JP2011217583A - Dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC-DC converter which can reduce switching loss, and reduce surge current and ringing in a diode.SOLUTION: A DC-DC converter includes a first diode 52 interposed on an input/output line 22 to be closer to an output terminal 16 than a coil 30, a first switching element 40 and a second switching element 44 that are connected in parallel between the input/output line 22 and a reference potential line 20, and a control means 60. The control means 60 sets a time lag from when the first switching element 40 is turned ON until the second switching element 44 is turned ON to a short amount of time during a period in which the current flowing through the first diode 52 is small. The control means 60 sets the time lag to a long amount of time during a period in which the current is large. The control means 60 repeatedly switches between a state in which the first switching element 40 and the second switching element 44 are both turned ON and a state in which the first switching element 40 and the second switching element 44 are both turned OFF.

Description

  The present invention relates to a DC-DC converter that raises a potential input to an input terminal and outputs it to an output terminal.

  Patent Document 1 discloses a DC-DC converter that raises a potential input to an input terminal (where a positive terminal of a power supply is connected) and outputs the voltage to an output terminal. A coil and a diode (upper arm side diode) are interposed in an input / output line connecting the input end and the output end. The diode is interposed on the output end side from the coil, and the cathode is interposed in a direction facing the output end side. A switching element (lower arm side switching element) is connected between the input / output line between the coil and the diode and the reference potential line. When the switching element is turned on, a current flows from the input end to the reference potential line via the coil and the switching element. When the switching element is turned off, a potential obtained by adding the induction voltage of the coil to the potential of the input terminal is applied to the anode of the diode. Therefore, a current flows from the input end to the output end via the coil and the diode. As a result, a potential higher than the potential at the input end is output to the output end. By repeatedly turning on and off the switching element, a high potential can be output to the output terminal.

JP 2006-42536 A

  As described above, in the DC-DC converter, a forward current flows through the diode when the switching element is off. When the switching element is turned on in this state, a reverse voltage is applied to the diode. When a reverse voltage is applied to the diode while a forward current is flowing through the diode, a large reverse current (hereinafter referred to as a surge current) instantaneously flows through the diode. In addition, after a surge current flows, a phenomenon called ringing in which the current flowing in the diode fluctuates periodically occurs. In order to prevent malfunction of equipment, it is necessary to reduce surge current and ringing as much as possible.

The value of the forward current flowing through the diode varies depending on the state of the load connected to the output terminal. For example, when a motor is connected to the output terminal via an inverter, the current value of the forward current flowing through the diode is large during a period when the work amount of the motor is large. During the period when the work of the motor is small, the current value of the forward current flowing through the diode is small.
When the switching element is turned on in a state where the current flowing in the diode in the forward direction is large, surge current and ringing increase. On the other hand, when the switching element is turned on in a state where the current flowing in the diode in the forward direction is small, the surge current and ringing are not so high in the diode.

  The magnitude of the surge current and ringing generated when a reverse voltage is applied to the diode varies depending on the switching speed of the switching element. Large surge currents and ringing are generated when switching at high speed, whereas only small surge currents and ringing are generated when switching at low speed.

As described above, in the DC-DC converter, the magnitude of the surge current and ringing generated when a reverse voltage is applied to the diode differs depending on the magnitude of the current value flowing in the forward direction of the diode and the switching speed of the switching element.
In the conventional technology, in order to protect the elements and circuits, the switching speed of the switching elements is reduced so that surge current and ringing can be sufficiently reduced even when the switching elements are turned on in a state where a high current flows through the diodes. It was set.
However, when the current value flowing through the diode is low, even if the switching speed is increased, the surge current and ringing are not so high. That is, in the conventional DC-DC converter, since the current flowing through the diode is low, the switching speed is slowed down to the point where there is no problem even if the switching is performed at a high speed. .

  In the present specification, a technique for realizing a DC-DC converter capable of reducing switching loss and reducing diode surge current and ringing is disclosed in view of the above-described situation.

  As one method for solving the above-described problem, it is conceivable to directly detect the current value flowing in the diode and control the switching speed of the switching element based on the detected value. However, this requires extremely fast processing and is practically difficult. The DC-DC converter disclosed in this specification has the following configuration.

The DC-DC converter disclosed in the present specification raises the potential input to the input end and outputs it to the output end. This DC-DC converter includes an input / output line connecting between an input end and an output end, a coil, a first diode, a reference potential line, a first switching element, a second switching element, and a control means. Have. The coil is interposed in the input / output line. The first diode is interposed in the input / output line on the output end side from the coil, and is interposed in the direction in which the cathode faces the output end. The first switching element is connected between an input / output line between the coil and the first diode and a reference potential line. The second switching element is connected in parallel with the first switching element. In the first high current period in which the time period in which the current value flowing toward the output end of the coil is equal to or greater than the reference value continues, the control means is less than the reference value and the time period in which the current value is equal to or greater than the reference value. A time difference from when the first switching element is turned on to when the second switching element is turned on is set longer than a low current period in which the time zone is repeated, and both the first switching element and the second switching element are turned on. And the state where both the first switching element and the second switching element are turned off are alternately switched.
The diode is referred to as the first diode and the high current period is referred to as the first high current period in order to distinguish the second diode and the second high current period described later.

In a period in which the work load of the load connected to the output terminal is large, a high current period in which a large current flows through the coil. In the high current period, the time zone in which the value of the current flowing on the output end side of the coil is equal to or greater than the reference value continues. In a period in which the workload of the load connected to the output terminal is small, a low current period in which a small current flows through the coil. In the low current period, the time zone in which the value of the current flowing on the output end side of the coil is greater than or equal to the reference value and the time zone that is less than the reference value are repeated.
In this DC-DC converter, in the low current period, the time difference from when the first switching element is turned on to when the second switching element is turned on is set short. The time difference may be shortened to zero. It can be evaluated that the first switching element and the second switching element connected in parallel constitute one switching device by cooperation. Setting the time difference short can be evaluated as a state in which the switching speed of the switching device is high. By setting the time difference short, switching loss due to the first switching element and the second switching element can be suppressed to a small value. In addition, since the current flowing through the diode is small in the low current period, even if the voltage applied to the diode is switched to the reverse voltage at a rapid speed, no high surge current or ringing occurs.
On the other hand, in the high current period state, the time difference from when the first switching element is turned on to when the second switching element is turned on is set to be long. The switching speed of the switching device composed of the first switching element and the second switching element is reduced. As a result, the anode potential of the diode gradually decreases, and the voltage applied to the diode is switched to the reverse voltage relatively slowly. As a result, the occurrence of high surge current and ringing is suppressed.

Thus, in this DC-DC converter, the difference between the turn-on times of the two switching elements is changed in accordance with the state of the load within a range where high surge current and ringing do not occur. Switching loss can be minimized as long as high surge current and ringing do not occur.
Further, whether the current period is the high current period or the low current period can be specified based on the past value of the current flowing through the coil. That is, it can be specified prior to switching of the switching element whether the current period is a high current period or a low current period. Therefore, the difference in turn-on time between the two switching elements can be appropriately controlled.

  The above-described DC-DC converter can also be used as a step-down converter. In this case, a third switching element connected in parallel with the first diode, a fourth switching element connected in parallel with the third switching element, and a first switching element connected in parallel with the first switching element. Two diodes are added. The second diode is connected so that the cathode faces the input / output line. In this case, the control means turns on the third switching element in the second high current period in which the time period in which the value of the current flowing through the coil toward the input end is equal to or greater than the reference value continues from the low current period. The time difference from when the fourth switching element is turned on is set to be long, both the first switching element and the second switching element are on, and both the third switching element and the fourth switching element are off. And the state where both the first switching element and the second switching element are turned off and the state where both the third switching element and the fourth switching element are turned on are alternately switched.

According to such a configuration, when the load becomes a generator and the potential at the output end increases, the potential at the output end can be lowered and supplied to the input end. Thereby, the power supply connected to the input end can be charged.
Further, in this DC-DC converter, during the second high current period (a period in which a high current flows through the second diode), there is a time difference from turning on the third switching element to turning on the fourth switching element. Since it is set to be long, the anode potential of the second diode gradually decreases, and the voltage applied to the second diode is switched to the reverse voltage relatively slowly. As a result, the occurrence of high surge current and ringing by the second diode is suppressed.
On the other hand, in the low current period (period in which no high current flows through the second diode), the time difference from turning on the third switching element to turning on the fourth switching element is set short (may be simultaneous). Therefore, the switching loss of the third switching element and the fourth switching element is reduced. In this case, since the current flowing through the second diode is small, surge current and ringing do not increase.
This DC-DC converter also serves as a step-down converter, can reduce the switching loss in the third switching element and the fourth switching element, and suppresses surge current and ringing generated when a reverse voltage is applied to the second diode. The size can be suppressed.

In the above-described DC-DC converter, it is preferable that the control means determines whether or not the low current period is in accordance with the detected value of the current flowing through the coil.
According to this DC-DC converter, by detecting the current flowing through the coil, it is possible to accurately specify whether the current is in the high current period or the low current period and to control the switching element.

1 is a circuit diagram of a DC-DC converter 10. FIG. Graph showing the current I _L in the power running period. Graph showing the current I _L in the regeneration period. 1 is a circuit diagram of a DC-DC converter 10. FIG. Graph showing the current I _L in the zero crossing period. The flowchart which shows the process which determines time difference (DELTA) t1 and (DELTA) t2. The graph which shows the electric current _ID which flows through the diode at the time of reverse voltage application. 1 is a circuit diagram of a DC-DC converter 200. FIG. Graph showing the current I _L in the high current period. Graph showing the current I _L in the low-current period.

The features of the embodiments described below are listed first.
(Feature 1) The first diode is composed of a pair of diodes connected in parallel. One first diode and the first switching element are connected in parallel, the other first diode and the second switching element are connected in parallel, and both parallel circuits are connected in parallel.
(Feature 2) The second diode is composed of a pair of diodes connected in parallel. One second diode and the third switching element are connected in parallel, the other second diode and the fourth switching element are connected in parallel, and both parallel circuits are connected in parallel.
(Feature 3) The reference value is set to zero current.
(Feature 4) A resistor is inserted in series with the coil, and a voltage difference detection circuit for the resistor is provided.

  FIG. 1 is a circuit diagram of a DC-DC converter 10 according to the first embodiment. The DC-DC converter 10 boosts the voltage applied between the input terminal 12 and the input-side reference terminal 14 by the DC power source 26 and outputs the boosted voltage between the output terminal 16 and the output-side reference terminal 18. The DC-DC converter 10 is mounted on a hybrid car. The terminals 16 and 18 of the DC-DC converter 10 are connected to a hybrid car driving motor (not shown) via an inverter.

  A DC power supply 26 and a resistor 28 are connected in series between the terminals 12 and 14. The input side reference terminal 14 is connected to the output side reference terminal 18 by a ground line 20. The earth line 20 is grounded and maintained at the ground voltage. The earth line 20 can be referred to as a reference potential line. An input line 22 is connected to the input terminal 12. An output line 24 is connected to the output terminal 16. A coil 30 is interposed in the input line 22. Hereinafter, the input line 22 on the input terminal 12 side of the coil 30 is referred to as a first input line 22a, and the input line 22 on the opposite side of the input terminal 12 across the coil 30 is referred to as a second input line 22b. A current measuring resistor 36 is interposed in the first input line 22a. A capacitor 32 is connected between the first input line 22 a closer to the input terminal 12 than the resistor 36 and the ground line 20. Between the second input line 22b and the ground line 20, an IGBT 40 (embodiment of the third switching element), a diode 42 (embodiment of the second diode), an IGBT 44 (embodiment of the fourth switching element), and a diode 46 (an example of the second second diode) are connected in parallel to each other. The diodes 42 and 46 are connected so that the second input line 22b side becomes a cathode. Between the second input line 22b and the output line 24, an IGBT 50 (embodiment of the first switching element), a diode 52 (embodiment of the first diode), an IGBT 54 (embodiment of the second switching element), and a diode 56 (examples of the second first diode) are connected in parallel to each other. The diodes 52 and 56 are connected so that the output line 24 side becomes a cathode. A capacitor 34 is connected between the output line 24 and the earth line 20. Although not shown, a gate control circuit 60 is connected to the gates of the IGBTs 40, 44, 50 and 54. The gate control circuit 60 controls the gate voltage of each IGBT 40, 44, 50, 54.

The gate control circuit 60 includes a state where the IGBTs 40, 44 are on and the IGBTs 50, 54 are off (hereinafter referred to as a lower arm on state), and a state where the IGBTs 40, 44, 50, 54 are off (hereinafter, all off states). And the state in which the IGBTs 40 and 44 are off and the IGBTs 50 and 54 are on (hereinafter referred to as the upper arm on state) are repeatedly realized. More specifically, the gate control circuit 60 controls the IGBTs 40, 44, 50, and 54 so that the respective states are repeated in the order of the lower arm on state, the all off state, the upper arm on state, and the all off state. The gate control circuit 60 repeats one cycle consisting of the lower arm on state, the all off state, the upper arm on state, and the all off state at a constant cycle. Specifically, the period during which the lower arm is turned on is about 40 μsec, the period during which the next all-off state is set is about 10 μsec, and the period during which the upper arm is turned on is about 40 μsec, resulting in the next all-off state. The period is about 10 μsec. That is, the one cycle is repeated with a period of about 100 μsec.
The current path in the DC-DC converter 10 in each of the above states varies depending on the state of the motor connected to the DC-DC converter 10. Hereinafter, a current path in the DC-DC converter 10 in each period will be described.

(Powering period)
When the motor is working, it is a power running period in which power is supplied from the DC-DC converter 10 to the motor. Figure 2 is the power running period shows the variation of current I _L that flows toward the coil 30 to the output terminal 16. In the following description, the direction through the coil 36 from the first input line 22a toward the second input line 22b, a positive current I _L.

In the time zone T1 of FIG. 2, the gate control circuit 60 is in the lower arm on state. In the lower arm on state, the IGBTs 40 and 44 are turned on, so that the potential of the second input line 22 b becomes substantially equal to the potential of the earth line 20. Therefore, a reverse voltage is applied to the diodes 52 and 56. In the lower arm on state, current flows from the input terminal 12 toward the input side reference terminal 14 through the IGBTs 40 and 44 as indicated by an arrow 100 in FIG. Under-arm state, the induced voltage (in this case, current I _L and the voltage applied to the opposite direction) of the coil 30 so gradually decreases, the time period T1 in the current I _L in FIG. 2 is gradually increased.

In the time zone T2, the gate control circuit 60 is fully turned off. Then, the induced voltage of the coil 30 is applied in the direction of boosting the second input line 22b. Therefore, the potential of the second input line 22b rises to a potential obtained by superimposing the induction voltage of the coil 30 on the voltage of the DC power supply 26. As a result, the potential of the second input line 22 b becomes higher than the potential of the output line 24. Therefore, a current flows from the input terminal 12 toward the output terminal 16 through the diodes 52 and 56 as indicated by an arrow 102 in FIG. In the full off state, the induced voltage of the coil 30 (in this case, the voltage applied in the same direction as the current I _L) so gradually decreases, the current I _L as shown in the time zone T2 of Fig. 2 gradually decreases To do.

In the time zone T3 of FIG. 2, the gate control circuit 60 is in the upper arm on state. Also in this case, a current flows in the same manner as in the fully off state (see arrow 102 in FIG. 1), and the current _IL gradually decreases.

In the time zone T4 in FIG. 2, the gate control circuit 60 is fully turned off. Also in this case, a current flows as indicated by an arrow 102 in FIG. 1, and the current _IL gradually decreases. When the time zone T4 ends, the time zones T1 to T4 are repeated again.

As described above, in the powering period, a state in which current flows through the path indicated by the arrow 100 in FIG. 1 (time zone T1 in FIG. 2) and a state in which current flows through the path indicated by the arrow 102 in FIG. The time periods T2 to T4) are repeated. As a result, a voltage obtained by increasing the voltage of the DC power supply 28 is applied between the output terminal 16 and the output side reference terminal 18. As shown in FIG. 2, in the power running period, the current _IL is always zero or more.

(Regeneration period)
When the motor is operating as a regenerative brake (that is, when the motor is generating power), a regeneration period in which power is supplied from the motor to the DC power supply 26 is set. Figure 3 is the regeneration period, shows the change in the current I _L flowing through the coil 30.

In the time zone T5 of FIG. 3, the gate control circuit 60 is in the upper arm on state. In the upper arm on state, the IGBTs 50 and 54 are turned on, so that the potential of the second input line 22 b becomes substantially equal to the potential of the output line 24. Accordingly, a reverse voltage is applied to the diodes 42 and 46. In the regeneration period, the potential of the output line 24 is high. Therefore, current flows from the output terminal 16 toward the input terminal 12 through the IGBTs 50 and 54 as indicated by the arrow 104 in FIG. Accordingly, as shown in FIG. 3, the current I _L flowing through the coil 30 will be negative. The upper arm state, the induced voltage (in this case, the voltage applied to the current I _L in the opposite direction) of the coil 30 so gradually decreases, the current I _L gradually gradually the absolute value of the decrease (current I _L To increase.

In the time zone T6 in FIG. 3, the gate control circuit 60 is fully turned off. Then, the induced voltage of the coil 30 is applied in a direction to step down the second input line 22b. As a result, the potential of the second input line 22b becomes lower than the potential of the earth line 20. For this reason, as indicated by an arrow 106 in FIG. 4, a current flows from the input-side reference terminal 14 toward the input terminal 12 through the diodes 42 and 46. In the full off state, the induced voltage of the coil 30 (in this case, the voltage applied in the same direction as the current I _L) so gradually decreases, the current I _L as shown in the time zone T6 in FIG. 3 is increased gradually (absolute value of the current _{I L} decreases gradually) to.

In the time zone T7 of FIG. 3, the gate control circuit 60 realizes the lower arm on state. Again, (see arrow 106 in FIG. 4) current in the same manner as the whole OFF state to flow, current I _L increases gradually (absolute value gradually decrease in current I _L).

In the time zone T8 in FIG. 3, the gate control circuit 60 realizes the all-off state. Again, a current flows as indicated by an arrow 106 in FIG. 4, current I _L increases gradually (the absolute value of the current I _L decreases gradually) to. When the time zone T8 ends, the time zones T5 to T8 are repeated again.

As described above, in the regeneration period, a state in which current flows through the path indicated by the arrow 104 in FIG. 3 (time zone T5 in FIG. 3) and a state in which current flows through the path indicated by the arrow 106 in FIG. The time periods T6 to T8) are repeated. As a result, a voltage obtained by reducing the voltage between the terminals 16 and 18 is applied between the terminals 12 and 14. As a result, the DC power supply 26 is charged. As shown in FIG. 3, in the regeneration period, the current _IL is always less than zero.

(Zero cross period)
When the work amount of the motor is small, or when the motor is not working or generating power, the period of time during which the electric power moving between the DC-DC converter 10 and the motor is small is set. In this case, as shown in FIG. 5, the period in which the current _IL is positive and the period in which the current _IL is negative are alternately repeated. In this specification, such a period through which current I _L that zero crossing period.

In the time zone T9 of FIG. 5, the gate control circuit 60 is in the lower arm on state. In the time zone T9, a current flows as indicated by an arrow 100 in FIG. 1, and the current _IL gradually increases. In the time zone T10, the gate control circuit 60 is fully turned off. Then, a current flows as shown by an arrow 102 in FIG. In the time zone T11, the gate control circuit 60 is in the upper arm on state. Even in the time zone T11, current flows as shown by an arrow 102 in FIG. In the time zone T10, T11, current _{I L} is gradually reduced. Induced voltage (in this case, the voltage applied in the same direction as the current I _L) of the coil 30 in the time period T11 to decrease the potential of the second input line 22b becomes lower than the potential of the output line 24, FIG. 4 A current flows as indicated by an arrow 104. That is, as shown in the time zone T12 of FIG. 5, the current _IL is negative. At time period T12, the current _{I L} decreases gradually (the absolute value of the current _{I L} increases). In the time zone T13, the gate control circuit 60 is fully turned off. Then, current flows as shown by an arrow 106 in FIG. In the time zone T14, the gate control circuit 60 is in the lower arm on state. Also in the time zone T14, current flows as indicated by an arrow 106 in FIG. At time period T13, T14, current _{I L} increases gradually (the absolute value of the current _{I L} decreases). Induced voltage (in this case, the voltage applied in the same direction as the current I _L) of the coil 30 in the time period T14 to decrease the potential of the second input line 22b is higher than the potential of the output line 24, the time zone Return to the state of T9. In this way, the time periods T9 to T14 are repeated.

  As described above, in the zero cross period, the period in which current flows through the paths indicated by the arrows 100, 102, 104, and 106 is sequentially repeated.

In each state described above, when the diode is switched from the forward voltage application state to the reverse energization state, surge current and ringing occur in the diode. For example, in the powering period, the diodes 52 and 56 are switched from the forward voltage application state to the reverse voltage application state at the timing when the time zone T4 (all off state) is switched to the time zone T1 (lower arm on state). In the regeneration period, the diodes 42 and 46 are switched from the forward voltage application state to the reverse voltage application state at the timing when the time zone T8 (all off state) is switched to the time zone T5 (upper arm on state). The surge current and ringing generated at this time tend to increase as the current value flowing through the diode increases in the forward voltage application state. In powering period, the current value flowing through the diode 52 and 56 because (substantially equal current as the current _{I L} in the time zone T4 in FIG. 2) is large, the diode tends to occur surge current and ringing 52, 56. In the regeneration period, the value of the current flowing through the diode 42, 46 because (substantially equal to the current and the absolute value of the current I _L in the time zone T8 in FIG. 3) is large, easily occurs surge current and ringing diode 42, 46 . On the other hand, the zero-crossing period, as shown in FIG. 5, the current _{I L} is always less, a large current does not flow through diode 42,46,52,56. For this reason, high surge current and ringing do not occur in the diode. Therefore, the gate control circuit 60 changes the control method of the IGBTs 40, 44, 50, 54 according to the state of the DC-DC converter 10. Hereinafter, the control contents of the gate control circuit 60 will be described in detail.

The gate control circuit 60, by detecting the voltage across the resistor 36, detects the current I _L. The gate control circuit 60 repeatedly detects the current I _L at short time intervals. As described above, the gate control circuit 60 performs control in the order of the upper arm on state, the all off state, the lower arm on state, and the all off state. The gate control circuit 60 repeats the detection of the current I _L over a plurality of times during one cycle, and stores the detection values of the detected current I _L. For example, if the current is in upper arm state stores each detected value of the current I _L has been detected between the arm ON state over the last until now. The gate control circuit 60, based on the respective detected values of the current I _L which stores and performs control according to the flowchart shown in FIG.

In step S2, from the respective detected values of the current I _L which is stored, the absolute value of which is the detected value is a minimum is identified. Then, it is determined whether or not the absolute value of the identified detection value is greater than or equal to the threshold value _ILTH . Threshold I _LTH is the value of the current I _L that can be regarded as substantially zero, and is set in consideration of noise or measurement error and the like. As shown in FIG. 5, when in the zero crossing period is the minimum value of the absolute value of the current I _L is zero. If it is in the zero cross period, NO is determined in step S2, and time differences Δt1 and Δt2 are set to 0 nsec in step S4. The time differences Δt1 and Δt2 will be described in detail later.

In step S6, it is determined whether the most recently detected current _IL is positive or negative.
If it is in the power running period, YES is determined in step S6. In this case, in step S8, the time difference Δt1 is set to 50 nsec, and the time difference Δt2 is set to 0 nsec.
On the other hand, if it is in the regeneration period, NO is determined in step S6. In this case, in step S10, the time difference Δt1 is set to 0 nsec, and the time difference Δt2 is set to 50 nsec.
The gate control circuit 60 repeatedly executes the process of FIG. 6 at a predetermined cycle, and sets the time differences Δt1 and Δt2 according to the state of the DC-DC converter 10 (powering period, regeneration period, or zero cross period). Note that the process of FIG. 6 may be executed for each cycle, or may be executed at an interval longer than the one cycle. When it is performed once in a plurality of cycles, in step S2, the determination may be made based on the minimum value in the immediately preceding cycle, or may be determined based on the minimum value in the plurality of cycles.

  The time difference Δt1 described above means a time difference from when the IGBT 40 is turned on to when the IGBT 44 is turned on when switching from the fully off state to the lower arm on state. The time difference Δt2 means a time difference from when the IGBT 50 is turned on to when the IGBT 54 is turned on when switching from the fully off state to the upper arm on state.

As described above, the time difference Δt1 is set to 50 nsec in the powering period. Therefore, when switching from the fully off state to the lower arm on state, the IGBT 44 is turned on 50 nsec after the IGBT 40 is turned on. For this reason, compared with the case where IGBT40 and IGBT44 turn on simultaneously, the fall rate of the electric potential of the 2nd input line 22b becomes small. As a result, when switching from the fully off state to the lower arm on state, the rate of decrease dI _D / dt of the current _ID flowing through the diodes 52 and 56 decreases. FIG. 7 shows changes in the current _ID flowing through the diodes 52 and 56 when switching from the fully off state to the lower arm on state. Graph A1 shows the current I _D in the case where the time difference Δt1 between 0 nsec, the graph A2 shows the current I _D in the case where the time difference Δt1 between 50 nsec. As shown in FIG. 7, when the time difference Δt1 is 50 nsec, the rate of decrease _{ID d D} / dt of the current _ID at the time of switching is smaller than when the time difference Δt1 is 0 nsec (the gradient at which the current decreases gradually). Become). As a result, the surge current Is generated after switching is reduced (that is, the absolute value of the surge current Is is reduced), and the ringing amplitude after the surge current Is is also reduced. As described above, during the power running period, a time difference is provided in the turn-on timing of the IGBT 40 and the IGBT 44, thereby suppressing high surge current and ringing in the diodes 52 and 56.

  In the regeneration period, the time difference Δt2 is set to 50 nsec. Therefore, when switching from the fully off state to the upper arm on state, the IGBT 54 is turned on 50 nsec after the IGBT 50 is turned on. For this reason, compared with the case where IGBT50 and IGBT54 turn on simultaneously, the raise rate of the electric potential of the 2nd input line 22b becomes small. This suppresses the occurrence of high surge current and ringing in the diodes 42 and 44 when switching from the fully off state to the upper arm on state. As described above, in the regeneration period, a difference in the turn-on timing of the IGBT 50 and the IGBT 54 is provided, so that a high surge current and ringing in the diodes 42 and 46 are suppressed.

  On the other hand, in the zero cross period, the time differences Δt1 and Δt2 are set to 0 nsec. Therefore, IGBT 40 and IGBT 44 are turned on substantially simultaneously when switching from the fully off state to the lower arm on state, and IGBT 50 and IGBT 54 are turned on substantially simultaneously when switching from the fully off state to the upper arm on state. In the zero crossing period, no high current flows through the diodes 42, 46, 52, and 56. Therefore, even if the potential of the second input line 22b changes suddenly at the time of switching, high surge current and ringing do not occur in the diode. In addition, by making the IGBT turn-on timing substantially the same as described above, it is possible to reduce the switching loss generated in the IGBT.

  As described above, in the DC-DC converter 10 of the present embodiment, between the IGBTs connected in parallel depending on whether the DC-DC converter 10 is in the power running period, the regeneration period, or the zero-cross period. The turn-on time difference is changed. In the power running period and the regeneration period in which surge current and ringing are likely to occur in the diode, the surge current and ringing are suppressed by shifting the turn-on timing of the IGBTs connected in parallel. Further, in the zero cross period in which the surge current and ringing are unlikely to occur in the diode, the switching loss is reduced by making the turn-on timings of the IGBTs connected in parallel substantially. According to the DC-DC converter 10, surge current and ringing exceeding a predetermined value are not generated, and switching loss can be reduced as compared with the conventional case.

In the first embodiment described above, the control circuit 60, based on upper arm state, the whole OFF state, the lower arm ON state, the respective detected values of the current I _L in one cycle of consisting of whole OFF state, DC-DC The state of converter 10 (that is, whether it is a power running period, a zero cross period, or a regeneration period) was determined. In this way, based on the current I _L in at least one cycle, it is possible to accurately determine the state of the DC-DC converter 10.
Incidentally, on the basis of the current I _L during a period greater than one cycle, it may determine the state of the DC-DC converter 10. However, if too long a period for use in the determination of the state, when the absolute value of the current I _L at the beginning of the period is less than the threshold value I _LTH absolute value of the current I _L is increased during that period Until then, there is a risk of being determined to be a zero-cross period. Therefore, the absolute value of the current I _L in the first period for the determination is less than the threshold value I _LTH, the maximum current I _L in the subsequent even current I _L is increased at a maximum rate of increase, during the period for determination The length of the determination period needs to be set so that the value becomes an appropriate current value (that is, a current value that does not cause excessive surge current or ringing). Maximum value of the increase rate of the current I _L is determined by the characteristics of the circuit.
In the first embodiment described above, to determine the state of the DC-DC converter 10 based on the minimum value of the absolute value of the current I _L during the period for determination, determines the state based on the other values May be. For example, it may be determined the status based on the maximum value or the average value of the current I _L during the period for determination.

  The correspondence between the above-described components of the first embodiment and the components of the claims will be described. The input line 22 and the output line 24 correspond to embodiments of input / output lines in the claims. Diodes 52 and 56 are embodiments of the first diode of the claims. One of the diodes 52 and 56 can be omitted. The IGBT 40 is an embodiment of the first switching element of the claims. The IGBT 44 is an embodiment of the second switching element of the claims. Diodes 42 and 44 are embodiments of the second diode of the claims. One of the diodes 42 and 46 can be omitted. The IGBT 50 is an embodiment of the third switching element of the claims. The IGBT 54 is an embodiment of the fourth switching element of the claims. The power running period is an example of the first high current period in the claims, the zero cross period is an example of the low current period in the claims, and the regeneration period is an example of the second high current period in the claims.

(Second embodiment)
In the first embodiment described above, the DC-DC converter capable of a regenerative state (a state in which a DC power source is charged when the motor is performing a regenerative operation) has been described. However, the above technique can also be applied to a DC-DC converter that cannot realize the regenerative state.

FIG. 8 shows a circuit diagram of the DC-DC converter 200 of the second embodiment. The DC-DC converter 200 has a configuration in which the IGBTs 50, 54 and the diodes 42, 46, 52 are removed from the DC-DC converter 10 of the first embodiment.
The gate control circuit 60 controls the IGBTs 40 and 44 so that the on state in which the IGBTs 40 and 44 are turned on and the off state in which the IGBTs 40 and 44 are turned off are alternately repeated.

Figure 9 shows the variation of current I _L when the motor is working. In the ON state shown in the time zone T15, current flows from the input terminal 12 toward the input side reference terminal 14 through the IGBTs 40 and 44, as indicated by an arrow 202 in FIG. In this case, current _{I L} increases gradually. When switched to the OFF state in the time zone T2, the potential of the second input line 22b rises due to the induced voltage of the coil 30. Therefore, current flows from the input terminal 12 toward the output terminal 16 through the diode 56 as indicated by an arrow 204 in FIG. In this case, as shown in the time zone T2 of FIG. 9, the current _IL gradually decreases. When the motor is working, as shown in FIG. 9, the first high current period in which the current _IL is always zero or more is set. Since a high current flows through the diode 42 in the first high current period, surge current and ringing are likely to occur in the diode 42 when switching from the off state to the on state (that is, when a reverse voltage is applied to the diode 42). .

Figure 10 shows the variation of current I _L when the workload of the motor is small. In this case, the potential of the output terminal 16 is already high. In this case, a current flows as indicated by an arrow 202 in FIG. 8 is in the on state, current I _L as shown in the time zone T17 in FIG. 10 gradually increases. When switched to the OFF state at time zone T18, the potential of the second input line 22b rises due to the induced voltage of the coil 30, and a current flows as shown by an arrow 204 in FIG. However, since the potential of the output terminal 16 is already high, the anode potential of the diode 42 becomes lower than the potential of the output terminal 16 when the induced voltage of the coil 30 decreases. As a result, no current flows through the diode 42, and the current _IL becomes substantially zero. When the motor is not working, as shown in FIG. 10, a period in which the current _IL is greater than zero and a period in which the current is substantially equal to zero are repeated. Since a high current does not flow through the diode 42 in the low current period, no surge current and ringing occur in the diode 42 even when switching from the off state to the on state.

In the DC-DC converter 200 of the second embodiment, the gate control circuit 60 repeatedly detects the current I _L at short time intervals, the current is detected several times during one cycle from the ON state to the OFF state I _L Each detected value is stored. Then, among the detected values of the current I _L stored therein, the detection value absolute value is minimum is specified. When the absolute value of the identified detection value is equal to or greater than the threshold value _ILTH (that is, in the first high current period), the time difference Δt1 is set to 50 nsec. Therefore, when switching from the off state to the on state, the IGBT 44 is turned on 50 nsec after the IGBT 40 is turned on. Thus, since the turn-on timings of the IGBTs 40 and 44 are shifted during the first high current period, the occurrence of high surge current and ringing in the diode 56 is suppressed.
Further, when the absolute value of the identified detected value (detected value of the minimum absolute value) is smaller than the threshold value I _LTH (i.e., when a low current period), the time difference Δt1 is set to 0 nsec. Therefore, when switching from the off state to the on state, the IGBT 40 and the IGBT 44 are turned on substantially simultaneously. Thus, in the low current period in which surge current and ringing are unlikely to occur in the diode 56, the IGBT 40 and the IGBT 44 are turned on substantially simultaneously, so that the switching loss is reduced.

  In the first and second embodiments described above, IGBTs are used as switching elements, but other switching elements such as MOS-FETs may be used.

  Also, the type of diode used in the first and second embodiments is not particularly limited. For example, a Schottky barrier diode using a wide band gap semiconductor material such as SiC or GaN may be used. Such diodes can significantly reduce surge currents compared to Si PiN diodes, but are susceptible to high amplitude ringing. When a Schottky barrier diode such as SiC or GaN is used in the above-described embodiment, switching loss can be reduced while mainly suppressing ringing. Further, when the Si PiN diode is used in the above-described embodiment, the switching loss can be reduced while mainly suppressing the surge current.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

10: DC-DC converter 12: input terminal 16: output terminal 20: earth line 22: input line 24: output line 26: DC power supply 28: resistor 30: coil 32: capacitor 34: capacitor 36: resistor 40: IGBT
42: Diode 44: IGBT
46: Diode 50: IGBT
52: Diode 54: IGBT
56: Diode 60: Gate control circuit

Claims (3)

A DC-DC converter that raises the potential input to the input terminal and outputs it to the output terminal.
An input / output line connecting the input end and the output end;
A coil interposed in the input / output line;
A first diode having a cathode disposed in an input / output line on the output end side of the coil so that the cathode faces the output end;
A reference potential line;
A first switching element connected between an input / output line between the coil and the first diode and a reference potential line;
A second switching element connected in parallel with the first switching element;
Control means,
Have
In the first high current period in which a time period in which a current value flowing toward the output end side of the coil is equal to or higher than a reference value continues, the control means A time difference from when the first switching element is turned on to when the second switching element is turned on is set longer than a low current period in which a certain period of time is repeated, and both the first switching element and the second switching element are turned on. A DC-DC converter characterized by alternately switching between a state in which the first switching element and the second switching element are turned off. A third switching element connected in parallel with the first diode;
A fourth switching element connected in parallel with the third switching element;
A second diode having a cathode connected in parallel with the first switching element and facing the input / output line;
In addition,
In the second high current period in which the time period in which the current value flowing toward the input end side of the coil is equal to or greater than the reference value continues, the control means turns on the third switching element from the low current period and then turns on the third switching element. A time difference until the four switching elements are turned on is set long, both the first switching element and the second switching element are turned on, and both the third switching element and the fourth switching element are turned off; 2. The state in which both the first switching element and the second switching element are turned off and the state in which both the third switching element and the fourth switching element are turned on are alternately switched. DC-DC converter.   3. The DC-DC converter according to claim 1, wherein the control unit determines whether or not the low current period is based on a detection value of a current flowing through the coil. 4.

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