Method for controlling the input voltage frequency of a DC-DC convertor

Abstract

A method for controlling the input voltage frequency of a DC-DC converter includes calculating a control frequency value of the DC-DC converter. If the measured voltage is greater than the upper voltage limit, the control frequency corresponds to the minimum control frequency. If the measured voltage is less than the lower voltage limit, the control frequency corresponds to the maximum control frequency. If the measured voltage is between the upper voltage limit and the lower voltage limit, the control frequency corresponds to an average frequency calculated as a function of the difference between the setpoint voltage value and the measured voltage, upper error values and lower error values, and maximum and minimum control frequency values.

Claims

1. A method comprising: controlling frequency of an input voltage of an LLC DC current to DC current converter operating with a duty cycle of 50% and controlled in terms of frequency, by defining a maximum control frequency value and a minimum control frequency value; defining a setpoint voltage value; defining an upper error value and an associated upper limit voltage value and a lower error value and an associated lower limit voltage value, said upper and lower limit voltage values defining an error amplitude around said setpoint voltage value; obtaining a measured value of the input voltage; and calculating a control frequency value of said DC current to DC current converter, wherein: when the measured input voltage is greater than said upper limit voltage, the control frequency corresponds to said minimum control frequency; when the measured input voltage is lower than said lower limit voltage, the control frequency corresponds to said maximum control frequency; and when the measured input voltage is between said upper limit voltage and said lower limit voltage, the control frequency corresponds to an average frequency calculated based on a difference between the setpoint voltage value and the measured input voltage, the upper and lower error values and the maximum and minimum control frequency values.

2. The method as claimed in claim 1, wherein, when the measured input voltage is between said upper limit voltage and said lower limit voltage, the control frequency is calculated by applying the following equation: $F_{\mathrm{MOY}}=\frac{\left(\mathrm{error}+\mathrm{eps}\right)*{\mathrm{FR}}_{\mathrm{MAX}}-\left(\mathrm{error}-\mathrm{eps}\right)*{\mathrm{FR}}_{\mathrm{MIN}}}{2*\mathrm{eps}}$ in which the value error corresponds to the difference between the setpoint voltage value and the measured input voltage, eps is the upper error value, FR.sub.MAX is the maximum control frequency value, FR.sub.MIN is the minimum control frequency value.

3. The method as claimed in claim 1, wherein a control operation is controlled at least in part by an open-loop controller.

4. The method as claimed in claim 3, wherein the control operation is controlled in terms of frequency by a proportional-integral controller only when the measured input voltage is between said upper limit voltage and said lower limit voltage.

5. A device comprising: circuitry configured to control frequency of an input voltage of an LLC DC current to DC current converter operating with a duty cycle of 50% and controlled in terms of frequency, by defining a maximum control frequency value and a minimum control frequency value, defining a setpoint voltage value, defining an upper error value and an associated upper limit voltage value and a lower error value and an associated lower limit voltage value, said upper and lower limit voltage values defining an error amplitude around said setpoint voltage value, obtaining a measured value of the input voltage, and calculating a control frequency value of said DC current to DC current converter, wherein: when the measured input voltage is greater than said upper limit voltage, the control frequency corresponds to said minimum control frequency, when the measured input voltage is lower than said lower limit voltage, the control frequency corresponds to said maximum control frequency, and when the measured input voltage is between said upper limit voltage and said lower limit voltage, the control frequency corresponds to an average frequency calculated based on a difference between the setpoint voltage value and the measured input voltage, the upper and lower error values and the maximum and minimum control frequency values.

6. A charger to charge an electric accumulator battery, the charger comprising: a power factor correction stage; an LLC resonant DC current to DC current converter; and a device including circuitry configured to control frequency of an input voltage of the LLC resonant DC current to DC current converter operating with a duty cycle of 50% and controlled in terms of frequency, by defining a maximum control frequency value and a minimum control frequency value, defining a setpoint voltage value, defining an upper error value and an associated upper limit voltage value and a lower error value and an associated lower limit voltage value, said upper and lower limit voltage values defining an error amplitude around said setpoint voltage value, obtaining a measured value of the input voltage, and calculating a control frequency value of said DC current to DC current converter, wherein: when the measured input voltage is greater than said upper limit voltage, the control frequency corresponds to said minimum control frequency, when the measured input voltage is lower than said lower limit voltage, the control frequency corresponds to said maximum control frequency, and when the measured input voltage is between said upper limit voltage and said lower limit voltage, the control frequency corresponds to an average frequency calculated based on a difference between the setpoint voltage value and the measured input voltage, the upper and lower error values and the maximum and minimum control frequency values.

Description

(1) Other features and advantages of the invention will become apparent on reading the description given below of one particular embodiment of the invention, given by way of indication but without limitation, with reference to the appended drawings, in which:

(2) FIG. 1 is a schematic view of an electric battery charger known from the prior art;

(3) FIG. 2 is a detailed view of a DC current to DC current converter for a charger according to FIG. 1;

(4) FIG. 3 is a simplified diagram of an LLC circuit of a DC current to DC current converter according to FIG. 2;

(5) FIG. 4a is a schematic depiction of the method according to one embodiment of the invention;

(6) FIG. 4b is a detailed view of a calculation step of the method according to the embodiment of FIG. 4a;

(7) FIG. 5 is a schematic depiction of the applied frequency control of the method, with time on the abscissa and volts on the ordinate, as a function of the limit voltages, the setpoint voltage and the measured voltage, of the calculation step of the method according to the embodiment of FIG. 4a; and

(8) FIG. 6 is a flowchart of the method implemented according to the embodiment of FIG. 4a.

(9) FIGS. 1 to 6 relate to the same embodiment and will be commented upon at the same time.

(10) With reference to FIG. 1, an electric battery 13 charger 1 connected to a three-phase electricity grid 10 comprises a power factor correction stage 11, also called PFC stage 11, and DC current to DC current converters DC-to-DC 12a and 12b each having an inverter 212.

(11) The three-phase electricity grid 10 is fitted on an input filter 14 transmitting filtered input currents to the PFC stage 11.

(12) At the output of the PFC 11, two DC voltage buses, connected to the terminals of the output capacitors of the PFC stage 11, are each coupled to a DC-to-DC converter 12a, 12b, connected at output in parallel with an accumulator battery 13.

(13) Each DC-to-DC 12a, 12b, just one example of which is shown in FIG. 2, comprises an input MOSFET bridge 120, an LLC circuit 121, a simplified circuit diagram of which is shown in FIG. 3, a transformer 22 and an output diode bridge 122.

(14) The charger 1 furthermore comprises means 15 for controlling the DC current to DC current converters 12, able to implement a control method 60 according to the invention.

(15) The control method 60 according to the invention aims to control the frequency of the input voltages of the DC current to DC current converters 12.

(16) With reference to FIGS. 4, 5 and 6, the method for controlling a DC current to DC current converter comprises a plurality of preliminary steps 61, 62, 63. These preliminary steps 61-63 are independent of one another. The preliminary steps 61-63 aim to define operating parameters of the method; they may be performed before the method is implemented, for example in a calibration phase, or dynamically at the start of the method.

(17) These preliminary steps 61-63 may furthermore be reproduced during the operation of the method 60 in order to dynamically modify the operating parameters of the method.

(18) First of all, a step of defining 61 a maximum control frequency value FR.sub.MAX and a minimum control frequency value FR.sub.MIN is implemented, for example in this case a maximum frequency FR.sub.MAX of 200 kHz, and a minimum frequency FR.sub.MIN of 60 kHz.

(19) A step of defining 62 a setpoint voltage value V.sub.DCM towards which the input voltage should converge is then implemented. In the exemplary embodiment of FIG. 5, V.sub.DCR=450 V.

(20) An error zone 51, defined by two error values, an upper error value eps and a lower error value −eps, is then defined 63, these two error values making it possible to define an upper limit voltage value V.sub.DRC+eps and a lower limit voltage value V.sub.DCR−eps.

(21) In this exemplary embodiment, an error voltage +eps=100 V and −eps=−100 V is defined.

(22) These upper V.sub.DCR+eps and lower V.sub.DCR−eps limit voltage values framing the setpoint voltage V.sub.DCR thus define an error amplitude around the setpoint voltage V.sub.DCR.

(23) In this embodiment, the upper error value eps and lower error value −eps have the same absolute value, so as to define a symmetrical error zone around the setpoint voltage value V.sub.DCR. However, the invention is not limited to these absolute values being the same, and there may be provision for an upper error value eps and a lower error value −eps having different absolute values.

(24) The method then implements a step of obtaining 64 a measured value of the input voltage V.sub.DCM.

(25) A step of calculating 65 a control frequency value of the DC current to DC current converter is then implemented.

(26) In this calculation step 65, the measured input voltage V.sub.DCM is compared with the upper V.sub.DCR+eps and lower V.sub.DCR−eps limit voltage values.

(27) If the measured voltage V.sub.DCM is greater than or equal to said upper limit voltage V.sub.DCR+eps, then a control frequency F equal to said minimum control frequency FR.sub.MIN is applied.

(28) If the measured voltage V.sub.DCM is less than or equal to the lower limit voltage V.sub.DCR−eps, then a control frequency F equal to the maximum control frequency FR.sub.MAX is applied.

(29) Lastly, if the measured voltage V.sub.DCM is strictly between said upper limit voltage V.sub.DCR+eps and said lower limit voltage V.sub.DCR−eps, the control frequency F corresponds to an average frequency F.sub.MOY that is calculated on the basis of the difference between the measured voltage and the setpoint voltage, the values of the upper and lower limit errors and the values of the maximum and minimum control frequency.

(30) This average frequency F.sub.MOY is calculated using the following equation:

(31) $F_{\mathrm{MOY}}=\frac{\left(\mathrm{error}+\mathrm{eps}\right)*{\mathrm{FR}}_{\mathrm{MAX}}-\left(\mathrm{error}-\mathrm{eps}\right)*{\mathrm{FR}}_{\mathrm{MIN}}}{2*\mathrm{eps}}$ in which: the value error corresponds to the difference between the setpoint voltage value V.sub.DCR and the measured voltage V.sub.DCM, that is to say error=V.sub.DCR−V.sub.DCM.

(32) In other words, the pair of error parameters −eps, eps makes it possible to define an error zone close to the setpoint V.sub.DCR, in which the control means calculate a frequency F.sub.MOY that makes it possible to converge precisely on the setpoint value V.sub.DCR.

(33) Specifically, when the error V.sub.DCR−V.sub.DRM reaches one of the thresholds −eps, eps, a control frequency is calculated so as to precisely reach the setpoint and cancel out the static error.

(34) Above or below this error zone, respectively, the minimum frequency FR.sub.MIN or maximum frequency FR.sub.MAX is applied as described by the following logic in order to ensure effective convergence.

(35) With reference to FIG. 4a, a proportional integral controller 42, more commonly called PI controller, is activated when the measured voltage V.sub.DCM is strictly between said upper limit voltage V.sub.DCR+eps and said lower limit voltage V.sub.DCR−eps. This makes it possible to refine the calculation of the frequency F to be applied and improves convergence of the measured voltage over a few volts.

(36) The output of the first control stage 41 therefore arrives as what is called a feed-forward open-loop control command and is added 43 to the results obtained by the PI controller 42.