Patent Application
20180294759
This invention relates to a method for controlling an electric fan and in particular a method for controlling the electric motor of an electric fan in automotive applications.
Electric fans are widely used in the automotive sector with functions of cooling and removing heat from radiating masses, that is, for cooling heat exchangers, for example radiators, for cooling motors (engine-cooling), radiators for air conditioning, radiators for cooling oil (oil-cooling).
The electric fans comprise, in short, an electric motor, electronics for controlling the motor and a fan driven by the motor which defines the entire system or drive.
A distinctive feature of the control electronics is also the possibility of protecting the electric motor and the electronics from any overheating or over-temperatures, determined, for example, by particularly severe operating conditions, such as a high ambient temperature or sudden drawbacks.
More specifically, the overheatings are delicate in electric fans comprising electric motors of the closed and/or sealed type with control electronics fitted inside, in which the heat dissipation is of even greater importance and must be significantly reduced.
In general, the electric fan and the control electronics are characterised by precise temperature ranges wherein the operation is optimum and safe and the nominal performance is guaranteed.
If there is a temperature increase in the motor above the permissible maximum values, even though it is operating at nominal values, it is necessary to intervene in order to protect the control electronics, especially the electronic components, against possible damage.
One control strategy comprises, in the case of temperature increases beyond the permissible values, “degrading” the motor, that is to say, reducing the efficiency and power outputs compared with the nominal performance levels, which are no longer guaranteed, in order to preserve the control electronics.
The degrading, also known as “thermal derating” is used, in practice, to lower the working temperature of the motor in order to counteract, for example, an increase in the outside temperature.
As part of the scenario, one of the design requirements of any derating method must be to ensure the maximum availability of the electric fan to operate at temperatures as close as possible to the limit values permitted by the specifications of the components used.
The most state-of-the-art control processes currently available for protection against over-temperatures, which receive feedback from one or more temperature sensors inside the drive, react to an overheating of the drive itself, in particular of the electronic board, reducing the speed of rotation of the motor controlled.
These processes attempt to lower the operating temperature, temporarily limiting the performance, that is, the speed of rotation of the motor.
This type of derating may, however, be excessive, since the direct reduction of the speed of the motor does not consider how much the absorbed electrical power is actually varying, and this fact translates nearly always into an over-protection of the drive.
Whilst, on the one hand, a similar approach favours the protection of the electric fan from potential breakage due to excess over-temperature of its components, on the other hand, the associated consequent reduction of performance could induce problems of overheating of the heat exchangers: in other words, the user could risk damage whilst the electric fan would be over-protected.
In general, the drive comprises, amongst the other electronic components, a microcontroller and a plurality of electronic power components, such as, for example, MOSFETs.
A known control method comprises monitoring the temperature of the microcontroller, or the board on which it is installed, and the power MOSFETs; if the temperature of the MOSFETs reaches a respective maximum threshold temperature, the motor is stopped.
With reference to
If the temperature of the microcontroller continuous to rise, despite the degrading, to a second threshold temperature Tmax, the motor is stopped and the speed is changed to 0.
In practice, the degrading is controlled by a regulating device, for example PI, based on the temperature error; in the case, not illustrated, in which the temperature of the microcontroller drops again below Tder before the motor stops, the speed is again increased to Vn.
The main drawback of this control and protection method is that, as mentioned, under certain conditions, the speed of rotation of the electric fan might be excessively reduced, placing at risk the entire vehicle on which the electric fan is installed, in cases in which the over-temperature is caused by a transient event which passes in a relatively short time.
In this context, the main aim of this invention is to overcome the above-mentioned drawback.
The aim of this invention is to propose a method for controlling an electric fan which increases the safety of the entire vehicle, avoiding a degrading or even a too sudden switching off of the electric fan.
A further aim of this invention is to propose a control method which allows the electric fan to provide the maximum performance at temperatures compatible with physical limits of the components used, without using, in practice, excessive protection.
The technical purpose indicated and at least the aims specified are substantially achieved by a control method according to claim 1.
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:
With reference to
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.
The electronic board is preferably housed inside the motor which in turn is preferably of the sealed type.
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.
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.
The microcontroller has a relative temperature TD and the MOSFETs have a relative temperature TM.
With reference to
In a first state, referred to as NORMAL and denoted by the numeral 10, the electric fan operates under nominal operating conditions until
T≤(T1+δ1)
where:
T is the temperature measured on the electronic board.
T is, for example, the temperature of the microcontroller or the temperature of the MOSFET both monitored, that is, T=TD or TM;
T1 is the maximum nominal operating temperature of the electronic board.
T1 is, for example, the maximum nominal operating temperature of the microcontroller or the maximum nominal operating temperature of the MOSFET.
δ1 is a hysteresis on the maximum nominal operating temperature beyond which it changes to thermal derating.
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 T1, or, for example, the measurement T is affected by measuring noise.
When T>(T1+δ1) changes to a second state, referred to as DERATING and denoted by the numeral 20.
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 T1 shown above, as described in detail below.
The DERATING state defines, in practice, a step for regulating the temperature T of the control electronics.
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.
The DERATING state is kept until T1≤T<T2.
T2 is the threshold operating temperature of the electronic board.
T2 is, for example, the maximum permissible temperature of the microcontroller or the maximum permissible temperature of the MOSFET.
T obviously feels the effect of the ambient temperature in which the electric fan is operating.
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<T1, the electric fan returns gradually, preferably in the manner described below, to the nominal operation, the NORMAL state.
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, T≥T2 it changes to a third state known as OVER_MAX and labelled 30.
This state interrupts the operation the electric fan until T≥T1.
When this condition becomes false (i.e. T<T1), the system returns to the NORMAL state and the electric fan can again operate normally.
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.
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.
With reference to
In the example embodiment illustrated, the system 100 comprises a first proportional-integral regulator PIPOWER denoted by the numeral 101.
The regulator 101 is configured to control the power absorbed by the electric motor to a predetermined value, producing a consequent variation Δfreq of the electricity supply frequency of the motor.
The regulator 101 has at the input a power set-point PIN,REF and a direct reading of the power absorbed by the motor PIIN, FEEDBACK and provides a contribution in terms of Δfreq.
The power set-point PIN,REF and the value PIIN, FEEDBACK add algebraically in an adder node 102 at the output of which a power error is available:
P
IN,REF
−PI
IN,FEEDBACK
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
The generator 103 provides a reference signal in order to change from a current power value PIN(tPMAX,ON) to a desired value PMAX.
The ramp which starts from PIN(tPMAX,ON) is considered by the actuation from when the control unit commands the change to power control from speed control.
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.
The regulator 101 preferably has the output limited to the following limiting values:
LIMPOWER,HIGH: maximum output value, set by default to the difference between a maximum regulating frequency in power control PMAX, EIFreqMAX, and a maximum frequency in speed control, EIFreqNEN;
LIMPOWER,LOW: minimum output value, set by default to 0; in that way, when in power control, PIPower keeps the power of the motor at PMAX by varying the electrical frequency between EIFreqNEN and EIFreqMAX, that is, in terms of ‘delta-frequency’:
0≤Δfreq≤(EIFreqMAX−EIfreqNEN).
In practice:
LIMPOWER,HIGH=EIFreqMAX−EIFreqNEN;
LIMPOWER,LOW=0 if derating OFF;
LIMPOWER,LOW=−(EIFreqMAX−EIFreqMIN) if derating ON.
Until PIIN, FEEDBACK remains less than PIN,REF, Δfreq is positive, determining an acceleration of the motor.
When PIIN, FEEDBACK=PIN,REF the regulator stops accelerating the motor.
In the case of thermal derating, DERATING ON, with reference to
The regulator 104 is preferably substantially similar to the regulator 101.
The regulator 104 reduces, with a relative dynamic, the power set-point PIIN,REF starting from an initial derating value PIN(tDERATING).
The regulator 104 has at the input, by means of an adder node 105, a temperature error TDERATING,REF−TFEEDBACK where:
TDERATING, REF is the reference temperature during the derating step.
TFEEDBACK is the temperature measured in the electronic board which corresponds to the above-mentioned T.
TFEEDBACK is greater than T1+δ1. upon the triggering of the derating.
Following the actuation it remains in the DERATING state for the entire time that the feedback is greater then or equal to T1
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 PIN(tDERATING) starts, provided by a corresponding block 107.
The adder node 106 determines a decreasing set-point for the electrical power PIN,REF, illustrated, for example, in
This set-point is provided at the input, in the case DERATING ON, at the adder node 102.
PIN,REF will settle at a steady state value when the output of PITEMP stops evolving, that is, when the temperature error (TDERATING,REF−TFEEDBACK)=0.
During the derating LIMPOWER,LOW=−(EIFreqMAX−EIFreqMIN), that is, the deference between the maximum and minimum electrical frequency allows the actuation in question.
The minus sign allows working with Δfreq<0 and, consequently, to obtain a deceleration linked to the reduction of power governed by PITEMP.
If the measured temperature is TFEEDBACK<TDERATING,REF, the output of PITEMP will increase again, increasing the set-point of PIPOWER, and producing an acceleration until returning the system to nominal operational conditions, that is, in the NORMAL state.
This invention achieves important advantages.
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.
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.
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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102015000067601 | Oct 2015 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2016/056503 | 10/28/2016 | WO | 00 |
