METHOD FOR DETECTING A REVERSE CURRENT IN A SWITCHING STRUCTURE SUPPLYING AN INDUCTIVE LOAD

• US 20190310323A1
• Filed: 12/18/2017
• Published: 10/10/2019
• Est. Priority Date: 12/20/2016
• Status: Active Grant

• Current Assignee: Vitesco Technologies GmbH (Continental AG)
• Original Assignee: Continental Automotive France (Continental AG), Continental Automotive GmbH (Continental AG)
• Inventors: Pasqualetto, Angelo
• Granted Patent: US 10,514,427 B2
• Time in Patent Office: Days
• CPC Class Codes: G01R 19/14 Indicating direction of current; Indicating polarity of voltage
• CPC Class Codes: G01R 31/40 Testing power supplies testing photovoltaic devices H02S50/10
• CPC Class Codes: G01R 31/42 AC power supplies

Abstract

A method for detecting a reverse current in a switching structure supplying power to an inductive load, having at least one switch and linked to an electric power source and to a ground for a control phase in which the current from the source supplies power to the load in accordance with a given duty cycle and a freewheeling phase in which the induced current from the load is decreasing, the reverse current being liable to be created during a freewheeling phase following a high duty cycle in a previous control phase creating a counter-electromotive force (cemf). The cemf is approximated proportionally to the integration of the duty cycle (integ[Dut cycl]) as a function of time (t), the reverse current either being calculated as a function of the estimated cemf or a reversal of the current criterion being established.

Claims

1. A method for detecting a reverse current in a switching structure supplying power to an inductive load, the switching structure comprising at least one power switch and being designed to drive a current in the load in accordance with a duty cycle, the switching structure being linked firstly to an electric power source (Vps) and secondly to a ground (mas) in order to control the inductive load, the method comprising a control phase in which the current from the power source (Vps) supplies power to the inductive load in accordance with a given duty cycle and a freewheeling phase in which the induced current from the inductive load decreasing, the reverse current being liable to be created in the switching structure during a freewheeling phase following a high duty cycle in a previous control phase creating a counter-electromotive force (cemf) in the inductive load t, wherein the counter-electromotive force (cemf) at a given instant is approximated as being substantially proportional to an integration of the duty cycle (integ[Dut cycl]) as a function of time, the reverse current either being calculated as a function of an estimated counter-electromotive force (cemf) or a reversal of a current criterion being established.

2. The method as claimed in claim 1, wherein the approximation of the counter-electromotive force (cemf) is calibrated with respect to the inductive load, and a coefficient of integration for the duty cycle is defined.

3. The method as claimed in claim 2, wherein an integration of the duty cycle of rank n integ[Dut cycl(n)] is defined by an integration of the previous duty cycle of rank n−

1;

integ[Dut cycl(n−

1)] and by the duty cycle of rank n dut cycl(n) according to the following equation, a being the coefficient of integration;

Integ[Dut cycl(n)]=a·

intea[Dut cycl(n−

1)]+(1−

a)·

dut cycl.

4. The method as claimed in claim 3, wherein, when a reversal of the current criterion is established, a gradient limit p on a curve of the integration of the duty cycle (integ[Dut cycl]) is estimated and a limit value b corresponding to the gradient limit for a temporal granularity g is set according to the equation:

b=p·

g

a current reversal criterion in relation to a difference between the integration of the duty cycle of rank n integ. Dut cycl (n) and the integration of the duty cycle of rank n−

1;

integ[Dut cycl(n−

1)] is then defined, and when this difference is less than −

b for an integration of the positive duty cycle, that is to say;

Integ[Dut cycl(n)]−

integ[Dut cycl(n−

1)]<

+b

or when this difference is greater than +b for an integration of the negative duty cycle, that is to say;

Integ[Dut cycl(n)]−

integ[Dut cycl(n−

1)]>

+b

it is estimated that a current reversal is effective.

5. The method as claimed in claim 4, wherein the limit b is able to be calibrated in accordance with the selected temporal granulometry and in accordance with the inductive load that is used as well as the frequency of the signal of a pulse width modulation.

6. The method as claimed in claim 1, wherein, when the reverse current I is calculated, this calculation is performed based on a current expressed as a function of the estimated counter-electromotive force cemf, of the measured voltage of the power source Vps, of the duty cycle dut cycl and of the resistance of the circuit R according to the following equation:

I=(dut cycl·

Vps−

cemf)/R.

7. An assembly of an inductive load and its electric power supply device, the power supply device comprising a switching structure comprising at least one power switch and being associated with a control unit comprising means for driving a current in the load in accordance with a pulse width modulation duty cycle, the switching structure being linked firstly to an electric power source (Vps) and secondly to a ground (mas), wherein the assembly implements a method for detecting a reverse current in the switching structure as claimed in claim 1, the control unit comprising means for integrating the duty cycle (integ[Dut cycl]), means for approximating a counter-electromotive force (cemf) as a function of the integration of the duty cycle (integ[Dut cycl]), means for calculating the reverse current from the approximation of the counter-electromotive force (cemf) or means for detecting a current reversal as a function of a reversal criterion kept in memory means of the control unit, the control unit also comprising means for transmitting current reversal information.

8. The assembly as claimed in claim 7, wherein the switching structure is an H-bridge.

9. The method as claimed in claim 2, wherein, when the reverse current I is calculated, this calculation is performed based on a current expressed as a function of the estimated counter-electromotive force cemf, of the measured voltage of the power source Vps, of the duty cycle dut cycl and of the resistance of the circuit R according to the following equation:

I=(dut cycl·

Vps−

cemf)/R.

10. The method as claimed in claim 3, wherein, when the reverse current I is calculated, this calculation is performed based on a current expressed as a function of the estimated counter-electromotive force cemf, of the measured voltage of the power source Vps, of the duty cycle dut cycl and of the resistance of the circuit R according to the following equation:

I=(dut cycl·

Vps−

cemf)/R.