CA1101056A - Plural bridge power converter - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A power converter comprises a plural pairs of electrical valve bridges which have a plurality of electrical valves connected in bridge between DC terminals and AC terminals connected to an AC load and a plurality of controllable DC
power means for pulsating unidirectional current fed into the DC
terminals of the electrical valve bridges or fed out of the DC
terminals whereby the unidirectional pulsating current is distri-buted to the plural pairs of electrical valve bridges for feeding to the AC load. The converter further comprises magnetically coupled reactors connected in unidirectional pulsating current lines or further comprises DC lines of said unidirectional pulsating current lines which are connected as a common lines.

Description

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The present invention relates to a power converter suitable for frequency conversion.
Various power converters for feeding to ~C motors have been proposed. They have been classified as the inverter system and the cycloconverter system. However, disadvantageously, the former have problems in commutation and the latter have problems in total capacity of desired power transistor element and the power-factor to power source.
The present invention provides a power converter which has advantageous characteristics of both the inverter system and the cycloconverter system.
According to the present invention there is provided a power converter which comprises a plurality of pairs of electrical valve bridges having a plurality of electrical valves connected in each bridge between DC terminals and AC terminals connected to an AC load, and a plurality of controllable DC
power means for feeding pulsating unidirectional current into the DC terminals of the electrical valve bridges or out oE the DC terminals, wherein said controllable DC power means are electrically connected to each other, and a plurality of reactors magnetically coupled to each other and connected in unidirectional pulsating current lines whereby the unidirectional pulsating current is allotted to the plurality of pairs of electrical valve bridges for feeding to the AC load.

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- ~L(~ 6 'rhe present inven~ion ~ill be further illustrated by way of the accompanying drawi.ngs i.n which:
Figures 1 to 4 are respectively diagrams of various embodiments of circuit connections of a power converter according to the present invention;
Fi.gures 5 to 8 are respectively waveforms in the operations of embodiments according to the present invention.
Referring to the accompanyi.ng drawings wherein like reference numerals designate identical or corresponding parts throughout the views, Figure 1 is a diagram of one embodiment of the circuit connection of -the power converter of the invention.
In Figure 1, the first and second electrical valve bridges (2a), (2b) are respectively connected through AC
s (Ul, Vl, Wl), (U2, V2,W2~ to the AC load (100) and respectively connected through DC terminals (Pl,Nl)(P2,N2) to the first and second DC closed circuits CLl, CL2, so as to form series connected assembly of closed c:ircuits. The DC closed circuits CLl, CL2 respectively comprise controllable DC power means (control rectifying power source or DC chopper) (3P1,3Nl) (3P2,3N2) which are control rectifying type DC power means in the embodiment of Figure 1. The control rectifylng type DC
power means are respectively connected to AC power sources (52a), (52b) which are secondary windings of rectifying transformer (5) having primary windings (51) connected to an AC power source .. ~ 2 LOS~

such as the original AC power source (not shown).
The firs-t and second DC closed circuit CLl, CL2 ,-comprise reactors (7) having magnetic coupling M. When the DC
power means (3Pl, 3Nl), (3P2, 3N2) in the closed circuits are the secondary windings (52a~, (52b) of the rectifying transformer under insulation, the closed circuits CLl and CL2 are independently separated and accordingly, one pair of the coupling reactors (7) can be disposed at desired positions. This is shown inFigure 1 (a).
When the DC power means (3Pl, 3Nl) (3P2, 3N2) in the closed circuits are not insulated, for example, the AC power sources (52a) (52b) are common noninsulated AC power sources (52), it is possible to have,the coupling reactor (7a) for positive line (ipl l.ine and ip2 line) and the coupling reactor (7b) for negative line (iNl line and iN2 line) as.Figure 1 (b). When the common power source (52) {non-insulation of (52a) and (52b)} is used, it is possible to use one.or two pair of the coupling reactors for connecting one positive line (ip2 or ipl) and the other negative line (iNl or iN2) as Figu.re l(a). It is also possible to give 4 winding reactors which form magnetic couplings of (7a) and (7h) in Figure l(b). Instead of t~e magnetic coupl.ing reactor (7), it is possible to have the common DC line DCP for each partial DC line of the first and second DC circuits.
The common DC line can have the DC reactor (7') if necessary.
The inductance of the common DC reactor (7') corresponds to mutual coupling inductance M of the coupling reactor (7) in the embodiment of Figure,r. Moreover, when the reactors (7"a), (7"b) are connected in the independent partial DC lines (arrow lines ipl, ip2, iNl, iN2) of the first and second DC closed lines as shown by the dotted line, the inductance of the independent DC
line inductance corresponds to the inductance of the non-coupling part of the coupling reactor in the embodiment of Figure 1.

In the embodiment of Figure 2, independent control ~IQ56 rectifying type controllable DC power means (3Pl, 3Nl, 3P2, 3N2) are respectively connected in each DC line (arrow lines ipl, iNl, ip2, iN2) to each of the positive and negative DC terminals of the electrical valve bridges (2a), (2b), and the means are respectively all wave bridge type rectifiers. The AC power - sources (52aP), (52bP), (52aN), (52bN) of the rectifiers are mutually insulated.
It is possibIe to form non-insulated common AC power source for positive lines or negative lines. These embodiments are illustrated referring to Figures 3 and 4.
The embodiments of Figure 1 and Figure 2 can be~
operated as follows.
Figure 5 to 8 show waveforms in the operations of the embodiments. The Y connection equated voltages in each of phases '~ ~oo~
of the AC -L~od (100) such as an AC motor are designated as Eu, Ev, Ew and the waveforms thereof are shown as Figures 5(a), 6(a), 7(a) and 8(a). In order to simplify the illustration, the waveforms are shown in the phase relation in the case of O

degree of AC load power-factor angle. However, it is the same e r e n c e, with the case of phase fqt~f-e-~-ence between voltage and current.
The operation of the embodiment in Figure 5 will be illustrated.

The Currents ~iPlr iNl) (ip2~ iN2) passing through the 1 1~ 2~ N2 of the electricaL valve bridges ) re ipl ~ iNl and ip2 iN2, and are the pulsating current which have triangle waveform having partially ~æe wave-form and are intermittent with different pulsating phases. l'he pulsation is given at a ratio of m ttmes per 1 cycle of the AC
load when n designates the number of phases of the AC terminals of the AC load. In the connection diagrams of Figures 1 and 2, m = 3 and accordingly, the case of m =3 will be illustrated referring to Figure 5. The pulsation is shifted for l/N period of the pulsation period (l/m N period of the AC output period) when W designates the number of the electrical valve bridges and the DC closed circuit CL. In the embodiment, N=2 and the sum of one wave of the first pulsa-ting current (ipl = iN1) and one wave of the second pulsating current (ip2 = iN2) is decided to be half-wave of the total AC output. In this embodiment, a sine half wave is formed.
Taking the U phase AC load current iu in Figures 1 and

2, the positive sine half-wave is given by composing the positive line component ipl of the first pulsating current passing through the eIectrical valve ~Pl of the first electrical valve bridge (2a) and the positive line component ip2 f the second pulsating current passing through the electrical valve UP2 of the second electrical valve bridge (2b). The U phase negative half-wav~ is given by composing the negative line component iN2 of the second ~ulsating current passing through the electrical valve UN2 of the second electrical valve bridge (2b) and the negative line component iNl of the first pulsating current passing through the electrical valve UNl of the first electrical valve bridge (2a). The first and second pulsating currents (ipl, iNl) (ip2, N2 through the first electrical valve bridge and the second electrical valve bridge on the other phases V and W as the same manner.
ln the distribution, the pulsating currents (ipl, iN2), (ip~r iN2) shown in Figures 5(c)(d) are passed thoru~h the electrical valves (VNl), (VN2), (VPl), (VP2) (WPl), (WP2), (WNl), (WN2) as shown in ( ) of Figure 5(c)(d). Thus, the sine wave AC can be given between the load (100). Figure shows a relation ofthephases in the case of feeding the current in the same phase of the load voltage. It is possible to pass the AC
current in a desired phase relation whereby the power can be applied as desired.
Figure 6 is the waveforms in the case of the pulsating Pl' Nl)' (ip2, iN2) having triangle waveforms as ~0~ 56 Figure 6(e) and -~he AC currents iu, iv, iw having trapezoid waveforms as Fi~ure 6(b), (c), (d). When the AC currents have a trapezoidal waveform, the sum of the pulsating currents (ip1, iNl) (ip2,iN2) is cons~ntwhereby the pulsation is not caused for -the current or the power to the power source (51) behind of the controllable DC power means (3P1, 3Nl), (3P2, 3N2).
In Figure 7, the pulsating current (ipl iN1) (ip2, iN2) having trapezoid waveform or rectangular waveform as Figure 7 (e).
In the case of the three-phase AC load in the -trapezoid waveform, the rising section, the peak flat section, the falling section, the quiescent section are respectively 1/12 period of the AC
output. The pulsating current (ipl, iNl) is shifted from the pulsating current (ip2, iN2) for 1/2 period (l/6 period of the AC output) o~ the pulsating period as the same with those of Figures 5 and 6. When the trapezoid pulsating currents (ipl, iNl) (ip2, iN2) are distributed to the AC load by the electrical valve bridges (2a) (2b) as the same manner of Figure 5, tile trapezoid waveform having broad flat part as shown in Figures 7 (b), (c), (d) can be formed.
In the operation of the embodiment as shown in Figure 7, non-current section of the pulsating current can be enough long whereby the commutation of the electrical valve bridges (2a), (2b) can be easily attained. Accordingly, in the case of the same controllable power means, it can be used for the AC load having higher frequency. Figure S is the waveform showing the operation of the other embodiment for pulsating current having longer pulsating period. In Figure 8, the pulsating currents ip1, and ip2 are alternatively passed and the pulsating currents iNl, and iN~ are alternatively passed, of course, this is controlled by the controllable DC power means. As shown in Figure 8 (e), (f), the pulsating current has the half-wave trapezoid waveform shown by the full line or the half-wave sine ,.. , ~.~

Q~i waveform Shown by the dotted line or the half-waye rectangular waveform. (not shown, 1/3 period of the AC output in the case of three-phase AC load). In the trapezoid waveform, the rising section and the falling section of the current can be 1/6 period of the AC output (shown by a chain line). The waveform can be selected as deslred in practice. The U shaped positive half-wave is alternatively given by the first pulsating positive current ipl passing through the UPl of the first electrical valve bridge (2a) and the second pulsatingpositive current ip2 passing through the UP2 of the second electrical valve bridge (2b). The U phase negative half-wave is alternatively given by the second pulsating negative currenk iN2 passing through the UN2 of the second electrical valve bridge (2b) and the first pulsating negative current iNl passing through the UNl of the first electrical valve bridge (2a). The V phase positive half-wave is altenratively given by ip2 passing through VP2 and ipl pa~sing through VP1. The V phase negative half-wave is alternative-ly given by iNl passing through VNl and iN2 passing through VN2.
The W phase positive half-wave is alternatively given by ip2 passing through WP2 and ipl passing through WP1. The W phase negative half-wave is alternatively given by iNl passing through WNl and iN2 passing through WN2. Thus, as shown in Figures 8(b), (c), (d), the AC current having trapezoid waveform~ sine waveform (including similar ones) or rectangular waveform can be formed and fed.
In the operation of the embodiment as shown in Figure 8 t thenon-current section (quiescent time) of the same pulsating current can be enough long, whereby the frequency of the AC
output by the same controllable power means can be increased.
Moreover, the pulsating period of the pulsating current is long whereby it can be used for the AC load having higher frequency.
When the operation of Figure 8 is given in the embodiment of .. . , :
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Figure 1, the controllable power means in the other groups should be return-pass each other because of ipl ~ iNl and ip2 ~ iN2.
Accordingly, it is difficult to operate it when it is fed from the insulated power sources (52d)l (52b) as shown in Figure l(a~, but it is possible to operate it in the embodiment connecting to the non-insulated common power sources (52) as shown in Figure l(b). The operation of Figure 8 can be attained in the non-insulated pulsating circuit systems having the joint lines for ipl and iN2 and the joint lines for ip2 and iNl as the embodiment of Figure l(b) and Figure 2. In the connection of Figure 1, the mutual inductance M of the coupling reactor (7) is affected as the common line inductance to the two pulsating currents (ipl, iNl)(ip2, iN2). That is, the increase of the current in one side causes the decrease of the current in the other side whereas the decrease of the current in one side causes the increase of the current in the other side. That is, it has the smoothing effect to the sum of both unidirectional pulsating currents, and the differential change of both unidirectional pulsating currents is not prevented. Accordingly, the change of the pulsating currents (ipl, iNl) (ip2, N2 directional change as shown in Figures 5 to 8, is not su~stantially prevented. The coupling inductance M is equivalent to the inductance (7') inserted in the common line DCP. Accordingly,~
the same operation can be attained in the embodiment of Figure 2.
In Figure 2, the common inductance (7') imparts the smoothing effect (small effect in a region having small di~dt near peak value of sine waveform) to (ipl -~ ip2) without preventing the differential change of (ipl - ip2). Thus, the increase of the unidirectional pulsating current in one side causes the decrease of the unidirectional pulsating current in the other side. In Figure 2, the inductances (7"a), (7"b) inserted in each unidirec-tional pulsating current line correspond to the non-coupling .

Q~j inductance of the reactor of Figure 1 and can be inserted as protective current limiting reactor. (dotted linel. In any case, it is possible to prevent the inhibition of the change of pulsating of each unidirectional pulsating current by coupling the unidirec-tional pulsating current line with the coupling reactor or by forming the common DC line.
Figure 3 is a connection diagram of the other embodiment.
The common DC power source (4) ls inserted to the common DC line - DCP of Figure 2, and the controllable DC power means (3Pl), (3P2), (3Nl), (3N2) are formed by multi-phase half-wave electrical valve circuits. The common DC power source (4) is connected to the secondary winding (52x) of thepower transformer (5) in a connection. The secondary windings (52p) of the transofrmer for half-wave electrical valve circuit of the controllable DC power means is Y connection whereby the reverse phase half-wave currents are respectively induced to the primary winding (51) of the power transformer each other to give the resultant current~ of the power source in equivalent to the Y connection aIl wave rectifi-cation.
When both AC voltages (line voltage) are equal, the resultant currents in the ~ connection of the secondary windings (52x? are power current corresponding to the 12 phase rectifica-tion.
The operation of the embodiment of Figure 3 can be attained as shown by the waveforms in ~gures 5 to 8. When the voltage of the AC load (100) is high, a part of the voltage -- can be given by the common DC power source (4) The ratio of the voltage given by the common DC power source can be varied as desired depending upon the ratio of the voltage of the first secondary winding (52Pl 52N) to the voltage o~ the second secondary winding (52x). The powe~r source commutation is increased, depending upon the ratio of voltage is increased.

~ lO~L~S6 The current can be fed to high power-factor load or delay power-factor load. The same secondary line voltages (ratio of voltage 1:1) is optimum for lowering higher harmonic wave o~
the power source (51~ and providing relatively high commutating function.
Figure 4 is a connection diagram of the other embodiment of the invention and is equivalent to give the same AC voltage of the second secondary winding (52x) with the AC voltage of the first secondary windings (52P, 52N) in the embodiment of Figure

3. The positive half-wave of the first secondary winding (52P) is used as the controllable DC power means (3Pl), (3P2) and the negative half-wave of the first secondary winding (52N) is used as the first half part (4a) of the common DC power source (4), and the negative half-wave of the first secondary winding (52N) is used as the controllable DC power means (3Nl), (3N2) and the positive half-wave of the first secondary winding (52N) is used as the second half part (4b) of the common DC power source (4). It is possible to connect the common DC power source (4c) and the secondary windin~ (52x) of the transform as shown by the dotted line. The operation can be attained as shown ~y the waveforms in Figures 5 to 8 as the same with those of Figure 3.
When the AC load (100) is an armature (101) of a synchronous machine, it is possible to have a separately excited field winding (102) and a proportlonal exciting winding (103) such as a series field winding or a compensating winding (or interpole winding). The proportional exciting circuit means-~t comprising the proportional exciting winding (103) and suitable polarity switching means (104) can be connected in series to the ~r9 ~/Oc~ 6 ~g~ ,3o~ 30 common DC lines x y as shown by the dotted'lline of^~*~e~4. It is also possible to separately control the proportional exciting winding (103) by excitation in proportional to the current of the common DC line.

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In the above-mentioned embodiments, the control operation for alloting -the unidirectional pulsating current to the AC load (100) by the electrical valve bridges (2a), (2b) has been illustrated. ~hen the AC load has an internal electro-motive force as the synchronous machine to be capable of feeding reactive power, the control DC power sources (3) are controlled by the continuous DC control in a relatively high~speed region h~ving enough electromotlve force whereby the unidirectional current is continued and the electrical valve bridge can be used as the natural commutation inverters which are commutated by internal electromotive force of machine itself and are operated in parallel.
Accordingly, it is possible to attain the two commuta-tion mode changing operation to operate by the above~mentioned pulsating commutation inthe low speed region and to operate by the natural internal electromotive force commutated inverter operation in the high spèed region. ~
In accordance with the embodiment of Figure 4, the common DC power source is connected to the common DC line to give the voltage corresponding to the load voltage as the same with that of Figure 3 and the use of the secondary windings (52P, 52N) of the transformer are increased in comparlson with that of the embodiment of Figure 3. (all wave secondary windings).
In accordance with the present invention, the lnhibition of pulsating varlation of the unldirectional pulsating currents can be minimi~ed by connecting the unidirectional pulsating line with the coupling reactor or using the common DC lines, and the symmetrical AC current can be fed to the AC
~ load hy pulsating at a rate-of m or m/2 times per 1 cycle to the AC load having m~phases of the terminals.

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Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A power converter which comprises a plurality of pairs of electrical valve bridges having a plurality of electrical valves connected in each bridge between DC terminals and AC
terminals connected to an AC load, and a plurality of controll-able DC power means for feeding pulsating unidirectional current along unidirectional pulsating current lines into the DC
terminals of the electrical valve bridges or out of the DC
terminals, wherein said controllable DC power means are electrically connected to each other, and a plurality of reactors magnetically coupled to each other and connected in said unidirectional pulsating current lines whereby the uni-directional pulsating current is allotted to the plurality of pairs of electrical valve bridges for feeding to the AC load.

2. A power converter according to claim 1, wherein each coupling reactor is connected to each of positive and negative lines of each unidirectional pulsating current line.

3. A power converter comprising:
a plurality of electrical valve bridges, each of the plurality of electrical valve bridges having a plurality of electrical valves, a pair of DC input nodes, and a plurality of AC output nodes respectively connected to a plurality of AC
input terminals of an AC load, each of the plurality of electrical valves being connected between one of the DC input nodes and one of the AC output nodes;
a plurality of DC power control means, each of the plurality of DC power control means having a pair of pulsating output terminals connected to the pair of DC input nodes of each of the plurality of electrical valve bridges through one pair of a plurality of pairs of pulsating DC lines;
pulsating direct currents being fed in different phase relation to the input nodes of the electrical valve bridges through the pulsating DC lines from the DC power control means and controlled by the DC power control means in synchronous relation with the control of the electrical valves; and a plurality of reactors magnetically coupled to each other and respectively inserted in series to a plurality of the pulsating DC lines;
whereby the pulsating direct currents are converted to alternating currents for feeding the alternating currents to the AC load, and commutation of the electrical valves is assisted by pulsation of the pulsating direct currents.

4. The power converter according to claim 3, including an AC power source and wherein each of said plurality of DC
power control means includes a controlled rectifier circuit having a source-terminal connected to the AC power source.

5. The power converter according to claim 4, wherein said AC power source includes a transformer having a primary winding and a plurality of secondary windings, each of the plurality of secondary windings connected to a source-terminal of each of the controlled rectifier circuits.

6. The power converter according to claim 3, wherein at least two of said DC power control means are together connected to a common source.

7. The power converter according to claim 6, wherein each of said reactors is inserted in series to each of positive and negative lines of each of the pairs of the plurality of pairs of said pulsating DC lines.

8. The power converter according to claim 3, wherein each said pulsating direct current has a waveform, wherein said waveform is a resolved waveform which is solution of:
a. half sine waveforms, b. triangular waveforms, or c. trapezoidal waveforms.

9. A power converter according to claim 1, wherein the pulsating frequency of one of said pulsating unidirectional currents is given to be equal to 1.5 times the frequency of said AC load which is three phase AC load.