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Title:
THREE-PHASE SYNCHRONOUS RECTIFIER FOR BATTERY CHARGER ON BOARD VEHICLE
Document Type and Number:
WIPO Patent Application WO/2019/171320
Kind Code:
A1
Abstract:
The three-phase synchronous rectifier (RT) for battery charger on board vehicle comprises: three rectification units (UA, UB, UC) provided with respective inputs connected to respective phases of a permanent magnet generator (G) and with respective outputs connected to a battery (B) of a vehicle; wherein the rectification units (UA, UB, UC) are configured to receive at input respective phase currents (IA, IB, IC) of the generator (G) and to supply at output rectified currents (IBATTA, IBATTB, IBATTC); and wherein each of the rectification units (UA, UB, UC) comprises a current sensor (S, S") connected to a respective phase of the generator (G) and a respective output circuit (O) connected to the battery and operatively connected to said current sensor (S, S"); the current sensor (S, S") being configured to receive at input a respective phase current (IA, IB, IC) and the output circuit (O) being configured to be piloted by means of the current sensor (S, S") to generate the rectified currents (IBATTA, IBATTB, IBATTC); wherein the current sensor (S, S") comprises at least one toroidal element (T) made of a magnetic material crossed by a lead (C) which conveys the phase current (IA, IB, IC) and at least one Hall effect sensor (H1, H2, H) connected to the toroidal element (T) and to the output circuit (O).

Inventors:
REGAZZI, Gianni (Via Marco Emilio Lepido 182, Bologna, 40132, IT)
CALABRI, Pierluigi (Via Marco Emilio Lepido 182, Bologna, 40132, IT)
Application Number:
IB2019/051853
Publication Date:
September 12, 2019
Filing Date:
March 07, 2019
Export Citation:
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Assignee:
DUCATI ENERGIA S.P.A. (Via Marco Emilio Lepido, 182, Bologna, 40132, IT)
International Classes:
H02J7/14; G01R15/20; H02M7/217; H02M7/219; G01R19/175; H02K1/02
Foreign References:
US20160049857A12016-02-18
US4020294A1977-04-26
US20050226298A12005-10-13
Attorney, Agent or Firm:
BRUNACCI, Marco (BRUNACCI & PARTNERS S.r.l, Via Scaglia Est 19-31, Modena, 41126, IT)
Download PDF:
Claims:
CLAIMS

1) Three-phase synchronous rectifier (RT) for battery charger on board vehicle, comprising:

three rectification units (UA, UB, UC) provided with respective inputs connected to respective phases of a permanent magnet generator (G) and with respective outputs connected to a battery (B) of a vehicle;

wherein said rectification units (UA, UB, UC) are configured to receive at input respective phase currents (IA, IB, IC) of said generator (G) and to supply at output rectified currents (IBATTA, IBATTB, IBATTC); and

wherein each of said rectification units (UA, UB, UC) comprises a current sensor (S’, S”) connected to a respective phase of said generator (G) and a respective output circuit (O) connected to said battery and operatively connected to said current sensor (S’, S”);

said current sensor (S’, S”) being configured to receive at input a respective phase current (IA, IB, IC) and said output circuit (O) being configured to be piloted by means of said current sensor (S’, S”) to generate said rectified currents (IBATTA, IBATTB, IBATTC);

characterized by the fact that said current sensor (S’, S”) comprises at least one toroidal element (T) made of a magnetic material crossed by a lead (C) which conveys said phase current (IA, IB, IC) and at least one Hall effect sensor (Hl, H2, H) connected to said toroidal element (T) and to said output circuit (O).

2) Three-phase synchronous rectifier (RT) according to claim 1, characterized by the fact that said current sensor (S’) comprises a first digital unipolar Hall sensor (Hl) and a second digital unipolar Hall sensor (H2) connected to said toroidal element (T) made of a magnetic material, said first and second unipolar Hall sensors (Hl, H2) being configured to operate in the presence of respective and predefined levels of magnetic flux on said toroidal element (T).

3) Three-phase synchronous rectifier (RT) according to claim 2, characterized by the fact that said toroidal element (T) is provided with an air gap (TR) and said first and second Hall sensors (Hl, H2) are arranged inside said air gap (TR) side by side and rotated by 180 degrees the one with respect to the other. 4) Three-phase synchronous rectifier (RT) according to one or more of claims 2 and 3, characterized by the fact that said first unipolar Hall sensor (Hl) is configured to:

switch its output voltage (VB) from a low voltage value (0V) to a high voltage value (Vcc) at a first predefined threshold value (In), when said phase current (IA, IB, IC) is positive and increasing;

switch its output voltage (VB) from a high voltage value (Vcc) to a low voltage value (0V) at a second predefined threshold value (Gti), when said phase current (IA, IB, IC) is positive and decreasing.

5) Three-phase synchronous rectifier (RT) according to one or more of claims 2 to 4, characterized by the fact that said second unipolar Hall sensor (H2) is configured to:

switch its output voltage (VA) from a low voltage value (0V) to a high voltage value (Vcc) at a first predefined threshold value (It2), when said phase current (IA, IB, IC) is negative and decreasing;

switch its output voltage (VA) from a high voltage value (Vcc) to a low voltage value (0V) at a second predefined threshold value (Gt2), when said phase current (IA, IB, IC) is negative and increasing.

6) Three-phase synchronous rectifier (RT) according to claim 1, characterized by the fact that said current sensor (S”) comprises a magnetic linear Hall sensor (H) connected to said toroidal element (T) made of a magnetic material, said linear Hall sensor (H) being configured to generate an output voltage (Vu) which reproduces the pattern of said phase current (IA, IB, IC) in the lead (C) with a voltage offset equal to a predefined value.

7) Three-phase synchronous rectifier (RT) according to claim 6, characterized by the fact that said toroidal element (T) is provided with an air gap (TR) and said linear Hall sensor (H) is arranged inside said air gap (TR).

8) Three-phase synchronous rectifier (RT) according to one or more of claims 6 and 7, characterized by the fact that said current sensor (S”) comprises a first voltage comparator (U1A) and a second voltage comparator (U1B), said linear Hall sensor (H) being connected to the inverting input of said first voltage comparator (U1A) and to the non-inverting input of the second voltage comparator (U1B).

9) Three-phase synchronous rectifier (RT) according to one or more of claims 6 to 8, characterized by the fact that said second voltage comparator (U1B) is configured to:

switch its output voltage (VB) from a low voltage value (0V) to a high voltage value (Vcc) at a first predefined threshold value (In), when said phase current (IA, IB, IC) is positive and increasing;

switch its output voltage (VB) from a high voltage value (Vcc) to a low voltage value (0V) at a second predefined threshold value (Gti), when said phase current (IA, IB, IC) is positive and decreasing.

10) Three-phase synchronous rectifier (RT) according to one or more of claims 6 to 9, characterized by the fact that said first voltage comparator (U1A) is configured to:

switch its output voltage (VA) from a low voltage value (0V) to a high voltage value (Vcc) at a first predefined threshold value (VT2), when said phase current (IA, IB, IC) is negative and decreasing;

switch its output voltage (VA) from a high voltage value (Vcc) to a low voltage value (0V) at a second predefined threshold value (V’T2), when said phase current (IA, IB, IC) is negative and increasing.

11) Three-phase synchronous rectifier (RT) according to one or more of the preceding claims, characterized by the fact that said sensor (S’, S”) comprises a plurality of windings of said lead (C) around at least one portion of said toroidal element (T).

12) Three-phase synchronous rectifier (RT) according to one or more of the preceding claims, characterized by the fact that said output circuit (O) comprises at least a first transistor Power MOS (Ql) and at least a second transistor Power MOS (Q2) operatively connected to said current sensor (S’, S”) and adapted to be piloted by means of said current sensor (S’, S”) to generate said rectified currents (IBATTA, IBATTB, IBATTC).

13) Three-phase synchronous rectifier (RT) according to claim 12, characterized by the fact that said output circuit (O) comprises at least one half-bridge driver (U2) operatively interposed between said current sensor (S’, S”) and said first and second transistors Power MOS (Ql, Q2).

14) Three-phase synchronous rectifier (RT) according to claim 13, characterized by the fact that said half-bridge driver (U2) is provided with a first input (HI) connected to said first unipolar Hall sensor (Hl) and with a second input (LI) connected to said second unipolar Hall sensor (H2).

15) Three-phase synchronous rectifier (RT) according to one or more of the preceding claims, characterized by the fact that it comprises a current limiting circuit (A, L) configured to limit the current supplied by said generator (G) to said battery (B) in the event of the voltage (VBatt) supplied to the battery (B) exceeding a predefined desired value.

16) Three-phase synchronous rectifier (RT) according to claim 15, characterized by the fact that said current limiting circuit (A, L) comprises an error amplifier circuit (A) configured to measure said voltage supplied to the battery (VBatt) and to supply a verification voltage signal (Ve) at output which varies between predefined voltage values acceptable for the correct operation of said battery.

17) Three-phase synchronous rectifier (RT) according to claim 16, characterized by the fact that said error amplifier circuit (A) comprises a measurement circuit (M) of said voltage (VBatt) supplied to the battery (B).

18) Three-phase synchronous rectifier (RT) according to claim 17, characterized by the fact that said error amplifier circuit (A) comprises at least one operational amplifier (U6) provided with a non-inverting input connected to a reference voltage and with an inverting input connected to said measurement circuit (M), said operational amplifier (U6) being configured to supply said verification voltage signal (Ve) at output.

19) Three-phase synchronous rectifier (RT) according to one or more of claims 15 to 18, characterized by the fact that said current limiting circuit (A, L) comprises, for each rectification unit (UA, UB, UC), at least one verification and limitation circuit (L) operatively connected to said current sensor (S’, S”), to said error amplifier circuit (A) and to said output circuit (O), said verification and limitation circuit (L) being configured to pilot said output circuit (O), to make a phase control of said rectified current (IBATTA, IBATTB, IBATTC) supplied to the battery (B) when said verification voltage signal (Ve) varies.

Description:
THREE-PHASE SYNCHRONOUS RECTIFIER FOR BATTERY CHARGER ON BOARD VEHICLE

Technical Field

The present invention relates to a three-phase synchronous rectifier for battery charger on board vehicle.

Background Art

It is well known that the increase in the demand for electricity on board vehicles has led to the development of electric generators capable of generating a current of more than 120 A with a voltage of 14V.

In the case of particular motor applications such as e.g. ATVs (All-Terrain Vehicles) or snowmobiles, conventional automotive-type generators cannot be used due to space constraints. For such applications, rare-earth permanent magnet generators with high power and good efficiency, together with reduced overall dimensions are preferred.

It is also known that, when current levels exceed 40A, the normal three-phase regulators of the shunt type or series with controlled rectifier bridge consisting of diodes and SCRs have a power dissipation that is difficult to manage in aluminum finned enclosures with reduced overall dimensions.

In this regard, with particular reference to document EP 1 601 078 B l, the use is known of shunt regulators with the power part consisting of three Power MOS transistors and three Schottky diodes, able to reduce the dissipated power to about 30% of the value referred to the diode and SCR solution.

Furthermore, the documents US 8,159,179 B2 and US 8,159,180 B2 describe the implementation of algorithms for controlling the angle of conduction of Power MOS transistors, used to optimize generator performance in relation to the rotation speed of the endothermic motor and electrical loads.

These known solutions are however subject to improvement, aimed in particular at the creation of a Power MOS three-phase synchronous rectifier with the function of regulating the voltage for charging a battery of a vehicle which is particularly simple and economical and which, at the same time, can be combined with three-phase generators with permanent magnets for high currents, including over 120A, for vehicles with electrical systems powered by 12V.

In particular, in recent years, improvements in the technology of Power MOS transistors have made possible the development of components which, voltage being equal, have values of conduction resistance (RDS(on)) that are considerably reduced (< 1 hiW with a voltage Vds > 40V).

Such devices are particularly suitable for the realization of three-phase shunt regulators to be combined with permanent magnet generators which, in addition to the current and voltage values mentioned above, have electrical frequencies even higher than l.5kHz.

Moreover, in the panorama of the electronic components dedicated to synchronous rectification, integrated circuits exist which are able to detect the voltage drop between the Drain terminal and the Source terminal of the Power MOS transistor and to synchronize the Gate drive based on the measured value of the aforementioned voltage drop.

However, in the case of Power MOS transistor with RDS(on) lower than IihW, it becomes particularly difficult to measure the aforementioned voltage drop to detect the zero-crossing of the current flowing in the transistor, as this would mean detecting voltage values of around only a few mV.

In addition to this, in the case of multipole permanent magnet generators with high currents combined with endothermic motors with speeds that can exceed 12,000 RPM, the response times of the current synchronization system in the Power MOS transistors with the driving of the Power MOS themselves are of particular importance.

Description of the Invention

The main aim of the present invention is to provide a three-phase synchronous rectifier for battery chargers on-board vehicle which allows accurately detecting the zero-crossing of the current of the generator phases while maintaining adequate response times of the synchronization system.

Another object of the present invention is to provide a three-phase synchronous rectifier for battery chargers on-board vehicle that ensures a low voltage drop between the generator and the battery.

Another object of the present invention is to provide a three-phase synchronous rectifier for battery chargers on-board vehicle that allows overcoming the aforementioned drawbacks of the prior art in a simple, rational, easy, effective to use and low-cost solution.

The aforementioned objects are achieved by the present three-phase synchronous rectifier for battery chargers on-board vehicle described in claim 1. Brief Description of the Drawings

Other characteristics and advantages of the present invention will be more evident from the description of a preferred, but not exclusive, embodiment of a three-phase synchronous rectifier for battery chargers on-board vehicle, illustrated by way of an indicative, but non-limiting example, in the attached tables of drawings in which:

Figure 1 is a general electrical diagram illustrating a first possible embodiment of the three-phase synchronous rectifier according to the invention;

Figures 2 and 3 illustrate different possible implementations of a current sensor that can be used in the first embodiment of the three-phase synchronous rectifier according to the invention;

Figure 4 is a graph illustrating the pattern of the output signal of a first Hall sensor according to the first embodiment of the three-phase synchronous rectifier;

Figure 5 is a graph illustrating the pattern of the output signal of a second Hall sensor according to the first embodiment of the three-phase synchronous rectifier;

Figure 6 graphically illustrates the patterns of the signals with reference to the first embodiment of the three-phase synchronous rectifier according to the invention;

Figure 7 is a general electrical diagram illustrating a second possible embodiment of the three-phase synchronous rectifier according to the invention; Figures 8 and 9 illustrate different possible implementations of a current sensor that can be used in the second embodiment of the three-phase synchronous rectifier according to the invention;

Figure 10 graphically illustrates the patterns of the signals with reference to the second embodiment of the three-phase synchronous rectifier according to the invention.

Embodiments of the Invention

With particular reference to these illustrations, reference RT globally indicates a three-phase synchronous rectifier, particularly usable in combination with a permanent magnet generator for the charge of the battery of a motor vehicle.

In particular, as schematized in Figures 1 and 7, the three-phase synchronous rectifier RT comprises three rectification units UA, UB, UC provided with respective inputs connected to respective phases of a permanent magnet generator G and with respective outputs connected to a battery B of a vehicle. The rectification units UA, UB, UC are configured to receive at input respective phase currents IA, IB, IC of the generator G and to supply at output rectified currents IBATTA, IBATTB , IBATTC to be supplied to the battery B of the vehicle. Each of the rectification units UA, UB, UC comprises a current sensor S’, S” connected to a respective phase of the generator G and a respective output circuit O connected to the battery B and operatively connected to the current sensor S’, S”. The current sensor S’, S” is configured to receive at input a respective phase current IA, IB, IC, while the output circuit O is configured to be piloted by means of the current sensor S’, S” to generate the rectified currents IBATTA, IBATTB, IBATTC.

Advantageously, a decisive aspect of the three-phase synchronous rectifier RT according to the invention consists in the fact that, on each rectification unit UA, UB, UC, the current sensor S’, S” comprises at least one toroidal element T made of a magnetic material crossed by a lead C which conveys the phase current IA, IB, IC and at least one Hall effect sensor Hl, H2, H connected to the toroidal element T and to the output circuit O.

In particular, the three-phase synchronous rectifier RT according to the invention can be implemented according to two possible and preferred embodiments: a first embodiment wherein the current sensor S’ of each of the three rectification units U A , U B , UC comprises two digital unipolar Hall sensors Hl and H2 (Figures 1-6); a second embodiment wherein the current sensor S” of each of the three rectification units U A , U B , UC comprises one linear Hall sensor H (Figures 7-10).

The first possible embodiment of the three-phase synchronous rectifier RT according to the invention is described below, wherein the current sensor S’ comprises two unipolar Hall effect magnetic sensors: a first unipolar Hall sensor Hl and a second unipolar Hall sensor H2. This first embodiment is illustrated in Figures 1-6.

With reference to this first embodiment, the first and second unipolar Hall sensors Hl, H2 are configured to be operate in the presence of respective and predefined levels of magnetic flux on the toroidal element (T).

As shown in the circuit diagram in Figure 1, the three-phase synchronous rectifier RT is connected to a three-phase permanent magnet generator G.

In particular, Figure 1 relates to a three-phase permanent magnet generator G wherein the three phase currents IA, IB, IC like the three currents supplied to the battery IBATTA, IBATTB, IBATTC, have the same value but with phase displacement between one another by 120 degrees. The three currents IBATTA, IBATTB, IBATTC supplied to the battery add up to a single total current IBATTS supplied to the battery.

It is pointed out that the following description of the operation of the three- phase synchronous rectifier RT with voltage regulation function makes reference to only one phase of the system, the operation of the other two phases being completely the same. Consequently, in the description and in the illustrations, only the first rectification unit U A , relating to the phase A, is detailed. The other two rectification units U B and Uc, relating to the phases B and C, are made and operate in a manner completely identical to the first rectification unit U A .

As shown in Figures 2 and 3, the toroidal element T is provided with an air gap TR and the two unipolar Hall sensors HI, H2 are arranged inside the air gap TR side by side and rotated by 180 degrees the one with respect to the other. In particular, as shown in Figure 4, the first unipolar Hall sensor Hl is configured to switch the output voltage VB from a low voltage value (0V) to a high voltage value (Vcc) at a first predefined threshold value In, when the phase current IA (or IB and Ic with reference to the other phases) is positive and increasing.

When, on the contrary, the phase current IA is positive and decreasing, the first unipolar Hall sensor Hl is configured to switch the output voltage VB from the high voltage value (Vcc) to the low voltage value (0V) at a second predefined threshold value Fn.

Therefore, the first unipolar Hall sensor Hl is configured to create a hysteresis at the predefined switch threshold values In, Fn.

Figure 5 shows the pattern of the output signal VA of the second unipolar Hall sensor H2 which, being flanked and rotated by 180° with respect to the first unipolar Hall sensor Hl, possesses a similar behavior even if referred to the negative values of the phase current IA. The threshold values of the currents for the switch of the second Hall sensor H2 are I T2 and F T 2 respectively.

In particular, the second unipolar Hall sensor H2 is configured to switch the output voltage VA from a low voltage value (0V) to a high voltage value (Vcc) at a first predefined threshold value IT2, when the phase current IA (or IB and Ic with reference to the other phases) is negative and.

When, on the contrary, the phase current IA is negative and decreasing, the second unipolar Hall sensor H2 is configured to switch the output voltage VA from the high voltage value (Vcc) to the low voltage value (0V) at a second predefined threshold value F T 2.

Examples of possible embodiments of the sensor S’ are illustrated in Figures 2 and 3.

In particular, as illustrated in the example of Figure 3, the sensor S’ can comprise a plurality of windings of the lead C around at least one portion of the toroidal element T.

In particular, in case of wanting to reduce in absolute value the current values of the thresholds In, I’n, In, F T 2, it is possible to pass twice or more times, instead of only one as shown in Figure 2, the lead that carries the phase current IA inside the magnetic toroidal element T. This way, the current values of the thresholds In, Fn, IT 2 , F T2 will be divided by the number of spirals of the lead C wound on the magnetic toroidal element T.

According to a preferred embodiment, shown in Figure 1, the unipolar Hall sensors Hl and H2 are of the“open collector” type. Alternative embodiments cannot however be ruled out wherein, for example, the sensors are of the“push- pull” type.

Furthermore, the use of unipolar Hall sensors cannot be ruled out with the output which is inverted with respect to that described in Figures 1, 4 and 5. In this case, to return to the operating conditions described above it is possible to invert the output signals of the magnetic sensors through the use of a transistor or of a signal inverter.

Furthermore, the possibility of using double unipolar Hall sensors cannot be ruled out, so as to replace the two unipolar Hall sensors Hl and H2 described above with a single sensor.

As shown in Figure 1 (and in Figure 7 with reference to the second embodiment), in each of the three rectification units UA, UB, UC the output circuit O comprises at least a first Power MOS transistor Ql and at least a second Power MOS transistor Q2 operatively connected to the current sensor S’ (to the sensor S” with reference to the second embodiment) and adapted to be piloted by means of the current sensor S’ (S”) to generate the rectified currents IBATTA, IBATTB, IBATTC.

Furthermore, the output circuit O comprises at least one half-bridge driver U2 operatively interposed between the current sensor S’ (S”) and the first and second Power MOS transistors Ql and Q2.

In particular, the half-bridge driver U2 is provided with a first input HI connected to the first unipolar Hall sensor Hl and with a second input LI connected to the second unipolar Hall sensor H2.

The unipolar digital Hall sensors Hl, H2 are usefully selected with response times short enough according to the electrical frequency of the generator G, so as not to generate excessive delays regarding the synchronization of the switch of the Power MOS transistors Ql and Q2.

When the endothermic motor starts up and the generator G reaches a speed so that in the stator windings Ll, L2 and L3 a voltage is generated which, exceeding that of the battery V Batt , directly polarizes the diodes inside the Power MOS transistors Ql and Q2, we have a current flow through the diodes themselves even if the Power MOS themselves are not piloted, as happens in a conventional three-phase rectifier diode bridge.

The operation of the half-bridge driver U2 and of the first and second Power MOS transistors Ql and Q2 is as follows.

Assuming the direction of the current which from the generator G flows towards the battery to be positive, when the current of phase IA which crosses the toroidal element T in ferrite exceeds the threshold value In, a magnetic flow is generated in agreement with the direction of the current IA itself which exceeds the magnetic threshold value In of the first unipolar Hall sensor Hl.

In this case, the output signal VB of the first unipolar Hall sensor Hl switches to a high logic value. In particular, the output signal VB of the first unipolar Hall sensor Hl switches to a high logic value through the resistor R4.

The logic value remains high until the current IA drops below the threshold value I’n.

Such signal VB is applied, through the resistor R13, at the input HI of the half bridge driver U2.

The half-bridge driver U2 is configured to pilot the output HO to the high value and, therefore, to positively polarize the gate of the Power MOS transistor Ql through the resistor R10, thus sending the first transistor Ql itself in conduction. The Power MOS transistor Ql will remain in this state as long as the input HI of the half-bridge driver U2 remains at a high logic value.

The purpose of the Zener diodes D3 and D5 is to protect the Gates of the first and of the second Power MOS transistors Ql and Q2, respectively.

In the same way as described above, when the sign of the current I A is inverted and becomes lower than the threshold value It 2 , a magnetic flux is generated in the toroidal element T in ferrite according to the direction of the current IA itself which exceeds the magnetic threshold value of the second unipolar Hall sensor H2.

The output signal V A of the second unipolar Hall sensor H2 switches to a high logic value through the resistor R5, and remains high until the current IA climbs above the threshold value Gt2.

In this configuration, the signal VA is applied, through the resistor Rl l, to the input LI of the half-bridge driver U2 which pilots the output LO at high value and, therefore, positively polarizes the Gate of the second Power MOS transistor Q2 through the resistor R16, thus sending the second transistor Q2 itself in conduction.

The second Power MOS transistor Q2 will remain in this state as long as the input LI of the half-bridge driver U2 remains at a high logic value.

The half-bridge driver U2, powered by the voltage Vcci with the decoupling capacitor Cl at the typical value of 10 V, which may differ from the Vcc value, uses the capacitor C2 as“bootstrap charging” to pilot the gate of Ql and also avoids the simultaneous conduction of the transistors Ql and Q2.

Different embodiments cannot however be ruled out wherein, for example, a device is used which integrates inside it three half -bridge drivers in a single container.

Figure 6 graphically illustrates the operation described above.

It should also be noticed that until the phase current IA is lower in absolute value than the switching thresholds of the unipolar Hall sensors Hl and H2, the circulation of the current occurs by means of the internal diodes of the Power Mos transistors Ql and Q2. These diodes have a typical voltage drop of around 0.7V, which is why it is important to limit the aforementioned switch thresholds In and I T2 to current values of around 3A, so as to limit dissipation during this transition phase before the Power Mos transistors Ql and Q2 enter conduction. What has been described thus far is the operation relating to the synchronous rectification which represents the case in which all the current supplied by the permanent magnet generator G is supplied to the battery and loads of the vehicle.

In the event of the battery voltage V Batt exceeding the desired value, which for lead batteries is normally 14.5V, the current supplied by the generator G to the battery in order to keep the regulating voltage constant must be limited.

Such function is implemented by limiting the angle of conduction of the Power MOS transistor Ql and at the same time putting in conduction the Power MOS transistor Q2 in the way described below.

The three-phase synchronous rectifier RT advantageously comprises a current limiting circuit A, L configured to limit the current supplied by the generator G to the battery B in the event of the voltage V Batt supplied to the battery B exceeding a predefined desired value.

In particular, the current limiting circuit A, L comprises an error amplifier circuit A configured to measure the voltage supplied to the battery V Batt and to supply a verification voltage signal Ve at output which varies between predefined voltage values acceptable for the correct operation of the battery.

The error amplifier circuit A specifically comprises a measurement circuit M of the voltage V Batt supplied to the battery B.

With reference to the specific preferred embodiments illustrated in the Figures 1 and 7, the measurement circuit M for measuring the voltage supplied to the battery V Batt comprises a couple of Zener diodes Dl, D4 connected in series the one to the other and to a resistive divider R15, R28, R30.

The battery voltage V Batt is measured by means of the Zener diodes Dl and D4 and by means of the resistive divider made up of the resistors R15, R28, R30. The resistive divider R15, R28, R30 together with a capacitor C4 furthermore constitutes a low-pass filter to limit the ripple on the battery voltage V Batt .

The sum of the voltages of the two Zener diodes Dl, D4 is selected between 13.0V and 13.6V in order to limit the current absorption from the battery with the endothermic motor of the generator G off.

In addition, the error amplifier circuit A comprises at least one operational amplifier U6 provided with a non-inverting input connected to a reference voltage and with an inverting input connected to the measurement circuit M. The operational amplifier U6 is configured to supply the verification voltage signal V e at output.

In particular, the reference voltage is determined by the voltage drop onto a diode D6 when this is crossed by the current limited by a resistor R27 connected between the voltage Vcc and the anode of the diode D6 itself.

Furthermore, the ratio between the resistance values of the resistors R26 and R29 connected between the inverting input and the output and between the inverting input and the measurement circuit M respectively, which is approximately 100, determines the gain of the operational amplifier U6 in the inverting configuration.

Therefore, by appropriately selecting the values of these resistors R26 and R29, the verification voltage signal Ve present at the output of the operational amplifier U6 will vary linearly from a minimum acceptable voltage value to a maximum acceptable voltage value. For example, the minimum acceptable voltage value may be 0V with a battery voltage of 14.4V, while the maximum acceptable voltage value may be V cc with a battery voltage of 14.6V. This excursion of the battery voltage value, which corresponds to the condition of full load and load absent at its ends respectively, is widely acceptable for the applications considered.

In addition, the current limiting circuit A, L comprises, for each rectification unit UA, UB, UC, at least one verification and limitation circuit L operatively connected to the current sensor S’, to the error amplifier circuit A and to the output circuit O. The verification and limitation circuit L is configured to pilot the output circuit O, in order to make a phase control of the rectified current IBATTA (IBATTB, IBATTC) supplied to the battery B when the verification voltage signal Ve varies.

When the output VB of the first unipolar Hall sensor Hl switches to a high logic value, the transistor Q5 will be piloted in conduction by means of the two resistors R18 and R23. At the same time, the transistor Q3 will be interdicted, because its base is not polarized, the current coming from the resistor R3 being short-circuit proof against earth by the transistor Q5. Because the transistor Q3 is interdicted, the capacitor C3 can charge itself with negative exponent rule at the asymptotic value resulting from the formula V CCxR20/ (R2+R20) .

The pattern of the voltage Vc3 of the capacitor C3 is shown in Figure 6.

The signal Vc3 is applied to the non-inverting input of the comparator U 1 , while to the inverting input is applied the output signal Ve of the operational amplifier U6.

When the value of the signal Vc3 exceeds the value of the signal Ve, the output of the comparator Ul switches to the high logic value by means of the resistor Rl. Such high logic value is applied by means of the diode D2 to the input LI of the half-bridge driver U2 and, by means of the resistive divider made up of the resistors R17 and R22, to the base of the transistor Q4, bringing it in conduction. The conduction of Q4 forces the input HI of the half-bridge driver U2 at a low logic value.

The inputs LI and HI of the half-bridge driver U2 being at high and low logic value respectively, the outputs LO and HO of the driver itself will be at high and low logic value respectively, and so the second Power Mos transistor Q2 will be in conduction while the first Power Mos transistor Ql will be interdicted.

Upon the variation in the value of the signal Ve, which is inversely proportionate to the value of the battery voltage Veatt, a phase control is thus achieved of the current Ie att A supplied by the generator G to the battery.

The second possible embodiment of the three-phase synchronous rectifier RT according to the invention, wherein the current sensor S” comprises a single magnetic linear Hall sensor (H). Such second embodiment is shown in Figures 7-10.

With reference to such second embodiment, the current sensor S” comprises a magnetic linear Hall sensor H connected to the toroidal element T made of a magnetic material. The linear Hall sensor H is configured to generate an output voltage Vu which reproduces the pattern of the phase current IA (IB, IC) in the lead C with a voltage offset equal to a predefined value. In particular, as shown in Figures 8 and 9, the toroidal element T is provided with an air gap TR and the linear Hall sensor H is arranged inside the air gap TR.

In particular, with reference to the use of a single Hall sensor H of linear type, the output voltage Vu of the sensor H reproduces the pattern of the current I A in the phase lead C with a voltage offset equal to Vcc/2. Such pattern of the voltage output Vu of the Hall sensor H is shown in Figure 10.

In this case, the current I A that passes inside the toroidal element T in ferrite induces a magnetic flow in the air gap TR proportionate to it which, in crossing the linear Hall sensor H, in turn generates an output voltage Vu with a value equal to VCC/2+(KXI A ), where K represents the proportionality constant between the current I A and the output voltage Vu.

Still with reference to the second possible embodiment of the three-phase synchronous rectifier RT, the current sensor S” comprises a first voltage comparator U1A and a second voltage comparator U1B. The linear Hall sensor H is connected to the inverting input of the first voltage comparator U1A and to the non-inverting input of the second voltage comparator U1B.

The second voltage comparator U1B is configured to:

switch its output voltage V B from a low voltage value (0V) to a high voltage value (Vcc) at a first predefined threshold value Vu, when the phase current I A is positive and increasing;

switch its output voltage V B from a high voltage value (Vcc) to a low voltage value (0V) at a second predefined threshold value V’ TI , when the phase current I A is positive and decreasing.

The first voltage comparator Ul A is configured to:

switch its output voltage V A from a low voltage value (0V) to a high voltage value (Vcc) at a first predefined threshold value V T2 , when the phase current I A is negative and decreasing;

switch its output voltage V A from a high voltage value (Vcc) to a low voltage value (0V) at a second predefined threshold value V’ T 2, when the phase current I A is negative and increasing. In particular, from the wiring diagram in Figure 7, it can be seen that the output signal Vu of the linear Hall sensor H is applied directly to the inverting input of the first voltage comparator U1A and, by means of the resistor R14, to the non inverting input of the second voltage comparator U1B.

The first voltage comparator U1A connected as shown in Figure 7 is configured to operate as an inverting voltage comparator with hysteresis and the trip threshold voltage values are defined by means of the resistance values selected for the resistors R7, R24 and R12.

The second voltage comparator U1B connected as shown in Figure 7 is configured to operate as a non-inverting voltage comparator with hysteresis and the trip threshold voltage values are defined by means of the resistance values selected for the resistors R8, R25, R19 and R14.

The trip voltage thresholds of the above comparators can be set by making reference to the current threshold values In, I’u, I T 2 and F T 2 already mentioned in case of use of the current sensor S’ with two unipolar Hall sensors Hl and H2 described above, making use of the formula shown above for the calculation of the output voltage value Vu.

By way of example, starting from the current threshold In the voltage threshold Vn is set equal to the value Vcc/2+(KxIn).

In the same way, the other trip thresholds can be set as follows: V’ T1 =Vcc/2+(KxF Tl ); VT2=VCC/2+(KXIT 2 ); V , T2=VCC/2+(KXF T 2 ).

The output signals V A and V B of the two voltage comparators U1A and U1B will behave exactly like the output signals V A and V B of the two unipolar Hall sensors Hl and H2 considered previously with reference to the first possible embodiment, leaving unchanged the operation of the downstream circuit of the voltage comparators U1A and U1B themselves.

Figure 10 shows the patterns of the signals described above in case of operation with a current sensor S” provided with a linear Hall sensor H.

With reference to both the embodiments, from the Figures 6 and 10 it appears evident that the battery current IBATTS is given by the sum of the 3 currents IBATTA, IBATTB and IBATTC relating to the 3 phases, identical to one another as regards value but out of phase by 120°. Having an effective balancing of the currents in the phases, we have as a consequence a“load sharing” among the phases themselves.

This feature helps to optimize the efficiency of the generator-regulator system, thus avoiding overheating of one phase compared to the others, as in the case of currents in different phases.

It has, in practice, been ascertained that the described invention achieves the intended objects.

In particular, the use of a current sensor consisting of a toroidal element made in a magnetic material, typically consisting of ferrite, crossed by the phase lead connected to the permanent magnet generator, together with the use of an air gap in the ferrite toroid inside which are placed one or two Hall sensors, makes it possible to accurately detect the zero-crossing of the current of the generator phases, while at the same time maintaining adequate response times of the synchronization system.

Furthermore, the use of the Power MOS devices which possess the conduction resistance RDS( OII ) below IihW, besides permitting low dissipation, allows a low voltage drop between the generator and the battery. In the case of a battery current of 40A, this drop passes from about 2V in the case of a three-phase diode or SCR bridge to just a few tenths of mV depending on the conduction resistance RDS(on) of the Power Mos transistor used.

This characteristic therefore enables the generator to supply more current above all at low rotation speeds.