EP2356474A1

EP2356474A1 - Circuit for measuring the efficient current of a signal to be monitored

Info

Publication number: EP2356474A1
Application number: EP09756701A
Authority: EP
Inventors: Luis De Sousa; Dominique Dupuis
Original assignee: Valeo Systemes de Controle Moteur SAS
Current assignee: Valeo Systemes de Controle Moteur SAS
Priority date: 2008-11-06
Filing date: 2009-11-05
Publication date: 2011-08-17
Also published as: CN102209900A; US20110234205A1; US8581573B2; JP2012507732A; FR2938070A1; KR20110088541A; FR2938070B1; MX2011004712A; MY152821A; BRPI0921677A2; WO2010052278A1; RU2011122617A

Abstract

The present invention relates to a circuit (22) for measuring an efficient current (i_eff(t)) of a signal to be monitored (i(t)), characterised in that the circuit includes means for making a continuous reference signal (i_DC(t)) depend on the signal to be monitored (i(t) so that the efficient current (i_DCeff(t)) of the continuous reference signal (i_DC(t)) is equal to the efficient current (ieff(t)) of the signal to be monitored (i(t)).

Description

Circuit for measuring the effective current of a signal to be controlled

The present invention relates to a circuit for measuring the effective current of a signal to be tested, in particular in the field of current control of electrical machines with variable inductance such as the actuators used for so-called electromagnetic valves ("camless" system). English) in motor vehicles.

More generally, the invention relates to any equipment requiring one or more simultaneous measurements of a true effective quantity, in particular an effective current, for monitoring, diagnosis or close protection, with respect to equipment in which there is no There are no numerical resources or computing powers available or sufficient to process the measurement, and in which it is not desired to introduce expensive analog components such as analog multipliers or other specific integrated circuits that are not widely available.

The invention is particularly interesting for a reliable diagnosis of an overload, in particular for an optimized solenoid valve system which one wishes to exploit the maximum of possibilities without exceeding the limits of operation.

Indeed, the equipment supplying a load with strong current must be supervised in particular to ensure the safety of the people and the material, to optimize the consumption of the loads, to detect a possible anomaly of these loads (overload) and / or to adapt the thresholds of protection in function of external and / or variable parameters such as temperature, starting mode or a particular configuration of the equipment.

In the case of a linear load, whether the current is alternating or continuous, it is sufficient to measure the peak current, the average current or the average rectified current to obtain an indirect measurement of the effective current.

In fact, there is a direct link between the quantity measured on the one hand and the consumption of the system or heating components that conduct the current. It is not necessary to perform an effective current measurement. However, when the load is non-linear and the current form factor is small and variable as a function of time, the peak current, average current or average rectified current measurements are no longer significant for the rms current. Considering, for example, the drive current represented in FIG. 1, the ratio between a mean average measurement and an effective measurement Ufficacθ is the square root of the duty cycle, the latter being defined as the ratio between the duration t1 of the signal over its period T. .

According to an example specific to the automotive field,

¹ / effective

I _{mOye «} mean ₌ K ₌ ^ ₃ ^^ ^ ₌ ^ ^ _{g {χ =} ^^

J effective V 'T

This situation occurs in an electromagnetic valve control, where the valve actuators consume a pulse current of frequency adapted to the engine speed. Thus, the width of the pulses varies little in contrast to their period so that the average of such a signal is constant while its effective current is not.

In this case, neither the peak value nor the average value can represent heating of the actuator, the power cables or any other component conducting the current.

The existing solutions provided by the prior art are mainly of five types:

the approach of the value of the rms current by the combination of the peak value and the average value: Such a method is described, for example, in the patent application W09505023 "METHOD AND APPARATUS FOR RMS CURRENT APPROXIMATION". This method is limited by the harmonic distortion rate of the signal. In addition, this method is very sensitive to external disturbances and different types of control which reduces its reproducibility.

In particular, this method can not be improved by a correction factor as proposed by the patent US5027060 "MEASURING DEVOTION OF THE RMS VALUE OF A SIGNAL, NOTABLY FOR CURRENT MEASUREMENT IN A SOLID-STATE TRIP DEVICE".

- the deduction of the value of the rms current by a numerical calculation:

The measurement of the rms current can be obtained by digital calculations based on analog-digital acquisitions which require a bandwidth and a sampling frequency large enough not to excessively filter the processed signals.

As a result, these calculations can monopolize important digital resources, particularly in terms of computing power, all the more significant as the number of current measurements to be monitored is high and the harmonic rate is high. This solution therefore has a high cost.

- the deduction of the value of the rms current by an analog calculation:

In order not to monopolize computation resources, one can resort to analog circuits.

There are various analog devices on the market that can be used to perform the calculations required to obtain the rms value, including multiplication and square root function. Using such analog devices, it is possible to obtain a value of the square of the rms value of a signal.

It is also possible to associate this measurement of the square of the rms value with a function intended to extract its square root and thus tend towards the value of the effective measurement. This is particularly the case for solutions based on Gilbert's cells, such as that proposed by US Pat. No. 7,002,394, LOW SUPPLY CURRENT RMS-TO-DC CONVERTER.

But when it is necessary to measure on a large number of channels, as in the case of an electronic control circuit of 8 or 16 electromagnetic valves, the cost of the function becomes high as in the previous method.

In addition, the square measure of the rms value does not provide good sensitivity over a large scale of value, the relative error and the resolution of the measures varying inversely squared.

- the use of the thermal effect:

Since the dissipated power is proportional to the square of the rms current, the value of the rms current can be found by controlling the rise in temperature of a resistance traversed by a direct current stabilized to that of a resistance traversed by an image current. measured current.

Such solutions are disclosed in US391 1359 and US3624525 "TRUE RMS CONVERTER" as well as in US2007024265 "SYSTEMS AND METHODS FOR MEASURING AN RMS VOLTAGE."

But this technique is very difficult to implement because it must ensure a symmetry of thermal impedance and insulation against the surrounding heat to not disturb the measurement. In addition, the integration time of this circuit is difficult to adjust and the thermal time constants limit the reactivity of the assembly.

- current disjunctions:

The current disjunction solutions generally used are fuses and electro-magneto-thermal circuit breakers.

These solutions have many defects: the tolerance on the threshold is wide and sensitive to the temperature, an external intervention is necessary for the replacement of the fuse or the reset of the breaker, the congestion is important and the thresholds of disjunction or the delays of trigger are not adjustable in real time.

In this context, the present invention aims at providing a circuit for measuring the effective current of a signal to be controlled having a low cost and a satisfactory reliability for an application such as the control of the supply current of electromagnetic valves of an engine. automobile. To this end, the invention proposes a circuit for measuring the effective current of a signal to be controlled, characterized in that it comprises means for controlling a continuous reference signal to the signal to be monitored so that the effective current of the signal continuous reference is equal to the effective current of the signal to be monitored.

A measuring circuit according to the invention has the following advantages:

Its cost is reduced in view of the fact that it can be implemented with inexpensive electronic circuits, analogically and without resorting to numerical calculations.

In addition, a circuit according to the invention can be implemented by means of low cost components, such as standard operational amplifiers. It does not require analog multipliers or specific integrated circuits. - Its use implements a continuous signal whose voltage or intensity are easily measurable.

Its bandwidth is limited only by the switching frequency and the speed of the components, such as operational amplifiers, which are used. Thus, this bandwidth can be adapted to the desired cost / performance ratio for the circuit.

Its time constant is adjustable, which again makes it possible to adapt this parameter to the desired cost / performance ratio.

Its implementation eliminates none of the harmonics included in the bandwidth, which prevents any excessive filtering of the current to be controlled. Its measurement of the signal to be controlled is carried out by means of a measurement proportional to the square of the effective current, which allows sensible measurements even for the low values of this effective current.

- Its bandwidth is adjustable. In the context of an effective current disjunction, this solution offers the possibility of adjusting the disjunction threshold in real time.

A circuit according to the invention may also have one or more of the following characteristics, considered individually or in any technically possible combination: In one embodiment, the circuit comprises a first modulator and a second modulator respectively processing the signal to be controlled or the reference signal to provide a first modulated signal or a second modulated signal whose average current is proportional, respectively, to the square of the current. effective signal to be measured or squared the effective current of the reference signal.

According to one embodiment, the circuit comprises means for modulating the first modulated signal and the second modulated pulse width and amplitude signal using a periodic signal. In one embodiment, the first modulator comprises means for the pulse width modulation to correspond to a duty cycle proportional to the intensity of the current to be controlled.

According to one embodiment, the circuit comprises means for modulating the signal to be monitored and the continuous reference signal with a switching frequency such that, over a period T of calculating the average value of the first modulated signal or the second modulated signal, this mean value is proportional to the square of the effective current of the signal to be measured or the reference signal.

In one embodiment, each modulator comprises an operational amplifier receiving, at a first input, a signal to be modulated and, at a second input, the periodic signal.

According to one embodiment, the circuit comprises:

a block performing the comparison between the effective currents of the modulated signals via their respective average values, and a block injecting the result of this comparison into the circuit, via a feedback loop, as being the continuous reference signal.

The invention also relates to a method for measuring the effective current of a signal to be tested, characterized in that a continuous reference signal is slaved to the signal to be monitored so that the effective current of the continuous reference signal is equal to the current effective signal to control by means of a circuit according to one of the previous achievements.

In one embodiment, the supply current of an electromagnetic valve actuator of a motor vehicle is measured. Other features and advantages of the invention will emerge clearly from the description given below, by way of indication and not limitation, of an embodiment of the invention with reference to the appended figures, among which: FIG. 1, already described, illustrates a drive current,

FIG. 2 represents a comparator circuit implemented for modulating a signal according to one embodiment of the invention;

FIG. 3 represents a doubly modulated pulse width and amplitude signal according to one embodiment of the invention; FIG. 4 is a block diagram of a measuring circuit according to one embodiment of the invention;

FIG. 5 represents operational amplifier and comparator circuits; and

FIG. 6 is an electrical diagram making it possible to perform the functions described in FIG. 4;

In all the figures, the common elements bear the same reference numbers.

According to the invention, a circuit for measuring the effective current of a signal to be controlled i (t) comprises means for controlling a continuous reference signal i _D c (t) to this signal i (t) to be controlled so that the effective current i _D ceff (t) of this reference signal i _D c (t) is equal to the effective current i _Θff (t) of the signal to be controlled.

To perform this servocontrol, a circuit in accordance with the invention can implement a dual modulation function applied to both the signal i (t) to be controlled and to the reference signal i _D c (t).

This double modulation, similar for the two signals, is described below vis-à-vis the signal i (t) to control. It comprises in particular: a first modulation in pulse width such that the duty cycle (t), that is to say the width of a pulse at time t, of the modulated signal u (t) is proportional to the intensity of the current to be measured i (t) according to the formula:

^• (t) = K ^* i (t) where K is a constant.

a second amplitude modulation such that the amplitude of the modulated signal u (t) is proportional to the intensity of the current to be measured i (t).

In practice, this double modulation of pulse width and amplitude can be achieved by means of a modulator 11 (FIG. 2) comprising an operational amplifier 10. For this purpose, the signal i (t) to be monitored is provided at the input V + (12) of the operational amplifier 10 while a periodic signal, typically sawtooth, is provided at the input V- (14) of the same operational amplifier 10. A resistance 16 of recall imposes the voltage of the signal i (t) when the voltage at the terminal V + (12) is greater than the voltage at the terminal V- (14) of the amplifier 10. If necessary, this voltage is zero.

The form of the signal u (t) resulting from such a double modulation is illustrated in FIG. 3 which represents, as a function of the time-axis of the abscissae 17, the intensity of this signal u (t) - ordinate axis 18.

By virtue of this double modulation, a signal u (t) is obtained whose average value can be, in practice, proportional to its effective intensity i _Θff (t).

Indeed, considering that the pulse period of the signal, also called the switching period, is large compared to an integration time T used to evaluate an average value U (T) of this signal u ( t), this average value U (T) can be written as follows:

KP _eff .

Subsequently, the average value U (T) of this signal u (t) resulting from the double modulation of the signal i (t) to be controlled can be compared with the average value U _D c (T) of the signal u _D c ( t) derived from the double modulation of the continuous reference signal i _D c (t).

Thus, it is possible to provide a servocontrol circuit powered by the difference between these two average values U (T) and U _D c (t) which tends to cancel 1st this gap. Therefore, the average value U (T) of the modulated signal obtained from the current i (t) to control tends to be identical to the average value U _DC (T) of the modulated signal obtained from the reference current i _D c (t). This equality is then written, over this period T: U _DC dt

= * ^ V- measure) eff ⁼ ^ V DC) eff = ^ Vmesure) eff ~ \ DC) eff

This equality thus reflects the function of the servocontrol circuit which tends to modify the reference signal i _D c (t) to a value such that its effective current i _D ceff (t) is equal to the effective current i _Θff (t) of control signal I (t).

With reference to FIG. 4, a circuit 22 in accordance with the invention thus comprises a servo-control loop - powered by the output signal of a comparator 24 - respective average values U (T) and U _DC (T). signals u (t), modulated from the current to be measured i (t), and u _D c (t), modulated from the reference current i _D c (t).

After processing by an amplifier 26, this output signal is the continuous reference signal i _D c (t) transmitted to the input of the modulator 19 whose operation is similar to the operation of the modulator 1 1 already described. In a practical way, the circuit 22 may be in the form of an operational amplifier circuit illustrated in FIG. 5. More specifically, an operational amplifier 30 can perform the function of the comparator 24 by receiving, at its input 32, the signal u (t) modulated from the current to be measured and, at its input 34, the signal u _D c (t) modulated from the reference current.

The loop 20 is implemented in the form of an operational amplifier integrator circuit 36 which integrates the measured difference and feeds it back into the circuit as a continuous reference signal. Functionally, a circuit according to the invention comprises in this embodiment four operational blocks, namely:

a block 1 1 effecting the double modulation of the signal to be tested i (t),

a block 19 effecting the double modulation of the reference signal i _D c (t),

a block 24 performing the comparison between the currents i _Θ ff (t) and ioceff (t) and then with the result,

a block 26 reinjecting the result of this comparison in the assembly as a reference signal i _Θ ff (t). By way of example, FIG. 6 represents the circuit diagram of a circuit according to the invention. It should be noted that the components used - operational amplifier, comparator and resistors - have a low cost and satisfactory reliability for the implementation of the invention. It will also be noted that the invention has been more particularly described in the case of using amplifiers making it possible to perform the functions described. However, other types of elements, in particular with transistors, can also be used without departing from the scope of the invention. Finally, any means can be replaced by equivalent means.

Claims

1. Circuit (22) for measuring the effective current (i _Θ ff (t)) of a signal to be tested (i (t)), characterized in that it comprises means for controlling a continuous reference signal (ioc ( t)) to the signal to be monitored (i (t)) so that the effective current (iDCeff (t)) of the continuous reference signal (ioc (t)) is equal to the effective current (i _Θ ff (t)) the signal to be checked (i (t)).

2. Circuit (22) according to claim 1, characterized in that it comprises a first modulator (11) and a second modulator (19) processing, respectively, the signal to be tested (i (t)) or the signal of reference (i _D c (t)) to provide a first modulated signal (u (t)) or a second modulated signal (u _D c (t)) whose average current (U (T), U _D c (T) )) is proportional, respectively, to the square of the effective current (i _Θ ft (t)) of the signal to be monitored (i (t)) or to the square of the effective current (ioceff (t)) of the reference signal (ioc (t) )).

3. Circuit (22) according to claim 2 characterized in that the first (1 1) and second (19) modulators comprise means for modulating the first modulated signal (u (t)) or the second modulated signal (uDc ( t)) in pulse width and amplitude using a periodic signal.

4. Circuit (22) according to claim 3 characterized in that the first (11) modulator comprises means for the pulse width modulation of the first modulated signal (u (t)) corresponds to a duty cycle (α) proportional to the intensity of the signal to be checked (i (t)).

5. Circuit (22) according to claim 4 characterized in that it comprises means for modulating the signal to be tested (i (t)) and the reference signal (iϋc (t)) with a switching frequency such that, over a period T of calculating the average value (U (T), U _DC (T)) of the first modulated signal or of the second modulated signal, this average value (U (T), U _DC (T)) is proportional to the square of the effective current (i _Θ ff (t), ioceff (t) of the signal to be tested (i (t)) or of the reference signal (i _Θ ft (t)).

6. Circuit (22) according to claim 3, 4 or 5 characterized in that each modulator (1 1, 19) comprises an operational amplifier (10) receiving at a first input (12) one of the signals to be processed ((i) ( t), (i _Θ ft (t)) and at a second input (14) the periodic signal.

7. Circuit (22) according to one of claims 2 to 6 characterized in that it comprises:

a block (24) performing the comparison between the effective currents (i _Θ ff (t), ioceff (t)) of the processed signals ((i (t), (i _Θ ft (t)) via their mean value respectively.

a block (26) injecting the result of this comparison into the circuit via a feedback loop as a reference signal (i _Θ ft (t)) for the circuit (22).

8. A method for measuring the effective current (i _Θ ft (t)) of a signal to be tested (i (t)), characterized in that a continuous reference signal (i _D c (t)) is servocontrolled to the signal to be controlled (i (t)) so that the effective current (ioceff (t)) of the continuous reference signal (i _D c (t)) is equal to the effective current (i _Θ ft (t)) of the signal at control (i (t)) by means of a circuit according to one of the preceding claims.

9. The method of claim 8 characterized in that a control signal relative to the supply current of an electromagnetic valve actuator of a motor vehicle.