Abstract:
In the present invention, switching circuits connected in middle points of power supply lines of a three-phase alternating-current power supply are switched to cause currents to intermittently flow on primary windings of a transformer, a voltage generated on a secondary winding is rectified and smoothed, and then is outputted to a load. The switching circuits each include: a series circuit including a first primary winding, a bidirectional switch and a second primary winding, which are connected in series in this order; a drive circuit power supply generating circuit generating a direct-current positive voltage and a direct-current negative voltage by use of an alternating-current power supply voltage applied between two ends of the series circuit; and a drive circuit performing on-off drive of the bidirectional switch. A reference potential point of the bidirectional switch is connected to a reference potential point of the drive circuit power supply generating circuit.

Description:
TECHNICAL FIELD 
     The present invention relates to an alternating current-direct current (AC-DC) converter device configured to convert alternating-current power into insolated direct-current power. More specifically, the present invention relates to a power supply circuit configured to provide a drive circuit power supply for supplying on-off signals to semiconductor switching elements that constitute a converter to convert alternating-current power into direct-current power. 
     BACKGROUND ART 
     A power converter device configured to covert alternating-current power into isolated direct-current power is used as a direct-current power supply for communications, for example. In general, this power converter device is a two-stage converter including a non-isolated power factor improvement circuit and a high frequency isolated DC-DC converter. Meanwhile, there is also disclosed a power converter device simplified in a circuit configuration in which a one-stage converter causes the alternating-current power to flow intermittently at high frequency and converts the alternating-current into the direct-current power. 
       FIG. 1  is a circuit diagram showing an example of a conventional AC-DC converter device disclosed in Japanese Patent Application Publication No. 2002-233155. The AC-DC converter device shown in  FIG. 1  is a one-stage conversion high frequency isolated PWM rectifier, in which a series circuit formed of a bidirectional switch Q 10  and a first primary winding  3   a  of a transformer  3  is connected between an alternating-current terminal (R phase)  2   a  and an alternating-current terminal (T phase)  2   c  of a three-phase alternating-current power supply  1 . A series circuit formed of a bidirectional switch Q 20  and a second primary winding  3   b  of the transformer  3  is connected between an alternating-current terminal (S phase)  2   b  and the alternating-current terminal  2   a  of the three-phase alternating-current power supply  1 . A series circuit formed of a bidirectional switch Q 30  and a third primary winding  3   c  of the transformer  3  is connected between the alternating-current terminal  2   c  and the alternating-current terminal  2   b  of the three-phase alternating-current power supply  1 . 
     The bidirectional switch Q 10  is formed of a series circuit including an insulated gate bipolar transistor (IGBT) Q 11  and an IGBT Q 12 . The bidirectional switch Q 20  is formed of a series circuit including an IGBT Q 21  and an IGBT Q 22 . The bidirectional switch Q 30  is formed of a series circuit including an IGBT Q 31  and an IGBT Q 32 . 
     An anode of a direct-current power supply  11   a  is connected to a cathode of a direct-current power supply  10   a , and an anode of the direct-current power supply  10   a  is connected to gates of the IGBTs Q 11  and Q 12  via a switch Sa 1  in a gate drive circuit  12   a . A cathode of the direct-current power supply  11   a  is connected to the gates of the IGBTs Q 11  and Q 12  via a switch Sa 2  in the gate drive circuit  12   a . The cathode of the direct-current power supply  10   a  and the anode of the direct-current power supply  11   a  are connected to emitters of the IGBTs Q 11  and Q 12 . 
     An anode of a direct-current power supply  11   b  is connected to a cathode of a direct-current power supply  10   b , and an anode of the direct-current power supply  10   b  is connected to gates of the IGBTs Q 21  and Q 22  via a switch Sb 1  in a gate drive circuit  12   b . A cathode of the direct-current power supply  11   b  is connected to the gates of the IGBTs Q 21  and Q 22  via a switch Sb 2  in the gate drive circuit  12   b . The cathode of the direct-current power supply  10   b  and the anode of the direct-current power supply  11   b  are connected to emitters of the IGBTs Q 21  and Q 22 . 
     An anode of a direct-current power supply  11   c  is connected to a cathode of a direct-current power supply  10   c , and an anode of the direct-current power supply  10   c  is connected to gates of the IGBTs Q 31  and Q 32  via a switch Sc 1  in a gate drive circuit  12   c . A cathode of the direct-current power supply  11   c  is connected to the gates of the IGBTs Q 31  and Q 32  via a switch Sc 2  in the gate drive circuit  12   c . The cathode of the direct-current power supply  10   c  and the anode of the direct-current power supply  11   c  are connected to emitters of the IGBTs Q 31  and Q 32 . 
     A rectifier  4  rectifies a high-frequency voltage generated on a secondary winding  3   d  of the transformer  3 . A series circuit formed of a smoothing reactor  5  and a smoothing capacitor  8  is connected between two terminals of the rectifier  4 . A load  7  is connected to two terminals of the smoothing capacitor  8 . 
     In the thus configured conventional AC-DC converter device shown in  FIG. 1 , the alternating-current power is inputted from the three-phase alternating-current power supply  1  at a commercial frequency to the bidirectional switches Q 10 , Q 20 , and Q 30  as well as the primary windings  3   a  to  3   c.    
     The gate drive circuits  12   a  to  12   c  turn the switches Sa 1 , Sb 1 , and Sc 1  on by use of a control signal from an unillustrated control circuit and turn the bidirectional switches Q 10 , Q 20 , and Q 30  on by applying anode voltages from the direct-current power supplies  10   a  to  10   c  to points between the gates and the emitters of the bidirectional switches Q 10 , Q 20 , and Q 30 . Meanwhile, the gate drive circuits  12   a  to  12   c  turn the switches Sa 2 , Sb 2 , and Sc 2  on and turn the bidirectional switches Q 10 , Q 20 , and Q 30  off by applying cathode voltages from the direct-current power supplies  11   a  to  11   c.    
     Specifically, the alternating-current power from the three-phase alternating-current power supply  1  is subjected to high frequency switching by use of the bidirectional switches Q 10 , Q 20 , and Q 30  whereby a high-frequency voltage having a higher frequency than the commercial frequency is generated on the primary windings  3   a  to  3   c  and the secondary winding  3   d  of the transformer  3 . This high-frequency voltage is rectified with the rectifier  4  and smoothed by the smoothing reactor  5  and the smoothing capacitor  8 , and the direct-current power is supplied to the load  7 . 
     However, the direct-current power supplies  10   a  to  10   c  and  11   a  to  11   c  are provided separately from a main circuit. Accordingly, it is not possible to supply the power of the direct current power supply  11   a  from the main circuit in a non-isolated manner when the alternating-current terminal  2   b  of the S phase is in the state of the lowest potential. For this reason, the direct-current power is supplied to the gate drive circuits  12   a  to  12   c  via an unillustrated separate isolated converter. 
     In other words, since it is necessary to use the separate isolated converter, the conventional configuration causes an increase in the number of components which leads to complication of the AC-DC converter device. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an AC-DC converter device which is capable of supplying direct-current power by use of non-isolated simple circuits. 
     The present invention is an alternating current-direct current converter device configured to cause a current to intermittently flow on a primary winding of a transformer by switching a switching circuit connected to a middle point of any of a power supply line of a single-phase alternating-current power supply and each power supply line of a three-phase alternating-current power supply, to rectify and smooth a voltage generated on a secondary winding of the transformer, and to output the voltage to a load, wherein the transformer includes a first primary winding and a second primary winding, the switching circuit includes: a series circuit including the first primary winding of the transformer, a bidirectional switch, and the second primary winding of the transformer which are connected one to another in series in this order; a drive circuit power supply generating circuit which generates a direct-current positive voltage and a direct-current negative voltage by use of an alternating-current power supply voltage applied between two ends of the series circuit; and a drive circuit which is connected between the drive circuit power supply generating circuit and the bidirectional switch, and which performs on-off drive of the bidirectional switch, and a reference potential point of the bidirectional switch is connected to a reference potential point of the drive circuit power supply generating circuit. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a circuit diagram showing an example of a conventional AC-DC converter device. 
         FIG. 2  is a circuit diagram showing an AC-DC converter device according to a first embodiment. 
         FIG. 3  is a circuit diagram showing an AC-DC converter device according to a second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Now, embodiments of an AC-DC converter device of the present invention will be described below in detail with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 2  is a circuit diagram showing an AC-DC converter device according to a first embodiment. The AC-DC converter device of the first embodiment shown in  FIG. 2  has the following different features from the conventional AC-DC converter device shown in  FIG. 1 . Note that the first embodiment will describe the AC-DC converter device of a three-phase type (R phase, S phase, and T phase). 
     A transformer  9  includes a first primary winding  9   a   1  and a second primary winding  9   a   2  which are connected in series between an alternating-current terminal  2   a  and an alternating-current terminal  2   c , a first primary winding  9   b   1  and a second primary winding  9   b   2  which are connected in series between the alternating-current terminal  2   a  and an alternating-current terminal  2   b , a first primary winding  9   c   1  and a second primary winding  9   c   2  which are connected in series between the alternating-current terminal  2   b  and the alternating-current terminal  2   c , and a secondary winding  9   d.    
     A bidirectional switch Q 1  made of a semiconductor switching element (such as GaN) is formed of a series circuit in which a source (one of main terminals) of a high electron mobility transistor (HEMT) Q 1   a  and a source of a HEMT Q 1   b  are connected in common. A bidirectional switch Q 2  is formed of a series circuit in which a source of a HEMT Q 2   a  and a source of a HEMT Q 2   b  are connected in common. A bidirectional switch Q 3  is formed of a series circuit in which a source of a HEMT Q 3   a  and a source of a HEMT Q 3   b  are connected in common. Each HEMT is made of wide band gap semiconductor such as gallium nitride (GaN) or silicon carbide (SiC). Here, the sources of the HEMTs Q 1   a  and Q 1   b , the HEMTs Q 2   a  and Q 2   b , and the HEMTs Q 3   a  and Q 3   b  are reference potential points of the bidirectional switches Q 1 , Q 2 , and Q 3 , respectively. 
     Although the HEMT is used as the bidirectional switch in the first embodiment, it is also possible to use an IGBT (isolated gate bipolar transistor), a MOSFET (metal-oxide-semiconductor Field-effect transistor), a JFET (junction gate field-effect transistor), and the like instead of the HEMT. 
     The first primary winding  9   a   1  of the transformer  9 , the bidirectional switch Q 1 , and the second primary winding  9   a   2  of the transformer  9  are connected in series in this order and constitute a first series circuit. An end of the first primary winding  9   a   1  of the transformer  9  is connected to the alternating-current terminal  2   c  while an end of the second primary winding  9   a   2  of the transformer  9  is connected to the alternating-current terminal  2   a.    
     The first primary winding  9   b   1  of the transformer  9 , the bidirectional switch Q 2 , and the second primary winding  9   b   2  of the transformer  9  are connected in series in this order and constitute a second series circuit. An end of the first primary winding  9   b   1  of the transformer  9  is connected to the alternating-current terminal  2   a  while an end of the second primary winding  9   b   2  of the transformer  9  is connected to the alternating-current terminal  2   b.    
     The first primary winding  9   c   1  of the transformer  9 , the bidirectional switch Q 3 , and the second primary winding  9   c   2  of the transformer  9  are connected in series in this order and constitute a third series circuit. An end of the first primary winding  9   c   1  of the transformer  9  is connected to the alternating-current terminal  2   b  while an end of the second primary winding  9   c   2  of the transformer  9  is connected to the alternating-current terminal  2   c.    
     An end of each of the first primary windings  9   a   1 ,  9   b   1 , and  9   c   1  of the transformer  9  is connected to an end of each of resistors  13   a ,  13   b , and  13   c  and to an end of each of resistors  17   a ,  17   b , and  17   c . An end of each of the first primary windings  9   a   2 ,  9   b   2 , and  9   c   2  of the transformer  9  is connected to an end of each of resistors  16   a ,  16   b , and  16   c  and to an end of each of resistors  20   a ,  20   b , and  20   c . Another end of each of the  13   a ,  13   b , and  13   c  is connected to a cathode of each of diodes  14   a ,  14   b , and  14   c.    
     An anode of each of the diodes  14   a ,  14   b , and  14   c  is connected to an anode of each of diodes  15   a ,  15   b , and  15   c , to an anode of each of zener diodes  23   a ,  23   b , and  23   c , to an end or each of capacitors  24   a ,  24   b , and  24   c , and to an end of each of switches Sa 2 , Sb 2 , and Sc 2 . A cathode of each of the diodes  15   a ,  15   b , and  15   c  is connected to another end of each of the resistors  16   a ,  16   b , and  16   c.    
     Another end of each of the  17   a ,  17   b , and  17   c  is connected to an anode of each of diodes  18   a ,  18   b , and  18   c . A cathode of each of the diodes  18   a ,  18   b , and  18   c  is connected to a cathode of each of diodes  19   a ,  19   b , and  19   c , to a cathode of each of zener diodes  21   a ,  21   b , and  21   c , to an end or each of capacitors  22   a ,  22   b , and  22   c , and to an end of each of switches Sa 1 , Sb 1 , and Sc 1 . 
     An anode of each of the zener diodes  21   a ,  21   b , and  21   c , another end of each of the capacitors  22   a ,  22   b , and  22   c , a cathode of each of the zener diodes  23   a ,  23   b , and  23   c , and another end of each of the capacitors  24   a ,  24   b , and  24   c  are connected to the source of each of the HEMTs Q 1   a , Q 2   a , and Q 3   a  and to the source of each of the HEMTs Q 1   b , Q 2   b , and Q 3   b . Another end of each of the switches Sa 1 , Sb 1 , and Sc 1  and another end of each of the switches Sa 2 , Sb 2 , and Sc 2  are connected to a gate (a control terminal) of each of the HEMTs Q 1   a , Q 2   a , and Q 3   a  and to a gate (a control terminal) of each of the HEMTs Q 1   b , Q 2   b , and Q 3   b.    
     The resistors  13   a ,  16   a ,  17   a , and  20   a , the diodes  14   a ,  15   a ,  18   a , and  19   a , the zener diodes  21   a  and  23   a , and the capacitors  22   a  and  24   a  collectively constitute a first drive circuit power supply generating circuit configured to generate a direct-current positive voltage and a direct-current negative voltage out of an alternating-current power supply voltage (a line voltage using the R phase and the T phase) of the three-phase alternating-current power supply  1 . The gate drive circuit  12   a  turns the bidirectional switch Q 1  on and off by applying the direct-current positive voltage and the direct-current negative voltage from the first drive circuit power supply generating circuit to a gate of the bidirectional switch Q 1 . 
     The resistors  13   b ,  16   b ,  17   b , and  20   b , the diodes  14   b ,  15   b ,  18   b , and  19   b , the zener diodes  21   b  and  23   b , and the capacitors  22   b  and  24   b  collectively constitute a second drive circuit power supply generating circuit configured to generate a direct-current positive voltage and a direct-current negative voltage out of an alternating-current power supply voltage (a line voltage using the R phase and the S phase) of the three-phase alternating-current power supply  1 . The gate drive circuit  12   b  turns the bidirectional switch Q 2  on and off by applying the direct-current positive voltage and the direct-current negative voltage from the second drive circuit power supply generating circuit to a gate of the bidirectional switch Q 2 . 
     The resistors  13   c ,  16   c ,  17   c , and  20   c , the diodes  14   c ,  15   c ,  18   c , and  19   c , the zener diodes  21   c  and  23   c , and the capacitors  22   c  and  24   c  collectively constitute a third drive circuit power supply generating circuit configured to generate a direct-current positive voltage and a direct-current negative voltage out of an alternating-current power supply voltage (a line voltage using the R phase and the T phase) of the three-phase alternating-current power supply  1 . The gate drive circuit  12   c  turns the bidirectional switch Q 3  on and off by applying the direct-current positive voltage and the direct-current negative voltage from the third drive circuit power supply generating circuit to a gate of the bidirectional switch Q 3 . 
     Next, an operation of the thus configured AC-DC converter device according to the first embodiment will be described. 
     First, the alternating-current power supply voltage is applied from the three-phase alternating-current power supply  1 , via the alternating-current terminals  2   a  to  2   c , to the first series circuit formed of the first primary winding  9   a   1  of the transformer  9 , the bidirectional switch Q 1 , and the second primary winding  9   a   2  of the transformer  9 , to the second series circuit formed of the first primary winding  9   b   1  of the transformer  9 , the bidirectional switch Q 2 , and the second primary winding  9   b   2  of the transformer  9 , and to the third series circuit formed of the first primary winding  9   c   1  of the transformer  9 , the bidirectional switch Q 3 , and the second primary winding  9   c   2  of the transformer  9 . 
     Then, the alternating-current power supply voltage from the three-phase alternating current power supply  1  is rectified by the diode  18   a  ( 19   a ) via the resistor  17   a  ( 20   a ) between the alternating-current terminal  2   a  and the alternating-current terminal  2   c , whereby the capacitor  22   a  obtains the direct-current positive voltage. Meanwhile, the alternating-current power supply voltage is rectified by the diode  14   a  ( 15   a ) via the resistor  13   a  ( 16 ), whereby the capacitor  24  obtains the direct-current negative voltage. The capacitor  22   a  obtains the direct-current positive voltage such that an upper end functions as the anode while a lower end functions as the cathode. 
     The capacitor  24   a  obtains the direct-current negative voltage such that an upper end functions as the anode while a lower end functions as the cathode. Here, the lower end of the capacitor  22   a  and the upper end of the capacitor  24   a  are the reference potential points of the first drive circuit power supply generating circuit. 
     Therefore, as the switch Sa 1  is turned on the direct-current positive voltage is applied from the capacitor  22   a  to the gates of the HEMTs Q 1   a  and Q 1   b , thereby turning the HEMTs Q 1   a  and Q 1   b  on. On the other hand, as the switch Sa 2  is turned on the direct-current negative voltage is applied from the capacitor  24   a  to the gates of the HEMTs Q 1   a  and Q 1   b , thereby turning the HEMTs Q 1   a  and Q 1   b  off. 
     Here, the primary side circuit of the transformer  9  between the alternating-current terminal  2   a  and the alternating-current terminal  2   b  and the primary side circuit of the transformer  9  between the alternating-current terminal  2   b  and the alternating-current terminal  2   c  are also operated similarly to the primary side circuit of the transformer  9  between the alternating-current terminal  2   a  and the alternating-current terminal  2   c , and the description thereof will be omitted. 
     As described above, according to the AC-DC converter device of the first embodiment, even when the alternating-current power supply voltage is applied to the series circuits formed by connecting in series the first primary windings  9   a   1 ,  9   b   1 , and  9   c   1  of the transformer  9 , the bidirectional switches Q 1 , Q 2 , and Q 3 , and the second primary windings  9   a   2 ,  9   b   2 , and  9   c   2  of the transformer  9  in this order, and is also applied to the drive circuit power supply generating circuits configured to generate the positive and negative power supplies for the drive circuits  12   a ,  12   b , and  12   c  configured to perform on-off drive of the bidirectional switches Q 1 , Q 2 , and Q 3 , the potential of each of the reference potential points is set to midpoint potential of the alternating-current power supply voltage irrespective of the polarity of the alternating-current power supply voltage because the reference potential points of the bidirectional switches Q 1 , Q 2 , and Q 3  are connected to the reference potential points of the drive circuit power supply generating circuits. Therefore, it is possible to supply the direct-current power by using the non-isolated simple circuits. 
     Second Embodiment 
       FIG. 3  is a circuit diagram showing an AC-DC converter device according to a second embodiment. The AC-DC converter device according to the first embodiment shown in  FIG. 2  applies the bidirectional switches Q 1  to Q 3  each of which includes the two semiconductor switching elements formed by connecting in series the two HEMTs serving as unidirectional switches. 
     On the other hand, an AC-DC converter device of a second embodiment shown in  FIG. 3  uses HEMTs Q 4  to Q 6 , each of which includes a single semiconductor switching element, as bidirectional switches. 
     Other features of this embodiment are the same as the configuration shown in  FIG. 2 . Accordingly, the same constituents are designated by the same reference numerals and description thereof will be omitted. 
     The HEMTs Q 4 , Q 5 , and Q 6  serving as the bidirectional switches have gates G, drains D, and sources S. Cathodes of diodes D 1 , D 3 , and D 5  are connected to the drains D while anodes of the diodes D 1 , D 3 , and D 5  and anodes of diodes D 2 , D 4 , and D 6  are connected in common. These connecting points constitute virtual sources IS 1 , IS 2 , and IS 3  and reference potential points of the bidirectional switches Q 4  to Q 6  at the same time. Each of these virtual sources IS 1 , IS 2 , and IS 3  is connected to each of connecting points between the capacitor  22   a ,  22   b  or  22   c  and the capacitor  24   a ,  24   b  or  24   c , to each of the anodes of the zener diodes  21   a ,  21   b , and  21   c , and to each of the cathodes of the zener diodes  23   a ,  23   b , and  23   c . Cathodes of the diodes D 2 , D 4 , and D 6  are connected to the sources S of the HEMT Q 4 , Q 5 , and Q 6  serving as the bidirectional switches. 
     As described above, the AC-DC converter device of the second embodiment is operated similarly to the AC-DC converter device of the first embodiment and achieves a similar effect even by use of the HEMTs Q 4  to Q 6  which function as the bidirectional switches. Moreover, the HEMT Q 4 , Q 5  or Q 6  serving as the bidirectional switch is the single semiconductor switching element and is therefore available at a low price. 
     It is to be noted that the present invention will not be limited only to the AC-DC converter devices of the first and second embodiments. Although the AC-DC converter devices of the first and second embodiments describe the AC-DC converter devices connected to the three-phase alternating-current power supply, the present invention is also applicable to an AC-DC converter device connected to a single-phase alternating-current power supply. First switching circuits  50   a  and  60   a  shown in  FIG. 2  and  FIG. 3  are only used in this case, and second switching circuits  50   b  and  60   b  and third switching circuits  50   c  and  60   c  shown therein may be deleted. 
     As described above, according to the present invention, even when the alternating-current power supply voltage is applied to the series circuit formed by connecting in series the first primary winding of the transformer, the bidirectional switch, and the second primary winding of the transformer in this order and to the drive circuit power supply generating circuit configured to generate the positive and negative power supplies for the drive circuit configured to perform on-off drive of the bidirectional switch, the potential of each of the reference potential points is set to midpoint potential of the alternating-current power supply voltage irrespective of the polarity of the alternating-current power supply voltage because the reference potential point of the bidirectional switch is connected to the reference potential point of the drive circuit power supply generating circuit. Therefore, it is possible to supply the direct-current power by using non-isolated simple circuits. 
     The present invention is applicable to a communication direct-current power supply or the like.