CN102192845B - Diagnosis method for 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

Diagnosis method for heat radiation system

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 cooling system fault, to 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 working temperature show that reliability and life-span that temperature reduces corresponding to semiconductor devices increase.ILS and the reliability that therefore, by the working temperature of control device effectively, can realize each device increase.Each device that thus, conventionally will guarantee this power electrical equipment is worked under the threshold temperature of design.

Heating radiator by through be commonly used to hot surface from heater members by heat dissipation to surrounding environment, for example, air.In the present embodiment, take air as example, 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, the surface area that air contacts, or improve speed air flow with fan.

But along with increasing service time, heating radiator can occur stopping up due to the deposition of dust etc., and fan also there will be aging, thereby the overall efficiency of cooling system is declined, can not guarantee that main electric part obtains fully cooling.And well-known, excess Temperature can cause electric part too fast aging, reduces the life-span of electric part, and likely causes electric part to break down.

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

But owing to not having at present a kind of method to diagnose cooling system, thereby unpredictable when cooling system goes wrong, therefore, because overheated meeting causes extemporal shutdown, thereby cause irretrievable and unnecessary loss.

If for example, in textile industry application, may radiating effect be declined due to the fiber in applied environment or filiform obstruction heating radiator or fan, frequency converter be shut down.If can be detected and be known that in advance fan or cooling system go wrong by system, prompting client clears up or changes fan in advance, can avoid uncertain shutdown.Or after shutting down, also can find very soon the reason of shutdown, take very soon relevant treatment measure.(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 the method, can to cooling system, diagnose at any time, and can preset according to deagnostic structure maintenance time and the replacing time of cooling system.

In order to realize object 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: obtain the relevant temperature value of thermal resistance value while normally working to cooling system; Utilize the power loss of system, the temperature value that the calculated with mathematical model based on system is relevant to the desirable thermal resistance value of design; Obtained value is compared with calculated value; And if the difference between the value of obtaining and the value calculated surpasses a predetermined threshold, determine that this cooling system work is undesired.Described cooling system work is undesired comprises that fan is aging, and fan failure or heating radiator are blocked.

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

Preferably, the described step of obtaining the value relevant to 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 environment temperature, and the described calculating value relevant to 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) for utilizing poor between the temperature of the heater element that the desirable thermal resistance value of design calculates and 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, described in obtain the value that the current actual thermal resistance value of cooling system is relevant step comprise the temperature of the heater element that measurement will be dispelled the heat, and calculate 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 for measures ambient temperature a temperature sensor, but can utilize existing temperature sensor in cooling system, and the measurement result of this temperature sensor is carried out to signal processing, can realize the diagnosis to cooling system.Thus, reduced the cost of whole method.

Accompanying drawing explanation

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

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

Fig. 2 is illustrated in place, sea level, in thering is 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 of sea level elevation places, in thering is 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 there is no 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 illustrating according to the first embodiment of diagnostic method of the present invention; And

Fig. 7 is the improved control chart illustrating the first embodiment.

Embodiment

Below, with reference to accompanying drawing, the preferred embodiment of the present invention is described.At this, it is to be noted, although the present invention be take the power model of frequency converter and is described as example, the present invention is in no way limited to frequency converter, but can be applied to any use cooling system, carries out cooling occasion.

Before describing diagnosis method for heat radiation system of the present invention, first provide the definition of some parameters:

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 dissipates in the course of the work.May also be referred to as the power loss of electrical equipment, because the power that electrical equipment loses will become heat, and this part heat needs the general power of heat radiation just.In order to select heating radiator, use maximum service rating to dissipate;

Tj: the maximum junction temperature of electric component, unit is degree Celsius, in typical electrical equipment, admissible Tj is in the scope from 120 degree, and for maximum working temperature, likely to 170 degree;

Tc: the case temperature of electric component, unit is degree Celsius, because the case temperature of electrical equipment depends on measuring position, it represents the maximum local temperature of housing conventionally;

Th: radiator temperature, unit is degree Celsius, 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 Celsius.

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

ΔT _ca＝Rth·P

ΔT _ca＝T _c-T _a

Wherein, Rth is thermal resistance.

The power model of frequency converter of take is example, and Tj refers to the temperature at the chip place of power model, and Tc refers to the temperature at power model housing place, and Ta refers to the environment temperature of the environment that frequency converter is worked.

τ: thermal time constant, adopts this parameter by homogeneous heating or when cooling at object.In this case, within preset time, from the object heat transmission of environment towards periphery, be proportional to the temperature difference of object in the middle of surrounding environment

τ＝Rth _ca·Cth _ca

Cth wherein _cathermal mass, 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 means the curve of the relation between the parameters such as thermal resistance, temperature rise.The curve of Fig. 1 is the combination of two independent curves, and they are combined in Fig. 1.Suppose that the device that will be cooled is correctly installed, and with respect to airflow direction (Down-Up), heating radiator is orientated in normally used installation.Curve from lower-left to upper right represents the natural convection curve of heating radiator temperature rise.Natural convection phenomenon is nonlinear.

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

Another parameter that need to consider is sea level elevation effect.Although the impact of height change can be controlled and not be subject to the air themperature of indoor environment conventionally, room air pressure can change along with height.Because a lot of frequency converters are arranged on different sea level elevation places, need to 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 to parameter.Shown in table 1 at different altitude height place the reduction parameter to different heating radiators.For example, for the actual thermal behavior of the sea level elevation place heating radiator beyond determining on sea level, the thermal resistance value of reading from performance curve will be removed by these reduction factors before comparing with required thermal resistance.

Table 1: sea level elevation reduction factor

Sea level elevation m/ft	Reduction factor
			0, 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, inventor finds the relation of thermal resistance under different condition:

In the situation that having fan, thermal resistance Rth-ha is the function of air velocity;

In the situation that having fan, thermal resistance Rth-ha is the function of sea level elevation;

In the situation that there is no fan, thermal resistance Rth-ha is the function of power loss;

In the situation that there is no fan, thermal resistance Rth-ha is the function of sea level elevation.

Fig. 2 is illustrated in place, sea level, that is, air pressure is in 1 atmospheric situation, in thering is 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, at fan, in normal operating conditions or heating radiator, do not have when blocked, thermal resistance value is approximately 0.4 ℃/W, and along with fan is aging or heating radiator by obstructions such as dusts, 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 safeguard in time or change.

Fig. 3 is illustrated in different altitude height place, in thering is 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, now, at fan under normal operating conditions, when air velocity is 3m/s, thermal resistance value is 0.46 ℃/W, the a little higher than thermal resistance value at place, sea level, that is to say, the thermal resistance value of now measuring need to be repaired by above-mentioned reduction factor.

Fig. 4 is illustrated in place, sea level, the relation of thermal resistance and power loss in there is no the cooling system of fan.As can be seen from Figure 4, in heating radiator lower time in shape, thermal resistance value is 1.4 ℃/W, and when heating radiator stops up, thermal resistance value is 3 ℃/W.

As can be seen from the above analysis; by according to the thermal resistance value of cooling system; can diagnose whole cooling system; that is to say judge whether the thermal resistance value of current cooling system surpasses a predetermined value, if surpassed; determine and need to safeguard or change cooling system; thus, user can preset equipment downtime according to diagnostic result, and cooling system is carried out to 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 (in the situation that of the sandwiched thermal grease conduction in centre, 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, then from heating radiator, be dissipated to air.

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

Regard power model as an integral body, whole model simplification is for as shown in Figure 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 native system, if apply a current step to RC circuit, the voltage U at capacitor C two ends will raise gradually, and final voltage will meet above-mentioned Ohm law.Model class of the present invention is similar to said system.

Above-mentioned model is carried out to 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 be derived into:

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

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), can find out, under cooling system normal operation, by design heating radiator, can obtain desirable Rth, and the Cth of heating radiator be also known, therefore, as long as calculate power loss P, can obtain Δ Tca.

In addition, can be by be defined as the thermal impedance Zth of whole cooling system _ca(t), obtain following formula (5-1):

ΔT _ca(t)＝Zth _ca(t)·P _ca(t) (5-1)

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

For the current of electric of U phase and the index of modulation of PWM, equal:

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

Wherein, I _pEAKit is maximum motor electric current I _u, it is to calculate from the current measurement value of three phase electric machine, ω ₀the 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:

$P_{\mathrm{mv}\_\mathrm{AV}}\&cong;I_{\mathrm{PEAK}}(\frac{1}{\mathrm{\&pi;}}({\mathrm{<figure-callout\; id="0"\; label="V\; CE"\; filenames="HSA00000037112600041.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{CE}}+V_{\mathrm{DF}0})+\frac{2(E_{\mathrm{ON}}+E_{\mathrm{OFF}}+E_{\mathrm{QN}})}{\mathrm{\&pi;}{V}_N{I}_N}{V}_{\mathrm{BUS}}{f}_{\mathrm{SW}}+I_{\mathrm{PEAK}}\left(\frac{(r_{\mathrm{CE}}+r_D)}{4}\right))$

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 recording;

F _sWit is inverter switching frequency;

V _nand I _nrespectively rated voltage and the rated current of motor;

E _oN, E _oFFand E _qNfor 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}the power loss of diode rectifier, in the situation that supply network has short-circuit capacity, P _{rec_AV}approximately P _{inv_AV}10% to 20%.

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

Referring to Fig. 6, Fig. 6 illustrates according to the control chart of the first embodiment of diagnostic method of the present invention.As can be seen from Figure 6, first measure Ta and Tc, obtain actual Δ Tca, and simultaneously, according to formula (5), calculate desirable Δ Tca, 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 fan are now aging.

That is to say, due to now 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, actual Δ Tca is increased, and when increase surpasses predetermined threshold, prove that cooling system now need to safeguard or change.

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

modified embodiment

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

Obtain following formula (5-2):

$\frac{d\&CenterDot;{\mathrm{\&Delta;T}}_{\mathrm{ca}}\left(t\right)}{\mathrm{dt}}=\frac{d\&CenterDot;T_c\left(t\right)}{\mathrm{dt}}=\frac{P_{\mathrm{AV}}}{{\mathrm{Cth}}_{\mathrm{ca}}}\&CenterDot;e^{\left(\frac{-t}{\mathrm{\&tau;}}\right)}---(5-2)$

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

Above, by preferred embodiment, the present invention has been described, this shows, main marrow of the present invention is as parameter of measurement, to diagnose cooling system whether exist aging or stop up by thermal resistance Rth, and by utilizing the temperature sensor having existed to obtain the temperature signal of heat generating components, this temperature (or the value obtaining after suitable processing) is as the Yi Ge intermediary parameter of actual thermal resistance Rth, Bing Jiang intermediary parameter and the threshold obtaining by design thermal resistance (desirable thermal resistance) Rth calculating, when intermediary's parameter is greater than this threshold value, show that this cooling system need to safeguard or change, thus, the present invention has realized the diagnosis to cooling system, and make user in the situation that not increasing any cost, to cooling system, to carry out real-time diagnosis, to find in time the problem of cooling system, and carry out planned maintenance and repair.

Claims (4)

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

Obtain the relevant temperature value of thermal resistance value while normally working to cooling system;

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

Obtained value is compared with calculated value; And

If the difference between the value of obtaining and the value calculated surpasses a predetermined threshold, determine that this cooling system work is undesired;

Wherein, the step of obtaining the value relevant to the current actual thermal resistance value of cooling system described in 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 environment temperature, and

The step of the value that wherein, described calculating is relevant to the desirable thermal resistance value of design comprises utilizes following formula:

$\mathrm{\&Delta;}{T}_{\mathrm{ca}}\left(t\right)=P_{\mathrm{AV}}\&CenterDot;{\mathrm{Rth}}_{\mathrm{ca}}\&CenterDot;(1-e^{\left(\frac{-t}{\mathrm{\&tau;}}\right)}),$

Wherein: Δ T _ca(t) for utilizing poor between the temperature of the heater element that the desirable thermal resistance value of design calculates and 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, Cth wherein _cathermal capacitance for cooling system.

2. a diagnostic method for cooling system, this diagnostic method is characterised in that and comprises:

Obtain the relevant temperature value of thermal resistance value while normally working to cooling system;

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

Obtained value is compared with calculated value; And

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

Wherein, the step of obtaining the value that the current actual thermal resistance value of cooling system is relevant described in comprises:

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

Calculate the time-derivative of this temperature,

The step of the value that wherein, desirable thermal resistance value described and design is relevant comprises utilizes following formula:

$\frac{d\&CenterDot;T_c\left(t\right)}{\mathrm{dt}}=\frac{P_{\mathrm{AV}}}{{\mathrm{Cth}}_{\mathrm{ca}}}\&CenterDot;e^{\left(\frac{-t}{\mathrm{\&tau;}}\right)}$

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 _cathermal capacitance for cooling system;

τ is the time constant of cooling system, τ=Rth _cacth _ca, Rth wherein _cadesirable thermal resistance value for design.

3. method as claimed in claim 1 or 2, wherein, described cooling system work is undesired comprises that fan is aging, fan failure or heating radiator are blocked.

4. method as claimed in claim 1 or 2, wherein, the power loss of described system is to be obtained or obtained by calculating by experience.

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