Abstract:
The present invention provides a resonant power converter including: a first switch circuit in which multiple normally-off switches Q 1  to Q 4  to which resonant capacitors  6   a  to  6   d  are connected in parallel respectively are connected in a single-phase or three-phase bridge configuration; and a second switch circuit connected to a DC power supply  1  and the first switch circuit, including a resonant switch Q 7  and a resonant reactor  5  which forms a resonant circuit together with each the resonant capacitor in the first switch circuit, and configured to provide zero voltage switching of the normally-off switches in the first switch circuit. The resonant switch in the second switch circuit is a normally-on switch, short-circuiting units  12   a  to  12   f  are connected to the normally-off switches in the first switch circuit and the normally-on switch in the second switch circuit, respectively, the short-circuiting units each configured to cause a short circuit between a control terminal and one main terminal of the corresponding one of the normally-off switches and the normally-on switch, and control is made on the short-circuiting units so that the short-circuiting units do not operate normally but operates in case of emergency.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a resonant power converter configured to reduce a load on a power semiconductor switch formed as a main component, and particularly to a technique to shut down a resonant power converter rapidly and reliably in case of emergency. 
       BACKGROUND ART 
       [0002]    A power converter converts AC power or DC power into AC power or DC power of different levels by using a switching operation of a power semiconductor switch. Such a power converter is used, for example, for an uninterruptible power supply system, an inverter for driving a motor, a communication DC power supply, or the like. 
         [0003]    Switching loss of the power semiconductor switch causes deterioration in power conversion efficiency and switching noise of the power semiconductor switch causes malfunctions of the power semiconductor switch itself or of other devices. In view of the above, a resonant power converter which reduces the switching loss or the switching noise is used. 
         [0004]      FIG. 1  is a circuit configuration diagram showing an example of a conventional resonant power converter described in Japanese Patent Application Publication No. 2000-262066. In  FIG. 1 , the positive electrode of a DC power supply  1  is connected to a positive DC terminal  3   a  while the negative electrode of the DC power supply  1  is connected to a negative DC terminal  3   b . Between the positive DC terminal  3   a  and the negative DC terminal  3   b , a series circuit including an insulated gate bipolar transistor (IGBT) Q 6 , a resonant reactor  5 , an IGBT Q 5 , and a capacitor  7  is connected. This series circuit constitutes a second switch circuit  30 . 
         [0005]    A first series circuit is connected to both ends of a series circuit including the resonant reactor  5 , the IGBT Q 5 , and the capacitor  7 . The first series circuit includes a first parallel circuit and a second parallel circuit. The first parallel circuit includes an IGBT Q 1 , a resonant capacitor  6   a , and a diode D 1  while the second parallel circuit includes an IGBT Q 2 , a resonant capacitor  6   b , and a diode D 2 . 
         [0006]    In addition, a second series circuit is connected to both ends of the series circuit including the resonant reactor  5 , the IGBT Q 5 , and the capacitor  7 . The second series circuit includes a third parallel circuit and a fourth parallel circuit. The third parallel circuit includes an IGBT Q 3 , a resonant capacitor  6   c , and a diode D 3  while the fourth parallel circuit includes an IGBT Q 4 , a resonant capacitor  6   d , and a diode D 4 . 
         [0007]    A node of the first parallel circuit and the second parallel circuit is connected to one end of a load  2  via an AC terminal  4   a  while a node of the third parallel circuit and the fourth parallel circuit is connected to the other end of the load  2  via an AC terminal  4   b . The first to fourth parallel circuits constitute a first switch circuit  20 . 
         [0008]    Between the gates and the emitters of the IGBTs Q 1  to Q 6 , gate drive circuits  10   a  to  10   f  are connected via resistors  11   a  to  11   f . The gate drive circuits  10   a  to  10   f  drive the IGBTs Q 1  to Q 6  on and off by applying gate signals to the IGBTs Q 1  to Q 6 , respectively. 
         [0009]    According to the conventional resonant power converter which is shown in  FIG. 1  and configured in this manner, the IGBTs Q 1  to Q 6  are turned on when the gate drive circuits  10   a  to  10   f  apply gate signals of +15 V, for example, between the gates and the emitters of the IGBTs Q 1  to Q 6 , while the IGBTs Q 1  to Q 6  are turned off when the gate drive circuits  10   a  to  10   f  apply 0 V or negative voltage, for example, between the gates and the emitters of the IGBTs Q 1  to Q 6 . In other words, the IGBTs Q 1  to Q 6  are normally-off switches. 
         [0010]    The gate drive circuits  10   a  to  10   f  perform on-off control on the IGBTs Q 1  to Q 6  based on a control signal from an unillustrated control circuit. Thereby, DC power from the DC power supply  1  is converted into AC power, and the AC power is then supplied to the load  2 . 
         [0011]    In this case, the IGBTs Q 1  to Q 4  and Q 6  perform zero voltage switching by the resonant operation between the resonant reactor  5  and the resonant capacitors  6   a  to  6   d  and  6   f  connected in parallel to the respective IGBTs Q 1  to Q 4  and Q 6 . Meanwhile, the IGBT Q 5  performs zero current switching by the resonant operation between the resonant capacitor  6   f  and the resonant reactor  5  connected in series with the IGBT Q 5 . Thus, the switching loss and the switching noise of the IGBTs Q 1  to Q 6  are reduced. 
         [0012]    However, in the resonant power converter as shown in  FIG. 1 , if the IGBT Q 5  is turned off forcibly while a current flows through the resonant reactor  5 , the IGBT Q 5  may be broken since the energy of the resonant reactor  5  flows into the IGBT Q 5 . 
         [0013]    Further, if the IGBTs Q 1  to Q 4  and Q 6  are turned on while the resonant capacitors  6   a  to  6   d  and  6   f  have a voltage, the IGBTs Q 1  to Q 4  and Q 6  may be broken since the energy of the resonant capacitors  6   a  to  6   d  and  6   f  flows into the respective IGBTs Q 1  to Q 4  and Q 6 . 
         [0014]    For this reason, it is preferable to turn on or turn off the IGBTs Q 1  to Q 6  at any given timing by providing a power absorption circuit, such as a snubber circuit, which absorbs the energy of the resonant reactor  5  or of the resonant capacitors  6   a  to  6   d  and  6   f.    
         [0015]    In addition, there is a need to shut down the converter rapidly in case of emergency, such as in a case where a microcomputer constituting the control circuit malfunctions or runs away or where there is an abnormality in the power source of the control circuit. In case of emergency, the conventional converter uses both an OFF signal which turns off the IGBTs Q 1  to Q 4  and Q 6  and an ON signal which turns on the IGBT Q 5 . In other words, the gate drive circuits  10   a  to  10   f  are complicated since the circuit configuration for the gate drive circuits  10   a  to  10   d  and  10   f  differs from the circuit configuration for the gate drive circuit  10   e.    
       SUMMARY OF INVENTION 
       [0016]    An object of the present invention is to provide a resonant power converter which can be shut down rapidly and reliably in case of emergency with a simple circuit. 
         [0017]    The present invention provides a resonant power converter including: a first switch circuit in which multiple normally-off switches to each of which a resonant capacitor is connected in parallel are connected in a single-phase or three-phase bridge configuration; and a second switch circuit connected to a DC power supply and the first switch circuit, including a resonant switch and a resonant reactor which forms a resonant circuit together with each the resonant capacitor in the first switch circuit, and configured to provide zero voltage switching of the normally-off switches in the first switch circuit, the resonant power converter configured to convert DC power from the DC power supply into AC power in the first switch circuit and to output the AC power. The resonant switch in the second switch circuit is a normally-on switch, a short-circuiting unit is connected to each of the normally-off switches in the first switch circuit and the normally-on switch in the second switch circuit, the short-circuiting unit configured to cause a short circuit between a control terminal and one main terminal of each of the normally-off switches and the normally-on switch, and control is made on the short-circuiting units so that the short-circuiting units do not operate normally but operates in case of emergency. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]      FIG. 1  is a circuit configuration diagram showing an example of a conventional resonant power converter. 
           [0019]      FIG. 2  is a circuit configuration diagram showing a resonant power converter according to a first embodiment. 
           [0020]      FIG. 3  is a circuit configuration diagram showing a resonant power converter according to a second embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0021]    Hereinbelow, embodiments of a resonant power converter according to the present invention will be described in detail with reference to the drawings. 
       First Embodiment 
       [0022]      FIG. 2  is a circuit configuration diagram showing a resonant power converter according to a first embodiment. The resonant power converter according to the first embodiment shown in  FIG. 2  is different from the resonant power converter shown in  FIG. 1 , and is characterized in that a normally-on switch Q 7  (resonant switch) is used instead of the IGBT Q 5  and that a protection circuit  14  (short-circuiting unit) and photo couplers including photo transistors  12   a  to  12   f  and photodiodes  13   a  to  13   f  are provided. IGBTs Q 1  to Q 4  and Q 6  are formed of the normally-off switches. 
         [0023]    Note that other configurations of the resonant power converter shown in  FIG. 2  are the same as those of the resonant power converter shown in  FIG. 1 . Thus, the same reference numerals are given to the same components, and the description thereof will be omitted. 
         [0024]    The normally-on switch Q 7  is made of a wide bandgap semiconductor, such as silicon carbide (SiC) or gallium nitride (GaN). The normally-on switch Q 7  is turned on when the gate-source voltage is 0 V. In this respect, the normally-on switch Q 7  is turned on with the gate-source voltage of +15 V and is turned off with the gate-source voltage of −10 V. Fabricating a normally-on device from such a wide bandgap semiconductor is easier than from an Si device. 
         [0025]    Gate drive circuits  10   a  to  10   f  output AC power to AC terminals  4   a  and  4   b  by performing on/off control on the normally-on switch Q 7  and the IGBTs Q 1  to Q 4  and Q 6 . 
         [0026]    The collectors of the photo transistors  12   a  to  12   d  are connected to the gates of the respective IGBTs Q 1  to Q 4  and respective resistors  11   a  to  11   d , the collector of the photo transistor  12   f  is connected to the gate of the IGBT Q 6  and a resistor  11   f , and the collector of the photo transistor  12   e  is connected to the source of the normally-on switch Q 7 , the anode of a diode D 7 , and a capacitor  7 . 
         [0027]    The emitters of the photo transistors  12   a  to  12   d  are connected to the emitters of the IGBTs Q 1  to Q 4 , the anodes of diodes D 1  to D 4 , and resonant capacitors  6   a  to  6   d , respectively. The emitter of the photo transistor  12   f  is connected to the emitter of the IGBT Q 6 , the anode of a diode D 6 , and a resonant capacitor  6   f . The emitter of the photo transistor  12   e  is connected to the gate of the normally-on switch Q 7  and a resistor  11   e.    
         [0028]    To both ends of the protection circuit  14 , a series circuit including the photodiodes  13   a  to  13   f  are connected. In case of emergency, the protection circuit  14  causes a short circuit between the gate and the emitter of each of the IGBTs Q 1  to Q 4  and Q 6  and between the gate (control terminal) and the source (one main terminal) of the normally-on switch Q 7  by feeding a current through the series circuit including the photodiodes  13   a  to  13   f.    
         [0029]    Next, an operation of the resonant power converter according to the first embodiment configured in this manner will be described. 
         [0030]    Firstly, in a normal state, the gate drive circuits  10   a  to  10   f  apply voltages (+15 V and −10V) to the gate of the normally-on switch Q 7  and to the gates of the IGBTs Q 1  to Q 4  and Q 6 , respectively, and the switches are thus turned on and off to output AC power to the AC terminals  4   a  and  4   b.    
         [0031]    In a case where an abnormality occurs in any of the gate drive circuits  10   a  to  10   f  or an unillustrated control circuit, the protection circuit  14  applies a protection signal to the series circuit including the photodiodes  13   a  to  13   f . Accordingly, the photodiodes  13   a  to  13   f  emit light, a current flows through the photo transistors  12   a  to  12   f , and thus short circuits are caused between the gates and the emitters of the IGBTs Q 1  to Q 4  and Q 6  and between the gate and the source of the normally-on switch Q 7 . 
         [0032]    Thus, the IGBTs Q 1  to Q 4  and Q 6  are turned off while the normally-on switch Q 7  is turned on. In this manner, in case of emergency, the IGBTs Q 1  to Q 4  and Q 6  are turned off while the normally-on switch Q 7  is turned on with a single protection signal from the protection circuit  14 . In other words, it is possible to turn on and off the switches Q 1  to Q 4 , Q 6 , and Q 7  reliably, and thus to shut down the resonant power converter rapidly and reliably in case of emergency. 
       Second Embodiment 
       [0033]      FIG. 3  is a circuit configuration diagram showing a resonant power converter according to a second embodiment. The resonant power converter according to the second embodiment shown in  FIG. 3  is characterized in that the present invention is applied to an auxiliary resonant commutated pole inverter. 
         [0034]    In  FIG. 3 , the positive electrode of a DC power supply  1  is connected to a positive DC terminal  3   a  while the negative electrode of the DC power supply  1  is connected to a negative DC terminal  3   b . Between the positive DC terminal  3   a  and the negative DC terminal  3   b , a series circuit including a capacitor  15  and a capacitor  16  is connected. The capacitor  16  has the same capacitance as the capacitor  15 . At a node of the capacitor  15  and the capacitor  16 , a voltage which is half the voltage of the DC power supply  1  is generated. 
         [0035]    To both ends of a series circuit including the capacitor  15  and the capacitor  16 , a first series circuit including a first parallel circuit and a second parallel circuit is connected. The first parallel circuit includes an IGBT Q 1 , a resonant capacitor  6   a , and a diode D 1  while the second parallel circuit includes an IGBT Q 2 , a resonant capacitor  6   b , and a diode D 2 . In addition, to both ends of the series circuit including the capacitor  15  and the capacitor  16 , a second series circuit including a third parallel circuit and a fourth parallel circuit is connected. The third parallel circuit includes an IGBT Q 3 , a resonant capacitor  6   c , and a diode D 3  while the fourth parallel circuit includes an IGBT Q 4 , a resonant capacitor  6   d , and a diode D 4 . 
         [0036]    A node of the first parallel circuit and the second parallel circuit is connected to one end of a load  2  via an AC terminal  4   a , while a node of the third parallel circuit and the fourth parallel circuit is connected to the other end of the load  2  via an AC terminal  4   b . Between a node of the first parallel circuit and the second parallel circuit and the node of the capacitor  15  and the capacitor  16 , a resonant reactor  5   a , a normally-on switch Q 8 , and a normally-on switch Q 9  are connected. 
         [0037]    The normally-on switches Q 8  and Q 9  constitute a bidirectional switch (resonant switch). The normally-on switches Q 8  and Q 9  are made of a wide bandgap semiconductor such as Sic or GaN. Instead, for example, GaN High Electron Mobility Transistor (HEMT) may be employed as a bidirectional switch. 
         [0038]    The drain of the normally-on switch Q 9  is connected to the cathode of a diode D 9  and the node of the capacitor  15  and the capacitor  16 . 
         [0039]    The source of the normally-on switch Q 9  is connected to the anode of the diode D 9 , the anode of a diode D 8 , the source of the normally-on switch Q 8 , and one end of each of gate drive circuits  10   e  and  10   f . The drain of the normally-on switch Q 8  is connected to the cathode of the diode D 8  and one end of the resonant reactor  5   a.    
         [0040]    The gate of the normally-on switch Q 8  is connected to the other end of the gate drive circuit  10   e  via a resistor  11   e  while the gate of the normally-on switch Q 9  is connected to the other end of the gate drive circuit  10   f  via a resistor  11   f.    
         [0041]    The emitter and the collector of a photo transistor  12   e  are connected to the gate and the source of the normally-on switch Q 8 , respectively, while the emitter and the collector of a photo transistor  12   f  are connected to the gate and the source of the normally-on switch Q 9 . 
         [0042]    Between a node of the third parallel circuit and the fourth parallel circuit and the node of the capacitor  15  and the capacitor  16 , a resonant reactor  5   b , a normally-on switch Q 10 , and a normally-on switch Q 11  are connected. 
         [0043]    The normally-on switches Q 10  and Q 11  constitute a bidirectional switch (resonant switch). The normally-on switches Q 10  and Q 11  are made of a wide bandgap semiconductor such as Sic or GaN. Instead, for example, GaN High Electron Mobility Transistor (HEMT) may be employed as a bidirectional switch. 
         [0044]    The drain of the normally-on switch Q 11  is connected to the cathode of a diode D 11  and the node of the capacitor  15  and the capacitor  16 . 
         [0045]    The source of the normally-on switch Q 11  is connected to the anode of the diode D 11 , the anode of a diode D 10 , the source of the normally-on switch Q 10 , and one end of each of gate drive circuits  10   g  and  10   h . The drain of the normally-on switch Q 10  is connected to the cathode of the diode D 10  and one end of the resonant reactor  5   b.    
         [0046]    The gate of the normally-on switch Q 10  is connected to the other end of the gate drive circuit  10   g  via a resistor  11   g  while the gate of the normally-on switch Q 11  is connected to the other end of the gate drive circuit  10   h  via a resistor  11   h.    
         [0047]    The emitter and the collector of a photo transistor  12   g  are connected to the gate and the source of the normally-on switch Q 10 , respectively, while the emitter and the collector of a photo transistor  12   h  are connected to the gate and the source of the normally-on switch Q 11 . Photodiodes  13   g  and  13   h  are connected in series with photodiodes  13   a  to  13   f . The photodiode  13   g  and the photo transistor  12   g  constitute a photo coupler, and the photodiode  13   h  and the photo transistor  12   h  constitute a photo coupler. 
         [0048]    Also in the resonant power converter according to the second embodiment configured in this manner, the IGBTs Q 1  to Q 4  are formed of the normally-off switches while the normally-on switches Q 8  to Q 11  are formed of the normally-on switches. For this reason, in case of emergency, the IGBTs Q 1  to Q 4  can be turned off while the normally-on switches Q 8  to Q 11  can be turned on with a single protection signal from the protection circuit  14 . In other words, it is possible to turn on and off the switches Q 1  to Q 4  and Q 8  to Q 11  reliably, and thus to shut down the resonant power converter rapidly and reliably in case of emergency. 
         [0049]    Subsequently, description will be given of a resonant operation between the IGBTs Q 1  and Q 2  of the resonant power converter according to the second embodiment. The gate drive circuits  10   a  to  10   f  turn on the normally-on switches Q 8  and Q 9  simultaneously during a dead time period of the IGBTs Q 1  and Q 2  (during a period in which the IGBTs Q 1  and Q 2  are both turned off). 
         [0050]    While the IGBT Q 4  is on but the IGBTs Q 1  and Q 2  are off, a current flows in a path of  4   a  and  4   b →Q 4 →Q 2 → 4   a  and  4   b . Since the current flows through the diode D 2  corresponding to the IGBT Q 2 , the collector-emitter voltage of the IGBT Q 2  becomes zero. For this reason, when the IGBT Q 1  is turned on, a DC voltage VDC from the DC power supply  1  is applied between the collector and the emitter of the IGBT Q 1 , and thus switching loss occurs. 
         [0051]    In order to prevent the switching loss from occurring in the IGBT Q 1 , the collector-emitter voltage of the IGBT Q 1  is set to zero during the dead time period immediately before switching of the IGBT Q 1 . 
         [0052]    During the dead time period of the IGBTs Q 1  and Q 2 , the normally-on switches Q 8  and Q 9  are turned on simultaneously. At this time, no current flows through the resonant reactor  5   a , resulting in zero current switching of the normally-on switches Q 8  and Q 9 . 
         [0053]    When the potential of the negative electrode of the AC power supply  1  is set as a standard, the potential at the node of the capacitor  15  and the capacitor  16  is half the VDC and the potential at the node of the IGBTs Q 1  and Q 2  is zero, and thus the voltage applied to the resonant reactor  5   a  is half the VDC. Then, the current flowing through the resonant reactor  5   a  increases. 
         [0054]    At the time when the current in the resonant reactor  5   a  reaches the level of the current flowing through the AC terminals  4   a  and  4   b , resonance occurs between the resonant reactor  5   a  and the capacitors  6   a  and  6   b . In this event, charges are discharged from the capacitor  6   a  connected in parallel to the IGBT Q 1  and the charges flow into the capacitor  6   b  connected in parallel to the IGBT Q 2 . 
         [0055]    At the time when the resonance is completed, the potential at the node of the IGBTs Q 1  and Q 2  becomes equal to the VDC. For this reason, zero voltage switching (soft switching) of the IGBT Q 1  can be achieved by turning on the IGBT Q 1  at this time. 
         [0056]    Since the potential at the node of the IGBTs Q 1  and Q 2  is equal to the VDC once the IGBT Q 1  is turned on, the resonant current decreases thereafter. By turning off the normally-on switches Q 8  and Q 9  at the time when the current in the resonant reactor  5   a  reaches zero, the loss of the normally-on switches Q 8  and Q 9  can be also reduced. 
         [0057]    While the IGBT Q 1  is on, a current flows in a path of  4   a  and  4   b →Q 4 → 1 →Q 1 → 4   a  and  4   b.    
         [0058]    When the IGBT Q 1  is turned off in this state, charges are discharged from the resonant capacitor  6   b  while charges are increased in the resonant capacitor  6   a . At this time, since only the resonant capacitor  6   a  is connected in parallel to the IGBT Q 1 , no switching loss occurs. For this reason, soft switching can be achieved in both the turning-on and the turning-off of the IGBT Q 1 , leading to no switching loss and achievement of high efficiency. The same applies to the IGBTs Q 3  and Q 4 . 
         [0059]    Note that the present invention is not limited to the resonant power converters according to the first and second embodiments. The resonant power converters according to the first and second embodiments are described using a DC/AC power converter which converts DC power from the DC power supply  1  into single-phase AC power and outputs the AC power to the load  2  through the AC terminals  4   a  and  4   b . However, the present invention is also applicable to a DC/AC power converter which converts DC power from the DC power supply  1  into three-phase AC power and outputs the AC power to a load through AC terminals. 
         [0060]    As has been described, according to the present invention, the short-circuiting unit is connected to each of the normally-off switches in the first switch circuit and the normally-on switch(es) in the second switch circuit, the short-circuiting unit configured to cause a short circuit between a control terminal and one main terminal of each of the normally-off switches and the normally-on switch(es). Accordingly, in case of emergency, the normally-off switches in the first switch circuit can be turned off while the normally-on switches in the second switch circuit can be turned on with a single signal. 
       INDUSTRIAL APPLICABILITY 
       [0061]    The present invention is applicable to an uninterruptible power supply, an inverter for driving a motor, a communication DC power supply, or the like.