METHOD FOR CONTROLLING AN ELECTRIC FAN

Abstract

A method for controlling an electric fan including an electric motor and electronics for controlling the electric motor, including a step for controlling the speed of the motor, a step for controlling the power of the motor as an alternative to the step for controlling the speed; the step for controlling the power including a step for monitoring the electrical power P.sub.IN;FEEDBACK absorbed by the motor and a step for regulating the electrical power P.sub.IN;FEEDBACK absorbed by the motor including a step of applying a variation freq to the electricity supply frequency of the motor as a function of a difference between a power set-point PI.sub.IN, REF and the power absorbed by the motor PI.sub.IN,FEEDBACK.

Claims

1. A method for controlling an electric fan comprising an electric motor and electronics for controlling the electric motor, comprising: a step of controlling the speed of the motor, the method wherein it comprises a step of power controlling the motor alternatively to the step of speed controlling, the power controlling step comprising: a step of monitoring the electrical power P.sub.IN;FEEDBACK absorbed by the motor; a step of regulating the electrical power P.sub.IN;FEEDBACK absorbed by the motor, comprising; a step of applying a variation freq to the electricity supply frequency of the motor as a function of a difference between a power set-point PI.sub.IN, REF and the power absorbed by the motor PI.sub.IN,FEEDBACK.

2. The method according to claim 1 wherein, in a first operating state of the electric fan, the power set-point PI.sub.IN, REF comes from a reference generator (103) which provides to a PI.sub.Power regulator a reference signal for varying the electrical power absorbed by the motor P.sub.IN;FEEDBACK from a measured value of absorbed power P.sub.IN(t.sub.PMAX,ON) to a predetermined value P.sub.MAX.

3. The method according to claim 2 wherein the regulator PI.sub.POWER- is limited at the output between a a maximum value LIM.sub.POWER,HIGH set by default to the difference between a maximum frequency EIFreq.sub.MAX corresponding to a maximum power absorbed by the motor during the power control and a maximum frequency EIFreq.sub.NEN permitted during the speed control and a minimum value LIM.sub.POWER,LOW set by default to 0; in that way, when in power control the PI.sub.POWER regulator- keeps the power of the motor to the predetermined value P.sub.MAX varying the electrical frequency between EIFreq.sub.NEN and EIFreq.sub.MAX.

4. The method according to claim 1, wherein the power set-point PI.sub.IN, REF is controlled by a second regulator PI.sub.TEMP which reduces the power set-point PI.sub.IN, REF starting from an initial value P.sub.IN(t.sub.DERATING).

5. The method according to claim 4 comprising a step for setting a maximum nominal operating temperature T.sub.1 of the control electronics; a step for setting a hysteresis .sub.1 on the maximum nominal operating temperature; a step of monitoring the temperature T of the control electronics; a step for regulating the temperature T of the control electronics, which starts when the temperature T of the control electronics exceeds the T.sub.1+.sub.1, using the step of regulating the electrical power P.sub.IN;FEEDBACK absorbed by the motor, wherein the second regulator PI.sub.TEMP has at the input, by means of an adder node, a temperature error T.sub.DERATING,REFT.sub.FEEDBACK where: T.sub.DERATING,REF is the reference temperature during the step of regulating the temperature T; T.sub.FEEDBACK is a temperature measured in the control electronics which corresponds to the temperature T, T.sub.FEEDBACK being greater than or equal to T.sub.1 during the step of regulating the temperature T, the output of the second regulator PI.sub.TEMP being a power set-point which is added, in a second adder node, to the electric power value P.sub.IN(t.sub.DERATING) recorded when the step of regulating the electric power P.sub.IN;FEEDBACK absorbed by the motor starts.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0024] Further features and advantages of this invention are more apparent in the detailed description below, with reference to a preferred, non-restricting, embodiment of a control method for an electric fan as schematically illustrated in the accompanying drawings, in which:

[0025] FIG. 1A illustrates an example of the temperature diagram of the microcontroller as a function of time in a control method of known type;

[0026] FIG. 1B illustrates a diagram of the rotation speed of the motor as a function of time correlated with the diagram of FIG. 1A of the control method of known type;

[0027] FIG. 2 illustrates a finished state machine which describes the control method according to this invention;

[0028] FIG. 3 illustrates a diagram of a system regulator for adjusting the temperature in the drive in a preferred embodiment of this invention;

[0029] FIG. 4 illustrates an example of the trend of a reference quantity as a function of reading time in the diagram of FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0030] With reference to FIG. 2, the numeral 1 denotes a finished state machine based which describes, in general terms, the method for controlling an electric fan.

[0031] The electric fan of the substantially known type and not illustrated preferably controlled according to this method comprises, very briefly, an electric motor, a fan driven by the electric motor and an electric or electronic board for driving and controlling the electric motor.

[0032] The electronic board is preferably housed inside the motor which in turn is preferably of the sealed type.

[0033] More specifically, by way of a non-limiting example, reference is made below to an actuator comprising an electronic system which commands and controls a three-phase brushless sinusoidal motor with permanent magnets, which in turn drives a ventilation unit (fan and conveyor) aimed at cooling groups of heat exchangers in automotive applications.

[0034] The electronic board comprises a microcontroller and electronic power means which comprise, for example and preferably, MOSFETs, to which explicit reference will be made, for controlling and powering the electric motor.

[0035] The microcontroller has a relative temperature T.sub.D and the MOSFETs have a relative temperature T.sub.M.

[0036] With reference to FIG. 2, in terms of state-based logic, this method comprises three operating states of the electric fan.

[0037] In a first state, referred to as NORMAL and denoted by the numeral 10, the electric fan operates under nominal operating conditions until

T(T.sub.1+.sub.1)

where:
T is the temperature measured on the electronic board.

[0038] T is, for example, the temperature of the microcontroller or the temperature of the MOSFET both monitored, that is, T=T.sub.D or T.sub.M;

[0039] T.sub.1 is the maximum nominal operating temperature of the electronic board.

[0040] T.sub.1 is, for example, the maximum nominal operating temperature of the microcontroller or the maximum nominal operating temperature of the MOSFET.

[0041] .sub.1 is a hysteresis on the maximum nominal operating temperature beyond which it changes to thermal derating.

[0042] The hysteresis is needed in order to not to unnecessarily activate the control method described in detail below, if there are only temperature oscillations close to the threshold T.sub.1, or, for example, the measurement T is affected by measuring noise.

[0043] When T>(T.sub.1+.sub.1) changes to a second state, referred to as DERATING and denoted by the numeral 20.

[0044] In the DERATING state the electrical power of the drive is controlled is in such a way as to reduce the temperature and adjust it to the value T.sub.1 shown above, as described in detail below.

[0045] The DERATING state defines, in practice, a step for regulating the temperature T of the control electronics.

[0046] In practice, a error in the temperature measured at the electronic board determines a regulation of the electrical power absorbed by the electric fan, in particular by the motor.

[0047] The DERATING state is kept until T.sub.1T<T.sub.2.

[0048] T2 is the threshold operating temperature of the electronic board.

[0049] T.sub.2 is, for example, the maximum permissible temperature of the microcontroller or the maximum permissible temperature of the MOSFET.

[0050] T obviously feels the effect of the ambient temperature in which the electric fan is operating.

[0051] Starting from the DERATING state if, for example due to a decrease in the ambient temperature, the temperature measured on the electronic board falls below the maximum nominal operating temperature, that is, T<T.sub.1, the electric fan returns gradually, preferably in the manner described below, to the nominal operation, the NORMAL state.

[0052] Starting from the DERATING state, if, on the other hand, due to an excessive overheating, the temperature measured on the electronic board exceeds the operational threshold of the electronic board, that is, TT.sub.2 it changes to a third state known as OVER_MAX and labelled 30.

[0053] This state interrupts the operation the electric fan until TT.sub.1.

[0054] When this condition becomes false (i.e. T<T.sub.1), the system returns to the NORMAL state and the electric fan can again operate normally.

[0055] Preferably, under normal operating conditions, the electric fan is controlled by speed (speed-control) by means of a suitable speed set-point, in a substantially known manner.

[0056] An appropriate command not described informs the drive of the need to pass to the above-mentioned power control. This command is, for example, imparted by a control unit of the vehicle in which the electric fan is installed. For example, the change to the power control takes place when the electric fan stops working under nominal conditions.

[0057] With reference to FIG. 3, the numeral 100 denotes a system regulator for regulating the temperature T of the electronic board by controlling the power absorbed by the motor.

[0058] In the example embodiment illustrated, the system 100 comprises a first proportional-integral regulator PI.sub.POWER denoted by the numeral 101.

[0059] The regulator 101 is configured to control the power absorbed by the electric motor to a predetermined value, producing a consequent variation freq of the electricity supply frequency of the motor.

[0060] The regulator 101 has at the input a power set-point P.sub.IN,REF and a direct reading of the power absorbed by the motor PI.sub.IN, FEEDBACK and provides a contribution in terms of .sub.freq.

[0061] The power set-point P.sub.IN,REF and the value PI.sub.IN, FEEDBACK add algebraically in an adder node 102 at the output of which a power error is available:

P.sub.IN,REFPI.sub.IN,FEEDBACK

[0062] A set-point of this regulator 101, under nominal conditions, that is, in the above-mentioned NORMAL state, that is, in DERATING OFF, as indicated in FIG. 3, comes from a reference generator P.sub.IN,REF, denoted by the reference numeral 103.

[0063] The generator 103 provides a reference signal in order to change from a current power value P.sub.IN(t.sub.PMAX,ON) to a desired value P.sub.MAX.

[0064] The ramp which starts from P.sub.IN(t.sub.PMAX,ON) is considered by the actuation from when the control unit commands the change to power control from speed control.

[0065] The electric fan is in practice controlled in a constant power operational mode; the electrical power absorbed by the motor is the quantity adjusted and the variation of the speed of rotation of the motor is, in practice, a consequence.

[0066] The regulator 101 preferably has the output limited to the following limiting values:

[0067] LIM.sub.POWER,HIGH: maximum output value, set by default to the difference between a maximum regulating frequency in power control P.sub.MAX, EIFreq.sub.MAX, and a maximum frequency in speed control, EIFreq.sub.NEN;

[0068] LIM.sub.POWER,LOW: minimum output value, set by default to 0; in that way, when in power control, PI.sub.Power keeps the power of the motor at P.sub.MAX by varying the electrical frequency between EIFreq.sub.NEN and EIFreq.sub.MAX, that is, in terms of delta-frequency:

0freq(EIFreq.sub.MAXEIfreq.sub.NEN).

In practice:

[0069] LIM.sub.POWER,HIGH=EIFreq.sub.MAXEIFreq.sub.NEN;

[0070] LIM.sub.POWER,LOW=0 if derating OFF;

[0071] LIM.sub.POWER,LOW=(EIFreq.sub.MAXEIFreq.sub.MIN) if derating ON.

[0072] Until PI.sub.IN, FEEDBACK remains less than P.sub.IN,REF, freq is positive, determining an acceleration of the motor.

[0073] When PI.sub.IN, FEEDBACK=P.sub.IN,REF the regulator stops accelerating the motor.

[0074] In the case of thermal derating, DERATING ON, with reference to FIG. 3, in order to have, in practice, a negative contribution to freq and reduce the power absorbed by the motor and therefore its speed of rotation, the regulator 101 PI.sub.POWER is controlled by a proportional-integral regulator PI.sub.TEMP, denoted by the reference numeral 104.

[0075] The regulator 104 is preferably substantially similar to the regulator 101.

The regulator 104 reduces, with a relative dynamic, the power set-point PI.sub.IN,REF starting from an initial derating value P.sub.IN(t.sub.DERATING).

[0076] The regulator 104 has at the input, by means of an adder node 105, a temperature error T.sub.DERATING,REFT.sub.FEEDBACK where:

[0077] T.sub.DERATING, REF is the reference temperature during the derating step.

[0078] T.sub.FEEDBACK is the temperature measured in the electronic board which corresponds to the above-mentioned T.

[0079] T.sub.FEEDBACK is greater than T.sub.1+.sub.1. upon the triggering of the derating.

[0080] Following the actuation it remains in the DERATING state for the entire time that the feedback is greater then or equal to T1

[0081] The output of the regulator 104 is a power set-point which is added, in an adder node 106, to the electrical power value recorded when the derating P.sub.IN(t.sub.DERATING) starts, provided by a corresponding block 107.

[0082] The adder node 106 determines a decreasing set-point for the electrical power P.sub.IN,REF, illustrated, for example, in FIG. 4, up to a value P.sub.IN,STEADY-STATE.

[0083] This set-point is provided at the input, in the case DERATING ON, at the adder node 102.

[0084] P.sub.IN,REF will settle at a steady state value when the output of PI.sub.TEMP stops evolving, that is, when the temperature error (T.sub.DERATING,REFT.sub.FEEDBACK)=0.

[0085] During the derating LIM.sub.POWER,LOW=(EIFreq.sub.MAXEIFreq.sub.MIN), that is, the deference between the maximum and minimum electrical frequency allows the actuation in question.

[0086] The minus sign allows working with freq<0 and, consequently, to obtain a deceleration linked to the reduction of power governed by PI.sub.TEMP.

[0087] If the measured temperature is T.sub.FEEDBACK<T.sub.DERATING,REF, the output of PI.sub.TEMP will increase again, increasing the set-point of PI.sub.POWER, and producing an acceleration until returning the system to nominal operational conditions, that is, in the NORMAL state.

[0088] This invention achieves important advantages.

[0089] The control method or algorithm makes it possible to protect the electric and electronic devices against over-temperatures which could occur during operation of the drive unit.

[0090] The method is in practice a thermal derating process based on the direct control of the maximum temperature permitted for the most critical components, always keeping it at the maximum permissible limit through a continuous control, guaranteeing to the user, in that way, the maximum possible thermal performance.

[0091] The above-mentioned control algorithm acts on the directly random factor of the over-temperatures inside the motor, that is, the power dissipated, which is directly correlated to the power absorbed by the motor itself, rather than on the indirect factor consisting of the motor speed, which, on the other hand, does not feel the effect of absorbed, and therefore dissipated, power variations, induced by phenomena such as the speed dynamics of the vehicle, change of air density due to temperature or altitude, etc.

[0092] The control method adjusts the maximum possible operating temperature in a direct and accurate manner through a continuous control of the power absorbed by the motor, which is measurable preferably by processing the voltage and current feedback signals.

[0093] Moreover, the control method enables the response, static and dynamic, to be summarised in a completely independent manner, unlike the other processes comprising the overall drive control system.

[0094] This differs from a system controlled simply by speed, wherein the drive receives an electrical frequency set-point to rotate, irrespective of the input power.