Bidirectional power supply system for powering battery management systems in electric vehicles

Abstract

The present disclosure relates to a bidirectional power supply system for powering a control unit (16) of an electric vehicle, the bidirectional power supply system comprising: a low-voltage main power supply adapted to power the control unit (16) in a first operating mode, the control unit (16) being a component of a low-voltage board network; a high-voltage traction battery (14) of the electric vehicle, the high-voltage traction battery (14) being a part of a high-voltage board network; and a bidirectional DC-DC converter (12) adapted to transfer energy from the low-voltage board network to the high-voltage board network via the main power supply in the first operating mode. In order to power components of the high-voltage grid, the bidirectional DC-DC converter (12) is further adapted to transfer energy from the high-voltage grid to the low-voltage grid via the high-voltage traction battery (14) in a second operating mode in the event of a disconnection of the main power supply so as to power the control unit (16); the bidirectional power supply system further comprises a measuring element (18) adapted to detect whether the main power supply is disconnected, and a switching element (18) adapted to switch the operation of the bidirectional DC-DC converter (12) from the first operating mode to the second operating mode in the event of a disconnection of the main power supply.

Description

Technical Field

[0001] The present invention relates to a bidirectional power supply system for supplying power to one or more components of a low-voltage board network of an electric vehicle, in particular a battery management system, and also to an electric vehicle comprising such a bidirectional power supply system. Background Art

[0002] In recent years, vehicles for transporting goods and people have been developed that use electricity as a power source. Such electric vehicles are cars driven by electric motors using energy stored in rechargeable batteries. Electric vehicles can be powered solely by batteries or in the form of hybrid vehicles powered by, for example, a gasoline generator. Furthermore, vehicles can include a combination of an electric motor and a conventional internal combustion engine. Typically, an electric vehicle battery (EVB) or traction battery is the battery used to power the propulsion of a battery electric vehicle (BEV). Electric vehicle batteries differ from starting, lighting, and ignition batteries in that they are designed to provide power for a sustained period of time. Rechargeable or secondary batteries differ from primary batteries in that they can be repeatedly charged and discharged, whereas the latter only provide irreversible conversion of chemical energy into electrical energy. Low-capacity rechargeable batteries are used as power sources for small electronic devices such as cell phones, laptops, and camcorders, while high-capacity rechargeable batteries are used as power sources for hybrid vehicles and the like.

[0003] Typically, a rechargeable battery includes an electrode assembly, a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes; a housing; and electrode terminals electrically connected to the electrode assembly. An electrolyte solution is injected into the housing so that the battery can be charged and discharged by an electrochemical reaction between the positive and negative electrodes and the electrolyte solution. The shape of the housing, such as cylindrical or rectangular, depends on the intended purpose of the battery. Lithium-ion (and similar lithium polymer) batteries are well known for their use in laptop computers and consumer electronics, and are currently at the forefront of the growing electric vehicle market.

[0004] Rechargeable batteries can be used as battery modules formed from multiple battery cells coupled in series and / or parallel to provide high energy density, particularly for driving electric motors in hybrid vehicles. Specifically, a battery module is formed by interconnecting the electrode terminals of multiple battery cells according to the required amount of power, thereby achieving a high-power rechargeable battery.

[0005] The battery module can be constructed in a block design or a modular design. In the block design, each battery is coupled to a common collector structure and a common battery management system, and its units are arranged in a housing. In the modular design, multiple battery cells are connected to form a submodule, and several submodules are connected to form a battery module. In automotive applications, the battery system is typically composed of multiple battery modules connected in series to provide the desired voltage. Among them, the battery module may include a stacked submodule with multiple battery cells, each stack including a plurality of cells connected in series and then connected in parallel (XpYs), or a plurality of cells connected in parallel and then connected in series (XsYp).

[0006] A battery pack is a group of any number of (preferably identical) battery modules. These battery modules can be configured in series, parallel, or a combination of the two to provide the desired voltage, capacity, or power density. The components of a battery pack include individual battery modules and the interconnects that provide electrical conductivity between them.

[0007] To meet the dynamic power demands of various electrical consumers connected to the battery system, static control of battery power output and charging is not sufficient. Therefore, a stable information exchange is required between the battery system and the controllers of the electrical consumers. This information includes the actual state of charge (SOC), potential electrical performance, charging capacity and internal resistance of the battery system, as well as the actual or predicted power demand or margin of the electrical consumers. Therefore, the battery system typically includes a battery management system (BMS) for obtaining and processing such system-level information, and multiple battery module managers (BMMs), which are part of the battery modules of the battery system and obtain and process module-level relevant information. Specifically, the BMS typically measures the system voltage, system current, local temperature at different locations within the system housing, and the insulation resistance between the live components and the system housing. In addition, the BMM typically measures the individual cell voltage and temperature of the battery cells in the battery module.

[0008] Therefore, a BMS / BMU (Battery Management Unit) is provided for managing the battery pack, such as by protecting the batteries from operating outside their safe operating area, monitoring their status, calculating secondary data, reporting that data, controlling their environment, and authenticating and / or balancing them.

[0009] Typically, an electric vehicle has a high-voltage (HV) grid, which includes a traction battery that supplies power to the propulsion components, and a low-voltage (LV) grid, which includes a low-voltage battery that supplies power to the vehicle's electrical consumers. Specifically, the battery management system (BMS) of the traction battery, located at the LV grid, is typically driven by the low-voltage battery. The LV and HV grids are electrically isolated from each other by a direct-current-to-direct-current (DC-DC) converter, which transfers energy from the LV grid to the HV grid, allowing components of the HV grid to also be powered by the low-voltage battery of the LV grid. The low-voltage battery, which serves as the main power source for the LV grid, can be, for example, a conventional lead-acid battery of the vehicle. Hereinafter, the electrodes of the low-voltage battery will be designated CL30 (for the positive electrode) and CL31 (for the negative electrode), respectively.

[0010] During vehicle operation, it's possible for CL30 (the connection to the positive terminal) to become accidentally disconnected (lost), de-energizing the BMS. This disconnection can also cause the main relays to disconnect, electrically disconnecting the battery cells from the HV grid, potentially damaging the relay contact surfaces. In this case, the BMS has no information about the current flowing through these relays at the time the contacts were disconnected, and therefore no information about any actual physical damage to the contact surfaces.

[0011] As a backup power source for the BMS, the traction battery of the electric vehicle can be used, which in the case of an HV battery (>60V) must be electrically isolated from the LV board network. Typically, such a backup power source is implemented as a separate functional block, which is idle during normal operation and is only started when the main power supply is disconnected. The conventional configuration of the BMS uses a shunt-based current measurement circuit, which is mainly located on the negative side of the battery cell stack or on the negative output of the battery. The shunt-based current measurement circuit includes a low-impedance current measurement resistor. This current measurement circuit must be electrically isolated from the rest of the LV-based BMS.

[0012] Since galvanic isolation is required, a DC-DC converter is used, which uses a transformer to transfer energy from the LV board net to the HV board net. This transformer is usually the most expensive part of the power supply.

[0013] EP 1 801 960 A2 describes a bidirectional DC-DC converter.

[0014] It is therefore an object of the present disclosure to overcome or reduce at least some of the disadvantages of the prior art and to provide a low voltage boardnet, bidirectional power supply system for electric vehicles that allows for reliable power supply. Summary of the Invention

[0015] According to one aspect of the present disclosure, a bidirectional power supply system for powering a first control unit of an electric vehicle is provided. The bidirectional power supply system includes: a low-voltage main power supply adapted to power the first control unit in a first operating mode, the first control unit being a component of a low-voltage grid; a high-voltage traction battery of the electric vehicle being a part of a high-voltage grid; and a bidirectional direct-current (DC-DC) converter adapted to transfer energy from the low-voltage grid to the high-voltage grid in the first operating mode to power components of the high-voltage grid via the main power supply. The bidirectional DC-DC converter is further adapted to transfer energy from the high-voltage grid to the low-voltage grid in a second operating mode to power the first control unit via the high-voltage traction battery if the main power supply is disconnected. The bidirectional power supply system further includes a measuring element adapted to detect whether the main power supply is disconnected, and a switching element adapted to switch the operation of the bidirectional DC-DC converter from the first operating mode to the second operating mode if the main power supply is disconnected.

[0016] According to another aspect of the present disclosure, an electric vehicle is provided, comprising the aforementioned bidirectional power supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Features will become apparent to those skilled in the art by describing in detail exemplary embodiments with reference to the accompanying drawings, in which:

[0018] Figure 1 A schematic diagram illustrating a bidirectional power supply system according to an embodiment is shown. DETAILED DESCRIPTION

[0019] Embodiments of the present disclosure seek to address, at least to some extent, at least one of the problems present in the prior art.

[0020] Specifically, the bidirectional power supply system for powering a battery management system of an electric vehicle according to the present invention comprises: a low voltage (LV) main power supply, which is adapted to power a control unit, in particular a battery management system (BMS), in a first operating mode, wherein the control unit (in particular, the BMS) is a component of a low voltage board network; a high voltage (HV) traction battery of the electric vehicle, which is part of a high voltage board network; and a bidirectional DC-DC converter, which is adapted to transfer energy from the low voltage board network to the high voltage board network via the main power supply in the first operating mode. The bidirectional DC-DC converter is further adapted to transfer energy from the high-voltage grid to the low-voltage grid via the high-voltage traction battery in a second operating mode in the event of a main power supply disconnection, so as to power the control unit (BMS) and possibly also power components of the low-voltage grid; the bidirectional power supply system further comprises a measuring element adapted to detect whether the main power supply is disconnected, and a switching element adapted to switch the operation of the bidirectional DC-DC converter from the first operating mode to the second operating mode in the event of a main power supply disconnection.

[0021] The bidirectional DC-DC converter includes a transformer adapted to transfer energy in both directions between the LV and HV grids, as described above. Specifically, the control unit may be a BMS. Furthermore, the control unit may be part of a BMS. Hereinafter, the control unit will be referred to as a BMS, without intending to be limiting.

[0022] During normal operation, the main power supply provides power / energy to the BMS and possibly to other or all components of the LV boardnet. The main power supply can, for example, be a 12V, 24V, or 48V power supply. Furthermore, the main power supply can provide power / energy to components of the HV boardnet, with energy being transferred from the LV boardnet to the HV boardnet via a bidirectional DC-DC converter. Specifically, the bidirectional DC-DC converter can convert the LV voltage of the main power supply to LV or HV voltage suitable for powering the components of the HV boardnet. Thus, the components of the HV boardnet can also be powered by LV, in particular by the LV voltage of the main power supply or by a suitably converted LV voltage. In the first operating mode, for example, a PWM (pulse width modulation) signal generator can be driven by the LV boardnet and triggered by the BMS.

[0023] If the main power supply is disconnected, for example by losing the connection from the main power supply to the LV board grid as described above, the second operating mode is activated. The bidirectional DC-DC converter is adapted to transfer energy in both directions, i.e. also to transfer energy from the HV board grid to the LV board grid. Thus, in the second operating mode, the HV traction battery of the electric vehicle serves as a backup power source for powering components of the low-voltage board grid, in particular the BMS. Preferably, in the second operating mode, only a portion of the battery cells or cell stacks of the HV traction battery serves as the backup power source. A measuring element is provided to detect whether the main power supply is disconnected. In addition, a switching element is provided to switch the operation of the bidirectional DC-DC converter from the first operating mode to the second operating mode if a disconnection of the main power supply is detected. The measuring element and the switching element can be the same element, in particular, they can be implemented by a PWM detector. The measuring element and / or the switching element can form part of the BMS. The measuring element and / or the switching element are preferably part of the HV board grid. The bidirectional power supply system can form part of a push-pull converter.

[0024] Therefore, if the main power source fails to deliver power / energy, for example due to an unexpected disconnection of the CL30, the bidirectional power supply system can automatically switch to the HV traction battery (also referred to as the HV battery) as a backup power source via the measuring and switching elements. As a result, uninterrupted power supply to the BMS can be ensured. This ensures the operation of the BMS. Specifically, the BMS can thus receive information about the current flowing through the relay when the contacts are open, allowing it to derive information about any physical damage to the contact surfaces. Furthermore, the use of the bidirectional DC-DC converter, and in particular its transformer, is cost-effective compared to using a second, independent transformer for transferring energy from the HV to the LV.

[0025] According to one embodiment, the measuring element includes a PWM detector disposed at the high-voltage board network, i.e., on the high-voltage side of the bidirectional DC-DC converter / transformer. The PWM detector is adapted to analyze a pulse-width modulated signal present on the high-voltage side of the bidirectional DC-DC converter and, based on the analyzed signal, detect whether the main power supply is disconnected. Thus, the PWM detector can function as a measuring element. The result of the signal analysis may be that the transformer is not switching / operating on the low-voltage side, which can be interpreted as a main power supply disconnection. According to another embodiment, the PWM detector is adapted to switch the bidirectional DC-DC converter to a second operating mode upon detecting a main power supply disconnection. Thus, the PWM detector can also function as a switching element. Therefore, if analysis of the pulse-width modulated signal present on the high-voltage side of the bidirectional DC-DC converter / transformer indicates a main power supply disconnection, the PWM detector can switch the operating mode so that the low-voltage board network, and in particular the BMS, is powered by the high-voltage traction battery. This PWM detector allows for an efficient and timely response to a main power supply disconnection.

[0026] According to another embodiment, at least one capacitor is provided that is adapted to supply power to the measuring element in the event of a mains power outage long enough to allow the measuring element to detect the mains power outage. Furthermore, the same or another capacitor can be provided that is adapted to supply power to the switching element long enough to allow the switching element to switch the operation of the bidirectional DC-DC converter to the second operating mode. Thus, the at least one capacitor can be specifically configured to supply power to the PWM detector in the event of a mains power outage long enough to allow the PWM detector to detect the mains power outage and switch the operation of the bidirectional DC-DC converter to the second operating mode. Thus, the at least one capacitor can serve as a temporary power source for the measuring and switching elements after a mains power outage and before switching to the HV board grid and its traction battery as a backup power source. During normal operation, i.e., during the first operating mode, the at least one capacitor can be charged via the mains power supply. The capacitor can ensure the switch to the second operating mode.

[0027] According to one embodiment, a bidirectional power supply system includes a control unit for generating pulse-width modulated signals during a first operating mode. The control unit is arranged at the low-voltage (LV) board network, i.e., on the LV side of the bidirectional DC-DC converter / transformer, wherein the control unit is adapted to detect a main power disconnection. The control unit may be part of a BMS or a separate control unit, such as a microcontroller unit (MCU). Generally, the purpose of the control unit is to generate one or more PWM signals during normal operation of the system, i.e., during the first operating mode. The control unit may detect a main power disconnection, for example, by detecting a disconnection of a CL30. Thus, a main power disconnection may also be detected on the LV side of the bidirectional DC-DC converter / transformer, allowing appropriate measures to be taken. Specifically, according to various embodiments, the control unit is further adapted to stop generating pulse-width modulated signals at the LV board network upon detecting a main power disconnection. Therefore, if the control unit detects a main power disconnection, it may immediately stop generating the PWM signal(s) at the LV board network. This is important for switching operation to the second operating mode. In this second operating mode, the PWM signal(s) may be generated by a PWM generator on the HV side.

[0028] Therefore, according to an embodiment, the bidirectional power supply system includes a PWM generator on the HV board grid, which is adapted to generate a PWM signal in the second operating mode. When the system switches to the second operating mode, the PWM generator can take over the PWM signal generation operations of the control unit. This ensures the generation of PWM signals and the correct operation of the system in the second operating mode.

[0029] According to an embodiment, the bidirectional power supply system includes a timer device, which is adapted to shut down the operation in the second operating mode after a predetermined time span. The timer device may include a timer circuit, which is adapted to shut down the operation in the second operating mode after a predetermined time span. Alternatively, the timer device may include a control unit, in particular a microcontroller unit (MCU), which is adapted to shut down the operation in the second operating mode via a corresponding control signal after a predetermined time span. The control unit may be part of the BMS. It may be advantageous to provide limitations for operation in the second operating mode (i.e. the HV to LV direction) to limit the load on the HV battery. In particular, if in the second operating mode power is drawn not from all cells of the HV battery but only from a part of the cell stack, the entire HV cell stack may become unbalanced.

[0030] According to an embodiment, the bidirectional power supply system includes a control element for providing cell voltage-dependent regulation of the frequency and / or width of the PWM signal during the second operating mode. The control element is preferably arranged on the HV onboard grid. The control element may include a voltage-controlled oscillator (VCO) for cell voltage-dependent frequency regulation. Because the cell voltage of the battery cells of the HV traction battery depends on the cell's state of charge, the PWM width or frequency should be varied so as not to exceed the transformer ET product for a given voltage. Therefore, when the voltage increases, the frequency should be increased or the pulse width of the PWM signal should be decreased. Correspondingly, when the voltage decreases, the frequency should be decreased or the pulse width of the PWM signal should be increased.

[0031] According to an embodiment, the bidirectional power supply system includes a device for current limitation of a switching element that is specifically arranged on the low-voltage board network. The switching element may include one or more MOSFETs (metal oxide semiconductor field effect transistors) working as switches and, for example, driven by one or more of the above-mentioned control units, in particular by a BMS. In particular, the switching element may include a push-pull switching MOSFET and / or a buffer and / or a voltage clamping circuit, which allows suppressing voltage transients in the circuit. Such current limitation can prevent excessive currents that could damage the system. Such a device for current limitation can also or optionally be provided on the HV board network side to prevent damage to the HV switching element (MOSFET) due to stress caused by overcurrent.

[0032] According to another aspect of the present disclosure, an electric vehicle is provided that includes the bidirectional power supply system described above. The electric vehicle includes the low-voltage and high-voltage switchgears, which are electrically isolated by the bidirectional DC-DC converter. The high-voltage traction battery supplies power to the low-voltage switchgears in the second operating mode. The low-voltage and high-voltage switchgears can also be considered to form part of the bidirectional power supply system.

[0033] Further aspects of the disclosure can be gathered from the dependent claims or the following description.

[0034] Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings. The effects and features of the exemplary embodiments and their implementation methods will be described with reference to the accompanying drawings. In the accompanying drawings, the same reference numerals represent the same elements, and redundant descriptions are omitted. However, the present disclosure can be implemented in various different forms and should not be construed as being limited to the embodiments shown herein. On the contrary, these embodiments are provided as examples so that the present disclosure will be thorough and complete and will fully convey the aspects and features of the present disclosure to those skilled in the art.

[0035] Therefore, processes, elements, and techniques that are not considered necessary for one of ordinary skill in the art to fully understand the aspects and features of the present disclosure may not be described.In the drawings, the relative sizes of elements, layers, and regions may be exaggerated for clarity.

[0036] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. In addition, when describing embodiments of the present disclosure, the use of "may" refers to "one or more embodiments of the present disclosure." In the following description of embodiments of the present disclosure, terms in the singular may include plural forms unless the context clearly indicates otherwise. When used after an element of a list, expressions such as "at least one of" modify the elements of the entire list rather than modifying the individual elements therein.

[0037] As used herein, the terms "substantially," "about," and similar terms are used as terms of approximation rather than terms of degree, and are intended to account for the inherent variations in measured or calculated values ​​that one of ordinary skill in the art would recognize. Additionally, if the term "substantially" is used in conjunction with a feature that can be expressed using a numerical value, the term "substantially" means a range of + / - 5% of the value centered around that value.

[0038] It should also be understood that the terms “include,” “comprising,” “including,” or “containing” specify properties, regions, fixed numbers, steps, processes, elements, components, and combinations thereof, but do not exclude other properties, regions, fixed numbers, steps, processes, elements, components, and combinations thereof.

[0039] Any suitable hardware, firmware, software or combination of software, firmware and hardware can be utilized to implement the electronic or electrical devices and / or any other related devices or components according to the embodiments of the present disclosure described herein. Specifically, an application specific integrated circuit (ASIC) implemented as a custom chip can be used, while specific firmware can be provided for the ASIC, i.e., flash memory is stored on a microcontroller to communicate with the ASIC and use the ASIC. In addition, the various components of these devices can be implemented on a flexible printed circuit film, a tape carrier package (TCP), a printed circuit board (PCB), or formed on a substrate. The electrical connections or interconnections described herein can be achieved by, for example, wires or conductive elements on a PCB or another circuit carrier. The conductive elements can include metallization, such as surface metallization and / or pins, and / or can include conductive polymers or ceramics. Further, electrical energy can be transmitted via a wireless connection, for example, using electromagnetic radiation and / or light.

[0040] In addition, those skilled in the art will recognize that the functionality of various computing devices may be combined or integrated into a single computing device, or that the functionality of a particular computing device may be distributed across one or more other computing devices without departing from the scope of the exemplary embodiments of the present disclosure.

[0041] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. It should also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology and / or this specification, and should not be interpreted as an idealized or overly formal meaning unless explicitly defined as such herein.

[0042] Figure 1 A circuit diagram of a bidirectional power supply system according to an embodiment based on a push-pull topology is schematically shown.

[0043] Figure 1 The figure shows a low-voltage (LV) grid on the left and a high-voltage (HV) grid on the right. A bidirectional DC-DC converter, utilizing transformer 12, is adapted to transfer energy in both directions between the LV and HV grids. Only transformer 12 of the bidirectional DC-DC converter is shown; the bidirectional DC-DC converter may include additional components. The LV grid includes a main LV power supply, which is not shown in the figure itself, but connections CL30 and CL31 to the positive and negative electrodes of the main LV power supply are shown. The HV grid includes an HV battery 14, which serves as the traction battery for the electric vehicle and propels the electric vehicle. As shown, HV battery 14 includes a plurality of battery cells 1 to n.

[0044] In the first operating mode, or "normal operation," the LV main power supply powers components of the LV board network, specifically the MCU (microcontroller unit) 16, which is part of the BMS. The BMS can also be referred to as a control unit. The MCU can reside on the BMS, being the main / only MCU on the BMS, or a dedicated MCU that only enables the functionality according to the present invention can be used. The LV main power supply also powers components of the HV board network, specifically the LV PWM detector 18. The LV voltage, which is prevalent on the LV board network, is converted to the electrically isolated LV or HV voltage on the HV board network via a bidirectional DC-DC converter. In the first operating mode, V_NORMAL (preferably 6V) is provided by a buck converter, which can be implemented using a system basis chip (SBC) 19. Interleaved PWM signals, including PWM_A and PWM_B, are provided by MCU 16, controlling the switching of MOSFETs M1 and M2. With a transformer ratio of 1:1, a voltage of approximately V_NORMAL minus two diode drops appears at the V_HV_SUPPLY node. This voltage then powers the operation of the current sensing circuitry (e.g., current measurement AFE / MCU) 22 on the HV side, and in particular, the operation of the LV PWM detector 18. Diodes D3 and D4 are optional. Specifically, if the MOSFET diodes can handle the load, diodes D3 and D4 can be omitted.

[0045] If the LV main power source is disconnected, such as if the connection to CL30 is disconnected, the bidirectional power supply system switches to a second operating mode in which power is supplied by the HV battery 14. This main power disconnection is detected by the LV PWM detector 18, which analyzes the signals present on the HV side of the transformer 12 (i.e., the LV PWM detector 18 can function as a measuring element). Upon detecting that the LV side is not the transformer 12, the bidirectional DC-DC converter switches to the second operating mode (i.e., the LV PWM detector 18 can function as a switching element), enabling power supply from cells 1 through 5 of the HV battery 14. This switching is performed via the LV PWM detector 18, which activates MOSFET M5 disposed on the HV onboard grid, which in turn enables power supply to the LV side via cells 1 through 5 of the HV battery 14, and activates MOSFET M6 disposed on the HV onboard grid, which enables PWM generation on the HV side via the PWM generator 20. From this point on, the transformer 12 operates in the second operating mode, ie in the HV to LV direction.

[0046] Thus, in the second operating mode, a portion of the cells of the electric vehicle's HV battery (eg, HV traction battery) 14 is used as a backup power source for powering components of the low voltage board network, in particular the BMS / MCU.

[0047] Furthermore, MCU 16, which generates PWM signals on the LV side, also detects a drop in CL30, i.e., a disconnection of the main power supply, via corresponding sensing elements 17. MCU 16 then immediately ceases generation of the PWM_A and PWM_B signals. Capacitors C1, C2, and C3 are provided to store sufficient energy to power the necessary components long enough to allow switching to the second operating mode. Specifically, this allows LV PWM detector 18 to detect the loss of operation of transformer 12 from the LV side and activate MOSFETs M5 and M6 to enable power supply from HV battery 14 and PWM generation on the HV side, respectively, as described above. In this second operating mode, PWM generator 20 takes over generation of the PWM signals from MCU 16, generating signals PWM_C and PWM_D on the HV side.

[0048] The second operating mode may be time limited since it does not balance the HV battery 14 and since it does not draw power from the entire cell stack but only from cells 1 to 5. Therefore, it is preferred that some kind of timer means is implemented which will switch off operation in the second operating mode after a certain time. The timer means may comprise a timer circuit which is adapted to switch off operation in the second operating mode after a predetermined time span. Alternatively, the timer means may comprise a control unit, in particular a microcontroller unit (MCU), which is adapted to switch off operation in the second operating mode via a corresponding control signal after a predetermined time span. Alternatively, a current measuring MCU or AFE device 22 may be provided on the HV board net, such as Figure 1 As shown by the middle dashed line, the MCU or analog front end (AFE) device is adapted to shut down the bidirectional DC-DC converter via a digital output.

[0049] Since the cell voltage of the HV battery 14 cells depends on the state of charge (the worst case range for 5 cells is about 10 to 21V), the PWM width or frequency should be changed to not exceed the transformer ET product for a given voltage. Generally, the frequency can be increased or the pulse width can be decreased as the voltage increases. Figure 1 In the embodiment shown, a voltage controlled oscillator (VCO) 24 provides frequency adjustment that is dependent on the cell voltage.

[0050] Thus, with the present invention, a bidirectional redundant power supply is provided to provide a shunt based current measurement circuit in normal mode (LV to HV direction) and to operate backwards (HV to LV direction) when a loss of vehicle power (CL30) is detected.

Claims

1. A bidirectional power supply system for supplying power to a first control unit of an electric vehicle, the bidirectional power supply system comprising: a low-voltage main power supply adapted to power the first control unit in a first operating mode, wherein the first control unit and the low-voltage main power supply form components of a low-voltage grid of the bidirectional power supply system, a high-voltage traction battery of the electric vehicle, which is part of a high-voltage grid of the bidirectional power supply system, and a bidirectional DC-DC converter, the bidirectional DC-DC converter being arranged to electrically isolate the low-voltage grid and the high-voltage grid from each other, wherein the bidirectional DC-DC converter is adapted to transfer energy from the low-voltage grid to the high-voltage grid in the first operating mode so as to power components of the high-voltage grid via the low-voltage main power supply, and the bidirectional DC-DC converter is further adapted to transfer energy from the high-voltage grid to the low-voltage grid in a second operating mode so as to power components of the high-voltage grid via the high-voltage main power supply if the low-voltage main power supply is disconnected. The first control unit is powered by a battery, and the bidirectional power supply system further includes a measuring element and a switching element, wherein the measuring element is adapted to detect whether the low-voltage main power supply is disconnected, and the switching element is adapted to switch the operation of the bidirectional DC-DC converter from the first operating mode to the second operating mode when the low-voltage main power supply is detected to be disconnected, wherein the measuring element includes a pulse width modulation detector arranged at the high-voltage board network, and the pulse width modulation detector is adapted to analyze the pulse width modulation signal present on the high-voltage side of the bidirectional DC-DC converter and detect whether the low-voltage main power supply is disconnected based on the analyzed signal, wherein the pulse width modulation detector is further adapted to serve as the switching element, and once the switching element detects that the low-voltage main power supply is disconnected, it will switch the operation of the bidirectional DC-DC converter to the second operating mode.

2. The bidirectional power supply system according to claim 1 , comprising at least one capacitor adapted to supply power to the measuring element for a sufficiently long time to allow the measuring element to detect the disconnection of the low-voltage main power supply, and / or at least one capacitor adapted to supply power to the switching element for a sufficiently long time to allow the switching element to switch the operation of the bidirectional DC-DC converter to the second operating mode.

3. The bidirectional power supply system according to claim 1 , comprising a first control unit, arranged at the low-voltage boardnet, for generating a pulse width modulation signal during the first operation mode, wherein the first control unit is adapted to detect a disconnection of the low-voltage main power supply. 4 . The bidirectional power supply system according to claim 3 , wherein the first control unit is further adapted to stop generating the pulse width modulation signal at the low voltage boardnet upon detecting that the low voltage main power source is disconnected. 5 . The bidirectional power supply system according to claim 1 , comprising a pulse width modulation generator on the high voltage panel grid, the pulse width modulation generator being adapted to generate a pulse width modulation signal in the second operation mode.

6. The bidirectional power supply system according to claim 1, comprising a timer device adapted to shut down operation in the second operating mode after a predetermined time span. 7 . The bidirectional power supply system according to claim 6 , wherein the timer arrangement comprises a timer circuit adapted to shut down operation in the second operating mode after a predetermined time span. 8 . The bidirectional power supply system according to claim 6 , wherein the timer device comprises a second control unit adapted to shut down the operation in the second operation mode via a corresponding control signal after a predetermined time span.

9. The bidirectional power supply system according to claim 1, comprising a control element for providing a cell voltage-dependent regulation of the frequency and / or width of the pulse width modulation signal during the second operating mode.

10. The bidirectional power supply system according to claim 1, comprising means for current limiting of the switching element on the low voltage panel.

11. An electric vehicle comprising the bidirectional power supply system according to any one of the preceding claims.

12. The electric vehicle of claim 11, comprising a low-voltage board grid and a high-voltage board grid, the low-voltage board grid and the high-voltage board grid being electrically isolated via a bidirectional DC-DC converter, wherein the high-voltage traction battery supplies power to the low-voltage board grid in the second operating mode.

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