METHOD OF CONTROLLING A DEVICE FOR REGULATING AN AUTOMOTIVE VEHICLE ALTERNATOR, CORRESPONDING REGULATING DEVICE AND ALTERNATOR

Abstract

The method of control according to the invention slaves a DC voltage generated by the alternator to a predetermined setpoint value by controlling an excitation current flowing in an excitation circuit comprising an excitation winding of a rotor of the alternator. The excitation current is controlled by means of a semiconductor switch, in turn controlled by a control signal having a predetermined period. The method comprises a detection of a failure of the excitation circuit. At least one short-circuit of the excitation winding is detected. According to another characteristic of the method, the control signal is generated on the basis of a combination of a setpoint signal formed by pulses of the predetermined period exhibiting a duty ratio representative of the setpoint value and of a detection signal indicative of the short-circuit.

Claims

1. A method for controlling a regulating device (4) of an automotive vehicle alternator slaving a DC voltage (B+A) generated by said alternator to a predetermined setpoint value, said alternator comprising an excitation circuit (3, 6) including an excitation winding (6) of a rotor of said alternator and a semiconductor switch (3), said DC voltage (B+A) slaved by controlling an excitation current (I.sub.D) flowing in said excitation circuit (3, 6) by means of said semiconductor switch (3) controlled by a control signal (V.sub.GS) having a predetermined period (T), said method comprising the step of detecting a failure of said excitation circuit (3, 6), wherein at least one short-circuit (SC) of said excitation winding (6) is detected.

2. The method according to claim 1, wherein said control signal (V.sub.GS) is generated on the basis of a combination (EXC_DR) of a setpoint signal (EXC) formed by pulses of said predetermined period (T) exhibiting a duty ratio (r) representative of said setpoint value and of a detection signal (Th_HEXCCD) indicative of said short-circuit (SC).

3. The method according to claim 2, wherein said semiconductor switch (3) as a transconductor is controlled by said control signal (V.sub.GS) during at least a first part of said predetermined period (T) with at least one predetermined current slope by limiting an intensity (IROT) of said excitation current (I.sub.D) to a predetermined limit value (ILIM).

4. The method according to claim 3, wherein said semiconductor switch (3) is changed into a conductive state (ON) by said control signal (V.sub.GS) during at least a second part of said predetermined period (T) by limiting said intensity (IROT) of said excitation current (I.sub.D) to said predetermined limit value (ILIM).

5. The method according to claim 3, wherein: as soon as said intensity (IROT) has reached a predetermined high threshold (TH_SC_HIGH), a first counter (17) is started (TIMER_EN) during a first predetermined time delay (T1); during (AV_EN) said first time delay (T1), an estimated value (IROT_AV) of the short-circuit is calculated on the basis of said intensity (IROT); after (TO) said first time delay (T1), if said estimated value (IROT_AV) of the short-circuit is greater (SCD) than a predetermined low threshold (TH_SC_LOW), said detection signal (Th_HEXCCD) is activated; if said estimated value (IROT_AV) of the short-circuit is less than the low threshold (TH_SC_LOW), said first counter (17) is re-initialised; after activation of said detection signal (Th_HEXCCD), said semiconductor switch (3) is controlled by said control signal (V.sub.GS) with said current slope to make a transition to an open state (OFF); a second predetermined time delay (T2) is generated by means of a second counter (20) and said semiconductor switch (3) in said open state (OFF) is maintained during said second time delay (T2).

6. The method according to claim 5, wherein said limit value (ILIM) and said first time delay (T1) are defined so that a power to be dissipated is less than a maximum power permissible by a heat sink of said semiconductor switch (3).

7. The method according to claim 5, wherein said estimated value of the short-circuit calculated on the basis of said intensity (IROT) is a median value (IROT_AV) of said intensity (IROT).

8. A regulating device (4) of an automotive vehicle alternator configured to implement the method according to claim 1, comprising: a slaving device (11) of slaving a DC voltage (B+A) generated by said alternator to a setpoint value predetermined by controlling an excitation current (I.sub.D) flowing in an excitation circuit (3, 6); and a failure detection device (12) for detecting a failure of said excitation circuit (3, 6); said excitation circuit (3, 6) comprising an excitation winding (6) of a rotor of said alternator and a semiconductor switch (3) controlled by a control signal (V.sub.GS) of a predetermined period (T), said failure detection device (12) detecting at least one short-circuit (SC) of said excitation winding (6).

9. The regulating device (4) according to claim 8, wherein said slaving device (11) comprises a regulation loop (11) generating a setpoint signal (EXC) formed by pulses exhibiting said predetermined period (T) of a duty ratio (r) representative of said setpoint value and said failure detection device (12) comprise a detection module (12) generating a detection signal (Th_HEXCCD) indicative of said short-circuit (SC), and wherein the regulating device (4) further comprises a combination device (10) to combine said setpoint signal (EXC) and said detection signal (Th_HEXCCD) for producing an input signal (EXC_DR) of a control circuit (13) generating said control signal (V.sub.GS).

10. The regulating device (4) according to claim 9, wherein said detection module (12) comprises: a memory device to memorise a predetermined high threshold (TH_SC_HIGH) and a predetermined low threshold (TH_SC_LOW); an acquisition device (16) to acquire an intensity (IROT) of an excitation current (I.sub.D) flowing in said excitation circuit (3, 6); first comparison device (15) to compare said intensity (IROT) with said predetermined high threshold (TH_SC_HIGH) and with said predetermined low threshold (TH_SC_LOW); a first counter (17) triggered (TIMER_EN) by said first comparison device (15) defining a first predetermined time delay (T1); a calculation device (18) to calculate an estimated value (IROT_AV) of the short-circuit on the basis of said intensity (IROT) during said first predetermined time delay (T1); second comparison device (19) to compare said estimated value (IROT_AV) of the short-circuit with said predetermined low threshold (TH_SC_LOW); a second counter (20) triggered by said second comparison device (19) defining a second predetermined time delay (T2).

11. Automotive vehicle alternator comprising a regulating device (4) according to claim 8.

12. The method according to claim 4, wherein: as soon as said intensity (IROT) has reached a predetermined high threshold (TH_SC_HIGH), a first counter (17) is started (TIMER_EN) during a first predetermined time delay (T1); during (AV_EN) said first time delay (T1), an estimated value (IROT_AV) of the short-circuit is calculated on the basis of said intensity (IROT); after (TO) said first time delay (T1), if said estimated value (IROT_AV) of the short-circuit is greater (SCD) than a predetermined low threshold (TH_SC_LOW), said detection signal (Th_HEXCCD) is activated; if said estimated value (IROT_AV) of the short-circuit is less than the low threshold (TH_SC_LOW), said first counter (17) is re-initialised; after activation of said detection signal (Th_HEXCCD), said semiconductor switch (3) is controlled by said control signal (V.sub.GS) with said current slope to make a transition to an open state (OFF); a second predetermined time delay (T2) is generated by means of a second counter (20) and said semiconductor switch (3) in said open state (OFF) is maintained during said second time delay (T2).

13. The method according to claim 6, wherein said estimated value of the short-circuit calculated on the basis of said intensity (IROT) is a median value (IROT_AV) of said intensity (IROT).

14. A regulating device (4) of an automotive vehicle alternator configured to implement the method according to claim 2, comprising a slaving device (11) for slaving a DC voltage (B+A) generated by said alternator to a setpoint value predetermined by controlling an excitation current (I.sub.D) flowing in an excitation circuit (3, 6) comprising an excitation winding (6) of a rotor of said alternator and a semiconductor switch (3) controlled by a control signal (V.sub.GS) of a predetermined period (T), said regulating device (4) further comprising a failure detection device (12) for detecting a failure of said excitation circuit (3, 6), wherein said failure detection device (12) detects at least one short-circuit (SC) of said excitation winding (6).

15. A regulating device (4) of an automotive vehicle alternator configured to implement the method according to claim 3, comprising a slaving device (11) for slaving a DC voltage (B+A) generated by said alternator to a setpoint value predetermined by controlling an excitation current (I.sub.D) flowing in an excitation circuit (3, 6) comprising an excitation winding (6) of a rotor of said alternator and a semiconductor switch (3) controlled by a control signal (V.sub.GS) of a predetermined period (T), said regulating device (4) further comprising a failure detection device (12) for detecting a failure of said excitation circuit (3, 6), wherein said failure detection device (12) detects at least one short-circuit (SC) of said excitation winding (6).

16. A regulating device (4) of an automotive vehicle alternator configured to implement the method according to claim 4, comprising a slaving device (11) for slaving a DC voltage (B+A) generated by said alternator to a setpoint value predetermined by controlling an excitation current (I.sub.D) flowing in an excitation circuit (3, 6) comprising an excitation winding (6) of a rotor of said alternator and a semiconductor switch (3) controlled by a control signal (V.sub.GS) of a predetermined period (T), said regulating device (4) further comprising a failure detection device (12) for detecting a failure of said excitation circuit (3, 6), wherein said failure detection device (12) detects at least one short-circuit (SC) of said excitation winding (6).

17. A regulating device (4) of an automotive vehicle alternator configured to implement the method according to claim 5, comprising a slaving device (11) for slaving a DC voltage (B+A) generated by said alternator to a setpoint value predetermined by controlling an excitation current (I.sub.D) flowing in an excitation circuit (3, 6) comprising an excitation winding (6) of a rotor of said alternator and a semiconductor switch (3) controlled by a control signal (V.sub.GS) of a predetermined period (T), said regulating device (4) further comprising a failure detection device (12) for detecting a failure of said excitation circuit (3, 6), wherein said failure detection device (12) detects at least one short-circuit (SC) of said excitation winding (6).

18. A regulating device (4) of an automotive vehicle alternator configured to implement the method according to claim 6, comprising a slaving device (11) for slaving a DC voltage (B+A) generated by said alternator to a setpoint value predetermined by controlling an excitation current (I.sub.D) flowing in an excitation circuit (3, 6) comprising an excitation winding (6) of a rotor of said alternator and a semiconductor switch (3) controlled by a control signal (V.sub.GS) of a predetermined period (T), said regulating device (4) further comprising a failure detection device (12) for detecting a failure of said excitation circuit (3, 6), wherein said failure detection device (12) detects at least one short-circuit (SC) of said excitation winding (6).

19. A regulating device (4) of an automotive vehicle alternator configured to implement the method according to claim 7, comprising a slaving device (11) for slaving a DC voltage (B+A) generated by said alternator to a setpoint value predetermined by controlling an excitation current (I.sub.D) flowing in an excitation circuit (3, 6) comprising an excitation winding (6) of a rotor of said alternator and a semiconductor switch (3) controlled by a control signal (V.sub.GS) of a predetermined period (T), said regulating device (4) further comprising a failure detection device (12) for detecting a failure of said excitation circuit (3, 6), wherein said failure detection device (12) detects at least one short-circuit (SC) of said excitation winding (6).

20. A regulating device (4) of an automotive vehicle alternator, comprising: a slaving device (11) slaving a DC voltage (B+A) generated by an alternator to a setpoint value predetermined by controlling an excitation current (I.sub.D) flowing in an excitation circuit (3, 6); a failure detection device (12) operably associated with said excitation circuit (3, 6); said excitation circuit (3, 6) comprising an excitation winding (6) of a rotor of said alternator and a semiconductor switch (3) controlled by a control signal (V.sub.GS) of a predetermined period (T), said failure detection device (12) detecting at least one short-circuit (SC) of said excitation winding (6).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 illustrates an overload of the excitation current in the event of short-circuit of the excitation winding of the rotor of an alternator without the regulating device according to the invention.

[0050] FIG. 2 shows a feature of a power transistor of the MOSFET type used in the regulating device according to the invention.

[0051] FIG. 3 illustrates a regulating device according to the invention and a model in transconductance mode of the power transistor, the feature of which is shown on FIG. 2.

[0052] FIG. 4a illustrates time diagrams illustrating the method for controlling the regulating device according to the invention if the short-circuit occurs when the power transistor is in an open state.

[0053] FIG. 4b illustrates time diagrams illustrating the method for controlling the regulating device according to the invention if the short-circuit occurs when the power transistor is in a conductive state.

[0054] FIG. 5 illustrates time diagrams illustrating an alternative method for controlling the regulating device according to the invention if the short-circuit occurs when the power transistor is in a conductive state.

[0055] FIG. 6 is a general diagram of detecting a short-circuit in the regulating device according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0056] Alternator regulators often integrate a function to protect against short-circuit currents. These functions are elementary designs with a cut-off by the power switch whenever the current is exceeded relative to a preset value Icc_Th, as shown on FIG. 1.

[0057] If a short-circuit occurs in the power switch when the Tr transistor is in the conductive state ON, intensity I of the current in the excitation winding increases very rapidly with an ascending slope 1 only depending on the impedances present in the excitation circuit.

[0058] The short-circuit period ΔT, i.e. the time during which the Tr transistor remains in the conductive state ON before the protection function commands it to switch to the open state OFF, depends on the reaction time of the electronics and is controlled to a minimum.

[0059] Therefore intensity I flowing in the excitation circuit can reach a very high Imax value whenever resistance R.sub.DS (ON) of a power transistor Tr of the MOSFET type remains very low, before intensity I decreases along a descending slope 2 when transistor Tr switches to an open state OFF.

[0060] The principle of the method for controlling a regulating device of an automotive vehicle alternator according to the invention is to use the dependence of a drain current I.sub.D of a MOSFET power transistor on a gate-source voltage V.sub.GS shown on FIG. 2 to control the “high side” switch 3 of the regulating device 4 shown on FIG. 3 in order to limit current I.sub.D in the power switch 5 when the excitation winding 6 is short-circuited.

[0061] In “common source” topology, outside the open mode OFF/conductive mode ON, a MOSFET transistor 3 can temporarily function in transconductance mode (in a saturation region “Sat.” outside an ohmic region “Res.” for a sufficiently high drain-source voltage V.sub.DS), i.e. as a voltage-controlled generator 7 of current with infinite impedance, as the equivalent model of FIG. 3 shows.

[0062] For a low gate-source voltage V.sub.GS1 (but above a threshold voltage V.sub.TH), the intensity of drain I.sub.D1 is low, for an average gate-source voltage V.sub.GS2, the corresponding intensity of drain I.sub.D2 is median and for a high gate-source voltage V.sub.GS3, the intensity of drain I.sub.D3 is strong, as FIG. 2 clearly shows.

[0063] In the inventive method, switch 3 is thus polarised with a gate-source voltage V.sub.GS such that the current flowing in switch 3 cannot exceed a predetermined value ILIM, as will be explained in connection with FIGS. 4a, 4b and 5.

[0064] For example, for the low gate-source voltage V.sub.GS1, the intensity of the excitation current I.sub.D will be limited to the shaded zone 8 of FIG. 2.

[0065] It will be noted that switch 3 as current generator 7 too will be advantageously used to control the current commutated between this switch 3 and a free wheel diode 9.

[0066] The operation of the power switch 5 lasts for a fixed period T or more rarely has a variable frequency; in both cases the duty ratio r is variable in order to slave the output voltage B+A of the alternator to a setpoint value.

[0067] On FIG. 3, it will be noted that the power switch 5 is controlled by a combination 10 EXC_DR of a setpoint signal EXC (pulse width modulation of a duty ratio r calculated by the regulation algorithm 11) and a short-circuit detection signal Th_HEXCCD formed in a detection module 12.

[0068] Combination EXC_DR is applied to an input of a control circuit 13 which controls the gate G of power switch 3 with voltage V.sub.GS.

[0069] When short-circuit SC occurs, two typical cases happen: [0070] short-circuit SC appears when switch 3 is in the open state OFF or during the transition of current conductance; [0071] short-circuit SC appears when switch 3 is in the conductive state ON.

[0072] In the first case illustrated on FIG. 4a, intensity IROT of the excitation current increases along a predetermined current slope, when switch 3 is operated in transconductance mode.

[0073] When intensity IROT reaches a predetermined high threshold TH_SC_HIGH, it is considered that excitation winding 6 has short-circuited.

[0074] Intensity IROT of the current is then limited to a predetermined limit value ILIM during a first predetermined time delay T1, then decreases again along the predetermined current slope.

[0075] The first time delay T1 and limit value ILIM are defined so that the dissipation capacity is less than the maximum power which a heat sink of switch 3 can evacuate.

[0076] In the second case illustrated on FIG. 4b, intensity IROT of the short-circuit current is limited to limit value ILIM during the first predetermined time delay T1, then decreases again along the predetermined current slope. A first solution is to use switch 3 to limit the current. This leads to the application of a gate-source voltage V.sub.GS less than a maximum value; the R.sub.DS (ON) is thus not minimum, which contributes to additional heating.

[0077] An alternative to this solution, when switch 3 is in the conductive state ON in the event of a short-circuit SC, is to change switch 3 to the conductive state, i.e. with a minimal drain-source resistance R.sub.DS (ON).

[0078] Whenever short-circuit SC is detected by the crossing of a threshold Icc_Th (FIG. 5), switch 3 immediately changes from the conductive/open mode to the transconductance mode and intensity IROT of the excitation current is limited to limit value ILIM during the first predetermined time delay T1.

[0079] It is noted that during the transition from the conductive state ON to the transconductance mode, the time for establishing the V.sub.GS voltage is not immediate. Intensity IROT of the short-circuit current in the worst case is B+A/R.sub.DS (ON), if an excitation circuit with no parasitic components is considered. Then it decreases to reach value ILIM, as FIG. 5 clearly shows. The current could have oscillations due to the capacitors and residual chokes present in the circuit.

[0080] A time of confirmation is determined by calculation so that an amount of heat generated by short-circuit SC can be dissipated by the heat sink of power switch 3. For this purpose, a second time delay T2 greater than a minimum time T retry min is fixed, before switch 3 changes to the conductive state because the short-circuit may occur at any time in comparison to the pulses of the setpoint signal EXC.

[0081] FIG. 6 shows an exemplary embodiment of the time of confirmation and control of the minimum time T_retry_min.

[0082] The generic algorithm which is implemented in the processor 14 of the regulating device 4 according to the invention is as follows: [0083] as soon as a first comparator 15 determines that a measurement of intensity IROT of the excitation current, obtained by means of acquisition and filtering 16 known per se, has reached the predetermined high threshold TH_SC_HIGH, a first counter 17 TIMER_EN is started to generate a first time delay T1 (of 10 μs for example). During this first time delay T1, an estimated value of a short-circuit in the form of a median value IROT_AV of intensity IROT of the excitation current is calculated by means of calculation 18 (AV_EN). [0084] at the end of counting TO and if a second comparator 19 determines that the calculated median value IROT_AV is greater than a predetermined low threshold TH_SC_LOW, short-circuit SC is detected (SCD) and the detection signal Th_HEXCCD is activated. If median value IROT_AV falls short of low threshold TH_SC_LOW, first counter 17 is re-initialised. [0085] as soon as the short-circuit detection signal Th_HEXCCD is active, power switch 3 is cut-off with a current slope command. [0086] switch 3 is maintained in the open state OFF during the second time delay T2 greater than minimum time T_retry_min necessary to dissipate the heat. A second programmable counter 20 enables this second time delay T2 (4 ms for example) to be adapted according to the application and generates a confirmation signal Th HEXCCD_latch.

[0087] It goes without saying that the invention is not limited to the sole preferred embodiments described above.

[0088] In particular, specific values of the first and second time delays T1, T2 shown above are only given as examples.

[0089] The same applies for the particular types of discrete components 3, 9, of analogue circuits 15, 19 or digital circuits 17, 20: they could, alternatively, be replaced by other analogue or digital electronic components which fulfil the same functions.

[0090] The invention thus embraces however all possible alternative embodiments which would remain within the framework defined by the claims below.