EP2206232A2

EP2206232A2 - System for powering an electric machine

Info

Publication number: EP2206232A2
Application number: EP08861897A
Authority: EP
Inventors: Yann Le Pecheur; Mickael Tihy
Original assignee: Valeo Systemes de Controle Moteur SAS
Current assignee: Valeo Systemes de Controle Moteur SAS
Priority date: 2007-10-01
Filing date: 2008-09-30
Publication date: 2010-07-14
Also published as: BRPI0817921A2; FR2921771A1; FR2921771B1; WO2009077668A2; JP2010541534A; US20100259205A1; WO2009077668A3

Abstract

The invention relates to a system (100) for powering an electric machine (M). One particularly interesting application of the present invention is to the field of powering electric motors used in automobiles. The system (100) comprises a voltage source (102), an electronic circuit (108) for supplying the electric machine (M), a first switch (101), wherein the voltage source (102) powers the electronic circuit (108) when the first switch (101) is in a closed position, at least one capacitor (104, 105) mounted in parallel on the voltage source (102) when the first switch (101) is in the closed position, and a precharge circuit (114) for the capacitor (104, 105). The system further includes a second switch (+APC), wherein the precharge circuit (114) is connected to the voltage source (102) when the second switch (+APC) is closed, and the first switch (101) is controlled so as to be closed after the precharge of the capacitor (104, 105).

Description

Electric machine supply system

The present invention relates to an electric machine supply system. A particularly interesting application of the invention lies in the field of supply of electric motors used in motor vehicles. In general, a power supply system of an electric machine such as an electric motor used in a motor vehicle comprises a power circuit for transmitting the voltage of the vehicle battery to an electronic card managing the power supply of said motor. .

An example of such a feed system 1 is shown schematically in FIG. 1. The system 1 comprises:

a voltage source 2 formed by the vehicle battery,

- a power circuit 3

- An electronic supply circuit 8 for supplying a motor M. The power circuit 3 comprises. o two capacitors 4 and 5 connected in parallel, o an inductor 6 connected between the positive terminal + Bat of the battery 2 and a first common terminal of the two capacitors 4 and 5. The function of the power circuit 3 is to transmit the voltage of the battery 2 to the electronic supply circuit 8. The power circuit is for example composed of several "bus-bar" ("bus bars" in French) unrepresented copper.

In the case of a motor M of brushless type ("brushless" in French) such as that used in an electric power steering, the electronic supply circuit 8 is composed of a switching power supply circuit comprising three bridge arms 9, 10 and 11 each comprising two transistors 12 and 13 connected in series, each transistor being provided with an antiparallel diode (the antiparallel diode is often present by construction on the field effect transistors of the MOSFET type ). Each of the three stator windings of the motor M is therefore powered by a bridges 9, 10 and 11. For the sake of clarity, the control circuits of the transistors have not been shown.

The chopping of the voltage caused by the electronic supply circuit 8 can disturb the entire on-board network and the battery voltage 2. The filter formed by the inductor 6 and the capacitors 4 and 5 is intended to stabilize the battery voltage 2 The filter makes it possible, in a way, to smooth the corrugated voltage. The value of the filtering capacitance is generally high: this is why, as in the example presented here, two parallel capacitors 4 and 5 discrete are often used, these capacitors 4 and 5 being preferably electrochemical capacitors of which the common positive pole is connected to the inductor 6.

Such a configuration however poses a problem insofar as the battery is always connected to both the power circuit and the electronic supply circuit. This permanent connection may involve leakage currents that could lead to unwanted heating.

Therefore, some manufacturers require the presence of a switch to cut power circuits. An example of a feed system 20 having such a configuration is shown in FIG.

The system 20 is identical to the system 1 of Figure 1 with the difference that it comprises a switch 21 for selectively connecting the battery to the power circuit and the electronic supply circuit. Such a switch 21 requires the presence of a pre-charge circuit

Capacitors, said pre-charge circuit belonging to the power circuit; the pre-charge circuit is designed to avoid inrush currents which could occur if the switch 21 is closed on capacitors initially discharged. Inrush currents that can reach 100 A (or 200 A) can adversely affect the battery, the various connectors, the relay contact, the chemical capacitors and even the fuses. The pre-charging circuit 22 comprises, for example, a field effect transistor 23 of the power MOSFET type: this transistor is for example controlled with pulses more frequently until it closes completely. Such a pre-charge circuit makes it possible to ensure a progressive charge of the electrochemical capacitors, the transistor 23 acting as a resistive load and forming with the capacitors an RC circuit: once the capacitors are charged, the transistor is held in position closed.

However, the implementation of the configuration as shown in FIG. 2 also poses certain difficulties.

Thus, the major disadvantage of this configuration lies in the modification of the power circuit and more particularly in the addition of an impedance (for example the power MOSFET transistor) in the filter contained in this power circuit. The presence of this impedance requires new connections, decreases the overall efficiency of the circuit and can have consequences in terms of EMC (Electro-Magnetic Compatibility) insofar as the filter was intended to function satisfactorily (without added impedance) in its electromagnetic environment without causing itself electromagnetic disturbances.

In addition, the addition of this impedance leads to a significant extra cost insofar as it requires the use of a transistor type component operating at high power and having a low impedance in the on state. In this context, the present invention aims to provide a power supply system for an electric machine comprising a pre-charge circuit, said system making it possible to overcome the above-mentioned EMC problems and having a high electrical efficiency and a relatively high overhead. low compared to systems without pre-charge circuit. To this end, the invention proposes a power supply system for an electric machine comprising:

- a source of tension,

an electronic circuit for supplying said electric machine, a first switch, said voltage source supplying said electronic circuit when said first switch is in the closed position,

at least one capacitor connected in parallel with said voltage source when said first switch is in the closed position,

a pre-charge circuit of said capacitor, said system being characterized in that it comprises a second switch, said pre-charge circuit being connected to said voltage source when said second switch is closed and said first switch being controlled for close after pre-charging said capacitor.

Pre-charge circuit is understood to mean a circuit enabling the capacitor to charge more slowly than in the absence of a pre-charge circuit and thus to avoid an excessive current draw of the capacitor discharged at the moment of closing. first switch. Thanks to the invention, a second switch is used which makes it possible to pre-charge the capacitor before closing the first switch serving to supply the electronic supply circuit of the electrical machine. This second switch makes it possible to separate the precharge function of the capacitor from the supply of the electronic supply circuit. Thus, the pre-charge circuit is external to the power circuit and does not introduce additional impedance which would lead to loss of efficiency and EMC problems.

In addition, the second switch is only used to pre-charge the capacitor and is not used in the context of the power supply of the electronic circuit; therefore, it is quite possible to employ a switch operating at low power and having a higher on-resistance than that of the transistors used in the aforementioned known solutions.

For this purpose, said pre-charge circuit and said second switch are mounted, for example, in series between the terminals of said first switch.

The system according to the invention may also have one or more of the following characteristics, considered individually or in any technically possible combination: said source of voltage is the battery of a motor vehicle.

said second switch is formed by the device for feeding after contact + APC.

said at least one capacitor is an electrochemical capacitor.

said pre-charge circuit comprises a transistor, the control of said transistor ensuring the pre-charge of said capacitor.

said transistor is controlled to open before the closing of said first switch. said pre-charge circuit comprises a resistor in parallel with a transistor.

- The system according to the invention comprises a second capacitor connected in parallel on said first capacitor.

said electronic supply circuit is a supply circuit of an electric motor.

said electronic supply circuit is formed by a switching power supply circuit.

said system comprises means for controlling said first closing switch after pre-charging said capacitor.

The invention also relates to the use of said system, as mentioned above, in which it controls closing said first switch after the pre-charge of said capacitor.

Other characteristics and advantages of the invention will become clear from the description given below, by way of indication and in no way limitative, with reference to the appended figures, among which:

- Figure 1 is a simplified schematic representation of a first power system of an electric machine according to the prior art;

- Figure 2 is a simplified schematic representation of a second power system of an electric machine according to the prior art;

- Figure 3 is a simplified schematic representation of a power system of an electric machine according to the invention. Figures 1 and 2 have been described above with reference to the prior art.

Figure 3 is a simplified schematic representation of a system 100 according to the invention. The system 100 comprises:

a source of voltage 102 formed by the battery of the vehicle,

- a power circuit 103

- An electronic supply circuit 108 for supplying a motor M. The power circuit 103 comprises.

A switch 101 such as an electromechanical relay for selectively connecting the battery 102 to the power circuit 103 and to the electronic supply circuit 108,

two electrochemical capacitors 104 and 105 mounted in parallel,

an inductor 106 connected between the positive terminal + Bat of the battery 102 and the common positive terminal of the two electrochemical capacitors 4 and 5.

The function of the power circuit 103 is to transmit the voltage of the battery 102 to the electronic supply circuit 108. The power circuit is for example composed of several "bus bars" ("bus bars" in French) of copper not represented.

In the case of a three-phase "brushless" motor M such as that typically used in an electrical assisted direction, the electronic supply circuit 108 is generally formed by an electronic card of the SMI type (Isolated Metal Substrate) composed of a switching power supply circuit comprising three bridge arms 109, 110 and 111 each comprising two transistors 112 and 113 connected in series, each transistor being provided with an antiparallel diode (the antiparallel diode is often present by construction on field effect transistors of the MOSFET type). Each of the three stator windings of the motor M is therefore powered by one of the bridges 109, 110 and 111. For the sake of clarity, the control circuits of the transistors have not been represented. The electronic supply circuit 108 further comprises a pre-charge circuit 114 formed for example by a bipolar transistor 115 (the presence of the relay 101 requires the presence of the pre-charge circuit 114 of the capacitors 104 and 105 to avoid This bipolar transistor is connected between the positive terminal of the electrochemical capacitors 104 and 105 and the vehicle after-ignition power supply device APC of the vehicle When the ignition of the vehicle is activated, the + APC of the vehicle vehicle sends a power signal to pass some electronic systems of the vehicle from their standby state or stop, to their nominal wakeup state. + APC after contact to connect the transistor 115 to the battery voltage source 102.

The filter formed by the inductor 106 and the electrochemical capacitors 104 and 105 is intended to stabilize the battery voltage 102, which can be chopped by the electronic circuit 108. The value of the filtering capacitance is generally high: this is why, two electrochemical capacitors 104 and 105 are used discretely connected in parallel. By way of example, the value of the capacitance of each of the electrochemical capacitors 104 and 105 in an application of this type is of the order of 3300 μF with an inductance 106 of 0.6 μH. The signal + APC and the relay 101 are for example controlled by the on-board computer.

The operation of the system 100 is as follows: after putting the + APC into contact (connection to the battery voltage via the ignition key which actuates a relay), the control electronics (not shown) controls the closing of the pre-charge transistor 115 ( for example via more and more frequent pulses) so that the capacitors 104 and 105 are gradually charged. Once the capacitors 104 and 105 have been loaded, the control electronics (not shown) controls the opening of the pre-charge transistor 115, then the on-board computer controls the closing of the relay 101, thus enabling the power circuits 103 to be powered. and 108 by the battery 102. The duration, imposed by the on-board computer, separating the + APC and the closing of the relay 101 must be sufficient to allow correct pre-charging of the capacitors 104 and 105. Thanks to the system 100 according to the invention, the pre-charge circuit does not come between the battery 102 and the motor M affecting the electrical efficiency. All the voltage delivered by the battery goes directly into the electronic circuit 108 via the power circuit 103 sized to have a minimum of losses (use of copper bus bar with low ohmic losses).

In addition, the bipolar transistor 115 used in the precharging circuit 114 is used only for the pre-charge of the capacitors and can therefore be a transistor having a lower performance (especially in terms of on-state impedance). (and therefore lower cost) than power transistors used in known pre-charge circuits.

Finally, the pre-charge circuit 114 belongs to the electronic card 108 and not to the power circuit 103 so that the pre-charge circuit does not modify the structure of the power circuit 103 and has no impact on the terms of EMC on the power circuit 103.

Of course, the invention is not limited to the embodiment just described.

In particular, we have described for illustrative purposes a precharge circuit composed of a bipolar transistor. It is however possible to use any type of transistor such as a field effect transistor for example.

In addition, the pre-charge circuit may also be formed by a transistor in parallel with a resistor.

Finally, any means can be replaced by equivalent means.

Claims

1. System (100) for powering an electric machine (M) comprising: - a voltage source (102),

an electronic circuit (108) supplying said electric machine (M),

a first switch (101), said voltage source (102) supplying said electronic circuit (108) when said first switch (101) is in the closed position,

at least one capacitor (104, 105) connected in parallel with said voltage source (102) when said first switch (101) is in the closed position,

a pre-charge circuit (114) of said capacitor (104, 105), said system (100) being characterized in that it comprises a second switch (+ APC), said pre-charge circuit (114) being connected said voltage source (102) when said second switch (+ APC) is closed and said first switch (101) being controlled to close after pre-charging said capacitor (104, 105).

2. System (100) power supply according to the preceding claim characterized in that said voltage source (102) is the battery (+ BAT) of a motor vehicle.

3. System (100) power supply according to the preceding claim characterized in that said second switch is formed by the supply device after contact + APC.

4. System (100) power supply according to one of the preceding claims characterized in that said at least one capacitor (104, 105) is an electrochemical capacitor.

5. System (100) power supply according to one of the preceding claims characterized in that said pre-charge circuit (114) comprises a transistor (115), the control of said transistor (115) ensuring the pre-charge said capacitor (104, 105).

6. System (100) power supply according to the preceding claim characterized in that said transistor (115) is controlled to open before closing said first switch (101).

7. Feeding system according to one of claims 1 to 4 charac- terized in that said pre-charge circuit comprises a resistor in parallel with a transistor.

8. System (100) power supply according to one of the preceding claims characterized in that it comprises a second capacitor (104) connected in parallel on said first capacitor (105).

9. System (100) power supply according to one of the preceding claims characterized in that said electronic circuit (108) of supply is a power supply circuit of an electric motor (M).

10. System (100) according to one of the preceding claims characterized in that said electronic supply circuit (108) is formed by a switching power supply circuit (109, 110, 111).

11. System (100) according to one of the preceding claims comprising means for controlling said first switch (101) closing after pre-charging said capacitor (104,105).

12. Use of the system (100) according to one of the preceding claims in which it is closed control said first switch

(101) after pre-charging said capacitor (104,105).