JP5362466B2 - Control device for power conversion circuit - Google Patents

Description

  The present invention includes a power switching element, a first free wheel diode connected in parallel to an input / output terminal of the power switching element, a second free wheel diode connected in series to the power switching element, and the second A soft switching coil connected in parallel to the freewheel diode, and a power conversion circuit in which a power conversion coil is connected to a connection point of the power switching element and the second freewheel diode. The present invention relates to a control device for a power conversion circuit that performs control to reduce a current flowing through a freewheeling diode by flowing it through the soft switching coil and that turns on the power switching element after the control is started.

  An example of this type of control device is described in Non-Patent Document 1 below. Here, in a situation where a forward current flows through the second freewheeling diode, a voltage is applied to the softswitching coil so that a current flows through the softswitching coil and eventually flows into the second freewheeling diode. Reduce directional current. Then, when the current flowing through the second freewheeling diode becomes zero, the power switching element is turned on. Thereby, although the current flowing through the power switching element gradually increases, the gradually increasing speed is limited by the decreasing speed of the current flowing through the soft switching coil. For this reason, the ON operation of the power switching element can be soft switching.

  Other conventional control devices for power conversion circuits include those described in Patent Documents 1 and 2 below, for example.

Japanese Patent Laid-Open No. 10-327585 JP 2006-141168 A

Saito, Kubota, “Zero Current Turn-On Inverter Using Pulse Transformer”, 2008 IEEE Japan, 4th volume, p128-129

  However, in the technique described in Non-Patent Document 1, although soft switching can be achieved by limiting the increase rate of the current flowing in the power switching element, the input / output terminals between the power switching elements are turned on. Since a current flows in the process of decreasing the voltage, power loss occurs. For this reason, the ON operation is insufficient as soft switching.

  Further, when the second free wheel diode is a body diode such as a super junction MOSFET, the reverse recovery current is increased. For this reason, when the decay rate of the reverse recovery current becomes larger than the decrease rate of the current flowing through the soft switching coil, a forward current for compensating for the decrease in the recovery current flows through the first free wheel diode. As a result, the voltage between the input and output terminals fluctuates before the power switching element is turned on, which may become a noise source.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a control device for a power conversion circuit that can more appropriately turn on the power switching element.

  Hereinafter, means for solving the above-described problems and the operation and effect thereof will be described.

  The invention according to claim 1 is a power switching element, a first free wheel diode connected in parallel to an input / output terminal of the power switching element, and a second free wheel diode connected in series to the power switching element. A power switching circuit including a soft switching coil connected in parallel to the second freewheel diode, and a power conversion coil connected to a connection point of the power switching element and the second freewheel diode. A control device for a power conversion circuit that performs control to reduce the current flowing through the second freewheeling diode by flowing it through the soft switching coil, and that turns on the power switching element after the start of the control The second freewheel diode Based on the recovery flowing through the current begins to decay, characterized in that it comprises a switching means for switching the switching state of the power switching element in the ON state.

  When the recovery current flowing through the second freewheeling diode starts to attenuate, if the absolute value of the attenuation rate is larger than the absolute value of the decreasing rate of the current flowing through the soft switching coil, the recovery current decrease is compensated. Therefore, a forward current flows through the first freewheeling diode. For this reason, the voltage between the input terminal and output terminal of a power switching element is restrict | limited to about the voltage drop amount of a 1st freewheel diode. For this reason, by turning on a power switching element at this time, this on operation can be made into zero voltage switching.

  According to a second aspect of the present invention, in the first aspect of the present invention, the switching means causes a forward current to flow through the first freewheel diode as the recovery current flowing through the second freewheel diode decays. The switching state of the power switching element is switched to an on state during the period.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, voltage output means for applying a voltage to the soft switching coil, and opening / closing means for opening and closing a loop circuit including the voltage output means. The switching unit may further determine the start of attenuation of the recovery current based on the voltage across the switching unit.

  In the said invention, the electric current which was flowing into the 2nd freewheel diode can be sent through the coil for soft switching by applying a voltage to the coil for soft switching by making an opening-and-closing means into a closed state. Thereafter, a recovery current flows through the second free wheel diode, which further decreases and a forward current flows through the first free wheel diode, thereby reducing a current flowing through the soft switching coil. Thereafter, when the recovery current decreases, the voltage across the switching means also changes. For this reason, a decrease in the recovery current can be detected as a change in voltage across the switching means.

  The invention according to claim 4 is the invention according to claim 3, wherein the soft switching coil constitutes a secondary side coil of a transformer, and the switching means and the voltage are connected to the primary side coil of the transformer. The output means is connected.

  There is a correlation between the current flowing through the primary coil of the transformer and the current flowing through the secondary coil. On the other hand, the decrease timing of the current flowing through the primary coil (soft switching coil) of the transformer corresponds to the decrease timing of the recovery current. For this reason, in the said invention, the reduction | decrease of a recovery current is detectable by the change of the voltage of the both ends of an opening / closing means. Moreover, in the said invention, a switching means can be insulated with respect to the coil for soft switching by using a transformer. For this reason, even if the power switching element or the like constitutes a high voltage system insulated from the low voltage system, it becomes easy to operate the switching means in the low voltage system.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the second free wheel diode is a body diode of a super junction MOS field effect transistor.

  Superjunction MOS field effect transistors tend to increase the absolute value of the reduction rate of the recovery current of the body diode. For this reason, it is suitable when there exists suitably the effect of the said invention.

1 is a system configuration diagram according to a first embodiment. FIG. The circuit diagram which shows the switching control aspect concerning the embodiment. The time chart which shows the switching control aspect concerning the embodiment. The time chart which shows the effect of the embodiment. The time chart which shows the comparative example with the same embodiment. The system block diagram concerning 2nd Embodiment.

(First embodiment)
Hereinafter, a first embodiment in which a control device for a power conversion circuit according to the present invention is applied to a control device for a power conversion circuit of a hybrid vehicle will be described with reference to the drawings.

  FIG. 1 shows a system configuration according to the present embodiment.

  The illustrated high voltage battery 10 constitutes an in-vehicle high voltage system insulated from the in-vehicle low voltage system. The high voltage battery 10 is a power storage means for direct power supply of the in-vehicle main unit. The high voltage battery 10 is connected to the inverter 12 via the converter CV. The inverter 12 is a power conversion circuit for converting a DC voltage into a pseudo AC voltage and applying it to the in-vehicle main unit.

  The converter CV boosts the voltage (for example, “200 V”) of the high voltage battery 10 and applies a predetermined high voltage (for example, “500 V”) to the inverter 12. Further, converter CV steps down the voltage input from inverter IV and applies it to high voltage battery 10 when the rotating electrical machine connected to inverter IV is in a regenerative operation. A capacitor 14 is connected in parallel to the pair of input terminals of the converter CV, and a capacitor 16 is connected in parallel to the pair of output terminals of the converter CV.

  Converter CV includes a series connection body of main switching elements Q1, Q2 connected between a pair of output terminals. These main switching elements Q1, Q2 are N-channel power MOS field effect transistors. Specifically, these are super junction MOSFETs. Free wheel diodes FD1 and FD2 are connected in antiparallel to these main switching elements Q1 and Q2, respectively. These free wheel diodes FD1 and FD2 are body diodes of the main switching elements Q1 and Q2.

  A conversion coil L is connected between the connection point of the main switching elements Q1 and Q2 and the high voltage battery 10. In addition, a series connection body of a soft switching coil L1 and a diode D1 is connected in parallel to the main switching element Q1. In addition, a series connection body of a soft switching coil L2 and a diode D2 is connected in parallel to the main switching element Q2. Here, the soft switching coil L1 is magnetically coupled to the primary side coil L3 to form a transformer having a turn ratio of “1”. A drive circuit Dr1 is connected to the primary coil L3.

  The drive circuit Dr1 includes a power supply B3, a capacitor C3, and a diode 28 that are connected in parallel to the primary coil L3. Here, the diode 28 is connected in antiparallel to the power source B3. Further, the drive circuit Dr1 includes a switching element Q3 that opens and closes a loop circuit including the power source B3 and the primary coil L3. Here, the switching element Q3 is a power MOS field effect transistor and includes a body diode (diode D3). The diode D3 has a negative side of the power source B3 as an anode side. And the detection circuit 20 for detecting the voltage (detection value ds1) between these is connected to the input terminal and output terminal of switching element Q3.

  The soft switching coil L2 is magnetically coupled to the primary coil L4 to form a transformer having a turn ratio “1”. A drive circuit Dr2 is connected to the primary coil L4.

  The drive circuit Dr2 includes a power supply B4, a capacitor C4, and a diode 28 that are connected in parallel to the primary coil L4. Here, the diode 28 is connected to the power supply B4 in antiparallel. Further, the drive circuit Dr2 includes a switching element Q4 that opens and closes a loop circuit including the power source B4 and the primary side coil L4. Here, the switching element Q4 is a power MOS field effect transistor and includes a body diode (diode D4). The diode D4 has a negative side of the power source B4 as an anode side. And the detection circuit 20 for detecting the voltage (detection value ds2) between these is connected to the input terminal and output terminal of switching element Q4.

  The control device 30 generates operation signals MQ1 and MQ2 for operating the main switching elements Q1 and Q2 and operation signals Md1 and Md2 for operating the switching elements Q3 and Q4 based on the voltage detected by the detection circuit 20 and the like. Output.

  Hereinafter, the boosting process of the converter CV performed by the control device 30 will be described. FIG. 2 shows a circuit in which a portion in which current flows in each step of boosting processing in converter CV is specified. Below, it demonstrates for each mode shown in FIG.

(Mode 1)
This is a mode in which the main switching element Q1 is turned off, the main switching element Q2 is turned on, and the drive circuits Dr1 and Dr2 are both turned off. In this case, a current flows from the high voltage battery 10 through the conversion coil L to the main switching element Q2.

(Mode 2)
This is a mode in which the drive circuit Dr2 is turned on by turning off the main switching element Q2 and turning on the switching element Q4. When the main switching element Q2 is turned off, no current flows through the main switching element Q2, and a forward current flows through the free wheel diode FD2. When the drive circuit Dr2 is turned on, the voltage of the power source B4 is applied to the primary side coil L4 and the soft switching coil L2. Thereby, a current starts to flow through the soft switching coil L2, and the current gradually increases. Along with this, the forward current of the freewheeling diode FD2 gradually decreases. The current increase rate at this time is a value obtained by dividing the voltage of the power supply B4 by the leakage inductance between the primary side coil L4 and the soft switching coil L2. For this reason, since the increase rate of the current flowing through the switching element Q4 is also limited by the leakage inductance between the primary side coil L4 and the soft switching coil L2, switching of the switching element Q4 to the ON state is zero current switching (ZCS ). Note that the voltage between the input terminal and the output terminal of the switching element Q4 increases with an increase in the current flowing therethrough. Incidentally, it is desirable that the leakage inductance is smaller than the inductance of the conversion coil L.

(Mode 3)
This is a mode in which the recovery current flows through the freewheeling diode FD2 when the forward current flowing through the freewheeling diode FD2 gradually decreases and becomes zero. This recovery current flows through the soft switching coil L2. Note that the voltage between the input terminal and the output terminal of the switching element Q4 increases with an increase in the current flowing therethrough.

(Mode 4)
This is a mode in which the recovery current of the freewheel diode FD2 is reduced. The rate of decrease at this time is determined by the device of the freewheel diode FD2. In particular, when a super junction MOSFET is used as the main switching element Q2 as in the present embodiment, the reduction rate of the recovery current increases. On the other hand, the change in the current flowing through the soft switching coil L2 is limited by the leakage inductance between the primary coil L4 and the soft switching coil L2. For this reason, when the absolute value of the reduction speed of the recovery current of the freewheel diode FD2 is larger than the absolute value of the reduction speed of the current flowing through the soft switching coil L2 defined by the leakage magnetic flux, the soft switching coil L2 In order to compensate the flowing current, the free wheel diode FD1 is turned on, and a forward current flows. At this time, the high voltage of the capacitor 16 is applied to the diode D2 and the soft switching coil L2, and the current flowing through the soft switching coil L2 gradually decreases.

  In this mode, the voltage between the input terminal and the output terminal of the switching element Q4 also decreases and is clamped by the forward voltage drop amount of the diode D4.

(Mode 5)
This is a mode in which the main switching element Q1 is turned on by detecting a decrease in the recovery current of the freewheel diode FD2 through detection of a decrease in voltage between the input terminal and the output terminal of the switching element Q4. Thereby, the main switching element Q1 can be switched to the ON state during a period in which the forward current flows through the freewheel diode FD1. In this case, since the voltage between the input terminal and the output terminal of the main switching element Q1 is substantially zero (more precisely, the voltage drop amount of the free wheel diode FD1), zero volt switching (ZVS) can be realized. In addition, at this time, the increasing speed of the current flowing through the main switching element Q1 becomes a decreasing speed of the current flowing through the soft switching coil L2, and thus is limited by the leakage inductance of the soft switching coil L2 and the primary side coil L4. The For this reason, the ON operation of the main switching element Q1 is also zero current switching (ZCS).

(Mode 6)
This is a mode in which the switching element Q4 is switched to an OFF state when the current flowing through the switching element Q4 becomes zero. Thereby, the OFF operation of the switching element Q4 can be set to zero current switching (ZCS).

  FIG. 3 shows the boosting process. Specifically, the operating state of the main switching elements Q1, Q2, switching elements Q3, Q4, the voltage VQ1 between the input and output terminals of the main switching element Q1, the current IQ1 flowing through the main switching element Q1, the voltage VD2 of the freewheel diode FD2, Changes in the current ID2 flowing through the freewheeling diode FD2, the current ID1 flowing through the freewheeling diode FD1, the voltage VQ4 between the input and output terminals of the switching element Q4, the current IQ4 flowing through the switching element Q4, and the current IL flowing through the conversion coil L. Show.

  FIG. 4A shows the effect of this embodiment. This figure shows the voltage VQ2 between the input and output terminals of the main switching element Q2, the current IQ2 flowing through the main switching element Q2, the voltage VQ1, the main switching element Q1 between the input and output terminals of the main switching element Q1, and the freewheeling diode FD1. A transition of current and current flowing through the switching element Q4 is shown.

  As shown in the figure, according to the present embodiment, the main switching element Q1 is turned on when the forward current flows through the freewheeling diode FD1, so that the main switching element Q1 is set to zero current switching and zero volt switching. Can do.

  On the other hand, FIG. 4B shows a case of the conventional example. In this case, the recovery current of the freewheeling diode FD2 decreases, so that a forward current flows through the freewheeling diode FD1 and the voltage between the input and output terminals of the main switching element Q1 decreases. On the other hand, the input and output terminals of the main switching element Q2 The voltage in between increases. When the current flowing through the freewheel diode FD1 becomes zero, when the current flowing through the soft switching coil L2 is smaller than the current flowing through the conversion coil L, the freewheel diode FD2 is turned on again. As a result, the voltage between the input and output terminals of the main switching element Q1 increases, and the voltage between the input and output terminals of the main switching element Q2 decreases. In the figure, the rise and fall of the voltage between the input and output terminals of the main switching elements Q1 and Q2 are shown as the phenomenon of the period Td. In fact, the same phenomenon is caused until the main switching element Q1 is turned on. Will be repeated. This phenomenon causes noise.

  Further, when the main switching element Q1 is turned on when no forward current flows through the freewheeling diode FD1, the voltage between the input and output terminals of the main switching element Q1 is about the voltage of the capacitor 16, so that zero volt switching is performed. And turn-on loss occurs.

  In FIG. 5, as the free wheel diode FD2, the absolute value of the reduction rate of the recovery current is larger than the absolute value of the change rate of the current determined by the leakage inductance between the soft switching coil L2 and the primary coil L4 ( The case where the first recovery diode) is used is shown. Specifically, FIG. 5A shows a case where hard switching is performed without providing the soft switching coil L2, and FIG. 5B shows a case where zero current switching is performed with the soft switching coil L2. Show. 5B, in the case of FIG. 5B, the voltage fluctuation shown in FIG. 4B is suppressed (period T1 in the figure), and the main switching element Q1 is turned on when the main switching element Q1 is turned on. Although the increase rate of the current flowing through the switching element Q1 can be limited by the leakage inductance of the soft switching coil L2 and the primary side coil L4, since it is not zero volt switching, the turn-on loss cannot be ignored (period T2 in the figure).

  On the other hand, in this embodiment, the absolute value of the reduction rate of the recovery current of the freewheel diode FD2 is larger than the absolute value of the current change rate determined by the leakage inductance between the soft switching coil L2 and the primary coil L4. By using the above and using the period in which the forward current flows through the free wheel diode FD1, complete soft switching can be performed.

  Regarding the step-down process, in the above description, the description of any one of the main switching elements Q1, Q2, the freewheel diodes FD1, FD2, and the soft switching coils L1, L2 is replaced with the description of the other. Similarly, the ON operation of the main switching element Q2 can be set to zero volt switching and zero current switching.

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) The switching state of the main switching element Q1 (Q2) is switched to the on state based on the start of the decay of the recovery current flowing through the freewheel diode FD2 (FD1). Thereby, this ON operation can be made into zero voltage switching.

  (2) Based on the voltage across the switching element Q3 (Q4), the start of decay of the recovery current of the freewheel diode FD1 (FD2) was determined. Thereby, it is possible to appropriately determine a decrease in the recovery current.

  (3) The coils connected in parallel to the freewheel diodes FD1 and FD2 to perform soft switching are the soft switching coils L1 and L2 of the transformer. As a result, the switching elements Q3 and Q4 can be mounted in the low voltage system, and the voltage detecting means between these input / output terminals can be configured in the low voltage system.

  (4) Super junction MOS field effect transistors were used as the main switching elements Q1 and Q2. Thereby, since the freewheel diode FD1 (FD2) can be turned on as the recovery current of the freewheel diode FD2 (FD1) decreases, the control of the above embodiment can be suitably realized.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  FIG. 6 shows a system configuration diagram according to the present embodiment. In FIG. 6, members corresponding to those shown in FIG. 1 are given the same reference numerals for convenience.

  As shown in the figure, in this embodiment, the soft switching coils L1 and L2 connected in parallel to the freewheel diodes FD1 and FD2 are not used as the secondary coils of the transformer, but have magnetic coupling with other coils. Not a single coil. Then, the power sources B3 and B4 of the drive circuits Dr1 and Dr2 are connected in series to the soft switching coils L1 and L2. In this case, in order to output the operation signal of the switching elements Q3 and Q4 from the control device 30 and to transmit the detected values ds1 and ds2 between the input and output terminals of the switching elements Q3 and Q4 to the control device 30, Insulation means such as a coupler is used.

  It is assumed that the absolute value of the reduction rate of the recovery current of the free wheel diodes FD1 and FD2 according to the present embodiment is larger than the absolute value of the change rate of the current flowing through the soft switching coils L1 and L2. Incidentally, it is desirable that the inductances of the soft switching coils L1 and L2 are smaller than the inductance of the conversion coil L.

  Also according to the present embodiment described above, the effects (1), (2), and (4) of the first embodiment can be achieved.

(Other embodiments)
Each of the above embodiments may be modified as follows.

  The means for detecting a decrease in the recovery current flowing through the freewheel diodes FD1 and FD2 is not limited to that exemplified in the above embodiments. For example, the main switching element Q1 and the free wheel diode FD1, or the main switching element Q2 and the free wheel diode FD2 may be a means for connecting a shunt resistor in series and detecting a current based on the voltage drop.

  -It is not restricted to what is provided with a means to detect the reduction | decrease of the recovery current which flows into freewheel diode FD1, FD2, For example, you may estimate. This can be performed, for example, by performing an experiment or the like in advance and determining that the recovery current is decreased based on the elapse of a specified time from the start of energization of the soft switching coils L1 and L2. If this method is used, switching to the on operation of the main switching elements Q1 and Q2 is determined by time-controlling the dead time.

  The power MOS field effect transistor constituting the main switching elements Q1 and Q2 is not limited to the super junction MOSFET, and may be any power field effect transistor. Even in this case, if the absolute value of the reduction speed of the recovery current of the freewheel diodes FD1 and FD2 is large, the main switching elements Q1 and Q2 can be turned on as described in the above embodiments.

  The main switching elements Q1 and Q2 are not limited to those composed of power field effect transistors. For example, an insulating gate bipolar transistor may be used. Even in this case, if a free wheel diode connected in parallel to this has a large absolute value of the reduction rate of the recovery current, the main switching elements Q1 and Q2 are turned on as described in the above embodiments. It can be performed.

  In the first embodiment, the turn ratio between the soft switching coil L2 and the primary coil L4 is “1”, but the present invention is not limited to this.

  In the first embodiment, the turn ratio between the soft switching coil L1 and the primary coil L3 is “1”, but the present invention is not limited to this.

  In each of the above embodiments, the complementary switching in which the main switching elements Q1 and Q2 are alternately turned on / off except for the dead time when both are turned off is assumed. However, the present invention is not limited to this. For example, in the step-up process, only the main switching element Q1 may be turned on, and in the step-down process, only the main switching element Q2 may be turned on.

  The rectifying means connected in series to the soft switching coils L1, L2 is not limited to the diodes D1, D2. For example, a transistor such as a MOS field effect transistor or a thyristor may be used. Even in this case, the voltage applied to the series connection body of the main switching element Q1 (Q2) and the freewheel diode FD2 (FD1) is directly applied to the soft switching coils L1 and L2 by switching control. Means to avoid can be configured.

  In the above-described invention, the present invention is applied to the power converter for a hybrid vehicle. However, the present invention is not limited to this, and may be applied to, for example, an electric vehicle. Furthermore, the present invention is not limited to one that converts the voltage of power storage means (high voltage battery 10) for direct power supply to the in-vehicle main unit.

  DESCRIPTION OF SYMBOLS 10 ... High voltage battery, 12 ... Inverter, 20, 22 ... Drive circuit, 30 ... Control apparatus, Q1, Q2 ... Main switching element, CV ... Converter.

Claims (5)

A power switching element; a first freewheel diode connected in parallel to an input / output terminal of the power switching element; a second freewheel diode connected in series to the power switching element; and the second freewheel diode. And a soft switching coil connected in parallel to each other, and a power conversion circuit in which a power conversion coil is connected to a connection point of the power switching element and the second free wheel diode, the second free wheel diode In the control device of the power conversion circuit that performs control to reduce the current that has been flowing by flowing the current to the soft switching coil and that turns on the power switching element after the start of the control,
An apparatus for controlling a power conversion circuit, comprising: switching means for switching a switching state of the power switching element to an on state based on a start of attenuation of a recovery current flowing through the second free wheel diode.   The switching means turns on the switching state of the power switching element during a period in which a forward current flows through the first free wheel diode as the recovery current flowing through the second free wheel diode decays. 2. The control apparatus for a power conversion circuit according to claim 1, wherein switching is performed. A voltage output means for applying a voltage to the soft switching coil; and an opening / closing means for opening and closing a loop circuit including the voltage output means,
3. The control device for a power conversion circuit according to claim 1, wherein the switching unit determines the start of attenuation of the recovery current based on a voltage across the switching unit.   4. The soft switching coil constitutes a secondary coil of a transformer, and the switching means and the voltage output means are connected to the primary coil of the transformer. Power conversion circuit control device.   5. The power conversion circuit control device according to claim 1, wherein the second free wheeling diode is a body diode of a super junction MOS field effect transistor. 6.