WO2013103711A2

WO2013103711A2 - Ventilation control system and method for power converters

Info

Publication number: WO2013103711A2
Application number: PCT/US2013/020137
Authority: WO
Inventors: Dimitrios Ioannidis
Original assignee: General Electric Company
Priority date: 2012-01-03
Filing date: 2013-01-03
Publication date: 2013-07-11
Also published as: WO2013103711A3

Abstract

A method comprises determining an estimated temperature of a semiconductor power device of a power converter. The method further comprises controlling a blower that provides a cooling fluid to cool the power converter, based on the estimated temperature and a temperature of the cooling fluid. The blower may be controlled further based on an electrical power level of the power converter and/or one or more thermal characteristics of the power converter.

Description

VENTILATION. CONTROL SYSTEM AND. METHOD FOR POWER CONVERTERS

FIELD OF THE INVENTION

[0001] Embodiments of the invention relate generally to cooling systems and methods. Other embodiments relate to cooling systems and methods for power converters.

BACKGROUND OF THE INVENTION

[0002] Traction vehicles such as, for example, most modern rail locomotives, employ electric traction motors for driving wheels of the vehicles. In many modern rail locomotives the traction motors are alternating cuixent (AC) motors whose speed and power are controlled by varying the frequency and current of AC electric power supplied to the motors.

Commonly, however, the electric power is supplied as direct current (DC) power and is thereafter inverted to AC power of controlled frequency and amplitude. The electric power may be derived from an on-board electrical generator/alternator, driven by an internal combustion engine (e.g., a diesel engine), or may be obtained from a wayside power source such as a third rail or overhead catenary.

[0003] Typically, the power is inverted utilizing one or more power converters, e.g., traction inverters, incorporating a plurality of power semiconductor devices such as diodes and insulated-gate bipolar transistors (IGBTs). In a locomotive, the amount of horsepower developed requires very high power handling capability by the associated traction inverter. This, in turn, requires power semiconductor switching devices capable of controlling such high power and of dissipating significant heat developed in the power semiconductor devices due to internal resistance.

[0004] In certain existing systems, the power semiconductor devices are mounted on heat transfer devices such as heat sinks which aid in transferring heat away from the power semiconductor devices and thus prevent thermal failure of the devices. For power semiconductor devices that operate at very high power levels, it is desirable to use heat sinks having generally hollow interiors through which cooling fluid, such as cooling air, may be forced to remove the accumulated heat.

[0005] In locomotive cooling applications the cooling fluid, e.g., cooling air, is typically derived from blowers drawing air from overhead the locomotive, the blowers being powered by the on-board diesel or other engine. Existing systems, however, require the blowers to operate close to 100% speed, even under reduced power and/or reduced ambient operation, i.e., without any consideration to the level of losses nor to the outside ambient temperature. As will be readily appreciated, therefore, this is unfavorable for fuel consumption and overall fuel efficiency.

BRIEF DESCRIPTION OF THE INVENTION

[0006] In an embodiment, a method comprises determining an estimated temperature of a semiconductor power device of a power converter. The method further comprises controlling a blower that provides a cooling fluid to cool the power converter, based on the estimated temperature and a temperature of the cooling fluid. The blower may be controlled further based on an electrical power level of the power converter and/or one or more thermal characteristics of the power converter.

[0007] In another embodiment, a ventilation control system for a power converter comprises a power source, a traction motor (e.g., an AC traction motor), a power converter, a blower, and a controller. The power source is configured to supply a first power, e.g., DC power. The power converter is operatively coupled to the power source and the traction motor. The power converter includes a semiconductor power device. The power converter is configured to convert the first power supplied by the power source to a different, second power (e.g., AC power) to be utilized by the traction motor. The blower is configured to be driven by the power source and configured to direct a flow of cooling fluid to cool the power converter. The controller is in electrical communication with the blower, and is configured to control the blower in dependence upon an estimated temperature of the semiconductor power device and a temperature of the cooling fluid. The controller may be configured to control the blower further in dependence upon an electrical power level of the power converter and/or one or more thermal characteristics of the power converter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:

[0009] FIG. 1 is a block diagram depicting the basic elements of a vehicle propulsion system according to an embodiment of the invention. [0010] FIG, 2 is a block diagram of a vehicle incorporating a ventilation control system for power converters according to an embodiment of the invention.

[0011] FIG. 3 is a steady state model utilized to estimate the temperature of a power converter component according to an embodiment of the invention.

[0012] FIGS. 4 and 5 are graphs depicting the temperature of a power converter component as a function of air temperature and Tj~Tair as a function of air temperature, respectively.

[0013] FIG. 6 is a steady state model incorporating an estimation of a "required"

SCFM (or other cooling fluid rate) of a blower.

DETAILED DESCRIPTION OF THE INVENTION

[0014] Reference will be made below in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numerals used throughout the drawings refer to the same or like parts. Although exemplary embodiments of the present invention are described with respect to locomotives and other rail vehicles, embodiments of the invention are also applicable for use with vehicles and stationary equipment, generally, including marine vessels automobiles, construction equipment and mining equipment. In an embodiment, stationary equipment may include utility and telecommunication sites, as well as cranes and the like.

[0015] As noted above, currently, traction inverter ventilation control for powered equipment requires the blower to operate close to 100% speed, regardless of whether the powered system is operating under reduced power and/or reduced ambient temperature operation. As will be readily appreciated, this "always on" state is unfavorable for fuel consumption. Accordingly, embodiments of the invention provide a system and method that aims to reduce the required power from an engine to ventilate one or more traction inverters in powered equipment, so as to reduce the required specific fuel consumption (SFC) and extend the life of one or more ventilation system components.

[0016] FIG. 1 is a block diagram depicting elements of a vehicle propulsion system

10 (e.g. a vehicle AC propulsion system). A vehicle power source 12 may include any desired power source including, for example, a diesel engine/alternator, battery, or wayside power source such as a third rail of high voltage catenary. Electrical power is conditioned by- one or more solid state power converters 14 (e.g., traction inverters), which have respective power converter controllers 16 to regulate the voltage and frequency applied to respective traction motors 18 (e.g., AC traction motors, or DC traction motors) in a manner consistent with the needs of the vehicle application. The power converters 14 are coordinated by a propulsion system controller 20 which controls each respective power converter controller 16 and power converter 14 for each motor, (For example, there may be one motor, and therefore one power converter and power converter controller, per axle of a vehicle, e.g., locomoti ve or other rail vehicle.) A vehicle level control system 22 can be used to send commands to the propulsion system controller 20.

[0017] With reference to FIG. 2, a vehicle 100 according to an embodiment of the invention is shown. As shown therein, the vehicle 100 may include the propulsion system 10 shown in FIG, 1 and described above. As further shown therein, the vehicle 100 includes a blower 102 powered by the power source 12, the blower 102 being configured to circulate a cooling fluid to/through the traction inverters or other power converters 14 in order to cool the IGBT's or other semiconductor power devices of the traction inverters or other power converters, in the manner described above. In an embodiment, the cooling fluid is air drawn from outside the vehicle 100.

[0018] As also shown in FIG. 2, the vehicle 100 includes a cooling fluid temperature sensor 104 in communication with the controller 20, which is configured to sense a temperature of the cooling fluid (e.g., ambient air) and send a signal indicative of the sensed temperature to the power converter controller 20. In an embodiment, the temperature sensor 104 is positioned adjacent to an inlet to fins of the heat sink associated with the power converter 14. A power converter temperature sensor 106 is associated with a device of the power converter 14 and is configured to sense a temperature thereof and relay a signal indicative of such temperature to the controller 20 in a similar manner. In an embodiment, the temperature sensor 106 is configured to monitor a temperature of the hottest point on the case of the IGBT or other semiconductor power device. (Although in FIG. 2 the term "Tj" is shown in reference to sensor 106, Tj may be estimated, as discussed below.)

[0019] In a method for reducing the required specific fuel consumption of a ventilation system for power converters, a standard cubic feet per minute (SCFM) value is determined, which can be used to control the blower 102 that blows air (cooling fluid) to cool the power converter 14. That is, the blower 102 is controlled by the controller 20 to provide the determined SCFM. The SCFM is determined based on various thermal models of the power converter, and factors such as "Tj" (estimated junction temperature of a semiconductor power device of the power converter) and "Tair" (temperature of the cooling air), as discussed in detail hereinafter. Specifically, SCFM is a function of Rth ha (thermal resistance of the heat sink of the power converter to air), and Rth_ha is a function of Tj, Tair, power output of the power converter 14, and thermal properties of the power converter 14. (in other embodiments, using other thermal models, etc.. it may be possible to control the blower based on one or more of the estimated temperature of the semiconductor power device, the temperature of the cooling fluid, the electrical power level of the power converter, and/or one or more thermal characteristics of the power converter.)

[0020] in the method, a thermal model of the IGBT (or other semiconductor power device) of a traction inverter or other power converter is constructed. First, the thermal resistance of the heat sink of the case of the IGBT or other semiconductor power device of the power converter 14 to air is determined. In a laboratory test, six heat sink samples (of the heat sink associated with the power converter 14) may be observed for example at 200A, 400A, and 600A: one sample at 150 standard cubic feet per minute (SCFM), 100 SCFM, 60 SCFM, 35 SCFM, and 0 SCFM to obtain the relationship between standard cubic feet per minute of the blower 102 and the thermal resistance of the heat sink (Rth_ha). In an embodiment, five more samples may be tested at 150SCFM to identify the part-to-part variation of the thermal resistance of the heat sink of the power converter to air. By monitoring the temperature of the case of the of the IGBT or other semiconductor power device of the power converter 14, the following equation can be derived:

Rth_ha + Rth ch ^:::: (Tmax thermocouple - Tair)/ Ptotal where:

Rth ch = Thermal resistance between case and heatsink (a typical value is 0.06degrC/W); and

Ptotal = Total Power to the Heatsink = Io*Vce, so that the thermal resistance of the heat sink of the power converter to air can be expressed as:

Rth_ha ^:::: (Tmax thermocouple - Tair)/ Ptotal - 0.06 Sample results (for Al heatsink samples) are indicated in Tables 1 and 2. Table 1.

Tabk

[0021] With reference to Table 3, the descriptive statistics at 150 SCFM are shown.

Table 3.

[0022] Using the mean standard deviation of the above data, and assuming a 3 sigma heat siak product, the Upper Spec Limits (USL) of the thermal resistance of the heat sink of the power converter to air (Rthj a) may be obtained for the different air flows. Sample results are shown in Table 4. Table 4.

[0023] The descriptive equation of the USL of Rth ha = f ( SCFM). Accordingly, the thermal resistance of the heat sink of the power converter to air can be expressed as:

Rth ha AS = 0.012167+0.3 i653/(l +((SCFM/7.2)^A0.974)

[0024] After determining the thermal resistance of the heat sink of the case of the

IGBT or other power semiconductor device of the power converter 14 to air, power loss parameters may be analyzed, in particular, using a commercially available Matlab tool, for example, the loss parameters of an IGBT module or other module at 1200A, 2500V E IGBT (for example) as functions of Ic, Vdc, and Tj may be simulated (where Tj is the estimated junction temperature of a device of the power converter 14).

[0025] Next, the thermal resistance between j nction and case for the power semiconductor device(s) (e.g., IGBT and diode (Rth jc)) of the power converter are determined. For example, for an IGBT and diode:

Rthjc IGBT = =0.008degrC/W; and

Rth jc Diode - =0.016degrC/W

[0026] Next, a thermal analysis of the power semiconductor device(s) may be conducted, such that equations describing power losses in the power semiconductor device(s) of the power converter 14 may be developed. Examples of these equations for an IGBT and diode are as follows:

Pss IGBT - Icp * Vee(sat)*( (1/8) + D* pf/(3*pi) )

Psw IGBT= ( Eon + Eoff) * Fsw / (pi) Pon diode = icp * Vf peak*( (1/8) - D*pf/(3*pi ))

Prr = Err * Fsw / pi, where:

« Pss IGBT is the power loss in the IGBT while it is ON (steady state);

® Psw IGBT is the power loss in the IGBT while it switches ON & OFF;

® Pon diode is the power loss in the diode while it is ON:

® Prr is the power loss in the diode due to reverse recovery;

* Icp = peak sinusoidal current through the IGBT;

« D = PWM depth factor (usually 0,5);

® Pf == power factor =cos (delay angle) here 0.7;

® Icp— peak sinusoidal output current;

* Vce(sat) is the on state voltage of IGBT @ Icp;

* Eon = energy per pulse while IGBT switches ON [ J/pulse] @ Icp;

® Eoff ^::: energy per pulse while IGBT switches OFF [ J/pulse] @ Icp;

« Vf - on state voltage of diode @ Icp;

« Err = energy per pulse while diode is in Reverse recovery [ J/pulse] @ Icp

[0027] With estimated power losses in an IGBT and diode (for example), the following equations may be used to estimate their junction temperatures:

Tj IGBT = Tair + Ptot IGBT*RthJc (IGBT) + (Ptot IGBT + Ptot diode) *(Rth_ch+

Rth_ha)

Tj Diode - Tair + Ptot Diode*RthJc(Diode) + (Ptot IGBT + Ptot diode) *(Rth_ch+

Rth ha) where:

Tair = temperature of cooling air

Ptot IGBT = Pss IGBT + Psw IGBT

Ptot Diode= Pon diode + Prr [0028] Using the information and equations above, a steady state model is constructed to estimate the junction temperature of the power semiconductor device (Tj). For example, for a power converter having an IGBT and diode (e.g., freewheeling diode coupled in parallel to the IGBT), Tj of the IGBT and the junction temperature of the diode (Tjd) in an E-type traction inverter (i.e., traction inverter 14) and an aluminum heat sink may be determined. This steady state model is shown in FIG. 3,

[0029] In an embodiment, the maximum operating conditions for powered equipment is as follows under both maximum steady (thermal rating) and maximum transient conditions. For maximum steady state (thermal rating) conditions: Vlink = 875V, 850Arms, 150SCFM, 12.138 V7Hz, full power at 85(⁾Vdc (31 Hz), Fsw = 54GHz, Tair at maximum of 61 degrees Celsius. For maximum transient conditions, Vlink = 900V, 1200Arms, 150SCFM, 12.138 V/Hz, full power at 850 Vdc (31 Hz), Fsw = 540Hz, Tair at maximum of 61 degrees Celsius.

[0030] Using a tool to estimate accurately the Tj of the IGBT, it is possible to estimate the delta Tj-Tair, "K", at a maximum steady state condition. This may be designated as an "allowable" delta Tj-Tair while operating at the maximum power of the thermal rating condition at any air temperature. This may indicate a "required" Rth_ha, which can be translated to a "required" SCFM (or other blower rating).

[0031] If the power semiconductor device is operating on a power that is less than the one of the thermal rating conditions, then the Tj, and therefore the K=Tj~Tair and the

"required" SCFM may be reduced. The control system may signal, for example, that a subset of the benefit of operating in lower powers may be used to reduce the airflow and another sub-set to reduce . This may contribute to longer device life because of reduced thermal cycling.

[0032] Using the thermal model of FIG. 3, the power loss and Tj of the power semiconductor device are estimated at the "rating" steady state conditions. For example, for the IGBT and diode discussed as an example above, sample values are listed in Table 5, below.

[0033] According to the graphic example illustrated in FIGS. 4 and 5, the maximum power loss, Ptmax, is 1296. IW, max cycling (Tj-Tair) is 51.61 degrC = K , when

dTjc(IGBT)=Pigbt*RthJc=975.82*0.008= 7.80 degrC.

[0034] As will be readily appreciated, Tj desired = (Tj-Tair) + Tair, and if K ~ Tj -

Tair, then Tj ^:::: +Tair. Moreover, Tj of the IGBT (or other device) can be found utilizing the following equation:

Tj ^::: Tair ^" Tjc ·+· Ten ~ Tha

where

Tjc = Tj - Tease = P__ IGBT*Rth (IGBT je);

Tch = Tease - Theatsink (hottest spot under the device) ^:::: (P__IGBT + P__diode) *Rth(ch); and Tha = Theatsink - Tair = (P IGBT + P diode) * Rthjtia

Tj ^::: Tair + P_IGBT*Rth (IGBT jc) + (P__ IGBT + P diode) *Rth_ch + (P IGBT + P__diode) * Rth ha

Put, P_IGBT + P diode = total losses in the module ^:::: say, Pt

P IGBT * Rth(IGBT jc) = dTjc

and:

Rth (IGBT jc) = 0.008 degrC/W

Rth_ch = 0.006 degrC/W, then

Ti = Tair+Pt * Rth ha + d Tic + Pt*0.006

From the two underlined equations above: K - Pi * Rth ha + d Tjc + Pt*0,0G6

K ·■ d Tjc Rth ha (Pt max) - 0.006 Pt max

Where, Pt max may be the total losses in the inverter operating at the specified "rating" conditions. If A(Ptmax) - -dTjc, then

Rthjia (Pt max) ^::: (A(Ptmax)/Pt max) ~ 0.006 eq.l

At a lower power operation, the total losses may decreasing (e.g., to Ptx) and Rth__(Ptx) is increasing to:

RthJia (Pt x) - (A(Ptx)/Pt x) - 0.006 eq.2

[0035] While maintaining " " the same it may be possible to operate with a higher

Rth, and therefore with less airflow and using less fuel. The system can use one poxtion of the benefit for fuel consumption (SFC) and another portion to reduce the delta T cycling (K). Using an average of eq.1 and 2 as the required Rth__ha to operate at Ptx po wer without exceeding K:

Rth ha (Pt x) = (A (Ptmax)*Ptx + A (Ptx) * Ptmax) / (2 * Ptmax * Ptx) - 0.006 eq. 3

Where Ptot max^:=:1296.1W, max cycling (Tj-Tair) is 51.61 degrC ^:::: K , dTjc ^::: 7.80 degrC, so A(Ptmax) = 51.61-7.80 = 43.81 , then equation 3 becomes:

Rth ha (Pt x) - (43.81 * Ptx + A (Pte)* 1296.1) / (2*1296.1 * Ptx) - 0.006 eq. 4

This is the required Rthjia to operate at Ptx power losses.

[0036] In additioxi, the following equation serves to translated the required Rthjia to required SCFM airflow: reqSCFM --2.5226+215.27*EXP(-reqRth_ha 0.0375)+3166.2*EXP(-reqRth ha/0.0067) [0037] With reference to FIG. 6, a steady state model incorporating an estimation of the "required" SCFM is shown, The required airflow may be utilized to cool the heat sink of the power converter 14 iri-the mariner hereinbefore described.

[0038] With reference to Table 5, the results of operating at the "thermal rating" conditions at a constant air flow of 150 SCFM are shown in Table 6, for an IGBT as an example.

Table 6.

[0039] Table 7 shows the results compared with the results obtained by running model FIG. 6.

Table 7.

[0040] At these maximum power losses, the IGBT needs ~150SCFM only when temperature of the air is at maximum of 61 degrees Celsius (ambient = 49 degrees Celsius).

[0041] By way of example, the fuel consumption (SFC) is measured at 60degrF

(15.56degrC). While measuring SFC, Tair = 15.56degrC+5+7=27.56 degrC. While measuring SFC, Inns in Traction is 440A (470A in some motors). Using the preceding data and the models from FIG. 3 (old ventilation method) and FIG. 6 (new ventilation method), it can be seen in Table 8 that only about less than half of the airflow provided by the old method is required for a reliable operation at the SCF measuring conditions. Accordingly, only 1/10 of the power used for cooling is necessary at that operation. Indeed, by utilizing the method of the present invention, the blower 102 may be operated at substantially less than a maximum capacity of the blower and. at greater than the blower being turned off. In an embodiment, substantially less means between 0 and 25% of maximum capacity, in at least one mode of operation.

Table 8.

[0042] The model of FIG. 6 containing the ventilation method of the embodiments of the invention may be run at the maximum transient conditions : Vlink=900V, 1200Arms, 150SCFM, 12.138 V Hz, full power at 850Vdc (3 lHz), Fsw=540Hz with the results shown in Table 9. Although at 49 degrC ambient Tj is high, the new system is requiring throughout the maximum air flow available of 150SCFM. The above problem may be eliminated if the system starts degrading power above Tj=137degrC or delta Tj-Tair above 86 degrC.

Table 9.

Notably, the capability of the E type tested IGBTs (Hitachi) is:

Tj<=150degrC

and thermal cycling:

delta Tj-Tair # of cycles

70 degrC 75,000

86degrC 30,000

[0043] Therefore, in an embodiment, a method comprises the steps of determining an estimated temperature of a semiconductor power device of a power converter and controlling a blower that provides a cooling fluid to cool the power converter, based on the estimated temperature and a temperature of the cooling fluid,

[0044] In an embodiment, the semiconductor power device is an insulated-gate bipolar transistor, In an embodiment, the semiconductor power device is a diode. In an embodiment, the power converter is a traction inverter (i.e., inverter for powering a traction motor).

[0045] in an embodiment, the method includes the step of controlling the blower based on one or more thermal characteristics of the power converter.

[0046] In an embodiment, the method includes the step of controlling the blower based on an electrical power level of the power converter.

[0047] In another embodiment, the method includes the steps of estimating the difference between the temperature of a semiconductor power device and the temperature of the cooling fluid at maximum steady state conditions and reducing the capacity of the blower if the power converter is operating on an electrical power level less than a thermal rating condition of the power converter.

[0048] In an embodiment, controlling the blower comprises running the blower at substantially less than a maximum capacity of the blower and greater than the blower being turned off.

[0049] Another embodiment of the invention relates to a method including the steps of determining an estimated temperature of a semiconductor power device of a power converter, and controlling a blower that provides a cooling fluid to cool the power converter based on the estimated temperature, a temperature of the cooling fluid, an electrical power level of the power converter, and one or more thermal characteristics of the power converter.

[0050] Another embodiment of the invention relates to a method including the steps of determining an estimated temperature of a semiconductor power device of a power converter, and controlling a blower that provides a cooling fluid to cool the power converter based on the estimated temperature, a temperature of the cooling fluid, an electrical power level of the power converter, and one or more thermal characteristics of the power converter, Controlling the blower comprises running the blower at substantially less than a maximum capacity of the blower and greater than the blower being turned off.

[0051] Another embodiment of the invention relates to a method including the steps of determining an estimated temperature of an IGBT or diode of a traction inverter or other power converter, and controlling a blower that provides a cooling fluid to cool the power converter based on the estimated temperature, a temperature of the cooling fluid, an electrical power level of the power converter, and one or more thermal characteristics of the power converter. In an embodiment, the method further includes the steps of estimating the difference between the temperature of a semiconductor power device and the temperature of the cooling fluid at maximum steady state conditions and reducing the capacity of the blower if the power converter is operating on an electrical power level less than a thermal rating condition of the power converter.

[0052] In another embodiment, a method comprises the steps of determining an estimated temperature of a semiconductor power device of a power converter, and controlling a blower that provides a cooling fluid to cool the power converter, based on the estimated temperature, a temperature of the cooling fluid, an electrical power level of the power converter, and one or more thermal characteristics of the power converter. The method further comprises estimating a difference between the estimated temperature of the semiconductor power device and the temperature of the cooling fluid at maximum steady state conditions. Controlling the blower comprises reducing a rate of the cooling fluid provided to cool the power converter, based on the difference, if the power converter is operating on an electrical power level less than a thermal rating condition of the power converter.

[0053] In another embodiment, a method comprises the steps of determining an estimated temperature of a semiconductor power device of a power converter, and controlling a blower that provides a cooling fluid to cool the power converter, based on the estimated temperature, a temperature of the cooling fluid, an electrical power level of the power converter, and one or more thermal characteristics of the power converter. The method further comprises estimating a difference between the estimated temperature of the semiconductor power device and the temperature of the cooling fluid at maximum steady state conditions. If the power converter is operating on an electrical power level less than a thermal rating condition of the power converter: (i) the blower is controlled to reduce a rate of the cooling fluid provided to cool the power converter, based on the difference; and (ii) at least one of the blower or the power converter is controlled to reduce the difference, whereby thermal cycling of the semiconductor power device is reduced.

[0054] In another embodiment, a ventilation control system for a power converter comprises a power source, a traction motor (e.g., an AC traction motor), a power converter, a blower, and a controller. The power source is configured to supply a first power, e.g., DC power. The power converter is operatively coupled to the power source and the traction motor. The power converter includes a semiconductor power device. The power converter is configured to convert the first power supplied by the power source to a different, second power (e.g., AC power) to be utilized by the traction motor. The blower is configured to be driven by the power source and configured to direct a flow of cooling fluid to cool the power converter. The controller is in electrical communication with the blower, and is configured to control the blower in dependence upon an estimated temperature of the semiconductor power device and a temperature of the cooling fluid. The controller may be configured to control the blower further in dependence upon an electrical power level of the power converter and/or one or more thermal characteristics of the power converter.

[0055] in yet another embodiment, a ventilation control system for a power converter is provided. The system includes a power source supplying direct current power, an alternating current traction motor, a power converter operatively coupled to the power source and the traction motor, the power converter having a semiconductor power device, the power converter being configured to invert the direct current power supplied by the power source to alternating current to be utilized by the traction motor, a blower driven by the power source and configured to direct a flow of cooling fluid through the power converter, and a controller. The controller is in electrical communication with the blower and is configured to control the blower in dependence upon an estimated temperature of the semiconductor power device, a temperature of the cooling fluid, an electrical power level of the power converter, and one or more thermal characteristics of the power converter.

[0056] in an embodiment, the controller is configured to run the blower at

substantially less than a maximum capacity of the blower and greater than the blower being turned off.

[0057] in an embodiment, the power source is a diesel engine.

[0058] In an embodiment, the power converter is a traction inverter. [0059] It is to be understood that the above, description is intended to.be. illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms "including" and "in which" are used as the plain- English equivalents of the respective terms "comprising" and "wherein."

Moreover, in the following claims, the terms "first," "second," "third," "upper," "lower," "bottom," "top," etc. are used merely as labels, and are not intended to impose numerical or positional requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. § 1 12, sixth paragraph, unless and until such claim limitations expressly use the phrase "means for" followed by a statement of function void of further structure.

[0060] This written description uses examples to disclose several embodiments of the invention, including the best mode, and also to enable one of ordinary skill in the art to practice the embodiments of invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to one of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

[0061] As used herein, an element or step recited in the singular and proceeded with the word "a" or "an" should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to "one embodiment" of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments "comprising," "including," or "having" an element or a plurality of elements having a particular property may include additional such elements not having that property. [0062] Since certain changes may be made in the above-described systems and methods, without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention

Claims

What is claimed is:

1. A method comprising the steps of:

determining an estimated temperature of a semiconductor power device of a power converter; and

controlling a blower that provides a cooling fluid to cool the power converter, based on the estimated temperature and a temperature of the cooling fluid.

2. The method of claim 1 , wherein the blower is controlled further based on one or more thermal characteristics of the power converter.

3. The method of claim 1, wherein the blower is controlled further based on an electrical power level of the power converter.

4. The method of claim 1, wherein the blower is controlled further based on an electrical power level of the power converter and one or more thermal characteristics of the power converter,

5. The method of claim 4, wherein controlling the blower comprises running the blower at substantially less than a maximum capacity of the blower and greater than the blower being turned off.

6. The method of claim 4, wherein:

the semiconductor power device is an insulated-gate bipolar transistor.

?■. The method of claim 4, wherein:

the semiconductor power device is a diode.

8. The method of claim 4, wherein:

the power converter is a traction inverter.

9. The method of claim 4, further comprising the steps of: estimating a difference between the estimated temperature of the semiconductor power device and the temperature of the cooling fluid at maximum steady state conditions; and

reducing the capacity of the blower if the power converter is operating on an electrical power level less than a thermal rating condition of the power converter.

10. The method of claim 4, wherein:

the method further comprises estimating a difference between the estimated temperature of the semiconductor power device and the temperature of the cooling fluid at maximum steady state conditions; and

controlling the blower comprises reducing a rate of the cooling fluid provided to cool the power converter, based on the difference, if the power converter is operating on an electrical power level less than a thermal rating condition of the power converter.

1 1. The method of claim 4, wherein:

if the power converter is operating on an electrical power level less than a thermal rating condition of the power converter:

the blower is controlled to reduce a rate of the cooling fluid provided to cool the power converter, based on the difference; and

at least one of the blower or the power converter is controlled to reduce the difference, whereby thermal cycling of the semiconductor power device is reduced.

12. A ventilation control system for a power converter, comprising:

a power source configured to supply a first power;

a traction motor;

a power converter operatively coupled to the power source and the traction motor, the power converter having a semiconductor power device, the power converter being configured to convert the first power supplied by the power source to a different, second power to be utilized by the traction motor;

a blower configured to be driven by the power source and configured to direct a flow of cooling fluid to cool the power converter; and a controller in electrical communication with the blower, the controller being configured to control the blower in dependence upon an estimated temperature of the semiconductor power device and a temperature of the cooling fluid.

13. The system of claim 12, wherein the controller is configured to control the blower further in dependence upon an electrical power level of the power converter.

14. The system of claim 12, wherein the controller is configured to control the blower further in dependence upon one or more thermal characteristics of the power converter.

15. The system of claim 12, wherein the controller is configured to control the blower further in dependence upon an electrical power level of the power converter and one or more thermal characteristics of the power converter.

16. The system of claim 12, wherein the first power is direct current power, the traction motor is an alternating current traction motor, and the second power is alieraating current power.

17. The system of claim 12, wherein:

the controller is configured to control the blower at substantially less than a maximum capacity of the blower and greater than the blower being turned off, based on the estimated temperature and the temperature of the cooling fluid.

18. The system of claim 12, wherein:

the power source is a diesel engine. . The system of claim 12, wherein:

the semiconductor power device is an insulated-gate bipolar transistor.

20. The system of claim 12, wherein:

the semiconductor power device is a diode.