Patent ID: 12194877

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS.1and2relate to an on-board battery charger in an electric vehicle, and illustrate one exemplary implementation of the AC/DC converter according to the invention.

FIG.1schematically shows an on-board charger1in the electric vehicle, which charger is designed for charging the traction batteries of this electric vehicle by connecting it to the AC electricity grid. Specifically, electric vehicles generally have two possibilities for charging their traction batteries: an external charging terminal comprising its own high-power charger; or an on-board charger such as that ofFIG.1which makes it possible to charge the electric vehicle on a domestic power outlet.

The on-board charger ofFIG.1is intended to be connected to the AC electricity grid like any other electrical appliance and must therefore comply with the standards and regulations in force with regard to the grid. In particular, the charger1comprises means for controlling the absorbed current for the purpose of promoting the stability of the electricity grid to which it is connected.

The charger1comprises an input connector2which is designed to be connected to a domestic power outlet for connection to the AC electricity grid3. In the present example, the charger1is a single-phase charger and the connector2thus comprises two power supply terminals4for the phase and the neutral (in addition to the protective conductor, not shown).

The output of the charger1is connected to the traction batteries of the vehicle, which are represented schematically by the generator5.

The function of the battery charger1is to receive electrical energy from the AC grid3at the input and to apply at the output a DC voltage across the terminals of the batteries5, this voltage being controlled in a known manner as a function of the charging cycle of the batteries5.

The charger1comprises here an AC/DC converter8and a DC/DC converter9. The AC/DC converter8has the function of converting the AC voltage from the grid into a fixed DC voltage, the value of which is 400 volts in the present example. The AC/DC converter8delivers this DC voltage to the DC/DC converter9which will intelligently control the charging of the batteries5while supplying a DC voltage to the batteries5, this voltage adapting to the needs of the batteries5as a function of the charging cycle. The DC/DC converters9designed to control the charging cycles of the batteries are known and will not be described in more detail here.

The AC/DC converter8comprises at input the connector2, a switching module6and a control module7.

The switching module6comprises, in a known manner, a rectifier assembly, as well as switching means linked to coils and capacitors, making it possible to generate a DC voltage. The switching means are generally constituted by a bridge of power switches such as power MOSFET or IGBT transistors.

The switching module6is controlled by the control module7.

In practice, the control module7is here constituted of a microcontroller which is connected to the grid of power switches of the switching module6and is designed to open or close the power switches according to a program.

Within the control module7, the microcontroller and its programs are arranged to constitute in particular a servo-control device10and a voltage measuring means11. The voltage measuring means11may be constituted by any known means that ensures the function as a voltmeter and that makes it possible to measure the voltage present across the output terminals of the switching module6.

This information on the voltage value across the output terminals of the switching module6is made available to the servo-control device10, which controls the power switches of the switching module6so as to adjust the switching in such a way that the output voltage of the switching module6is equal to a setpoint value, which here is 400 volts.

In a known manner, the AC/DC converter8is a converter with power factor correction and the control module7controls the power switches of the switching module6accordingly.

FIG.2is a curve illustrating the profile of the voltage Umc across the output terminals of the switching module6, and therefore at the output of the AC/DC converter8, as a function of time. This voltage Umc is therefore the voltage delivered by the AC/DC converter8.

The setpoint voltage Vc, which here is 400 volts, is represented inFIG.2by a straight horizontal line, this line corresponding to the setpoint voltage for the servo-control device10.

Taking into account the constraints related to the nature of common electronic components, the real voltage at the output of the AC/DC converter is a voltage which oscillates either side of this setpoint voltage Vc. Furthermore, manufacturing tolerances of the electronic components lead to an uncertainty on the servo control of this voltage which, instead of oscillating exactly like the solid-line curve12, oscillates somewhere between the uncertainty curves Vr-min and Vr-max (dashed inFIG.2).

The gap between the two curves Vr-min and Vr-max corresponds here to the uncertainty generated by the error range of the voltage measuring means11. For example, an error range of 5% corresponds to +20 V for a voltage of 400 V.

FIG.2also shows two thresholds embodied by a straight horizontal line Smin and Smax. The threshold Smin corresponds to the minimum threshold below which the voltage Umc must not drop in order for the AC/DC converter8to be able to fulfill its function of power factor correction, and the threshold Smax corresponds to the voltage withstand threshold of the electronic components.

For example, in a country where the RMS grid voltage is 230 V with a tolerance of 15%, the maximum peak voltage will be (230 V+15%)×√2, that is to say 375 V. The DC voltage at the output of the AC/DC converter must therefore be greater than 375 volts in order for the function of power factor correction to be ensured. The threshold Smin is therefore fixed at 375 V in this example.

The threshold Smax is, for example, 440 volts in this example. Components with such a voltage threshold are common, inexpensive and accurate components.

In the prior art, taking into account the thresholds Smin and Smax led to raising the setpoint voltage Vc, for example to a value of around 410 to 420 volts, so as to guarantee that the low uncertainty curve Vr-min is above the threshold S-min. This led to the possibility of the high uncertainty curve Vr-max exceeding the threshold Smax, reaching, in critical cases, 450 volts, and therefore damaging the components (this is the case illustrated inFIG.2where the high uncertainty curve Vr-max may exceed the threshold Smax).

The invention makes it possible to overcome the uncertainty limits Vr-max and Vr-min by positioning the curve12of the voltage Umc as accurately as possible such that it is systematically positioned between the thresholds Smin and Smax.

To this end, at the end of production of an AC/DC converter8, or of the complete charger1, a method for calibrating the AC/DC converter8is implemented.

In a context of mass production in a factory, these operations will preferably be performed when the assembly of the charger1and its connection to the batteries5have been completed, with in particular covers and safety locks preventing operator access to voltages that present a risk of electrocution, the connection between the output of the AC/DC converter8and the input of the DC/DC converter9being in particular inaccessible.

The calibration method starts by connecting the input connector2to an accurate DC power supply making up part of the production line. This power supply delivers a predetermined DC voltage between the power supply terminals4. This step is a counter-intuitive use of the input connector2, which is normally provided for the AC electricity grid, but this step is performed in a context of production, outside of its recommended use for the end user.

The predetermined DC voltage may be any voltage whose value is known to a satisfactory degree of accuracy. This satisfactory degree of accuracy must in particular be greater than the accuracy of the measuring means11, for example an accuracy of better than +1%. Preferably, the predetermined DC voltage is close to the setpoint voltage Vc, or even equal to this setpoint voltage Vc. In the present example, this predetermined DC voltage is 400 volts and is applied across the power supply terminals4by a power supply whose accuracy is 400 V+0.2%, which is a common accuracy for a laboratory power supply.

During this first step, the power switches of the switching module are not activated because the voltage at the input of the converter is, unlike its normal operation, already DC. The predetermined DC voltage is found in the exact same way across the output terminals of the AC/DC converter8, except that it is influenced by the electronic components that are present in the switching module6with their manufacturing and assembly tolerance.

During a second step, the voltage present across the output terminals of the converter8by virtue of the measuring means11, this voltage being called resulting calibration voltage Vr. The voltage Vr corresponds to the voltage which is effectively present at the output of the switching module6, when the predetermined DC voltage is applied at the input. The resulting voltage Vr would be equal to the predetermined DC voltage if the assembly was perfect. In the actual assembly, the measured resulting voltage Vr will be different from the predetermined DC voltage and will encompass the measurement error specific to the voltage measuring means11, taking into account its accuracy.

For the example, it will be assumed that:the predetermined DC voltage is 400 volts;the measured resulting voltage Vr is 405 volts.

Taking into account the difference between 405 V and 400 V will make it possible to calibrate the converter8so as to ensure the correct positioning of the curve12(FIG.2) of this particular converter, between the thresholds Smin and Smax.

During a third step, the AC/DC converter8is calibrated by calibrating only the voltage measuring means11. The voltage measuring means is calibrated by modifying its calibration such that the currently measured resulting voltage Vr (405 V in the example) corresponds to the predetermined DC voltage (400 V in the example). In other words, the calibration of the voltage measuring means will cause the latter to indicate a voltage equal to the predetermined DC voltage (400 V in the example) when it is in the presence of a voltage equal to Vr (405 V in the example).

Within the voltage measuring means11, the resulting voltage Vr is thus calibrated to the level of the predetermined DC voltage (the resulting voltage Vr is brought back to the level of the predetermined DC voltage, from the point of view of the voltage measuring means).

The voltage measuring means11will be deliberately deregulated so as to cause it to measure a value equal to the predetermined DC voltage while it is in the presence of the resulting calibration voltage Vr (which would be the case if the components were perfect).

According to the example mentioned above, after calibration, when the voltage measuring means11is in the presence of a voltage of 405 volts, it will deliver information to the control module7, according to which information the measured voltage is 400 volts.

The calibration of the voltage measuring means11therefore causes the latter to give voltage values to the servo-control device10which are false in absolute terms, but this will lead the servo control to proceed in the same way and to produce a curve12of the same profile, but whose positioning in height will be different because the setpoint voltage Vc will be better centered. Thus, regardless of the positioning of the curve12before the calibration, this curve is re-centered by the calibration between the two extreme thresholds Smin and Smax. The setpoint voltage, and therefore the gap between the uncertainty curves Vr-min and Vr-max, is thus also centered between the two extreme thresholds Smin and Smax, such that there is no risk of crossing one of these thresholds.

The calibration method is concluded by storing this calibration of the voltage measuring means11in the microcontroller, a calibration which could be kept for the entire lifetime of the charger1.

However, during maintenance phases, it is also possible to implement this calibration method again so as to re-center the setpoint Vc again between the thresholds Smin and Smax, in response to a drift of the components related for example to the aging of these components.

To implement the method that has just been described, the control module7comprises at least the following two modes:a nominal mode of operation in which the input connector2is connected to the AC electricity grid and the servo-control device10proceeds with the servo control, at a setpoint voltage Vc, of the DC voltage delivered by the switching module6;a calibration mode in which the input connector2is connected to a predetermined DC voltage power supply, and the voltage measuring means11is calibrated by a calibration bringing the resulting voltage delivered by the switching module6back to the level of the predetermined DC voltage.

These modes can be programmed in a microcontroller constituting the control module7, the microcontroller being programmed to switch from the nominal mode of operation to the calibration mode by an external command or when the connection to a power supply delivering the predetermined DC voltage is detected.

Variant embodiments may be implemented without departing from the scope of the invention. For example, the charger1may be provided for the three-phase grid, the input connector2then comprising four phases.