FR2693321A1 - On-board electric vehicle battery charger drawing sinusoidal current at unity power factor - uses high frequency converter with pulse width modulation to switch rectifier-transformer primary circuit - Google Patents

Abstract

The converter (AA), interposed between the single phase or three-phase mains supply (Sv) and the rectifier-transformer (TR) primary (P1,P2), contains series (Ta) and shunt (Tb) connected transistor switches, opened and closed alternately by the controller (CD), the pulse width varying with the supply voltage (Ve). Short-circuit current is limited by locally augmenting the system impedance (L). The controller produces appropriate pulses by comparing a saw-tooth waveform, internally generated at, e.g. 50 kHz, with the 50 Hz supply waveform (Ve), and so applies them to the converter switches so that the current (I) supplied by the source (Se) is always of the same frequency as the source voltage, and in phase with it. Several variants are described. USE/ADVANTAGE - Esp. for on-board chargers for electric vehicles. Compact, with good waveform and power factor, optimising charge time.

Description

BATTERY CHARGER
The invention relates to battery chargers, in particular for vehicles with an electric motor.

Battery chargers are generally intended to be supplied from the electrical energy distribution network which supplies a single-phase or polyphase alternating voltage. Also, they must first be designed so as to comply with the standards in force aimed at limiting the production of harmonic currents which disturb the network. Compliance with these standards as well as the search for good efficiency have the effect that a power factor very close to 1 must be obtained. In addition, if the charger is intended to be loaded in the vehicle, it should be that its weight and its size are as small as possible.

Conventional chargers use a transformer inserted between the network which constitutes a voltage source and a rectifier. Under these conditions, the transformer operates at low frequency and is therefore bulky. In addition, the absorbed current is rich in harmonics at low frequency and the fundamental of the current is strongly out of phase with respect to the voltage. If the source is also limited in current, the possibilities of charging are reduced and the charging time is important.

 There are more complex chargers for improving performance. One can for example directly rectify the network voltage by means of diodes, the DC voltage obtained is then filtered then rippled at high frequency by a second converter. A transformer performs the voltage adaptation and galvanic isolation. The transformer secondary voltage is then rectified. This solution notably limits the size of the transformer but requires the installation of several converters and the absorbed current, although in phase with the voltage, remains strongly disturbed.

The previous solutions lead to non-sinusoidal current absorption. The power factor of the converter is then significantly less than 1, which leads to a high charging time.

The invention aims to remedy the above drawbacks by proposing a battery charger having the following properties - the absorbed current is sinusoidal and in phase with the
voltage, the power factor being substantially
unitary in order to optimize the charging time, and
reduce conducted disturbances; - the transformer operates at high frequency thanks to
to a single direct converter designed to avoid
the addition of additional capacities, which
leads to a high specific power.

To this end, the subject of the invention is a battery charger intended to be connected to a power source equivalent to an alternating voltage source having at least one phase and having an inductive internal impedance, characterized in that it comprises - a converter comprising input terminals
intended to be linked to said source
supply and output terminals, - a transformer comprising at least one winding
primary and secondary winding, the said one or more
primary windings being connected to the terminals of
output of the converter, - rectifier means mounted between said one or more
secondary windings and the battery to be charged, - a control circuit for said converter ,.

in that said converter comprises controlled switch means arranged so as to allow supply phases to establish the supply of at least one of the primary windings by the supply source and short-circuit phases to put in short -circuit the power source and in that said control circuit controls said switch means by high frequency pulses so that the durations and the sequencing of the supply and short-circuit phases ensure that the harmonic fundamental of the voltage present at the input terminals of the converter has the same frequency as the voltage of the voltage source with a phase and an amplitude such that the fundamental harmonic of the current flowing in the power source is in phase with the voltage from the voltage source.

The high frequency cutting of the current flowing in the transformer makes it possible to limit its size.

To obtain optimal use of the transformer, avoid saturation of its magnetic circuit.

For this, it suffices that the currents flowing in the primary windings of the transformer do not have a continuous component.

For this purpose and according to an additional characteristic of the invention, the battery charger is characterized in that said switch means are arranged so as to be able to impose the polarity of the voltage applied to the terminals of the primary winding (s) independently of the polarity of the voltage of the power source and in that the control circuit is designed to cause an inversion of said polarity at each new power phase.

In the case where the charger is supplied by the electrical energy distribution network, according to an additional characteristic of the invention, provision may be made to increase, if necessary, the inductive effect of its internal impedance by connecting an inductive impedance in series in each of its phases.

Advantageously and according to yet another aspect of the invention, the supply phases are represented by a pulse signal at fixed frequency and modulated in width.

Other characteristics of the invention relating in particular to particular structures of the converter and its control circuit will appear in the following description with reference to the figures - FIG. 1 is a schematic representation of the
charger according to the invention in the case of a
single-phase power; - Figure 2 is another schematic representation
in the case of a three-phase supply; - Figures 3 to 6 show several variants of
structures of the converter usable for the setting
of the invention; - Figures 7 and 8 show two examples of
realization of controlled switches usable in
the converter; - Figure 9 is the complex representation of
low frequency voltages and current supplying the
converter;; - Figure 10 is a timing diagram representing the
electrical quantities of FIG. 9; - Figure 11 shows the timing diagrams of
different electrical quantities allowing
to explain the operation of the charger according to the invention; - Figure 12 shows the overall diagram of a
converter control circuit; - Figures 13 to 19 show examples of
realization of the circuits constituting the circuit of
ordered; - Figure 20 shows timing diagrams allowing
explain the operation of the control circuit.

The converter according to the invention shown in FIG. 1 is supplied by a single-phase power supply Sv consisting of a voltage source Se connected in series with an inductor L. In practice, the voltage source Se is the distribution network of electrical energy supplying a sinusoidal voltage Ve having for example an effective value of 220 Volts and a frequency of 50 Hertz. The inductance L corresponds to the internal impedance of the network to which the inductance of an additional inductor connected in series with the network is added. The value of this self can be determined experimentally by analyzing the shape of the absorbed current.

The power source Sv is connected to the input terminals B1, B2 of a converter AA made up of controlled switches Ta, Te. The output terminals
B3, B4 of the converter AA are connected to the primary windings P1, P2 of a transformer TR.

The power source Sv injects into the converter AA an instantaneous current i under the instantaneous voltage v present between the input terminals B1, B2.

The switches Ta, Te of the converter AA are controlled by a control circuit CD providing pulses modulated in width as a function of the supply voltage Ve and possibly of the effective value I of the fundamental harmonic at 50 Hertz of the instantaneous current i , and of the phase of the current i with respect to ve.

The secondary windings S1, S2 of the transformer TR are connected to the battery to be charged B by means of a semiconductor rectifier AC.

The rectifier AC can generally consist of simple diodes although, in certain cases, provision may be made for the use of switches controlled by the control circuit CD.

As we will see in detail later, the invention can be implemented by means of numerous variant embodiments, both with regard to the structure of the converter AA and that of the transformer TR, the primary and secondary of which may include one or more windings linked together by a midpoint M, N. Depending on the type of transformer TR used, the converter AA will have a structure such that the controlled switches which constitute it can establish supply and short-circuit phases respectively allowing the supply of at least one primary winding by the source. Sv and the short-circuiting of this same source. Depending on the structure chosen, the control circuit CD will be designed to supply high frequency pulses to control the switches of the converter AA so that the harmonic fundamental V of the voltage v has the same frequency as the sinusoidal voltage Ve of the voltage source Se with a phase and an amplitude such that the fundamental harmonic I of the current i is permanently in phase with the voltage Ve. Various possible embodiments will be explained in detail, by way of illustration, with reference to FIGS. 3 to 6.

Of course, the invention can also be applied to a polyphase system. In this case, it will suffice to provide a polyphase transformer and a converter whose structure allows for each phase operation in accordance with the preceding indications.

FIG. 2 shows by way of example an implementation of the invention in the case of a three-phase system.

The three-phase power source Sv consists of three three-phase voltage sources ea, eb, ec connected in series with the inductances La, Lb, Lc respectively.

The power source Sv is connected to the input of a three-phase converter AA controlled by the control circuit CD. This converter is connected to the primary windings Pa, Pb, Pc of a three-phase transformer TR whose secondary windings Sa, Sb, Sc supply the battery B via a three-phase rectifier AC. The transformer TR shown here has its primary and secondary windings mounted in a star.

Of course, depending on the context of use, it may be necessary to choose other configurations such as triangle-star or triangle-triangle and also provide several windings for each primary and / or secondary phase of the transformer.

Analogously to the single-phase embodiment of FIG. 1, the converter AA is provided with controlled switches arranged so as to allow, for each phase, supply and short-circuit phases in response to the high frequency pulses delivered by the circuit. CD command. For each phase ea, eb, ec, the operation will be analogous to that of the single-phase embodiment, it being understood that the commands associated with a phase are out of phase with respect to the other two of + 2fi / 3 and -2ff / 3.

We will set out in the following description several possibilities for producing a single-phase system whose transpositions into three-phase and polyphase versions can be easily deduced by those skilled in the art.

The first embodiment shown in Figure 3 uses a transformer whose primary and secondary have a double winding at midpoint M, N. The converter consists of four switches Ta, Tb, Tc, Td, the switches Tc and Td being connected respectively in parallel with the two primary windings of the transformer. The switches Ta and Tb are connected in series and this assembly is connected in parallel with the series assembly formed by the switches Tc and Td. The power source Sv is connected between the midpoint M of the primary and the common terminal B1 to the switches
Ta, Tb. The point common to the switches Tc, Td which is connected to the midpoint M of the primary constitutes the second input terminal B2 of the converter, while the other two terminals of these switches constitute the output terminals B3, B4. secondary consists of two diodes Da, Db, in a so-called "half-bridge" arrangement according to which the cathodes of the diodes Da, Db are connected to each other as well as to the positive terminal of the battery B whose negative terminal is connected at the midpoint L, the anodes of the diodes Da,
Db being connected respectively to the two other terminals of the secondary windings. The currents flowing respectively in the diodes Da and Db are designated by ia and ib whose positive directions are identified in the figure by two corresponding arrows. As a variant, it is also possible to use a full diode bridge (bridge of
Graetz) if the transformer secondary has a single winding.

The switches Ta, Tb, Tc, Td are controlled respectively by the signals CTa, CTb, CTc, CTd supplied by the control circuit CD. Thus, the supply phases of the primary windings will for example correspond to the closing of the switches
Ta or Tb, while the short-circuit phases correspond to the closing of switches Ta and Tc or switches Tb and Td. As we will see in detail later, the sequences and durations of the control pulses applied to the switches are adjusted so that the fundamental harmonic of the instantaneous voltage v of the power source has the same frequency as the source of voltage while ensuring that the fundamental harmonic I at 50 Hz of the instantaneous current i flowing in the source is in phase with the voltage Ve the voltage source Se.

FIG. 4 represents an alternative embodiment of the converter AA. This embodiment differs from that of FIG. 3 simply by the fact that the switches Tc and Td are replaced by a single switch Te connected in parallel with the power source Sv. The overall operation of the converter remains unchanged but the switch Te is in high demand.

FIG. 5 shows another variant using a transformer with a single primary winding. The converter has only two switches Ta, Te respectively controlling the supply and short-circuit phases. This embodiment simplifies the structure of the converter. However, in the case of a single-phase embodiment, it has the drawback that the rectifier switches must be controllable and bidirectional in current so that the battery can impose the magnetization flux as well as the voltage u during the phases of short circuit.

The assembly shown in Figure 6 uses a single primary winding and a full bridge structure for the converter. Compared to the case presented with reference to FIG. 3, only the phases of injection of current into the transformer differ, those of short-circuit taking place in the same way.

The detailed operation of the converter will be described with reference to FIGS. 17 and 20.

Figures 7 and 8 show two embodiments of the controlled and bidirectional switches that can be used in the AA converter.

The switch of FIG. 7 uses two bipolar npn transistors whose bases receive the control signal CT, whose transmitters are connected together and whose collectors constitute the external terminals of the switch. Two diodes have their anodes connected respectively to the emitters of the two transistors and their cathodes respectively connected to the external terminals of the switch.

The embodiment shown in FIG. 8 has the same structure but the bipolar transistors are replaced by MOS transistors whose gates receive the control signal CT, whose sources are connected together and whose drains constitute the external terminals of the switch .

The operations of the circuits in FIGS. 7 and 8 are identical: when the control signal CT has zero potential, the two transistors are blocked while when the potential is positive only one of the transistors is on and, depending on the polarity of the voltage present between the external terminals of the switch, a current can flow through the passing transistor and one of the diodes.

Figures 9 and 10 will allow us to physically justify the result obtained by the invention. The quantities Ve, V, I are respectively the complex representations of the supply voltage and the fundamental harmonics of the instantaneous voltage v and the instantaneous current i. Assuming that the internal resistance of the network is negligible, we have
V = Ve - jLnI, where n is the pulsation of the supply voltage. As a result, the voltage V must be in phase advance with respect to the supply voltage Ve in accordance with the diagram in FIG. 9. This means that the switches of the converter must be controlled so as to be able to adjust both the phase and the amplitude of the voltage V in order to keep the current I in phase with the supply voltage Ve. The timing diagram of FIG. 10 is another representation of the magnitudes V, Ve and I.

The timing diagrams a to f of FIG. 11 will now allow us to explain the control principle of the converter to obtain the phase and amplitude relationships between V and Ve to achieve the desired goal. The proposed solution consists, for example, in using high frequency width modulated control pulses. A sawtooth generator is then provided providing a sawtooth voltage v2 at the frequency for example of 50 kilohertz which is compared to a signal vl obtained by rectification of a sinusoidal reference signal adjustable in phase and in amplitude and having the same frequency (50 Hz) as the supply voltage Se. As shown schematically in the timing diagram a, this comparison makes it possible to define pulses of variable durations. Depending on this pulse width modulation, the switches of the converter are then controlled so as to impose an instantaneous voltage v at the terminals of the source. feed with the appearance of a timing diagram b. The voltage v is in the form of high frequency pulses whose amplitude is constant in absolute value because imposed by the voltage of the battery. The time intervals during which this voltage is zero and not zero correspond respectively to the short-circuit and supply phases.

Still thanks to an appropriate control of the switches of the converter, the instantaneous voltage u at the primary of the transformer at the speed represented on the timing diagram c. As for the voltage v, the voltage u has the form of high frequency pulses whose amplitude is constant in absolute value, but whose polarity is reversed from one pulse to the other. As a result, the voltage applied to the transformer primary is a high frequency alternating voltage imposed by the frequency of the sawtooth generator.

The timing diagram d represents the instantaneous currents i and it circulating respectively in the power source Sv and in the primary windings of the transformer. It can be seen that the fundamental harmonic of current i is a low frequency current which is in phase advance with respect to the fundamental harmonic of voltage v. On the other hand, the current it is a high frequency alternating current in phase with the voltage u.

The timing diagrams e and f respectively represent the algebraic values of the currents ia, and ib flowing in the diodes Da and Db of the rectifier.

FIG. 12 represents an overall diagram of the converter control circuit. This circuit essentially comprises a generator G of reference signal vr connected to a rectifier 4 supplying the rectified signal vl of the reference signal vr. This circuit also includes a high frequency sawtooth signal generator 6 providing the sawtooth signal v2. The signals v1 and v2 are compared in a comparator 5 supplying a comparison signal H applied to the input of a logic circuit CL which generates control signals C'a, C'b, C'c, C'd applied to the converter switches via isolation 11 and amplification circuits 12, 13.

The generator G comprises a step-down transformer 1, the primary of which is supplied by the supply voltage Ve and the secondary of which supplies a voltage k Ve applied to an adjustable phase shifter circuit 2 itself connected to an adjustable amplifier 3, the output of which provides the reference voltage vr.

The logic circuit CL consists for example of a flip-flop 7 and logic gates 8, 9 possibly supplemented by adjustable delay circuits 10. The logic functions performed by the circuit CL will of course depend on the structure of the type of converter used. Nevertheless, the circuit CL must always define supply phases D1, D2 and short-circuits C1, C2 with a duty ratio proportional to the effective value of the fundamental harmonic V allowing the phase setting of the current I relative to the supply voltage Ve.

FIG. 13 represents an exemplary embodiment of the phase shifter 2. The output voltage kVe of the transformer 1 is applied on the one hand to the inverting input of an operational amplifier by means of a first resistor R1 and on the other hand at its direct input via a variable resistance
R2. The direct input of the amplifier is connected to ground via a capacitor. The output of the amplifier supplying a voltage ve is connected to its inverting input by means of a feedback resistance Ri. Depending on the value of the resistor R2, the phase of the output voltage ve relative to the input k Ve may take a value between 0 and -1800.

FIG. 14 shows an embodiment of the adjustable amplifier 3. The voltage ve from the phase shifter 2 is applied to the inverting input of an operational amplifier via a variable resistor R4. The output of the operational amplifier providing the reference voltage vr is connected to its inverting input via a feedback resistance R3. The direct input of the operational amplifier is connected to ground.

FIG. 15 represents an embodiment of the rectifier 4.

The reference voltage vr is applied to the inverting input of an operational amplifier via a resistor R6. The output of the operational amplifier is connected to its inverting input via a feedback resistor R5. The direct input of the operational amplifier is connected to ground. The output of the operational amplifier is connected to the anode of a first diode, the cathode of which is connected to the cathode of a second diode, the anode of which receives the reference voltage vr. The signal present on the cathodes of the two diodes corresponds to the rectified voltage vl of the reference signal vr.

FIG. 16 represents an embodiment of the comparator 5 consisting of a simple operational amplifier receiving respectively on its direct and inverse inputs the signals v2 and vl and supplying the synchronization signal H. The signal H is applied to the input of a flip-flop JK 7 of the logic circuit CL. An inverter supplies the signal H * in addition to the synchronization signal H. The flip-flop JK supplies the signals Q and Q *.

FIG. 17 shows by way of illustration the logic circuits 8, 9 which produce the signals Ca, Cb, Cc, Cd making it possible to control the switches of the converter shown in FIG. 6.

To facilitate understanding of the operation, the signals supplied by the circuits of FIGS. 16 and 17 are represented in FIG. 20. The timing diagram a represents the signals v1 and v2 supplied respectively by the rectifier 4 and the sawtooth generator 6.

The timing diagram b represents the signal H * complementary to the synchronization signal H which is represented on the timing diagram c. The timing diagram d represents one of the output signals Q of the flip-flop JK 7. The timing diagrams e to h respectively represent the output signals ac to cd of the logic circuit 9 shown in FIG. 17.

The logic circuit 8 in FIG. 17 consists of 4 AND gates with two inputs, the outputs of which supply the signals C1, D2, C2, D1 respectively as a function of the signals H, H *, Q and, Q *. The signal D1 corresponds to a first supply phase obtained by the simultaneous closing of the switches Ta and Td and the signal D2 corresponds to another supply phase obtained by the closing of the switches Tb and Tc. The signal C1 corresponds to a first short-circuit phase resulting from the closing of the switches Ta and Tc and the signal C2 corresponds to a second? short-circuit phase resulting from the closing of the switches Tb and Td. The control of the switches Ta to Td is obtained using four OR gates 9 receiving the signals C1 as input,
C2, D1, D2 according to the assembly shown in Figure 17.

We can easily verify that the commands Ca to Cd define command pulses for the switches
Ta to Td whose sequencing and widths make it possible to obtain the instantaneous voltages v and u of the timing diagrams b and c of FIG. 11.

The signals Ca to Cd are advantageously applied to the input of delay circuits 10 shown in FIG. 11 making it possible to adjust the delay on initiation and blocking of the corresponding switches. Each delay circuit consists of an AND gate with two inputs, a first input being connected to a positive voltage Vcc while the other input receives the control signal Ca-Cd via a first diode mounted in the direct direction in series with a variable resistor R7 and by a diode mounted in the opposite direction in series with a variable resistor R8. The second input of the AND gate is also connected to ground via a capacitor C. The values of the variable resistors R7 and R8 allow the time constants R7.C and R8.C involved to be set respectively. when the corresponding switches are primed and blocked. These variable delay circuits allow precise adjustment of the opening and closing times of the switches.

The signals of the outputs C'a-C'd supplied by the delay circuits 10 are applied to the control inputs of the corresponding switches by means of photocouplers as shown in FIG. 19 and of inversion and amplification circuits 12, 13. These additional circuits which are well known per se allow galvanic isolation and the voltage adaptations required by the use of power semiconductors.

The control circuit which has just been described in detail corresponds to the particular structure of FIG. 6.

Of course, this circuit will have to be adapted if other structures are chosen. This adaptation being within the reach of those skilled in the art, it is therefore unnecessary to give a detailed description for each possible embodiment.

Likewise, a person skilled in the art will be able to design from the preceding indications the appropriate control circuit for each of the various possible embodiments of a battery charger supplied with polyphase voltage.

Claims (11)

1. Battery charger intended to be connected to a power source (Sv) equivalent to a source (Se) of alternating voltage (Ve) having at least one phase and having an inductive internal impedance (L), characterized in that '' it includes - a converter (AA) comprising terminals  input (B1, B2) intended to be connected to said  power source (Sv) and terminals  output (B3, B4), - a transformer (TR) comprising at least one  primary winding (P1, P2) and one winding  secondary (S1, 82), the said winding (s)  primary (P1, P2) being connected to the output terminals  (B3, B4) of the converter (AA), - rectifier means (AC) mounted between said one or more  secondary windings (S1, S2) and the battery  load (B), - a control circuit (CD) of said converter (AA), in that said converter (AA) comprises controlled switch means (Ta, Tb, Tc, Td) arranged so as to allow phases of power supply to establish the power supply of at least one of the primary windings (P1, P2) by the power source (Sv) and short-circuit phases to short-circuit the power source (Sv) and in that said control circuit (CD) controls said switch means (Ta, Tb, Tc, Td) by high frequency pulses so that the durations and the sequencing of the supply and short-circuit phases ensure that the fundamental harmonic (V) of the voltage (v) present at the input terminals (B1, B2) of the converter (AA) has the same frequency as the voltage (Ve) of the voltage source (Se) with a phase and an amplitude such that the fundamental harmonic (I) of the current (i) flowing in the power source (Sv) is in phase with the voltage (Ve) of the voltage source (Se). 2. Battery charger according to claim 1, characterized in that said switch means (Ta, Tb, Tc, Td) are arranged so as to be able to impose the polarity of the voltage (u) applied to the terminals of the primary winding (s) ( P1, P2) independently of the polarity of the voltage (v) of the power source (Sv) and in that the control circuit (CD) is designed to cause an inversion of said polarity at each new power phase . 3. Battery charger according to one of claims 1 or 2, characterized in that said power source (Sv) consists of the electrical energy distribution network (Se) each phase of which is connected in series with an impedance inductive (L). 4. Battery charger according to one of claims 1 to 3, characterized in that the power source (Sv) is single-phase, in that said transformer (TR) comprises a single primary winding (P1) and in that said switch means are formed by four switches (Ta, Tb, Tc, Td) mounted in a bridge. 5. Battery charger according to one of claims 1 to 3, characterized in that the power source (Sv) is single-phase, in that said transformer (TR) comprises two primary windings (P1, P2) connected together by a midpoint (M), in that said switch means comprise a first series arrangement formed by first and second switches (Tc, Td), said first and second switches (Tc, Td) being respectively connected at parallel with the two primary windings (P1, P2) and a second series circuit formed by a third and a fourth switch (Ta, Tb) connected in series, said second series circuit being connected in parallel with said first series circuit and in that the power source (Sv) is connected between said midpoint (M) and the common terminal (B1) at said third and fourth switches (Ta, Tb). 6. Battery charger according to one of claims 1 to 3, characterized in that the power source (Sv) is single-phase, in that said transformer (TR) comprises two primary windings (P1, P2) connected together by a midpoint (M) and in that said switch means are formed by two switches (Ta, Tb) mounted in half-bridge and a single switch (Te) connected in parallel with the source (Sv). 7. Battery charger according to one of claims 1 to 6, characterized in that the signal (H *) representative of the supply phases is a pulse signal at fixed frequency and modulated in width. 8. Battery charger according to claim 3, characterized in that the short-circuit phases cause the short-circuit of at least one primary winding (P1, P2) of said transformer (TR). 9. Battery charger according to one of claims 7 or 8, characterized in that said control circuit (CD) comprises - a generator (G) providing an alternating signal from  reference (vr) synchronized by the voltage source  (Ve) and adjustable in amplitude and in phase, - a rectifier circuit (4) providing a signal  rectified (vl) of said reference signal (vr), - a generator (6) of sawtooth signal (v2) to  high frequency, - a comparator (5) receiving said rectified signal (vl)  and said sawtooth signal (v2) and providing  a comparison signal (H), - a logic circuit (CL) for developing pulses  control (Ca, Cb, Cc, Cd> of said interrup means  teurs (Ta, Tb, Tc, Td) as a function of said signal  comparison (H) and - means of isolation (11) and amplification  (12, 13) arranged between said logic circuit (CL) and  the control inputs of said switch means  (Ta, Tb, Tc, Td). 10. Battery charger according to one of claims 1 to 9, characterized in that the power source (Sv) is single-phase, in that the transformer (TR) has two secondary windings (S1, S2) connected together by a midpoint (N) and in that said rectifier means (AC) are formed by two diodes (Da, Db) mounted in a half-bridge. 11. Battery charger according to one of claims 1 to 10, characterized in that the amplitude and the phase of said reference signal (vr) are controlled as a function of the effective value of the current (I) flowing in the source d 'food (Sv).