CN102192845A - Method for diagnosing heat radiation system - Google Patents

Abstract

The invention discloses a method for diagnosing a heat radiation system, comprising the steps of obtaining a temperature value related to a heat resistance value during the normal working of the heat radiation system, figuring out a temperature value related to a designed ideal heat resistance value according to a mathematical model of the system by using the power loss of the system; comparing the obtained value with the calculated value; and determining that the heat radiation system works abnormally if the difference between the obtained value and the calculated value exceeds a preset threshold. Therefore, by using the method disclosed by the invention, the working status of the heat radiation system can be determined in advance so that maintenance and repairing are arranged for the heat radiation system according to working.

Description

The cooling system diagnostic method

Technical field

The present invention relates to a kind of method that cooling system is diagnosed, and relate in particular to and use straightforward procedure to detect the cooling system fault, so that prepare for the maintenance of cooling system and renewal.

Background technology

Along with the heat radiation increase of power electrical equipment and reducing of global shape factor, it is more and more important that heat management becomes.

The temperature of the performance reliability of power electrical equipment and life-span and each device of equipment is inversely proportional to.Typically, the reliability of silicon semiconductor device and the relation between the working temperature show that reliability and life-span that temperature reduces corresponding to semiconductor devices increase.Therefore, can realize that by the working temperature of control device effectively the ILS of each device and reliability increase.Thus, each device that will guarantee this power electrical equipment is usually worked under the threshold temperature of design.

Heating radiator is dissipated to heat the surrounding environment from the surface of the heat of heater members through being commonly used to, for example, and air.In the present embodiment, be example with the air, but can be other media, as oil.In order to improve the radiating efficiency of heating radiator, usual way is to increase heating radiator and cooling medium, and promptly the contacted surface area of air perhaps uses fan to improve speed air flow.

But along with increasing service time, heating radiator can be because stopping up appears in the deposition of dust etc., and to wear out also can appear in fan, thereby makes the overall efficiency of cooling system descend, and can not guarantee that main electric part is fully cooled off.And well-known, the too high meeting of temperature causes electric part too fast aging, reduces the life-span of electric part, and might cause electric part to break down.

Owing to high temperature is damaged, in common electrical equipment, for example in frequency converter, the place is provided with temperature sensor at power model for fear of electric part, when the measured temperature of temperature sensor surpasses a predetermined value, then stops the work of frequency converter.

But owing to do not have a kind of method to come cooling system is diagnosed at present, thereby unpredictable when cooling system goes wrong, and therefore, because overheated meeting causes extemporal shutdown, thereby causes irretrievable and unnecessary loss.

If for example in textile industry is used, may make radiating effect descend because fiber in the applied environment or filiform stop up heating radiator or fan, frequency converter be shut down.Know that in advance fan or cooling system go wrong if can detect by system, the prompting client clears up or changes fan in advance, can avoid uncertain shutdown.Also can find the reason of shutdown after perhaps shutting down very soon, take the relevant treatment measure very soon.(renewing fan or cleaning heating radiator)

Summary of the invention

In view of the above problems, the present invention has been proposed.Therefore, the object of the present invention is to provide a kind of diagnostic method of cooling system, utilize this method, can diagnose cooling system at any time, and can preset the maintenance time and the replacing time of cooling system according to deagnostic structure.

In order to realize purpose of the present invention, according to the present invention, provide a kind of diagnostic method of cooling system, this diagnostic method is characterised in that and comprises: the relevant temperature value of thermal resistance value when obtaining with the cooling system operate as normal; Utilize the power loss of system, based on the calculated with mathematical model of the system temperature value relevant with the desirable thermal resistance value of design; The value that is obtained is compared with the value of being calculated; And if the difference between value of being obtained and the value calculated surpasses a predetermined threshold, determine that then this cooling system work is undesired.The undesired fan that comprises of described cooling system work is aging, and fan failure or heating radiator are blocked.

Thus,, can determine the working condition of cooling system in advance, so that realize arranging the maintenance and repair of cooling system according to work by diagnostic method of the present invention.

Preferably, the described step of obtaining the value relevant with the current actual thermal resistance value of cooling system comprises poor between the temperature of the heater element that acquisition will be dispelled the heat and the environment temperature, and the described calculating value relevant with the desirable thermal resistance value of design comprises following formula:

${\mathrm{\ΔT}}_{\mathrm{ca}}\left(t\right)=P_{\mathrm{AV}}\·{\mathrm{Rth}}_{\mathrm{ca}}\·(1-e^{\left(\frac{-t}{\mathrm{\τ}}\right)}),$

Wherein: Δ T _Ca(t) poor between the temperature of the heater element that calculates for the desirable thermal resistance value of utilizing design and the environment temperature;

P _AVAverage power loss for system;

Rth _CaDesirable thermal resistance value for design;

τ is the time constant of cooling system, is τ=Rth _CaCth _Ca

Preferably, the step of the value that the described current actual thermal resistance value of obtaining cooling system is correlated with comprises the temperature of the heater element that measurement will be dispelled the heat, and calculates the time-derivative of this temperature, and the relevant value of desirable thermal resistance value described and design comprises following formula:

$\frac{d\·T_c\left(t\right)}{\mathrm{dt}}=\frac{P_{\mathrm{AV}}}{{\mathrm{Cth}}_{\mathrm{ca}}}\·e^{\left(\frac{-t}{\mathrm{\τ}}\right)}$

Wherein:

Time-derivative for the temperature of the heater element that calculates according to desirable thermal resistance value;

P _AVAverage power loss for system;

Cth is the thermal capacitance of cooling system;

τ is the time constant of cooling system, τ=Rth _CaCth _Ca

Pass through said method, can avoid additionally increasing a temperature sensor for measures ambient temperature, but can utilize existing temperature sensor in the cooling system, and the measurement result of this temperature sensor is carried out signal Processing, promptly can realize diagnosis to cooling system.Thus, reduced the cost of entire method.

Description of drawings

Below, describe in detail according to a preferred embodiment of the invention with reference to accompanying drawing, still, it is to be noted that following description only is exemplary, and be not construed as limiting the invention, among the figure:

Fig. 1 is the curve of the relation between the parameters such as expression thermal resistance, temperature rise;

Fig. 2 is illustrated in the place, sea level, in having the cooling system of fan, and thermal resistance and the relation curve that flows through the air velocity of heating radiator;

Fig. 3 is illustrated in 2500 meters sea level elevation places, in having the cooling system of fan, and the curve of the relation of thermal resistance and air velocity;

Fig. 4 is illustrated in place, sea level, the relation curve of thermal resistance and power loss in not having the cooling system of fan;

Fig. 5 A is the view that the model of cooling system is shown to 5C;

Fig. 6 is the control chart that illustrates according to first embodiment of diagnostic method of the present invention; And

Fig. 7 is the improved control chart that illustrates first embodiment.

Embodiment

Below, with reference to accompanying drawing, preferred implementation of the present invention is described.It is to be noted that at this though the present invention is that example is described with the power model of frequency converter, the present invention is in no way limited to frequency converter, but can be applied to the occasion that any use cooling system cools off.

Before describing cooling system diagnostic method of the present invention, provide the definition of some parameters earlier:

P: the general power of heat radiation or rate of heat dissipation, or the power loss of electrical equipment, unit is W, represents the heat speed that electric component dissipated in the course of the work.May also be referred to as the power loss of electrical equipment, because the power that electrical equipment lost will become heat, and this part heat needs the general power of dispelling the heat just.In order to select heating radiator, use maximum service rating to dissipate;

Tj: the maximum junction temperature of electric component, unit is degree centigrade, in typical electrical equipment, admissible Tj is in the scopes of 120 degree, and for the working temperature of maximum, might arrive 170 degree;

Tc: the case temperature of electric component, unit are degree centigrade that because the case temperature of electrical equipment depends on the measuring position, it represents the maximum local temperature of housing usually;

Th: radiator temperature, unit be degree centigrade, and this parametric representation is at the heating radiator maximum temperature of the position heating radiator of close electric component;

Ta: environment temperature, unit is degree centigrade.

Utilize above-mentioned parameter, heat transference efficiency can be expressed as between two diverse locations:

ΔT _ca＝Rth·P

ΔT _ca＝T _c-T _a

Wherein, Rth is a thermal resistance.

Power model with frequency converter is an example, and Tj is meant the temperature at the chip place of power model, and Tc is meant the temperature at power model housing place, and Ta is meant the environment temperature of the environment that frequency converter is worked.

τ: thermal time constant, adopt this parameter when object is evenly heated or cools off.In this case, in preset time, be proportional to the temperature difference of object in the middle of surrounding environment from the object heat transmission of environment towards periphery

τ＝Rth _ca·Cth _ca

Cth wherein _CaBe thermal mass, be also referred to as thermal capacity, for heating radiator, this thermal capacity Cth _CaIt is the function of radiator material and heating radiator volume.

Fig. 1 is the curve of the relation between the parameters such as expression thermal resistance, temperature rise.The curve of Fig. 1 is the combination of two independent curves, and they are combined among Fig. 1.Suppose that the device that will be cooled is correctly installed, and with respect to airflow direction (making progress the end of from), heating radiator is in normally used installation orientation.From the lower-left to the natural convection curve of upper right curve representation heating radiator temperature rise.The natural convection phenomenon is non-linear.

From curve left to bottom right is the forced convertion curve of thermal resistance with respect to gas velocity.In forced convertion, the linear ratio of Δ Tca and P, Rth thus _CaIrrelevant with P, and only be the function of flow velocity.

Another parameter that need consider is the sea level elevation effect.Though the air themperature of indoor environment usually can Be Controlled and is not subjected to the influence of height change, room air pressure can change along with height.Because a lot of frequency converters are installed in different sea level elevation places, need consider: at higher sea level elevation place, air pressure reduces and atmospheric density reduces, and the radiating efficiency of heating radiator can be affected thus, and following table 1 illustrates sea level elevation sink-efficiency is reduced parameter.Shown in the table 1 at the different altitude height place to the reduction parameter of different heating radiators.For example, for the actual thermal behavior of the sea level elevation place heating radiator beyond determining on the sea level, the thermal resistance value of from performance curve, reading with to be removed by these reduction factors before required thermal resistance is compared.

Table 1: sea level elevation reduction factor

Sea level elevation m/ft	Reduction factor
		0, the sea level	1.00
1000/3000	0.95
		1500/5000	0.90
2000/7000	0.86
		3000/10000	0.80
3500/12000	0.75

By research, the inventor finds the relation of thermal resistance under different condition:

Have under the situation of fan, thermal resistance Rth-ha is the function of air velocity;

Have under the situation of fan, thermal resistance Rth-ha is the function of sea level elevation;

Do not having under the situation of fan, thermal resistance Rth-ha is the function of power loss;

Do not having under the situation of fan, thermal resistance Rth-ha is the function of sea level elevation.

Fig. 2 is illustrated in the place, sea level, that is, air pressure is under 1 atmospheric situation, in having the cooling system of fan, and thermal resistance and the relation that flows through the air velocity of heating radiator.As can be seen from Figure 2, when air velocity is 3.0m/s, promptly being in normal operating conditions or heating radiator at fan does not have when blocked, thermal resistance value is approximately 0.4 ℃/W, and aging or heating radiator is by obstructions such as dusts along with fan, and thermal resistance value increases, and when air velocity is 0.5m/s, thermal resistance value is approximately 0.9 ℃/W, and this just shows that cooling system goes wrong, and needs in time to safeguard or change.

Fig. 3 is illustrated in the different altitude height place, in having the cooling system of fan, and the curve of the relation of thermal resistance and air velocity.As shown in Figure 3, when sea level elevation is 2500m, air pressure is 0.737 atmospheric pressure, at this moment, under fan is in normal operating conditions, when promptly air velocity is 3m/s, thermal resistance value is 0.46 ℃/W, a little higher than thermal resistance value at the place, sea level that is to say that the thermal resistance value that measure this moment need be repaired by above-mentioned reduction factor.

Fig. 4 is illustrated in place, sea level, the relation of thermal resistance and power loss in not having the cooling system of fan.As can be seen from Figure 4, in heating radiator following time in shape, thermal resistance value is 1.4 ℃/W, and when heating radiator stopped up, thermal resistance value was 3 ℃/W.

From top analysis as can be seen; by thermal resistance value according to cooling system; can diagnose the entire heat dissipation system; that is to say judge whether the thermal resistance value of present cooling system surpasses a predetermined value, if surpass; then determine to need to safeguard or change cooling system; thus, the user can preset equipment downtime according to diagnostic result, and cooling system is carried out maintenance and repair.

Below, will describe diagnostic method of the present invention in detail by means of preferred embodiment.

Preferred embodiment

Fig. 5 is the hot loop figure of the power model cooling system of frequency converter, and wherein, with reference to the analytical approach of RC circuit, the hot loop from the chip of power model to heating radiator can be equivalent to Fig. 5 B and 5C.Wherein Rth represents thermal resistance, and Zth represents thermal impedance.

As shown in Figure 5, in this model, heat from chip in series the interface of interface, base plate and the heating radiator of interface, circuit board and the base plate of the wiring copper layer of interface, scolder and the circuit board by chip and scolder (insert and put in the centre under the situation of thermal grease conduction, also comprise the interface of base plate and thermal grease conduction and the interface of thermal grease conduction and heating radiator) etc. flow to heating radiator, be dissipated to the air from heating radiator then.

Response time of model hereto, power loss P for the step of an input, response time from the chip to the base plate is very fast, be approximately 100 microseconds, and the response time from the base plate to the heating radiator is approximately a few minutes, but the response time of (air) is approximately several hrs from the heating radiator to the surrounding environment, therefore the response time of surrounding environment can be thought infinity, then the temperature T a of surrounding environment can be thought an invariable constant basis.

Regard power model as an integral body, then whole model simplification is shown in Fig. 5 C.

Be similar to Ohm law, U=R * I, U is similar to the Δ Tca of native system, R is similar to the Rthca of native system, and I is similar to the P (power loss) in the native system, if apply a current step to the RC circuit, then the voltage U at capacitor C two ends will raise gradually, and final voltage will satisfy above-mentioned Ohm law.Model class of the present invention is similar to said system.

Above-mentioned model is carried out modeling, to obtain the real-time status equation of this model:

P(t)＝P _Rth(t)+P _Cth(t) (1)

Be similar to the real-time analysis equation of RC circuit:

I(t)＝I _r(t)+I _c(t)

I _r(t)＝U(t)/R

I _c(t)＝C·d/dt(U(t))

Above-mentioned formula (1) can derive:

$P\left(t\right)=\frac{{\mathrm{\ΔT}}_{\mathrm{ca}}\left(t\right)}{{\mathrm{Rth}}_{\mathrm{ca}}}+{\mathrm{Cth}}_{\mathrm{ca}}\·\frac{d}{\mathrm{dt}}\·{\mathrm{\ΔT}}_{\mathrm{ca}}\left(t\right)---\left(2\right)$

For the step signal of an input P, carry out Laplace transform, obtain:

$\frac{P\left(s\right)}{s}=\frac{{\mathrm{\ΔT}}_{\mathrm{ca}}\left(s\right)}{{\mathrm{Rth}}_{\mathrm{ca}}}+{\mathrm{Cth}}_{\mathrm{ca}}\·s\·{\mathrm{\ΔT}}_{\mathrm{ca}}\left(s\right)---\left(3\right)$

${\mathrm{\ΔT}}_{\mathrm{ca}}\left(s\right)=\frac{{\mathrm{Rth}}_{\mathrm{ca}}\·\frac{1}{{\mathrm{Rth}}_{\mathrm{ca}}\·{\mathrm{Cth}}_{\mathrm{ca}}}}{s\·(s+\frac{1}{{\mathrm{Rth}}_{\mathrm{ca}}\·{\mathrm{Cth}}_{\mathrm{ca}}})}\·P\left(s\right)---\left(4\right)$

As mentioned above, τ=Rth _CaCth _Ca

Inverse Laplace transform obtains

${\mathrm{\ΔT}}_{\mathrm{ca}}\left(t\right)=P_{\mathrm{AV}}\·{\mathrm{Rth}}_{\mathrm{ca}}(1-e^{\left(\frac{-1}{{\mathrm{Rth}}_{\mathrm{ca}}\·{\mathrm{Cth}}_{\mathrm{ca}}}\right)})=P_{\mathrm{AV}}\·{\mathrm{Rth}}_{\mathrm{ca}}\·(1-e^{\left(\frac{-t}{\mathrm{\τ}}\right)})---\left(5\right)$

From formula (5) as can be seen, under the cooling system normal operation,, can obtain desirable Rth, and the Cth of heating radiator also is known, therefore, promptly can obtains Δ Tca as long as calculate power loss P by the design heating radiator.

In addition, can with Be defined as the thermal impedance Zth of entire heat dissipation system _Ca(t), then obtain following formula (5-1):

ΔT _ca(t)＝Zth _ca(t)·P _ca(t) (5-1)

Usually, the power loss of frequency converter is to calculate like this, at first, supposes: output current (current of electric) is sinusoidal wave and is symmetrical that mean P WM (power width modulated) is sinusoidal wave.

Equal for the current of electric of U phase and the index of modulation of PWM:

$m_U\left(t\right)=\frac{1}{2}(1+M\sin \left({\mathrm{\ω}}_{0}t\right))$

Wherein, I _PEAKIt is the maximum motor electric current I _U, it is to calculate ω from the current measurement value of three phase electric machine ₀Be the angular frequency (function of stator motor frequency) of motor, and

It is the phase shift of current of electric.Average power loss in inverter is:

$P_{\mathrm{mv}\_\mathrm{AV}}\≅I_{\mathrm{PEAK}}(\frac{1}{\mathrm{\π}}(V_{\mathrm{CE}0}+V_{\mathrm{DF}0})+\frac{2(E_{\mathrm{ON}}+E_{\mathrm{OFF}}+E_{\mathrm{QN}})}{\mathrm{\π}{V}_N{I}_N}{V}_{\mathrm{BUS}}{f}_{\mathrm{SW}}+I_{\mathrm{PEAK}}\left(\frac{(r_{\mathrm{CE}}+r_D)}{4}\right))$

Wherein:

V _CE0, V _DF0, r _CEAnd r _DIt is the static parameter of IGBT and fly-wheel diode;

V _BUSIt is the DC bus bar voltage that records;

f _SWIt is inverter switching frequency;

V _NAnd I _NBe respectively the rated voltage and the rated current of motor;

E _ON, E _OFFAnd E _QNBe for IN and VN, the switching loss of IGBT.

Total average power loss of frequency converter is:

P _AV＝P _{inv_AV}+P _{rec_AV}

Wherein, P _{Rec_AV}Be the power loss of diode rectifier, have under the situation of short-circuit capacity P at supply network _{Rec_AV}Approximately be P _{Inv_AV}10% to 20%.

Thereby, will be updated in the formula (5) through the P that said method calculates, can be in the hope of Δ Tca ideally.

Referring to Fig. 6, Fig. 6 illustrates the control chart according to first embodiment of diagnostic method of the present invention.As can be seen from Figure 6, at first measure Ta and Tc, obtain actual Δ Tca, and simultaneously, calculate desirable Δ Tca according to formula (5), desirable Δ Tca is compared with the Δ Tca of actual measurement, draw the poor of the two, and when the difference of the two surpasses a predetermined threshold, determine that heating radiator obstruction or the fan of this moment is aging.

That is to say, because this moment is because heating radiator is blocked or because fan is aging, the Rth of actual cooling system compares increase with design Rth, therefore, the radiating efficiency of cooling system reduces, make actual Δ Tca increase, and when increase surpasses predetermined threshold, prove that the cooling system of this moment need be safeguarded or change.

Because in the frequency converter of prior art, be provided with temperature sensor and measured Tc, therefore, in order to realize the method for first embodiment, the power loss that a temperature sensor comes measures ambient temperature Ta and needs the accurate Calculation frequency converter need be set in addition.

Improve embodiment

Measure Ta for fear of increasing a temperature sensor, as shown in Figure 7, because the Ta that mentions in the above can regard a steady state value basically as, therefore, Tca differentiates to Δ, can avoid increasing a temperature sensor like this and measure Ta.

Obtain following formula (5-2):

$\frac{d\·{\mathrm{\ΔT}}_{\mathrm{ca}}\left(t\right)}{\mathrm{dt}}=\frac{d\·T_c\left(t\right)}{\mathrm{dt}}=\frac{P_{\mathrm{AV}}}{{\mathrm{Cth}}_{\mathrm{ca}}}\·e^{\left(\frac{-t}{\mathrm{\τ}}\right)}---(5-2)$

By such improvement, can avoid increasing a temperature sensor and come measures ambient temperature Ta, and increase the robustness of system thus.

Above, by preferred embodiment the present invention has been described, this shows, main marrow of the present invention is to diagnose cooling system whether to exist aging or obstruction by thermal resistance Rth as weighing parameter, and by utilizing the temperature sensor that has existed to obtain the temperature signal of heat generating components, this temperature (or the value through obtaining after suitably handling) is as intermediary's parameter of actual thermal resistance Rth, and with intermediary's parameter and the threshold that obtains by design thermal resistance (desirable thermal resistance) Rth calculating, in intermediary's parameter during greater than this threshold value, show that this cooling system need safeguard or change, thus, the present invention has realized the diagnosis to cooling system, and make the user to carry out real-time diagnosis to cooling system under any condition of cost not increasing, so that in time find the problem of cooling system, and carry out planned maintenance and repair.

Claims (7)

1. the diagnostic method of a cooling system, this diagnostic method is characterised in that and comprises:

The relevant temperature value of thermal resistance value when obtaining with the cooling system operate as normal;

Utilize the power loss of system, based on the calculated with mathematical model of the system temperature value relevant with the desirable thermal resistance value of design;

The value that is obtained is compared with the value of being calculated; And

If the difference between value of being obtained and the value of being calculated surpasses a predetermined threshold, determine that then this cooling system work is undesired.

2. the undesired fan that comprises of the method for claim 1, wherein described cooling system work is aging, and fan failure or heating radiator are blocked.

3. the method for claim 1, wherein the power loss of described system is to obtain or obtain by calculating by experience.

4. as each described method in the claim 1 to 3, wherein:

The described step of obtaining the value relevant with the current actual thermal resistance value of cooling system comprises:

The temperature of the heater element that acquisition will be dispelled the heat;

Measures ambient temperature; And

Calculate poor between the temperature of heater element and the environment temperature.

5. method as claimed in claim 4, wherein, the value that described calculating is relevant with the desirable thermal resistance value of design comprises following formula:

${\mathrm{\ΔT}}_{\mathrm{ca}}\left(t\right)=P_{\mathrm{AV}}\·{\mathrm{Rth}}_{\mathrm{ca}}\·(1-e^{\left(\frac{-t}{\mathrm{\τ}}\right)}),$

Wherein: Δ T _Ca(t) poor between the temperature of the heater element that calculates for the desirable thermal resistance value of utilizing design and the environment temperature;

P _AVAverage power loss for system;

Rth _CaDesirable thermal resistance value for design;

τ is the time constant of cooling system, is τ=Rth _CaCth _Ca

6. as each described method in the claim 1 to 3, wherein, the step of the value that the described current actual thermal resistance value of obtaining cooling system is correlated with comprises:

The temperature of the heater element that measurement will be dispelled the heat; And

Calculate the time-derivative of this temperature.

7. method as claimed in claim 6, wherein, the relevant value of desirable thermal resistance value described and design comprises following formula:

$\frac{d\·T_c}{\mathrm{dt}}=\frac{P_{\mathrm{AV}}}{{\mathrm{Cth}}_{\mathrm{ca}}}\·e^{\left(\frac{-t}{\mathrm{\τ}}\right)}$

Wherein:

Time-derivative for the temperature of the heater element that calculates according to desirable thermal resistance value;

P _AVAverage power loss for system;

Cth is the thermal capacitance of cooling system;

τ is the time constant of cooling system, τ=Rth _CaCth _Ca

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