Power conversion device with temperature protection

Provided is a power conversion device capable of directly performing a protection operation according to the state of a cooler. A control unit includes: a semiconductor switching element loss calculation unit which calculates a loss in a semiconductor switching element with use of a switching state of the semiconductor switching element, and a current detection value or a voltage detection value; and a cooler state estimation unit which estimates a state of a cooler on the basis of a loss calculation value from the semiconductor switching element loss calculation unit and a temperature detection value from a temperature detector. The control unit limits current flowing to the semiconductor switching element on the basis of the state of the cooler.

BACKGROUND OP THE INVENTION

1. Field of the Invention

The present disclosure relates to a power conversion device.

2. Description of the Background Art

Power conversion devices for electric vehicles are required to operate without failure under various conditions and to enable a vehicle to continuously operate in an abnormal state.

A semiconductor switching element of a power conversion device may fail if power loss is generated in a switching operation and the junction temperature of the semiconductor switching element exceeds a predetermined value. Thus, it is important to accurately detect the junction temperature. However, since a junction is a joined portion of a semiconductor chip, it is difficult to directly measure the junction temperature.

To solve this problem, methods are disclosed in which the temperature of a semiconductor switching element is detected and a junction temperature is estimated using the detected temperature value and a loss calculated from an operation of the semiconductor switching element (for example, Patent Document 1).

In the method disclosed in Patent Document 1, although the junction temperature is estimated from a correlation between the calculated loss and increase in the temperature, change in the state of a cooler is not considered. Therefore, when the state of the cooler is changed, a problem arises in that the junction temperature cannot be accurately estimated, and protection cannot be reliably performed.

SUMMARY OF THE INVENTION

The present disclosure has been made to solve the above problems, and an object of the present disclosure is to provide a power conversion de/ice capable of directly performing a protection operation according to the state of a cooler through determination of the state of the cooler.

The power conversion device disclosed in the present disclosure includes: a semiconductor switching element which converts power by a switching operation; a cooler which cools the semiconductor switching element; a control unit which controls the semiconductor switching element; a temperature detector which detects a temperature of the semiconductor switching element; a current detector which detects current flowing to the semiconductor switching element; and a voltage detector which detects voltage applied to the semiconductor switching element. The control unit includes: a semiconductor switching element loss calculation unit which calculates a loss in the semiconductor switching element with use of a switching state of the semiconductor switching element and both or either of a current detection value and a voltage detection value; and a cooler state estimation unit which estimates a state of the cooler from a loss calculation value from the semiconductor switching element loss calculation unit and a temperature detection value from the temperature detector. The control unit limits current flowing to the semiconductor switching element on the basis of the state of the cooler.

According to the power conversion device disclosed in the present disclosure, a power conversion device capable of reliably performing a protection operation even when the state of the cooler is changed, is obtained.

First Embodiment

A first embodiment relates to a power conversion device including: semiconductor switching elements which convert power; a cooler which cools the semiconductor switching elements; a control unit which controls the semiconductor switching elements; temperature detectors which detect temperatures of the semiconductor switching elements; current detectors which detect currents flowing to the semiconductor switching elements; and voltage detectors which detect voltages that are applied to the semiconductor switching elements. The control unit calculates losses in the semiconductor switching elements with use of switching states of the semiconductor switching elements, and current detection values or voltage detection values. The control unit estimates the state of the cooler from the loss calculation values and temperature detection values. The control unit limits currents flowing to the semiconductor switching elements on the basis of the state of the cooler.

Hereinafter, a configuration and an operation of the power conversion device according to the first embodiment will be described with reference toFIG. 1which is a block diagram showing the configuration of the power conversion device,FIG. 2which is a schematic diagram of a cooler thermal network for explaining influence of change in the state of the cooler, andFIG. 3which is a block diagram showing a configuration of the cooler stats estimation unit.

First, the configuration of a power conversion device100according to the first embodiment will be described with reference toFIG. 1.

The power conversion device100includes a power conversion circuit10and a control unit50A.

The power conversion device100according to the first embodiment is assumed to be used in an electric vehicle such as an electric automobile or a plug-in hybrid automobile and is assumed to drive a motor serving as a driving force source by power from a high-voltage battery.

The power conversion device100converts power by a switching operation using semiconductor switching elements such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal Oxide Semiconductor Field Effect Transistors).

The power conversion circuit10is a two-phase interleaved step-up DC/DC converter circuit. The power conversion circuit10is broadly divided into an input section, a power conversion section, and an output section.

The input section of the power conversion circuit10includes an input smoothing capacitor11and step-up reactors12aand12b. Here, input voltage is denoted by Vi.

The power conversion section of the power conversion circuit10includes semiconductor switching elements13aand13bwhich are a pair of switching elements, and semiconductor switching elements13cand13dwhich are also a pair of switching elements.

The output section of the power conversion circuit10includes an output smoothing capacitor14. Here, output voltage is denoted by Vo.

The power conversion circuit10further includes a cooler35which cools the semiconductor switching elements13ato13d. The cooler35of the power conversion device100according to the first embodiment is assumed to be a water-based cooler.

Each of the semiconductor switching elements13ato13dis an MOSFET in which a diode is included between the source and the drain.

The types and the number of the semiconductor switching elements, and the type of the power conversion device, are not limited thereto. For example, each semiconductor switching element may be an IGBT, a SiC-MOSFET, or the like, and the power conversion device may be an inverter or the like.

Next, the detectors of the power conversion circuit10will be described.

In the power conversion section of the power conversion circuit10, temperature detectors17a,17b,17c, and17das the temperature detectors are disposed inside or near the semiconductor modules30ato30d, respectively, to detect the temperatures of the semiconductor switching elements13ato13d.

The temperature detectors17ato17dwhich detect the temperatures of the semiconductor switching elements13ato13dmay be disposed inside the semiconductor modules30ato30dor disposed, near the semiconductor modules30ato30d, on a board on which the semiconductor modules30ato30dare disposed. The temperature detectors are assumed to be thermistors.

The input section of the power conversion circuit10includes an input voltage detector15and reactor current detectors16aand16b.

The output section of the power conversion circuit10includes an output voltage detector18.

Next, the control unit50A will be described.

The control unit59A includes a semiconductor switching element loss calculation unit52, a cooler state estimation unit53, a step-up operation control unit54a, and a gate drive circuit55.

InFIG. 1, the semiconductor switching element loss calculation unit is written as an element loss calculation unit.

An output signal from each of the detectors and functional, units will be described before a function and an operation of the control unit50A are described.

A detected value from the input voltage detector15is referred to as an input voltage detection value21a. Detected values from the reactor current detectors16aand16bare referred to as reactor current detection values23aand23b. Detected values from the temperature detectors17ato17dare referred to as temperature detection values22ato22d. A detected value from the output voltage detector18is referred to as an output voltage detection value21b. The temperature detection values22ato22dare, as appropriate, referred to as temperature detection values22, where the temperature detection values22ato22ddo not particularly need to be distinguished from one another. Similarly, the reactor current detection values23aand23bare, as appropriate, referred to as reactor current detection values23.

The reactor current detection values23aand23band the temperature detection values22ato22dare not shown inFIG. 1.

An output signal from the semiconductor switching element loss calculation unit52is referred to as a semiconductor switching element loss calculation value24. An output signal from the cooler state estimation unit53is referred to as cooler state information25. Output signals from the step-up operation control unit54aare referred to as semiconductor switching element loss calculation information26and a gate control signal27. An output signal from the gate drive circuit55is referred to as a gate drive signal28.

The semiconductor switching element loss calculation unit52receives semiconductor switching element loss calculation information26from the step-up operation control unit54a, calculates losses in the semiconductor switching elements, and outputs semiconductor switching element loss calculation values24.

The cooler state estimation unit53receives the semiconductor switching element loss calculation values24from the semiconductor switching element loss calculation unit52and temperature detection values22from the temperature detectors17ato17d, estimates a state of the cooler35, and outputs cooler state information25.

The step-up operation control unit54areceives the cooler state information25from the cooler state estimation unit53, an input voltage detection value21afrom the input voltage detector15, reactor current detection values23from the reactor current detectors16aand16b, and an output voltage detection value21bfrom the output voltage detector18.

When receiving them, the step-up operation control unit54aoutputs a gate control signal27for controlling the step-up operation of the power conversion circuit10by switching ON/OFF of the semiconductor switching elements13ato13d. In addition, the step-up operation control unit54aoutputs semiconductor switching element loss calculation information26.

The gate drive circuit55converts, into a gate drive signal28, the gate control signal27generated by the step-up operation control unit54a.

Next, increases in the junction temperatures of the semiconductor switching elements and a cooling effect of the cooler will be described with reference toFIG. 2to ease the understanding of a function and an operation of the power conversion device100according to the first embodiment.

FIG. 2shows a thermal network for each semiconductor switching element, the corresponding temperature detector, and the cooler35, in an example of the power conversion device in which the cooler35is used.

Change, due to change in the state of the cooler, in a correlation between heat resistance or electrical loss and increase in the temperature will be described. The

Elements composing the coder thermal network will be described with reference toFIG. 2.

Each semiconductor nodule30is composed of the semiconductor switching element13, a bus bar31, solder32, a substrate33, and the temperature detector17.

The semiconductor switching element13and the temperature detector17are disposed on the substrate33, and the bus bar31is connected onto the semiconductor switching element13by solder32.

The semiconductor module30is joined to the cooler35via an insulating member34, and the cooler35is cooled by cooling water36.

Although the temperature detector17is provided to detect the junction temperature of the semiconductor switching element13, the temperature detector17cannot be directly disposed at a junction for structural reasons. Thus, as shown inFIG. 2, the temperature detector17is disposed near the semiconductor switching element13.

Next, heat resistances composing the thermal network will be described.

Heat resistances on a direct heat transmission path from the junction of the semiconductor switching element13to the temperature detector17, are referred to as heat resistances37,38a,38b, and40.

Heat resistances on a heat transmission path extending via the cooler35, are referred to as heat resistances39a,39b,39c,41a, and41b.

Heat resistances on a heat dissipation path to the cooling water36, are referred to as heat resistances42a,42b, and42c.

Here, when the state of the cooler35is normal, an increase in the temperature corresponding to a loss generated in the semiconductor switching element13is determined by the thermal network inFIG. 2on the basis of the temperature of the cooling water36.

Therefore, the junction temperature of the semiconductor switching element13, the temperature detection value from the temperature detector17, and the temperature of the cooling water36are uniquely determined.

Since the thermal network inFIG. 2has a known configuration, the junction temperature of the semiconductor switching element13can be estimated from the temperature detected by the temperature detector17.

However, in leakage of cooling water as an example of the change in the state of the cooler35, the cooling water36flows out, and thus the heat dissipation path to the cooling water36is lost. In this case, the heat resistances42ato42cin the thermal network inFIG. 2are not given.

FIG. 2shows the thermal network only with the heat resistances for simplification. However, in fact, heat capacities are given in parallel to the heat resistances. The junction temperature of the semiconductor switching element13and the temperature detected by the temperature detector17each experience a transient temperature change with the heat capacities being dominant, from the initial state with a temperature distribution obtained when the cooling water36is lost.

As described above, when the state of the cooler35is changed, the thermal network is changed, and thus the relationship between the junction temperature of the semiconductor switching element13and the temperature detected by the temperature detector17is changed.

The purpose of the power conversion device100according to the first embodiment is to enable power conversion operation to appropriately continue so as to adapt to the change in the state of the cooler35.

Hereinafter, a fundamental operation principle of the power conversion device110according to the first embodiment will be described.

In the control unit50A, the step-up operation control unit54adetermines and controls switching patterns of the semiconductor switching elements13ato13don the basis of the input voltage detection value21afrom the input voltage detector15, the output voltage detection value21bfrom the output voltage detector18, and the reactor current detection values23from the reactor current detectors16aand16bsuch that the output voltage Vo becomes a target value. In addition, the step-up operation control unit54aperforms a predetermined protection operation on the basis of the cooler state information25from the cooler state estimation unit53and the temperature detection values22from the temperature detector17ato17daccording to the state of the cooler35and the temperature detection values22.

Next, a method for estimating the state of the cooler35which is the main feature of the power conversion device100according to the first embodiment, will be described.

The cooler state estimation unit53estimates the state of the cooler35on the basis of the semiconductor switching element loss calculation values24from the semiconductor switching element loss calculation unit52and the temperature detection values22.

Losses in the semiconductor switching elements13ato13dare calculated on the basis of the semiconductor switching element loss calculation information26outputted from the step-up operation control unit54a.

The semiconductor switching element loss calculation information26is calculated on the basis of a carrier frequency and a switching-ON time generated by the step-up operation control unit54a, the reactor current detection values23from the reactor current detectors16aand16b, the input voltage detection value21afrom the input voltage detector15, and the output voltage detection value21bfrom the output voltage detector18.

The semiconductor switching element loss calculation unit52holds loss characteristics of the switching elements and flyback diodes in advance, and calculates, as each semiconductor switching element loss calculation value24, the total value of conduction losses and switching losses which are calculated for each switching element and each flyback diode with use of the loss characteristics.

The calculation of the semiconductor switching element loss calculation value24by the semiconductor switching element loss calculation unit52may be performed using all the information described above related to semiconductor switching losses, or may be performed using minimum necessary information, e.g., the carrier frequency and the switching-ON time, and the reactor current detection values23or the output voltage detection value21b.

Next, a configuration and a function of the cooler state estimation unit53will be described with reference toFIG. 3.

FIG. 3is a block, diagram showing a configuration of the cooler state estimation unit53.

The cooler state estimation unit53includes a temperature detection value holding unit53A, a temperature detection value estimation unit53B, an adder/subtractor53C, and a cooler state determination unit53D.

The temperature detection value holding unit53A holds previous temperature detection values22detected by the temperature detectors17ato17d.

The temperature detection value estimation unit53B estimates a present temperature detection value on the basis of each previous temperature detection value22held by the temperature detection value holding unit53A and the corresponding semiconductor switching element loss calculation value24from the semiconductor switching element loss calculation unit52.

The adder/subtractor53C calculates the difference between an estimated value of the present temperature detection value and the corresponding temperature detection value22.

The cooler state determination unit53D determines the state of the cooler35from the output the difference between the estimated value of; the present temperature detection value and the temperature detection value22) from the adder/subtractor53C.

Here, the cooler35of the power conversion device100according to the first embodiment is assumed to be a water-based cooler. The state of the cooler35to be determined by the cooler state determination unit53D is classified into two types which are a normal cooler state and an abnormal cooler state due to leakage of cooling water.

In the temperature detection value estimation unit53B, a correlation between each temperature detection value22and a loss in the corresponding semiconductor switching element is stored in advance.

The temperature detection value estimation unit53B estimates a present temperature detection value to be detected, on the basis of the present loss in the semiconductor switching element, the previous temperature detection value22, and the correlation stored in the temperature detection value estimation unit53B. An “estimated temperature detection value to be detected” is referred to as an “estimated value of the temperature detection value”.

Here, the temperature detection value to be detected means a temperature detection value when the cooler35is normal.

The cooler state determination unit53D sets a threshold value for the difference between the estimated value of the temperature detection value and the temperature detection value22. If the difference exceeds the set threshold value, the cooler state determination unit53D outputs, as the cooler state information25, the indication that the cooler is abnormal.

The correlation between the temperature detection value22and the loss in the semiconductor switching element is approximated by a zero- or higher-order lag element.

When the protection in a steady operation for which no temporal element has to be considered is intended, approximation at zero order (approximation only by the heat resistances) is enough to implement the present invention, and processing load in the control unit50A can be reduced.

Meanwhile, when variation in the output from the power conversion circuit10is great and a temporal element needs to be considered, approximation by a first- or higher-order lag element (approximation by the heat resistances and the heat capacities) is preferable. As the order for the correlation is increased, the correlation can be approximated with higher accuracy, but the processing load in the control unit50A becomes greater. Thus, it is necessary to select an appropriate order.

Next, a predetermined protection operation in the power conversion device100according to the first embodiment will be described.

In the predetermined protection operation, if the temperature detection values22exceed threshold values having been set for the temperature detection values22, the switching patterns of the semiconductor switching elements13ato13dare controlled so as to limit currents flowing in the semiconductor switching elements13ato13d.

Each threshold value is set on the assumption that the state of the cooler35is normal. The threshold value is set for the purpose of performing the protection operation if a predetermined operation range is exceeded.

In addition, if the cooler state information25which is the output from the cooler state estimation unit53indicates the cooler abnormality, the power conversion device100controls the switching patterns of the semiconductor switching elements13ato13dso as to limit currents in the semiconductor switching elements13ato13din the same manner.

As described above, in the power conversion device100according to the first embodiment, the state of the cooler35is estimated, and the protection operation is performed according to the state of the cooler. Accordingly, although conventional methods do not allow appropriate protection to be performed when the state of the cooler35is changed, the protection operation can be reliably performed also in the case.

In addition, since the state of the cooler35is estimated using the correlation approximated by a zero- or higher-order lag element, it is possible to estimate the state of the cooler so as to accurately follow a time-dependent change in the output while reducing the processing load in the control unit50a.

As described above, the power conversion device according to the first embodiment includes: the semiconductor switching elements which convert power; the cooler which cools the semiconductor switching elements; the control unit which controls the semiconductor switching elements; the temperature detectors which detect the temperatures of the semiconductor switching elements; the current detectors which detect currents flowing to the semiconductor switching elements; and the voltage detectors which detect voltages that are applied to the semiconductor switching elements. The control unit calculates losses in the semiconductor switching elements with use of the switching states of the semiconductor switching elements, and the current detection values or voltage detection values. The control unit estimates the state of the cooler from the loss calculation values and the temperature detection values. The control unit limits currents flowing to the semiconductor switching elements on the basis of the state of the cooler. Accordingly, the power conversion device according to the first embodiment enables the protection operation to be reliably performed even when the state of the cooler is changed.

Second Embodiment

A power conversion device according to a second embodiment is different from the power conversion device according to the first embodiment in that a junction temperature calculation unit is additionally provided to the control unit so as to also allow a protection operation based on junction temperature calculation values.

Hereinafter, an operation of the power conversion device according to the second embodiment will be described focusing on differences from that in the first embodiment with reference toFIG. 4which is a block diagram showing a configuration of the control unit andFIG. 5which is a block, diagram showing a configuration of the junction temperature calculation unit.

InFIG. 4which is the block diagram showing the configuration of the control unit in the second embodiment, parts that are the same as or correspond to those in the first embodiment are denoted by the same reference characters.

The power conversion device, the control unit, and the step-up operation control unit are denoted by200,508, and54b, respectively, for discrimination from those in the first embodiment.

The power conversion device200according to the second embodiment includes the power conversion circuit10and the control unit50B. The power conversion circuit10is the same as that of the power conversion device100according to the first embodiment, and thus a configuration and a function of the control unit50B will be described.

The control unit50B includes the semiconductor switching element loss calculation unit52, the cooler state estimation unit53, the step-up operation control unit54b, the gate drive circuit55, and further a junction temperature calculation unit56.

The junction temperature calculation unit56includes a junction temperature increase characteristic selection unit56A, a junction temperature increase calculation unit56B, and an adder/subtractor56C.

Information added to the power conversion device according to the first embodiment will be described before the function and the operation of the control unit50B are described.

An output signal from the junction temperature calculation unit56is referred to as a junction temperature calculation value29. An output signal from the junction temperature increase characteristic selection unit56A is referred to as a junction temperature increase characteristic29a. An output signal from the junction temperature increase calculation unit56B is referred to as a junction temperature increase value29b.

The semiconductor switching element loss calculation unit52receives the semiconductor switching element loss calculation information26from the step-up operation control unit54b, calculates the losses in the semiconductor switching elements, and outputs the semiconductor switching element loss calculation values24.

The cooler state estimation unit53receives the semiconductor switching element loss calculation values24from the semiconductor switching element loss calculation unit52and the temperature detection values22from the temperature detectors17ato17d, estimates the state of the cooler35, and outputs the cooler state information25.

The step-up operation control unit54breceives the cooler state information25from the cooler state estimation unit53, the input voltage detection value21afrom the input voltage detector15, the reactor current detection values23from the reactor current detectors16aand16b, and the output voltage detection value21bfrom the output voltage detector18.

When receiving them, the step-up operation control unit54boutputs the gate control signal27for controlling the step-up operation of the power conversion circuit10by switching ON/OFF of the semiconductor switching elements13ato13d. In addition, the step-up operation control unit54boutputs the semiconductor switching element loss calculation information26.

The gate drive circuit55converts, into the gate drive signal28, the gate control signal27generated by the step-up operation control unit54b.

The junction temperature calculation unit56receives the cooler state information25from the cooler state estimation unit53, the semiconductor switching element loss calculation values24from the semiconductor switching element less calculation unit52, and the temperature detection values22, and outputs junction temperature calculation values29.

The step-up operation control unit54bof the control unit50B of the power conversion device200according to the second embodiment determines and controls the switching patterns of the semiconductor switching elements13ato13dsuch that the output voltage Vo becomes the target value, as does the step-up operation control unit54aof the control unit50A in the first embodiment.

In addition, the step-up operation control unit54bperforms a predetermined protection operation on the basis of the cooler state information25from the cooler state estimation unit53, the junction temperature calculation values29from the junction temperature calculation unit56, and the temperature defection values22from the temperature detectors17ato17d.

A method for estimating junction temperatures which is the main feature of the power conversion device200according to the second embodiment, will be described.

The junction temperature calculation unit56calculates the junction temperatures of the semiconductor switching elements13ato13don the basis of the semiconductor switching element loss calculation values24from the semiconductor switching element loss calculation unit52, the cooler state information25from the cooler state estimation unit53, and the temperature detection values22from the temperature detectors17ato17d.

Here, the junction temperature calculation values29outputted from the junction temperature calculation unit56can be fed back and inputted to the semiconductor switching element loss calculation unit52.

If the junction temperature calculation values29are inputted to the semiconductor switching element loss calculation unit52, a junction temperature dependence can be added to the loss characteristics of the switching elements and the flyback diodes held in advance in the semiconductor switching element loss calculation unit52. Accordingly, the semiconductor switching element loss calculation unit52can more accurately derive the losses in the semiconductor switching elements.

Next, a function of the junction temperature calculation unit56will be described with reference toFIG. 5.

The junction temperature increase characteristic selection unit56A receives the cooler state information25from the cooler state estimation unit53, and selects a junction temperature increase characteristic29acorresponding to the state of the cooler35.

The junction temperature increase calculation unit56B receives the junction temperature increase characteristic29afrom the junction temperature increase characteristic selection unit56A and the semiconductor switching element loss calculation values24from the semiconductor switching element loss calculation unit, and calculates junction temperature increase values23b.

The adder/subtractor56C adds the junction temperature increase values29bfrom the junction temperature increase calculation unit56B and the temperature detection values22, to obtain the junction temperature calculation values29.

As in the first embodiment, the cooler35of the power conversion device200according to the second embodiment is assumed to be a water-based cooler. The state of the cooler35to be determined by the cooler state determination unit53D is classified into two types which are a normal cooler state and an abnormal cooler state due to leakage off cooling water.

The junction temperature increase characteristic29aselected by the junction temperature increase characteristic selection unit56A is a temperature increase characteristic that corresponds to either of the two types of states of the cooler35, i.e., the normal cooler state and the abnormal cooler state due to leakage of cooling water.

For each state of the cooler35, the junction temperature increase characteristic selection unit56A stores, in advance, a correlation between the difference in temperature between each of the temperature detectors17ato17dand the junction of the corresponding one of the semiconductor switching elements13ato13dand the loss in the semiconductor switching element. The junction temperature increase characteristic selection unit56A selects and outputs an appropriate one of the correlations on the basis of the cooler state information25about the cooler35.

Here, the correlation between the difference in temperature between each of the temperature detectors17ato17dand the junction of the corresponding one of the semiconductor switching elements13ato13dand the loss in the semiconductor switching element, is approximated by a zero- or higher-order lag element for the same reason as that for the correlation between temperature detection value22and the loss in the semiconductor switching element.

A predetermined protection operation of the power conversion device200according to the second embodiment will be described.

In the predetermined protection operation, if the junction temperature calculation values29exceed threshold values having been set for the junction temperature calculation values29, the switching patterns of the semiconductor switching elements13ato13dare controlled so as to limit currents flowing in the semiconductor switching elements.

Each threshold value is set on the assumption that the state of the cooler35is normal. The threshold value is set to perform the protection operation if a predetermined operation range is exceeded.

In addition, if the cooler state information25indicates a cooler abnormality, currents are limited by controlling the switching patterns of the semiconductor switching elements13ato13dsuch that the junction temperature of each of the semiconductor switching elements13ato13dbecomes a predetermined threshold value or smaller.

As described above, in the power conversion device200according to the second embodiment, the correlation between the difference in temperature between each of the temperature detectors17ato17dand the junction of the corresponding one of the semiconductor switching elements13ato13dand the loss in the semiconductor switching element, is appropriately selected according to the state of the cooler35, and the junction temperature is estimated.

Accordingly, even when the state of the cooler35is changed, the junction temperatures of the semiconductor switching elements13ato13dcan be accurately estimated. In addition, since the junction temperatures are monitored even in the abnormal, cooler state, the protection operation can be reliably performed.

The power conversion device according to the second embodiment is different from the power conversion device according to the first embodiment in that the junction temperature calculation unit is additionally provided to the control unit so as to allow the protection operation based on the junction temperature calculation values.

Therefore, the power conversion device according to the second embodiment enables the protection operation to be reliably performed even when the state of the cooler is changed. Furthermore, since the junction temperatures are monitored, the protection operation can be reliably performed.

Third Embodiment

In a power conversion device according to a third embodiment, one of a plurality of abnormal cooler states is determined relative to the case where the cooler is normal, and, for the abnormal state, a corresponding one of predetermined appropriate protection operations is performed.

In addition, a modification of the power conversion device according to either of the first and second embodiments will be described in the third embodiment.

Hereinafter, a configuration of the power conversion device according to the third embodiment is the same as the configuration of the power conversion device according to each of the first and second embodiments.

An operation of the power conversion device according to the third embodiment will be described focusing on differences from those in the first and second embodiments.

In the power conversion device according to each of the first and second embodiments, the state of the cooler35is assumed to be classified into two types of states, i.e., the normal state and the abnormal state.

However, the abnormality of the cooler35is considered to include not only cooling water being lost but also different levels of abnormalities such as leakage of cooling water.

In the power conversion device according to the third embodiment, the abnormal state is classified into a plurality of levels from minor water leakage to cooling water being lost relative to the case where the cooler is normal, and, for each level, a corresponding one of the predetermined appropriate protection operations is performed.

Next, the states of the cooler and the protection operations in the power conversion device according to the third embodiment will be described.

A plurality of threshold values corresponding to the states of the cooler35are set for the difference between an estimated value of the temperature from any of the temperature detectors17assumed to be obtained in the normal cooler state and a detected value of the temperature, and one of the abnormal states of the cooler35is determined.

According to the determined one of the plurality of abnormal states of the cooler35, the power conversion device according to the third embodiment performs the corresponding one of the predetermined protection operations.

An example of the predetermined protection operations is current limitation. Specifically, the switching patterns of the semiconductor switching elements13ato13dare controlled so as to limit currents flowing in the semiconductor switching elements13ato13d. According to the state of the cooler35, the value for the current limitation is changed, or the operations of the semiconductor switching elements13ato13dare stopped.

If the protection operations are optimally set according to the abnormal stare of the cooler35, it is possible to perform the protection operations while minimizing loss of the function as the power conversion device in the abnormal state.

Next, a modification of the power conversion device according to either of the first and second embodiments will be described.

Although each semiconductor module30in the power conversion device according to each of the first and second embodiments is composed of one semiconductor switching element13and one temperature detector17, the present invention is not limited thereto. The semiconductor module30may be composed of, for example, a plurality of semiconductor switching elements and one temperature detector.

In this case, the one temperature detector is disposed at such a predetermined location as to establish a correlation with the temperature of each semiconductor switching element.

Here, correlations between temperature detection values and losses in the semiconductor switching elements are each approximated by a zero- or higher-order lag system, and the temperature detection value estimation unit53B stores the sum of the correlations obtained through the approximation by the zero- or higher-order lag system. The cooler state estimation unit53determines the state of the cooler with use of the sum of the correlations.

The estimations of the junction temperatures of the respective semiconductor switching elements are performed in the following manner: for each semiconductor switching element, a correlation between the difference in temperature between the one temperature detector and the junction of the semiconductor switching element and the loss in the semiconductor switching element, is approximated by a zero- or higher-order lag system and stored in the junction temperature increase characteristic selection unit56A, and the junction temperature calculation unit56calculates a junction temperature with use of the correlation for the semiconductor switching element.

With this configuration, the plurality of semiconductor switching elements can be protected with the one temperature detector, and thus overheat protection can be performed without increasing the number of components, whereby the cost for and the size of the power conversion device can be reduced.

The power conversion device according to either of the first and second embodiments may include a plurality of groups of semiconductor switching elements and temperature detectors near the semiconductor switching elements.

In the estimations of the junction temperatures, the thermal correlations between the semiconductor switching elements and the temperature detectors are intense, and less interference from other semiconductor switching elements leads to higher accuracies of the estimations.

When the power conversion device is composed of the plurality of semiconductor switching elements, if the power conversion device includes a plurality of groups which are each composed of one temperature detector and a plurality of semiconductor switching elements, the number of interfering factors, i.e., the semiconductor switching elements, per temperature detector is less, and thus the accuracies of the estimations of the junction temperatures can be increased.

In the power conversion device according to each of the first and second embodiments, it is assumed that the cooler is a water-based cooler and the state of the cooler is classified into the normal cooler state and leakage of cooling water. However, the present invention is not limited thereto. For example, an abnormality in the temperature of the cooler may be classified into one of the abnormal cooler states.

In the power conversion device according to each of the first and second embodiments, the cooler is a water-based cooler. However, the cooler is not limited thereto, and may be, for example, a cooling fan. In this case, the state of the cooler to be determined is assumed to be classified into cooler normality and cooler abnormality, including cooling fan failure and clogging in the fan.

In the power conversion device according to the third embodiment, one of the plurality of abnormal cooler states is determined relative to the case where the cooler is normal, and, for the abnormal state, a corresponding one of the predetermined appropriate protection operations is performed.

Therefore, the power conversion device according to the present third embodiment can reliably perform the protection operation even when the state of the cooler is changed. Furthermore, the power conversion device can perform the optimal protection operation according to the abnormal state of the cooler.

DESCRIPTION OF THE REFERENCE CHARACTERS

10power conversion circuit

13,13ato13dsemiconductor switching element

16a,16breactor current detector

21a,21binput voltage detection value

22temperature detection value

23reactor current detection value

24semiconductor switching element loss calculation value

25cooler state information

26semiconductor switching element loss calculation information

27gate control signal

28gate drive signal

29junction temperature calculation value

29ajunction temperature increase characteristic

29bjunction temperature increase value

37heat resistance (between junction of semiconductor switching element and substrate)

42ato42cheat resistance (between cooling water and cooler)

50A,50B control unit

52semiconductor switching element loss calculation unit

53cooler state estimation unit

53A temperature detection value holding unit

53B temperature detection value estimation unit

53D cooler state determination unit

54a,54bstep-up operation control unit

55gate drive circuit

56junction temperature calculation unit

56A junction temperature increase characteristic selection unit

56B junction temperature increase calculation uni

100,200power conversion device