Power supply of an electric motor

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.

Claims

1. A power supply system for an electric motor comprising: a power circuit, the input terminals of which are connected to a DC voltage source; an electronic circuit for controlling the electric motor depending on a control signal representing a set speed of the motor; a MOSFET transistor forming a safety switch which, in a closed position, allows connection of the power circuit to said DC voltage source; and a controller that controls a gate of the MOSFET transistor able to set said transistor in the closed position in a saturated operation mode for a set speed higher than said threshold speed, or in a closed position in a linear operation mode for a set speed less than a threshold speed, wherein the MOSFET transistor is able to reduce the value of the DC voltage received by the power circuit during starting of the electric motor and/or during the operating phases where the set speed of the electric motor is less than the threshold speed.

2. The power supply system as claimed in claim 1, wherein said value of the DC voltage received by the power circuit corresponds, during starting of the electric motor and/or during the operating phases where the set speed of the electric motor is less than a threshold speed, to the DC voltage supplied by the source reduced by a value increasing linearly as a function of the set speed.

3. The power supply system as claimed in claim 1, wherein, in said linear operation mode, the MOSFET transistor is controlled so as to produce, between the drain and the source, a voltage increasing linearly as a function of the set speed.

4. The power supply system as claimed in claim 1, wherein said control means comprises a microcontroller designed to generate a Pulse Width Modulation (PWM) signal proportional to the set speed.

5. The power supply system as claimed in claim 1, wherein said control means comprises an electronic circuit.

6. The power supply as claimed in claim 1, wherein said electronic circuit is formed by a chopper power supply circuit.

7. The power supply system as claimed in claim 1, designed to power a brushless electric motor, wherein the threshold speed is equal to 20% of the maximum possible speed of the electric motor.

Description

(1) Further characteristic features and advantages of the invention will emerge clearly from the description thereof which is provided below, by way of a non-limiting example, with reference to the attached figures in which:

(2) FIG. 1 is a simplified schematic representation of a power supply system of an electric motor according to the prior art;

(3) FIG. 2 is a simplified schematic representation of a power supply system of an electric motor according to a possible embodiment of the invention;

(4) FIG. 3 shows in schematic form a preferred mode of implementation allowing a reduction in the value of the DC voltage value received by the power circuit in FIG. 1;

(5) FIG. 4 shows, by way of example, the power supply voltage supplied as a function of the operating phases of the electric motor.

(6) FIG. 1 was described further above with reference to the prior art. FIG. 2 is a simplified diagrammatic representation of a power supply system of an electric motor 1 according to the invention.

(7) This comprises, as explained above within the context of the prior art:

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

(9) an electronic control circuit 4 intended to power the motor 1 depending on a control signal representing the set speed of the motor, and

(10) preferably, a safety switch 5 allowing the battery to be connected selectively to the power circuit 3 and to the electronic control circuit 4.

(11) As mentioned further above, during conventional operation, namely 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 supplied by the vehicle battery, typically in the region of 13 volts.

(12) The tests carried out by the Applicant have been able to show that the sound emissions, in particular those associated with the stator windings in the case of a brushless motor, are proportional to the value of the DC power supply voltage.

(13) Based on this finding, it is proposed to provide the power supply system with a control module 6 such that the system is able to reduce the value of the DC voltage received by the power circuit during the operating phases of the motor where the sound emissions are the loudest, typically during starting of the electric motor and/or during the operating phases where the set speed of the electric motor is less than a threshold speed.

(14) The role of the control module 6, which is represented here schematically in the form of an electronic circuit arranged between the safety switch 5 and the input of the power circuit 3 is therefore that of:

(15) allowing the power circuit 3 to be powered by the DC voltage output by the battery when the set speed for the motor is greater than the threshold speed and

(16) reducing otherwise the DC voltage value, preferably by a value increasing linearly as a function of the set speed.

(17) A large number of electronic or software operations may be implemented in order to ensure such a control of the power supply voltage value.

(18) FIG. 3 shows a particularly ingenious implementation arrangement where the best possible use is made of the components already available in the system, in particular the MOSFET transistor 5 used as safety switch for interrupting the power supply in the event of overheating, or for putting the system on standby.

(19) In accordance with the embodiment of the invention, the way in which the transistor gate is controlled is modified so that it is not used as a simple switch. More specifically, the transistor which hitherto was used only in saturated mode, whatever the set speed, will now be driven depending on the set speed so as to:

(20) operate in a conventional saturated condition when the set speeds are higher than the threshold value;

(21) operate otherwise in a linear manner otherwise, so as to reduce the value of the voltage actually supplied to the circuit 3 by a value increasing linearly as a function of the set speed.

(22) This principle is illustrated in FIGS. 3 and 4. When the transistor 5 is in a saturated operation zone, the circuit downstream of the transistor receives in a conventional manner the power supply +BAT output by the battery. This zone corresponds to the part 2 in FIG. 4.

(23) On the other hand, when the transistor 5 is in its linear operation zone, it generates a non-zero voltage V_SW between its drain and its source, so that the downstream circuit receives the voltage:
+BAT−V_SW

(24) The part 1 in FIG. 4 shows the variations in voltage received by the circuit 3 as a function of the set speed of the motor. In the example shown, the threshold speed is in the region of 20% of the maximum speed possible for the electric motor.

(25) The control signal SW_CMD is generated by the module 6 depending on the set speed S.sub.CONS.

(26) The control module 6 may be entirely software-based, being managed for example by a microcontroller able to generate, for linear operation, a Pulse Width Modulation (PWM) signal which is proportional to the set speed.

(27) By way of a variant, a specific electronic circuit able to generate a command proportional to the set speed may also be used.

(28) In both cases a feedback loop may be added for regulation purposes.