JP2017188975A - Insulated power converter - Google Patents

Abstract

The present invention provides an isolated power conversion device that quickly detects short-circuit abnormalities in a load with low loss. [Solution] A transformer 20 including primary windings 30, 40 and a secondary winding 50, switches SW1, SW2 connected to each primary winding 30, 40, and LC resonance as a load on the secondary side of the transformer 20. In the insulated power conversion device 10 including the capacitor 60 forming a circuit, the short-circuit determination unit 801 determines that "when the first switch SW1 is turned off and the second switch SW2 is turned on, the short circuit is induced in the transformer 20, and the primary winding 30, 40 is detected based on the first switch voltage Vsw1, and a short-circuit abnormality of the load is determined based on the detected value of the excitation winding voltage Vc. Specifically, the short circuit determination unit 801 determines that the load is normal if the excitation winding voltage Vc monotonically changes during the detection period, and that the load is short-circuited if the excitation winding voltage Vc is constant. [Selection diagram] Figure 4

Description

  The present invention relates to an insulated power conversion apparatus that converts electric power input from a DC power supply by a transformer and supplies the converted electric power to a load.

  Conventionally, in a power conversion device that converts input power and supplies it to a load by the operation of a switching element (hereinafter referred to as “switch”), an overcurrent abnormality due to a short circuit on the load side is detected, and the switching operation of the switch is stopped. The technology to do is known. For example, in the technology disclosed in Patent Document 1, a current detection resistor is provided in the input-side current path of the inverter, and an overcurrent abnormality is detected based on the output of an amplification comparison circuit connected between the terminals of the current detection resistor. ing.

JP 2008-17649 A

Although the prior art of Patent Document 1 relates to a non-insulated inverter, this technique is similarly applied to a configuration in which a short-circuit abnormality of a secondary load is detected by a current flowing in a primary side in an insulated power converter. Can be applied. In the prior art disclosed in Patent Document 1, although an amplification comparison circuit is provided to reduce the resistance value of the current detection resistor, there is no change in connecting a resistor to a path through which a large current flows, and loss occurs. .
Therefore, there is a method of using a current sensor to prevent loss. However, if a current sensor is used, the current detection delay increases, and it takes time to determine that an overcurrent abnormality has occurred. As a result, the stop of the switching operation is delayed, and there is a possibility that the device is destroyed.

  The present invention has been created in view of the above points, and an object of the present invention is to provide an insulated power converter that detects a load short-circuit abnormality quickly with low loss.

The insulated power converter of the present invention includes a first primary winding (30) and a second primary winding (40), a first switch (SW1) and a second switch (SW2), and one or more secondary windings. A winding (50), a capacitor (60), a drive signal generation unit (70), and a short-circuit determination unit (801, 802, 803) are provided.
One end of each of the first primary winding and the second primary winding is connected to one electrode of the DC power source (15), and constitutes the primary side of the transformer (20). The first switch and the second switch are connected between the other ends of the first primary winding and the second primary winding and the other electrode of the DC power supply.
Note that the DC power source here includes a smoothing capacitor.

One or more secondary windings constitute the secondary side of the transformer.
The capacitor is connected to both ends of the secondary winding, and forms an LC resonance circuit as a “load” together with the leakage inductance (52) of the secondary winding.
The drive signal generation unit generates a drive signal that drives the first switch and the second switch to be turned on / off in a complementary manner.
Note that the capacitor is not limited to an independent element, and various components having a capacitance component or an assembly of a plurality of components may be regarded as a capacitor.

Here, a voltage that is induced in the transformer when the first switch is turned off and the second switch is turned on and is generated in the excitation inductances (31, 41) of the primary winding is defined as “excitation winding voltage (Vc)”.
The short circuit determination unit detects the excitation winding voltage based on a first switch voltage (Vsw1) that is a drain-source voltage of the first switch. Then, the short circuit determination unit determines a load short circuit abnormality based on the detected value of the excitation winding voltage.
The term “short circuit” in this specification is not limited to the case where the resistance is completely 0 [Ω], but includes all abnormalities in which the resistance is extremely smaller than that in the normal state and overcurrent exceeding the allowable range flows. Strictly speaking, the term “drain-source voltage”, which is the term of a field effect transistor, is interpreted as including “collector-emitter voltage” in a bipolar transistor.

Under normal conditions, the excitation winding voltage changes monotonously in an S-shaped curve during the detection period, which is the ON period of the second switch, due to the resonance of the LC resonance circuit that occurs in response to the ON operation of the second switch. On the other hand, when the load is short-circuited, the constituent element of the load is only the leakage inductance of the secondary winding, and LC resonance does not occur. Therefore, the excitation winding voltage becomes a constant value during the detection period.
Further, the excitation winding voltage can be detected based on the first switch voltage of the first switch that is turned off when the first switch is turned off and the second switch is turned on.

In the present invention, paying attention to this point, the short circuit determination unit determines the short circuit abnormality of the load based on the detected value of the excitation winding voltage. Specifically, the short-circuit determining unit determines that the excitation winding voltage is normal when the excitation winding voltage changes monotonically in the detection period, and that the load is short-circuit abnormality when the excitation winding voltage is constant. As a result, it is not necessary to connect a resistor to a path through which a large current flows, so that loss can be reduced as compared with the prior art.
Moreover, an overcurrent abnormality can be quickly detected as compared with a technique using a current sensor. Therefore, by quickly stopping the switching operation of the switch when an abnormality is detected, it is possible to appropriately prevent damage to the device and adverse effects on peripheral devices and the like.

Specifically, the short-circuit determining unit may compare the time change rate of the excitation winding voltage with a predetermined change rate threshold value, for example.
Alternatively, the short-circuit determination unit sets a range including a constant value of the excitation winding voltage when the load is short-circuited as a specified range, and the number of times that the AD conversion value of the excitation winding voltage is within the specified range, or the excitation winding voltage May be compared with the respective thresholds.

The figure explaining the general structure of the insulation type power converter device of each embodiment, and the current path at the time of (a) SW1 ON / SW2 OFF, (b) SW1 OFF / SW2 ON. The figure which shows the change of (a) the equivalent circuit at the time of SW2 ON in the normal time, and (b) exciting winding voltage. The figure which shows the change of the equivalent circuit at the time of (a) SW2 ON at the time of load short circuit, (b) Excitation winding voltage. The block diagram of the insulation type power converter device of 1st Embodiment. The time chart at the time of normality by 1st Embodiment. Time chart at the time of load short-circuit according to the first embodiment The block diagram of the insulation type power converter device of 2nd Embodiment. The time chart at the time of normality by 2nd Embodiment. Time chart at the time of load short-circuit according to the second embodiment The block diagram of the insulation type power converter device of 3rd Embodiment. The time chart at the time of normal by 3rd Embodiment. Time chart at load short-circuit according to the third embodiment The block diagram of the short circuit determination by (a) 1st comparative example and (b) 2nd comparative example.

Hereinafter, embodiments of an insulated power converter will be described with reference to the drawings. This insulated power conversion device is a device that converts electric power input from a DC power supply by a transformer and supplies it to a load. In the present embodiment, a DC-AC converter that converts DC power into AC power is illustrated.
[General configuration and operation of insulated power converter]
Initially, the general structure and effect | action of the insulation type power converter device of this embodiment are demonstrated with reference to FIG.

The insulated power converter 10 generally has a transformer 20, two switches SW1 and SW2 provided on the primary side of the transformer 20, a capacitor 60 provided on the secondary side of the transformer 20, and a drive signal generation unit 70. With. The primary side of the transformer 20 is constituted by two primary windings 30 and 40, and the secondary side is constituted by one secondary winding 50.
The switches SW1 and SW2 are semiconductor switching elements, and for example, MOSFETs having body diodes are used. In addition, an IGBT or the like in which reflux diodes are connected in parallel may be used. Of the two primary windings 30 and 40, a switch connected to the first primary winding 30 is referred to as a first switch SW1, and a switch connected to the second primary winding 40 is referred to as a second switch SW2.

The primary side center tap CT is connected to the positive electrode of the battery 15 as a “DC power supply”. The first primary winding 30 and the second primary winding 40 have one end connected to the center tap CT and the other end connected to the drains of the switches SW1 and SW2. The sources of the switches SW1 and SW2 are connected to the negative electrode of the battery 15.
The capacitor 60 is connected to both ends of the secondary winding 50. The capacitor 60 is not limited to an independent element, and various parts having a capacitance component or an assembly of a plurality of parts may be regarded as a capacitor.
In the figure, Vin is a power supply voltage of the battery 15, and Vo is an output voltage applied between the electrodes of the capacitor 60.

The drive signal generator 70 generates a drive signal that drives the first switch SW1 and the second switch SW2 to be turned on / off in a complementary manner.
When the first switch SW1 is turned on and the second switch SW2 is turned off, as shown in FIG. 1A, the primary side current flows through the first primary winding 30 and the first switch SW1. At this time, a secondary current in the opposite direction to the current flowing through the first primary winding 30 flows through the secondary winding 50.
When the second switch SW2 is turned on and the first switch SW1 is turned off, the primary current flows via the second primary winding 40 and the second switch SW2, as shown in FIG. At this time, a secondary current flows in the secondary winding 50 in the direction opposite to the current flowing in the second primary winding 40, that is, in the direction opposite to that in the case of FIG.

Thus, an alternating voltage with alternating positive and negative is generated between the electrodes of the capacitor 60 by the on / off operation of the first switch SW1 and the second switch SW2.
A period in which the first switch SW1 and the second switch SW2 are turned on once is defined as “one cycle” of the switching cycle. If the lengths of the ON periods of both switches SW1 and SW2 are the same, and the dead time during which both switches SW1 and SW2 are simultaneously turned off is ignored, the length of the ON period of one switch is equal to “2 minutes of the switching period. It corresponds to “one period”.

In the insulated power conversion device 10 having such a configuration, when an overcurrent flows due to a short circuit on the secondary side load, there is a risk of element destruction or the like. As noted in the section “Means for Solving the Problems”, “short circuit” in this specification is not limited to the case where the resistance is completely 0 [Ω], but the resistance is extremely small as compared with the normal state. Including abnormalities that cause overcurrent exceeding the allowable range.
Here, FIG. 13 is referred with respect to the configuration of the short circuit determination according to the comparative example assumed based on the prior art. In FIG. 13, components substantially the same as those in FIG. 1 of the present embodiment are denoted by the same reference numerals and description thereof is omitted.

The first comparative example shown in FIG. 13A is an application of the non-insulated inverter technology disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2008-17649) to an insulated power converter. In the device 108 of the first comparative example, the detection voltage of the current detection resistor R provided in the primary side current path is amplified by the amplification comparison circuit 808, and when the amplified voltage exceeds the threshold, a short circuit abnormality is determined. By amplifying the detection voltage, the resistance value of the current detection resistor R can be lowered. However, there is no change in connecting a resistor to a path through which a large current flows, and loss occurs.
In addition, in the configuration in which overcurrent is determined using a current sensor, loss can be prevented, but it takes time to determine overcurrent abnormality. As a result, the stop of the switching operation is delayed, and the switch or the like may be destroyed.

  The second comparative example shown in FIG. 13B is based on the technique disclosed in Japanese Patent Laid-Open No. 2001-72401. In the device 109 of the second comparative example, a detection winding 39 dedicated to abnormality detection is provided on the primary side of the transformer 29. Further, the short-circuit determining unit 809 connected to the detection winding 39 detects a short-circuit abnormality based on the voltage of the detection winding 39 in which information on the power supply voltage Vin and the output voltage Vo is reflected. However, in this configuration, it is necessary to provide a detection winding 39 dedicated to abnormality detection, which increases the size of the apparatus. In addition, the discharge characteristics are not effectively used, which is inefficient.

In contrast to such a comparative example, the present embodiment pays attention to the voltage change caused by the on / off switching of the switches SW1 and SW2, and does not require a dedicated winding, and quickly detects a load short-circuit abnormality with low loss. This realizes a detectable configuration.
Next, the principle of short circuit abnormality determination according to the present embodiment will be described with reference to FIGS.
Hereinafter, in the present embodiment, attention is paid to the voltage change in the “state where the first switch SW1 is turned off and the second switch SW2 is turned on”. An ON period of the second switch SW2 corresponding to a half of the switching period is referred to as a “detection period”.

  FIG. 2A shows an equivalent circuit when the second switch SW2 is turned on when the load is normal, and FIG. 3A shows a case where the load is short-circuited. The second switch SW2 in the on state is considered to be equivalent to a conducting wire. A first switch voltage Vsw1, which is a drain-source voltage, is generated across the first switch SW1 in the off state. A current I1 flows through the second primary winding 40, and a current I3 flows through the secondary winding 50. Here, the turn ratio between the second primary winding 40 and the secondary winding 50 is “n: 1”. In FIG. 3, which shows a state in which the load is short-circuited, the capacitor 60 is considered equivalent to a conducting wire.

The windings 30, 40, and 50 are schematically described by dividing them into "winding components 31, 41, 51 that generate excitation inductance" and "winding components 32, 42, 52 that generate leakage inductance". Hereinafter, “winding components 31, 41, 51 that generate excitation inductance” are omitted and referred to as “excitation inductances 31, 41, 51”, and “winding components 32, 42, 52 that generate leakage inductance” are omitted. It is referred to as “leakage inductance 32, 42, 52”.
When normal, the leakage inductance 52 and the capacitor 60 of the secondary winding 50 constitute an LC resonance circuit on the secondary side, and the LC resonance voltage appears in the output voltage Vo.

Here, when the first switch SW1 is turned off and the second switch SW2 is turned on, the voltage induced in the excitation inductances 31 and 41 of the primary windings 30 and 40 when the first switch SW2 is turned on is defined as “excitation winding voltage Vc”. To do. A voltage (Vc / n) of “1 / n” proportional to the turn ratio is generated in the excitation inductance 51 of the secondary winding 50 with respect to the excitation winding voltage Vc.
The meanings of the following symbols in FIGS. 2 and 3 are as follows.
L1: Primary side leakage inductance L3: Secondary side leakage inductance R2: Resistance of the second switch SW2 and the second primary winding 40 R3: Resistance of the secondary winding 50

Based on the physical quantity described above, the excitation winding voltage Vc is expressed by Expression (1). The term “R × I” corresponds to the voltage drop due to resistance.

Assuming that the resistors R2 and R3 are very small in the equation (1), the excitation winding voltage Vc is expressed by the equation (2).

When normal, the LC resonance voltage appears in the output voltage Vo, which is the second term of the equation (2). Therefore, as shown in FIG. 2B, the excitation winding voltage Vc monotonously increases in an S-shaped curve from the initial voltage S to the ultimate voltage F during the detection period in which the second switch SW2 is on.
On the other hand, when the load is short-circuited, the C component of the capacitor 60 is lost, and the constituent element of the load is only the leakage inductance 52 of the secondary winding 50. That is, since LC resonance does not occur, the output voltage Vo is a constant voltage. Therefore, assuming that the power supply voltage Vin does not change suddenly, the excitation winding voltage Vc becomes a constant value K in the detection period as shown in FIG.

Therefore, in the detection period when the first switch SW1 is turned off and the second switch SW2 is turned on, it is normal when the excitation winding voltage Vc monotonously increases, and when the excitation winding voltage Vc is constant, a short-circuit abnormality occurs. Can be determined to have occurred. Note that “monotonically increasing” may be read as “monotonically decreasing” depending on whether the excitation winding voltage Vc is positive or negative. Generally speaking, when the exciting winding voltage Vc “monotonously changes”, it is determined that the load is normal.
In addition to the general configuration shown in FIG. 1, the insulated power converter 10 according to the present embodiment includes a short-circuit determination unit that determines a short-circuit abnormality of a load based on the above-described determination principle. The short circuit determination unit detects the excitation winding voltage Vc based on the first switch voltage Vsw1, and determines a load short circuit abnormality based on the detected value of the excitation winding voltage Vc.

[Configuration of short-circuit determination unit]
Hereinafter, a plurality of embodiments according to the short circuit determination unit will be described in order. As a reference diagram corresponding to each embodiment, a configuration diagram of a control block of the short circuit determination unit and a time chart of signals sequentially processed by the short circuit determination unit when the load is normal and when the short circuit is abnormal are attached.
4, 7, and 10, which are configuration diagrams of the respective embodiments, the same reference numerals are given to the substantially same configurations as those of the above-described embodiments, and the description thereof is omitted. In each configuration diagram, the secondary-side capacitor 60 is shown in a form in which two capacitors 61 and 62 are connected in series. The capacitor 61 is connected in parallel with two Zener diodes 63 and 64 whose cathodes are connected to each other.

(First embodiment)
First, a first embodiment will be described with reference to FIGS.
As shown in FIG. 4, the short circuit determination unit 801 of the first embodiment includes an excitation winding voltage detection (“Vc detection” in the figure) unit 81, an AD conversion unit 82, a time change rate calculation unit 83, and a threshold comparison unit 861. And an SW off signal hold unit 87.

In addition, in the insulated power converter 10, an AND circuit 75 is provided between the drive signal generator 70 and the switches SW1 and SW2. The AND circuit 75 receives the drive signal for turning on the switch SW1 or SW2 from the drive signal generation unit 70 and the SW on signal from the SW off signal hold unit 87. A drive signal is output. On the other hand, when the input of the SW on signal from the SW off signal hold unit 87 is cut off, the drive signal is not output to the switches SW1 and SW2 regardless of the drive signal from the drive signal generation unit 70.
In short, when the load is normal, the short circuit determination unit 801 outputs a SW on signal to the AND circuit 75 to drive the switches SW1 and SW2, and when the load short circuit is abnormal, the short circuit determination unit 801 blocks the output of the SW on signal to the AND circuit 75. The switching operation of the switches SW1 and SW2 is stopped.

Next, the operation of each control block in the short circuit determination unit 801 will be described in order.
The excitation winding voltage detector 81 acquires the first switch voltage Vsw1, and detects the excitation winding voltage Vc based on the first switch voltage Vsw1. If the excitation winding voltage Vc is to be accurately obtained, it is necessary to calculate the excitation winding voltage Vc by the equation (3) using information on the power supply voltage Vin.
Vc = Vsw1-Vin (3)

  However, as will be described later, in the first embodiment, only the information on the time change rate of the excitation winding voltage Vc is used, and the overall offset need not be considered. Therefore, the power supply voltage Vin may be considered as a constant on the assumption that the power supply voltage Vin is stable at least during the detection period. For this reason, the time change rate of the first switch voltage Vsw1 may be handled as the time change rate of the excitation winding voltage Vc as it is.

The AD conversion unit 82 performs AD conversion on the analog value Vc_a of the excitation winding voltage at a predetermined conversion cycle, and outputs an AD conversion value Vc_d. 5 and 6, the AD conversion timing in the detection period is represented as t1 to t9, and the period between the AD conversion timings is represented as P1 to P9.
As shown in FIGS. 5 and 6B, the AD conversion value Vc_d of the excitation winding voltage is displayed as a discrete digital value. Since the AD conversion value at time t10 when the detection period elapses is not used for control, the point at time t10 is outlined.

The time change rate calculation unit 83 calculates the time change rate of the AD conversion value Vc_d of the excitation winding voltage, that is, the slope in FIGS. 5 and 6B.
The time rate of change α (i) appearing in the i-th (i ≧ 2) period Pi is expressed by the equation (4) between the current value Vc_d (i) and the previous value Vc_d (i−1) of the excitation winding voltage. It is calculated by dividing the difference by the conversion period Δt.

The threshold comparison unit 861 compares the time change rate α calculated by the time change rate calculation unit 83 with the change rate threshold value α_th. As shown in FIGS. 5 and 6C, the change rate threshold value α_th is set as the lower limit value of the normal range for the time change rate α. When the time change rate α is less than the change rate threshold value α_th, the threshold value comparison unit 861 determines that the load is in short circuit abnormality and outputs a SW off signal.
Here, in the above-described example, the sign is defined so that the excitation winding voltage Vc is a positive value, but the positive / negative definition of the excitation winding voltage Vc may be changed as appropriate. Generally speaking, the threshold value comparison unit 861 determines that the load is short-circuit abnormality when the absolute value of the time change rate α is less than the change rate threshold value α_th.

When normal, the AD conversion value Vc_d of the excitation winding voltage monotonously increases from the initial voltage S to the ultimate voltage F while drawing an S-shaped curve, as shown in FIG.
In FIG. 5C, for example, the rate of change from time t1 to time t2 is reflected in the period P2, and the rate of change from time t5 to time t6 is reflected in the period P6. That is, a value delayed by the conversion period Δt with respect to the theoretical differential value is obtained as the time change rate α. The time change rate α is maximum near the center of the detection period, and is small at the beginning and end of the detection period.

Here, the change rate threshold value α_th is set to be greater than 0 and less than or equal to the minimum time change rate α reflected in the period P2. Therefore, the time change rate α does not become less than the change rate threshold value α_th during the detection period.
In FIG. 5D, the SW on signal is output unconditionally during the first period P1 in which the time change rate α is not calculated. Further, since the time change rate α after the period P2 is always equal to or higher than the change rate threshold value α_th, the SW on signal continues.

On the other hand, when the load is short-circuited, the AD conversion value Vc_d of the excitation winding voltage becomes constant at a value K as shown in FIG. Accordingly, as shown in FIG. 6C, the time change rate α after the period P2 is always 0, which is less than the change rate threshold value α_th.
Therefore, in FIG. 6D, after the period P1 during which the SW on signal is output unconditionally, the SW off signal is output.
The SW off signal hold unit 87 holds the SW off signal. As a result, the output cut-off state of the SW on signal to the AND circuit 75 is maintained. Therefore, the switching operation of the switches SW1 and SW2 is stopped when the load short circuit is abnormal.

As described above, the short circuit determination unit 801 of the first embodiment determines the short circuit abnormality of the load depending on whether or not the time change rate α of the AD conversion value Vc_d of the excitation winding voltage is zero.
The insulation type power conversion device 10 of the present embodiment including the following second and third embodiments includes such a short-circuit determination unit 801 so that a resistor flows in a path through which a large current flows as in the first comparative example. Since there is no need to connect the power supply, loss can be reduced.
Moreover, an overcurrent abnormality can be quickly detected as compared with a technique using a current sensor. Therefore, by quickly stopping the switching operation of the switches SW1 and SW2 when an abnormality is detected, it is possible to appropriately prevent damage to the device and adverse effects on peripheral devices and the like.
Furthermore, unlike the second comparative example, the winding for exclusive use of abnormality detection is not required, so that an increase in size and cost of the apparatus can be avoided.

(Second Embodiment)
Next, a second embodiment will be described with reference to FIGS.
As shown in FIG. 7, the short-circuit determining unit 802 of the second embodiment is different from the short-circuit determining unit 801 of the first embodiment in the excitation winding voltage detection unit 81, the AD conversion unit 82, and the SW off signal hold unit 87. Have in common. In addition, the short circuit determination unit 802 includes a specified range comparison unit 84, a counter 852, and a threshold value comparison unit 862 as a specific configuration.

Furthermore, the short circuit determination unit 802 includes a power supply voltage (“Vin detection” in the figure) unit 91 that detects the power supply voltage Vin, and a specified range setting unit 92 that sets a specified range Rs. The specified range setting unit 92 variably sets a range including the constant value K of the excitation winding voltage Vc when the load is short-circuited as the specified range Rs according to the power supply voltage Vin. Specifically, as shown in FIG. 8B, the specified range Rs is set to an intermediate region between the initial voltage S and the ultimate voltage F.
In the second embodiment, the excitation winding voltage detection unit 81 obtains a detection value of the power supply voltage Vin, and based on the power supply voltage Vin and the first switch voltage Vsw1, the current excitation winding is calculated according to Expression (3). The voltage Vc may be accurately calculated.

The specified range comparison unit 84 of the second embodiment compares the AD conversion value Vc_d of the excitation winding voltage output from the AD conversion unit 82 with the specified range Rs set by the specified range setting unit 92, and the excitation winding. When the voltage AD conversion value Vc_d is within the specified range Rs, the hit signal is output discretely. The counter 852 counts the number Ns of times the hit signal is output.
The threshold comparison unit 862 compares the number of counts Ns by the counter 852 with the number of times threshold N_th. As shown in FIG. 8 and FIG. 9C, the number threshold N_th is set as the upper limit value of the normal range for the count number Ns. When the number Ns of times that the AD conversion value Vc_d of the excitation winding voltage is within the specified range Rs exceeds the number threshold N_th, the threshold comparison unit 862 determines that the load is short-circuit abnormality and outputs a SW off signal. To do.

In FIGS. 8 and 9, as in FIGS. 5 and 6 of the first embodiment, AD conversion timings in the detection period are represented as t1 to t9, and periods between the AD conversion timings are represented as P1 to P9. In this example, the width of the specified range Rs is set to be relatively narrow.
At normal time, as shown in FIG. 8B, the AD conversion value Vc_d of the excitation winding voltage increases somewhat from the previous AD conversion timing value at all AD conversion timings t1 to t9. Yes. The AD conversion value Vc_d of the excitation winding voltage is outside the specified range Rs at times t1 to t5 and t7 to t9, and is within the specified range Rs only at time t6. Therefore, the hit signal is output once in the period P6 in which the comparison result at time t6 is recognized.

  Therefore, as shown in FIG. 8C, the number of times Ns = 1 is counted in the period P6, and then maintained until time t10 when the detection period ends. The count Ns is reset at time t10 when the detection period has elapsed. Here, the number threshold N_th is set to a value larger than 1, and the count number Ns does not exceed the number threshold N_th during the detection period. Therefore, as shown in FIG. 8D, the SW on signal continues.

On the other hand, when the load is short-circuited, as shown in FIG. 9B, the AD conversion value Vc_d of the excitation winding voltage is constant at the value K and is within the specified range Rs at all AD conversion timings from time t1 to t9. Therefore, the hit signal is output once for all the periods P1 to P9.
Therefore, as shown in FIG. 9C, the number of counts Ns increases stepwise in each period from P1 to P9 and is reset at time t10. In this example, the count number Ns = 9 in the final period P9. If the number threshold N_th is set between 1 and 2, the count number Ns exceeds the number threshold N_th in the period P2. Then, as shown in FIG. 9D, the SW off signal is output after the period P2.

The SW off signal hold unit 87 holds the SW off signal in the same manner as the short circuit determination unit 801 of the first embodiment. As a result, the output cut-off state of the SW on signal to the AND circuit 75 is maintained. Therefore, the switching operation of the switches SW1 and SW2 is stopped when the load short circuit is abnormal.
Thus, in the second embodiment, the load short-circuit abnormality is determined by comparing the AD conversion value Vc_d of the excitation winding voltage with the specified range Rs. Therefore, the same effect as the first embodiment can be obtained. Further, since the specified range setting unit 92 variably sets the specified range Rs according to the detected value of the power supply voltage Vin, even when the power supply voltage Vin fluctuates, it is possible to reliably detect a load short circuit abnormality.

(Third embodiment)
Next, a third embodiment will be described with reference to FIGS.
As shown in FIG. 10, the short-circuit determining unit 803 of the third embodiment is different from the short-circuit determining unit 802 of the second embodiment in the excitation winding voltage detecting unit 81, the specified range comparing unit 84, and the SW off signal holding unit 87. The power supply voltage detection unit 91 and the specified range setting unit 92 are shared. The short circuit determination unit 803 does not include the AD conversion unit 82, and includes a timer 853 and a threshold comparison unit 863 instead of the counter 852 and the threshold comparison unit 862.

  Similar to the second embodiment, the specified range setting unit 92 variably sets the range including the constant value K of the excitation winding voltage Vc when the load is short-circuited as the specified range Rs according to the power supply voltage Vin. Specifically, as shown in FIG. 11A, the specified range Rs is set to an intermediate region between the initial voltage S and the ultimate voltage F. For the sake of consistency with FIGS. 8 and 9, (b) in FIGS. 11 and 12 are omitted.

The specified range comparison unit 84 of the third embodiment compares the analog value Vc_a of the excitation winding voltage acquired from the excitation winding voltage detection unit 81 with the specified range Rs set by the specified range setting unit 92, and excitation winding When the analog value Vc_a of the line voltage is within the specified range Rs, the hit signal is continuously output. The timer 853 measures the time Ts when the hit signal is output.
The threshold comparison unit 863 compares the time Ts measured by the timer 853 with the time threshold T_th. As shown in FIGS. 11 and 12C, the time threshold T_th is set as the upper limit value of the normal range for the measurement time Ts. When the time Ts during which the analog value Vc_a of the excitation winding voltage is within the specified range Rs exceeds the time threshold T_th, the threshold comparison unit 863 determines that the load is short-circuit abnormality and outputs a SW off signal. .

At normal time, as shown in FIG. 11A, the analog value Vc_a of the excitation winding voltage increases with time from the initial voltage S to the ultimate voltage F, and passes through the specified range Rs in a relatively short time Ts. A hit signal is output only during the passage time Ts and is measured by the timer 853. Note that when the detection period has elapsed, the measurement time Ts is reset.
As shown in FIG. 11C, the measurement time Ts at this time is equal to or less than the time threshold T_th. Therefore, the SW on signal continues as shown in FIG.

On the other hand, when the load is short-circuited, as shown in FIG. 12A, the analog value Vc_a of the excitation winding voltage is constant at the value K and is within the specified range Rs throughout the detection period. Therefore, a hit signal is always output during the detection period.
As shown in FIG. 12C, when the measurement time Ts by the timer 853 exceeds the time threshold T_th at time tx, the SW off signal is output after time tx, as shown in FIG. When the SW-off signal holding unit 87 holds the SW-off signal, the output cutoff state of the SW-on signal to the AND circuit 75 is maintained. Therefore, the switching operation of the switches SW1 and SW2 is stopped when the load short circuit is abnormal.
The third embodiment has the same effect as the second embodiment.

(Other embodiments)
(A) In the description of the short-circuit determination units 801 to 803 in the above-described embodiment, processing for eliminating erroneous determination due to detection error, noise, or the like is omitted. Actually, there is a possibility that the time conversion rate α of the first embodiment temporarily falls below the threshold due to disturbances such as noise even though the load is normal, and the excitation windings of the second and third embodiments. It is assumed that the voltage values Vc_d and Vc_a may temporarily enter the specified range Rs. Conventionally, as a technique for eliminating such erroneous determination and improving detection reliability, for example, a method of determining an abnormality when a temporary determination state continues for a predetermined number of times or time is known.
Therefore, the structure which combined those well-known techniques with the structure of the short circuit determination part of this embodiment mentioned above is also interpreted as being included in the technical scope of the present invention.

  (B) The short-circuit determination units 802 and 803 of the second and third embodiments include the power supply voltage detection unit 91 and the specified range setting unit 92, and the specified range Rs is variably set according to the detected value of the power supply voltage Vin. To do. On the other hand, for example, when the fluctuation range of the power supply voltage Vin is relatively narrow or predictable, the fixed specified range Rs is set so as to include the upper and lower limits of the constant value K corresponding to the fluctuation range of the power supply voltage Vin. May be. Thereby, the structure of a short circuit determination part can be simplified.

  (C) When the short-circuit determining unit 801-803 of the above embodiment determines that the load is a short-circuit abnormality, the output of the SW on signal to the AND circuit 75 is interrupted and the switching operation of the switches SW1 and SW2 is stopped. . In other embodiments, for example, a power supply relay provided on the battery 15 side may be forcibly cut off as a measure for a load short circuit abnormality.

  (D) The above embodiment exemplifies a DC-AC converter that includes one secondary winding 50, energizes the alternating current flowing through the secondary winding 50 without rectification, and outputs AC power to the load. Yes. In another embodiment, the present invention is applied to a push-pull DC-DC converter that includes a plurality of secondary windings, alternately rectifies and energizes currents flowing through the secondary windings, and outputs DC power to a load. You may apply.

(E) In addition to the first primary winding 30 and the second primary winding 40, a third or more primary winding may be provided as the primary winding of the insulated power converter. Two of the windings have the same configuration as described above, and if the action is not hindered by the third or more windings, it is interpreted as being included in the scope of the present invention.
As mentioned above, this invention is not limited to the said embodiment at all, In the range which does not deviate from the meaning of invention, it can implement with a various form.

10: Insulated power converter,
15 ... Battery (DC power supply),
20 ... Transformer,
30 ... 1st primary winding, 40 ... 2nd primary winding,
50 ... secondary winding,
60: Capacitor,
801, 802, 803 ... short-circuit determination unit,
SW1 ... 1st switch, SW2 ... 2nd switch.

Claims (6)

A first primary winding (30) and a second primary winding (40), one end of which is connected to one electrode of the DC power source (15) and constituting the primary side of the transformer (20);
A first switch (SW1) and a second switch (SW2) connected between the other ends of the first primary winding and the second primary winding and the other electrode of the DC power source;
One or more secondary windings (50) constituting the secondary side of the transformer;
A capacitor (60) connected to both ends of the secondary winding and constituting a LC resonance circuit as a load together with a leakage inductance (52) of the secondary winding;
A drive signal generator (70) for generating a drive signal for driving the first switch and the second switch so as to complementarily turn on and off;
When the first switch is turned off and the second switch is turned on, the exciting winding voltage (Vc), which is induced in the transformer and generated in the exciting inductance (31, 41) of the primary winding, is A short-circuit determination unit (801, 802, 801) that detects a short-circuit abnormality of the load based on a detection value of the excitation winding voltage that is detected based on a first switch voltage (Vsw1) that is a drain-source voltage of one switch. 803),
An insulated power conversion device comprising: The short circuit determination unit (801)
The insulated power converter according to claim 1, wherein when the absolute value of the time change rate of the excitation winding voltage is less than a predetermined change rate threshold (α_th), the load is determined to be in a short circuit abnormality. The short circuit determination unit (802)
Set the range including the constant value of the excitation winding voltage when the load is short-circuited as a specified range,
The excitation winding voltage is AD-converted at a predetermined conversion cycle, and when the number of times that the AD conversion value is within the specified range exceeds a predetermined number of times threshold (N_th), it is determined that the load is in short circuit abnormality. The insulated power converter according to claim 1. The short circuit determination unit (803)
Set the range including the constant value of the excitation winding voltage when the load is short-circuited as a specified range,
2. The insulated power converter according to claim 1, wherein when the time that the excitation winding voltage is within the specified range exceeds a predetermined time threshold (T_th), it is determined that the load is in a short circuit abnormality. The short circuit determination unit (802, 803)
The insulated power converter according to claim 3 or 4, wherein the specified range is variably set according to a power supply voltage (Vin) of the DC power supply. When the short-circuit determining unit determines that the load is a short-circuit abnormality,
The insulation type power converter according to any one of claims 1 to 5 which stops switching operation of said 1st switch and said 2nd switch.

Images