Three-Phase Unidirectional Rectifiers with Open-End Source and Cascaded Floating Capacitor H-Bridges

ABSTRACT

This paper presents two typologies of three-phase semi controlled rectifiers suitable for open-end ac power sources. The rectifiers are composed by a combination of two-level three phase bridges (controlled, semi controlled or uncontrolled), and three single-phase floating capacitor h-bridges (controlled). These typologies generate two powered dc-links, each one belonging to a three-phase bridge. They present a reduced number of controlled power switches if compared to other open-end configurations of similar complexity found in the literature.

S V P WM

It is also proposed a space-vector pulse width modulation (S V P WM) approach and a method of floating capacitor voltage control dedicated to the typologies, with an equivalent approach based on the level-shifted P WM (LS-P WM). The proposed S V P WM solving method is based on a redundant state selection (RS S) technique, which allows the floating capacitors voltage regulation. On the other hand, the LS-P WM solving method is based on the neutral voltage selection, which is shown to be equivalent to the S V P WM RS S technique seen from the control system. Simulation results are shown to validate proposed typologies, as well as the S V-P WM and LS-P WM techniques, and the control strategy. Experimental results are shown to demonstrate proposed configurations feasibility.

BLOCK DIAGRAM:

Fig. 1: Proposed configurations with open-end power source and cascaded floating h-bridges. (a) Configuration 1, where converter A is a three-phase diode bridge. (b) Configuration 2, where converters A and B have semi-controlled legs.

 EXPECTED SIMULATION RESULTS

Fig. 2: Simulation graphics for the conventional configuration 0. (a) Currents i k. (b) Voltages v k, v r k and v 0 s 0. (c) Mean voltages v k, v r k and v 0 s 0.

Fig. 3: Currents i k from simulation results for both proposed configurations with the LS-P WM. (a) For configuration 1. (b) For configuration 2.

Fig. 4: Voltages v 1, v r 1 and v 0 b 0 a from simulation results for both proposed configurations. (a) For configuration 1 with S V-P WM. (b) For configuration 1 with LS-P WM. (c) For configuration 2 with S V-P WM. (d) For configuration 2 with LS-P WM.

Fig. 5: Mean voltages v 1, v r 1 and v 0 b 0 a for both proposed configurations. (a) For configuration 1 with S V-P WM. (b) For configuration 1 with LS-P WM. (c) For configuration 2 with S V-P WM. (d) For configuration 2 with LS-P WM.

Fig. 6: DC capacitors voltages v C ck from simulation results for both proposed configurations with the LS-P WM. (a) For configuration 1. (b) For configuration 2.

Fig. 7: Pole voltages v a 1 0 a, vb 10 b, v c p 10 c 1 and v c n 10 c 1 for both proposed configurations. (a) For configuration 1 with S V-P WM. (b) For configuration 1 with LS-P WM. (c) For configuration 2 with S V-P WM. (d) For configuration 2 with LS-P WM.

CONCLUSION

In this paper, two configurations of unidirectional rectifiers were proposed. They were based on the cascaded connection of two three-phase bridges with three floating capacitor h bridges (one per-phase), which was allowed by the open-end configuration of the three-phase power source. The voltage regulation of the floating capacitor h-bridges was realized by two proposed PWM solving techniques. The first was applied to the SV-PWM, where methods for redundancy selection and state switching minimization were also proposed. The second was proposed for the LS-PWM as an alternative to the SVPWM.

L S P WM

In this case, the floating capacitors voltage regulation was based in solving the P WM for appropriately selected neutral voltage references. Simulation results were provided to supply evidence that proposed typologies are viable and that proposed S V-P WM redundancy selection technique is effective within the control system. It was also shown that the control based on the LS-P WM was effective and equivalent to the S V-P WM. It could be concluded that the proposed configurations could present lower current TH D and voltage W TH D with fixed switching frequency, as well as lower semiconductor losses with matched current TH D, if compared to the conventional three-phase I B GT rectifier bridge. Simulation results also provided to show the feasibility of proposed typologies and control strategy.

REFERENCES

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