JP6201447B2 - Power converter and control method of power converter - Google Patents

Description

  The present invention relates to a power converter and a method for controlling the power converter.

  Generally, a power converter is provided with a smoothing capacitor for smoothing a ripple component generated when DC power from a DC power source is converted into AC power. For this reason, when the supply of DC power from the DC power supply is stopped or the circuit to which the DC power is supplied is disconnected, it is necessary to discharge the charge stored in the smoothing capacitor for maintenance or the like. In Patent Document 1, two switching elements connected in series between a positive side and a negative side of a smoothing capacitor are simultaneously turned on, and the switching elements are turned off before an overcurrent occurs, so that residual charges are reduced. A method for discharging is disclosed.

JP 2009-232620 A

  However, in the method described in Patent Document 1, since the upper and lower switching elements are simultaneously turned on and discharged, the current flowing through the switching elements is limited to a predetermined current level or less so as not to destroy the switching elements. There is a problem that current detection means is required.

  An object of the present invention is to provide a technique for discharging charges accumulated in a charge accumulating means while preventing an excessive current from flowing through a switch means without requiring a current detecting means.

The power conversion device according to the present invention is connected in parallel with the first switch means, the second switch means connected in series with the first switch means, and the first switch means and the second switch means connected in series. Charge storage means, and control means for controlling the operation of the first switch means and the second switch means. The control means operates so that the first switch means and the second switch means are alternately turned on / off when discharging the charge accumulated in the charge storage means, and the control dead time is set to be normal. And a control period in which the first switch means and the second switch means are simultaneously turned on is generated .

  According to the present invention, the charge accumulated in the charge accumulating means is discharged by operating the first switch means and the second switch means so as to be alternately conducted / non-conducted. Therefore, it is possible to prevent an excessive current from flowing through the switch means.

FIG. 1 is a diagram illustrating a configuration of a power conversion device according to an embodiment. FIG. 2A is a diagram showing temporal changes in the control signals and drive signals of the switching elements Q1 and Q2 during the normal operation of the power converter, and FIG. 2B is the charge stored in the smoothing capacitor 3. FIG. It is a figure which shows the time change of the control signal of the switching elements Q1 and Q2 at the time of discharge of, and a drive signal. FIG. 3 is a diagram for explaining a difference in discharge time when the control dead time is changed. FIG. 4 is a diagram illustrating a difference in through current when the dead time in control is different. FIG. 5 is a flowchart illustrating a flow of a method for controlling the power conversion device according to the embodiment.

  FIG. 1 is a diagram illustrating a configuration of a power conversion device according to an embodiment. This power converter converts DC power from the DC power source 4 into AC power and supplies it to the three-phase AC motor 6. Further, AC power from the three-phase AC motor 6 can be converted to DC power and supplied to the DC power source 4. This power conversion device is mounted and used in an electric vehicle, for example. When mounted on an electric vehicle, the three-phase AC motor 6 serves as a drive source for the vehicle.

  The power conversion device according to the embodiment includes a plurality of switching elements Q1 to Q6, diodes D1 to D6 connected in antiparallel with the switching elements Q1 to Q6, and a drive circuit 1 that drives the switching elements Q1 to Q6. The control circuit 2 that transmits a control signal to the drive circuit 1 and the smoothing capacitor 3 are provided. Switching elements Q1-Q6 are IGBTs, for example.

  Switching elements Q1 and Q2 are connected in series, and the connection point of both switching elements Q1 and Q2 is connected to the U phase of three-phase AC motor 6. Switching elements Q3 and Q4 are connected in series, and the connection point of both switching elements Q3 and Q4 is connected to the V phase of three-phase AC motor 6. Switching elements Q5 and Q6 are connected in series, and the connection point of both switching elements Q5 and Q6 is connected to the W phase of three-phase AC motor 6.

  A smoothing capacitor 3 is connected in parallel with the switching elements Q1 and Q2 (Q3 and Q4, Q5 and Q6) connected in series. The smoothing capacitor 3 smoothes the DC voltage from the DC power supply 4.

  A relay switch 5 is provided between the smoothing capacitor 3 and the DC power supply 4, more specifically, on the positive electrode side of the DC power supply 4. The relay switch 5 is turned on / off based on a control signal from the control circuit 2.

  In the normal operation of the power conversion device, when switching control of the switching elements Q1 to Q6 is performed, the upper and lower switching elements are provided in order to prevent the upper switching element and the lower switching element from being simultaneously turned on and being short-circuited. There is a dead time in which both are turned off. Note that the normal operation time is a power conversion operation time other than the time of discharging the charge stored in the smoothing capacitor 3 described later.

  FIG. 2A is a diagram showing temporal changes in the control signals and drive signals of the switching elements Q1 and Q2 during the normal operation of the power conversion device. Here, the control of the switching elements Q1 and Q2 will be described, but the same applies to the switching elements Q3 and Q4 and the switching elements Q5 and Q6.

  The control signal is a signal transmitted from the control circuit 2 to the drive circuit 1 in order to control on / off of the switching elements Q1 to Q6. The drive signal is based on the control signal input from the control circuit 2. This signal is transmitted from the drive circuit 1 to each of the switching elements Q1 to Q6 in order to turn on / off the switching elements Q1 to Q6. Hereinafter, the control signal and the drive signal of the switching element Q1 are described as a Q1 control signal and a Q1 drive signal, and the control signal and the drive signal of the switching element Q2 are described as a Q2 control signal and a Q2 drive signal.

  A drive signal for operating the switching elements Q1 to Q6 is transmitted to the switching elements Q1 to Q6 by the drive circuit 1 that has received the control signal from the control circuit 2. However, in the drive circuit 1, operation delay occurs due to the presence of various electronic components. This operation delay time is called a delay time. The delay time from when the turn-on control signal is input to the drive circuit 1 until the turn-on drive signal is transmitted to the switching elements Q1 to Q6 is the turn-on delay time, and the turn-off control signal is the drive circuit. A delay time from when the signal is input to 1 to when the turn-off drive signal is transmitted to the switching elements Q1 to Q6 is referred to as a turn-off delay time.

In the example shown in FIG. 2A, the time from the time T2 when the Q1 control signal is turned on to the time T3 when the Q1 drive signal is turned _on is called a turn-on delay time td _(on). The time from the time T1 when the Q2 control signal is turned off to the time T2 when the Q2 drive signal is turned _off is referred to as a turn-off delay time td _(off) . The time from the time T1 when the Q2 control signal is turned off to the time T2 when the Q1 control signal is turned on and turned on is called a control dead time t _dead .

In order to provide a dead time during which the upper and lower switching elements are both turned off when switching the switching elements Q1 and Q2 on and off, a control dead time t _dead and a turn-on delay time t _{d ( on)} and the turn-off delay time t _{d (off)} , the relationship of the following equation (1) needs to be satisfied.
t _dead > t _{d (off)} −t _{d (on)} (1)

  When the relationship of Formula (1) is materialized, the upper and lower switching elements to be paired are not short-circuited.

When the supply of the DC power from the DC power supply 4 is stopped or the circuit to which the DC power is supplied is disconnected, it is necessary to discharge the charge stored in the smoothing capacitor 3 for maintenance or the like. In the present embodiment, when discharging the charge stored in the smoothing capacitor 3, the control dead time t _dead is made shorter than that during normal operation. More specifically, the control dead time t _dead at the time of charge discharge is set to satisfy the relationship of the following equation (2).
t _dead <t _{d (off)} −t _{d (on)} (2)

  When the relationship of Expression (2) is established, when the upper and lower switching elements that are paired are alternately turned on / off, a control period in which the upper and lower switching elements are simultaneously turned on is in a conductive state. . Since the control period in which the conduction state is established occurs while the switching elements are alternately turned on / off, the period does not become too long.

FIG. 2B is a diagram showing temporal changes in the control signals and drive signals of the switching elements Q1 and Q2 when the electric charge stored in the smoothing capacitor 3 is discharged. As is clear from FIG. 2A showing the control during normal operation, the control dead time t _dead during charge discharge is shorter than the control dead time t _dead during normal operation. Further, since the Q1 drive signal is turned from OFF to ON at time T4 and the Q2 drive signal is turned from ON to OFF at time T5, both the switching elements Q1 and Q2 are connected from time T4 to time T5. The conductive state is turned on, and a through current flows through the switching elements Q1 and Q2. Similarly, from time T6 when the Q2 drive signal is turned on to off until time T6 when the Q1 drive signal is turned on and off, the switching elements Q1 and Q2 are both in a conductive state in which they are turned on. A through current flows through elements Q1 and Q2.

FIG. 3 is a diagram for explaining a difference in discharge time when the control dead time t _dead is changed. In FIG. 3, t _dead1 is a value that satisfies the relationship of Equation (1), and t _dead2 and t _dead3 are values that _satisfy the relationship of Equation (2). In addition, t _dead1 , t _dead2 , and t _{dead3 satisfy} the relationship of the following equation (3).
t _dead3 <t _dead2 <t _dead1 (3)

When the relationship of formula (1) is established, the charge stored in the smoothing capacitor 3 is not discharged, but the switching operation is performed by the parasitic capacitances of the switching elements Q1 to Q6 and the diodes D1 to D6. When done, a small amount of through current flows. The discharge time for the dead time t _{dead1 in} FIG. 3 is due to this through current.

As shown in FIG. 3, as the control dead time becomes shorter in the order of t _dead1 , t _dead2 , t _dead3 , the discharge time of the charge stored in the smoothing capacitor 3 becomes shorter.

FIG. 4 is a diagram showing the difference in through current when the control dead time t _dead is different. In Figure 4, the dead time of the control is shown in the case of t _Dead1 satisfying the relation of Formula (1), the through current in the case of t _Dead3 satisfying the relationship of formula (2). As shown in FIG. 4, the through current in the case of the control dead time t _dead3 satisfying the relationship of the equation (2) is the through current in the case of the control dead time t _dead1 satisfying the relationship of the equation (1). It is considerably larger than that.

Here, in order to prevent the switching element from being destroyed by the through current flowing through the switching element during the discharge of the charge, the conduction state time in which the upper and lower switching elements are simultaneously turned on is set to be shorter than the short-circuit tolerance t _SC. To do. That is, the control dead time t _dead is defined so that the relationship of the following equation (4) is satisfied. Note that an appropriate value is set for the short-circuit tolerance t _SC by, for example, experiments.
| T _dead − (t _{d (off)} −t _{d (on)} ) | <t _SC (4)

By defining the control dead time t _dead so that the relationship of Expression (4) is established, it is possible to prevent the switching element from being destroyed by a through current during charge discharge.

  FIG. 5 is a flowchart illustrating a flow of a method for controlling the power conversion device according to the embodiment. The process starting from step S10 is performed by the control circuit 2.

  In step S10, it is determined whether or not a discharge operation is performed. For example, the discharge operation is performed at the timing when the supply of DC power from the DC power supply 4 is stopped, the timing when the circuit to which the DC power is supplied is disconnected, or the like. If it is determined that it is time to perform the discharge operation, the process proceeds to step S20.

In step S20, the control dead time t _dead is set to a value that satisfies the relationship of Expression (2).

In step S30, a control signal for turning on / off the upper and lower switching elements is transmitted to the drive circuit 1. The drive circuit 1 transmits a drive signal for alternately turning on / off the switching elements Q1 to Q6 based on the control signal. Since the control dead time t _dead is set so that the relationship of Expression (2) is established, the conductive state in which the upper and lower switching elements are simultaneously turned on at the time of control for alternately turning on and off the upper and lower switching elements. Therefore, the electric charge of the smoothing capacitor 3 is discharged.

  In step S40, it is determined whether or not the discharge is completed. For example, when a predetermined time has elapsed since the start of the discharge operation, it is determined that the discharge has been completed. If it is determined that the discharge has not been completed, the process returns to step S30 to continue the discharge operation. If it is determined that the discharge has been completed, the process of the flowchart is terminated.

On the other hand, if it is determined in step S10 that it is not time to perform the discharge operation, the process proceeds to step S50. In step S50, the control dead time t _dead is set to a value that satisfies the relationship of Expression (1). Thereafter, as a control during normal operation, when a control signal for turning on / off the upper and lower switching elements is transmitted to the drive circuit 1, the drive circuit 1 alternately switches the upper and lower switching elements based on the control signal. A drive signal for turning on / off is transmitted.

  As mentioned above, according to the power converter device in one embodiment, when discharging the electric charge accumulated in smoothing capacitor 3, switching elements Q1 and Q2 (Q3 and Q4, Q5 and Q6) are alternately turned on and off. To make it work. In the conventional method in which the upper and lower switching elements are simultaneously turned on to discharge the electric charge accumulated in the smoothing capacitor 3, current detection means is used to limit the current flowing through the switching elements to a predetermined current level or less. However, according to the power conversion device of the present embodiment, the electric charge is discharged by alternately turning on and off the upper and lower switching elements. No detection means is required. Further, in the conventional method for limiting the current flowing through the switching element to a predetermined current level or less, it takes time to discharge the residual charge. However, according to the power conversion device of this embodiment, the current flowing through the switching element is Since there is no need to limit the current level or less, the residual charge can be discharged quickly.

  According to the power conversion device in one embodiment, the control dead time when discharging the charge accumulated in the smoothing capacitor 3 is set shorter than the control dead time during normal operation. In particular, the control dead time is determined by changing the turn-off delay time when one of the upper and lower switching elements is switched from the conductive state to the non-conductive state, and when switching the other switching element from the non-conductive state to the conductive state. Set to a time shorter than the difference from the turn-on delay time. As a result, when controlling the upper and lower switching elements to be alternately turned on and off, the upper and lower switching elements are turned on at the same time and a through current flows, so that the residual charge can be quickly discharged only by changing the control method. it can.

  In addition, when discharging the electric charge accumulated in the smoothing capacitor 3, the operation of the switching element is controlled so that the time during which the upper and lower switching elements are in a conductive state simultaneously becomes a predetermined time or less. Thereby, it is possible to prevent the switching element from being destroyed by the through current during charge discharge.

  According to the power conversion device in one embodiment, when discharging the electric charge accumulated in the smoothing capacitor 3, the operation of alternately turning on and off the upper and lower switching elements is repeatedly performed. It can be performed.

  The present invention is not limited to the embodiment described above. For example, this power conversion device can be used by being mounted not only on an electric vehicle but also on a hybrid vehicle or a fuel cell vehicle, and can also be used for applications other than an automobile. Further, the structure of the power converter is not limited to the structure shown in FIG.

DESCRIPTION OF SYMBOLS 1 ... Drive circuit 2 ... Control circuit (control means)
3. Smoothing capacitor (charge storage means)
4 ... DC power supply Q1-Q6 ... Switching element (switch means)

Claims (5)

First switch means;
Second switch means connected in series with the first switch means;
Charge storage means connected in parallel with the first switch means and the second switch means connected in series;
Control means for controlling operations of the first switch means and the second switch means;
With
The control means operates to alternately turn on and off the first switch means and the second switch means when discharging the charge accumulated in the charge accumulation means, and to control dead time. Is set to be shorter than the control dead time during normal operation, and a control period in which the first switch means and the second switch means are simultaneously turned on is generated . The power conversion device according to claim 1 ,
The control means determines a control dead time when discharging the charge accumulated in the charge accumulation means, and switches one of the first switch means and the second switch means from a conduction state to a non-conduction state. A power conversion device characterized in that a time shorter than a difference between a turn-off delay time when switching to a state and a turn-on delay time when switching the other switch means from a non-conductive state to a conductive state is set. In the power converter device according to claim 1 or 2 ,
The control means is configured to discharge the charge accumulated in the charge accumulation means so that the first switch means and the second switch means are simultaneously turned on for a predetermined time or less. A power conversion apparatus for controlling operations of the switch means and the second switch means. In the power converter device according to any one of claims 1 to 3 ,
The control means causes the first switch means and the second switch means to repeatedly conduct / non-conduct an operation when discharging the charge accumulated in the charge accumulation means. Conversion device. A first switch means; a second switch means connected in series with the first switch means; a first switch means connected in series; and a charge storage means connected in parallel with the second switch means. A control method for a power conversion device provided,
When discharging the electric charge accumulated in the charge accumulating means, the first switch means and the second switch means are operated so as to be alternately conducted / non-conducted , and the control dead time is set to the normal operation time. A control method for a power converter , wherein the control period is set to be shorter than a control dead time and a control period in which the first switch means and the second switch means are simultaneously turned on is generated .