JP6950353B2 - Power converter controller - Google Patents

Description

The present invention relates to a control device for a power converter.

Conventionally, a power converter including an inductor and a switch for controlling the storage of electric power in the inductor is known. In the power converter, when the switch is turned on, power is stored in the inductor, and when the switch is turned off, the power stored in the inductor is output to the power supply target.

A short-circuit failure may occur in which the switch of the power converter is kept on. If a short-circuit failure occurs in the switch, the inductor may become magnetically saturated, and in some cases, an overcurrent may flow in the power converter.

Patent Document 1 discloses a control device that detects a current flowing through a switch connected in series with an inductor and compares the current detection result with an overcurrent threshold value to determine whether or not an overcurrent state is present. There is.

Patent Gazette No. 6002465

The rate of increase of the current flowing through the switch when a short-circuit failure occurs in the switch is determined by the input voltage supplied from the power source, the combined resistance of the electric path from the power source to the inductor, and the like. Therefore, even if a short-circuit failure occurs in the switch when the input voltage is low, the rate of increase of the current flowing through the switch may not increase. Therefore, in the control device described in Patent Document 1, the timing at which the current detection result exceeds the overcurrent threshold value may be delayed, and a short-circuit failure of the switch may not be determined quickly. A similar problem may occur even when the current flowing through the switch is maintained at a value lower than the normal value.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a control device for a power converter capable of quickly determining whether a short-circuit failure of a switch has occurred.

In order to solve the above problems, the present invention comprises an inductor that stores electric power to be supplied to a power supply target, and an inductor that stores electric power in the inductor by power supply from a power source and is turned off by being turned on. The present invention relates to a control device applied to a power converter including a switch for outputting the electric power stored in the inductor and a current detection unit for detecting a current flowing through the switch. The control device includes a switch control unit that outputs an operation signal including an on operation command that controls the switch to the on state and an off operation command that controls the switch to the off state, and a detection value and a predetermined value of the current detection unit. Based on the comparison with the overcurrent threshold value of, the overcurrent determination unit that determines the overcurrent state in which the overcurrent is flowing in the switch, the main short-circuit threshold value smaller than the overcurrent threshold value, and the operation signal. It is provided with a short-circuit determination unit for determining that a short-circuit failure of the switch has occurred based on a comparison with a detection value of the current detection unit during the period in which is the off operation command.

In a power converter in which the power stored in the inductor is output to the power supply target when the switch is turned off, no current flows through the switch during the period when the switch is turned off. Here, if a short-circuit failure occurs in the switch, the on state of the switch is continued and the current continues to flow in the switch even during the period of the off operation command of the operation signal. Therefore, a state in which a current is continuously flowing through the switch during the period when the operation signal is an off operation command is a state in which a short-circuit failure has occurred in the switch.

In the first invention, it is determined that a short-circuit failure of the switch has occurred based on the comparison between the main short-circuit threshold value and the detected value of the current detection unit in the period including the period in which the operation signal is the off operation command. In this case, since it is sufficient to determine that the current is flowing during the period of the off operation command, it is not necessary to determine the magnitude of the current value, and the main short circuit threshold for determining the short circuit failure of the switch is the overcurrent threshold. Can be smaller than. Therefore, according to the first invention, it is quickly determined that a short-circuit failure of a switch has occurred even when the rate of increase of the current flowing through the switch does not increase when a short-circuit failure of the switch occurs. be able to.

Here, the first invention can be embodied as in the second invention, for example. In the second invention, when the short-circuit determination unit determines that the period during which the detection value of the current detection unit becomes larger than the main short-circuit threshold value is longer than the period during which the operation signal becomes the on operation command. , It is determined that a short-circuit failure of the switch has occurred.

Further, the first invention can be embodied as in the third invention, for example. In the third invention, a state determination unit for determining whether the operation signal is the off operation command or the on operation command is provided, and the short circuit determination unit is provided with the operation signal by the state determination unit. When it is determined that the detection value of the current detection unit is larger than the main short-circuit threshold value in the period when the off operation command is determined, it is determined that a short-circuit failure of the switch has occurred.

In the fourth invention, the short-circuit determination unit determines that a short-circuit failure has occurred in the switch even when the detection value of the current detection unit exceeds the sub-short-circuit threshold value larger than the main short-circuit threshold value.

Due to a short-circuit failure of the switch, the current rising speed of the current flowing through the switch may be higher than the current rising speed assumed in the second invention. When the current rise rate is large, it is better to judge the short circuit failure in a shorter time than the judgment using the main short circuit threshold value. Therefore, in the fifth invention, it is determined that a short-circuit failure occurs in the switch even when the detected value of the current detection unit exceeds the sub-short-circuit threshold value larger than the main short-circuit threshold value. In this case, when the current rise rate is large, the short-circuit failure is determined, so that the short-circuit failure can be determined quickly.

A fifth invention includes a stop control unit that stops power supply from the power source to the inductor when the short-circuit failure is determined.

When a short-circuit failure occurs in a switch, a continuous current flows through the power converter, which may cause the elements constituting the power converter to become overheated and deteriorate the power converter. In this regard, in the above configuration, when a short-circuit failure is determined, the power supply from the power source to the inductor is stopped. In this case, it is possible to prevent the current from continuously flowing, and it is possible to prevent the power converter from deteriorating.

In the sixth invention, in the power converter, a capacitor is connected in parallel to the inductor in an input side electric path for supplying power from the power source to the inductor, and the power source feeds the inductor to the inductor. A start determination unit for determining the start is provided, and the short-circuit determination unit determines that the short-circuit failure has occurred within a predetermined period after the start of power supply is determined by the start determination unit.

In order to stabilize the input voltage supplied to the inductor, a configuration in which a capacitor is connected in parallel to the inductor in the input side electric path may be adopted. In this case, since the capacitor is installed immediately after the start of power supply, the input voltage supplied to the inductor gradually increases. Therefore, immediately after the start of power supply, the current value flowing through the switch becomes a low value. From the viewpoint of quickly determining a short-circuit failure, it is desirable to be able to determine the short-circuit failure at the same time as the start of power supply. Therefore, in the sixth invention, it is determined that a short-circuit failure has occurred within a predetermined period after the start of power supply from the power source to the inductor is determined. In this case, the short-circuit failure can be quickly determined after the power supply is started.

Configuration diagram of the power converter. A timing chart explaining the operation of the power converter. A timing chart explaining the operation of the power converter. A flowchart illustrating a short circuit protection process. The figure explaining the effect of a power conversion device. The figure explaining the effect of a power conversion device. The flowchart explaining the short circuit protection process which concerns on 2nd Embodiment. The block diagram of the power conversion apparatus which concerns on 3rd Embodiment.

(First Embodiment)
Hereinafter, embodiments that embody the control device of the power converter will be described with reference to the drawings. FIG. 1 is a configuration diagram of a power conversion device 90 including a control device according to the present embodiment.

The power converter 90 includes a power converter 10 that converts the power supplied from the DC power source 100 as a power source. The positive electrode terminal of the DC power supply 100 as a power source is connected to the input terminal Ti on the input side of the power converter 10, and the power supply target is connected to the output terminals To1 and To2 on the output side. The negative electrode terminal of the DC power supply 100 is connected to the ground. In the present embodiment, the power converter 10 is a flyback converter that raises and lowers the voltage Vb between terminals of the DC power supply 100 to supply power to the power supply target. For example, the power supply target is a drive circuit of a switch constituting a three-phase inverter.

The power converter 10 includes a primary side circuit 11 connected to a DC power supply 100 through an input terminal Ti, a secondary side circuit 30 connected to a power supply target through output terminals To1 and To2, and primary side circuits 11 and 2. A transformer 20 for connecting to the next circuit 30 is provided. The DC power supply 100 and the input terminal Ti are connected by a power supply line 110 such as a harness member.

The primary side circuit 11 includes an input side electric path L1, an input side coil 12, a first capacitor 13, a load switch 14, a second capacitor 15, a drive switch 50, and a current detection circuit 60. There is.

An input terminal Ti is connected to the first end of the input side electric path L1. The first end of the primary coil 21 of the transformer 20 is connected to the second end of the input side electric path L1. An input side coil 12 is provided in the input side electric path L1. A load switch 14 is provided between the input side coil 12 and the primary coil 21 in the input side electric path L1. The first end of the first capacitor 13 is connected between the input side coil 12 and the load switch 14 in the input side electric path L1. The second end of the first capacitor 13 is connected to the ground.

In the present embodiment, the load switch 14 is composed of a P-channel MOSFET. The source of the load switch 14 is connected to the input side coil 12, and the drain of the load switch 14 is connected to the primary coil 21. Further, the source of the load switch 14 and the gate are connected through the resistor R1. When the load switch 14 is closed, power can be supplied from the DC power supply 100 to the primary coil 21. Further, when the load switch 14 is opened, it is impossible to supply power from the DC power supply 100 to the primary coil 21.

The first end of the second capacitor 15 is connected between the load switch 14 and the primary coil 21 in the input side electric path L1. The second end of the second capacitor 15 is connected to the ground. The second capacitor 15 is connected in parallel to the primary coil 21 of the transformer 20 in the input side electric path L1.

The drive switch 50 is a switch for controlling the electric power stored in the transformer 20. In the present embodiment, the drive switch 50 is composed of an N-channel MOSFET. The primary coil 21 is connected to the drain of the drive switch 50, and the first end of the current detection circuit 60 is connected to the source. The second end of the current detection circuit 60 is connected to the ground. During the period when the load switch 14 is in the closed state, the drive switch 50 is in the closed state (on state), so that a closed circuit including the DC power supply 100, the input side electric path L1 and the primary coil 21 is formed, and the closed circuit is formed. Current flows through the circuit.

The current detection circuit 60 detects the current value flowing through the drive switch 50 through the primary coil 21 of the transformer 20 as the current detection value CS. In this embodiment, the current detection circuit 60 is composed of a shunt resistor. The primary coil 21 of the transformer 20 corresponds to an inductor.

The transformer 20 further includes a secondary coil 22 connected to the secondary circuit 30. Magnetic energy is stored in the transformer 20 by the voltage supplied from the primary circuit 11 to the primary coil 21.

The secondary circuit 30 supplies the electric power output from the secondary coil 22 of the transformer 20 to the power supply target. The secondary side circuit 30 includes a first output side electric path L2, a second output side electric path L3, a diode 31, and a smoothing capacitor 32. The first end of the secondary coil 22 is connected to the first end of the first output side electric path L2, and the first output terminal To1 is connected to the second end of the first output side electric path L2. .. A diode 31 is provided in the first output side electric path L2. The anode of the diode 31 is connected to the secondary coil 22, and the cathode is connected to the first output terminal To1. The second end of the secondary coil 22 is connected to the first end of the second output side electric path L3, and the second output terminal To2 is connected to the second end of the second output side electric path L3. .. The smoothing capacitor 32 is connected between the first output side electric path L2 and the second output side electric path L3.

In the present embodiment, when the load switch 14 and the drive switch 50 are closed, the first end of the primary coil 21 and the second end of the secondary coil 22 are positive, and the second end of the primary coil 21 is positive. The end and the first end of the secondary coil 22 are negative electrodes.

The power conversion device 90 includes a control device 40 that controls the drive of the load switch 14 and the drive switch 50. The control device 40 is composed of, for example, a microcomputer, and is connected to the primary circuit 11 through terminals 41, 42, 43, and 44, respectively.

Specifically, the voltage terminal 41 is connected to the connection point K between the input side coil 12 and the load switch 14 in the input side electric path L1 via the supply line 16. The control device 40 receives the supply of the power supply voltage Vcc through the supply line 16. The power supply voltage Vcc is a voltage required for the control device 40 to operate.

The start terminal 42 is connected to the gate of the load switch 14 via the resistor R2. For example, when the start terminal 42 is connected to the open drain circuit inside the control device 40, the load switch 14 is closed when the start signal SD is in the low state. As a result, the power converter 10 is put into the activated state. On the other hand, when the start signal SD is in the high state, the gate is connected to the ground (not shown) and the load switch 14 is in the open state. As a result, the power converter 10 goes into hibernation.

An operation signal OUT for controlling the drive switch 50 to be turned on or off is output from the drive terminal 43 to the gate of the drive switch 50. During the period when the operation signal OUT is in the high state (on operation command), the drive switch 50 is in the closed state. On the other hand, during the period when the operation signal OUT is in the low state (off operation command), the drive switch 50 is in the open state. The operation signal OUT is generated according to the required output value (for example, the required output voltage) from the output terminals To1 and To2 of the power converter 10. Specifically, the larger the required output value, the larger the due diligence (= Ton / Tsw) indicating the ratio of the on-period Ton to the one switching cycle Tsw in the drive switch 50. The control device 40 corresponds to the switch control unit.

The first end of the current detection circuit 60 is connected to the current detection terminal 44. The control device 40 acquires the current detection value CS via the current detection terminal 44.

Next, the operation of the power converter 10 will be described with reference to FIG. FIG. 2A shows the transition of the operation signal OUT. FIG. 2B shows the transition of the current detection value CS.

At time t1, the load switch 14 is closed and the power converter 10 is activated.

After that, when the operation signal OUT is in the high state, the drive switch 50 is in the closed state. Therefore, the primary current I1 flows through the primary coil 21, and electric power is stored in the transformer 20. At this time, a current tries to flow out from the secondary coil 22, but the current flow is blocked by the diode 31. During the period when the operation signal OUT is in the high state, the current from the primary coil 21 flows into the current detection circuit 60 through the drive switch 50, and the current detection value CS is generated at the current detection terminal 44 (see FIG. 2B). ).

When the operation signal OUT is in the low state, the drive switch 50 is in the open state. Therefore, the electric power stored in the transformer 20 is output through the diode 31. During the period when the operation signal OUT is in the low state, no current flows through the current detection circuit 60, so the current detection value CS becomes 0. Then, after the secondary current I2 becomes 0, the drive switch 50 is switched from the off state to the on state again by the operation signal OUT.

The control device 40 uses the current detection value CS to perform an overcurrent protection process for protecting the power converter 10 from overcurrent. In the overcurrent protection process, the overcurrent state of the power converter 10 is determined by comparing the current detection value CS with the overcurrent threshold TC. In the overcurrent protection process, when the current detection value CS exceeds the overcurrent threshold TC, the power supply from the DC power supply 100 to the primary circuit 11 is stopped.

Here, a short-circuit failure of the drive switch 50 in which the on (conducting) state of the drive switch 50 is maintained may occur. If a short-circuit failure occurs in the drive switch 50, the transformer 20 may be magnetically saturated and an overcurrent may flow in the primary circuit 11 of the power converter 10. In FIG. 2, a short-circuit failure of the drive switch 50 occurs immediately before the time t2. Therefore, although the operation signal OUT is in the low state, the on (conducting) state of the drive switch 50 is maintained. Therefore, when the current continues to flow in the primary coil 21 and the drive switch 50 and the current detection value CS exceeds the overcurrent threshold TC at time t3, the control device 40 determines that the overcurrent is flowing.

The rate of increase of the primary current I1 that flows when a short-circuit failure of the drive switch 50 occurs is determined according to the input voltage from the DC power supply 100, the resistance value of the power supply line 110, and the combined resistance in the input side electric path L1. For example, the resistance value increases due to the deterioration of the power supply line 110 connecting the DC power supply 100 and the power converter 10 with time, so that the rate of increase of the primary current I1 flowing through the primary coil 21 decreases. Further, for example, because the output voltage of the DC power supply 100 is low, the rate of increase of the primary current I1 becomes low.

FIG. 3 shows the transition of each waveform when the rising speed of the primary current I1 is lower than the rising speed of the primary current I1 shown in FIG. 3 (a) and 3 (b) correspond to FIGS. 2 (a) and 2 (b).

Also in FIG. 3, the primary current I1 flows through the primary circuit 11 during the period when the operation signal OUT is in the high state. The rate of increase of the primary current I1 is lower than that shown in FIG. 2 (b). In FIG. 3B, the slope of the current detection value CS according to the rising speed of the primary current I1 is smaller than the slope of the current detection value CS shown in FIG. 2B (shown by the alternate long and short dash line). There is.

It is assumed that a short-circuit failure of the drive switch 50 occurs immediately before the time t11. In this case, the ON state of the drive switch 50 is maintained even during the period when the operation signal OUT is subsequently in the low state. However, the rising speed of the primary current I1 flowing through the primary coil 21 is low, and the time required for the current detection value CS to exceed the overcurrent threshold TC is the overcurrent threshold at the rising speed of the current detection value CS indicated by the one-point chain line. It is longer than the time required to exceed TC (P1). As a result, the timing of determining the short-circuit failure of the drive switch 50 is delayed. Even if the primary current I1 flowing at the time of a short circuit failure is a low value, the primary side circuit 11 may be overheated due to the primary current I1 flowing for a long time. In this case, there is a possibility that the elements constituting the primary side circuit 11 may malfunction.

The characteristic configuration of this embodiment for dealing with the above-mentioned problems will be described. In the power converter 10, when the drive switch 50 is opened, the storage of electric power in the transformer 20 is stopped, and a period in which the primary current I1 does not flow in the primary circuit 11 occurs. Here, when a short-circuit failure occurs in the drive switch 50, the drive switch 50 is kept on (energized) even during the period when the operation signal OUT is in the low state, and the primary current I1 continues to flow in the drive switch 50. Therefore, it is possible to determine the short-circuit failure of the drive switch 50 from the state in which the primary current I1 is continuously flowing through the drive switch 50 while the operation signal OUT is in the low state. In this case, it is not necessary to determine the magnitude of the current value because it is sufficient if it can be determined that the primary current I1 is flowing. Therefore, the threshold value for determining the short-circuit failure can be made smaller than the overcurrent threshold value TC.

Therefore, in the present embodiment, the control device 40 determines the short-circuit failure of the drive switch 50 during the period when the operation signal OUT is in the low state, based on the main short-circuit threshold TS1 smaller than the overcurrent threshold TC. Then, when the control device 40 determines either a short-circuit failure or an overcurrent state, the control device 40 stops the power supply from the DC power supply 100 to the transformer 20.

Next, the short-circuit protection process performed by the control device 40 will be described with reference to FIG. The process shown in FIG. 4 is repeatedly performed at a predetermined cycle.

In step S10, the current detection value CS is acquired. Step S10 corresponds to the current detection unit.

In step S11, it is determined whether or not the power supply starting period from the DC power supply 100 to the transformer 20 is in progress. In the present embodiment, the power supply start period is a period from when the load switch 14 is switched from the open state to the closed state until a predetermined period elapses. During a predetermined period from the start of power supply from the DC power supply 100 to the transformer 20, the input voltage supplied to the primary coil 21 gradually increases according to the capacitance of the second capacitor 15 and the opening / closing speed of the load switch 14. I will do it. Therefore, in a predetermined period from the start of power supply, even if a short-circuit failure occurs in the drive switch 50, the rate of increase of the primary current I1 becomes a low value. Therefore, in the present embodiment, the short-circuit failure can be quickly determined by determining the short-circuit failure of the drive switch 50 using the main short-circuit threshold TS1 during the power supply start period.

The power supply start period is, for example, the time required for the voltage between the terminals of the second capacitor 15 to become larger than a predetermined voltage after the charging of the second capacitor 15 is started by the input voltage. Step S11 corresponds to the start determination unit. That is, in the present embodiment, the determination of the short-circuit failure is continuously performed from the start of the power converter 10 to the power supply start period.

In steps S13 to S17, the short-circuit failure of the drive switch 50 is determined based on the comparison between the current detection value CS and the main short-circuit threshold TS1 during the period when the operation signal OUT is in the low state. Due to a short-circuit failure, the primary current I1 continues to flow even during the period when the operation signal OUT is in the low state. Therefore, the period during which the current detection value CS becomes larger than the main short-circuit threshold value TS1 is longer than that when the short-circuit failure does not occur. Therefore, in the present embodiment, the duration at which the current detection value CS becomes larger than the main short-circuit threshold value TS1 is calculated as the first measurement time Co1. Then, when the first measurement time Co1 exceeds the predetermined first excess time T1, it is determined that a short-circuit failure of the drive switch 50 has occurred. Steps S13 to S17 correspond to the short circuit determination unit.

First, in step S13, it is determined whether or not the current detection value CS is larger than the main short-circuit threshold value TS1. The main short-circuit threshold value TS1 is a value within the range of the primary current I1 assumed when no overcurrent is flowing through the primary coil 21 during the period when the operation signal OUT is in the high state.

If the current detection value CS is larger than the main short-circuit threshold value TS1, the process proceeds to step S14. In step S14, the first measurement time Co1 indicating the duration at which the current detection value CS becomes larger than the main short-circuit threshold value TS1 is increased. In step S15, it is determined whether or not the first measurement time Co1 increased in step S13 is equal to or greater than the first excess time T1. In the present embodiment, the first excess time T1 is set to be longer than the one switching cycle Tsw of the drive switch 50. The first excess time T1 may be set to a fixed value, for example.

The first excess time T1 may be variably set according to the required output value of the power converter 10. The on-period Ton of the drive switch 50 becomes longer as the required output value increases. Therefore, the first excess time T1 may be set to be longer than the ON period Ton of the drive switch 50 based on the required output value.

If the current detection value CS is less than the main short-circuit threshold value TS1 in step S13, the process proceeds to step S17. In step S17, the first measurement time Co1 is reset to 0. Then, the process of FIG. 4 is temporarily terminated. Therefore, the increase of the first measurement time Co1 is continued while the period in which the current detection value CS is larger than the main short-circuit threshold value TS1 continues.

In step S15, when the first measurement time Co1 is smaller than the first excess time T1, the process of FIG. 4 is temporarily terminated.

Since the period in which the current detection value CS is larger than the main short-circuit threshold value TS1 continues, it is determined in step S15 that the first measurement time Co1 is equal to or greater than the first excess time T1. In the following step S16, it is determined that a short-circuit failure of the drive switch 50 has occurred.

In step S18, the load switch 14 is opened by changing the start signal SD to the high state. Therefore, the power supply from the DC power supply 100 to the transformer 20 is stopped, and the power converter 10 is put into hibernation state. Then, the process of FIG. 4 is temporarily terminated.

If it is determined in step S11 that the power supply start period is not in progress, the process proceeds to step S20. That is, in the present embodiment, the determination of the short circuit failure using the main short circuit threshold value TS1 is not performed after the elapse of the power supply start period.

In steps S20 to S26, the overcurrent state of the power converter 10 is determined.

Specifically, in step S20, it is determined whether or not the current detection value CS is larger than the sub-short circuit threshold value TS2. The sub-short-circuit threshold value TS2 is a value larger than the main short-circuit threshold value TS1 and is a value determined according to the rate of increase of the primary current I1 in which it is desirable to put the power converter 10 in a dormant state. In the present embodiment, the sub-short circuit threshold TS2 has a value larger than the overcurrent threshold TC.

In the determination of the short circuit failure using the sub-short circuit threshold value TS2, the time during which the current detection value CS is continuously larger than the sub-short circuit threshold value TS2 is longer than the first excess time T1 for determining the first measurement time Co1 in step S15. I'm shortening it. In the present embodiment, in step S20, the time during which the current detection value CS continuously becomes larger than the sub-short circuit threshold value TS2 is set to 0. Therefore, when the current detection value CS becomes larger than the sub-short circuit threshold value TS2, the process proceeds to step S25. In step S25, a short-circuit failure of the drive switch 50 is determined. In step S27, the load switch 14 is opened by changing the start signal SD to the high state. Therefore, the power converter 10 goes into hibernation. Then, the process shown in FIG. 4 is temporarily terminated.

If the current detection value CS is smaller than the sub-short circuit threshold value TS2, the overcurrent state of the power converter 10 is determined in steps S21 to S24 and S26. Steps S21 to S24 and S26 correspond to the overcurrent determination unit.

In step S21, it is determined whether or not the current detection value CS is larger than the overcurrent threshold TC. In the present embodiment, the overcurrent threshold TC is a value larger than the main short-circuit threshold TS1 and smaller than the sub-short-circuit threshold TS2. In the present embodiment, the overcurrent state is determined based on the period during which the current detection value CS becomes larger than the overcurrent threshold TC. First, in step S22, the second measurement time Co2, which indicates the elapsed time when the current detection value CS becomes larger than the overcurrent threshold value TC, is increased. If the current detection value CS is smaller than the overcurrent threshold value TC in step S21, the process proceeds to step S24, and the second measurement time Co2 is reset to 0. Therefore, the second measurement time Co2 increases as the period in which the current detection value CS becomes larger than the overcurrent threshold TC continues.

In step S23, it is determined whether or not the second measurement time Co2 is equal to or greater than the second excess time T2. The second excess time T2 is, for example, a time for distinguishing between a temporary increase in the current detection value CS and an overcurrent state, and is a value determined by experiments and calculations. If the second measurement time Co2 is less than the second excess time T2, the process of FIG. 4 is temporarily terminated.

If the second measurement time Co2 is the second excess time T2 or more, the process proceeds to step S26. In step S26, it is determined that the power converter 10 is in an overcurrent state. Since the short-circuit failure is determined at the time of startup, if an affirmative determination is made in step S26, there is a high possibility that the drive switch 50 has not undergone a short-circuit failure. In the overcurrent state, unlike the short-circuit failure, the primary current I1 does not flow through the primary side circuit 11 by setting the operation signal OUT to the low state. Here, when the start terminal 42 is connected to the open drain circuit, the start signal SD is in the low state, so that the start terminal 42 is connected to a ground (not shown). In this state, a large current may flow into the control device 40 through the start terminal 42. Therefore, when proceeding to step S28, the drive switch 50 is opened by keeping the operation signal OUT in the high state. Then, the process shown in FIG. 4 is temporarily terminated. In step S28, in addition to opening the drive switch 50, the load switch 14 may be opened.

In the present embodiment, the maintenance of the operation signal OUT in the low state is released in the next control cycle of the process of FIG. The power converter 10 may be stopped when the determination of the overcurrent state is repeated in a control cycle of a predetermined number of times or more. Steps S18, S27, and S28 correspond to the stop control unit.

Next, the effects according to the present embodiment will be described with reference to FIGS. 5 and 6. FIG. 5 is a timing chart for explaining the determination of short-circuit failure in a predetermined period from the start of power supply. FIG. 5A shows the transition of the operation signal OUT, and FIG. 5B shows the transition of the current detection value CS. FIG. 5C shows the transition of the first measurement time Co1, and FIG. 5D shows the transition of the driving state of the load switch 14. FIG. 5 illustrates a case where a short-circuit failure of the drive switch 50 occurs immediately before the time t27.

At time t21, when the current detection value CS becomes a value larger than the main short-circuit threshold value TS1, the increase of the first measurement time Co1 is started. Since the short-circuit failure of the drive switch 50 has not occurred, the drive switch 50 is switched from the closed state to the open state at the time t22 when the operation signal OUT is in the low state. Therefore, at time t22, the current detection value CS becomes equal to or less than the main short-circuit threshold value TS1, and the first measurement time Co1 is reset. The period from time t21 to t22, the period from time t23 to t24, and the period from time t25 to t26 are the same as the period from time t21 to t22.

At the timing immediately before the time t27, a short-circuit failure of the drive switch 50 occurs. Therefore, at time t27, when the current detection value CS becomes a value larger than the main short-circuit threshold value TS1, the increase of the first measurement time Co1 is started. Since the drive switch 50 has a short-circuit failure, the first measurement time Co1 continues to increase even at the time when the operation signal OUT is in the low state after the time t27. Then, at time t28, when the first measurement time Co1 becomes the first excess time T1 or more, the load switch 14 is opened and the power converter 10 is put into hibernation state.

Next, the determination of the overcurrent state after a lapse of a predetermined period from the start of power supply will be described with reference to FIG. 6 (a), (b), and (d) correspond to FIGS. 5 (a), (b), and (d), respectively. FIG. 6C shows the transition of the second measurement time Co2. FIG. 6 illustrates a case where a short-circuit failure of the drive switch 50 occurs immediately before the time t31.

After a lapse of a predetermined period from the start of power supply, the voltage between the terminals of the second capacitor 15 is higher than before the lapse, and the rate of increase of the primary current I1 is higher than that shown in FIG. 5 (b).

A short-circuit failure of the drive switch 50 occurs immediately before the time t31. At time t32, when the current detection value CS becomes larger than the overcurrent threshold value TC, the increase of the second measurement time Co2 is started. Due to the short-circuit failure of the drive switch 50, the second measurement time Co2 continues to increase. Before the second measurement time Co2 becomes the second excess time T2 or more, the current detection value CS exceeds the sub-short circuit threshold TS2 at time t33. Therefore, the load switch 14 is opened and the power converter 10 is hibernated.

According to the present embodiment described above, the following effects are obtained.

When the current detection value CS is continuously larger than the main short-circuit threshold value TS1 and the first measurement time Co1 is longer than the first excess time T1 indicating the period during which the ON operation command is issued, the control device 40 is driven by the drive switch 50. It was determined that a short-circuit failure had occurred. In this case, since the main short-circuit threshold value TS1 can be made smaller than the overcurrent threshold value TC, the short-circuit failure can be appropriately determined even when the rate of increase of the current flowing at the time of the short-circuit failure is low. Further, the short-circuit failure determination condition is that the period during which the current detection value CS becomes larger than the main short-circuit threshold value TS1 is longer than the period during which the on-operation command is issued. This makes it possible to prevent erroneous determination of short-circuit failure due to noise or the like.

The control device 40 determines that a short-circuit failure has occurred in the drive switch 50 even when the current detection value CS exceeds the sub-short-circuit threshold TS2, which is larger than the main short-circuit threshold TS1. In this case, when the current rise rate is large, the short-circuit failure is determined, so that the short-circuit failure can be determined quickly.

When the control device 40 determines that a short-circuit failure has occurred, the load switch 14 is switched to the open state to stop the power supply from the DC power supply 100 to the transformer 20. In this case, it is possible to prevent each element constituting the power converter 10 from deteriorating due to overheating caused by a short-circuit failure.

The control device 40 determines the short-circuit failure of the drive switch 50 within a predetermined period after determining the start of power supply by the DC power supply 100. Since the second capacitor 15 is provided, the rate of increase of the current flowing through the drive switch 50 tends to decrease within a predetermined period from the start of power supply. Even in this case, the short-circuit failure of the drive switch 50 can be quickly determined.

(Second Embodiment)
In the second embodiment, a configuration different from that of the first embodiment will be mainly described.

In this second embodiment, the period for comparing the current detection value CS with the main short-circuit threshold value TS1 is limited to the period during which the operation signal OUT is in the low state.

FIG. 7 is a flowchart illustrating a short-circuit protection process carried out by the control device 40 according to the second embodiment. The process shown in FIG. 7 is repeatedly performed by the control device 40 at a predetermined cycle.

If it is determined in step S11 that power supply is being started, the process proceeds to step S31. In step S31, it is determined whether or not the operation signal OUT is in the low state. If the operation signal OUT is not in the low state, the process of FIG. 7 is temporarily terminated. If the operation signal OUT is in the low state, the process proceeds to step S13. Step S31 corresponds to the state determination unit.

In step S13, it is determined whether or not the current detection value CS is larger than the main short circuit threshold value TS1. If the current detection value CS is larger than the main short-circuit threshold value TS1, the process proceeds to step S16, and it is determined that a short-circuit failure of the drive switch 50 has occurred. Then, the process proceeds to step S18.

Also in this second embodiment, if it is determined in step S11 that the power supply start period is not in progress, the process proceeds to step S20.

According to the present embodiment described above, the same effect as that of the first embodiment can be obtained.

(Third Embodiment)
In the third embodiment, a configuration different from that of the first embodiment will be mainly described.

In the third embodiment, as shown in FIG. 8, the power converter 10 includes two drive switches, and it is determined whether or not a short-circuit failure of each drive switch has occurred. FIG. 8 is a configuration diagram of the power converter 10 according to the third embodiment. FIG. 8 shows a push-pull type power converter as a power converter including two drive switches.

In the power converter 10, the primary side circuit 11 and the secondary side circuit 30 are coupled via a transformer 70. The primary coil 71 of the transformer 70 is provided with a primary side center tap CT1. The primary side center tap CT1 is connected to the drain of the load switch 14. Of the primary coil 71, the primary side center tap CT1 to the first end is referred to as the first coil portion 73, and the primary side center tap CT1 to the second end is referred to as the second coil portion 74. The secondary coil 72 of the transformer 70 is provided with a secondary center tap CT2. The secondary side center tap CT2 is connected to the first output side electric path L2 via the output side coil 35. Of the secondary coil 72, the part from the secondary side center tap CT2 to the first end of the secondary coil 72 is referred to as the third coil portion 75, and the part from the secondary side center tap CT2 to the second end is referred to as the fourth coil portion 76. I will do it.

The third coil portion 75 is connected to the cathode of the first diode 33, and the fourth coil portion 76 is connected to the cathode of the second diode 34. The anodes of the first and second diodes 33 and 34 are connected to the second output side electric path L3.

In the present embodiment, the first switch 51 and the second switch 52 are provided as drive switches. In this embodiment, the first and second switches 51 and 52 are N-channel MOSFETs. Each drain of the first switch 51 and the second switch 52 is connected to both ends of the primary coil 71. Specifically, the first switch 51 is connected to the first coil portion 73 of the primary coil 71, and the second switch 52 is connected to the second coil portion 74.

The power converter 10 includes a first detection circuit 61 and a second detection circuit 62 as current detection circuits. The first end of the first detection circuit 61 is connected to the source of the first switch 51, and the second end is connected to the ground. The first end of the second detection circuit 62 is connected to the source of the second switch 52, and the second end is connected to the ground. Also in this embodiment, the first and second detection circuits 61 and 62 are composed of shunt resistors.

The control device 40 includes a first drive terminal 45 and a second drive terminal 46 as drive terminals for outputting an operation signal OUT, and first detection terminals 48 and second as detection terminals for detecting the current detection value CS. The detection terminal 47 is provided. From the first drive terminal 45, a first operation signal OUT1 that controls the drive of the first switch 51 is output. From the second drive terminal 46, a second operation signal OUT2 that controls the drive of the second switch 52 is output. The first end of the first detection circuit 61 is connected to the first detection terminal 48. Further, the first end of the second detection circuit 62 is connected to the second detection terminal 47.

The first and second switches 51 and 52 are controlled to a closed state and an open state according to the first and second operation signals OUT1 and OUT2 output from the control device 40, respectively. When the first switch 51 is closed and the second switch 52 is opened, a closed circuit including the DC power supply 100, the first coil portion 73 of the primary coil 71, and the first detection circuit 61 is included. Is formed, and the primary current I1 flows through this closed circuit. Further, when the first switch 51 is closed and the second switch 52 is opened, the DC power supply 100, the second coil portion 74 of the primary coil 71, and the second detection circuit 62 are included. A closed circuit is formed, and a primary current I1 flows through this closed circuit.

During the period when the first switch 51 is in the open state, no current flows through the first detection circuit 61, and during the period when the second switch 52 is in the open state, no current flows through the second detection circuit 62. Therefore, the control device 40 determines the short-circuit failure of the first switch 51 when it is determined that the period during which the first current detection value CS1 is continuously larger than the main short-circuit threshold value TS1 is equal to or longer than the first excess time T1. do. Further, the control device 40 determines the short-circuit failure of the second switch 52 when the period in which the second current detection value CS2 continuously increases from the main short-circuit threshold value TS1 exceeds the first excess time T1.

(Other embodiments)
In the first embodiment, the short-circuit failure determination of the drive switch 50 using the sub-short-circuit threshold value TS2 may be performed in a predetermined period from the start of power supply. In this case, for example, after step S12 in FIG. 4, the control device 40 compares the current detection value CS with the sub-short circuit threshold value TS2. Then, if it is determined that the current detection value CS is larger than the sub-short circuit threshold value TS2, the process proceeds to step S16 to determine the short-circuit failure. On the other hand, if it is determined that the current detection value CS is less than the sub-short circuit threshold TS2, the process proceeds to step S13, and the current detection value CS and the main short-circuit threshold TS1 are compared.

-The determination of the short circuit failure and the determination of the overcurrent state may be performed in the same period. In this case, the control device 40 may determine the short-circuit failure and the overcurrent state by comparing the current detection value CS in the order of the sub-short-circuit threshold TS2, the overcurrent threshold TC, and the main short-circuit threshold TS1.

-In step S20 of FIG. 4, the time during which the current detection value CS continuously becomes larger than the sub-short circuit threshold value TS2 may be determined. In this case, the time during which the current detection value CS continuously increases from the sub-short circuit threshold value TS2 may be shorter than the first excess time T1 for determining the first measurement time Co1 in step S15. For example, in step S20, the time during which the current detection value CS continuously becomes larger than the sub-short circuit threshold value TS2 is measured as the measurement time. Then, when the measurement time is larger than the third excess time T3, which indicates a time shorter than the first excess time T1, the process proceeds to step S25, and a short-circuit failure of the drive switch 50 is determined.

-The installation location of the current detection unit that detects the current flowing through the drive switch is not limited to that shown in FIG. For example, any location on the electrical path from the second end of the primary coil 21 to the ground may be used as the installation location.

The power converter may be a non-isolated and chopper type DC / DC converter.

10 ... power converter, 40 ... control device, 50 ... drive switch, 100 ... DC power supply.

Claims (5)

An inductor (20) that stores magnetic energy and
A switch (50) that stores magnetic energy in the inductor by power supply from the power source (100) when it is turned on, and outputs power from the inductor to the power supply target when it is turned off.
A current detection unit (60) that detects the current flowing through the switch, and
A power converter control device ( L1) applied to a power converter including a capacitor (15) connected in parallel to the inductor in an input-side electrical path (L1) that supplies power from the power source to the inductor. In 40),
A switch control unit that outputs an operation signal (OUT) including an on operation command that controls the switch to the on state and an off operation command that controls the switch to the off state.
An overcurrent determination unit that determines an overcurrent state in which an overcurrent is flowing through the switch based on a comparison between the detection value of the current detection unit and a predetermined overcurrent threshold value (TC).
A start determination unit that determines the start of power supply from the power source to the inductor, and
Within a predetermined period after the start determination unit determines the start of power supply, the current in a period including a main short-circuit threshold value (TS1) smaller than the overcurrent threshold value and a period in which the operation signal becomes the off operation command. A control device for a power converter including a short-circuit determination unit for determining that a short-circuit failure of the switch has occurred based on a comparison with a detection value (CS) of the detection unit. In the short-circuit determination unit, the period during which the detection value of the current detection unit becomes larger than the main short-circuit threshold within the predetermined period after the determination of the start of power supply is the period during which the operation signal is the on operation command. The control device for a power converter according to claim 1, wherein it is determined that a short-circuit failure of the switch has occurred when it is determined that the length is longer than that of the switch. A state determination unit for determining whether the operation signal is the off operation command or the on operation command is provided.
The short-circuit determination unit of the current detection unit is within the predetermined period after the power supply start is determined, during the period when the state determination unit determines that the operation signal is the off operation command. The control device for a power converter according to claim 1, wherein when it is determined that the detected value is larger than the main short-circuit threshold value, it is determined that a short-circuit failure of the switch has occurred. The short determination unit, a short circuit after the said feed start has elapsed the predetermined period is determined, before Symbol switch when the detected value of the current detection unit exceeds the sub-short circuit threshold greater than said main short threshold The control device for a power converter according to claim 2, wherein it is determined that a failure has occurred. The control device for a power converter according to any one of claims 1 to 4, further comprising a stop control unit for stopping power supply from the power source to the inductor when the short-circuit failure is determined.

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