EP3072232A2

EP3072232A2 - Power supply of an electric motor

Info

Publication number: EP3072232A2
Application number: EP14799483.4A
Authority: EP
Inventors: Xavier Goumain; Xavier ROUSSEIL
Original assignee: Valeo Systemes Thermiques SAS
Current assignee: Valeo Systemes Thermiques SAS
Priority date: 2013-11-20
Filing date: 2014-11-18
Publication date: 2016-09-28
Also published as: US20160294315A1; CN105850028B; JP6445556B2; FR3013534B1; WO2015075039A3; CN105850028A; WO2015075039A2; JP2016539614A; US9722527B2; FR3013534A1

Abstract

The invention relates to a power supply system of an electric motor (1) comprising a power circuit (3), the input terminals of which are connected to a DC voltage source, and an electronic circuit (4) for controlling the electric motor (1) based on a control signal representative of the set speed of the motor. According to the invention, the system comprises a means (6) capable of reducing the DC voltage value received by the power circuit (3) during the starting of the electric motor (1) and/or during operating phases in which the set speed of the electric motor (1) is below a threshold speed.

Description

POWER SUPPLY OF AN ELECTRIC MOTOR

The present invention relates to the supply of electric motors. 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 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 power supply system is shown diagrammatically in FIG. 1 for the supply of a three-phase electronically commutated motor 1 capable of driving a fan 2 of a heating, ventilation and air-conditioning system of a motor vehicle. . Such a motor 1, also known under the name of "brushless" motor (English terminology meaning "brushless"), or synchronous motor self-controlled magnets, comprises three stator windings, represented here in a triangle assembly, of which the voltages U, V and W are delivered by the power system. This power system includes:

a power circuit 3 whose input terminals are connected to a voltage source (not shown) formed by the vehicle battery, and an electronic control circuit 4 for powering the motor

1.

The power circuit 3 is an input filter comprising for example an inductor L connected in series on the positive terminal + BAT of the battery two capacitors each mounted between the negative terminal -BAT and one of the terminals of the inductor. Its function is to transmit the voltage of the battery to the electronic control circuit 4. The electronic control circuit 4 is composed of a switching power supply circuit comprising three bridge arms 9, 10, 11 each comprising two mounted switches in series, each switch being provided with an antiparallel diode. Each of the three stator windings of the motor 1 is powered by one of the bridges. To avoid a permanent connection of the battery to the circuit of power and electronic control circuit which could involve leakage currents may cause unwanted heating, the power system further comprises a safety switch 5 for selectively connecting the battery to the power circuit 3 and the circuit 4. In the example shown, this safety switch 5 is placed in series on the -BATT connection terminal, but could equivalently be connected in series to the + BATT terminal. The safety switch 5 is traditionally an enhancement type MOSFET transistor, for example N type, whose drain and source are connected in series on the -BATT connection terminal, and whose gate receives a control signal SW_CMD allowing to switch the transistor between a blocked state (open switch), or a saturated operating state (closed switch) in which the transistor behaves between its drain and its source as a very low value resistor.

One of the problems with this type of electric motor is the level of acoustic noise emission that can remain significant compared to surrounding noise emissions. In particular, the studies of the Applicant have shown that the noise generated by such engines could be important during certain phases of operation, especially during engine start-up phases, where again when the engine is controlled to run at relatively fast speeds. low.

In this context, the present invention aims at providing a solution which makes it possible to improve the acoustic performance, in particular to reduce the sound emission level, of an electric motor as a function of the operating phase in which the engine is located. .

To this end, the invention proposes a power supply system for an electric motor comprising:

a power circuit whose input terminals are connected to a DC voltage source,

an electronic circuit for controlling the electric motor as a function of a control signal representative of the reference speed of the motor, said system being characterized in that it is able to reduce the DC voltage value received by the power circuit during starting of the electric motor and / or during operating phases for which the reference speed of the electric motor is lower than a threshold speed.

Thanks to the invention, the fact of reducing the supply voltage during very precise operating phases of the engine for which the set speed is low makes it possible to significantly reduce the noise emissions due to the stator windings.

The system according to the invention may also have one or more of the following characteristics, considered individually or in any technically possible combination:

the value of DC voltage received by the power circuit corresponds, during the starting of the electric motor and / or during operating phases for which the reference speed of the electric motor is lower than a threshold speed, to the DC voltage delivered by the reduced source of a linearly increasing value as a function of the set speed.

- The power system further comprises a MOSFET transistor forming a safety switch, which, in the closed position, allows the connection of the power circuit to said DC voltage source, and a gate control means of the MOSFET transistor suitable for placing said transistor in the closed position in a saturated operating mode for a set speed higher than said threshold speed, or in a closed position in a linear operating mode for a set speed lower than said threshold speed.

- In said linear operating mode, the MOSFET transistor is controlled to produce between the drain and the source a voltage increasing linearly as a function of the set speed.

the threshold speed is between 10% and 30% of the maximum speed possible for the electric motor. the threshold speed is preferably equal to 20% of the maximum speed possible for the electric motor.

- The electric motor is brushless or with brushes.

the electric motor is preferably without brushes.

Other features and advantages of the invention will emerge clearly from the description which is given below, as an indication and in no way limiting, with reference to the appended figures, among which:

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

- Figure 2 is a simplified schematic representation of a power system of an electric motor according to a possible embodiment of the invention;

FIG. 3 schematically illustrates a preferred implementation for reducing the value of the DC voltage received by the power circuit of FIG. 1;

FIG. 4 illustrates, by way of example, the supply voltage delivered as a function of the operating phases of the electric motor.

Figure 1 has been described above with reference to the prior art. Figure 2 is a simplified schematic representation of a power system of an electric motor 1 according to the invention.

It is found, as explained above in the context of the prior art:

a power circuit 3 whose input terminals are connected to a voltage source (not shown) formed by the vehicle battery, and

an electronic control circuit 4 for supplying the motor 1 as a function of a control signal representative of the reference speed of the motor, and

- Preferably, a safety switch 5 for selectively connecting the battery to the power circuit 3 and the electronic control circuit 4.

As has been indicated above, in conventional operation, that is to say when the safety switch 5 is closed, the power circuit 3, and consequently the electronic control circuit 4, are powered by the value of the voltage as delivered by the vehicle battery typically of the order of 13 volts.

However, the tests conducted by the Applicant have made it possible to demonstrate that the noise emissions, in particular those related to the stator windings in the case of a brushless motor, are proportional to the value of the DC supply voltage.

With this in mind, it is proposed to provide the power system with a control module 6 making the system capable of reducing the value of DC voltage received by the power circuit during the operating phases of the engine for which the emissions sound are the most troublesome, typically when starting the electric motor and / or during operating phases for which the target speed of the electric motor is below a threshold speed.

The role of the control module 6, represented here schematically in the form of an electronic circuit interposed between the safety switch 5 and the input of the power circuit 3 is therefore:

- Let the power circuit 3 be powered by the DC voltage from the battery when the target speed for the motor is greater than the threshold speed and

- To reduce the value of DC voltage otherwise preferably a value increasing linearly according to the set speed.

A large number of implementations, electronic or software, can be envisaged to ensure such a control of the value of the supply voltage.

FIG. 3 illustrates a particularly clever implementation in that it makes best use of the components already available in the system, in particular the MOSFET transistor 5 used as a safety switch to interrupt the power supply in the event of overheating, or to put on standby the system.

In accordance with the embodiment of the invention, the way the gate of the transistor is controlled so that it is not used as a simple switch. More specifically, the transistor that was until now only used in saturated mode, regardless of the setpoint speed, will now be driven according to the target speed so as to:

- presenting a conventional saturated operation when the setpoint speeds are greater than the threshold value;

- To present a linear operation otherwise, so as to reduce the voltage value actually supplied to the circuit 3 of a linearly increasing value as a function of the set speed.

Figures 3 and 4 illustrate this principle. When the transistor 5 is in a saturated operating zone, the circuit downstream of the transistor conventionally receives the power supply + BAT from the battery. This area corresponds to Part 2 in Figure 4.

On the other hand, when the transistor 5 is in its linear operating zone, it develops a non-zero voltage V_SW between its drain and its source, so that the downstream circuit receives the voltage:

+ BAT - V_SW

Part 1 in FIG. 4 illustrates the variations of the voltage received by the circuit 3 as a function of the engine speed. In the example given, the threshold speed is of the order of 20% of the maximum speed possible for the electric motor.

The control signal SW_CMD is generated by the module 6 as a function of the set speed SCONS -

The control module 6 can be entirely software, managed for example by a microcontroller capable of generating, for linear operation, a Pulse Width Modulation (PWM) signal proportional to the reference speed.

Alternatively, a specific electronic circuit capable of generating a command proportional to the set speed can also be used. In either case, a feedback loop can be added for regulation purposes.

Claims

1. Power system of an electric motor (1) comprising:

a power circuit (3) whose input terminals are connected to a DC voltage source,

an electronic circuit (4) for controlling the electric motor (1) as a function of a control signal representative of the reference speed of the motor,

said system being characterized in that it is able to reduce the DC voltage value received by the power circuit (3) when starting the electric motor (1) and / or during operating phases for which the set speed of the electric motor (1) is below a threshold speed.

2. Feeding system according to claim 1, characterized in that said DC voltage value received by the power circuit (3) corresponds, when starting the electric motor (1) and / or during operating phases for which the set speed of the electric motor (1) is lower than a threshold speed, the DC voltage delivered by the reduced source of a linearly increasing value as a function of the set speed.

3. Power system according to any one of the preceding claims, further comprising a MOSFET transistor (5) forming a safety switch, which, in the closed position, allows the connection of the power circuit (3) to said source of power. DC voltage, characterized in that it comprises means (6) for controlling the gate of the MOSFET transistor (5) capable of placing said transistor in the closed position in a saturated operating mode for a reference speed greater than said threshold speed , or in the closed position in a linear operating mode for a set speed lower than said threshold speed.

4. Power supply system according to claim 3, characterized in that, in said linear operating mode, the MOSFET transistor is controlled to produce between the drain and the source a voltage increasing linearly according to the set speed.

5. Power supply system according to any one of claims 3 or 4, characterized in that said means (6) for controlling comprises a microcontroller capable of generating a pulse width modulation type (PWM) signal proportional to the setpoint speed.

6. Feeding system according to any one of claims 3 or 4, characterized in that said means (6) for controlling comprises an electronic circuit.

7. Power system according to any one of the preceding claims, characterized in that said electronic control circuit (4) is formed by a switching power supply circuit.

8. Fuel system according to any one of the preceding claims, adapted to power a brushless type electric motor, characterized in that the threshold speed is equal to 20% of the maximum speed possible for the electric motor.