Three-phase ac-to-dc-to-ac converter

• US 20060133120A1
• Filed: 12/13/2005
• Published: 06/22/2006
• Est. Priority Date: 12/17/2004
• Status: Abandoned Application

• Current Assignee: Sanken Electric Company Limited
• Original Assignee: Sanken Electric Company Limited
• Inventors: Sato, Shinji, Nagamatsu, Fumio, Iyama, Osamu, Kawauchi, Shoichi, Fuse, Yuji, Kanata, Takahiro
• Application Number:
  US11/302,775
• Publication Number:
  US 20060133120A1
• Time in Patent Office: Days
• US Class Current: 363/37
• CPC Class Codes: H02M 5/4585 having a rectifier with controlled elements

Abstract

A non-outage power supply system comprises three-phase ac input terminals and three-phase ac output terminals, between which there are sequentially connected a three-phase ac-to-dc converter circuit, a capacitor, and a three-phase dc-to-ac converter circuit. A bypass switch is connected between a preselected one of the three-phase ac input terminals and a preselected one of the three-phase ac output terminals. A bypass switch control circuit holds the bypass switch closed when the three-phase ac inputs are in phase with the three-phase ac outputs, and open when they are not. Part or all of the effective current demanded by the load bypasses the three-phase dc-to-ac converter circuit when the bypass switch is closed, with a consequent reduction of power loss.

Claims

1. A three-phase ac-to-dc-to-ac power converter system with reduced power loss, comprising:

(a) a first, a second and a third ac input terminal for inputting a first-, a second- and a third-phase ac voltage;

(b) a first, a second and a third ac output terminal for outputting a first-, a second- and a third-phase ac voltage;

(c) a three-phase ac-to-dc converter circuit connected to the ac input terminals, the three-phase ac-to-dc converter circuit comprising a plurality of ac-to-dc conversion switches and a pair of outputs for providing a dc output voltage;

(d) storage means connected between the pair of outputs of the three-phase ac-to-dc converter circuit for storing output energy therefrom;

(e) a three-phase dc-to-ac converter circuit connected between the storage means and the ac output terminals, the three-phase dc-to-ac converter circuit comprising a plurality of dc-to-ac conversion switches for providing the three-phase ac output voltages;

(f) a bypass switch connected between a preselected one of the ac input terminals and a preselected one of the ac output terminals;

(g) ac-to-dc converter control means connected to the three-phase ac-to-dc converter circuit for controllably driving the ac-to-dc conversion switches thereof;

(h) dc-to-ac converter control means connected to the three-phase dc-to-ac converter circuit for controllably driving the dc-to-ac conversion switches thereof either in or out of synchronism with the three-phase ac input voltages; and

(i) bypass switch control means connected to the bypass switch for holding the bypass switch closed when the three-phase dc-to-ac converter circuit is being driven in synchronism with the three-phase ac input voltages, and open when the three-phase dc-to-ac converter circuit is being driven out of synchronism with the three-phase ac input voltages.

2. A three-phase ac-to-dc-to-ac power converter system as defined in claim 1, wherein the bypass switch control means comprises:

(a) input parameter detector means connected to at least one of the ac input terminals for providing an ac input parameter signal indicative of a preselected parameter of the corresponding phase ac input voltage;

(b) target output parameter generator means for providing a target output parameter signal indicative of a target value of the preselected parameter of the three-phase ac output voltages;

(c) comparison means connected to the input parameter detector means and the target output parameter generator means for comparing the ac input parameter signal and the target output parameter signal in order to determine whether the three-phase ac input voltages are in or out of synchronism with the three-phase ac output voltages, the comparison means outputting a bypass switch control signal for closing the bypass switch when the three-phase ac input voltages are in synchronism with the three-phase ac output voltages, and opening the bypass switch when the three-phase ac input voltages are out of synchronism with the three-phase ac output voltages.

3. A three-phase ac-to-dc-to-ac power converter system as defined in claim 2, wherein the input parameter detector means of the bypass switch control means comprises:

(a) a phase detector for providing an ac input phase signal; and

(b) a differentiating circuit connected to the phase detector for providing an ac input frequency signal.

4. A three-phase ac-to-dc-to-ac power converter system as defined in claim 2, wherein the target output parameter generator means of the bypass switch control means comprises:

(a) a frequency generator for providing a target output frequency signal; and

(b) an integrating circuit connected to the frequency generator for providing a target output phase signal.

5. A three-phase ac-to-dc-to-ac power converter system as defined in claim 2, wherein the power converter system further comprises selector means responsive to the bypass switch control signal from the comparison means for selectively passing the ac input parameter signal from the input parameter detector means and the target output parameter signal from the target output parameter generator means according to whether the three-phase ac input voltages are in or out of synchronism with the three-phase ac output voltages, the selected ac input parameter signal or target output parameter signal being delivered to the dc-to-ac converter control means.

6. A three-phase ac-to-dc-to-ac power converter system as defined in claim 5, wherein the dc-to-ac converter control means comprises:

(a) reference wave generator means connected to the selector means for providing a set of three sinusoidal reference waves in prescribed time relationship to the incoming ac input parameter signal or target output parameter signal;

(b) a three-phase ac output voltage detector connected the output terminals for providing ac output detect signals indicative of the three-phase ac output voltages;

(c) subtractor means connected to the reference wave generator means and the ac output voltage detector for providing difference signals indicative of differences between the sinusoidal reference waves and the ac output detect signals;

(d) a periodic wave generator for providing a periodic wave signal which is higher in frequency than the sinusoidal reference waves; and

(e) a dc-to-ac converter control signal generator circuit connected to the subtractor means and the periodic wave generator for providing pulse-width-modulated dc-to-ac converter control signals by comparison of the difference signals and the periodic wave signal, thereby to drive the dc-to-ac conversion switches of the three-phase dc-to-ac converter circuit.

7. A three-phase ac-to-dc-to-ac power converter system as defined in claim 1, wherein the ac-to-dc converter control means comprises:

(a) a three-phase ac input voltage detector connected to the ac input terminals for providing three-phase ac input voltage detect signals indicative of the three-phase ac input voltages;

(b) a dc voltage detector connected to the storage means for providing a dc voltage detect signal indicative of a dc voltage across the same;

(c) a source of a reference voltage indicative of a target value of the dc voltage across the storage means;

(d) first subtractor means connected to the dc voltage detector and the reference voltage source for providing a first difference signal indicative of a difference between the actual and target values of the dc voltage across the storage means;

(e) a first multiplier connected to the three-phase ac input voltage detector and the first subtractor means for providing a first product signal indicative of the product of multiplication of the second-phase ac input voltage detect signal and the first difference signal;

(f) a second multiplier connected to the three-phase ac input voltage detector and the first subtractor means for providing a second product signal indicative of the product of multiplication of the third-phase ac input voltage detect signal and the first difference signal;

(g) current detector means for providing a first and a second ac input current detect signal indicative respectively of second- and third-phase currents flowing through the second and third ac input terminals;

(h) second subtractor means connected to the first multiplier and the current detector means for providing a second difference signal indicative of a difference between the first product signal and the first ac input current detect signal;

(i) third subtractor means connected to the second multiplier and the current detector means for providing a third difference signal indicative of a difference between the second product signal and the second ac current detect signal;

(j) a periodic wave generator for providing a periodic wave signal which is higher in frequency than the second- and third-phase ac input voltage detect signal; and

(k) an ac-to-dc converter control signal generator circuit connected to the second and the third subtractor means and the periodic wave generator for providing a first, a second and a third pulse-width-modulated ac-to-dc converter control signal by comparison of the difference signals and the periodic wave signal, thereby to drive the ac-to-dc conversion switches of the three-phase ac-to-dc converter circuit.

8. A three-phase ac-to-dc-to-ac power converter system as defined in claim 1, wherein the converter system further comprises a first, a second and a third inductor connected respectively between the first, the second and the third ac input terminal and the three-phase ac-to-dc converter circuit, and wherein the ac-to-dc converter circuit further comprises:

(a) a first diode having an anode connected to the first ac input terminal via the first inductor and a cathode connected to the storage means;

(b) a second diode having an anode connected to the storage means and a cathode connected to the first ac input terminal via the first inductor;

(c) a third diode having an anode connected to the second ac input terminal vie the second inductor and a cathode connected to the storage means;

(d) a fourth diode having an anode connected to the storage means and a cathode connected to the second ac input terminal vie the second inductor;

(e) a fifth diode having an anode connected to the third ac input terminal via the third inductor and a cathode connected to the storage means; and

(f) a sixth diode having an anode connected to the storage means and a cathode connected to the third ac input terminal via the third inductor.

9. A three-phase ac-to-dc-to-ac power converter system as defined in claim 8, wherein the ac-to-dc conversion switches of the three-phase ac-to-dc converter circuit are comprised of a first, a second, a third, a fourth, a fifth and a sixth ac-to-dc conversion switch which are connected respectively in parallel with the first, the second, the third, the fourth, the fifth and the sixth diode, and wherein the power converter system further comprises selective drive means connected to the ac-to-dc converter control means for permitting the same to drive the third, the fourth, the fifth and the sixth ac-to-dc conversion switch of the three-phase ac-to-dc converter circuit, and to hold the first and the second ac-to-dc conversion switch open, when the bypass switch is closed, and to drive all of the first to the sixth ac-to-dc conversion switch of the three-phase ac-to-dc converter circuit when the bypass switch is open.