harmonic current modulated front-end structure which is well appropriate for medium/higher power applications. The experimental prototype of hybrid front-end converter is developed in the laboratory to validate the MATLAB simulation results.
- Current modulation circuit
- Front-end rectifier
- Power quality
- Third harmonic current injection
- Three-level boost converter
- Zig-zag transformer
Fig. 1. Schematic diagram of proposed front-end AC-DC converter
EXPECTED SIMULATION RESULTS
Fig. 2. Simulation results of input phase voltage, input phase current, input voltage and current, DC-link voltage, and DC current for the proposed front-end converter under load variations.
Fig. 3. Frequency spectrum of input line current ias at (a) Light load condition
(20%) (b) Full load condition (100%).
Fig. 4. Comparison of power quality indices with varying load of front-end AC-DC converter with six-pulse DBR (a) Variation of THD of input current with load and (b) Variation of PF of input current with load.
In this paper, a front-end AC-DC converter employed with third harmonic current injection circuit using a zig-zag transformer and three-level boost converter has implemented for medium and high-power applications. The three-level boost converter has realized with less boost inductance, an only half rating of the conventional boost converter inductance thereby resulting in less ripple current and also the device rating has reduced by half of the output voltage. The third order current harmonic reduction has achieved by the zig-zag transformer. With less magnetic rating, only 20% of the load rating is sufficient to realize the zig-zag transformer. The proposed converter has modeled, designed and its performance was analyzed by MATLAB simulation under varying load conditions. An experimental setup has been developed, and the performance of the system is verified from the hardware results. The proposed scheme resulted in less input current and voltage THD and maintained PF close to unity. Also, the other power quality parameters such as displacement PF and distortion factor are well within the IEEE standards.
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