FR3014261A1 - METHOD AND SYSTEM FOR CONTROLLING A BI - DIRECTIONAL CHARGER FOR A MOTOR VEHICLE. - Google Patents

Abstract

A method of controlling a bidirectional charger of a battery (5) of a motor vehicle, the charger comprising a rectifier stage (1) input connected to a power supply network (3) and output to a continuous conversion stage continuous, the DC-DC conversion stage (2) being connected to the battery (5), the DC-DC conversion stage (2) comprising a first set of transistors connected between the rectifier stage (1) and the first winding of a transformer, the second winding of the transformer being connected to a second set of transistors, furthermore connected to the battery (5). The method comprises the steps of: determining the control signals of the transistors of the first set at the resonance frequency of the DC-DC conversion stage (2), and determining a duty cycle applied to the control signals to modulate the voltage across the capacitor (4) as a function of the required battery voltage.

Description

Method and system for controlling a bidirectional charger for a motor vehicle

The invention relates to the technical field control of the charge of motor vehicle batteries. As part of the development of low-cost electric vehicles, the charging system has, like the electric powertrain (GMPe) or the high-voltage battery (HT), a significant cost item that should be reduced. The limitation of the charging power represents a first way to reduce the cost of the charging system. It is thus appropriate to associate the electric vehicle a recharging system said "slow", that is to say that takes its energy on the single-phase network with a power less than or equal to 7kW. Such a charger typically absorbs 10A, 16A or 32A on the single-phase network and is compatible with a household outlet. Furthermore, the chargers of electric vehicles are currently non-reversible, that is to say that the flow of energy flows only from the electrical network to the battery. In the future, it will be interesting to have two-way chargers, that is to say also able to circulate energy from the battery to the power grid.

Such chargers make it possible, for example, to smooth the load curve of the electrical network by using the energy storage represented by the battery of the connected vehicle. The battery is thus charged during consumption hollows during which the infrastructure and the means of production are underutilized, and provides energy during peaks to avoid the use of little used and expensive means of production and than overloading the power grid. In this case, the massive deployment of the electric vehicle does not imply additional investments of production or infrastructure, but on the other hand allows to smooth peaks of expensive consumptions to provide (with a generally very carbonaceous energy). Two-way chargers facilitate the deployment of renewable energies by optimally adapting the consumption of energy produced to the production hazards specific to green energy and benefit from a better performance in terms of carbon dioxide (CO2) emissions from the environment. electric vehicle while facilitating the introduction of renewable energy production.

Bi-directional chargers also enable the creation of new activities related to the control and optimization of energy consumption without degradation of service. Today, the charger is required to perform the energy conversion between the network and the battery. This conversion requires the charger to adapt to wide input voltage ranges (90V to 250V AC) and battery voltage (250V to 400V DC). FIG. 1 illustrates the main elements of a charger which comprise an input rectifier stage 1 connected to the network 3 and providing the power factor correction function, denoted PFC (acronym for "Power Factor Corrector"), and a stage 2 DC / DC conversion, allowing the galvanic isolation of the battery 5. An electromagnetic interference filter noted EMI (acronym for "Electromagnetic Interferences") can be arranged between the network 3 and the floor input rectifier, while an output filter can be arranged between the DC-DC conversion stage and the battery 5. The difficulty lies in being able to adapt to all the voltage levels mentioned above. above without sacrificing either the efficiency or the cost of the conversion stage while keeping the possibility of carrying out a bidirectional load. With regard to the bi-directional charge of electric vehicles, the state of the art today relies essentially on non-isolated topologies, that is to say that there is no galvanic isolation between the network and battery.

Regarding the design of insulated chargers, in general, the first stage consists of a boost topology to perform the PFC function while being voltage booster. In order to limit switching losses and frequency increase (synonymous with cost, volume, weight reduction), it is strongly recommended that the second stage uses a resonant circuit. Between these two stages, an electrolytic capacitance is positioned in order to smooth the current in constant current and to manage a constant power flow and no longer variable in sine.

Since the first stage has a voltage booster function, the DC (DC bus) voltage between the two stages is generally greater than the battery voltage. This implies that the DC / DC stage must have a voltage gain of less than unity. With a resonant isolated circuit, the total voltage gain is obtained by the product between the transformer transformation factor and the gain of the resonant circuit. The transformation factor is fixed and dependent on the design. It can not help adjust the gain during a vehicle load. However, when a vehicle is recharged, the battery voltage varies according to its state of charge SoC (state of charge), this requires in real time that the DC / DC stage adapts its gain for to convert the voltage of the DC bus to the battery voltage. This voltage adaptation can be made only by the operation of the resonant circuit. Generally, the use of the series-parallel LLC resonant topology (acronym referring to the use of a circuit comprising the combination of two inductances each denoted L and a capacity denoted C) is applied in the DC converter. DC. The variation of the switching frequency during charging makes it possible to vary the voltage gain of the resonant circuit. The frequency used is always greater than the natural frequency fo of the resonant circuit, which then operates in a hyper-resonance regime. The use of a resonant circuit in hyper-frequency makes it possible to have ZVS (Zero Voltage Switching) zero switching switching soft switching when closing the transistors. However, this solution has two important problems.

A first problem lies in the fact that the control dynamics of the DC / DC conversion resonating in hyper-frequency depends on the flow of power passing through it. To solve this problem, an electrolytic capacitance (voluminous, expensive and unreliable) must be put in place between the PFC and the DC / DC in order to smooth the flow of power. Such a capacitance is noted 4 in FIG. 1. A second problem lies in the fact that the operation in hyper-frequency makes it possible to limit the losses during the closing of the transistors but not at the time of their opening. If the switching frequency of the switches is equal to the natural frequency fo, it is possible to combine the ZVS closure with zero opening loss limitation in zero current switching ZCS (acronym for "Zero Current Switching"). From the state of the art, the following documents are known. US20110273130 discloses a bi-directional insulated charger which is however not used for vehicle charging applications. However, like all chargers of this type, it includes a current rectification stage performed with an electrolytic capacitance which has a significant cost. Patent application number FR1255070 discloses a resonant topology for charging a battery without using power factor correction. However, the control of such a topology is variable frequency, inducing operation in ZVS. Such an operation generates non-negligible switching losses limiting the operating frequency. This limitation indirectly involves additional costs. Document US 577-116-5A discloses a two-stage converter of the PFC boost and DC continuous conversion (DC / DC) type. However, this converter uses an electrolytic capacitance between the two stages so as to smooth the power flow in the converter. In addition, the DC / DC stage does not make it possible to combine the ZVS and ZCS switches at the transistors located before the resonant circuit.

An object of the invention is a method of controlling a bidirectional charger of a motor vehicle battery, the charger comprising a rectifier stage connected at the input to a power supply network and at output to a continuous conversion stage. continuous and at a capacity, the DC-DC conversion stage being connected to the battery. The DC-DC conversion stage comprises a first set of transistors connected at the input to the rectifier stage and at the output in series to a resonant circuit and to the first winding of a transformer, the second winding of the transformer being connected to a second set of transistors. The second set is also connected to the battery. The method comprises the following steps: controlling the second set of transistors in an on state, determining the control signals of the transistors of the first set at the resonance frequency of the DC-DC conversion stage, and determining a ratio cyclic applied to the control signals of the first set of transistors to modulate the voltage across the capacitor as a function of the required battery voltage. The duty cycle can be determined as a function of open loop control including mapping dependent on the value of the current across the capacitance. The current at the terminals of the capacitor can be determined as a function of a power setpoint of the rectifier stage, of the voltage at the terminals of the capacitance and of the frequency of the power supply network. The duty cycle can be corrected by summing a correction resulting from a closed-loop correction, which is a function of the difference between a measurement and an instruction of the minimum voltage across the capacitance. It is possible to determine a control signal modulated by the duty cycle to the first transistor and to the second transistor and another control signal modulated by the same duty cycle to the third transistor and the fourth transistor, the two control signals. being out of phase with each other. Another object of the invention is a control system of a bidirectional charger of a motor vehicle battery, the charger comprising a rectifier stage connected at input to a power supply network and at output to a continuous conversion stage continuous, the DC-DC conversion stage being connected to the battery. The DC-DC conversion stage comprises a first set of transistors connected at the input to the rectifier stage and at the output in series to a resonant circuit and to the first winding of a transformer, the second winding of the transformer being connected to a second set of transistors. The second set is also connected to the battery. The system comprises: means for determining the control signals of the transistors of the first set at the resonance frequency of the DC-DC conversion stage and the second set of transistors in an ON state, and means for determining a cyclic ratio applied to the control signals of the first set of transistors for modulating the voltage across the capacitor as a function of the required battery voltage. The means for determining a duty cycle may comprise an open-loop control means capable of determining the duty cycle as a function of a map depending on the value of the current across the capacitor. The means for determining a duty cycle may comprise means for determining the current across the capacitor as a function of a power setpoint of the rectifier stage, of the voltage at the terminals of the capacity and of the frequency of the network. power supply. The means for determining a duty cycle may comprise a closed-loop correction means capable of determining a correction that is a function of the difference between a measurement and an instruction of the minimum voltage across the capacitors. The control system may comprise a control signal determining means adapted to determine a control signal modulated by the duty cycle to the first transistor and to the second transistor and another control signal modulated by the same duty cycle to destination of the third transistor and the fourth transistor, the two control signals being out of phase with each other. The first advantage of bidirectional charger control is to stay at the resonant frequency, which reduces switching losses. The second advantage of this control combined with a good regulation of the primary voltage, is to allow a very fast power transfer from the power supply network to the battery at the mains frequency (typically 50 or 60 Hz). It is then possible to remove the electrolytic capacitance conventionally installed between the rectifier stage and the continuous DC conversion stage and replace it with a lower value film capacitor. Other objects, features and advantages of the invention will become apparent on reading the following description, given solely by way of nonlimiting example and with reference to the appended drawings in which: FIG. 1 illustrates the main elements of a bidirectional charger; - Figure 2 illustrates the main elements of a continuous DC conversion stage, and - Figure 3 illustrates the main elements of a bidirectional charger control system.

Fig. 1 shows the bidirectional charger comprising an input rectifier stage 1 and an output DC-DC conversion stage 2. The input rectifier stage 1 generates a DC bus voltage and ensures absorption of a sinusoidal current on the power supply network 3. The input rectifier stage 1 is connected in parallel with a capacitor 4 and a continuous DC conversion stage 2, the conversion stage being connected at the output to a battery 5.

Unlike the state of the prior art, the input rectifier stage 1 of the bidirectional charger according to the invention is also able to regulate the charge of the battery through the variation of the DC bus voltage (325 V). 400V). In FIG. 2, it can be seen that the DC-DC conversion stage 2 is series-resonant and galvanically isolated via a transformer 6, the assembly operating at a constant switching frequency. A first input of the conversion stage is connected to the collector of a first transistor T1 and the collector of a third transistor T3, a second input of the conversion stage being connected to the emitter of a second transistor T2 and to the emitter of a fourth transistor T4. The emitter of the first transistor T1 and the collector of the second transistor T2 are connected to a first intermediate point, the emitter of the third transistor T3 and the collector of the fourth transistor T4 being connected to a second intermediate point. The first intermediate point is connected in series with a first capacitor C1, a first inductor L1, at a first end of the first winding of a transformer 6, the second end of the first winding of the transformer 6 being connected to the second intermediate point. One end of the second winding of the transformer 6 is connected to the emitter of a fifth transistor T5 and to the collector of a sixth transistor T6, the collector of the fifth transistor T5 being connected to the collector of a seventh transistor T7 and to a first output of the conversion stage. The emitter of the sixth transistor T6 is connected to the emitter of an eighth transistor T8 and to a second output of the conversion stage. The other end of the second winding is connected to the emitter of the seventh transistor T7 and to the collector of the eighth transistor T8. A first diode D1 is connected by its anode to the emitter of the first transistor Ti and by its cathode to the collector of the first transistor Ti.

A second diode D2 is connected by its anode to the emitter of the second transistor T2 and by its cathode to the collector of the second transistor T2. A third diode D3 is connected by its anode to the emitter of the third transistor T3 and by its cathode to the collector of the third transistor T3. A fourth diode D4 is connected by its anode to the emitter of the fourth transistor T4 and its cathode to the collector of the fourth transistor T4. A fifth diode D5 is connected by its anode to the emitter of the fifth transistor T5 and its cathode to the collector of the fifth transistor T5. A sixth diode D6 is connected by its anode to the emitter of the sixth transistor T6 and its cathode to the collector of the sixth transistor T6.

A seventh diode D7 is connected by its anode to the emitter of the seventh transistor T7 and by its cathode to the collector of the seventh transistor T7. An eighth diode D8 is connected by its anode to the emitter of the eighth transistor T8 and by its cathode to the collector of the eighth transistor T8. The gates of the transistors receive control signals, in particular pulse width modulation transmitted at a constant frequency.

The second set of transistors (T5, T6, T7, T8) allows bidirectional operation. When discharging the battery to the power supply network, the behavior of the first set of transistors (T1, T2, T3, T4) and the second set of transistors (T5, T6, T7, T8) are exchanged with respect to each other. operation when charging the battery. The bidirectional charger described in FIGS. 1 and 2 is controlled by a process that differs from the methods generally employed because of a specific control of transistors T1 to T4.

For this purpose, control signals having a specific duty cycle are generated. The control signals may in particular be PWM pulse width modulation type (acronym for Pulse Width Modulation). The adaptation of the voltage gain between the DC bus (Vred) and the battery 5 is achieved by a step-down ratio using this duty cycle. It is recalled that the voltage Vred is measured at the terminals of the capacitor 4. Thus, it is possible to modulate the voltage gain while remaining at the resonance. The determination of the cyclic ratios will now be exposed. The DC-DC conversion stage 2 is governed by the following equations: Vbat = a Vred (Eq 1) With: the gain (or attenuation) obtained by the transformer, a: the attenuation obtained by the duty cycle at the level primary winding of the transformer.

The voltage of the battery is located essentially between a theoretical voltage Vbat th (for example 350 V) and a maximum voltage Vbat max (for example 400 V). We choose a transformation ratio X. to obtain a maximum load efficiency between the voltages Vbat th and Vbat max. Between the minimum voltage of the battery Vbat min and the theoretical voltage Vbat th, an attenuation is used by the duty cycle of the control signal of the transistors T1 to T4 connected to the primary winding of the transformer.

We have the following constraint: Vres. + OFST = Vbat (Eq 2) ka With: Vres: the voltage of the power supply network (RMS value), OFST: an offset voltage ("Offset" in English) allowing the good operation of the PFC stage The worst case corresponds to a mains voltage Vres equal to the maximum Vres max of the voltage of the power supply network. The equation Eq. 2 then becomes: Vres .. + OFST = Vbat (Eq.3) X, - a The value X, is obtained for a value of the battery voltage Vbat equal to the theoretical voltage Vbat th. The offset voltage OFST is then minimal (for example 40V). Equation 3 then becomes: Vbat th (Eq.4) Vres max.J If we consider the values Vbat th = 350V and Vres max = 250V, we obtain a value of the transformation ratio X of 0.875. For a given bidirectional charger, this value of the transformation ratio X is fixed since it fixes the number of turns at the primary winding and at the secondary winding of the transformer 6. The modulation can then be achieved only through the transformation report a.

With such a value of X, the charger has the following behavior: Between the battery voltages Vbat th and Vbat max, the offset voltage increases gradually to satisfy equation 2. The voltage Vred therefore reaches the maximum value: Vred max = Vbat max / X, = 460 V. Between the battery voltages Vbat min and Vbat th, the duty cycle a is decreased to satisfy equation 2, the maximum attenuation is reached for the duty cycle am ,. Next: Vbat min G (min - Vred min max - X, With Vred min max = minimum voltage Vred necessary to obtain the maximum Vres max of the power supply voltage Vred min max = Vres max + OFST (Eq 6) If we consider the following values of Vbat min = 290V, Vred min max = 457V, we obtain an amine value equal to 0.725.

The cyclic ratios thus determined are applied through the control method. For this, a closed-loop correction is combined with the voltage Vred and an open-loop control on the current Ired injected by the rectifier stage 1 onto the capacitor 4. FIG. 3 illustrates a control system 7 of the bidirectional charger comprising a closed-loop correction means 8 according to the voltage Vred, an open-loop control means 9 which is a function of the current Ired, an adder 10 connected at input to the closed-loop correction means 8 and to the open-loop control means 9, and connected at output to a saturation means 11 able to limit the extreme values. Indeed, the output signal of the saturation means is a duty cycle whose expected value is (Eq.5) between 0 and 1. Any values outside this range must be saturated at the nearest terminal. The saturation means 11 is connected to a means 12 for generating the control signals. The open-loop control means 8 determines a value of the duty cycle which is summed to a correction of the control means 9 in a closed loop in order to obtain a corrected duty cycle, denoted DUTY. The open-loop control means 9 comprises mapping as a function of the current Ired.

The current Ired is determined as a function of the power setpoint of the rectifier stage 1 by the following relation: Ired = PFC reference power 2 sin (2n - fres - t) (Eq.7) Vred With fres: the frequency of the network Power supply, and PCF setpoint power: the power setpoint of the rectifier stage 1. The mapping can be determined by prior measurements on a bidirectional charger in which only the DC-DC conversion stage 2 operates.

The closed-loop correction means 8 generates a correction of the duty cycle as a function of the voltage error between the measurement of the voltage Vred and an instruction equal to the voltage Vred min, the minimum voltage required for the proper operation of the stage. rectifier 1. The method employed may be of the integral corrector type. The corrected duty cycle DUTY in turn generates a first PWM1 control signal for the first transistor T1 and the second transistor T2, and a second control signal PWM2 for the third transistor T3 and the fourth transistor T4. In the control of a bridge of transistors such as that formed by the transistors T1, T2, T3 and T4, a phase difference exists between the control of the transistors T1 and T2 and the control of the transistors T3 and T4. By the application of the duty cycle, this phase shift is accentuated and requires the generation of two separate control signals. The generation of the control signal is known to those skilled in the art which may for example use a comparator of the desired value of the duty cycle to a carrier signal, in particular of triangular shape. The control system thus makes it possible to carry out power transfer at grid frequency (typically 50 Hz), with a very small Cred capacity (typically 30 pF).

Claims (10)

REVENDICATIONS1. A method of controlling a bidirectional charger of a battery (5) of a motor vehicle, the charger comprising a rectifier stage (1) connected at the input to a power supply network (3) and at output to a conversion stage ( 2) DC-DC and at a capacitance (4), the DC-DC conversion stage (2) being connected to the battery (5), the DC-DC conversion stage (2) comprising a first transistor set (T1, T2, T3, T4) input connected to the rectifier stage (1) and in series output to a resonant circuit (L1, C1) and to the first winding of a transformer (6), the second winding of the transformer (6) being connected to a second set of transistors (T5, T6, T7, T8), the second set (T5, T6, T7, T8), being furthermore connected to the battery (5), characterized in that it comprises the following steps: controlling the second set of transistors (T5, T6, T7, T8) in an on state, determining the control signals of the transistors (T1, T2, T3, T4) of the first set at the resonant frequency of the DC-DC conversion stage (2), and a duty cycle applied to the control signals of the first set of transistors (T1, T2, T3, T4) for modulating the voltage across the capacitor (4) according to the required battery voltage. 2. Control method according to the preceding claim, wherein the duty cycle is determined according to an open-loop control comprising a map dependent on the value of the current across the capacitor (4). 3. Control method according to claim 2, wherein the current is determined across the capacitor (4) as a function of a power setpoint of the rectifier stage (1), the voltage at the terminals of the capacitor ( 4) and the frequency of the power supply network (3). 4. Control method according to any one of claims 2 or 3, wherein the duty cycle is corrected by summing a correction from a closed loop correction function of the difference between a measurement and a minimum voltage setpoint at the terminals of the capacitor (4). 5. Control method according to any one of the preceding claims, wherein there is determined a control signal modulated by the duty cycle to the first transistor (T1) and to the second transistor (T2) and another control signal. modulated by the same duty cycle to the third transistor (T3) and the fourth transistor (T4), the two control signals being out of phase with each other. 6. A control system of a bidirectional charger of a battery (5) of a motor vehicle, the charger comprising a rectifier stage (1) connected at the input to a power supply network (3) and output in parallel to a conversion stage (2) continuous-DC and at a capacitance (4), the DC-DC conversion stage (2) being connected to the battery (5), the DC-DC conversion stage (2) comprising a first set of transistors (T1, T2, T3, T4) connected at input to the rectifier stage (1) and in serial output to a resonant circuit (L1, C1) and to the first winding of a transformer (6), the second winding of the transformer (6) being connected to a second set of transistors (T5, T6, T7, T8), the second set (T5, T6, T7, T8) being furthermore connected to the battery (5), characterized by the fact that it comprises: a means for determining the control signals of the transistors (T1, T2, T3, T4) of the first set to the en resonance ratio of the DC-DC conversion stage (2) and the second set of transistors (T5, T6, T7, T8) in an on state, and a duty cycle determination means applied to the control signals of the first set of transistors (T1, T2, T3, T4) to modulate the voltage across the capacitor (4) as a function of the required battery voltage. 7. Control system according to claim 6, wherein the means for determining a duty cycle comprises an open loop control means capable of determining the duty cycle as a function of a map depending on the value of the current across the terminals. the capacity (4). 8. Control system according to claim 7, wherein the means for determining a duty cycle comprises means for determining the current across the capacitor (4) as a function of a power setpoint of the rectifier stage ( 1), the voltage across the capacitor (4) and the frequency of the power supply network (3). A control system according to any one of claims 7 or 8, wherein the means for determining a duty cycle comprises a closed-loop correction means adapted to determine a correction dependent on the difference between a measurement and a setpoint of the minimum voltage across the capacitor (4). 10. Control system according to any one of claims 6 to 9, comprising a means for determining the control signals adapted to determine a control signal modulated by the duty cycle to the first transistor (T1) and to the second. transistor (T2) and another control signal modulated by the same duty cycle to the third transistor (T3) and the fourth transistor (T4), the two control signals being out of phase with each other.