WO2012176240A1

WO2012176240A1 - Half bridge capable of reducing reverse recovery currents of reflux diodes

Info

Publication number: WO2012176240A1
Application number: PCT/JP2011/003599
Authority: WO
Inventors: Shouichi Tanaka
Original assignee: Three Eye Co., Ltd.
Priority date: 2011-06-23
Filing date: 2011-06-23
Publication date: 2012-12-27

Abstract

A half bridge has a simple compensating leg capable of reducing reverse recovery currents of a pair of reflux diodes of the half bridge. The compensating leg consists of a common compensating power source, and a sub diode bridge connected to the half bridge in parallel. A connecting point of the sub diode bridge consisting of an upper sub diode and a lower sub diode connected in series is connected to a connecting point of the half bridge through the common compensating power source. The common compensating power source supplies a compensating current to both of reflux diode of the half bridge in order to reduce a reverse recovery power losses of both reflux diodes of the half bridge.

Description

HALF BRIDGE CAPABLE OF REDUCING REVERSE RECOVERY CURRENTS OF REFLUX DIODES

Background of Invention

1. Field of the Invention
The present invention relates to a half bridge capable of reducing reverse recovery currents of reflux diodes, particularly a three-phase inverter, a single-phase inverter and a DC/DC converter, which have at least one half bridge.

2. Description of the Related Art
A half bridge consisting of an upper arm and a lower arm connected in series is broadly adopted in a DC/AC inverter and an AC/DC converter. For driving an inductive-load, each of the upper arm and the lower arm includes a reflux diode (a free-wheeling diode) connected in anti-parallel to a switching element, which generally consists of a transistor. A free wheeling current flows through the reflux diode, after the transistor has been turned off.

It is well-known that a reverse recovery current flows through the reflux diode in order to recover the reflux diode after the free wheeling current becomes zero. The reverse recovery current generates a large reverse recovery power loss, if a DC link voltage applied to the half bridge is high. Moreover, the reverse recovery current generates electro-magnetic noise, too. A plurality of ideas is proposed for reducing the reverse recovery power loss as explained hereinafter.

U.S. Patent Ser. No. 7,778,054 proposes a pair of compensating arms for reducing reverse recovery currents as shown in Figures 1. In Figure 1, the upper compensating arm 1 is connected in parallel to an upper arm 3 of the half bridge. Similarly, the lower compensating arm 2 is connected in parallel to a lower arm 4 of the half bridge. Upper compensating arm 1 consists of a sub diode 11 and an inductance element 12 connected in series to the sub diode 11. Lower compensating arm 2 consists of a sub diode 21 and an inductance element 22 connected in series to the sub diode 21.

The upper arm 3 consists of a transistor 31 and anti-parallel-connected reflux diode 32. The lower arm 4 consists of a transistor 41 and anti-parallel-connected reflux diode 42. A DC voltage is applied across an upper DC terminal 101 and a lower DC terminal 102 of the half bridge. A middle terminal 103 of the half bridge is connected to an inductive load (not shown) such as a phase winding of a motor. The

inductance elements

12 and 22 have larger inductances than line inductances of the upper arm 3 and the lower arm 4.

In Figure 1, a main component of the reflux current IL returns to upper DC terminal 101 through reflux diode 32, and a sub component of the reflux current IL returns to upper DC terminal 101 through sub diode 11 and inductance element 12. The reflux current (the free wheeling current) is decreased, after lower transistor 41 is turned on. A compensating current Ic supplied from inductance element 12 to reflux diode 32 reduces a reverse recovery current of reflux diode 32, after the main component of the reflux current has become zero.

Figure 2 shows a period when the free-wheeling current (the reflux current) IL through lower reflux diode 42. In Figure 2, a main component of reflux current IL returns to middle terminal 103 through reflux diode 42, and sub component of reflux current IL returns to middle terminal 103 through sub diode 21 and inductance element 22. The reflux current (the free wheeling current) is decreased after upper transistor 31 is turned on. A compensating current Ic supplied from inductance element 22 to reflux diode 42 reduces a reverse recovery current of reflux diode 42, after the main component of the reflux current has become zero.

Two

inductance elements

12 and 22 must have larger inductance value than line inductances of upper arm 3 and lower arm 4 in order accumulate reverse recovery energy. However, the large inductance values of

inductance elements

12 and 22 reduce the reflux current passing through

inductance elements

12 and 22.

Inductance elements

12 and 22 must have a low electrical resistance value each, because predetermined amplitude of the sub free-wheeling currents must be supplied to

sub diodes

11 and 21. It causes that

inductance elements

12 and 22 must have a large size each.

U.S.Patent Ser. No. 6,058,037 proposes another type of the compensating arms for reducing reverse recovery currents as shown in Figure 3. In Figure 3, compensating

current circuits

13 and 23 are employed instead of

inductance elements

12 and 22 shown in Figures 1 and 2. The compensating current circuit 13 supplies the compensating current with a predetermined waveform, when the reverse recovery current flows through reflux diodes 32.

The compensating current circuit 23 supplies the compensating current with a predetermined waveform, when the reverse recovery current flows through reflux diodes 42. However, the compensating

current circuits

13 and 23 require a complicate circuit topology each in order to supply the compensating currents to

reflux diodes

32 and 42 just after the reflux current of

reflux diodes

32 and 42 become zero.

Japan Unexamined Patent Publication Pub. No. 2011-62039 proposes another type of the compensating arms for reducing reverse recovery currents as shown in Figure 4. In Figure 4, the compensating

current circuits

13 and 23 supply the compensating currents via

transformers

14 and 24. By means of employing the

transformers

14 and 24, the compensating

current circuits

13 and 23 enable to be insulated from the half bridge with upper arm 3 and lower arm 4. However, the two transformers require increasing the production cost and the size largely.

Japan Unexamined Patent Publication Pub. No. 2011-19358 proposes compensating arms, which is same circuit configuration as Japan Unexamined Patent Publication Pub. No. 2011-62039. The compensating arms are used for soft switching of the half bridge.

After all, in the above prior arts, each compensating arm consists of the sub diode and a compensating power source connected in series to each other. In Figures 1 and 2, the compensating power source consists of the inductance element. In Figure 3, the compensating power source consists of the compensating current circuit. In Figure 4, the compensating power source consists of the compensating current circuit with the transformer. However, a large scale of the above compensating circuit topology increases a production cost. For example, six compensating arms are required in a three-phase inverter. The reflux diode is sometimes called an anti-parallel diode or a free wheeling diode.

U.S.Patent Ser. No. 7,778,054 U.S.Patent Ser. No. 6,058,037 Japan Unexamined Patent Publication Pub. No. 2011-62039 Japan Unexamined Patent Publication Pub. No. 2011-19358

It is an object of the present invention to provide a half bridge having a simple compensating leg capable of reducing reverse recovery currents of reflux diodes.

As for a first aspect of the invention, a half bridge has an upper arm and a lower arm connected in series. For example, the half bridge is provided for a DC/AC inverter or a DC/DC converter. The upper arm consists of an upper reflux diode connected in anti-parallel to an upper switching element. The lower arm consists of a lower reflux diode connected in anti-parallel to a lower switching element. The above circuit topology of the half bridge is well-known.

According to a feature of the invention, the half bridge further has a compensating leg with a common compensating power source and a sub diode leg consisting of an upper sub diode and a lower sub diode connected in series to each other. The sub diode leg is connected in parallel to a switching leg consisting of the upper arm and the lower arm, which are connected in series to each other. A connecting point between the upper arm and the lower arm is connected to a connecting point between the upper sub diode and the lower sub diode via the common compensating power source. The common compensating power source supplies a compensating current to the upper reflux diode of the upper arm and the lower reflux diode of the lower arm, when a reverse recovery current flows through the upper reflux diode or the lower reflux diode. Accordingly, reverse recovery power losses of a pair of the reflux diodes are reduced by a simple circuit topology.

According to a preferred embodiment, the common compensating power source applies an alternative voltage via a transformer to the upper reflux diode and the lower reflux diode. Accordingly, it is capable of insulating the common compensating power source from a DC link voltage applied to the upper arm and the lower arm of the half bridge. Moreover, according to the embodiment, only one transformer is required for a half bridge. For example, a three-phase inverter with three half bridges (three legs) needs only three transformers. By reduction of a number of the transformers, a size, a weight and a cost of the three-phase inverter are improved largely.

According to another preferred embodiment, the common compensating power source has a single-phase full bridge inverter supplying a single-phase alternative power to a primary winding of the transformer. Accordingly, the alternative voltage is generated simply. According to another preferred embodiment, the upper switching element and the lower switching element consist of a MIS FET, for example a SJ MOS FET. The upper reflux diode and the lower reflux diode consist of a body diode each. Accordingly, the reverse recovery power losses of the body diodes are reduced largely.

Fig. 1 is a circuit topology configuration showing a prior half bridge with sub diodes and inductance elements for circulating a compensating current through an upper reflux diode; Fig. 2 is a circuit topology configuration showing the prior half bridge with sub diodes and inductance elements for circulating a compensating current through a lower reflux diode; Fig. 3 is a circuit topology configuration showing another prior half bridge having sub diodes and compensating power sources. Fig. 4 is a circuit topology configuration showing another prior half bridge having sub diodes, compensating power sources and transformers. Fig. 5 is a circuit topology configuration showing a three-phase inverter of employing a first embodiment of the present invention having a compensating leg of a transformer type; Fig. 6 is a circuit topology configuration showing a compensating current circulating through the upper reflux diode shown in Figure 5; Fig. 7 is a circuit topology configuration showing a compensating current circulating through the lower reflux diode shown in Figure 5; Fig. 8 is a timing chart showing a reverse recovery current and a compensating current, which flow through the reflux diode shown in Figure 5; Fig. 9 is a circuit topology configuration showing a compensating power source shown in Figure 5; Fig. 10 is another circuit topology configuration showing a compensating current circulating through the upper reflux diode shown in Figure 5; Fig. 11 is an arranged circuit topology configuration showing a compensating current circulating through the lower reflux diode shown in Figure 5; Fig. 12 is a circuit topology configuration of a second embodiment, which shows a compensating current circulating through the upper reflux diode of a half-bridge with a compensating leg of an inductance type; and Fig. 13 is another circuit topology configuration of the second embodiment, which shows a compensating current circulating through the lower reflux diode shown in Figure 12.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A first embodiment of the present invention is described referring to Figures 5-9. Figure 5 shows a three-phase inverter having a compensating leg for compensating reverse recovery currents of reflux diodes. In Figure 5, the three-phase inverter 10 has a U-phase leg, a V-phase leg and a W-phase leg, which are connected in parallel to each other. The U-phase leg consists of an upper arm 3U and a lower arm 4U connected in series. The V-phase leg consists of an upper arm 3V and a lower arm 4V connected in series. The W-phase leg consists of an upper arm 3W and a lower arm 4W connected in series.

A DC voltage Vdc is applied across a high potential terminal 101 and a low potential terminal 102 of the three-phase inverter 10. Each of upper arms 3U, 3V and 3W consist of one MOS transistor 31 having a body diode constituting an upper reflux diode 32 each. Each of lower arms 4U, 4V and 4W consist of one MOS transistor 41 having a body diode constituting a lower reflux diode 42 each.

The compensating leg consists of three transformers 6U, 6V and 6W, a compensating power source 7 and three diode legs 9U, 9V and 9W. Each of diode legs 9U, 9V and 9W consists of an upper sub diode 11 and a lower sub diode 21 connected in series to each other. Diode legs 9U, 9V and 9W are connected to the three-phase inverter 10 in parallel to each other.

A connecting point 103 of U-phase leg of inverter 10 is connected to a connecting point 104 of the U-phase diode leg 9U through a secondary winding 62 of a U-phase transformer 6U. A connecting point 103 of V-phase leg of inverter 10 is connected to a connecting point 104 of the V-phase diode leg 9V through a secondary winding 62 of a V-phase transformer 6V. A connecting point 103 of W-phase leg of inverter 10 is connected to a connecting point 104 of the W-phase diode leg 9W through a secondary winding 62 of a W-phase transformer 6W.

The compensating power source 7 has a U-phase compensating power source 7U, a V-phase compensating power source 7V and a W-phase compensating power source 7W. Each of the phase compensating power sources 7U, 7V and 7W applies a compensating voltage to each of transformers 6U, 6V and 6W respectively. U-phase compensating power source 7U applies the compensating voltage to a primary winding 61 of U-phase transformer 6U. V-phase compensating power source 7V applies the compensating voltage to a primary winding 61 of V-phase transformers 6V. W-phase compensating power source 7W applies the compensating voltage to a primary winding 61 of W-phase transformers 6W.

Inverter 10 outputs a three-phase voltage to a three-phase motor (not shown). The U-phase leg applies U-phase voltage Vu to a U-phase terminal of the motor (not shown). V-phase leg applies V-phase voltage Vv to a V-phase terminal of the motor (not shown). W-phase leg applies W-phase voltage Vw to a W-phase terminal of the motor (not shown). It is abbreviated to explain PWM-switching operation of three-phase inverter 10, because it is known as a skilled electronic engineer.

Operation of the compensating leg having three transformers 6U, 6V and 6W, compensating power source 7 and three phase diode legs 9U, 9V and 9W is explained referring to Figures 6 and 7. Figure 6 shows a compensating current Ic circulating through one upper reflux diode 32 shown in Figure 5. Figure 7 shows a compensating current Ic circulating through one lower reflux diode 42 shown in Figure 5. In Figure 5, each compensating operation of three phase legs is essentially same except operated timings. Accordingly, the compensating operation of one phase leg of inverter 10 is explained referring to Figures 5-7.

Figure 7 is a timing chart showing currents and voltages in a return mode that a free-wheeling current (a reflux current) IL returns from the motor to the half bridge. A gate voltage Vgh is applied to a gate electrode of upper MOS transistor 31. A gate voltage Vgl is applied to a gate electrode of lower MOS transistor 41.

Before a time point t1 shown in Figure 8, a gate voltage Vgh applied to upper MOS transistor 31 is high, and a free-wheeling current ILh, which is the free-wheeling current IL flowing through upper arm 3, mostly flows through a channel of upper MOS transistor 31. After the time point t1, the free-wheeling current ILh flows through upper reflux diode 32 because of the turning-off of MOS transistor 31.

After a gate voltage Vgl applied to lower MOS transistor 41 is high at a time point t2, free-wheeling current ILh is decreased. A free-wheeling current ILl, which is the free-wheeling current IL flowing through lower MOS transistor 41 increases. Free-wheeling current ILh becomes zero at a time point t4. A reverse recovery current Ir flowing through upper reflux diode 32 is increased after time point t4. After the reverse recovery current Ir reaches a top point at time point t4, reverse recovery current Ir is decreased and mostly becomes zero at a time point t5.

A compensating power source 7 applies a rectangular-shaped pulse voltage Vc to primary winding 61 of transformer 6 during a compensating period from t3 to t4. Accordingly, a compensating current Ic is supplied from compensating power source 7 to an upper circuit path including upper reflux diode 32 and an upper sub diode 11 as shown in Figure 6. Transformer 6 has a primary leak inductance of primary winding 61 and a secondary leak inductance of secondary winding 62. Thus the compensating current Ic is increased in a period from t3 to t4 and is decreased after a time point t4. A circulating direction of the compensating current Ic shown in Figure 6 is same as the reverse recovery current Ir of reflux diode 32.

Accordingly, the reverse recovery current Ir mostly consists of compensating current Ic. It means that reverse recovery current Ir does not flow to lower arm 4, and reverse recovery power loss is decreased largely, even though the DC voltage Vdc applied to the half bridge is high. An amplitude of the compensating voltage Vc is enable to change in accordance with a detected free-wheeling current (reflux current) ILh.

Figure 8 is a timing chart showing currents and voltages in a supplying mode that free-wheeling current (reflux current) IL returns from inverter 10 to the motor. Compensating power source 7 applies a rectangular-shaped pulse voltage Vc to primary winding 61 of transformer 6 during a compensating period from t3 to t4. However, it is important that a direction of voltage Vc shown in Figure 7 is opposite to voltage Vc shown in Figure 6. Accordingly, compensating current Ic has the circulating direction shown in Figure 7. The compensating power source 7 supplies the reverse recovery current Ir flowing through the lower diode 42. After all, the compensating power source 7 supplies both of reverse recovery currents Ir to both of

reflux diodes

32 and 42.

The time point t3 can be decided in accordance with amplitude of the free-wheeling current of

reflux diodes

32 and 42, because the free-wheeling current reaches zero at the time point t3. The time point t4 is changed in accordance with amplitude of free-wheeling current IL. A period from time point t3 to time point t4 is extended, if the amplitude of the free-wheeling current IL is large. A period from time point t3 to time point t4 is shortened, if the amplitude of the free-wheeling current IL is small. It is enable to control the amplitude of voltage Vc in accordance with detected amplitude of the free wheeling current.

As the result, an output period Tc applying the compensating voltage Vc can be decided in accordance with the amplitude of the free wheeling current. A skilled electronics engineer can selects an analog circuit topology or a digital circuit topology or a comparator technology in order to decide the both of time points t3 and t4.

One example of compensating power source 7 is explained referring to Figure 9. Compensating power source 7 has a controlling circuit portion 70, a full bridge inverter 8 and a voltage controller 85. Transformer 6 has primary winding 61, secondary winding 62 and a sensing winding 63, which are connected magnetically. The voltage controller 85 applies a DC control voltage to the full bridge inverter 8.

The controlling circuit portion 70 receives a voltage induced across the sensing winding 63. The sensing winding 63 induces the voltage, when the free-wheeling current flows through the upper arm 3 and the lower arm 4, because a small component of the free-wheeling current flows through the sensing winding 63. The controlling circuit portion 70 decides the timing t3 and t4 in accordance with the induced voltage received from the sensing winding 63.

The full bridge inverter 7 outputs the compensating voltage Vc to primary winding 61. The controlling circuit portion 70 turns on an upper transistor 81 and a lower transistor 84 during the decided period from t3 to t4, if the freewheeling current flows through reflux diode 32. The controlling circuit portion 70 turns on an upper transistor 83 and a lower transistor 82 during the decided period from t3 to t4, if the freewheeling current flows through reflux diode 42. A direction of a current passing through secondary winding 62 is opposite to a direction of the current passing through secondary winding 62. Amplitude (a height) of voltage Vc is controlled by the voltage controller 85. The amplitude (a height) of voltage Vc is changed in accordance with detected amplitude of the voltage across the sensing winding 63 before the time point t1.

An arranged embodiment of the above first embodiment is explained referring to Figures 10 and 11. Figure 10 shows the compensating current supplied to upper reflux diode 32. Figure 11 shows the compensating current supplied to lower reflux diode 42.

In Figures 10 and 11, transformer 6 has two primary windings 61A and 61B. The compensating power source has a controlling circuit portion 70 and two

lower transistors

82 and 84. The transistor 82 controls a current of the primary winding 61A. The transistor 84 controls a current of the primary winding 61B.

An arranged timing control of the period Tc shown in Figure 8 is explained hereinafter. In the above embodiment, the compensating voltage Vc is applied during the period Tc from a time point t3 to a time point t4 as shown in Figure 8. However, the period Tc for applying the compensating voltage Vc can be set in a different period. For one example, the compensating voltage Vc is applied during a dead time from t1 to t2. In this case, the free wheeling current of the

reflux diodes

32 and 42 are decreased, and the free wheeling current of the

sub diodes

11 and 21 are increased. It becomes easy to control the timing control of the compensating voltage Vc. For another example, the compensating voltage Vc is applied from a starting time point ts to an ending time point te. The starting time point ts is set in a dead time period from t1 to t2. The ending time point te is set after a time point t5.

A second embodiment of the present invention is described referring to Figures 12 and 13. Figure 12 shows compensating current Ic circulating through upper reflux diode 32 and upper sub diode 11. Figure 13 shows compensating current Ic circulating through lower reflux diode 42 and lower sub diode 21.

According to the second embodiment shown in Figures 12 and 13, the compensating power source consists of an inductance element 5 having a predetermined inductance value, which is larger than an inductance value of a line inductance 33 of upper arm 3 and lower arm 4. The inductance element 5 connects the connecting point 103 of the half bridge to the connecting point 104 of the sub diode bridge.

Operation of the compensating leg having the inductance element 5, upper sub diode 11 and lower sub diode 21 is explained referring to Figures 8, 12 and 13.

In Figure 12, free-wheeling current (the reflux current) IL returns from the motor to the half bridge. A free-wheeling current ILh flows through upper arm 3 including a line inductance 33. The remaining of free-wheeling current IL flows through the inductance element 5 and sub diode 11. After the turning-off of upper transistor 31, free-wheeling current ILh flows through reflux diode 32.

After the turning-on of lower transistor 41, free-wheeling current ILh flowing through reflux diode 32 is decreased. Similarly, the remaining of free-wheeling current IL flowing through inductance element 5 is decreased. However, the remaining of free-wheeling current IL flowing through inductance element 5 reaches zero later than a time when free-wheeling current of reflux diode 32 reaches zero, because inductance element 5 has larger inductance value than the line inductance of upper arm 3. As the result, inductance element 5 performs as the compensating power source explained above.

In Figure 13, free-wheeling current IL flows out from the half bridge to the inductance load (not shown). Free-wheeling current ILl flows through lower arm 4 including line inductance 43. The remaining of free-wheeling current IL flows through inductance element 5 and sub diode 21. After the turning-off of lower transistor 41, free-wheeling current ILl flows through reflux diode 42.

After the turning-on of the upper transistor 31, free-wheeling current ILl flowing through reflux diode 42 is decreased. Similarly, the remaining of the free-wheeling current IL flowing through inductance element 5 is decreased. However, the remaining of free-wheeling current IL flowing through inductance element 5 reaches zero later than a time when free-wheeling current of reflux diode 42 reaches zero. As the result, inductance element 5 performs as the compensating power source explained above.

Claims

A half bridge comprising an upper arm (3), a lower arm (4) and a compensating leg, the upper arm (3) comprising an upper switching element (31) and an upper reflux diode (32) connected in parallel to the upper switching element (31), the lower arm (4) comprising a lower switching element (41) and a lower reflux diode (42) connected in parallel to the lower switching element (41), and the compensating leg capable of compensating a reverse recovery current of the upper reflux diode (32) and the lower reflux diode (42), wherein:
the compensating leg has an upper sub diode (11), a lower sub diode (21) and a compensating power source (5, 7);
a pair of the upper sub diode (11) and the lower sub diode (21) connected in series to each other is connected in parallel to a pair of the upper arm (3) and the lower arm (4) connected in series to each other;
a connecting point (103) between the upper arm (3) and the lower arm (4) of the half bridge is connected via the compensating power source (5, 7) to a connecting point (104) between the upper sub diode (11) and the lower sub diode (21); and
the compensating power source (7) supplies a compensating current to the upper reflux diode (32) and the lower reflux diode (42) via the upper sub diode (11) and the lower sub diode (21).
The half bridge according to claim 1, the compensating power source (7) output an alternative power to the reflux diodes (32 and 32) via a transformer (6) of which a secondary winding (62) connects the connecting point (103) to the connecting point (104).
The half bridge according to claim 2, the compensating power source (7) has a single-phase full bridge inverter supplying a single-phase alternative power to a primary winding (61) of the transformer (6).
The half bridge according to claim 1, the compensating power source consists of an inductance element (5) having larger inductance value than each inductance value of line inductances of the upper arm (3) and the lower arm (4) of the half bridge.
The half bridge according to claim 1, the compensating power source (7) has three pairs of transformers (6U, 6V and 6W) for supplying three alternative voltages to three legs of a three-phase inverter respectively.
The half bridge according to claim 1, the upper switching element and the lower switching element consist of a MIS FET each; and
each of the upper reflux diode and the lower reflux diode consists of a body diode of the MIS FET.
The half bridge according to claim 6, the MIS FET consists of a super junction MOS FET (SJ-MOST).
The half bridge according to claim 1, the upper switching element and the lower switching element consist of a IGBT each; and
each of the upper reflux diode and the lower reflux diode consists of a junction diode.