JP6575362B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device including a cooler.

  2. Description of the Related Art Conventionally, in a power conversion device including a power converter such as an inverter, a technique for protecting an element such as a semiconductor switching element (hereinafter referred to as “power element”) that switches conduction or interruption of power current from overheating is known. For example, Patent Document 1 discloses an overheat protection device that estimates the junction temperature of a power element that is a heat-generating component and limits the current so that the estimated temperature does not exceed the allowable upper limit value.

JP 2014-64435 A

In the overheat protection control device of Patent Document 1, the temperature of the power element is estimated by detecting the temperature of the heat sink. For example, in a configuration using a liquid-cooled heat sink in which a refrigerant flows, it is assumed that the temperature of the refrigerant is detected.
However, the refrigerant temperature sensor is usually installed in a flow path outside the casing of the power conversion device due to space and wiring restrictions, and directly detects the maximum temperature of the refrigerant in the immediate vicinity of the power element. It is difficult. Therefore, since the maximum temperature of the refrigerant is estimated from the detected temperature at a remote location, an estimation error occurs. In order to absorb the error on the safe side from the viewpoint of overheat protection, a large temperature margin must be set.

  As a result, even if it is actually within the allowable range, it is determined that the power element is overheated, and the temperature lowering control is performed by unnecessary increase in the refrigerant flow rate or current limitation. Unnecessary temperature lowering control has a problem that the cooling system for increasing the flow rate of refrigerant causes an increase in size of the cooling system and a decrease in power efficiency. In the first place, this problem is considered to be caused by the idea of trying to grasp the cooling capacity of the refrigerant by the temperature.

  The present invention has been created in view of such a point, and an object thereof is to provide a power conversion device capable of accurately grasping the cooling capacity of the refrigerant flowing through the cooling pipe.

The power conversion device of the present invention includes a plurality of power converters (30, 31, 32), a cooler (5 0 ), phase detection means (601, 602, 603), and a boiling determination unit (71).
The power converter converts power by switching operations of the plurality of power elements (43, 44) and outputs the converted power. The power converter includes, for example, a converter, a regeneration inverter, and a power running inverter.
The cooler cools the power converter that generates heat by energizing the plurality of power elements by circulating the refrigerant.
The phase detection means detects a predetermined physical quantity that reflects the difference between the liquid phase state and the gas phase state of the refrigerant flowing through the cooling pipe (5 3 ) of the cooler for each power converter .
A boiling determination part determines that the refrigerant | coolant which flows through a cooling pipe is boiling based on the physical quantity which the phase detection means detected.
The power element is configured in the form of a power module (41, 42) in which a heat spreader (45) having thermal conductivity contacts both surfaces.
The cooler includes a plurality of cooling tubes arranged alternately and stacked with a plurality of power modules, and a refrigerant flows from one introduction side to the other non-introduction side in the stacking direction. A refrigerant introduction pipe (51) for introducing the refrigerant into (531) and a refrigerant outlet pipe (52) for extracting the refrigerant from the outlets (532) of the plurality of cooling pipes are provided.
The phase detection means is a region corresponding to an end portion on the outlet side of the power module on the outlet side with respect to the center of the inlet side and outlet side of the cooling pipe for each power converter, and is laminated. It is arrange | positioned in the anti-introduction side with respect to the center of the introduction side and anti-introduction side of the refrigerant | coolant inlet tube in a direction.

  In general, when a substance undergoes a phase change from a liquid phase state to a gas phase state, the thermal conductivity rapidly decreases, so that the cooling capacity of the refrigerant is significantly reduced. The present invention pays attention to this point and is characterized by grasping the cooling capacity of the refrigerant not by the temperature of the refrigerant but by the change from the liquid phase state to the gas phase state. Is provided. The phase detection means detects “a predetermined physical quantity that reflects the difference between the liquid phase state and the gas phase state of the refrigerant flowing through the cooling pipe”. A boiling determination part determines that the refrigerant | coolant which flows through a cooling pipe is boiling based on the physical quantity which the phase detection means detected. Thereby, the cooling capacity of the refrigerant flowing through the cooling pipe can be accurately grasped.

Specifically, the following configuration or the like can be adopted as the phase detection means and the boiling determination unit.
(A) The phase detection means (601) detects a potential difference between a pair of electrodes (61, 62) facing each other inside the cooling pipe. The boiling determination unit determines that the refrigerant flowing through the cooling pipe is boiling based on the electric capacity of the refrigerant calculated from the potential difference or an impedance inversely proportional to the electric capacity.
(B) The phase detection means (602) detects the reflected wave of the ultrasonic wave generated in the refrigerant by the ultrasonic generator (67). A boiling determination part determines that the refrigerant | coolant which flows through a cooling pipe is boiling based on the time from transmission of an ultrasonic wave to reception of a reflected wave.
(C) The phase detection means (603) detects the reflected wave of the light emitted from the optical fiber probe (68) into the refrigerant. The boiling determination unit determines that the refrigerant flowing through the cooling pipe is boiling based on the refractive index of the emitted light.

  The power conversion device of the present invention preferably further includes a refrigerant temperature control unit (72) that executes “temperature decrease control” for reducing the temperature of the refrigerant when the boiling determination unit determines that the refrigerant is boiling. . In the temperature drop control, for example, the refrigerant temperature control unit increases the flow rate of the refrigerant with respect to the refrigerant supply unit (73) that supplies the refrigerant, or controls the current supplied to the power element (74). ) Is output to limit the current.

In the conventional technique for grasping the cooling capacity of the refrigerant based on the refrigerant temperature, unnecessary temperature lowering control may be performed even when the actual refrigerant temperature is lower than the threshold by setting the temperature margin in consideration of the estimation error. Therefore, there is a problem that the cooling system is enlarged and the power efficiency is lowered.
On the other hand, in the present invention, it is determined that the refrigerant flowing through the cooling pipe is boiling based on the physical quantity detected in a state where the refrigerant has actually undergone a phase change, and the temperature lowering control is started for the first time at the determination timing. Therefore, normal control can be continued without increasing the refrigerant flow rate or limiting the current to the limit of the temperature at which liquid cooling is possible. Therefore, it can contribute to size reduction and efficiency improvement of the cooling system.

The top view of the power converter device of 1st Embodiment. (A) II-II sectional view taken on the line of FIG. (B) The figure which shows the change of refrigerant | coolant temperature. The circuit diagram of the power converter of a 1st embodiment. The schematic cross section of the cooler of a 1st embodiment. The time chart which shows the impedance change by the temperature fall control of 1st Embodiment. The flowchart which shows the temperature fall control process of 1st Embodiment. The schematic cross section of the cooler of 2nd, 3rd embodiment. The (a) top view and (b) schematic cross section of the cooler of a 4th embodiment.

Hereinafter, a plurality of embodiments of a power converter of the present invention are described based on a drawing. The fourth embodiment corresponds to a reference form.
The power conversion device of each embodiment is applied to, for example, a power system that converts power between a high-voltage battery and a motor generator in a hybrid vehicle or an electric vehicle. In the plurality of embodiments, substantially the same configuration is denoted by the same reference numeral, and description thereof is omitted.

(First embodiment)
The power converter device of 1st Embodiment is demonstrated with reference to FIGS.
The cooler 50 which comprises the power converter device of 1st Embodiment is shown to FIG.1 and FIG.2 (a).
The cooler 50 includes a refrigerant introduction pipe 51 and a refrigerant outlet pipe 52 arranged substantially in parallel, and a plurality of cooling pipes 53 arranged in a direction intersecting with the refrigerant introduction pipe 51 and the refrigerant outlet pipe 52. . A plurality of cooling pipes 53 formed in a flat cylindrical shape with a heat conductive material such as aluminum are alternately stacked with a plurality of power modules 41 and 42.
In addition, illustration of the housing | casing of the cooler 50, a bus bar, a terminal, etc. is abbreviate | omitted except one part.

In the refrigerant introduction pipe 51, the refrigerant flows from one introduction side (that is, the upper side in FIG. 1) in the stacking direction toward the other opposite side (that is, the lower side in FIG. 1). Introduce refrigerant into the inlet.
The refrigerant outlet pipe 52 leads the refrigerant from the outlets of the plurality of cooling pipes 53.
1, the refrigerant flows downward from the upper left of FIG. 1 through the refrigerant introduction pipe 51, branches into a plurality of cooling pipes 53, flows from the left to the right, and merges with the refrigerant outlet pipe 52. To do. Then, it flows upward through the refrigerant outlet pipe 52 toward the upper right in FIG.

In this specification, a semiconductor switching element such as an IGBT to which a power current used for driving a load or the like is supplied is referred to as “power element”. A module in which a heat spreader 45 (see FIG. 4) having thermal conductivity is in contact with both surfaces or one surface of a semiconductor chip of a power element is referred to as a “power module”.
The reference numerals of the power element and the power module are distinguished from those constituting the upper arm of the power converter and those constituting the lower arm. The sign of the power element of the upper arm is “43”, and the sign of the power element of the lower arm is “44”. Also, the power module including the upper arm power element 43 is denoted by “41”, and the power module including the lower arm power element 44 is denoted by “42”. These codes are commonly used regardless of the type and phase of the power converter.

  The power module 41 and the power module 42 of the upper and lower arms form a pair, and the cooler 50 forms one layer of a laminated structure. The upper arm power module 41 is disposed on the refrigerant introduction pipe 51 side, and the lower arm power module 42 is disposed on the refrigerant outlet pipe 52 side. Therefore, the refrigerant flows so as to cool the power module 42 of the lower arm after cooling the power module 41 of the upper arm first.

  In FIG. 2A, a region where the power modules 41 and 42 and the cooling pipe 53 overlap when viewed from the stacking direction is represented as “module region Rm”. Further, the region on the refrigerant introduction pipe 51 side with respect to the module region Rm is referred to as “inlet region Rin”, and the region on the refrigerant outlet tube 52 side with respect to the module region Rm is referred to as “outlet region Rout”. The inlet region Rin and the outlet region Rout are regions where the power modules 41 and 42 and the cooling pipe 53 do not overlap when viewed from the stacking direction.

FIG. 2B shows the relationship between the position of the cooling pipe 53 and the refrigerant temperature in the refrigerant flow direction.
The refrigerant temperature is relatively low on the inlet 531 (see FIG. 4) side of the cooling pipe 53 and relatively high on the outlet 532 (see FIG. 4) side. That is, the temperature gradually increases in the module region Rm that receives heat from the power modules 41 and 42, and reaches the maximum temperature in the vicinity of the boundary region between the module region Rm and the outlet region Rout.
In the first embodiment, the phase state of the refrigerant is set in the “boundary region between the module region Rm and the outlet region Rout”, in other words, the “region corresponding to the end portion on the outlet side of the power module 42 of the lower arm”. A phase detecting means 601 for detecting is arranged. Details of the phase detection means 601 will be described later.

  Returning to FIG. 1, in the first embodiment, a configuration in which the power modules 41 and 42 are stacked in a total of 11 stages is exemplified. The eleven-stage power modules 41, 42 constitute three types of power converters, a power running inverter 32, a regeneration inverter 31, and a converter 30 in order from the introduction side of the refrigerant introduction pipe 51.

Here, FIG. 3 is referred about the circuit structure of the power converter with which the power converter device of 1st Embodiment is provided.
The power conversion device 20 is provided between the battery 15 as a “DC power supply” and the two motor generators 81 and 82, and includes three types of power converters: a converter 30, a regeneration inverter 31, and a power running inverter 32. Including.

The two motor generators 81 and 82 are, for example, permanent magnet synchronous three-phase AC motors, and are mounted on a series-parallel hybrid vehicle or the like. The first motor generator (“MG1” in the figure) 81 mainly functions as a generator that generates electric power using torque transmitted from the engine and driving wheels. The second motor generator (“MG2” in the figure) 82 mainly functions as an electric motor that generates torque for driving the drive wheels by a power running operation.
The first motor generator 81 and the second motor generator 82 correspond to “generator” and “load” recited in the claims.

Converter 30 includes power elements 43, 44 of upper and lower arms, and a reactor 21 connected between battery 15 and a midpoint between power elements 43, 44. Reactor 21 can store and release electric energy due to an induced voltage generated with a change in current. A filter capacitor 22 for removing power supply noise from the battery 15 is provided at an input portion from the battery 15 to the converter 30.
The converter 30 boosts the DC voltage of the battery 15 and outputs the boosted voltage to the power running inverter 32 during power running by the complementary switching operation of the power elements 43 and 44, and reduces the voltage of the regeneration inverter 31 during regeneration. Regenerate to 15.

The regenerative inverter 31 and the power running inverter 32 are each constituted by a plurality of power elements 43 and 44 of three-phase (that is, U-phase, V-phase, and W-phase) upper and lower arms that are bridge-connected. A smoothing capacitor 23 for smoothing the input voltage is provided at the input portions of the inverters 31 and 32.
The regenerative inverter 31 converts the AC power generated by the first motor generator 81 into DC power and regenerates it to the battery 15 via the converter 30.
The power running inverter 32 converts DC power input from the battery 15 through the converter 30 into AC power and supplies the AC power to the second motor generator 82.

  In the example of FIG. 3, the regenerative inverter 31 is composed of a pair of power elements 43 and 44 and upper and lower arms of each phase, whereas the converter 30 and the power running inverter 32 are two sets connected in parallel. The upper and lower arms of each phase are constituted by the power elements 43 and 44. Each power element 43, 44 is connected in parallel with a free wheel diode that allows a current from the low potential side to the high potential side.

  In general, the converter 30 and the power running inverter 32 in which the energization amount during power running is larger than that of the regeneration inverter 31 require a power element having a relatively large rating. However, using separate parts for the regeneration inverter 31, the converter 30 and the power running inverter 32 is not preferable from the viewpoint of design standardization. In addition, if a power element matched to the rating for the converter 30 or the power running inverter 32 is used for the regenerative inverter 31, it becomes excessive specifications and waste occurs.

Therefore, it is efficient to use the power element for the regenerative inverter 31 as a standard product, and to connect and use a plurality of standard power devices in the converter 30 and the power running inverter 32 in parallel. 3 includes two sets of converters 30, three sets of regenerative inverters 31, six sets of power running inverters 32, and a total of eleven sets of power elements 43 and 44 for the upper and lower arms. ing. Corresponding to this circuit configuration, as shown in FIG. 1, a laminated structure of eleven power modules 41 and 42 is formed. In particular, in the example of FIG. 1, the power running inverter 32 having a large energization amount is arranged on the most introduction side in the stacking direction.
However, in other embodiments, not only the circuit configuration of FIG. 3, the power elements 43 and 44 of the upper and lower arms of each phase of each power converter may all be configured as one set, or three or more sets may be parallel. It may be configured to be connected. Further, the arrangement order of the power converters in the stacking direction may be changed as appropriate.

  In the power conversion device 20, a path connecting the reactor 21 of the converter 30 and the intermediate points of the power elements 43 and 44 is connected by a bus bar 35. Further, a path connecting each phase output terminal of the regenerative inverter 31 and each phase winding of the first motor generator 81, each phase output terminal of the power running inverter 32, and each phase winding of the second motor generator 82, Are connected by bus bars 36 and 37, respectively.

  In addition, the power converter 20 is provided with a current sensor that detects a phase current, and a voltage sensor that detects a battery voltage and an inverter input voltage. The energization of each power converter is controlled based on the torque command output from the upper control circuit and feedback information from the current sensor, voltage sensor, rotation angle sensor provided in the motor generators 81 and 82, and the like. The Of the configuration relating to such energization control, only the energization control unit 74 is illustrated in FIG. In addition, since the configuration of the current sensor and the like is not a feature in the embodiment of the present invention, illustration and detailed description thereof are omitted.

  The power converters of the converter 30, the regenerative inverter 31, and the power running inverter 32 execute power conversion by switching the power elements 43 and 44 in accordance with the drive signals from the energization control units 74 corresponding thereto. The drive signal by the energization control unit 74 is generated using, for example, current feedback control or PWM control based on a current command. Since control of such a converter and an inverter is a well-known technique, detailed description is abbreviate | omitted.

Next, the characteristic configuration of the first embodiment will be described with reference mainly to FIG. 4 schematically showing a partial cross section in the stacking direction of FIG. In FIG. 4, the thickness in the stacking direction is exaggerated with respect to the length in the direction orthogonal to the stacking direction, that is, in the direction of the cooling pipe 53.
The power modules 41 and 42 are provided in a form in which heat spreaders 45 are in contact with both surfaces of the semiconductor chips of the power elements 43 and 44. The heat spreader 45 formed of a heat conductive material such as a copper plate has a surface opposite to the power elements 43 and 44 in contact with the wall of the cooling pipe 53, and generates heat generated by energization of the power elements 43 and 44. Diversify from both sides. In this specification, the power modules 41 and 42 having such a configuration are referred to as “double-sided heat radiation type power modules”.

The refrigerant circulates from the refrigerant introduction pipe 51 through the cooling pipe 53 and the refrigerant outlet pipe 52 by the pump function of the refrigerant supply unit 73. Therefore, the refrigerant inside the cooling pipe 53 flows from the inlet 531 connected to the refrigerant inlet pipe 51 toward the outlet 532 connected to the refrigerant outlet pipe 52 as indicated by a block arrow. At this time, the refrigerant in the cooling pipe 53 rises in temperature by receiving heat from the power modules 41 and 42, and bubbles due to boiling may be generated.
If the boiling of the refrigerant is left unattended, the liquid cooling function is lowered, and the power elements 43 and 44 are not sufficiently cooled. Therefore, the power elements 43 and 44 and other electronic elements on the circuit board may be destroyed by overheating. There is.

Conventionally, in order to prevent overheating destruction of the element, the refrigerant temperature is detected by a refrigerant temperature sensor installed in a flow path or the like outside the casing of the power converter, and when the detected temperature exceeds a predetermined value, the flow rate of the refrigerant is reduced. A technique for protecting an element from overheating by increasing or limiting a current is known. That is, the conventional technology tries to grasp the state of the refrigerant based on the temperature.
However, since the temperature of the refrigerant flowing through the cooling pipe closest to the power element is estimated from the detected temperature at a location away from the power element, an estimation error occurs. In order to absorb the error on the safe side from the viewpoint of overheat protection, a large temperature margin must be set.

As a result, even if it is actually within the allowable range, it is determined that the power element is overheated, and the temperature lowering control is performed by unnecessary increase in the refrigerant flow rate or current limitation. Unnecessary temperature lowering control has a problem that the cooling system for increasing the flow rate of refrigerant causes an increase in size of the cooling system and a decrease in power efficiency.
In view of this, the power conversion device 20 according to the embodiment of the present invention uses the “phase detection means 601 for detecting a predetermined physical quantity that reflects the difference between the liquid phase state and the gas phase state of the refrigerant flowing in the cooling pipe 53” as a cooler. 50, and as a control configuration, a boiling determination unit 71 and a refrigerant temperature control unit 72 are provided.

The boiling determination unit 71 determines that “the refrigerant flowing through the cooling pipe 53” is boiling based on the physical quantity detected by the phase detection unit 601.
When the boiling determination unit 71 determines that the refrigerant is boiling, the refrigerant temperature control unit 72 performs “temperature decrease control” that reduces the temperature of the “refrigerant flowing through the cooling pipe 53”. By this temperature lowering control, the refrigerant temperature control unit 72 performs control so that the refrigerant that has boiled and is in the gas phase state is returned to the liquid phase state.
Here, the temperature and the phase state of the refrigerant vary depending on the position of the refrigerant in the refrigerant introduction pipe 51, the cooling pipe 53, and the refrigerant outlet pipe 52. In this specification, in order to specify the refrigerant to be detected or temperature controlled, it is described as “refrigerant flowing through the cooling pipe 53”. The “refrigerant flowing through the cooling pipe 53” particularly means “refrigerant in the boundary region between the module region Rm and the outlet region Rout of the cooling tube 53”.

Further, in the wording definition, the temperature lowering control is to lower the temperature of the “refrigerant flowing through the cooling pipe 53”, but the object to be substantially cooled in the temperature lowering control is the power element 43, 44 or “cooling”. Any of “the refrigerant flowing through the pipe 53” may be used. That is, the cooling of the power elements 43 and 44 may be promoted by improving the cooling capacity of the refrigerant, and conversely, the heat receiving of the refrigerant may be suppressed by suppressing the heat generation of the power elements 43 and 44. .
In any case, it is considered that the temperature of both of the power elements 43 and 44 and the “refrigerant flowing through the cooling pipe 53” is lowered as a result of the interaction.

The phase detection means 601 of the first embodiment is as follows: “Because the dielectric constant of gas is smaller than the dielectric constant of liquid, the capacitance between a pair of electrodes installed in the gas is between the pair of electrodes installed in the liquid. On the contrary, the impedance of inversely proportional to the capacitance is larger in the gas than in the liquid. ”The principle of the capacitance void ratio meter is applied.
Specifically, the phase detection unit 601 includes a pair of electrodes 61 and 62, a pair of insulating plates 63 and 64, and a potential difference detector 65. The pair of electrodes 61 and 62 are provided on the flow path walls 54 facing each other inside the cooling pipe 53 via a pair of insulating plates 63 and 64. The potential difference detector 65 detects a potential difference between the pair of electrodes 61 and 62.

Here, the potential difference V [V] includes electric charge Q [C], electric capacity (electrostatic capacity) C [F], vacuum permittivity ε ₀ [F · m ⁻¹ ], relative permittivity ε _r [−]. Using the electrode area S [m ² ] and the inter-electrode distance d [m], this is expressed by the equation (1).

Since the relative dielectric constant of the gas is smaller than that of the liquid, when the “refrigerant flowing through the cooling pipe 53” boils and bubbles are generated, the potential difference V detected by the phase detection means 601 increases.
The boiling determination unit 71 calculates an electric capacity or an impedance that is inversely proportional to the electric capacity from the potential difference V detected by the phase detection unit 601 according to the equation (1). Then, it is determined that the “refrigerant flowing through the cooling pipe 53” is boiling by comparing the electric capacity or impedance with a determination threshold value. Note that when “the refrigerant flowing through the cooling pipe 53” boils, the electric capacity decreases and the impedance increases.

When the boiling determination unit 71 determines that the refrigerant is boiling, the refrigerant temperature control unit 72 outputs a temperature decrease command to the refrigerant supply unit 73 or the energization control unit 74 as the temperature decrease control.
For example, the refrigerant supply unit 73 is commanded to increase the flow rate of the refrigerant. As a result, since the cold refrigerant is newly supplied earlier than the temperature of the refrigerant in the cooling pipe 53 increases, the temperature of the “refrigerant flowing through the cooling pipe 53” decreases.
In addition, the energization control unit 74 is instructed to limit the current energized to the power element. As a result, since heat generation of the power elements 43 and 44 can be suppressed and the amount of heat received by the refrigerant can be reduced, the temperature of the “refrigerant flowing through the cooling pipe 53” decreases.

Further, the first embodiment is characterized in that the phase detection means 601 is arranged at an optimal position. As described above with reference to FIG. 2B, the temperature of the “refrigerant flowing through the cooling pipe 53” is the highest in the boundary region between the module region Rm and the outlet region Rout.
Therefore, the phase detection means 601 is arranged at least “on the outlet 532 side with respect to the center between the inlet 531 side and the outlet 532 side of the cooling pipe 53” in order to detect the phase state at the position where the maximum temperature is reached. It is preferred that In particular, it is more preferable to arrange in the “region corresponding to the end of the lower arm power module 42 on the outlet 532 side”.
“Arranged in the region corresponding to the end” means that the phase detecting means 601 is disposed across the module region Rm and the outlet region Rout as shown in FIGS. May be. Or the phase detection means 601 may be arrange | positioned in the position close | similar to a boundary line in either the module area | region Rm side or the outflow area | region Rout side.

Further, as shown in FIG. 1, it is preferable that at least one phase detection unit 601 is provided for each of the converter 30, the regeneration inverter 31, and the power running inverter 32 whose energization is individually controlled.
In the stacking direction, the refrigerant temperature rises from the introduction side of the refrigerant introduction pipe 51 toward the non-introduction side. Therefore, the phase detector 601 is disposed at least “on the opposite side to the center between the introduction side and the non-introduction side of the refrigerant introduction pipe 51 in the stacking direction” for each of the power converters 30, 31, 32. Is preferred. In particular, it is more preferable to arrange in the vicinity of the power module 42 of the lower arm farthest from the introduction side.

Next, the temperature lowering restriction process by the refrigerant temperature control unit 72 will be described with reference to the time chart of FIG. The vertical axis in FIG. 5 represents the impedance between the electrodes at the location where the phase detection means 601 is provided in the cooling pipe 53.
Two impedance threshold values Z1 and Z2 are set. The first threshold value Z1 corresponds to an impedance value in a state where there is a slight amount of bubbles that can be detected in the liquid phase. The second threshold value Z2 lower than the first threshold value Z1 corresponds to an impedance value in a state where the refrigerant is liquefied with certainty. In the impedance region between the first threshold value Z1 and the second threshold value Z2, for example, a state where the boundary between the liquid phase and the gas phase is fluctuating, or a minute amount of bubbles less than the detection limit amount exists in the liquid phase. Corresponds to the state image. These threshold values are determined by the electrical characteristics of the capacitor formed by the pair of electrodes 61 and 62 and the physical properties of the refrigerant.

From the initial t0 in FIG. 5 to the time t1, the impedance is equal to or less than the first threshold value Z1, and at this time, energization of the power converter is normally controlled. When the impedance exceeds the first threshold value Z1 at time t1, the boiling determination unit 71 determines that the refrigerant is boiling.
Thereafter, when the state where the impedance exceeds the first threshold value Z1 continues for a predetermined time Tc until time t2, the refrigerant temperature control unit 72 starts the temperature lowering control. Here, the predetermined time Tc is set within a time when the chips of the power elements 43 and 44 reach destruction.

In the temperature decrease control, the refrigerant temperature control unit 72 outputs a temperature decrease command to the refrigerant supply unit 73 so as to increase the flow rate of the refrigerant or to limit the current to the energization control unit 74.
When the temperature of the “refrigerant flowing through the cooling pipe 53” is lowered by the temperature lowering control, the impedance is lowered. Immediately after time t2 when the temperature lowering control is started, the impedance slightly overshoots due to a response delay and then starts to decrease.
For example, the refrigerant temperature control unit 72 may acquire the current value of the successive impedance and feedback control the temperature decrease command output by PI control calculation based on a deviation from the second threshold value Z2 that is the target value. Thereby, the coolant flow rate and the current limit value can be finely adjusted in response to the change in the actual impedance value.

Thereafter, the impedance falls below the first threshold Z1 at time t3, but the refrigerant temperature control unit 72 continues to output the temperature lowering command. When the impedance decreases to the second threshold value Z2 at time t4, the refrigerant temperature control unit 72 stops outputting the temperature decrease command and ends the temperature decrease control.
When the temperature lowering control is finished and the normal energization control is resumed, the temperature of the refrigerant rises again due to the heat generated by the power elements 43 and 44, and the impedance rises accordingly. Also at this time, the impedance starts to rise after being slightly undershooted by the response delay.
As described above, the increase in impedance during normal control and the decrease in impedance during temperature decrease control are alternately repeated.

Then, the flowchart of FIG. 6 is referred about the routine of a temperature fall restriction | limiting process. In the description of the flowchart below, the symbol “S” means a step. This processing routine is repeatedly executed during the operation of the power conversion device 20.
In S <b> 1, the phase detection unit 601 detects the potential difference between the electrodes 61 and 62. The boiling determination unit 71 calculates the impedance between the electrodes from the potential difference V according to the equation (1).

In S2, the boiling determination unit 71 determines whether or not the impedance exceeds the first threshold value Z1. When the impedance is equal to or lower than the first threshold value Z1 (S2: NO), the process is terminated.
On the other hand, when the impedance exceeds the first threshold value Z1 (S2: YES), the boiling determination unit 71 determines that the refrigerant is boiling.
Then, in S3, the refrigerant temperature control unit 72 starts counting the continuation time, that is, the time during which the state in which the impedance is determined to exceed the first threshold value Z1 by the boiling determination unit 71 continues.

Thereafter, the refrigerant temperature control unit 72 repeats counting the duration until it is determined in S4 that the duration has reached the predetermined time Tc.
When the duration time reaches the predetermined time Tc (S4: YES), the refrigerant temperature control unit 72 outputs a refrigerant flow rate increase command or a current limiting temperature lowering command in S5. The output of the temperature lowering command is continued until it is determined in S6 that the impedance has decreased below the second threshold value Z2.
When it is determined that the impedance has decreased to the second threshold value Z2 or less (S6: YES), the refrigerant temperature control unit 72 ends the temperature decrease control (S7).

(effect)
The effect of the first embodiment will be described.
(1) In the prior art, the cooling capacity of the refrigerant is grasped by the temperature of the refrigerant, whereas the power conversion device 20 of the first embodiment grasps the cooling capacity of the refrigerant by the change from the liquid phase state to the gas phase state. As means for doing so, a phase detection means 601 and a boiling determination unit 71 are provided.
The phase detection means 601 detects the potential difference between the pair of electrodes 61 and 62 as “a predetermined physical quantity that reflects the difference between the liquid phase state and the gas phase state of the refrigerant flowing through the cooling pipe 53”. The boiling determination unit 71 determines that “the refrigerant flowing through the cooling pipe 53” is boiling based on the potential difference detected by the phase detection unit 601.
Thereby, the cooling capacity of “the refrigerant flowing through the cooling pipe 53” can be accurately grasped.

(2) When the boiling determination unit 71 determines that the refrigerant is boiling, the power conversion device 20 further includes a refrigerant temperature control unit 72 that performs temperature lowering control that reduces the temperature of the refrigerant.
In the conventional technique for grasping the cooling capacity of the refrigerant based on the refrigerant temperature, unnecessary temperature lowering control may be performed even when the actual refrigerant temperature is lower than the threshold by setting the temperature margin in consideration of the estimation error. Therefore, there is a problem that the cooling system is enlarged and the power efficiency is lowered.

  On the other hand, in the first embodiment, it is determined that the “refrigerant flowing through the cooling pipe 53” is boiling based on the potential difference detected in a state where the refrigerant has actually undergone a phase change, and the temperature lowering control is performed for the first time at the determination timing. To start. Therefore, normal control can be continued without increasing the refrigerant flow rate or limiting the current to the limit of the temperature at which liquid cooling is possible. Therefore, it can contribute to size reduction and efficiency improvement of the cooling system.

  (3) The phase detection means 601 is “the outlet 532 side with respect to the center between the inlet 531 side and the outlet 532 side of the cooling pipe 53”, and “the outlet 532 side of the power module 42 of the lower arm” It is arranged in the “region corresponding to the end”. Thereby, the phase state at the position where “the refrigerant flowing through the cooling pipe 53” reaches the maximum temperature can be detected.

(4) In the cooler 50, a plurality of double-sided heat radiation type power modules 41 and 42 and a plurality of cooling pipes 53 are stacked. Thereby, since the heat of the power elements 43 and 44 can be released from both surfaces, the cooling efficiency is improved.
(5) In the cooler 50 having the laminated structure, the phase detecting means 601 is provided for each of the power converters 30, 31, 32, “anti-introduction with respect to the centers of the introduction side and the anti-introduction side of the refrigerant introduction pipe 51 in the lamination direction Further, it is arranged “in the vicinity of the power module 42 of the lower arm on the anti-introduction side”. Thereby, the phase state at the position where “the refrigerant flowing through the cooling pipe 53” reaches the maximum temperature in the stacking direction can be detected.

(6) The phase detection means 601 of the first embodiment applies the principle of the capacitance void ratio meter and detects a potential difference between a pair of opposed electrodes 61 and 62 provided inside the cooling pipe 53. Thereby, the phase state of “the refrigerant flowing through the cooling pipe 53” can be accurately detected with a simple configuration.
(7) The refrigerant temperature control unit 72 starts the temperature lowering control when the state where the boiling determination unit 71 determines that the impedance exceeds the first threshold value Z1 continues for a predetermined time, and the impedance is set to the first threshold value Z1. When the temperature falls below the lower second threshold value Z2, the temperature lowering control is terminated. By separately setting the first threshold value Z1 for starting the temperature decrease control and the second threshold value Z2 for ending the temperature decrease control, it is possible to prevent a hunting phenomenon in which control is frequently turned on and off with an impedance near the threshold value.

(Second and third embodiments)
The power converters of the second and third embodiments will be described with reference to FIG. 7 which is a common schematic configuration diagram. The second and third embodiments differ from the first embodiment in the configuration of the phase detection means.
The phase detection means 602 of the second embodiment applies the principle that “the speed at which ultrasonic waves are transmitted changes when gas is present in the liquid”, and uses the ultrasonic generator 67 to generate ultrasonic waves generated in the refrigerant. Detect reflected waves. The boiling determination part 71 acquires the detection signal of the phase detection means 602, and determines that the refrigerant | coolant is boiling based on the time from transmission of an ultrasonic wave to reception of a reflected wave.

The phase detection means 603 of the third embodiment applies the principle that “the emitted light is refracted in the liquid and reflected when it reaches the gas”, and reflects the light emitted from the optical fiber probe 68 into the refrigerant. Detect waves. The boiling determination unit 71 acquires the detection signal of the phase detection unit 603 and determines that the refrigerant is boiling based on the refractive index of the emitted light.
The second and third embodiments share the effects (1) to (5) of the first embodiment after rereading the matter relating to the physical quantity detected by the phase detection means.

(Fourth embodiment)
The power converter device of 4th Embodiment is demonstrated with reference to FIG. FIG. 8B is a schematic cross-sectional view taken along the line VIIIb-VIIIb of FIG. The cooler 50 of the first to third embodiments is a stacked cooler in which a plurality of double-sided heat radiation type power modules 41 and 42 and a plurality of cooling pipes 53 are alternately stacked. The cooler 56 of the embodiment is configured as a single-sided heat dissipation type cooler.
The power elements 43 and 44 of the upper and lower arms are respectively configured in the form of single-sided heat radiation type power modules 47 and 48 in which the heat spreader 45 is in contact with one surface. FIG. 8 illustrates a power converter in which each of the three phases includes a pair of power modules 47 and 48.

  The power module 47 of each phase upper arm is arranged on the refrigerant introduction pipe 51 side, and the power module 48 of each phase lower arm is arranged on the refrigerant outlet pipe 52 side. The cooling pipe 57 branched into three from the refrigerant introduction pipe 51 on the inlet side passes directly under the power modules 47 and 48 of each phase, and merges with the refrigerant outlet pipe 52 on the outlet side. The heat generated by the power elements 43 and 44 is radiated to the cooling pipe 57 through the heat spreader 45 in contact with one side.

The phase detection means 601 is “on the outlet side with respect to the center between the inlet side and the outlet side of the cooling pipe 57”, for example, at the end on the outlet side of the power module 48 of the lower arm of the W phase. It is arranged in the “corresponding area”. In the configuration using the capacitance type phase detection means 601 similar to that of the first embodiment, the pair of electrodes 61 and 62 are paired with the pair of insulating plates 63 and 64 on the channel walls 58 facing each other inside the cooling pipe 57. Is provided.
4th Embodiment of the said structure has the effects (1)-(3) of 1st Embodiment in common.
As a modification of the fourth embodiment, in the single-side heat dissipation type cooler 56, the phase detection means 602, 603 of the second embodiment or the third embodiment may be combined.

(Other embodiments)
(A) In the cooler 50 shown in FIG. 1, three types of power converters, that is, a converter 30, a regeneration inverter 31, and a power running inverter 32 are arranged side by side. In other embodiments, any number of power converters may be arranged in any order with respect to one cooler.
In each power converter, the number of power elements that perform the same switching operation may be one, or any number of power elements may be connected in parallel. The inverter is not limited to a three-phase inverter, and may be a four-phase or more multi-phase inverter.

(B) The configuration of the phase detection means of the present invention is not limited to that illustrated in the first to third embodiments, but a physical quantity that reflects the difference between the liquid phase state and the gas phase state of the refrigerant flowing through the cooling pipe. Anything to detect may be used. These include new methods and techniques that are newly created or put into practical use due to advances in science and technology since the filing of the present application.
(C) As a temperature drop control method by the refrigerant temperature control unit, in addition to increasing the refrigerant flow rate or limiting the current, a method of driving the fan to forcibly cool the cooler, a method of reducing the temperature of the refrigerant itself supplied by the chiller, etc. May be adopted.

  (D) The power conversion device may not include the refrigerant temperature control unit and may perform the boiling determination by the boiling determination unit. For example, the cooling capacity of the cooler is sufficiently set for the heat generation of a normal power element, and there is a possibility that boiling judgment may be made except in the case of a serious failure such as `` coolant supply completely stopped '' Assume no. Under this assumption, if the boiling determination unit determines that the “refrigerant flowing through the cooling pipe” is boiling, the power converter determines that a serious failure has occurred and immediately You may make it stop operation | movement of a converter.

(E) The power conversion device of the present invention is not limited to a power system that converts power between a high voltage battery and a motor generator in a hybrid vehicle or an electric vehicle, and may be applied to any system. Further, the load to which the power running inverter 32 supplies AC power is not limited to a rotating machine such as a motor generator. The effect of the present invention is effectively exhibited if the power converter is configured to cool the power converter that generates heat by energizing the power element by circulating the refrigerant.
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.

20 ... Power converter,
30 ... Converter (power converter),
31 ... Regenerative inverter (power converter),
32 ... Power running inverter (power converter),
41, 42, 47, 48 ... power modules,
43, 44 ... power elements,
45 ... heat spreader,
50, 56 ... cooler,
53, 57 ... cooling pipes,
601, 602, 603... Phase detection means,
71 ... boiling judgment part,
72: Refrigerant temperature control unit.

Claims (10)

A plurality of power converters (30, 31, 32) that convert and output power by switching operations of the plurality of power elements (43, 44);
A cooler ( 50 ) that cools the power converter that has generated heat by energization of the plurality of power elements by circulating refrigerant;
Phase detection means (601, 602, 603) for detecting a predetermined physical quantity reflecting the difference between the liquid phase state and the gas phase state of the refrigerant flowing through the cooling pipe (5 3 ) of the cooler for each power converter. )When,
A boiling determination section (71) for determining that the refrigerant flowing through the cooling pipe is boiling based on the physical quantity detected by the phase detection means;
Equipped with a,
The power element is configured in the form of a power module (41, 42) in which a heat spreader (45) having thermal conductivity is in contact with both surfaces,
The cooler is
A plurality of the cooling pipes alternately stacked with the plurality of power modules; and
A refrigerant introduction pipe (51) for introducing the refrigerant into the inlets (531) of the plurality of cooling pipes through which the refrigerant flows from one introduction side in the stacking direction toward the other non-introduction side;
A refrigerant outlet tube (52) for extracting refrigerant from the outlets (532) of the plurality of cooling tubes;
Have
The phase detection means is for each power converter,
The region corresponding to the end portion on the outlet side of the power module on the outlet side with respect to the center of the inlet side and the outlet side of the cooling pipe, and the introduction side of the refrigerant introduction pipe in the stacking direction a power converter that is arranged on the counter-introducing side with respect to the center of the anti-introducing side. The power converter is
A converter (30) that transforms the voltage input / output to / from the DC power source (15), and an inverter for regeneration that converts AC power generated by the generator (81) into DC power and regenerates the DC power via the converter ( 31), and a power running inverter (32) that converts the DC power output from the converter into AC power and supplies it to the load (82),
2. The power conversion device according to claim 1 , wherein at least one phase detection unit is provided for each of the converter, the regeneration inverter, and the power running inverter. The phase detection means (601) detects a potential difference between a pair of electrodes (61, 62) facing each other inside the cooling pipe,
The electric power according to claim 1 or 2 , wherein the boiling determination unit determines that the refrigerant flowing through the cooling pipe is boiling based on an electric capacity calculated from a potential difference or an impedance inversely proportional to the electric capacity. Conversion device. 4. The power converter according to claim 3 , wherein the pair of electrodes is provided on a flow path wall (54, 58) facing each other inside the cooling pipe via a pair of insulating plates (63, 64). The phase detection means (602) detects the reflected wave of the ultrasonic wave generated in the refrigerant by the ultrasonic generator (67),
The power converter according to claim 1 or 2 , wherein the boiling determination unit determines that the refrigerant flowing through the cooling pipe is boiling based on a time from transmission of an ultrasonic wave to reception of a reflected wave. The phase detection means (603) detects a reflected wave of light emitted from the optical fiber probe (68) into the refrigerant,
The power conversion device according to claim 1 or 2 , wherein the boiling determination unit determines that the refrigerant flowing through the cooling pipe is boiling based on a refractive index of emitted light. Wherein when the refrigerant is determined to be boiling by boiling determining section, any claim 1-6, further comprising a refrigerant temperature control unit (72) for executing cooling control to reduce the temperature of the refrigerant flowing through the cooling pipe The power conversion device according to claim 1. When the boiling determination unit determines that the refrigerant is boiling, the refrigerant determination unit further includes a refrigerant temperature control unit (72) that performs a temperature lowering control to reduce the temperature of the refrigerant flowing through the cooling pipe,
The refrigerant temperature controller is
For impedance that is inversely proportional to the capacitance calculated from the potential difference between the pair of electrodes (61, 62) detected by the phase detection means (601),
When the state where the impedance is determined to exceed the first threshold by the boiling determination unit continues for a predetermined time, the temperature decrease control is started,
5. The power conversion device according to claim 3, wherein when the impedance falls below a second threshold value that is lower than the first threshold value, the temperature lowering control is terminated. The refrigerant temperature controller is
The power conversion device according to claim 7 or 8 , wherein, in the temperature lowering control, a temperature lowering command is output so as to increase a flow rate of the refrigerant to a refrigerant supply unit (73) that supplies the refrigerant. The refrigerant temperature controller is
The power conversion device according to claim 7 or 8 , wherein, in the temperature lowering control, a temperature lowering command is output so as to limit a current to an energization control unit (74) that controls a current energized to the power element.

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