Backup power supply system

Abstract

The present invention relates to a backup power supply system, and more particularly to a balancing system for balancing the corresponding voltages of N capacitors connected in series during charging or discharging, comprising a balancing unit (BUj), each balancing unit comprising an electromagnetic coil (Lj) and a pair of associated switches (SWj1, SWj2). The switch inter-point is connected to the capacitor inter-point of the corresponding capacitor group through the electromagnetic coil (Lj). The control and generation circuit (30) generates a PWM control signal and sends the generated PWM control signal to each switch. The PWM control signal has a fixed duty cycle, which does not change temporarily during the charging or discharging of the N capacitors. The duty cycles of the two PWM control signals to be sent to the two associated switches are complementary for each balancing unit.

Description

Technical Field

[0001] The present disclosure relates to the field of power supply systems, and more specifically, to backup power supply systems. Such systems can be used in vehicles, for example, to provide power to vehicle circuits in the event of a momentary interruption of the vehicle battery. Background Art

[0002] In a vehicle, a battery (usually a 12V battery) is provided on board to supply power to the vehicle's electrical devices. In some cases, the power supply from the battery may be temporarily interrupted, typically during a time interval from a few milliseconds to a few seconds, due to an undesired disconnection of the battery. In this case, it is necessary to supply power to the vehicle's electrical devices from a backup power supply system. Capacitors are often used as energy buffers in such backup power supply systems.

[0003] Fig.11 Schematically a power source is shown, for example a battery with a voltage V_bat supplying a current i(t) to a load P. A plurality of capacitors C connected in series are connected in parallel to the load P and act as an energy buffer. When the connection of the load P to the power bar is interrupted, as schematically represented when the switch SW is off, the battery supply is interrupted and the capacitors C supply a current i(t) to the load P.

[0004] In vehicles, devices such as ADAS (Advanced Driver Assistance System) controllers require such backup power.

[0005] In order to face a battery disconnection lasting several seconds, a large amount of energy needs to be stored. For this purpose, it is known to use specific capacitors called supercapacitors (or ultracapacitors). Supercapacitors are high-capacity capacitors with much higher capacitance values ​​than other capacitors, but with lower voltage limits. The maximum charge of a supercapacitor is, for example, around 2.5V. Charging a supercapacitor beyond its maximum charge may cause damage. Therefore, in order to provide the required high voltage (higher than the voltage limit imposed by the capacitors) for the backup power supply, it is necessary to connect multiple capacitors in series. In a vehicle with a 12V battery, six or seven capacitors connected in series are required to achieve the backup power supply.

[0006] The capacitance values ​​of manufactured capacitors with the same maximum charge are usually very dispersed. Typically, a variation of about 20% to 30% can be observed.

[0007] From the above results, it can be seen that when a stack of capacitors including N capacitors connected in series is charged from a power supply, the voltages of the different capacitors need to be balanced to avoid one or more capacitors being charged beyond their maximum charge.

[0008] Different techniques are known to balance the voltages of capacitors in a stack of capacitors.

[0009] Reference Fig.12 , a first technique uses a resistor R half bridge to balance the voltage of at least two capacitors C1, C2 connected in series. The higher the resistance value, the longer the charging time period. For capacitors with a capacitance value of about kilofarad and a resistor R with a resistance value of about 10 kΩ, the time constant of the capacitor is about megaseconds, so the charging time is very long. In practice, this solution is not interesting.

[0010] Reference Fig.13 The second technique, which is a variation of the first technique, is based on a circuit also having a resistor R half-bridge connected to at least two capacitors C1, C2 connected in series, wherein the point between the resistors is connected to the point between the capacitors via a series-connected amplifier R and a damping resistor r. This balancing circuit enables fairly fast balancing, but generates a lot of heat.

[0011] Linear Technology Corporation designs and manufactures high current supercapacitor chargers and backup power supplies, such as the LTC 3350 and LTC 3625. Such products provide automatic balancing of the capacitors, but have two major disadvantages. These products are expensive and the automatic balancing takes several minutes to achieve balance.

[0012] In an automotive environment, a maximum equilibration time of a few seconds is expected.

[0013] Reference Fig.14 , the third technique uses a switching power supply (or switch-mode regulator) with a feedback (or regulation) loop. Fig.14 As shown, in order to charge two capacitors C1 and C2 connected in series, for example, two switches SW1 and SW2 connected in series are connected in parallel to the two capacitors C1 and C2, and the switch inter-point and the capacitor inter-point are connected through an electromagnetic coil L. The two switches SW1, SW2 and the two capacitors C1 and C2 are connected to a power supply (providing a voltage u_total and a current i_charge) to charge the capacitors C1 and C2. The controller CT generates PWM control signals PWM1 and PWM2 to control the switches SW1 and SW2, respectively, so that the capacitor voltages u_C1 and u_C2 are balanced. In addition, the voltage of the capacitor is measured and transmitted to the controller CT as a feedback signal V_fb (a voltage signal at the capacitor inter-point). The controller CT modulates or adjusts the duty cycle of the PWM control signals PWM1 and PWM2 sent to the two switches SW1 and SW2 according to the feedback signal to balance the capacitor voltages u_C1 and u_C2. This switching power supply system with a feedback loop provides fast and effective balancing. However, it has the main disadvantage of being expensive.

[0014] There is a need to improve this situation. More specifically, there is a need to provide a cheaper backup power supply system that can achieve fast and efficient balancing of series capacitors. Summary of the invention

[0015] The present disclosure relates to a balancing system for balancing respective voltages of N consecutively connected capacitors of a backup power supply system during charging or discharging of the N capacitors, wherein n groups of at least two consecutive capacitors are defined by the N capacitors, wherein n≤N-1, the balancing system comprising:

[0016] - a plurality (n) of balancing units, each for n groups of capacitors, each balancing unit comprising an electromagnetic coil and a pair of associated switches connected via a switch inter-point connected to a capacitor inter-point of a respective capacitor group via the electromagnetic coil; and

[0017] - a control and generation circuit for generating a PWM control signal and sending the generated PWM control signal to each switch;

[0018] It is characterized in that the control and generation circuit is configured to generate a PWM control signal with a fixed duty cycle, which does not temporarily change during the charging or discharging of the N capacitors, and the duty cycles of the two PWM control signals to be transmitted to the two associated switches are complementary for each balancing unit.

[0019] In the present disclosure, for each or some capacitor inter-nodes (or nodes), a balancing circuit having a pair of connected switches is connected to the capacitor inter-nodes through a coil, which schematically takes the form of a half H bridge. Each capacitance value of the capacitor causes the charge in different capacitors to increase differently. Therefore, the imbalance between the capacitor voltages generates a balancing current through the coil, which helps to balance the capacitor voltages. According to the present disclosure, the two switches are controlled by a fixed duty cycle that does not change temporarily during the charging or discharging of the N capacitors. In other words, the two switches are turned on / off at a fixed duty cycle (which does not change temporarily during the charging or discharging) during the charging or discharging period.

[0020] The present disclosure also relates to a backup power supply system comprising a stack of N capacitors connected in series and a balancing system as defined above for balancing the respective voltages of the N capacitors during charging or discharging of the N capacitors.

[0021] Advantageously, the stack of N capacitors connected in series has two terminals, and each pair of associated switches is connected to said terminals of the stack of N capacitors.

[0022] Advantageously, the capacitor is a supercapacitor.

[0023] In a particular embodiment, each pair of connected switches is connected to N capacitors.

[0024] Advantageously, N capacitors with corresponding indexes i from 1 to N have, for each balancing unit, a capacitor inter-node connected to the switch inter-node between two capacitors with corresponding indexes i and i+1, and the control and generation circuit is configured to generate a first PWM control signal with a duty cycle equal to (Ni) / N and a second PWM control signal with a duty cycle equal to i / N.

[0025] In another particular embodiment, for each balancing unit, an associated switch pair is connected to two terminals of a corresponding capacitor bank.

[0026] Advantageously, the control and generation circuit is configured to generate PWM control signals all having a 50% duty cycle.

[0027] This control and generation circuit is simpler.

[0028] In a particular embodiment, each group of capacitors includes only two capacitors.

[0029] Advantageously, the control and generation circuit comprises a frequency divider based on a flip-flop.

[0030] Advantageously, the control and generation circuit is configured to be connected to a power supply and to be provided with a clock signal from said power supply.

[0031] Advantageously, the control and generation circuit comprises at least one flip-flop and a logic gate.

[0032] Advantageously, the control and generation circuit comprises n flip-flops, wherein n is calculated according to the relation 2 n-1 <N≤2 n Determined by the number N of capacitors.

[0033] Advantageously, the system further comprises a power supply configured to:

[0034] - generating a fixed charging current during the first charging phase; and

[0035] - During the second charging phase, after the voltage of the stack of serially connected capacitors has reached a predetermined target value, a charging current is generated which is modulated to maintain the voltage of the plurality of capacitors connected in series at a predetermined target value.

[0036] The system may be integrated into a vehicle and provide power to circuits of the vehicle, and the power source may include a battery of the vehicle.

[0037] Advantageously, the N capacitors are arranged to supply power to an electrical circuit of the vehicle when a battery of the vehicle is temporarily disconnected from the electrical circuit.

[0038] The present disclosure also relates to a vehicle comprising a backup power supply system as previously defined, the backup power supply system being configured to charge from a power source comprising a battery of the vehicle and to supply power to electrical circuits of the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Other features, objects and advantages of the present disclosure will become more apparent from reading the detailed description of non-limiting embodiments made with reference to the accompanying drawings.

[0040] Figure 1 A schematic and simplified representation of a first exemplary embodiment of a backup power supply system having two capacitors and a pair of associated switches is shown.

[0041] Figure 2 A second exemplary embodiment of a backup power supply system is schematically shown having four capacitors and three pairs of associated switches.

[0042] Figure 3A Shows that when Figure 2 Simulation results of capacitor voltage convergence when charging and balancing the backup power system.

[0043] Figure 3B Shown in Figure 3A PWM control signals transmitted to the switches of the backup power supply system in the simulation and the capacitor voltage after convergence (between 29.950ms and 30ms after starting the balancing operation).

[0044] Figure 4 A third exemplary embodiment of a backup power supply system is shown having three capacitors and two pairs of associated switches.

[0045] Figure 5 A fourth exemplary embodiment of a backup power supply system is shown, which has three capacitors and two pairs of associated switches. Figure 4 An alternative implementation of the implementation of .

[0046] Figure 6 A fifth exemplary embodiment of a backup power supply system is shown, which has N capacitors and N-1 pairs of associated switches, N being an odd number;

[0047] Figure 7 A sixth embodiment of a backup power supply system is shown, having N capacitors and N-1 pairs of associated switches, N being an even number.

[0048] Figure 8 A seventh exemplary embodiment of a backup power supply system is shown during charging of capacitors from a power source, having N capacitors and N-1 pairs of associated switches (only a portion of the N capacitors and N-1 pairs of switches are shown for clarity).

[0049] Fig. 9 The figure shows the period during which the capacitor is discharged to supply power to the load (or device). Figure 8 A seventh exemplary embodiment of a backup power supply system.

[0050] Fig.10 shows the control used to generate Figure 2 An exemplary embodiment of a circuit for providing a PWM control signal for a switch of a backup power supply system.

[0051] Fig.11 An exemplary embodiment of a prior art power supply system for supplying power to a load P is shown, which has a power source connected in parallel with a plurality of capacitors connected in series (for buffering energy).

[0052] Fig.12 A first exemplary embodiment of a balancing circuit for capacitors of a power supply system of the prior art is shown.

[0053] Fig.13 A second exemplary embodiment of a capacitor balancing circuit of a power supply system of the prior art is shown. Fig.12 A modified variation of the first exemplary embodiment.

[0054] Fig.14 A third exemplary embodiment of a prior art improved balancing circuit for capacitors of a power supply system is shown. DETAILED DESCRIPTION

[0055] It is noted in advance that identical, similar or corresponding elements shown in different figures have the same reference numerals unless stated otherwise.

[0056] The present disclosure relates to a backup power supply system 100, which can be used, for example, in a vehicle as an energy reserve available when needed (e.g., when battery power is interrupted due to battery disconnection). The backup power supply system 100 is charged by a power source 200, such as a battery (typically a 12V battery) in the vehicle. When the battery power is interrupted, the backup power source is discharged to provide current to one or more loads, which are electrical devices of the vehicle.

[0057] The backup power supply system 100 has:

[0058] a set or stack 10 of N capacitors C1, C2, ..., Ci, ..., CN connected in series, and

[0059] - A balancing circuit 20 for balancing the respective voltages of the N capacitors during charging or discharging of the N capacitors.

[0060] Advantageously, the capacitors C1 , C2 , . . . , Ci, . . . , CN are supercapacitors.

[0061] From the N capacitors 10, n groups of at least two consecutive capacitors are defined, where n≤N-1. Generally, in this specification, an index j represents an index of a group of at least two capacitors, 1≤j≤n.

[0062] For each group of capacitors indexed as j, the balancing circuit 20 has a pair of switches associated and connected in series. In the figure, the pair of associated switches is referred to as SWj1 and SWj2 (i.e., SW11, SW12, ..., SWj1, SWj2, ..., SWn1, SWn2), where 1≤j≤n. The switch inter-node or node associated with each pair of associated switches (i.e., the junction or node between two switches) is connected to the capacitor inter-node or node associated with the capacitor group (i.e., the junction or node between two capacitors of the same group) through electromagnetic coils L1, ..., Lj, ..., Ln. The group includes:

[0063] - a set of at least two capacitors indexed j,

[0064] - a corresponding pair of associated switches SWj1 and SWj2, and

[0065] - Corresponding electromagnetic coils Lj, which form balancing units referred to in the description as BUj.

[0066] The backup power supply system 100 further includes a control and generation circuit 30 for generating PWM (pulse width modulation) control signals PWMj1, PWMj2 and sending the generated PWM control signals PWMj1, PWMj2 to respective switches SWj1, SWj2 so as to control the switches. In the present disclosure, the control and generation circuit generates PWM control signals PWMj1, PWMj2 with a fixed duty cycle.

[0067] The expression "fixed duty cycle" means that the corresponding duty cycle does not change temporarily during the charging or discharging of the N capacitors. In other words, the duty cycle of the control signal for turning on / off the switch is constant over time during the charging or discharging.

[0068] For each balancing unit BUj, the two generated PWM control signals PWMj1, PWMj2 are complementary This means that when the second signal PWMj2 is OFF (or low level), the first signal PWMj1 is ON (or high level). Therefore, the sum of the fixed duty cycles DC of the two PWM control signals PWMj1 and PWMj2 (sent to two associated switches SWj1 and SWj2, respectively (where 1≤j≤n)) is equal to 100%.

[0069] The backup power supply system 100 is based on the switching frequency f sw For example, the backup power supply system 100 uses a clock signal from the power supply 200 (eg, a power DCDC converter) as the basic frequency f b To control the switch. For a stack of N capacitors, the switching frequency f sw Equal to the fundamental frequency f b Divide by N: f sw =f b / N. This configuration offers the advantage that no frequency generation is required. As a result, the number of resources or components can be reduced. Alternatively, an external baseband generator can be used. In this case, the frequency f is advantageously determined according to the switching frequency required for the balancing capacitor b =f sw .N.

[0070] When the capacitors are charged, they are connected to the power supply 200. More precisely, two terminals of the stack of N series-connected capacitors are connected to two terminals of the power supply 200. Typically, the capacitor with index 1 is connected to the positive terminal of the power supply 200 and the capacitor with index N is connected to the negative terminal of the power supply 200 (e.g., to ground). Reference numerals u_total and i_charge denote the voltage and current provided by the power supply 200. When the capacitors are used to power one or more loads, the connection to the power supply 200 is interrupted and the stack of N series-connected capacitors is connected to the loads.

[0071] During the charging (or discharging) of the N stacked capacitors, for each balancing unit BUj balancing a group of capacitors, the imbalance between the respective capacitor voltages of the different capacitors within the group causes a current i_bal through the coil Lj. This current i_bal enables the capacitor voltages to be balanced. The basic principle is that the capacitor with the highest voltage discharges into the capacitor with the smallest voltage (in the case of a group with two capacitors).

[0072] We first assume that N series-connected capacitors are grouped by two capacitors and that two adjacent groups of two capacitors have one intermediate capacitor in common. This means that N-1 groups of two consecutive capacitors are defined.

[0073] Figure 1A schematic diagram of a very simplified backup power supply system 100 according to a first exemplary embodiment is shown. In this simplified embodiment, the backup power supply system 100 has only one balancing unit BU. More precisely, the backup power supply system 100 has only two capacitors C1, C2 and a pair of two associated switches SW1, SW2 connected to each other via an inter-switch point. The two switches SW1 and SW2 are connected "in parallel" to the two capacitors C1, C2 (i.e., the two terminals of the switch pair SW1, SW2 are connected to the two terminals of the stack of capacitors C1, C2, respectively), but the inter-capacitor point between the two capacitors C1 and C2 and the inter-switch point between the two switches SW1, SW2 are connected via a coil L. The backup power supply system 100 also has a control and generation circuit 30, which generates two PWM control signals PWM1 and PWM2 and sends them to the two switches SW1 and SW2, respectively, so as to control the two switches here. The respective duty cycles DC of the two PWM control signals PWM1 and PWM2 are fixed and are both equal to 50%. In order to charge the two capacitors C1 and C2, the balancing unit BU is connected to the power supply 200, as Figure 1 As shown (BU is connected to a terminal of the power supply 200). The control and generation circuit 30 may also be connected to the power supply 200 and powered thereby.

[0074] During operation of charging the capacitors C1, C2 by the balancing circuit 20, the capacitor voltages converge to the same value u_total / 2, u_total (which is the voltage of the power supply 200) in a short period of time (less than one second), which will be explained in more detail in the following description. Figure 1 , reference numeral i_bal12 represents the current through the coil when the top capacitor C1 is discharged into the bottom capacitor C2, and reference numeral i_bal21 represents the current through the coil when the top capacitor C2 is discharged into the bottom capacitor C1.

[0075] Figure 2 A schematic diagram of a backup power supply system 100 according to a second exemplary embodiment is shown.

[0076] In the second exemplary embodiment, the backup power supply system 100 has a stack of four capacitors C1, C2, C3 and C4 (N=4) connected in series (i.e., continuously), and three pairs of associated switches SW11-SW12, SW21-SW22, SW31-SW32. Each pair of switches SW11-SW12 (SW21-SW22 and SW31-SW32) is "connected in parallel" to the stack of capacitors C1-C4 (i.e., the two terminals of each pair of switches SW11-SW12, SW21-SW22, SW31-SW32 are respectively connected to the two terminals of the stack of capacitors C1-C4). The three capacitor inter-points are connected to the three switch inter-points of the three pairs of switches SW11-SW12, SW21-SW22, SW31-SW32 through three coils L1, L2 and L3, respectively.

[0077] Control and generation circuits ( Figure 2 ) generates a PWM control signal with a fixed duty cycle to control switches SW11-SW12, SW21-SW22, SW31-SW32. The value of the duty cycle for controlling SW11-SW12, SW21-SW22, SW31-SW32 is as follows:

[0078] -DC11=75%,DC12=25%

[0079] -DC21=50%,DC22=50%

[0080] -DC31=25%,DC32=75%,

[0081] So that after balancing, the voltages of the nodes between C1 and C2, between C2 and C3, and between C3 and C4 are set to 75%.u_total, 50%.u_total, and 25%.u_total, respectively.

[0082] Figure 3A The simulation results of the time variation of the capacitor voltages u_C1, u_C2, u_C3, u_C4 of the four capacitors C1, C2, C3, and C4 through the balancing circuit 20 when these capacitors are charged from the power supply 200 are shown. For the simulation, the voltage u_total of the power supply 200 is set to 7.2 V, for example. Therefore, the target value of the capacitor voltage of each capacitor C1, C2, C3, and C4 is equal to 1.8 V (7.2 V divided by 4).

[0083] Initially, the capacitor voltages u_C1 , u_C2, u_C3, u_C4 are, for example, equal to zero or close to zero. The variation over time of the different capacitor voltages u_C1 , u_C2, u_C3, u_C4 is similar, but different for capacitors with different capacitance values.

[0084] The charging operation has two main phases: a first fast phase I and a second slow phase II. The first fast charging phase I has a first (or initial) part T1 during which there is no balance. The capacitor voltages u_C1, u_C2, u_C3, u_C4 start to increase but disperse, which means that they become increasingly different from each other due to lack of balance. This phenomenon is due to the fact that the balancing circuit 20 needs to reach a certain amount of voltage (for example a voltage threshold of 3V or 4V at the terminals of the stack of N series capacitors) in order for the switch to start working. However, depending on the technology used for the switch, the latter can work before this N capacitor voltage threshold is reached.

[0085] Once balancing begins, the capacitor voltages u_C1, u_C2, u_C3, u_C4 converge, which means that they approach each other. This corresponds to the second and subsequent part T2 of the fast charging phase I. Then, once the maximum total voltage u_total across the capacitor stack is reached (7.2V in this example), the slow phase II begins. During the slow phase II, the capacitor voltages u_C1, u_C2, u_C3, u_C4 across the different capacitors increase more slowly or decrease a little and converge to a common voltage. From Figure 3A It can also be seen in FIG. 4 that the capacitor voltages u_C1 , u_C2 , u_C3 , u_C4 of all capacitors C1 to C4 reach and remain at a value equal to or very close to the target value of 1.8 V after a short time period of about 15 ms.

[0086] exist Figure 3A In an exemplary embodiment, during the first stage I of charging, the power supply 200 generates a fixed charging current. During the second stage II of charging, after the voltage of the N stacked capacitors has reached a predetermined target value (u_total), the power supply 200 generates a modulated or regulated charging current so as to maintain the voltage of the N stacked capacitors at the predetermined target value (u_total).

[0087] Figure 3B The PWM control signals PWM11 , PWM21 and PWM31 sent to the switches SW11 , SW21 and SW31 , respectively, and the time variations of the capacitor voltages u_C1 , u_C2 , u_C3 , u_C4 during a time period between 29.950 ms and 30 ms (from the start of the charging operation) are shown. Figure 3B It is shown that after a period of about 30 ms from the start of the charging operation, all capacitor voltages u_C1 , u_C2 , u_C3 , u_C4 have reached and maintained a voltage value equal to the capacitor voltage target value (1.8 V) with an accuracy of about 2% or 3%.

[0088] The balancing circuit 20 allows each of the N stacked capacitors to reach a target voltage value in a fast, accurate, and efficient manner.

[0089] Figure 4 A third exemplary embodiment is shown, which differs from the second exemplary embodiment only in that the capacitor stack has only three capacitors C1, C2, C3 connected in series and two pairs of associated switches SW11-SW12 and SW21-SW22. The switch inter-node is connected to the two capacitor inter-nodes via two coils L1, L2, respectively.

[0090] In some exemplary embodiments (e.g., the second exemplary embodiment and the third exemplary embodiment), each pair of associated switches is connected "in parallel" to the stack of N series-connected capacitors (i.e., the two terminals of each pair of switches are connected to the two terminals of the N stacked capacitors, respectively). For each balancing unit BUj, the switch inter-node between SWj1 and SWj2 is connected to the capacitor inter-node between two capacitors of corresponding indexes i and i+1 of the same group j through a coil Lj, and the control and generation circuit 20 generates a first PWMj1 control signal with a duty cycle equal to (Ni) / N and a second PWMj2 control signal with a duty cycle equal to i / N.

[0091] In other exemplary embodiments (which are variations of the above embodiments), for each balancing unit BUj associated with a group j of at least two capacitors, the associated switch pair SWj1-SWj2 is connected in parallel to the group j of stacked capacitors. When n groups of at least two consecutive capacitors are defined from N capacitors, the n pairs of associated switches connect the n groups of capacitors "in parallel", respectively. In addition, for each balancing unit BUj associated with a group j of at least two capacitors, the switch inter-node between SWj1 and SWj2 is connected to the capacitor inter-node between the two capacitors of the corresponding indexes i and i+1 of the group j through a coil Lj. In these variant embodiments, the control and generation circuit generates a PWM control signal having a fixed duty cycle of 50% for all switches SWj1-SWj2 (1≤j≤n).

[0092] Figure 5 is a fourth exemplary embodiment according to a variation of the above disclosure. More specifically, Figure 5 The implementation method is based on the above paragraph Figure 4 A variation of the embodiment of Figure 5In the embodiment, the stack of capacitors has three capacitors C1, C2, C3 connected in series and two pairs of associated switches SW11-SW12 and SW21-SW22 to balance the capacitor voltages. More precisely, the switch pair SW11-SW12 is connected "in parallel" to the two capacitors C1, C2 (i.e., the two terminals of the switch pair SW11-SW12 are connected to the two terminals of the capacitors C1-C2), and the switch pair SW21-SW22 is connected "in parallel" to the two capacitors C2, C3 (i.e., the two terminals of the switch pair SW21-SW22 are connected to the two terminals of the capacitors C2-C3). The switch inter-node is connected to the capacitor inter-node through coils L1 and L2. The duty cycle of all PWM control signals sent to the switches SW11-SW12 and SW21-SW22 is fixed and equal to 50%.

[0093] Figure 6 Shown as Figure 5 A fifth exemplary embodiment is a summary of the fourth embodiment of the present invention, wherein there are N series-connected (stacked) capacitors, N being an odd number. For each balancing unit BUj, the associated switch pair SWj1-SWj2 is connected "in parallel" to the corresponding set of two capacitors (i.e., the two terminals of the switch SWj1-SWj2 are connected to the two terminals of the corresponding set of two capacitors), and the switch inter-node is connected to the capacitor inter-node through the coil Lj. There are N-1 coils that respectively connect each of the N-1 capacitor inter-nodes to the N-1 switch inter-nodes belonging to the N-1 pairs of associated switches SWj1-SWj2 (where 1≤j≤N-1).

[0094] Figure 7 A sixth embodiment is shown which differs from the fifth embodiment only in that the number N of series-connected (stacked) capacitors is an even number.

[0095] Figure 8 A seventh exemplary embodiment is shown, which is Figure 2 and Figure 4A summary of an embodiment of the invention is provided, with N series-connected (stacked) capacitors. The N series-connected capacitors have respective indexes i from 1 to N. Capacitor C1 is connected to the positive terminal of the power supply 200, and capacitor CN is connected to the negative terminal (here ground) of the power supply 200. For each balancing unit BUj, the associated switch pair SWj1-SWj2 is connected "in parallel" to the N series-connected (stacked) capacitors (i.e., the two terminals of the associated switch pair SWj1-SWj2 are connected to the two terminals of the N stacked capacitors), and the switch inter-node between SWj1 and SWj2 is connected to the capacitor inter-node through a coil Lj. When the capacitor inter-node between capacitors Ci and Ci+1 is connected to the switch inter-node between SWj1 and SWj2, a first PWM control signal having a duty cycle equal to (Ni) / N is generated and sent to the first switch SWj1 of the two associated switches, and a second PWM control signal having a duty cycle equal to i / N is sent to the second switch SWj2 of the two associated switches. The first switch SWj1 is connected to the positive terminal of the power source 200 , and the second switch SWj2 is connected to the negative terminal (here, grounded) of the power source 200 .

[0096] Fig. 9 The following diagram shows the discharge of N capacitors to supply power to a load P. Figure 8 A backup power supply system of a seventh embodiment of the present invention. The connection between the stack of N capacitors and the power supply is interrupted, and the capacitors are discharged into the load. The balancing circuit enables the corresponding voltages of the N capacitors to be balanced during the discharge of the N capacitors.

[0097] In an eighth exemplary embodiment of the backup power supply system, n groups of two or more capacitors are defined by N capacitors, and at least a portion of the n groups has more than two capacitors. Such an embodiment is appropriate when the number N of capacitors is important.

[0098] According to the present disclosure, a control and generation circuit generates a PWM control signal with a fixed duty cycle, which enables fast balancing of capacitor voltages of N series-connected capacitors without a feedback loop.

[0099] In some exemplary embodiments, each pair of associated switches is connected "in parallel" to N series-connected capacitors. In other exemplary embodiments, j pairs of associated switches are connected "in parallel" to j groups of at least two capacitors.

[0100] The generation of these PWM control signals with a fixed duty cycle can be realized using flip-flops and logic gates. The control and generation circuits use a clock signal sent from the power supply. The flip-flops work as frequency dividers. x flip-flops enable the generation of up to 2 xMore generally, the control and generation circuit 30 has n flip-flops, where n is proportional to the duty cycle of the capacitor. n-1 <N≤2 n Determined by the number N of capacitors.

[0101] Fig.11 An exemplary embodiment of a circuit for generating three PWM control signals having duty cycles of 25%, 50% and 75% respectively is shown.Such circuits are well known to those skilled in the art and will not be described in further detail.

[0102] The generation of a PWM control signal with a common duty cycle of 50% allows the use of simple control and generation circuits with smaller components and generates less current ripple.

[0103] Especially when the fundamental frequency for controlling the switching and balancing capacitors is provided by the power supply 200, the reduction of current fluctuations is significant. For example, for a stack of four capacitors C1 to C4, multiple PWM control signals each having a duty cycle of 25%, 50% and 75% are generated, which means that the fundamental frequency is divided by four to obtain the switching (or balancing) frequency. The generation of PWM control signals produces higher current ripples for lower frequencies. The generation of PWM control signals with only a 50% duty cycle only requires dividing the fundamental frequency by two. Therefore, less current fluctuations are generated by the higher switching frequency of the balancing circuit (the fundamental frequency divided by two). When an external fundamental frequency generator is used and its frequency is determined according to the desired switching frequency for balancing the capacitors, there is no significant difference in current fluctuations.

[0104] As mentioned above, the backup power supply system 100 is integrated in a vehicle, for example, and supplies power to the circuit of the vehicle. In this case, the power supply 200 is a battery of the vehicle, for example, a 12V battery. When the battery of the vehicle is temporarily disconnected from the circuit, N capacitors connected in series supply power to the circuit of the vehicle.

[0105] The present disclosure also relates to a balancing circuit 20 for balancing the respective voltages of N capacitors of a backup power supply system during charging or discharging of said N series-connected capacitors, as previously mentioned, n groups of at least two consecutive capacitors are defined by N capacitors, wherein n≤N-1.

[0106] In particular, the balancing circuit 20 has:

[0107] - (for each group of capacitors) having a pair of associated and connected switches with an inter-switch point connected to an inter-capacitor point of the capacitor bank via an electromagnetic coil, the capacitor bank, the associated pair of switches and the electromagnetic coil forming a balancing unit; and

[0108] - a control and generation circuit for generating a PWM control signal and sending the generated PWM control signal to each switch, the control and generation circuit generating the PWM control signal with a fixed duty cycle.

[0109] The duty cycles of the two PWM control signals sent to the two associated switches are complementary for each balancing unit.

[0110] The present invention also relates to a vehicle integrating the above backup power supply system and / or balancing circuit.

Claims

1. A balancing system for balancing the respective voltages of N consecutively connected capacitors of a backup power supply system during charging or discharging of the N capacitors, wherein n groups of capacitors are defined by the N capacitors, each group of capacitors having at least two consecutive capacitors, wherein: n≤N-1, the balancing system comprises: - n balancing units (BUj) for the n groups of capacitors, each balancing unit (BUj) comprising an electromagnetic coil (Lj) and a pair of associated switches (SWj1, SWj2) connected via a switch inter-node, the switch inter-node being connected to the capacitor inter-node of the corresponding group of capacitors via the electromagnetic coil (Lj); and - a control and generation circuit (30) for generating a PWM control signal and sending the generated PWM control signal to each switch; The invention is characterized in that the control and generation circuit (30) is configured to generate a PWM control signal with a fixed duty cycle, which does not change temporarily during the charging or discharging of the N capacitors, and the duty cycles of the two PWM control signals to be sent to the two associated switches are complementary for each balancing unit, wherein the control and generation circuit (30) includes a logic gate and n flip-flops, and wherein n is determined by the number of capacitors N according to the relationship 2 n-1 <N≤2 n Sure.

2. A backup power supply system (100), comprising a stack (C1, ..., CN) of N capacitors connected in series and a balancing system according to claim 1, wherein the balancing system is used to balance the corresponding voltages (u_C1, ..., u_CN) of the N capacitors during charging or discharging of the N capacitors.

3. The backup power supply system according to claim 2, characterized in that: The stack of N capacitors connected in series has two terminals, and each pair of associated switches (SWj1-SWj2) is connected to the terminals of the stack of N capacitors (C1, ..., CN).

4. The backup power supply system according to claim 3, characterized in that: The N capacitors have respective indexes i from 1 to N, for each balancing unit (BUj), the N capacitors have a capacitor inter-node between two capacitors with respective indexes i and i+1, the capacitor inter-node being connected to the switch inter-node, the control and generation circuit (30) being configured to generate a first PWM control signal and a second PWM control signal, the first PWM control signal having a duty cycle equal to (Ni) / N, the second PWM control signal having a duty cycle equal to i / N.

5. The backup power supply system according to claim 2, characterized in that: For each balancing unit (BUj), an associated switch pair (SWj1-SWj2) is connected to the two terminals of the corresponding set of capacitors.

6. The backup power supply system according to claim 5, characterized in that: The control and generation circuit is configured to generate PWM control signals all having a 50% duty cycle.

7. The backup power supply system according to any one of claims 2 to 6, characterized in that: Each capacitor group includes only two capacitors.

8. The backup power supply system according to claim 2, characterized in that: The control and generation circuit (30) comprises a flip-flop based frequency divider.

9. The backup power supply system according to claim 8, characterized in that: The control and generation circuit (30) is configured to be connected to a power source (200) and is provided with a clock signal from the power source (200).

10. The backup power supply system according to claim 2, further comprising a power supply (200), wherein the power supply (200) is configured to: - generating a fixed charging current during a first charging phase (Phase_I); and - During a second charging phase (Phase_II), after the voltage of the stack of serially connected capacitors has reached a predetermined target value, a modulated charging current is generated in order to keep the voltage of the stack of serially connected capacitors at said predetermined target value (u_total).

11. The backup power supply system according to claim 2, characterized in that: The serially connected N capacitors are configured to provide power to an electrical circuit of the vehicle when a battery of the vehicle is temporarily disconnected from the electrical circuit of the vehicle.

12. A vehicle comprising a backup power supply system according to any one of claims 2 to 11, the backup power supply system being configured to be charged from a power source (200) comprising a battery of the vehicle and to supply power to an electric circuit of the vehicle.

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